Enterobacter bacteremia: clinical features and emergence of antibiotic resistance during therapy

Clinical and microbiological characteristics of persistent Staphylococcus aureus bacteremia, risk factors for mortality, and the role of CD4+ T cells

This study evaluated the determinants of mortality and the T cell immune response in patients with persistent Staphylococcus aureus bacteremia (SAB). This was a prospective cohort study and patients with confirmed SAB were enrolled from 2008 to 2020. We compared clinical, microbiological, and genotypic features between surviving and deceased patients with persistent SAB. The concentrations of cytokines and the proportions of IFN-γ secreting CD4+ T cells were measured serially during the bacteremia period. Of the 1760 patients, 242 had persistent bacteremia (PB), and 49 PB patients died within 30 days. In the multivariate analysis, the APACHE II score and female sex were independently associated with 30 days mortality. The level of IL-10 was significantly increased in the plasma of patients with a high Pitt bacteremia score and those who died within 12 weeks from the index day. The proportion of IFN-γ-secreting CD4+ T cells were the highest just before the positive-to-negative conversion of blood cultures in patients with a low Pitt bacteremia score and those who survived for 12 weeks. The level of IL-10 is correlated with clinical outcomes in PB patients. IFN-γ secreting CD4+ T cells might play a pivotal role in SAB PB.

Risk factors for vancomycin treatment failure in heterogeneous vancomycin-intermediate Staphylococcus aureus bacteremia

The incidence of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) infection is increasing and is associated with vancomycin treatment failures. However, studies investigating the risk factors for treatment failure in hVISA infection are limited. Patients with hVISA bacteremia treated with vancomycin over 7 days between August 2008 and June 2020 were enrolled in this study. Clinical and microbiological characteristics were compared between vancomycin treatment failure and success groups to identify the risk factors for vancomycin treatment failure. Among the 180 patients with hVISA bacteremia, 102 patients treated with vancomycin over 7 days were included. Vancomycin treatment failed in 80 (78%) patients. Patients in the vancomycin treatment failure group were older (P < 0.001) and more frequently had solid cancer (P = 0.04) than those in the vancomycin treatment success group. Solid organ transplantation (SOT) was more frequent (P < 0.001) in the vancomycin treatment success group. The Charlson comorbidity index (P = 0.01) and Acute Physiology and Chronic Health Evaluation II scores (P < 0.001) were higher in the vancomycin treatment failure group. In multivariate analysis, independent risk factors for vancomycin treatment failure were old age and severity of bacteremia. SOT and vancomycin minimal inhibitory concentration (MIC) ≤ 1.0 mg/L using the broth microdilution (BMD) method were associated with successful vancomycin treatment. Old age and infection severity were independent risk factors for vancomycin treatment failure. Vancomycin MIC using the BMD method is an important risk factor for vancomycin treatment failure, and its use should be considered in hVISA bacteremia.IMPORTANCEIn this study, we assessed the clinical and microbiological characteristics of heterogeneous vancomycin-intermediated Staphylococcus aureus (hVISA) bacteremia and identified risk factors for vancomycin treatment failure. We found that advanced age and severity of infection were independent risk factors for vancomycin treatment failure. On the other hand, solid organ transplantation and a low vancomycin minimal inhibitory concentration were associated with successful vancomycin treatment. This study highlights the importance of vancomycin minimal inhibitory concentration in hVISA bacteremia.

A rare case of successful treatment of peritoneal dialysis patient with Serratia marcescens peritonitis without catheter removal: case report and literature review

Serratia marcescens, as a Gram-negative opportunistic pathogen, is a rare cause of peritonitis and has worse clinical outcomes than Gram-positive peritonitis. In this case report, we describe a case of Serratia marcescens associated peritonitis that was successfully cured without catheter removal. A 40-year-old male patient with peritoneal dialysis who worked in the catering industry was admitted to the hospital for 16 hours after the discovery of cloudy peritoneal dialysate and abdominal pain. Ceftazidime and cefazolin sodium were immediately given intravenously as an empirical antibiotic regimen. After detecting Serratia marcescens in the peritoneal diasate culture, the treatment was switched to ceftazidime and levofloxacin. The routine examination of peritoneal dialysate showed a significant decrease in white blood cells, the peritoneal dialysate became clear, and the peritoneal dialysis catheter was retained. The patient was treated for 2 weeks and treated with oral antibiotics for 1 week. It is necessary to further strengthen the hygiene of work environment to prevent Serratia marcescens infection in peritoneal dialysis patients. We recommend that patients with Serratia marcescens associated peritonitis should be treated with a combination of antibiotics as early as possible empirically, and at the same time, the peritoneal dialysis fluid culture should be improved, and the antibiotic regimen should be timely adjusted according to the drug sensitivity results. For patients with clinical symptoms for more than 3 days, considering the strong virulence of Serratia marcescens, whether to use meropenem directly or not can provide a reference for clinical decision-making. Further clinical studies are needed to achieve more precise anti-infective treatment.

Bioaerosol Sampling Devices and Pretreatment for Bacterial Characterization: Theoretical Differences and a Field Experience in a Wastewater Treatment Plant

Studies on bioaerosol bacterial biodiversity have relevance in both ecological and health contexts, and molecular methods, such as 16S rRNA gene-based barcoded sequencing, provide efficient tools for the analysis of airborne bacterial communities. Standardized methods for sampling and analysis of bioaerosol DNA are lacking, thus hampering the comparison of results from studies implementing different devices and procedures. Three samplers that use gelatin filtration, swirling aerosol collection, and condensation growth tubes for collecting bioaerosol at an aeration tank of a wastewater treatment plant in Trieste (Italy) were used to determine the bacterial biodiversity. Wastewater samples were collected directly from the untreated sewage to obtain a true representation of the microbiological community present in the plant. Different samplers and collection media provide an indication of the different grades of biodiversity, with condensation growth tubes and DNA/RNA shieldTM capturing the richer bacterial genera. Overall, in terms of relative abundance, the air samples have a lower number of bacterial genera (64 OTUs) than the wastewater ones (75 OTUs). Using the metabarcoding approach to aerosol samples, we provide the first preliminary step toward the understanding of a significant diversity between different air sampling systems, enabling the scientific community to orient research towards the most informative sampling strategy.

Differences in clinical outcomes of bloodstream infections caused by Klebsiella aerogenes, Klebsiella pneumoniae and Enterobacter cloacae: a multicentre cohort study

BACKGROUND

Klebsiella aerogenes has been reclassified from Enterobacter to Klebsiella genus due to its phenotypic and genotypic similarities with Klebsiella pneumoniae. It is unclear if clinical outcomes are also more similar. This study aims to assess clinical outcomes of bloodstreams infections (BSI) caused by K. aerogenes, K. pneumoniae and Enterobacter cloacae, through secondary data analysis, nested in PRO-BAC cohort study.

METHODS

Hospitalized patients between October 2016 and March 2017 with monomicrobial BSI due to K. aerogenes, K. pneumoniae or E. cloacae were included. Primary outcome was a composite clinical outcome including all-cause mortality or recurrence until 30 days follow-up. Secondary outcomes were fever ≥ 72 h, persistent bacteraemia, and secondary device infection. Multilevel mixed-effect Poisson regression was used to estimate the association between microorganisms and outcome.

RESULTS

Overall, 29 K. aerogenes, 77 E. cloacae and 337 K. pneumoniae BSI episodes were included. Mortality or recurrence was less frequent in K. aerogenes (6.9%) than in E. cloacae (20.8%) or K. pneumoniae (19.0%), but statistical difference was not observed (rate ratio (RR) 0.35, 95% CI 0.08 to 1.55; RR 0.42, 95% CI 0.10 to 1.71, respectively). Fever ≥ 72 h and device infection were more common in K. aerogenes group. In the multivariate analysis, adjusted for confounders (age, sex, BSI source, hospital ward, Charlson score and active antibiotic therapy), the estimates and direction of effect were similar to crude results.

CONCLUSIONS

Results suggest that BSI caused by K. aerogenes may have a better prognosis than E. cloacae or K. pneumoniae BSI.

Validation of a new risk stratification system-based management for methicillin-resistant Staphylococcus aureus bacteraemia: analysis of a multicentre prospective study

PURPOSE

Distinguishing between complicated and uncomplicated Staphylococcus aureus bacteraemia (SAB) is therapeutically essential. However, this distinction has limitations in reflecting the heterogeneity of SAB and encouraging targeted diagnostics. Recently, a new risk stratification system for SAB metastatic infection, involving stepwise approaches to diagnosis and treatment, has been suggested. We assessed its applicability in methicillin-resistant SAB (MRSAB) patients.

METHODS

We retrospectively analysed data of a 3-year multicentre, prospective cohort of hospitalised patients with MRSAB. We classified the patients into three risk groups: low, indeterminate, and high, based on the new system and compared between-group management and outcomes.

RESULTS

Of 380 patients with MRSAB, 6.3% were classified as low-, 7.6% as indeterminate-, and 86.1% as high-risk for metastatic infection. No metastatic infection occurred in the low-, 6.9% in the indeterminate-, and 19.6% in the high-risk groups (P < 0.001). After an in-depth diagnostic work-up, patients were finally diagnosed as 'without metastatic infection (6.3%)', 'with metastatic infection (17.4%)', and 'uncertain for metastatic infection (76.3%)'. 30-day mortality increased as the severity of diagnosis shifted from 'without metastatic infection' to 'uncertain for metastatic infection' and 'with metastatic infection' (P = 0.09). In multivariable analysis, independent factors associated with metastatic complications were suspicion of endocarditis in transthoracic echocardiography, clinical signs of metastatic infection, Pitt bacteraemia score ≥ 4, and persistent bacteraemia.

CONCLUSIONS

The new risk stratification system shows promise in predicting metastatic complications and guiding work-up and management of MRSAB. However, reducing the number of cases labelled as 'high-risk' and 'uncertain for metastatic infection' remains an area for improvement.

Genomic, functional, and metabolic enhancements in multidrug-resistant Enterobacter bugandensis facilitating its persistence and succession in the International Space Station

BACKGROUND

The International Space Station (ISS) stands as a testament to human achievement in space exploration. Despite its highly controlled environment, characterised by microgravity, increased CO2 levels, and elevated solar radiation, microorganisms occupy a unique niche. These microbial inhabitants play a significant role in influencing the health and well-being of astronauts on board. One microorganism of particular interest in our study is Enterobacter bugandensis, primarily found in clinical specimens including the human gastrointestinal tract, and also reported to possess pathogenic traits, leading to a plethora of infections.

RESULTS

Distinct from their Earth counterparts, ISS E. bugandensis strains have exhibited resistance mechanisms that categorise them within the ESKAPE pathogen group, a collection of pathogens recognised for their formidable resistance to antimicrobial treatments. During the 2-year Microbial Tracking 1 mission, 13 strains of multidrug-resistant E. bugandensis were isolated from various locations within the ISS. We have carried out a comprehensive study to understand the genomic intricacies of ISS-derived E. bugandensis in comparison to terrestrial strains, with a keen focus on those associated with clinical infections. We unravel the evolutionary trajectories of pivotal genes, especially those contributing to functional adaptations and potential antimicrobial resistance. A hypothesis central to our study was that the singular nature of the stresses of the space environment, distinct from any on Earth, could be driving these genomic adaptations. Extending our investigation, we meticulously mapped the prevalence and distribution of E. bugandensis across the ISS over time. This temporal analysis provided insights into the persistence, succession, and potential patterns of colonisation of E. bugandensis in space. Furthermore, by leveraging advanced analytical techniques, including metabolic modelling, we delved into the coexisting microbial communities alongside E. bugandensis in the ISS across multiple missions and spatial locations. This exploration revealed intricate microbial interactions, offering a window into the microbial ecosystem dynamics within the ISS.

CONCLUSIONS

Our comprehensive analysis illuminated not only the ways these interactions sculpt microbial diversity but also the factors that might contribute to the potential dominance and succession of E. bugandensis within the ISS environment. The implications of these findings are twofold. Firstly, they shed light on microbial behaviour, adaptation, and evolution in extreme, isolated environments. Secondly, they underscore the need for robust preventive measures, ensuring the health and safety of astronauts by mitigating risks associated with potential pathogenic threats. Video Abstract.

Rhodococcus infection: a 10-year retrospective analysis of clinical experience and antimicrobial susceptibility profile

Rhodococcus equi is an opportunistic pathogen known to cause pulmonary and extrapulmonary disease among immunocompromised patients. Treatment is frequently challenging due to intrinsic resistance to multiple antibiotic classes. While non-equi Rhodococcus spp. are prevalent, their clinical significance is poorly defined. There is also limited data on antibiotic susceptibility testing (AST) of Rhodococcus infection in humans. We conducted a single-center, retrospective cohort study evaluating clinical characteristics, microbiologic profile, and AST of Rhodococcus infections between June 2012 and 2022 at our tertiary academic medical center. Identification of Rhodococcus spp. was performed by Sanger 16S rRNA gene sequencing and/or matrix-assisted laser desorption ionization-time of flight mass spectrometry, and AST was performed by agar dilution. Three hundred twenty-two isolates of Rhodococcus spp. were identified from blood (50%), pulmonary (26%), and bone/joint (12%) sources. R. equi/hoagii, R. corynebacterioides, and R. erythropolis were the most frequently isolated species, with 19% of isolates identified only to genus level. One hundred ninety-nine isolates evaluated for AST demonstrated high-level resistance to amoxicillin/clavulanate, cephalosporins, and aminoglycosides. More than 95% susceptibility to imipenem, vancomycin, linezolid, rifampin, and clarithromycin was observed. Non-equi species showed a significantly more favorable AST profile relative to R. equi. Clinically significant Rhodococcus infection was rare with 10 cases diagnosed (majority due to R. equi) and managed. The majority of patients received 2- or 3-drug combination therapy for 2-6 months, with favorable clinical response. Significant differences in AST were observed between R. equi and non-equi species. Despite high antimicrobial resistance to several antibiotic classes, imipenem and vancomycin remain appropriate empiric treatment options for R. equi. Future research evaluating mechanisms underlying antimicrobial resistance is warranted.

Divergent genetic landscapes drive lower levels of AmpC induction and stable de-repression in Serratia marcescens compared to Enterobacter cloacae

The chromosomally encoded AmpC beta-lactamase is widely distributed throughout the Enterobacterales. When expressed at high levels through transient induction or stable de-repression, resistance to ceftriaxone, a commonly used antibiotic, can develop. Recent clinical guidance suggests, based on limited evidence, that resistance may be less likely to develop in Serratia marcescens compared to the better-studied Enterobacter cloacae and recommends that ceftriaxone may be used if the clinical isolate tests susceptible. We sought to generate additional data relevant to this recommendation. AmpC de-repression occurs predominantly because of mutation in the ampD peptidoglycan amidohydrolase. We find that, in contrast to E. cloacae, where deletion of ampD results in high-level ceftriaxone resistance (with ceftriaxone MIC = 96 µg/mL), in S. marcescens deletion of two amidohydrolases (ampD and amiD2) is necessary for AmpC de-repression, and the resulting ceftriaxone MIC is 1 µg/mL. Two mechanisms for this difference were identified. We find both a higher relative increase in ampC transcript level in E. cloacae ΔampD compared to S. marcescens ΔampDΔamiD2, as well as higher in vivo efficiency of ceftriaxone hydrolysis by the E. cloacae AmpC enzyme compared to the S. marcescens AmpC enzyme. We also observed higher relative levels of transient AmpC induction in E. cloacae vs S. marcescens when exposed to ceftriaxone. In time-kill curves, this difference translates into the survival of E. cloacae but not S. marcescens at clinically relevant ceftriaxone concentrations. In summary, our findings can explain the decreased propensity for on-treatment ceftriaxone resistance development in S. marcescens, thereby supporting recently issued clinical guidance.

Evaluating antimicrobial duration for Gram-negative bacteremia in patients with neutropenia due to hematologic malignancy or hematopoietic stem cell transplantation

BACKGROUND

In the management of Gram-negative bloodstream infection (GN-BSI), short antimicrobial courses have been increasingly demonstrated to be non-inferior to prolonged therapy, with lower risk of Clostridioides difficile infection (CDI) and emergence of multi-drug resistant (MDR) organisms. However, immunocompromised hosts were excluded from these studies. We investigated outcomes of short (≤10 days), intermediate (11-14 days), and prolonged (≥15 days) antimicrobial durations for GN-BSI in neutropenic patients.

METHODS

A retrospective cohort study was conducted on neutropenic patients with monomicrobial GN-BSI between 2018 and 2022. The primary outcome was a composite of all-cause mortality and microbiologic relapse within 90 days after therapy completion. The secondary outcome was a composite of 90-day CDI and development of MDR-GN bacteria. Cox regression analysis with propensity score (PS) adjustment was used to compare outcomes between the three groups.

RESULTS

A total of 206 patients were classified into short (n = 67), intermediate (n = 81), or prolonged (n = 58) duration. Neutropenia was predominantly secondary to hematopoietic stem cell transplantation (48%) or hematologic malignancy (35%). The primary sources of infection included intra-abdominal (51%), vascular catheter (27%), and urinary (8%). Most patients received definitive therapy with cefepime or carbapenem. No significant difference in the primary composite endpoint was observed for intermediate versus short (PS-adjusted hazard ratio [aHR] 0.89; 95% confidence interval [95% CI] 0.39-2.03) or prolonged versus short therapy (PS-aHR 1.20; 95% CI 0.52-2.74). There was no significant difference in the secondary composite endpoint of CDI or MDR-GN emergence.

CONCLUSION

Our data suggest that short antimicrobial courses had comparable 90-day outcomes as intermediate and prolonged regimens for GN-BSI among immunocompromised patients with neutropenia.

Clinical Outcomes of Third-Generation Cephalosporin Definitive Therapy for Bloodstream Infections Due to Enterobacterales with Potential AmpC Induction: A Single-Center Retrospective Study

The recommended therapy for severe infections caused by AmpC-inducible Enterobacterales (AmpC-E) typically involves cefepime or carbapenems. In an era of emerging resistance to these antimicrobials, we aim to assess the impact of third-generation cephalosporins (3GCs) vs. alternative antibiotics on clinical outcomes in bloodstream infections (BSIs) due to AmpC-E. We retrospectively included hospitalized adult patients with BSIs caused by 3GC-susceptible AmpC-E between 2012 and 2022, comparing the outcomes of 3GC and non-3GC definitive therapies. The primary outcome was overall treatment failure (OTF), encompassing 90-day all-cause mortality, 90-day reinfection, and 90-day readmission. Secondary outcomes comprised components of the OTF, in-hospital all-cause mortality, and length-of-stay. Within a total cohort of 353 patients, OTF occurred in 46.5% and 41.5% in the 3GC- and non-3GC-therapy groups, respectively (p = 0.36). The 3GC-therapy group exhibited a longer length-of-stay (38 vs. 21 days, p = 0.0003) and higher in-hospital mortality (23.3% vs. 13.4%, p = 0.019). However, the 90-day mortality, 90-day reinfection, and 90-day readmission were comparable between the therapy groups. Subgroup analyses involving high-risk AmpC-E and 3GC vs. standard-of-care yielded similar conclusions. Overall, our findings suggest that 3GC definitive therapy may not result in poorer clinical outcomes for the treatment of BSIs caused by AmpC-E.

Enterobacter cloacae infection characteristics and outcomes in battlefield trauma patients

Enterobacter cloacae is a Gram-negative rod with multidrug-resistant potential due to chromosomally-induced AmpC β-lactamase. We evaluated characteristics, antibiotic utilization, and outcomes associated with battlefield-related E. cloacae infections (2009-2014). Single initial and serial E. cloacae isolates (≥24 hours from initial isolate from any site) associated with a clinical infection were examined. Susceptibility profiles of initial isolates in the serial isolation group were contrasted against last isolate recovered. Characteristics of 112 patients with E. cloacae infections (63 [56%] with single initial isolation; 49 [44%] with serial isolation) were compared to 509 patients with bacterial infections not attributed to E. cloacae. E. cloacae patients sustained more blast trauma (78%) compared to non-E. cloacae infections patients (75%; p<0.001); however, injury severity scores were comparable (median of 34.5 and 33, respectively; p = 0.334). Patients with E. cloacae infections had greater shock indices (median 1.07 vs 0.92; p = 0.005) and required more initial blood products (15 vs. 14 units; p = 0.032) compared to patients with non-E. cloacae infections. Although E. cloacae patients had less intensive care unit admissions (80% vs. 90% with non-E. cloacae infection patients; p = 0.007), they did have more operating room visits (5 vs. 4; p = 0.001), longer duration of antibiotic therapy (43.5 vs. 34 days; p<0.001), and lengthier hospitalizations (57 vs. 44 days; p<0.001). Patients with serial E. cloacae had isolation of infecting isolates sooner than patients with single initial E. cloacae (median of 5 vs. 8 days post-injury; p = 0.046); however, outcomes were not significantly different between the groups. Statistically significant resistance to individual antibiotics did not develop between initial and last isolates in the serial isolation group. Despite current combat care and surgical prophylaxis guidelines recommending upfront provision of AmpC-inducing antibiotics, clinical outcomes did not differ nor did significant antibiotic resistance develop in patients who experienced serial isolation of E. cloacae versus single initial isolation.

Whole-genome sequencing analysis of Klebsiella aerogenes among men who have sex with men in Guangzhou, China

Klebsiella aerogenes is a common infectious bacterium that poses a threat to human health. Nevertheless, there are limited data on the population structure, genetic diversity, and pathogenicity of K. aerogenes, especially among men who have sex with men (MSM). The present study aimed to clarify the sequence types (STs), clonal complexes (CCs), resistance genes, and virulence factors of popular strains. Multilocus sequence typing was used to describe the population structure of K. aerogenes. The Virulence Factor Database and Comprehensive Antibiotic Resistance Database were used to assess the virulence and resistance profiles. In this study, next-generation sequencing was performed on nasal swabs specimens collected in an HIV Voluntary Counseling Testing outpatient department in Guangzhou, China, from April to August 2019. The identification results showed that a total of 258 K. aerogenes isolates were collected from 911 participants. We found that the isolates were most resistant to furantoin (89.53%, 231/258) and ampicillin (89.15%, 230/258), followed by imipenem (24.81%, 64/258) and cefotaxime (18.22%, 47/258). The most common STs in carbapenem-resistant K. aerogenes were ST4, ST93, and ST14. The population has at least 14 CCs, including several novel ones identified in this study (CC11-CC16). The main mechanism of drug resistance genes was antibiotic efflux. Based on the presence of the iron carrier production genes irp and ybt, we identified two clusters according to virulence profiles. In cluster A, CC3 and CC4 carry the clb operator encoding the toxin. Increased monitoring is needed for the three main ST type strains carried by MSM. The main clone group CC4 has a large number of toxin genes, and it spreads among MSM. Caution is needed to prevent further spread of this clone group in this population. In sum, our results may provide a foundation for the development of new therapeutic and surveillance strategies for treating MSM.

Draft genome sequences of rare Lelliottia nimipressuralis strain MEZLN61 and two Enterobacter kobei strains MEZEK193 and MEZEK194 carrying mobile colistin resistance gene mcr-9 isolated from wastewater in South Africa

OBJECTIVES

Antimicrobial-resistant bacteria of the order Enterobacterales are emerging threats to global public and animal health, leading to morbidity and mortality. The emergence of antimicrobial-resistant, livestock-associated pathogens is a great public health concern. The genera Enterobacter and Lelliottia are ubiquitous, facultatively anaerobic, motile, non-spore-forming, rod-shaped Gram-negative bacteria belonging to the Enterobacteriaceae family and include pathogens of public health importance. Here, we report the first draft genome sequences of a rare Lelliottia nimipressuralis strain MEZLN61 and two Enterobacter kobei strains MEZEK193 and MEZEK194 in Africa.

METHODS

The bacteria were isolated from environmental wastewater samples. Bacteria were cultured on nutrient agar, and the pure cultures were subjected to whole-genome sequencing. Genomic DNA was sequenced using an Illumina MiSeq platform. Generated reads were trimmed and subjected to de novo assembly. The assembled contigs were analysed for virulence genes, antimicrobial resistance genes, and extra-chromosomal plasmids, and multilocus sequence typing was performed. To compare the sequenced strains with other, previously sequenced E. kobei and L. nimipressuralis strains, available raw read sequences were downloaded, and all sequence files were treated identically to generate core genome bootstrapped maximum likelihood phylogenetic trees.

RESULTS

Whole-genome sequencing analyses identified strain MEZLN61 as L. nimipressuralis and strains MEZEK193 and MEZEK194 as E. kobei. MEZEK193 and MEZEK194 carried genes encoding resistance to fosfomycin (fosA), beta-lactam antibiotics (blaACT-9), and colistin (mcr-9). Additionally, MEZEK193 harboured nine different virulence genes, while MEZEK194 harboured eleven different virulence genes. The phenotypic analysis showed that L. nimipressuralis strain MEZLN61 was susceptible to colistin (2 μg/mL), while E. kobei MEZEK193 (64 μg/mL) and MEZEK194 (32 μg/mL) were resistant to colistin.

CONCLUSION

The genome sequences of strains L. nimipressuralis MEZLN6, E. kobei MEZEK193, and E. kobei MEZEK194 will serve as a reference point for molecular epidemiological studies of L. nimipressuralis and E. kobei in Africa. In addition, this study provides an in-depth analysis of the genomic structure and offers important information that helps clarify the pathogenesis and antimicrobial resistance of L. nimipressuralis and E. kobei. The detection of mcr-9, which is associated with very low-level colistin resistance in Enterobacter species, is alarming and may indicate the undetected dissemination of mcr genes in bacteria of the order Enterobacterales. Continuous monitoring and surveillance of the prevalence of mcr genes and their associated phenotypic changes in clinically important pathogens and environmentally associated bacteria is necessary to control and prevent the spread of colistin resistance.

β-Lactam Resistance in ESKAPE Pathogens Mediated Through Modifications in Penicillin-Binding Proteins: An Overview

Bacteria acquire β-lactam resistance through a multitude of mechanisms among which production of β-lactamases (enzymes that hydrolyze β-lactams) is the most common, especially in Gram-negatives. Structural changes in the high-molecular-weight, essential penicillin-binding proteins (PBPs) are widespread in Gram-positives and increasingly reported in Gram-negatives. PBP-mediated resistance is largely achieved by accumulation of mutation(s) resulting in reduced binding affinities of β-lactams. Herein, we discuss PBP-mediated resistance among ESKAPE pathogens that cause diverse hospital- and community-acquired infections globally.

Leptotrichia Bacteremia: 10-Year Retrospective Clinical Analysis and Antimicrobial Susceptibility Profiles

Leptotrichia species are anaerobic, Gram-negative bacilli increasingly recognized as pathogens capable of causing invasive infections such as bloodstream infection (BSI), particularly among immunocompromised patients. However, there is a paucity of data regarding epidemiology, antimicrobial susceptibility, optimal treatment, and clinical outcomes among patients with Leptotrichia bacteremia. Patient risk factors, treatment approaches, and outcomes of a retrospective cohort of adult patients with Leptotrichia BSI at a tertiary medical center (Mayo Clinic Rochester [MCR]) were evaluated. Concurrently, species, temporal trends, and antimicrobial susceptibility testing (AST) results of Leptotrichia isolates submitted to a reference laboratory (Mayo Clinic Laboratories) over the past 10 years were examined. We identified 224 blood culture isolates of Leptotrichia species, with 26 isolates from patients treated at MCR. The most frequent species included L. trevisanii (49%), L. buccalis (24%), and L. wadei (16%). Leptotrichia species demonstrated >90% susceptibility to penicillin, metronidazole, ertapenem, and piperacillin-tazobactam. However, 96% (74/77) of isolates were resistant to moxifloxacin. For patients treated at MCR, the mean patient age was 55 years (standard deviation [SD], 17), with 9 females (35%), and all were neutropenic at the time of BSI. The primary sources of infection were gastrointestinal (58%), intravascular catheter (35%), and odontogenic (15%). Patients were treated with metronidazole (42%), piperacillin-tazobactam (27%), or carbapenems (19%). The mean duration of treatment was 11 days (SD, 4.5), with a 60-day all-cause mortality of 19% and no microbiologic relapse. Leptotrichia species are rare but important causes of BSI in neutropenic patients. Due to evolving antimicrobial susceptibility profiles, a review of AST results is necessary when selecting optimal antimicrobial therapy.

Clinical significance and outcomes of Clostridium tertium bacteremia: analysis of 62 cases in neutropenic and non-neutropenic patients

The clinical significance of Clostridium tertium bacteremia is still uncertain. We evaluated the incidence, clinical characteristics, and outcomes of C. tertium bacteremia and identified differences between neutropenia and non-neutropenia. All adult patients with C. tertium bacteremia in a 2700-bed tertiary center between January 2004 and November 2021 were retrospectively enrolled. The first episode of C. tertium bacteremia in each patient was included in the analysis. Among 601 patients with Clostridium species bacteremia, 62 (10%) had C. tertium bacteremia, and of these 62 patients, 39 (63%) had had recent chemotherapy, and 31 (50%) had neutropenia or hematologic malignancy. C. tertium bacteremia originated frequently from a gastrointestinal tract infection such as enterocolitis (34%), primary bacteremia (29%), and secondary peritonitis (18%), and 34% of patients had polymicrobial bacteremia. Hematologic malignancy, prior antibiotic treatment, neutropenic enterocolitis, and primary bacteremia were significantly associated with C. tertium bacteremia in neutropenic patients, whereas solid tumor, hepatobiliary disease, secondary peritonitis, polymicrobial bacteremia, and a higher frequency of eradicable infection foci were significantly associated with C. tertium bacteremia in non-neutropenic patients. There was 15% 30-day mortality. APACHE II score (adjusted odds ratio [aOR], 1.5; 95% confidence interval [CI], 1.1-2.1) and secondary peritonitis (aOR, 25.9; 95% CI, 3.0-224.7) were independent risk factors for 30-day mortality. The prevalence of C. tertium bacteremia is low, and the characteristics of C. tertium bacteremia are significantly different between neutropenic and non-neutropenic patients. Appropriate investigation for gastrointestinal mucosal injury should be performed to improve treatment outcomes in this form of bacteremia.

Serratia marcescens antibiotic resistance mechanisms of an opportunistic pathogen: a literature review

Serratia marcescens is a ubiquitous bacterium from order Enterobacterales displaying a high genetic plasticity that allows it to adapt and persist in multiple niches including soil, water, plants, and nosocomial environments. Recently, S. marcescens has gained attention as an emerging pathogen worldwide, provoking infections and outbreaks in debilitated individuals, particularly newborns and patients in intensive care units. S. marcescens isolates recovered from clinical settings are frequently described as multidrug resistant. High levels of antibiotic resistance across Serratia species are a consequence of the combined activity of intrinsic, acquired, and adaptive resistance elements. In this review, we will discuss recent advances in the understanding of mechanisms guiding resistance in this opportunistic pathogen.

Cefepime, not Piperacillin/Tazobactam use, for empirical treatment of bloodstream infections caused by Enterobacter spp.: Results from a population pharmacokinetic/pharmacodynamic analysis

OBJECTIVE

There is a paucity of published data to evaluate the efficacy and safety of imipenem, cefepime and piperacillin/tazobactam dosing regimens against bloodstream infections caused by Klebsiella aerogenes (BSIs-Kae) and Enterobacter cloacae complex (BSIs-Ecc) in patients with various degrees of renal function.

METHODS

Pathogens were isolated from China's blood bacterial resistant investigation network. The dosing regimens of imipenem, cefepime and piperacillin were simulated with intermittent infusion and extended infusion. Monte Carlo simulation was performed to calculate the probability of target attainment and a cumulative fraction of response (CFR) against BSIs-Kae/Ecc.

RESULTS

In total, 203 BSIs-Kae, and 785 BSIs-Ecc were isolated from the surveillance network. Imipenem showed the highest in vitro activity against BSIs-Kae/Ecc, followed by cefepime (85%) and piperacillin/tazobactam (70-80%). The MIC₉₀ values of imipenem, cefepime and piperacillin/tazobactam aginst BSIs-Kae and BSIs-Ecc were 1/1 mg/L, 16/16 mg/L, and 64/128 mg/L, respectively. The simulation results showed imipenem achieved the highest CFRs in patients with normal or decreased renal function, with values of 91-99%, followed by FEP (88-96%), without risk of excessive dosing. However, the intermittent and extended dosing regimens of piperacillin/tazobactam were unlikely to provide adequate exposure for empirical management of BSIs-Kae/Ecc (CFRs, 50-80%), regardless of renal function. Besides, the traditional intermittent piperacillin/tazobactam dosing regimens were highly likely to contribute to suboptimal therapeutic exposure when MIC was close to clinical breakpoints.

CONCLUSIONS

Cefepime, not piperacillin/tazobactam, can be a reasonable carbapenem-sparing option in empirically treating BSIs-Kae/Ecc.

A comprehensive description of the TolC effect on the antimicrobial susceptibility profile in Enterobacter bugandensis

Background

Enterobacter bugandensis is an emerging human pathogen in which multidrug resistant strains have been continuously isolated from various environments. Thus, this organism possesses the potential to pose challenges in human healthcare. However, the mechanisms, especially the efflux pumps, responsible for the multidrug resistance in E. bugandensis remain to be well elucidated.

Methods

The Enterobacter strain CMCC(B) 45301 was specifically identified using whole genome sequencing. The specific CMCC(B) 45301 homologues of the TolC dependent efflux-pump genes characterized in Escherichia coli were identified. The tolC deletion mutant in CMCC(B) 45301 was constructed and subjected to susceptibility tests using 26 different antimicrobial agents, along with the wild type strain. The synergistic effects combining the Bacillus crude extract (BCE) and several other TolC-affected compounds against CMCC(B) 45301 were assayed.

Results

We reclassified the Enterobacter CMCC(B) 45301 strain from species cloacae to bugandensis, on the basis of its whole genome sequence. We found that the CMCC(B) 45301 TolC, AcrAB, AcrD, AcrEF, MdtABC, EmrAB, and MacAB exhibit high similarity with their respective homologues in E. coli and Enterobacter cloacae. Our results for the susceptibility tests revealed that lacking tolC causes 4- to 256-fold decrease in the minimal inhibitory concentrations of piperacillin, gentamicin, kanamycin, tetracycline, norfloxacin, ciprofloxacin, chloramphenicol, and erythromycin against CMCC(B) 45301. In addition, the inhibition zones formed by cefuroxime, cefoperazone, amikacin, streptomycin, minocycline, doxycycline, levofloxacin, florfenicol, trimethoprim-sulfamethoxazole, azithromycin, lincomycin, and clindamycin for the tolC mutant were larger or more obvious than that for the parent. Our data suggested the important role played by TolC in CMCC(B) 45301 susceptibility to common antibiotic families covering ß-lactam, aminoglycoside, tetracycline, fluoroquinolone, phenicol, folate pathway antagonist, macrolide, and lincosamide. Deletion for tolC also increased the susceptibility of CMCC(B) 45301 to berberine hydrochloride and BCE, two natural product-based agents. Finally, we found that erythromycin, norfloxacin, and ciprofloxacin can potentiate the antibacterial activity of BCE against CMCC(B) 45301.

Discussion

The present study elaborated the comprehensive TolC effect on the antimicrobial susceptibility profile in E. bugandensis, which might contribute to the development of more therapeutic options against this nosocomial pathogen.

Controversies over the management of infections caused by Amp-C- and ESBL-producing Enterobacterales : what questions remain for future studies?

PURPOSE OF REVIEW

The continuous rise in infections caused by third-generation cephalosporin-resistant Enterobacterales (e.g. extended-spectrum beta-lactamase- or AmpC-producing Enterobacterales ) is a major health concern. Carbapenems are regarded as the antibiotics of choice for the treatment of these infections. However, their indiscriminant use is not without consequences, and has contributed to the emergence of carbapenem-resistant Enterobacterales .In this review, we discuss the available evidence supporting the use of other betalactams, nonbetalactams and the new betalactams/beta-lactamase inhibitors (BLA/BLI) to treat these infections. We also analyze unresolved issues in this field.

RECENT FINDINGS

Piperacillin tazobactam (PTZ) was classically recommended as a carbapenem-sparing agent. However, data have emerged against its use and it is now a controversial recommendation. IDSA, European and British guidelines reject the empirical use of PTZ for these pathogens, reserving its use for rare clinical situations.Other issues that continue to generate debate are the use of extended infusion (3 h) PTZ, the use of older antibiotics, a shortened course of carbapenems and reserving the new BLA/BLI for these infections.

SUMMARY

New treatment strategies should be based on clinical evidence, local epidemiology and the microbiological activity of these drugs.

Clinical outcome of wild-type AmpC-producing Enterobacterales infection in critically ill patients treated with β-lactams: a prospective multicenter study

Background

β-lactams are the main antibiotics used against wild-type AmpC-producing Enterobacterales (wtAE). However, they may fail or select AmpC-overproducing mutants. Our aim was to assess factors associated with clinical failure of β-lactams in the treatment of wtAE infection.

Methods

From September 2017 to December 2020, we prospectively included all consecutive patients treated by definitive β-lactams therapy for wtAE infection in four university ICUs. Clinical failure was defined as inadequate response to antimicrobial therapy leading to death or to the switch for a broader-spectrum antibiotic.

Results

177 patients were included and 29.4% progressed to clinical failure. E. cloacae was the most prevalent species (42.4%) and ventilator-associated pneumonia (VAP) was the most frequent wtAE infection (69.5%). Cefepime and cefotaxime were used as definitive antibiotic treatment in 42.9% and 27.7% of patients, respectively. Occurrence of AmpC-overproduction was documented in 5.6% of patients and was associated with clinical failure (p = 0.004). In multivariate analysis, VAP (p < 0.001, OR 11.58 [95% CI 3.11–43.02] and K. aerogenes (p = 0.030, OR 3.76 [95% CI 1.13–12.46]) were independently associated with clinical failure. Conversely, cefotaxime as definitive treatment was found inversely associated with the risk of clinical failure (p = 0.022, OR 0.25 [95% CI 0.08–0.82]). After inverse probability weighting, cefotaxime showed a 20% risk reduction of clinical failure (95% CI  5–35%, p = 0.007) whatever the location of infection, the SOFA score on the day of wtAE infection, or the bacterial species.

Conclusions

Clinical failure in the treatment of wtAE infections is associated with the infection site and the causal microorganism. Additionally, cefotaxime use is probably protective against clinical failure in wtAE infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01079-5.

The Clinical Evaluation of Third-generation Cephalosporins as Definitive Therapy for Enterobacter spp. and Klebsiella aerogenes Bacteremia

Background Third-generation cephalosporins (3GCs) may be susceptible in vitro to Enterobacter spp. and Klebsiella aerogenes. However, treatment with mainly fourth-generation cephalosporins or carbapenems is currently recommended. Diversification of antimicrobial agents in therapy is required to avoid the selection pressure of resistant organisms by broad-spectrum antimicrobial agents. Aims This study investigated the clinical efficacy of 3GC therapy for Enterobacter spp. and Klebsiella aerogenes bacteremia in a multicenter, retrospective, observational study. Methods Patients with Enterobacter spp. or Klebsiella aerogenes detected in blood cultures and treated with a susceptible antimicrobial agent were included in the study. Propensity score matching was performed to align patient background bases, and clinical outcomes between the 3GC and non-3GC groups were compared. Treatment success was defined as having no need for treatment escalation or the addition of other antimicrobial agents, no recurrence, or no death within 30 days. Results The study included 188 cases, of which 57 and 131 were included in the 3GC and non-3GC treatment groups, respectively; 53 patients in each group were matched by propensity score matching. There were no significant differences between groups in rates of switching to a susceptible antimicrobial or adding another agent, relapse within 30 days, or death within 30 days. In the 3GC group, source control was associated with favorable clinical outcomes. Conclusions Definitive 3GC therapy for susceptible Enterobacter spp. and Klebsiella aerogenes bacteremia is as clinically effective and valuable a targeted therapy as non-3GC therapy and can be implemented under conditions in which infection source control measures are in place.

Clinical Impact of a Pharmacist-Driven Prospective Audit with Intervention and Feedback on the Treatment of Patients with Bloodstream Infection

Evidence for the utility of pharmacist-driven antimicrobial stewardship programs remains limited. This study aimed to evaluate the usefulness of our institutional pharmacist-driven prospective audit with intervention and feedback (PAF) on the treatment of patients with bloodstream infections (BSIs). The effect of pharmacist-driven PAF was estimated using an interrupted time series analysis with a quasi-experimental design. The proportion of de-escalation during BSI treatment increased by 44% after the implementation of pharmacist-driven PAF (95% CI: 30−58, p < 0.01). The number of days of therapy decreased by 16 per 100 patient days for carbapenem (95% CI: −28 to −3.5, p = 0.012) and by 15 per 100 patient days for tazobactam/piperacillin (95% CI: −26 to −4.9, p < 0.01). Moreover, the proportion of inappropriate treatment in empirical and definitive therapy was significantly reduced after the implementation of pharmacist-driven PAF. Although 30-day mortality did not change, compliance with evidenced-based bundles in the BSI of Staphylococcus aureus significantly increased (p < 0.01). In conclusion, our pharmacist-driven PAF increased the proportion of de-escalation and decreased the use of broad-spectrum antibiotics, as well as the proportion of inappropriate treatment in patients with BSI. This indicates that pharmacist-driven PAF is useful in improving the quality of antimicrobial treatment and reducing broad-spectrum antimicrobial use in the management of patients with BSI.

Molecular characterization of Enterobacter aerogenes isolated from urinary tract infections in Iran

The prevalence of multidrug-resistant Enterobacter aerogenes strains in UTIs is increasing. Therefore, the purpose of this study was to examine the mechanisms of resistance in Enterobacter aerogenes strains isolated from the urinary tract of infected patients. To achieve this goal, 786 urine samples from Shahrekord, Iran, were collected from June 2019 to February 2020. After isolating and identifying E. aerogenes samples, antibiotic susceptibility testing was done on the strains using Kirby-Bauer's disk diffusion method. The biofilm formation assays were performed to study the link between antibiotic resistance and biofilm formation and virulence genes. As a result, amongst the 786 urine samples, 50 strains were identified as E. aerogenes. The lowest rate of resistance was observed with imipenem (30%). This study also reports that all the strains of E. aerogenes are biofilm producers, with 50% of isolates producing a large amount, 30% a moderate amount, and 20% a small amount of biofilm. 42% were identified in the phenotypic study of ESBLs. In the PCR test, (64%) produced broad-spectrum beta-lactamases. Prevalence of qnrC, qnrB, qnrA, tetA, tet B, acc(3)IIa, acc(2)IIa, ant(2)Ia and Sul1 in strong producing isolates reported 100%, 80.95%,% 58.14, 87.5%, 81.58%, 86.67%, 82.14, 81.48% and 90% respectively. In the statistical analysis based on the chi-square test, a statistically significant relationship was reported between qnrA, qnrB, tetA, tetB, Sul1, ant(2)Ia, ant(3)I, aac(3)II, and biofilm formation. Resistance to cephalothin, ceftriaxone, cefotaxime and ceftazidime were reported 40%, 34%, 30% and 30%, respectively. Out of 50 Enterobacter aerogenes, 32 isolates (64%) were identified in the phenotypic study of ESBLS, prevalence of bla_CTX-M, bla_TEM and bla_SHV reported 30%, 20% and 14% respectively. There is a significant relationship between resistance to ceftriaxone and bla_CTX-M. Prevalence of csgA, ybtS, markD, rmpA, csgD and fimH in strong biofilm formation isolates reported 84%, 83.33%, 80%, 80%, 80% and 66% respectively. The chi-square test showed a statistically significant relationship between biofilm production and resistance genes fimH, csgA, csgD, ybtS, and mrkD. The findings of this study indicate that the ability to produce biofilms is associated with the increase of antibiotic resistance and virulence genes. These agents enable bacteria to produce biofilms that ultimately lead to colonization and bacterial survival in the body.

Lelliottia steviae sp. nov. isolated from Stevia rebaudiana Bertoni

A Gram-negative, aerobic, chemoheterotrophic, rod-shaped, and motile bacterium, designated as LST-1^T, was isolated from wild Stevia rebaudiana Bertoni and subjected to a polyphasic taxonomic analysis. The LST-1 strain grew optimally at 37 °C and pH 6.0-7.0 in the presence of 0.5% (w/v) NaCl. Phylogenetic analysis based on the 16S rDNA sequence indicated that LST-1 is closely related to Lelliottia jeotgali PFL01^T (99.85%), Lelliottia nimipressuralis LMG10245^T (98.82%), and Lelliottia amnigena LMG2784^T (98.54%). Multi-locus sequence typing of concatenated partial atpD, infB, gyrB, and rpoB genes was performed to improve the resolution, and clear distinctions between the closest related type strains were observed. The results of average nucleotide identify analyses and DNA-DNA hybridization with four species (16S rDNA similarity > 98.65%) were less than 90 and 40%, respectively, verifying the distinct characteristics from other species of Lelliottia. The cellular fatty acid profile of the strain consisted of C16:0, Summed Feature3, and Summed Feature8 (possibly 16:1 w6c/16:1 w7c and 18:1 w6c) as major components. The major polar lipids included phosphatidylethanolamine, phosphatidylglycerol, an aminophospholipid, three non-characteristic phospholipids, and a non-characteristic lipid. The genome of LST-1^T was 4,611,055 bp in size, with a G + C content of 55.02%. The unique combination of several phenotypic, chemotaxonomic, and genomic characteristics proved that strain LST-1^T belongs to a novel species, for which the name Lelliottia steviae sp. nov. is proposed. The type strain is LST-1^T (= CGMCC 1.19175^T = JCM 34938^T).Repositories: The genbank accession numbers for the 16S rRNA gene and genome sequences of strain LST-1T are MZ497264 and CP063663, respectively.

Clinical impact of and microbiological risk factors for qacA/B positivity in ICU-acquired ST5-methicillin-resistant SCCmec type II Staphylococcus aureus bacteremia

Concern about resistance to chlorhexidine has increased due to the wide use of the latter. The impact of the qacA/B and smr chlorhexidine tolerance genes on the outcome of methicillin-resistant Staphylococcus aureus (MRSA) infections is unclear. We evaluated the prevalence and clinical impact of, and microbiological risk factors for, qacA/B tolerance in MRSA bacteremia. MRSA bacteremia that occurred more than two days after intensive care unit admission between January 2009 and December 2018 was identified from a prospective cohort of S. aureus bacteremia in a tertiary-care hospital from South Korea. A total of 183 MRSA blood isolates was identified, and the major genotype found was ST5-MRSA-II (87.4%). The prevalences of qacA/B and smr were 67.2% and 3.8%, respectively. qacA/B-positive isolates were predominantly ST5-MRSA-II (96.7% [119/123]), the dominant hospital clone. In a homogenous ST5-MRSA-II background, qacA/B positivity was independently associated with septic shock (aOR, 4.85), gentamicin resistance (aOR, 74.43), and non-t002 spa type (aOR, 74.12). qacA/B positivity was found to have decreased significantly in ST5-MRSA-II in association with a decline in qacA/B-positive t2460, despite the increasing use of chlorhexidine since 2010 (P < 0.001 for trend). Continuous surveillance of the qac genes, and molecular characterization of their plasmids, are needed to understand their role in MRSA epidemiology.

Clinical Impact of Time-to-Positivity of Blood Cultures on Mortality in Patients with Pseudomonas aeruginosa Bacteremia

OBJECTIVES

To investigate the impact of the time-to-positivity of blood cultures (TTP) on 30-day mortality in patients with Pseudomonas aeruginosa (PA) bacteremia.

METHODS

All non-duplicated episodes of PA monomicrobial bacteremia in adult patients from January 2013 to February 2020 were analysed. Epidemiological and clinical data were collected. TTP for PA isolates was automatically recorded. Multivariate analysis identified factors predicting 30-day overall mortality.

RESULTS

A total of 328 patients were identified. The median TTP for PA isolates was 15 h (IQR 12-18 h). All MDR/XDR episodes were positive within the first 36 h. The 30-day mortality rate was 32.3%. The best cut-off value of the TTP for predicting mortality was 16 h (AUC 0.62, 95% CI 0.56-0.67, P=0.001). The 30-day mortality rate was significantly higher in the TTP ≤16 h group (41.0% versus 19.5%, P<0.001). In a multivariate analysis, severe neutropenia (aOR 2.67, 95% CI 1.4-5.09, P=0.002), septic shock (aOR 3.21, 95% CI 1.57-5.89, P<0.001), respiratory source (aOR 4.37, 95% CI 2.24-8.52, P<0.001), nosocomial acquisition (aOR 1.99, 95% CI 1.06-3.71, P=0.030), TTP≤ 16 h (aOR 2.27, 95% CI 2.12-4.25, P=0.010) and MDR/XDR phenotype (aOR 2.54, 95% CI 1.38-4.67, P=0.002) were independently associated with 30-day mortality.

CONCLUSIONS

A short TTP (≤16 h) was independently associated with increased 30-day mortality. After local validation, this routinely microbiological parameter might be useful for guiding empirical antipseudomonal therapies and supporting the close monitoring of patients with PA bacteremia.

Development and validation of BLOOMY prediction scores for 14-day and 6-month mortality in hospitalised adults with bloodstream infections: a multicentre, prospective, cohort study

BACKGROUND

The burden of bloodstream infections remains high worldwide and cannot be confined to short-term in-hospital mortality. We aimed to develop scores to predict short-term and long-term mortality in patients with bloodstream infections.

METHODS

The Bloodstream Infection due to Multidrug-resistant Organisms: Multicenter Study on Risk Factors and Clinical Outcomes (BLOOMY) study is a prospective, multicentre cohort study at six German tertiary care university hospitals to develop and validate two scores assessing 14-day and 6-month mortality in patients with bloodstream infections. We excluded patients younger than 18 years or who were admitted to an ophthalmology or psychiatry ward. Microbiological, clinical, laboratory, treatment, and survival data were prospectively collected on day 0 and day 3 and then from day 7 onwards, weekly. Participants were followed up for 6 months. All patients in the derivation cohort who were alive on day 3 were included in the analysis. Predictive scores were developed using logistic regression and Cox proportional hazards models with a machine-learning approach. Validation was completed using the C statistic and predictive accuracy was assessed using sensitivity, specificity, and predictive values.

FINDINGS

Between Feb 1, 2017, and Jan 31, 2019, 2568 (61·5%) of 4179 eligible patients were recruited into the derivation cohort. The in-hospital mortality rate was 23·75% (95% CI 22·15-25·44; 610 of 2568 patients) and the 6-month mortality rate was 41·55% (39·54-43·59; 949 of 2284). The model predictors for 14-day mortality (C statistic 0·873, 95% CI 0·849-0·896) and 6-month mortality (0·807, 0·784-0·831) included age, body-mass index, platelet and leukocyte counts, C-reactive protein concentrations, malignancy (ie, comorbidity), in-hospital acquisition, and pathogen. Additional predictors were, for 14-day mortality, mental status, hypotension, and the need for mechanical ventilation on day 3 and, for 6-month mortality, focus of infection, in-hospital complications, and glomerular filtration rate at the end of treatment. The scores were validated in a cohort of 1023 patients with bloodstream infections, recruited between Oct 9, 2019, and Dec 31, 2020. The BLOOMY 14-day score showed a sensitivity of 61·32% (95% CI 51·81-70·04), a specificity of 86·36% (83·80-88·58), a positive predictive value (PPV) of 37·57% (30·70-44·99), and a negative predictive value (NPV) of 94·35% (92·42-95·80). The BLOOMY 6-month score showed a sensitivity of 69·93% (61·97-76·84), a specificity of 66·44% (61·86-70·73), a PPV of 40·82% (34·85-47·07), and a NPV of 86·97% (82·91-90·18).

INTERPRETATION

The BLOOMY scores showed good discrimination and predictive values and could support the development of protocols to manage bloodstream infections and also help to estimate the short-term and long-term burdens of bloodstream infections.

FUNDING

DZIF German Center for Infection Research.

TRANSLATION

For the German translation of the abstract see Supplementary Materials section.

Antimicrobial resistance of Escherichia coli, Enterobacter spp., Klebsiella pneumoniae and Enterococcus spp. isolated from the feces of giant panda

Background

Escherichia coli, Enterobacter spp., Klebsiella pneumoniae and Enterococcus spp., common gut bacteria in giant pandas, include opportunistic pathogens. The giant panda is an endangered species, classified as vulnerable by the World Wildlife Foundation. Continuous monitoring for the emergence of antimicrobial resistance (AMR) among bacterial isolates from giant pandas is vital not only for their protection but also for public health.

Results

A total of 166 E. coli, 68 Enterobacter spp., 116 K. pneumoniae and 117 Enterococcus spp. isolates were collected from fecal samples of 166 giant pandas. In the antimicrobial susceptibility tests, 144 E. coli isolates, 66 Enterobacter spp. isolates, 110 K. pneumoniae isolates and 43 Enterococcus spp. isolates were resistant to at least one antimicrobial. The resistant isolates carried antimicrobial resistance genes (ARGs), including sul3, bla_TEM, bla_SHV and tetA. The differences in the prevalence of the bla types implied that the genetic basis for β-lactam resistance among the E. coli, Enterobacter spp. and K. pneumoniae isolates was different. The strain K. pneumoniae K85 that was resistant to sixteen antimicrobials was selected for whole genome sequencing. The genome contained Col440I, IncFIB_K and IncFII_K plasmids and altogether 258 ARGs were predicted in the genome; 179 of the predicted ARGs were efflux pump genes. The genetic environment of the β-lactamase genes bla_CTX-M-3 and bla_TEM-1 in the K. pneumoniae K85 genome was relatively similar to those in other sequenced K. pneumoniae genomes. In comparing the giant panda age groups, the differences in the resistance rates among E. coli, K. pneumoniae and Enterobacter spp. isolates suggested that the infections in giant pandas of different age should be treated differently.

Conclusions

Antimicrobial resistance was prevalent in the bacterial isolates from the giant pandas, implying that the gut bacteria may pose serious health risks for captive giant pandas. The resistance genes in the genome of K. pneumoniae K85 were associated with insertion sequences and integron-integrase genes, implying a potential for the further spread of the antimicrobial resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02514-0.

Impact of antibiotic susceptibility reporting on broad spectrum antibiotic use in serratia and morganella bacteremia

To minimize broad-spectrum antibiotic use, our microbiology laboratory changed antibiotic susceptibility reporting for AmpC-beta-lactamase producing Serratia marcescens and Morganella morganii in blood cultures to include results of narrow spectrum 3rd generation cephalosporins. We assessed the impact of this change on broad-spectrum antibiotic use and clinical outcomes. All adult patients with Serratia marcescens or Morganella morganii in blood culture 2 years pre- and post-change of susceptibility reporting were retrospectively reviewed. Exclusion: more than one pathogen isolated in their blood culture, did not receive antibiotics or died within 48 hours of positive blood culture. Outcomes: Rates of broad-spectrum antibiotic use, in-hospital mortality, clinical response and microbiologic success. There were 30 patients pre-change and 46 patients post-change of reporting. Cefepime use (broad-spectrum) decreased from 46.7% to 6.5% (p < 0.001) and 3^rd generation cephalosporin (narrow-spectrum) use increased (3.3% vs 34.8%, p = 0.0013) in the post-change cohort. This demonstrates the potential role of selective susceptibility reporting in antimicrobial stewardship.

Infectious Diseases Society of America Guidance on the Treatment of AmpC β-lactamase-Producing Enterobacterales, Carbapenem-Resistant Acinetobacter baumannii, and Stenotrophomonas maltophilia Infections

BACKGROUND

The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. A previous guidance document focused on infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa). Here, guidance is provided for treating AmpC β-lactamase-producing Enterobacterales (AmpC-E), carbapenem-resistant Acinetobacter baumannii (CRAB), and Stenotrophomonas maltophilia infections.

METHODS

A panel of six infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated questions about the treatment of AmpC-E, CRAB, and S. maltophilia infections. Answers are presented as suggestions and corresponding rationales. In contrast to guidance in the previous document, published data on optimal treatment of AmpC-E, CRAB, and S. maltophilia infections are limited. As such, guidance in this document is provided as "suggested approaches" based on clinical experience, expert opinion, and a review of the available literature. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States.

RESULTS

Preferred and alternative treatment suggestions are provided, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Suggestions apply for both adult and pediatric populations.

CONCLUSIONS

The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of September 17, 2021 and will be updated annually. The most current versions of IDSA documents, including dates of publication, are available at www.idsociety.org/practice-guideline/amr-guidance-2.0/.

Development and validation of a risk score for predicting positivity of blood cultures and mortality in patients with bacteremia and fungemia

INTRODUCTION

Bacteremia is a major cause of morbidity and mortality in hospitalized patients. Predictors of mortality are critical for the management and survival of hospitalized patients. The objective of this study was to determine the factors related to blood culture positivity and the risk factors for mortality in patients whose blood cultures were collected.

METHODS

A prospective 2-cohort study (derivation with 784 patients and validation with 380 patients) based on the Pitt bacteremia score for all patients undergoing blood culture collection. The score was obtained from multivariate analysis. The Kaplan-Meier survival curve of the cohort derivation and the cohort validation groups was calculated, and the difference was assessed using a log-rank test. Mortality-related factors were older age, extended hospitalization, > 10% of immature cells in the leukogram, lower mean blood pressure, elevated heart rate, elevated WBC count, and elevated respiratory rate. These continuous variables were dichotomized according to their significance level, and a cut-off limit was created.

RESULTS

The area under the ROC curve (AUC) was 0.789. The score was validated in a group of 380 patients who were prospectively evaluated.

CONCLUSION

Prolonged hospitalization, body temperature, and elevated heart rate were related to positive blood cultures. The Pitt score can be used to assess the risk of death; however it can be individualized according to the epidemiology of each hospital.

Comparison of Ceftriaxone and Antipseudomonal β-Lactam Antibiotics Utilized for Potential AmpC β-Lactamase-Producing Organisms

Background: Induction of antibiotic resistance is associated with increased morbidity and mortality in AmpC β-lactamase producing Enterobacteriaceae. The use of ceftriaxone is controversial for treatment of these organisms due to concerns for inducible resistance. This study was designed to compare treatment failure rates between ceftriaxone and antipseudomonal β-lactam antibiotics when used as definitive therapy for organisms most commonly associated with chromosomal AmpC β-lactamase production. Methods: A retrospective, single-center cohort study was performed enrolling patients hospitalized with monomicrobial Enterobacter, Citrobacter, or Serratia spp. infections. The primary objective compared proportion of treatment failure between groups. All patients received either ceftriaxone or an antipseudomonal β-lactam alone within 24 hours of culture finalization, and with a duration of at least 72 hours for definitive treatment. Treatment failure was defined as either clinical failure (abnormal white blood cell count or temperature on day 7 or 14 post-antibiotics) or microbiologic failure (regrowth of the same organism at same site within 14 or 21 days). Results: Of 192 total patients, treatment failure was observed in 24/71 patients (34%) receiving ceftriaxone and in 42/121 patients (35%) receiving antipseudomonal β-lactam (P = .98). No difference was observed between clinical or microbiologic failure rates between groups. The ceftriaxone group had significantly more patients undergoing treatment for urinary tract infections (51% vs 17%, P < .001), but treatment failure rates remained similar between groups when comparing infections of all other sources. Conclusion: Ceftriaxone has comparable treatment failure rates to antipseudomonal β-lactams for susceptible Enterobacteriaceae infections and may be considered as a therapeutic option. Further, prospective research is needed to validate optimal dosing and application in all sites of infection.

Modified Pitt bacteremia score for predicting mortality in patients with candidaemia: A multicentre seven-year retrospective study conducted in Japan

BACKGROUND

Several severity indexes have been reported for critically ill patients. The Pitt bacteremia score (PBS) is commonly used to predict the risk of mortality in patients with bacteraemia.

OBJECTIVES

To develop a scoring system for predicting mortality in candidaemia patients.

METHODS

Medical records at five Japanese tertiary hospitals were reviewed. Factors associated with mortality were analysed using logistic regression modelling. The discriminatory power of scoring models was evaluated by assessing the area under the receiver operating characteristic curve (AUC), net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

RESULTS

In total, 422 candidaemia patients were included. Higher PBS, dialysis and retainment of central venous catheter were independent risk factors for all-cause 30-day mortality. However, among the five PBS components, fever was not associated with mortality; therefore, we developed a modified version of the PBS (mPBS) by replacing fever with dialysis. AUC for PBS and mPBS were 0.74 (95% confidence interval [CI]: 0.68-0.80) and 0.76 (95% CI: 0.71-0.82), respectively. The increase in predictive ability of mPBS for 30-day mortality was statistically significant as assessed by NRI (0.24, 95% CI: 0.01-0.46, p = .04) and IRI (0.04, 95% CI: 0.02-0.06, p = .0008). When patients were stratified by mPBS into low (scores 0-3), moderate (4-7) and high risk (≥8), there were significant differences among the survival curves (p < .0001, log-rank test), and 30-day mortality rates were 13.8% (40/290), 36.8% (28/76) and 69.4% (34/49), respectively.

CONCLUSIONS

mPBS can be a useful tool for predicting mortality in candidaemia patients.

Risk factors for microbiologic failure in children with Enterobacter species bacteremia

Background

Enterobacter species are an important cause of healthcare-associated bloodstream infections (BSI) in children. Up to 19% of adult patients with Enterobacter BSI have recurrence of infection resistant to third-generation cephalosporins (3GCs) while on therapy with a 3GC. Data are lacking regarding the incidence of and risk factors for recurrence of infection in children with Enterobacter BSI.

Methods

We conducted a retrospective case-control study of patients aged ≤21 years old admitted to Texas Children’s Hospital from January 2012 through December 2018 with Enterobacter BSI. The primary outcome was microbiologic failure from 72 hours to 30 days after the initial BSI (cases). The secondary outcome was isolation of a 3GC non-susceptible Enterobacter sp. from a patient with an initial 3GC-susceptible isolate.

Results

Twelve patients (6.7%) had microbiologic failure compared to 167 controls without microbiologic failure. Of the 138 patients (77.1%) with an Enterobacter sp. isolate that was initially susceptible to 3GCs, 3 (2.2%) developed a subsequent infection with a non-susceptible isolate. Predictors of microbiologic failure were having an alternative primary site of infection besides bacteremia without a focus or an urinary tract infection (OR, 9.64; 95% CI, 1.77–52.31; P < 0.01) and inadequate source control (OR, 22.16; 95% CI, 5.26–93.36; P < 0.001).

Conclusions

Source of infection and adequacy of source control are important considerations in preventing microbiologic failure. In-vitro susceptibilities can be used to select an antibiotic regimen for the treatment of Enterobacter BSI in children.

Sickle cell disease children's gut colonization by extended-spectrum β-lactamase (ESBL)-producing Enterobacterales: an antibiotic prophylaxis effect?

Introduction. Sickle cell disease (SCD) children have a high susceptibility to pneumococcal infection. For this reason, they are routinely immunized with pneumococcal vaccines and use antibiotic prophylaxis (AP).Hypothesis/Gap Statement. Yet, little is known about SCD children's gut microbiota. If antibiotic-resistant Enterobacterales may colonize people on AP, we hypothesized that SCD children on AP are colonized by resistant enterobacteria species.Objective. To evaluate the effect of continuous AP on Enterobacterales gut colonization from children with SCD.Methodology. We analysed 30 faecal swabs from SCD children on AP and 21 swabs from children without the same condition. Enterobacterales was isolated on MacConkey agar plates and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) (bioMérieux, Marcy l'Etoile, France). We performed the antibiogram by Vitek 2 system (bioMérieux, Marcy l'Etoile, France), and the resistance genes were identified by multiplex PCR.Results. We found four different species with resistance to one or more different antibiotic types in the AP-SCD children's group: Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii, and Citrobacter farmeri. Colonization by resistant E. coli was associated with AP (prevalence ratio 2.69, 95 % confidence interval [CI], 1.98-3.67, P<0.001). Strains producing extended-spectrum β-lactamases (ESBL) were identified only in SCD children, E. coli, 4/30 (13 %), and K. pneumoniae, 2/30 (7 %). The ESBL-producing Enterobacterales were associated with penicillin G benzathine use (95 % CI, 22.91-86.71, P<0.001). CTX-M-1 was the most prevalent among ESBL-producers (3/6, 50 %), followed by CTX-M-9 (2/6, 33 %), and CTX-M-2 (1/6, 17 %).Conclusion. Resistant enterobacteria colonize SCD children on AP, and this therapy raises the chance of ESBL-producing Enterobacterales colonization. Future studies should focus on prophylactic vaccines as exclusive therapy against pneumococcal infections.

Clinical characteristics, appropriateness of empiric antibiotic therapy, and outcome of Pseudomonas aeruginosa bacteremia across multiple community hospitals

There is relatively little contemporary information regarding clinical characteristics of patients with Pseudomonas aeruginosa bacteremia (PAB) in the community hospital setting. This was a retrospective, observational cohort study examining the clinical characteristics of patients with PAB across several community hospitals in the USA with a focus on the appropriateness of initial empirical therapy and impact on patient outcomes. Cases of PAB occurring between 2016 and 2019 were pulled from 8 community medical centers. Patients were classified as having either positive or negative outcome at hospital discharge. Several variables including receipt of active empiric therapy (AET) and the time to receiving AET were collected. Variables with a p value of < 0.05 in univariate analyses were included in a multivariable logistic regression model. Two hundred and eleven episodes of PAB were included in the analysis. AET was given to 81.5% of patients and there was no difference in regard to outcome (p = 0.62). There was no difference in the median time to AET in patients with a positive or negative outcome (p = 0.53). After controlling for other variables, age, Pitt bacteremia score ≥ 4, and septic shock were independently associated with a negative outcome. A high proportion of patients received timely, active antimicrobial therapy for PAB and time to AET did not have a significant impact on patient outcome.

Characterization of Enterobacter cloacae and Citrobacter freundii species complex isolates with decreased susceptibility to cephalosporins from United States hospitals and activity of ceftazidime/avibactam and comparator agents

Objectives

To evaluate the antimicrobial susceptibility and resistance mechanisms to β-lactams among Enterobacter cloacae and Citrobacter freundii from United States medical centres.

Methods

2571 E. cloacae and 1008 C. freundii species complex isolates were consecutively collected from 77 medical centres and susceptibility tested by broth microdilution method. Isolates displaying MIC values ≥16 mg/L for ceftazidime or ≥2 mg/L for cefepime (n = 914) were tested for β-lactamase-encoding genes using whole genome sequencing.

Results

Overall susceptibility to ceftazidime and cefepime were 73.9% and 91.2% among E. cloacae and 74.2% and 93.5% among C. freundii, respectively. Sixty-three isolates harboured a carbapenemase gene, including 56 bla_KPC, 2 bla_NMC-A, and 5 metallo-β-lactamase genes. Among non-carbapenemase producers, 121 isolates had at least one ESBL-encoding gene, mainly bla_SHV (81) or bla_CTX-M (61), and 15 had a transferable AmpC gene, mainly bla_DHA-1 (8) or bla_FOX-5 (6). Carbapenemase, ESBL, or transferable AmpC-encoding genes were not identified among 718 of 914 (78.6%) isolates sequenced. The most active agents against isolates with a decreased susceptibility to ceftazidime and/or cefepime were ceftazidime/avibactam (MIC_50/90, 0.5/1 mg/L; 99.3% susceptible), amikacin (MIC_50/90, 1/4 mg/L; 99.5% susceptible), and meropenem (MIC_50/90, 0.06/0.5 mg/L; 92.9% susceptible). The isolates resistant to ceftazidime/avibactam were the five MBL producers and one E. cloacae isolate with a reduced expression of OmpF and overexpression of AcrAB-TolC.

Conclusions

Hyperproduction of chromosomal AmpC appears to be the most common mechanism of resistance to ceftazidime and/or cefepime in E. cloacae and C. freundii. Ceftazidime/avibactam remained highly active against most isolates showing decreased susceptibility to ceftazidime and/or cefepime.

Enterobacter cloacae complex outbreak in a neonatal intensive care unit: multifaceted investigations and preventive measures are needed

We report the investigation to control an Enterobacter cloacae complex outbreak in a neonatal intensive care unit from November 2020 to February 2021. Pulsed-field gel electrophoresis showed that five of eight cases were infected with a clonal strain. Breast pumps, shared among mothers in the unit, could have contributed to the spread of the clonal spread.

Difference in the Clinical Outcome of Bloodstream Infections Caused by Klebsiella aerogenes and Enterobacter cloacae Complex

Background

The difference in clinical outcomes between Klebsiella aerogenes (formerly Enterobacter aerogenes) bacteremia (KAB) and Enterobacter cloacae complex bacteremia (ECB) is controversial.

Methods

We compared the clinical outcomes of patients with KAB and ECB and examined the risk factors associated with mortality. We conducted a retrospective case-control study of hospitalized patients with monobacterial KAB and ECB between January 2011 and June 2020. The primary outcome measure was 30-day all-cause mortality. Multiple logistic regression and propensity-score (PS) matching were used to identify independent risk factors for mortality. The models included demographic characteristics, comorbidities, recent healthcare contact, patient status at the onset of bacteremia, and severity of infection as covariates.

Results

A total of 282 patients with KAB or ECB were included, among whom 194 patients were selected after PS matching. The 30-day all-cause mortality rate was higher in the ECB group than in the KAB group (24.1% vs 10.6%, P = .003). In a multivariable model, ECB was an independent risk factor for 30-day mortality in both overall and PS-matched cohorts (adjusted odds ratio, 3.528; 95% confidence interval, 1.614–7.714; P = .002). Stay in the intensive care unit at the onset of bacteremia and higher Pitt bacteremia score were found to be independent risk factors for 30-day mortality.

Conclusions

In our study, mortality was significantly higher in patients with ECB than in those with KAB. Further studies are warranted to clarify the virulence mechanisms of E cloacae complex.

Changing characteristics of S. aureus bacteremia caused by PVL-negative, MRSA strain over 11 years

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) has emerged as an important cause of infection. We conducted a longitudinal study to evaluate changes in clinical and microbiological characteristics as well as outcomes of sequence type (ST) 72 MRSA bacteremia. We reviewed adult patients enrolled in a prospective cohort with ST72 MRSA bacteremia from August 2008 to December 2018 at Asan Medical Center, Seoul, South Korea. Changes in clinical characteristics, outcomes, and microbiological characteristics of patients over time were evaluated. Generalized linear and linear regression models were used to evaluate changes. Of the 1,760 isolates, 915 (62%) were MRSA bacteremia and 292 (31.9%) were ST72 MRSA. During the study period, the relative risk (RR) of MRSA bacteremia decreased annually by 3.7%; however, among MRSA bacteremia, RR of ST72 MRSA increased annually by 8.5%. Vancomycin minimum inhibitory concentration (MIC) decreased over the study period. Metastatic infection, persistent bacteremia, and recurrence of bacteremia within 12 weeks decreased significantly. There were no significant changes in 30-d and 12-week mortality. Antibiotic susceptibility of ST72 MRSA was evaluated, and the resistance rate to erythromycin decreased significantly. ST72 MRSA incidence increased annually; its vancomycin MIC and erythromycin resistance rate decreased over the 11 years.

Meropenem Versus Piperacillin-Tazobactam for Definitive Treatment of Bloodstream Infections Caused by AmpC β-Lactamase-Producing Enterobacter spp, Citrobacter freundii, Morganella morganii, Providencia spp, or Serratia marcescens: A Pilot Multicenter Randomized Controlled Trial (MERINO-2)

Background

Carbapenems are recommended treatment for serious infections caused by AmpC-producing gram-negative bacteria but can select for carbapenem resistance. Piperacillin-tazobactam may be a suitable alternative.

Methods

We enrolled adult patients with bloodstream infection due to chromosomal AmpC producers in a multicenter randomized controlled trial. Patients were assigned 1:1 to receive piperacillin-tazobactam 4.5 g every 6 hours or meropenem 1 g every 8 hours. The primary efficacy outcome was a composite of death, clinical failure, microbiological failure, and microbiological relapse at 30 days.

Results

Seventy-two patients underwent randomization and were included in the primary analysis population. Eleven of 38 patients (29%) randomized to piperacillin-tazobactam met the primary outcome compared with 7 of 34 patients (21%) in the meropenem group (risk difference, 8% [95% confidence interval {CI}, –12% to 28%]). Effects were consistent in an analysis of the per-protocol population. Within the subcomponents of the primary outcome, 5 of 38 (13%) experienced microbiological failure in the piperacillin-tazobactam group compared to 0 of 34 patients (0%) in the meropenem group (risk difference, 13% [95% CI, 2% to 24%]). In contrast, 0% vs 9% of microbiological relapses were seen in the piperacillin-tazobactam and meropenem arms, respectively. Susceptibility to piperacillin-tazobactam and meropenem using broth microdilution was found in 96.5% and 100% of isolates, respectively. The most common AmpC β-lactamase genes identified were bla_CMY-2, bla_DHA-17, bla_CMH-3, and bla_ACT-17. No ESBL, OXA, or other carbapenemase genes were identified.

Conclusions

Among patients with bloodstream infection due to AmpC producers, piperacillin-tazobactam may lead to more microbiological failures, although fewer microbiological relapses were seen.

Clinical Trials Registration

NCT02437045.

C-reactive protein predicts persistent bacteremia caused by community-acquired methicillin-resistant Staphylococcus aureus strain

There is limited data on persistent bacteremia (PB) caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Here, we aimed to investigate the clinical and microbiological characteristics of PB caused by the major CA-MRSA strain in Korea (ST72-SCCmecIV). All adult patients with S. aureus bacteremia were prospectively investigated from August 2008 to December 2018. Patients with ST72 MRSA bacteremia were included in the study. Patients were stratified into the PB group (defined as positive blood cultures for ≥ 3 days) and short bacteremia (SB) group. A total of 291 patients were included, comprising 115 (39.5%) with PB and 176 (60.5%) with SB. Although the 30-day mortality did not differ between PB and SB, recurrent bacteremia within 12 weeks was significantly more common in PB (8.7% vs 1.7%; P = 0.01). Multivariate analysis showed risk factors of PB were liver cirrhosis (adjusted odds ratio [aOR], 3.27; 95% confidence interval [CI], 1.50-7.12), infective endocarditis (aOR, 7.13; 95% CI, 1.37-37.12), bone and joint infections (aOR, 3.76; 95% CI, 1.62-8.77), C-reactive protein ≥ 10 mg/dL (aOR, 2.20; 95% CI, 1.22-3.95), metastatic infection (aOR, 7.35; 95% CI, 3.53-15.29), and agr dysfunction (aOR, 2.47; 95% CI, 1.05-5.81). PB occurred in approximately 40% of bacteremia caused by ST72 MRSA with a significantly higher recurrence rate. Patients with risk factors of PB, including liver cirrhosis, high initial CRP, infective endocarditis, or bone and joint infections, might require early aggressive treatment.

Comparison of outcomes in urinary tract infections caused by AmpC-harboring organisms treated with AmpC stable versus AmpC susceptible agents

There is minimal data on the optimal treatment of lower inoculum infections such as urinary tract infections (UTIs) caused by SPICE organisms which encode the betalactamase enzyme, AmpC. This single-center, retrospective review of adult hospitalized patients with UTIs caused by a SPICE organism compared outcomes amongst patients treated with drugs susceptible to AmpC hydrolysis versus drugs stable against AmpC. Of 156 patients, similar rates of clinical response, 30-day infection related readmission, 30-day infection recurrence, 30-day mortality rates, and median length of hospital stay were found between the two groups. Notably, 44% of patients with ceftriaxone resistance reported had recent β-lactam exposure versus only 11% of patients without ceftriaxone resistance (P = 0.002). Based on our data, there does not appear to be a difference in clinical response or any of the secondary outcomes in patients with UTIs treated with AmpC stable and AmpC susceptible agents.

Molecular epidemiology of Enterobacter cloacae complex isolates with reduced carbapenem susceptibility recovered by blood culture

The Enterobacter cloacae complex (ECC) is one of the most common causes of bacteremia and leads to poor clinical outcomes. The aim of this study was to clarify the antimicrobial susceptibility profiles and genetic backgrounds of non-carbapenemase-producing reduced-carbapenem-susceptible (RCS) ECC blood isolates in Japan using agar dilution antimicrobial susceptibility testing, whole-genome sequencing, and quantitative polymerase chain reaction for assays of ampC, ompC and ompF transcripts. Forty-two ECC blood isolates were categorized into RCS and carbapenem-susceptible groups based on imipenem minimum inhibitory concentration. RCS ECC blood isolates belonged to distinct species and sequence types and produced varying class C β-lactamases. The E. roggenkampii, E. asburiae, and E. bugandensis isolates belonged only to the RCS group. Some E. hormaecheii ssp. steigerwaltii isolates of the RCS group exhibited AmpC overexpression caused by amino acid substitutions in AmpD and AmpR along with ompF gene downregulation. These findings suggest that non-carbapenemase-producing RCS ECC blood isolates are genetically diverse.