Risk factors and clinical features of infections caused by plasmid-mediated AmpC beta-lactamase-producing Enterobacteriaceae

Rapid detection of plasmid-mediated AmpC-producers by eazyplex® SuperBug AmpC assay compared to whole-genome sequencing

Current methods for plasmid-mediated AmpC β-lactamase (pAmpC) detection in routine microbiological laboratories are based on various phenotypic tests. Eazyplex®SuperBug AmpC assay is a molecular assay based on isothermal amplification for rapid detection of the most common pAmpC types from bacterial culture: CMY-2 group, DHA, ACC and MOX. Our aim was to evaluate the diagnostic performance of this assay. The assay was evaluated on 64 clinical isolates of Enterobacterales without chromosomal inducible AmpC, and with phenotypically confirmed AmpC production. The results were confirmed, and isolates further characterized by whole-genome sequencing (WGS). eazyplex®SuperBug AmpC assay correctly detected the two most common pAmpC types CMY-2 group (16/16) and DHA (19/19). Detection of ACC and MOX could not be evaluated on our set of isolates since there was only one isolate harbouring ACC and none with MOX. pAmpC encoding genes could be detected in only eight of 36 investigated Escherichia coli isolates. The remaining 28 E. coli isolates harboured previously described mutations in the blaEC promoter, leading to the overexpression of chromosomally encoded E. coli specific AmpC β-lactamase. All results were 100% concordant with the results of WGS. eazyplex®SuperBug AmpC assay enabled rapid and reliable detection of pAmpC-encoding genes in Enterobacterales like Klebsiella spp. and Proteus spp. and the distinction between plasmid-mediated and chromosomally encoded AmpC in E. coli.

Carriage of β-lactamase and carbapenemase-producing Enterobacteriaceae in hospitalized patients at debre tabor comprehensive specialized hospital

Background

Antimicrobial resistance has remained global public health threat. Carriage with drug-resistant bacterial pathogens, particularly beta-lactamase and carbapenemase-producing Enterobacteriaceae is among the most concerning. The purpose of this study was to look into the magnitude, antimicrobial resistance patterns, and associated risk factors among hospitalized patients.

Methods

A facility-based cross-sectional study was conducted on 383 hospitalized patients at Debre Tabor Comprehensive Specialized Hospital between September 2022 and May 2023. A pre-tested structured questionnaire was used to collect sociodemographic and clinical data. The data on the etiologic agent was collected using standard bacteriological techniques. Briefly, stool specimens were collected aseptically into sterile, leak-proof stool cups. The stool sample was inoculated onto MacConkey agar and incubated aerobically at 37 °C for 24 h. The species isolation and antimicrobial resistance patterns were then performed adhering to bacteriological procedures. In the analysis, a p-value of <0.05 was considered statistically significant.

Results

There were 383 study participants, and men made up the majority (55.6%). The study participants' mean age was 33 ± 18 years. Three hundred and seventy-seven (88%) of the study's participants had no previous history of antibiotic use. There were 102 (26.6%) and 21 (5.5%) cases of gastrointestinal carriage caused by Enterobacteriaceae that produce beta-lactamase and carbapenemase, respectively. In total, 175 isolates of Enterobacteriaceae were detected. E. coli (n = 89) and K. pneumoniae (n = 51) were the most frequently recovered. In this study, 46 (79.3%) and 8 (13.8%) isolates of E. coli that produce beta-lactamase were resistant to ampicillin and amoxicillin/clavulanic acid, respectively. Furthermore, participants who had previously used antibiotics experienced a two-fold increase in exposure to gastrointestinal tract carriage by carbapenemase-producing Enterobacteriaceae [AOR, 95% CI (2.01, 1.06-2.98), p = 0.001].

Conclusions

The emergence of drug-resistant pathogens is a growing concern. An increase in the prevalence of drug-resistant infections in hospitalized patients is warranting further investigation.

Genotypic Determination of Extended Spectrum β-Lactamases and Carbapenemase Production in Clinical Isolates of Klebsiella pneumoniae in Southwest Nigeria

INTRODUCTION

Klebsiella pneumoniae is a major pathogen implicated in healthcare-associated infections. Extended-spectrum β-lactamase (ESBL) and carbapenemase-producing K. pneumoniae isolates are a public health concern. This study investigated the existence of some ESBL and carbapenemase genes among clinical isolates of K. pneumoniae in Southwest Nigeria and additionally determined their circulating clones.

MATERIALS AND METHODS

Various clinical samples from 420 patients from seven tertiary hospitals within Southwestern Nigeria were processed between February 2018 and July 2019. These samples were cultured on blood agar and MacConkey agar, and the isolated bacteria were identified by Microbact GNB 12E. All K. pneumoniae were confirmed by polymerase chain reaction (PCR) using the 16s rRNA gene. Antibiotic susceptibility testing (AST) was done on these isolates, and the PCR was used to evaluate the common ESBL-encoding genes and carbapenem resistance genes. Genotyping was performed using multi-locus sequencing typing (MLST).

RESULTS

The overall prevalence of K. pneumoniae in Southwestern Nigeria was 30.5%. The AST revealed high resistance rates to tetracyclines (67.2%), oxacillin (61.7%), ampicillin (60.2%), ciprofloxacin (58.6%), chloramphenicol (56.3%), and lowest resistance to meropenem (43.0%). All isolates were susceptible to polymyxin B. The most prevalent ESBL gene was the TEM gene (47.7%), followed by CTX-M (43.8%), SHV (39.8%), OXA (27.3%), CTX-M-15 (19.5%), CTX-M-2 (11.1%), and CTX-M-9 (10.9%). Among the carbapenemase genes studied, the VIM gene (43.0%) was most detected, followed by OXA-48 (28.9%), IMP (22.7%), NDM (17.2%), KPC (13.3%), CMY (11.7%), and FOX (9.4%). GIM and SPM genes were not detected. MLST identified six different sequence types (STs) in this study. The most dominant ST was ST307 (50%, 5/10), while ST258, ST11, ST147, ST15, and ST321 had (10%, 1/10) each.

CONCLUSION

High antimicrobial resistance in K. pneumoniae is a clear and present danger for managing infections in Nigeria. Additionally, the dominance of a successful international ST307 clone highlights the importance of ensuring that genomic surveillance remains a priority in the hospital environment in Nigeria.

β-lactam resistance associated with β-lactamase production and porin alteration in clinical isolates of E. coli and K. pneumoniae

β-lactam resistance represents a worldwide problem and a serious challenge for antimicrobial treatment. Hence this research was conducted to recognize several mechanisms mediating β-lactam resistance in E. coli and K. pneumoniae clinical isolates collected from Mansoura University hospitals, Egypt. A total of 80 isolates, 45 E. coli and 35 K. pneumoniae isolates, were collected and their antibiotic susceptibility was determined by the Disc diffusion method followed by phenotypic and genotypic detection of extended-spectrum β-lactamases (ESBLs), AmpC β-lactamase, carbapenemase enzymes. The outer membrane protein porins of all isolates were analyzed and their genes were examined using gene amplification and sequencing. Also, the resistance to complement-mediated serum killing was estimated. A significant percentage of isolates (93.8%) were multidrug resistance and showed an elevated resistance to β-lactam antibiotics. The presence of either ESBL or AmpC enzymes was high among isolates (83.75%). Also, 60% of the isolated strains were carbapenemase producers. The most frequently detected gene of ESBL among all tested isolates was bla_CTX-M-15 (86.3%) followed by bla_TEM-1 (81.3%) and bla_SHV-1 (35%) while the Amp-C gene was present in 83.75%. For carbapenemase-producing isolates, bla_NDM1 was the most common (60%) followed by bla_VIM-1 (35%) and bla_OXA-48 (13.8%). Besides, 73.3% and 40% of E. coli and K. pneumoniae isolates respectively were serum resistant. Outer membrane protein analysis showed that 93.3% of E. coli and 95.7% of K. pneumoniae isolates lost their porins or showed modified porins. Furthermore, sequence analysis of tested porin genes in some isolates revealed the presence of frameshift mutations that produced truncated proteins of smaller size. β-lactam resistance in K. pneumoniae and E. coli isolates in our hospitals is due to a combination of β-lactamase activity and porin loss/alteration. Hence more restrictions should be applied on β-lactams usage to decrease the emergence of resistant strains.

Detection of CMY-type beta-lactamases in Escherichia coli isolates from paediatric patients in a tertiary care hospital in Mexico

Background

The aim of this study was to detect CMY-type beta-lactamases in E. coli isolates obtained from paediatric patients.

Methods

In total, 404 infection-causing E. coli isolates resistant to third and fourth generation cephalosporins (3GC, 4GC) were collected from paediatric patients over a 2 years period. The identification and susceptibility profiles were determined with an automated microbiology system. Typing of bla_CMY and other beta-lactamase genes (bla_TEM, bla_SHV, bla_CTX-M, bla_VIM, bla_IMP, bla_KPC, bla_NDM, bla_OXA and bla_GES) was realized by PCR and sequencing. Phenotypic detection of AmpC-type enzymes was performed using boronic acid (20 mg/mL) and cloxacillin (20 mg/mL) as inhibitors, and the production of extended-spectrum beta-lactamases was determined with the double-disk diffusion test with cefotaxime (CTX) and ceftazidime (CAZ) discs alone and in combination with clavulanic acid. The CarbaNP test and modified carbapenem inhibition method (mCIM) were used for isolates with decreased susceptibility to carbapenems. The clonal origin of the isolates was established by pulsed-field gel electrophoresis (PFGE), phylotyping method and multilocus sequence typing.

Results

CMY-type beta-lactamases were detected in 18 isolates (4.5%). The allelic variants found were CMY-2 (n = 14) and CMY-42 (n = 4). Of the E. coli strains with CMY, the AmpC phenotypic production test was positive in 11 isolates with cloxacillin and in 15 with boronic acid. ESBL production was detected in 13 isolates. Coexistence with other beta-lactamases was observed such as CTX-M-15 ESBL and original spectrum beta-lactamases TEM-1 and TEM-190. In one isolate, the CarbaNP test was negative, the mCIM was positive, and OXA-48 carbapenemase was detected. Phylogroup A was the most frequent (n = 9) followed by B2, E and F (n = 2, respectively), and through PFGE, no clonal relationship was observed. Eleven different sequence types (ST) were found, with ST10 high-risk clone being the most frequent (n = 4). Seventy-two percent of the isolates were from health care-associated infections; the mortality rate was 11.1%.

Conclusions

This is the first report in Mexico of E. coli producing CMY isolated from paediatric patients, demonstrating a frequency of 4.5%. In addition, this is the first finding of E. coli ST10 with CMY-2 and OXA-48.

Phenotypic and molecular characterization of antimicrobial resistant Escherichia coli from urinary tract infections in Port-Harcourt, Nigeria

Introduction

Multidrug resistance among Escherichia coli causing Urinary Tract Infections (UTIs) is a major public health problem, threatening the effective treatment of UTIs. This study investigated the phenotypic and molecular characteristics of E. coli associated with UTIs in Port-Harcourt, Nigeria.

Methods

Twenty-five non-duplicate isolates of E. coli from UTIs patients at the University of Port-Harcourt Teaching Hospital, Nigeria were identified using Matrix-Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry. The antimicrobial susceptibility patterns were determined using Kirby-Bauer disc diffusion technique. Phenotypic expression of Extended Spectrum Beta Lactamases (ESBLs) and AmpC beta-lactamase were determined using standard laboratory methods and polymerase chain reaction (PCR) was used to detect ESBLs, AmpC, Quinolones and Aminoglycosides resistance genes.

Results

The isolates exhibited high rates of resistance to co-trimoxazole (76%), nalidixic acid (68%), ciprofloxacin (60%), gentamicin (44%) and low resistance to cefotaxime (20%) but were fully susceptible to cefoperazone/sulbactam, amikacin, nitrofurantoin, colistin and carbapenems. Phenotypic expression of ESBLs was recorded in 6(24%) isolates while genotypic detection revealed the highest prevalence of blaTEM 22(88%), followed by blaCTX-M-15 16(64%), blaSHV 7(28%) and blaOXA-1 6(24%) while AmpC (blaCMY-2) gene was detected in 8(32%) isolates. Amongst the quinolone resistant isolates, qnr variants (qnrB, qnrD and qnrS) and aac(6')-Ib genes were detected in 7(28%) and 3(12%) isolates respectively while all gentamicin resistant isolates possessed the aacC2 gene. The co-expression of blaCTX-M-15 with quinolones and aminoglycoside genes were 20% and 40% respectively. The prevalence of multiple drug resistance was 52%.

Conclusion

A high proportion of the studied E. coli isolates co-expressed ESBLs, quinolones and aminoglycosides resistance genes which call for prompt antibiotic stewardship and preventive strategies to limit the spread of these genes.

Quantifying the impact of treatment history on plasmid-mediated resistance evolution in human gut microbiota

To understand how antibiotic use affects the risk of a resistant infection, we present a computational model of the population dynamics of gut microbiota including antibiotic resistance-conferring plasmids. We then describe how this model is parameterized based on published microbiota data. Finally, we investigate how treatment history affects the prevalence of resistance among opportunistic enterobacterial pathogens. We simulate treatment histories and identify which properties of prior antibiotic exposure are most influential in determining the prevalence of resistance. We find that resistance prevalence can be predicted by 3 properties, namely the total days of drug exposure, the duration of the drug-free period after last treatment, and the center of mass of the treatment pattern. Overall this work provides a framework for capturing the role of the microbiome in the selection of antibiotic resistance and highlights the role of treatment history for the prevalence of resistance.

Evaluation of the AID AmpC line probe assay for molecular detection of AmpC-producing Enterobacterales

OBJECTIVES

In this study, the commercially available AID AmpC line probe assay (LPA) was evaluated for detection of plasmid-mediatedbla_AmpC β-lactamase genes in Enterobacterales as well as chromosomal mutations in the bla_AmpC promoter/attenuator regions in Escherichia coli.

METHODS

Accuracy of the AID AmpC probes was assessed using Enterobacterales clinical isolates harbouring diverse plasmid-mediated AmpC enzymes (ACC, ACT, DHA, FOX, CMY and MOX) and E. coli clinical isolates with mutations in the chromosomal bla_AmpC promoter/attenuator regions. The diagnostic performance of the AID AmpC LPA for bla_AmpC detection directly from clinical specimens was determined using 99 clinical urine specimens with bacterial cell counts >10⁵CFU/mL and the results were compared with culture-based phenotypic drug susceptibility testing (DST).

RESULTS

Detection of bla_AmpC genes in Enterobacterales clinical isolates showed 100% congruence with phenotypic DST results. The AID AmpC LPA showed 100% specificity [95% confidence interval (CI) 96-100%] and 100% sensitivity (95% CI 75-100%) for detection of plasmid-meditated bla_AmpC and E. coli genomic bla_AmpC promoter/attenuator mutations directly from clinical urine specimens. The AID AmpC LPA detected three AmpC-producers in urine specimens with bacterial cell counts >10⁵CFU/mL that were missed by culture-based phenotypic DST, thereby displaying higher diagnostic sensitivity.

CONCLUSION

The AID AmpC LPA is an accurate, sensitive and easy-to-use test that can be readily implemented in any diagnostic laboratory for molecular detection of bla_AmpC genes in Enterobacterales.

Changing paradigm of antibiotic resistance amongst Escherichia coli isolates in Indian pediatric population

Antimicrobial resistance happens when microorganisms mutates in manners that render the drugs like antibacterial, antiviral, antiparasitic and antifungal, ineffective. The normal mutation process is encouraged by the improper use of antibiotics. Mutations leading to quinolone resistance occur in a highly conserved region of the quinolone resistance-determining region (QRDR) of DNA gyrAse and topoisomerase IV gene. We analyzed antibiotic resistant genes and single nucleotide polymorphism (SNP) in gyrA and parC genes in QRDR in 120 E. coli isolates (both diarrheagenic and non-pathogenic) recovered from fresh stool samples collected from children aged less than 5 years from Delhi, India. Antibiotic susceptibility testing was performed according to standard clinical and laboratory standards institute (CLSI) guidelines. Phylogenetic analysis showed the clonal diversity and phylogenetic relationships among the E. coli isolates. The SNP analysis depicted mutations in gyrA and parC genes in QRDR. The sul1 gene, responsible for sulfonamide resistance, was present in almost half (47.5%) of the isolates across the diseased and healthy samples. The presence of antibiotic resistance genes in E. coli isolates from healthy children indicate the development, dissemination and carriage of antibiotic resistance in their gut. Our observations suggest the implementation of active surveillance and stewardship programs to promote appropriate antibiotic use and minimizing further danger.

Prevalence of plasmid-mediated AmpC in Enterobacteriaceae isolated from humans and from retail meat in Zagazig, Egypt

Background

The objective of this study was to determine the prevalence of plasmid-mediated AmpC (pAmpC) among Enterobacteriaceae isolated from humans and from retail meat in Egypt.

Methods

Enterobacteriaceae were isolated from patients with suspected bloodstream infection, human fecal samples, retail chicken meat samples and retail sheep meat samples. All group I Enterobacteriaceae were analyzed for presence of pAmpC genes by PCR. Antibiotic susceptibility testing was performed in all pAmpC positive isolates, followed by phenotypic and genotypic ESBL and carbapenemase testing on indication.

Results

The prevalence of pAmpC among group I Enterobacteriaceae isolated from 225 patients with bloodstream infection was 5.6% [95%CI 2.2–13.4]. Among 100 patients with community-onset gastroenteritis the prevalence in fecal samples was 4.8% [95%CI 2.1–10.7]. The prevalence among 112 chicken carcasses and 100 sheep meat samples was 2.4% [95%CI 0.7–8.4] and 1.1% [95%CI 0.2–5.7], respectively. In half of the AmpC positive isolates we detected an ESBL gene and 2 isolates harbored a carbapenemase gene. In five isolates there was resistance to at least three important alternative antibiotic drugs.

Conclusions

We consider the prevalence of pAmpC in Egypt, as found in our study, moderately low. To follow future trends in prevalence of pAmpC worldwide, a standardized screening algorithm for the detection of pAmpC is needed.

Stability and low induction propensity of cefiderocol against chromosomal AmpC β-lactamases of Pseudomonas aeruginosa and Enterobacter cloacae

Objectives

The siderophore cephalosporin cefiderocol possesses in vitro activity against MDR Gram-negative bacteria. The stability of cefiderocol against serine- and metallo-type carbapenemases has been reported previously, but little is known about how cefiderocol interacts with chromosomal AmpC β-lactamases. We investigated a number of features of cefiderocol, namely antibacterial activity against AmpC overproducers, stability against AmpC β-lactamases and propensity for AmpC induction using Pseudomonas aeruginosa and Enterobacter cloacae.

Methods

MICs were determined by broth microdilution according to CLSI guidelines. The MIC of cefiderocol was determined in iron-depleted CAMHB. Hydrolysis of the antibiotics was determined by monitoring the changes in the absorbance in the presence of AmpC β-lactamase, and AmpC induction was evaluated by double disc diffusion and nitrocefin degradation assays.

Results

The MICs of ceftazidime and cefepime for PAO1 increased 4- to 16-fold with inactivation of either ampD or dacB, whereas cefiderocol MICs were little affected by these inactivations (<2-fold increase). Cefiderocol has 17- and 740-fold lower affinity (higher Ki) to AmpCs of P. aeruginosa SR24-12 and E. cloacae P99, respectively, compared with ceftazidime. Both disc diffusion and nitrocefin degradation assays indicated that cefiderocol did not induce AmpC β-lactamases of P. aeruginosa PAO1 and ATCC 27853 and E. cloacae ATCC 13047, whereas imipenem did.

Conclusions

Cefiderocol showed in vitro activity against the AmpC-overproducing strains, low affinity for chromosomal AmpC β-lactamases, and a low propensity of temporal induction of AmpC β-lactamases of P. aeruginosa and E. cloacae. These features relating to chromosomal AmpC could explain the potent antibacterial activity of cefiderocol against drug-resistant strains producing AmpC β-lactamases.

In-Hospital Surgery as a Risk Factor for Onset of AmpC-Producing Escherichia coli Blood Stream Infections

There has been a progressive rise in the incidence of blood stream infections (BSI) caused by multidrug-resistant Gram-negative organisms (MDR GN), which cause increased morbidity and mortality. For this reason, recent studies have focused on risk factors of acquisition of carbapenemase-producing Enterobacteriaceae and extended-spectrum beta-lactamase producers. However, there is limited data on risk factors for BSI caused by AmpC-producing Enterobacteriaceae (AmpC EC), especially in low prevalence settings such as Australia. This study was performed to identify risk factors for acquisition of AmpC E. coli, using a retrospective matched case control design over a 3-year period. Patients with BSI caused by AmpC E. coli were matched with controls (third generation cephalosporin susceptible E. coli) by age and site of infection (n = 21). There was no significant difference in age, sex, clinical outcome, time to onset of BSI, recent antibiotic use (last 3 months), comorbidities (type 2 diabetes mellitus, renal failure) intensive care unit admission, underlying hematological condition, immunosuppressant use, APACHE II score, or any recent urological procedures (within last 3 months) between the two groups. On univariate analysis, the AmpC E. coli group were more likely to have had a surgical procedure in hospital and lived in a residential aged care facility. On multivariate logistic regression analysis, a recent surgical procedure was associated with the onset of AmpC E. coli BSI (Odd's Ratio (OR) 4.78, p = 0.034). We concluded that in a relatively low prevalence setting such as Australia, AmpC E. coli BSI is potentially associated with surgery performed in hospital due to previous antibiotic exposure and longer hospitalization.

Emphysematous endocarditis caused by AmpC beta-lactamase-producing Escherichia coli: A case report

RATIONALE

Infective endocarditis (IE) is a life-threatening disease, mostly caused by gram-positive bacteria. Gram-negative bacteria were identified as a causative organism in relatively small number of cases. Although, antibiotic-resistant Escherichia coli is common cause of gram-negative endocarditis, AmpC beta-lactamase (BL)-harboring E coli is very rare cause of IE. Furthermore, emphysematous endocarditis is also a very rare manifestation of E coli infection.

PATIENT CONCERNS

We report a case of 80-year-old female patient presenting with dizziness, fever, and altered mental status, who was finally diagnosed with emphysematous endocarditis caused by E coli harboring an AmpC BL gene.

DIAGNOSIS

Her chest computed tomography revealed air bubbles surrounding the annulus of a mitral valve and a transesophageal echocardiogram revealed a hyperechogenic mass fixed on the posteromedial side of the mitral annulus with 2 eccentric mitral regurgitation jets. Blood cultures grew E coli which harbored the DHA-type AmpC BL. The organism belonged to a B2 phylogenic group, and multilocus sequence typing analyses revealed that the strains were of ST-95.

INTERVENTIONS

She was treated with meropenem following the resistant profiles, and surgery was recommended by the healthcare professional, but denied by the patient's guardians. She was transferred to another hospital due to a refusal for further treatment.

LESSONS

Emphysematous endocarditis is an uncommon complication of E coli bacteremia. Certain phylogenetic groups may be associated with development of E coli endocarditis.

Multiplex PCR scheme for variant plasmid mediated class C β-lactamase typing

BACKGROUND

An increasing of prevalence and diversification of plasmid-mediated AmpC (pAmpC) has been emerged worldwide. The incidence of pAmpC resulted in increasing β-lactamase production and conferred resistance to almost all β-lactam antibiotics excluding carbapenems. The lack of standard method for pAmpC identification and classification exert a challenge in epidemiological surveillance and infection control practices.

METHODS

A robust, single tube multiplex PCR has been developed to classify six different pAmpC groups including CIT (CMY-2 like, LAT and CFE), ECB (ACT, MIR), MOX & CMY-1 like, DHA, ACC, and FOX. The developed method was optimized and validated by testing of sensitivity and specificity.

RESULTS

Developed method can detect crude extracted DNA template at nano-scale (2.5 ηg) and has high discriminatory power as compared to phenotypic and commercial genotypic method.

CONCLUSION

The developed method can be utilized for tracking the changes of clinically important resistance patterns and further investigation of occurrence and distribution of plasmid-mediated AmpC types.

Clinical features and molecular epidemiology of plasmid-mediated DHA-type AmpC β-lactamase-producing Klebsiella pneumoniae blood culture isolates, Hong Kong

Knowledge of risk factors and clinical characteristics of bacteraemia caused by plasmid-mediated AmpC β-lactamase (pAmpC)-producing Klebsiella pneumoniae (pAmpC-Kp) is not well described. This was a retrospective cohort study of patients with K. pneumoniae bacteraemia in three Hong Kong regional hospitals. Demographic and clinical data were retrieved from medical records. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed for molecular epidemiology. A total of 109 patients were included, divided into four groups: bacteraemia due to K. pneumoniae with (i) DHA-type pAmpC (n=23), (ii) extended-spectrum β-lactamase (ESBL) (n=37), (iii) DHA-type pAmpC+ESBL (n=26) and (iv) controls (n=23). Nursing home residence was independently associated with pAmpC-Kp bacteraemia compared with ESBL-Kp bacteraemia [adjusted odds ratio (aOR)=7.13, 95% confidence interval (CI) 1.36-37.54] and controls (aOR=41.47, 95% CI 4.55-377.75). Compared with controls, patients with pAmpC-Kp bacteraemia also suffered from more severe illness [median Acute Physiology and Chronic Health Evaluation (APACHE) II scores 16 and 25, respectively; P=0.006]. Importantly, the pAmpC group received discordant empirical antimicrobial therapy more frequently (OR=24.00, 95% CI 5.01-114.97), resulting in higher 7-day mortality (OR=20.17, 95% CI 2.32-175.67) and 30-day mortality (OR 4.68, 95% CI 1.29-16.98). PFGE detected six pulsotypes, corresponding to the predominant sequence type 11. Severity of illness and mortality of patients with bacteraemia caused by pAmpC-Kp were high. Patients who are nursing home residents presenting nosocomial sepsis should be treated with broad-spectrum antimicrobials.

Previous Antibiotic Exposure Increases Risk of Infection with Extended-Spectrum-β-Lactamase- and AmpC-Producing Escherichia coli and Klebsiella pneumoniae in Pediatric Patients

The objective of this study was to determine whether antibiotic exposure is associated with extended-spectrum-beta-lactamase- or AmpC-producing Escherichia coli or Klebsiella pneumoniae infections in children. We collected extended-spectrum-beta-lactamase- or AmpC-producing E. coli or K. pneumoniae isolates and same-species susceptible controls from normally sterile sites of patients aged ≤21 years, along with associated clinical data, at four free-standing pediatric centers. After controlling for potential confounders, the relative risk of having an extended-spectrum-beta-lactamase-producing isolate rather than a susceptible isolate was 2.2 times higher (95% confidence interval [CI], 1.49 to 3.35) among those with antibiotic exposure in the 30 days prior to infection than in those with no antibiotic exposure. The results were similar when analyses were limited to exposure to third-generation cephalosporins, other broad-spectrum beta-lactams, or trimethoprim-sulfamethoxazole. Conversely, the relative risk of having an AmpC-producing versus a susceptible isolate was not significantly elevated with any antibiotic exposure in the 30 days prior to infection (adjusted relative risk ratio, 1.12; 95% CI, 0.65 to 1.91). However, when examining subgroups of antibiotics, the relative risk of having an AmpC-producing isolate was higher for patients with exposure to third-generation cephalosporins (adjusted relative risk ratio, 4.48; 95% CI, 1.75 to 11.43). Dose-response relationships between antibiotic exposure and extended-spectrum-beta-lactamase-producing or AmpC-producing isolates were not demonstrated. These results reinforce the need to study and implement pediatric antimicrobial stewardship strategies, and they indicate that epidemiological studies of third-generation cephalosporin-resistant E. coli and K. pneumoniae isolates should include resistance mechanisms when possible.

Significant publications on infectious diseases pharmacotherapy in 2014

PURPOSE

The most important articles on infectious diseases (ID) pharmacotherapy published in the peer-reviewed literature in 2014, as nominated and selected by panels of pharmacists and others with ID expertise, are summarized.

SUMMARY

Members of the Houston Infectious Diseases Network were asked to nominate articles published in 2014 from prominent peer-reviewed journals that were felt to have a major impact in the field of ID pharmacotherapy. A list of 19 nominated articles on general ID-related topics and 9 articles specifically related to human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) was compiled. In a national online survey, members of the Society of Infectious Diseases Pharmacists (SIDP) were asked to select from the list 10 general ID articles believed to have made a significant contribution to the field of ID pharmacotherapy and 1 article contributing to HIV/AIDS pharmacotherapy. Of the 291 SIDP members surveyed, 134 (46%) and 56 (19%) participated in the selection of general ID-related articles and HIV/AIDS-related articles, respectively. The 11 highest-ranked papers (10 general ID-related articles, 1 HIV/AIDS-related article) are summarized here.

CONCLUSION

With the vast number of articles published each year, it is difficult to remain up-to-date on current, significant ID pharmacotherapy publications. This review of significant publications in 2014 may be helpful by lessening this burden.

Molecular characterisation of acquired and overproduced chromosomal blaAmpC in Escherichia coli clinical isolates

Escherichia coli recovered from three hospitals in Barcelona (Spain) were studied to determine the prevalence of isolates with acquired AmpC (ac-AmpC) and/or overproduced chromosomal AmpC (c-AmpC). Mechanisms involved in blac-AmpC overexpression, blaac-AmpC and the plasmids associated with their distribution as well as the prevalence of plasmid-mediated quinolone resistance (PMQR) in AmpC-producing isolates were also determined. Isolates were selected according to their resistance phenotype. blaac-AmpC, alterations in the blac-AmpC promoter/attenuator, and PMQR genes [qnrA, qnrB, qnrS, aac(6')-Ib-cr and qepA] were characterised by PCR and sequencing. blac-AmpC expression was determined by qRT-PCR. Population structure analysis was performed using PFGE, MLST and phylogenetic group PCR. Plasmids carrying blaac-AmpC were characterised by PCR-based replicon typing and S1-PFGE. IncI1 and IncF plasmids were also analysed by plasmid MLST and replicon sequence typing, respectively. Among 21563 E. coli isolates, 240 (1.1%) overproduced AmpC β-lactamases, including 180 (75.0%) harbouring ac-AmpC (132 CMY-2 variants and 48 DHA-1) and 60 (25.0%) c-AmpC enzymes. Three mutation profiles in the blac-AmpC promoter/attenuator were associated with a 72.5-, 19.9- and 5.8-fold increased expression, respectively. Moreover, 63.3% of ac-AmpC and 43.3% of c-AmpC isolates belonged to B2, D, E or F phylogenetic groups. PMQR was found in 31% of ac-AmpC isolates [38 qnrB4, 8 aac(6')-Ib-cr, 6 qnrS1 and 3 qnrB19] and in 10% of c-AmpC isolates [5 aac(6')-Ib-cr and 1 qnrS1]. IncI1-ST12 and IncF were associated with blaCMY-2 and blaDHA-1, respectively. These results suggest that ac-AmpC β-lactamases were the main mechanism of AmpC production. Isolates and plasmids both showed high genetic diversity.

Significant publications on infectious diseases pharmacotherapy in 2013

PURPOSE

The most important articles on infectious diseases (ID) pharmacotherapy published in the peer-reviewed literature in 2013, as nominated and selected by panels of pharmacists and others with ID expertise, are summarized.

SUMMARY

Members of the Houston Infectious Diseases Network were asked to nominate articles published last year in prominent biomedical journals that had a major impact in the field of ID pharmacotherapy. A list of 27 nominated articles on ID-related topics in general and 26 articles specifically focused on human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS) was compiled. In a national online survey conducted in January 2014, members of the Society of Infectious Diseases Pharmacists (SIDP) were asked to select from the list those articles that they felt had made the greatest contributions to the field of ID pharmacotherapy. Of 168 SIDP members surveyed, 108 (64%) and 53 (32%) participated in the selection of ID- and HIV/AIDS-related articles, respectively. Summaries of the top-ranked articles in both categories are presented.

CONCLUSION

Major topics explored in the top-ranked ID articles of 2013 include the use of cefepime for gram-negative infections due to AmpC or extended-spectrum β-lactamase-producing Enterobacteriaceae, optimizing antibiotic therapy through the use of extended- or continuous-infusion regimens, the use of the oral integrase inhibitor dolutegravir to combat HIV disease, and new approaches to treatment of Clostridium difficile infection and enterococcal endocarditis.

Microbiological screening is necessary to distinguish carriers of plasmid-mediated AmpC beta-lactamase-producing enterobacteriaceae and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae because of clinical similarity

Objectives

Plasmid-mediated AmpC beta-lactamase-producing (pAmpC) Enterobacteriaceae are increasing worldwide, difficult to identify and often confounded with extended-spectrum beta-lactamase (ESBL) producers. The low prevalence precludes routine universal admission screening. Therefore, we evaluated potential risk factors for carriage of pAmpC-producing Enterobacteriaceae that would allow targeted screening to improve yield and reduce cost.

Patients and methods

We performed a case control study at a tertiary care center from 1/2006 to 12/2010. Cases were adult patients in whom pAmpC-producing Enterobacteriaceae were isolated; controls were chosen among carriers of ESBL-producing Enterobacteriaceae. Both infected and colonized patients were included.

Results

Over five years, we identified 40 pAmpC producers in 39 patients among 16,247 screened consecutive isolates of Enterobacteriaceae. The pAmpC prevalence was low (0.25%), but more than 30% of pAmpC carriers received incorrect empirical antibiotic treatment. When compared with 39 ESBL controls, pAmpC carriage was associated with clinically confirmed infections in 74% (versus 51%) (p=0.035), mainly of the urinary tract, previous antibiotic exposure in 63% (versus 36%) (p=0.035) and carriage of a nasogastric tube in 23% (versus 0%) (p=0.002). In the multivariate regression analysis only clinically confirmed infections remained significantly associated with pAmpC carriage (OR 1.44 (95%CI 1.15-2.57)). No other clinical and blood test-associated risk factor allowed discrimination of pAmpC-carrying patients from ESBL controls. The type of acquisition – nosocomial versus community-acquired – was also non-informative for resistance type, as 46% of pAmpC- and 44% of ESBL-producing Enterobacteriaceae were community-acquired.

Conclusions

This study could not identify a clinical profile that would allow targeted screening for pAmpC-producing Enterobacteriaceae when compared to ESBL carriers. Because empiric antimicrobial therapy was inappropriate in more than 30%, rapid identification of pAmpC carriers is needed. New microbiological methods are therefore required to simplify rapid and reliable detection of pAmpC carriers.

Antimicrobial resistance: impact on clinical and economic outcomes and the need for new antimicrobials

INTRODUCTION

Antimicrobial resistance is a well-recognized global threat; thus, the development of strong infection control policies coupled with antimicrobial stewardship strategies and new therapies is required to reverse this process. In its 2013 report on antimicrobial resistance, the Centers for Disease Control and Prevention focused on this problem while presenting estimated annual rates of infections with antimicrobial-resistant organisms and their related mortality rates. Whereas some resistant pathogens were considered less threatening, others such as carbapenem-resistant Enterobacteriaceae were associated with higher mortality rates owing to limited treatment options.

AREAS COVERED

An overview of the most common antimicrobial-resistant pathogens, focusing on risk factors for acquisition, clinical and economic outcomes, as well as current treatment options. Strategies to optimize antimicrobial therapy with currently available agents, in addition to newly developed antimicrobials are also discussed.

EXPERT OPINION

The emergence of pathogens with a variety of resistance mechanisms has intensified the challenges associated with infection control and treatment strategies. Therefore, prudent use of currently available antimicrobial agents, as well as implementing measures to limit spread of resistance is paramount. Although several new antimicrobials have been recently approved or are in the pipeline showing promise in the battle against resistance, the appropriate use of these agents is required as the true benefits of these treatments are to be recognized in the clinical care setting.

Epidemiology and risk factors for infections due to AmpC β-lactamase-producing Escherichia coli

OBJECTIVES

To describe the prevalence and risk factors for infection due to AmpC β-lactamase-producing Escherichia coli (AmpC-EC).

METHODS

For the prevalence study, all clinical isolates of E. coli with reduced susceptibility to third-generation cephalosporins were prospectively included from June 2010 to November 2011. For risk factor analysis, a case-control study was conducted. Cases were patients with an infection due to AmpC-EC. Controls were patients infected with cephalosporin-susceptible E. coli, matched 1 : 2. Detection of blaAmpC genes was done with a multiplex AmpC-PCR, and hyperproduction of E. coli chromosomal blaAmpC by quantitative RT-PCR. Alteration of the blaAmpC promoter was studied by PCR and sequencing.

RESULTS

We identified 243 (1.1%) AmpC-EC strains out of 21 563 clinical isolates. Three cases with strains carrying ESBLs, 18 strains that were considered due to colonization and 8 cases lost to clinical follow-up were excluded. Finally, 214 cases were included in the analysis. Ninety-one cases (42.5%) and 269 (62.8%) controls were strictly community acquired (P < 0.001). Thirty-five (16.3%) cases and 186 controls (43.5%) did not have any identifiable risk factor (P < 0.001). Among cases, 158 (73.8%) were found to harbour an acquired AmpC (73.4% CMY-2). Previous use of fluoroquinolones [OR 2.6 (95% CI 1.12-3.36); P = 0.008] was independently associated with AmpC-EC in the multivariate analysis.

CONCLUSIONS

Prevalence of AmpC in E. coli remains low in our area. Plasmid acquisition (CMY type) represents the main mechanism of AmpC production. A high proportion of community-acquired isolates and patients with no identifiable risk factors were found. Previous use of fluoroquinolones was identified as a risk factor.

Risk factors for faecal colonisation with Escherichia coli producing extended-spectrum and plasmid-mediated AmpC β-lactamases in dogs

The aim of this study was to assess the prevalence and risk factors for faecal carriage of extended-spectrum β-lactamase (ESBL) and plasmidic AmpC β-lactamase (pAmpC) Escherichia coli producers in dogs. A three-month cross-sectional study was conducted and 151 rectal swabs were obtained from healthy dogs. ESBL and pAmpC genes were detected by PCR and were sequenced. Logistic regression models were used to investigate risk factors for the carriage of ESBL and pAmpC-producing E. coli. About 15 per cent of the isolates carried ESBL genes (blaCTX-M-32 n=8, blaCTX-M-15 n=5, blaCTX-M-1 n=3, blaCTX-M-9-like n=4) and 20 per cent carried pAmpC genes (blaCMY-2 n=23, blaCMY-2-like n=2). Thirteen dogs carried an E. coli isolate with both an ESBL and a pAmpC gene. One E. coli isolate harboured the human blaDHA-1 pAmpC gene, which has not been previously reported in companion animals in Europe. Dogs with a history of antimicrobial therapy in the past year had a higher risk of being carriers of ESBL-producing (P=0.003, OR =7.85) and pAmpC-producing (P=0.005, OR=6.28) E. coli. Dogs from shelter/breeders were approximately three times more likely to have an ESBL- or a pAmpC-producing E. coli than dogs from private owners. Males have a reduced risk of carrying a pAmpC-producing E. coli than females (P=0.017, OR =0.28). The knowledge of potential risk factors may help to limit the impact of resistance through implementation of effective control measures and judicious antimicrobial therapy.

Phenotypic and molecular characterization of plasmid mediated AmpC β-lactamases among Escherichia coli, Klebsiella spp., and Proteus mirabilis isolated from urinary tract infections in Egyptian hospitals

The incidence of resistance by Enterobacteriaceae to β-lactam/β-lactamase inhibitors combination is increasing in Egypt. Three phenotypic techniques, comprising AmpC disk diffusion and inhibition dependent methods using phenylboronic acid (PBA) and cloxacillin, were compared to PCR based method for detection of plasmid mediated AmpC β-lactamase in common urinary tract isolates. A total of 143 isolates, including E. coli, Klebsiella pneumonia, and Proteus mirabilis, were collected from urinary tract infections cases in Egyptian hospitals. Plasmid encoded AmpC genes were detected by PCR in 88.46% of cefoxitin resistant isolates. The most prevalent AmpC gene family was CIT including CMY-2, CMY-4, and two CMY-2 variants. The second prevalent gene was DHA-1 which was detected in E. coli and Klebsiella pneumonia. The genes EBC, FOX, and MOX were also detected but in small percentage. Some isolates were identified as having more than one pAmpC gene. The overall sensitivity and specificity of phenotypic tests for detection of AmpC β-lactamase showed that AmpC disk diffusion and inhibition dependent method by cloxacillin were the most sensitive and the most specific disk tests. PCR remains the gold standard for detection of AmpC β-lactamases. This study represents the first report of CMY-2 variants of CMY-42 and CMY-102 β-lactamase-producing E. coli, Klebsiella pneumonia, and Proteus mirabilis isolates in Egypt.

Bugs, hosts and ICU environment: countering pan-resistance in nosocomial microbiota and treating bacterial infections in the critical care setting

ICUs are areas where resistance problems are the largest, and these constitute a major problem for the intensivist's clinical practice. Main resistance phenotypes among nosocomial microbiota are (i) vancomycin-resistance/heteroresistance and tolerance in grampositives (MRSA, enterococci) and (ii) efflux pumps/enzymatic resistance mechanisms (ESBLs, AmpC, metallo-betalactamases) in gramnegatives. These phenotypes are found at different rates in pathogens causing respiratory (nosocomial pneumonia/ventilator-associated pneumonia), bloodstream (primary bacteremia/catheter-associated bacteremia), urinary, intraabdominal and surgical wound infections and endocarditis in the ICU. New antibiotics are available to overcome non-susceptibility in grampositives; however, accumulation of resistance traits in gramnegatives has led to multidrug resistance, a worrisome problem nowadays. This article reviews microorganism/infection risk factors for multidrug resistance, suggesting adequate empirical treatments. Drugs, patient and environmental factors all play a role in the decision to prescribe/recommend antibiotic regimens in the specific ICU patient, implying that intensivists should be familiar with available drugs, environmental epidemiology and patient factors.

Multiplex high-resolution melting analysis as a diagnostic tool for detection of plasmid-mediated AmpC β-lactamase genes

High-resolution melting (HRM) analysis can be a diagnostic tool to evaluate the presence of resistance genes with the added bonus of discriminating sequence modifications. A real-time, multiplex PCR assay using HRM was designed for the detection of plasmid-mediated ampC genes. The specificity and sensitivity of this assay were 96% and 100%, respectively.

Risk factors of community-onset urinary tract infections caused by plasmid-mediated AmpC β-lactamase-producing Enterobacteriaceae

BACKGROUND

The AmpC β-lactamase (AmpC)-producing Enterobacteriaceae emerged worldwide. This study was conducted to determine the risk factors of community-onset urinary tract infections (UTIs) caused by plasmid-mediated AmpC-producing Enterobacteriaceae.

METHODS

Patients who were diagnosed as community-onset UTIs caused by Enterobacteriaceae in a tertiary-care teaching hospital from December 2010 to January 2012 were included. Extended-spectrum β-lactamase (ESBL)-producing isolates were excluded. We identified plasmid-mediated AmpC-producing Enterobacteriaceae both phenotypically (by disk potentiation test and double-disk synergy test) and genotypically (by Multiplex polymerase chain reaction (PCR) assay). The demographic data, clinical characteristics, and risk factors of acquisition were described.

RESULTS

Among the 323 non-ESBL-producing Enterobacteriaceae identified in community-onset UTIs, 50 isolates were phenotypically positive for AmpC. Escherichia coli was the most common AmpC-producing organism (60%), followed by Klebsiella pneumonia (8%), and Enterobacter cloacae and Proteus mirabilis (6% for each species). The independent risk factors for acquisition of AmpC-producing Enterobacteriaceae included prior history of cerebral vascular accident [odds ratio (OR) = 2.014; 95% confidence interval (CI) = 1.007-4.031; p = 0.0048], and prior use of fluoroquinolones (OR = 4.049; 95% CI = 1.759-9.319; p = 0.001) and cephamycin (OR = 9.683; 95% CI = 2.007-45.135; p = 0.004). AmpC-producing isolates were multidrug resistant. Carbapenems, cefepime, and piperacillin/tazobactam had the best in vitro efficacy. The most commonly identified plasmid-mediated AmpC gene was bla(CIT), followed by bla(DHA)/bla(EBC), and bla(MOx).

CONCLUSION

For community-onset UTIs, AmpC-producing Enterobacteriaceae should be suspected in those with prior history of cerebral vascular accident and prior use of antimicrobials. To treat these multiple-resistant isolates, carbapenems, cefepime, and piperacillin/tazobactam may be considered.

Extended spectrum ß-lactamase- and constitutively AmpC-producing Enterobacteriaceae on fresh produce and in the agricultural environment

The attribution of fresh produce to the overall community-associated exposure of humans to ESBL- or AmpC-producing bacteria is currently unknown. To address this issue, the prevalence of ESBL- and AmpC-producing Enterobacteriaceae on fresh produce produced in the Netherlands was determined. Seven vegetable types that are consumed raw were selected: blanched celery, bunched carrots, chicory, endive, iceberg lettuce, mushrooms, and radish. The vegetables were mostly obtained from supermarkets. To determine whether the agricultural environment is the source of ESBL-producing Enterobacteriaceae on fresh produce, iceberg lettuce was also obtained directly from three farms, in conjunction with soil and irrigation water. ESBL-producing Enterobacteriaceae isolated from vegetables and environment were all environmental species: Rahnella aquatilis (n = 119), Serratia fonticola (n = 45) and Pantoea agglomerans (n = 1). ESBL genes of R. aquatilis and S. fonticola were identified as blaRAHN-1 and blaRAHN-2 and blaFONA-1, blaFONA-2, blaFONA-3/6 and blaFONA-5, respectively. For R. aquatilis and S. fonticola, different prevalence numbers were observed using different isolation methods, which could at least partially be explained by an inverse correlation between the level of cefotaxime resistance of these species and incubation temperature. R. aquatilis was isolated from 0 to 46% of soil samples and 11 to 83% of vegetable samples, and S. fonticola from 2 to 60% of soil samples and 0 to 1.3% of vegetable samples. Third generation cephalosporin-resistant faecal Enterobacteriaceae were isolated from 2.7%, 1.3% and 1.1% of supermarket vegetables, iceberg lettuce from farms, and agricultural soil respectively. Faecal Enterobacteriaceae were all identified as Citrobacter and Enterobacter species and, with the exception of one Citrobacter koseri strain, all had phenotypes indicative of constitutive AmpC production. Comparison of fresh produce and its agricultural environment indicates that the Enterobacteriaceae population on fresh produce reflects that of the soil it is grown in. Public health risks associated with exposure to ESBL- and AmpC-producing bacteria through consumption of uncooked fresh produce are diverse. They range from occasional ingestion of 3GC-resistant opportunistic pathogens which may result in difficult-to-treat infections, to frequent ingestion of relatively harmless ESBL-producing environmental bacteria that may therewith constitute a continuously replenished intestinal reservoir facilitating dissemination of ESBL genes to (opportunistic) pathogens.

The use of cefepime for treating AmpC β-lactamase-producing Enterobacteriaceae

BACKGROUND

 AmpC β-lactamase-producing organisms are associated with significant morbidity and mortality. Induction of resistance to third-generation cephalosporins after exposure to these agents complicates treatment options and carbapenems are considered optimal therapy. The role of cefepime, however, remains unclear. Our objective was to compare clinical outcomes for patients receiving cefepime compared with meropenem for invasive infections caused by organisms expressing AmpC β-lactamases.

METHODS

 Hospitalized patients with blood, bronchoalveolar lavage, or intra-abdominal fluid cultures growing Enterobacter spp, Serratia spp, or Citrobacter spp were evaluated using the cefotetan-boronic acid disk test and the cefotetan-cloxacillin Etest to identify organisms with AmpC β-lactamase production from February 2010 to January 2011. In patients with organisms hyperproducing AmpC β-lactamases (positive by both methods), clinical outcomes for patients receiving cefepime or meropenem therapy were compared. To minimize the possibility of treatment selection bias, 1:1 nearest neighbor propensity score matching was performed prior to regression analysis.

RESULTS

 Of 399 patients meeting eligibility criteria, 96 (24%) had confirmed infections with AmpC β-lactamase-producing organisms. Propensity score matching of patients infected with AmpC β-lactamase-positive organisms treated with cefepime or meropenem yielded 32 well-balanced patient pairs with no difference in 30-day mortality (odds ratio, 0.63; 95% confidence interval [CI], .23-2.11; P = .36) or length of hospital stay after infection (relative risk, 0.96; 95% CI, .79-1.26; P = .56) between the 2 groups.

CONCLUSIONS

 Cefepime may be a reasonable option for the treatment of invasive infections due to AmpC β-lactamase-producing organisms, particularly when adequate source control is achieved.

Consequences of revised CLSI and EUCAST guidelines for antibiotic susceptibility patterns of ESBL- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates

OBJECTIVES

This study aimed to: (i) analyse the antibiotic susceptibility testing (AST) profiles of extended spectrum β-lactamase (ESBL)- and AmpC β-lactamase-producing clinical Enterobacteriaceae isolates applying EUCAST 2013 AST guidelines; and (ii) evaluate discrepancies in AST profiles according to EUCAST 2010 guidelines, EUCAST 2013 guidelines, CLSI 2009 guidelines and CLSI 2013 guidelines.

METHODS

The 195 ESBL- and/or AmpC β-lactamase-producing Enterobacteriaceae isolates used in this study were systematically characterized by disc diffusion AST interpreted according to the 2013 guidelines of EUCAST and CLSI, the EUCAST 2010 guidelines and the CLSI 2009 guidelines.

RESULTS

Individual cephalosporin AST patterns according to EUCAST 2013 guidelines were described for individual ESBL and AmpC β-lactamase genotypes. Significant differences in the susceptibility rates of important cephalosporins such as cefepime, ceftazidime and cefotaxime applying EUCAST 2013 and CLSI 2013 AST guidelines were demonstrated for ESBL- and AmpC β-lactamase-producing isolates.

CONCLUSIONS

The confirmation of ESBL and/or AmpC β-lactamase production can support the selection of an adequate antibiotic drug therapy. Despite a harmonized CLSI and EUCAST 'report as found' strategy for cephalosporins and ESBL-producing isolates, AST interpretation according to the CLSI 2013 and EUCAST 2013 guidelines shows significant differences in susceptibility rates for mainstay cephalosporins such as cefepime, ceftazidime and cefotaxime. Thus, further harmonization of clinical breakpoints is warranted.

Public health risks of enterobacterial isolates producing extended-spectrum β-lactamases or AmpC β-lactamases in food and food-producing animals: an EU perspective of epidemiology, analytical methods, risk factors, and control options

The blaESBL and blaAmpC genes in Enterobacteriaceae are spread by plasmid-mediated integrons, insertion sequences, and transposons, some of which are homologous in bacteria from food animals, foods, and humans. These genes have been frequently identified in Escherichia coli and Salmonella from food animals, the most common being blaCTX-M-1, blaCTX-M-14, and blaCMY-2. Identification of risk factors for their occurrence in food animals is complex. In addition to generic antimicrobial use, cephalosporin usage is an important risk factor for selection and spread of these genes. Extensive international trade of animals is a further risk factor. There are no data on the effectiveness of individual control options in reducing public health risks. A highly effective option would be to stop or restrict cephalosporin usage in food animals. Decreasing total antimicrobial use is also of high priority. Implementation of measures to limit strain dissemination (increasing farm biosecurity, controls in animal trade, and other general postharvest controls) are also important.

Development of a TaqMan multiplex PCR assay for detection of plasmid-mediated ampC β-lactamase genes

A multiplex, real-time TaqMan assay was designed to identify clinical isolates carrying plasmid-mediated ampC genes. The specificity and sensitivity of this assay were 100% when testing characterized AmpC/non-AmpC-producing isolates and randomly selected clinical isolates. This is a rapid assay that can be performed in a clinical microbiology laboratory.

Colonisation and infection due to Enterobacteriaceae producing plasmid-mediated AmpC β-lactamases

OBJECTIVES

To investigate the epidemiology and clinical features of infections caused by Enterobacteria producing plasmid-mediated AmpC β-lactamases (pAmpC), which are emerging as a cause of resistance to extended-spectrum cephalosporins.

METHODS

A prospective multicentre cohort of patients with infection/colonisation due to pAmpC-producing Enterobacteriaceae was performed in 7 Spanish hospitals from February throughout July 2009. pAmpCs were characterised by PCR and sequencing.

RESULTS

140 patients were included; organisms isolated were Escherichia coli (n = 100), Proteus mirabilis (n = 20), Klebsiella pneumoniae (n = 17), and others (n = 3). Overall, 90% had a chronic underlying condition. The acquisition was nosocomial in 43%, healthcare-associated in 41% (14% of those were nursing home residents), and community in 16%. Only 5% of patients had no predisposing feature for infection with multidrug-resistant bacteria. Nineteen percent of patients were bacteraemic. Inappropriate empirical therapy was administered to 81% of bacteraemic patients, who had a crude mortality rate of 48%. The most frequent enzyme was CMY-2 (70%, predominantly in E. coli and P. mirabilis) followed by DHA-1 (19%, predominantly in K. pneumoniae).

CONCLUSION

pAmpC-producing Enterobacteriaceae caused nosocomial, healthcare-associated and community infections mainly in predisposed patients. Invasive infections were associated with high mortality which might be partly related to inappropriate empirical therapy.

Practical approach for reliable detection of AmpC beta-lactamase-producing Enterobacteriaceae

In this prospective study all Enterobacteriaceae isolates (n = 2,129) recovered in the clinical microbiology laboratory during October 2009 to April 2010 were analyzed for AmpC production. Clinical and Laboratory Standards Institute (CLSI) cefoxitin and cefotetan susceptibility breakpoints and CLSI critical ESBL diameters were used to screen for potential AmpC producers. In total, 305 isolates (211 potential AmpC producers and 94 AmpC screen-negative isolates as a control group) were further analyzed by multiplex PCR for the detection of plasmid-encoded ampC beta-lactamase genes and by ampC promoter sequence analysis (considered as the gold standard). Cefoxitin and cefotetan were assessed as primary screening markers. The sensitivities of cefoxitin and cefotetan for the detection of AmpC production were 97.4 and 52.6%, respectively, and the specificities were 78.7 and 99.3%, respectively. As a phenotypic confirmation test, the Etest AmpC and the cefoxitin-cloxacillin double-disk synergy method (CC-DDS) were compared. The sensitivities for the Etest AmpC and the CC-DDS method were 77.4 and 97.2%, respectively, and the specificity was 100% for both methods. The results of the Etest AmpC were inconclusive for 10 isolates. With the CC-DDS method 2 inconclusive results were observed. Based on this study, we propose a comprehensive diagnostic flow chart for the detection of AmpC production consisting of a simple phenotypic screening and a single phenotypic confirmation test with inconclusive results being resolved by molecular analysis. For the proposed flow chart using (i) cefoxitin as a screening marker for AmpC production, (ii) the CC-DDS method as phenotypic confirmation, and (iii) molecular methods in case of inconclusive results, the sensitivity and specificity for AmpC detection would have been 97.4 and 100%, respectively, with respect to the studied isolates. The phenotypic methods used in the AmpC algorithm are simple to perform and easy to implement in the diagnostic laboratory.

Clinical laboratory detection of AmpC β-lactamase: does it affect patient outcome?

Plasmid-mediated AmpC-producing Escherichia coli and Klebsiella pneumoniae have been associated with poor clinical outcomes, but they are not readily identified in hospital microbiology laboratories. We tested 753 gram-negative bloodstream isolates for AmpC by using the EDTA disk test and the modified Hodge test (n = 172) and the modified Hodge test alone (n = 581). The 30-day mortality for the AmpC group was 9% (2/23) and was 6% (3/51) for the control group. The clinical response was similar: afebrile on day 2 (AmpC group, 16/23 [70%]; control group, 32/45 [71%]) and on day 4 (AmpC group, 19/22 [86%]; control group, 37/44 [84%]). Patients with isolates in the AmpC group were more likely to be in an intensive care unit at the time of the positive blood culture (P = .01) and more likely to be intubated (P = .05) than patients with isolates in the control group. Effective antibiotic treatment within the first 48 hours was given to 47 (92%) of 51 patients with isolates in the control group but to only 14 (61%) of 23 patients with isolates in the AmpC group (P = .001). The modified Hodge test and the EDTA disk test did not identify patients at risk for a poor outcome from AmpC-producing bacterial infections.