Nosocomial and community-acquired Enterobacter cloacae bloodstream infection: risk factors for and prevalence of SHV-12 in multiresistant isolates in a medical centre

Clinical Characteristics, Prognosis and Treatment of Bloodstream Infections with Enterobacter Cloacae Complex in a Chinese Tertiary Hospital: A Retrospective Study

Objective

This research aimed to analyze the clinical characteristics, prognosis, and antimicrobial treatment of bloodstream infections (BSI) caused by Enterobacter cloacae complex (ECC).

Methods

The clinical data of patients with bloodstream infections caused by Enterobacter cloacae complex from April 2017 to June 2023 were collected retrospectively. These data were then analyzed in subgroups based on the detection results of extended-spectrum β-lactamase (ESBL), 30-day mortality, and the type of antimicrobial agent used (β-lactam/β-lactamase inhibitor combinations (BLICs) or carbapenems).

Results

The proportion of ESBL-producing Enterobacter cloacae complex was 32.5% (37/114). Meanwhile, ICU admission, receiving surgical treatment within 3 months, and biliary tract infection were identified as risk factors for ESBL-producing ECC-BSI. Additionally, immunocompromised status and Sequential Organ Failure Assessment (SOFA) score ≥ 6.0 were identified as independent risk factors of 30-day mortality in patients with ECC-BSI (n = 108). Further analysis in BSI patients caused by non-ESBL-producing ECC revealed that patients treated with BLICs (n = 45) had lower SOFA scores and lower incidence of hypoproteinemia and sepsis compared with patients treated with carbapenems (n = 20). Moreover, in non-ESBL-producing ECC-BSI patients, the univariate Cox regression analysis indicated a significantly lower 30-day mortality rate in patients treated with BLICs compared to those treated with carbapenems (hazard ratios (HR) [95% CI] 0.190 [0.055-0.662], P = 0.009; adjusted HR [95% CI] 0.106 [0.013-0.863], P = 0.036).

Conclusion

This study investigated the factors influencing the susceptibility to infection by ESBL-producing strains and risk factors for 30-day mortality in ECC-BSI patients. The results revealed that ESBL-negative ECC-BSI patients treated with BLICs exhibited significantly lower 30-day mortality compared to those treated with carbapenems. BLICs were found to be more effective in ECC-BSI patients with milder disease (ESBL-negative and SOFA ≤6.0).

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.

Clinical and molecular characteristics and risk factors for patients acquiring carbapenemase-producing and non-carbapenemase-producing carbapenem-nonsusceptible-Enterobacterales bacteremia

BACKGROUND/PURPOSE

Carbapenem-nonsusceptible Enterobacterales (CNSE) are a growing global threat. Carbapenemases are often produced by plasmids, which allow rapid transmission. This study aimed to investigate (1) the bacterial type (2) resistant genes (3) antimicrobial susceptibility and (4) risk factors for acquisition of carbapenemase-producing carbapenem-nonsusceptible Enterobacterales (CP-CNSE) and non-carbapenemase-producing carbapenem-nonsusceptible Enterobacterales (non-CP-CNSE) bacteremia.

METHODS

There were a total of 113 isolates of Enterobacterales from 2013 to 2018. After excluding nonblood isolates and including only one sample from each patient, 99 isolates were analyzed and the medical charts of these patients were reviewed. Carbapenemase genes, β-lactamase genes and antimicrobial susceptibility of the isolates were determined. Multilocus sequence typing (MLST) was performed on CP-CNSE isolates.

RESULTS

CP-CNSE carried more bla_SHV (P = 0.004) and were more resistant to imipenem than non-CP-CNSE (P < 0.001). In the univariate analyses, we found that CP-CNSE bloodstream infection was associated with patient <65 years of age (odds ratio, 3.90; 95% confidence interval [CI], 1.16 to 13.10; P = 0.027), mechanical ventilation at the time of bloodstream infection (BSI) (odds ratio, 3.85; 95% CI, 1.16-12.78; P = 0.028) and exposure to piperacillin/tazobactam (odds ratio, 3.96; 95% CI, 1.09-14.38; P = 0.037). However, on multivariate analyses, no independent predictor for CP-CNSE was identified in this study.

CONCLUSION

CP-CNSE carried more bla_SHV and were more resistant to imipenem when compared to non-CP-CNSE. No independent predictor for CP-CNSE was identified after multivariate analysis. This is the first study conducted in Taiwan comparing risk factors between CP-CNSE and non-CP-CNSE from both clinical and molecular aspects.

Prevalence of ESKAPE pathogens in the environment: Antibiotic resistance status, community-acquired infection and risk to human health

The ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens are characterised by increased levels of resistance towards multiple classes of first line and last-resort antibiotics. Although these pathogens are frequently isolated from clinical environments and are implicated in a variety of life-threatening, hospital-associated infections; antibiotic resistant ESKAPE strains have been isolated from environmental reservoirs such as surface water, wastewater, food, and soil. Literature on the persistence and subsequent health risks posed by the ESKAPE isolates in extra-hospital settings is however, limited and the current review aims to elucidate the primary reservoirs of these pathogens in the environment, their antibiotic resistance profiles, and the link to community-acquired infections. Additionally, information on the current state of research regarding health-risk assessments linked to exposure of the ESKAPE pathogens in the natural environment, is outlined.

Emergence and nosocomial spread of ST11 carbapenem-resistant Klebsiella pneumoniae co-producing OXA-48 and KPC-2 in a regional hospital in Taiwan

Purpose. Carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged as a major challenge for global healthcare systems. The objectives of this study were to determine the nosocomial spread of CRKP clones and analyse the molecular characteristics of CRKP in our hospital.Methodology. Ninety-eight non-duplicated clinical CRKP isolates were collected from March 2014-June 2015. Clinical, demographic and microbiological data of patients with CRKP were reviewed. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing were applied to investigate the genetic relationship between the 98 isolates. Antibiotic resistance genes were identified by conventional PCR-sequencing.Results. PFGE patterns were grouped into 26 clusters. Two main PFGE clusters were identified: L (53 isolates, belonging to ST11) and N (11 isolates, belonging to ST11). The most dominant ST was ST11 (79 %, 77/98), followed by ST273 (5 %, 5/98). KPC-2 (n=82) was the predominant carbapenemase followed by OXA-48 (n=64). Fifty isolates (51 %, 50/98) harboured bla _KPC-2 and bla _OXA-48 simultaneously, and three of these isolates were detected with the third carbapenemase genes (bla _IMP-8 or bla _VIM-1).Conclusion. The clonal spread of K. pneumoniae ST11 expressing OXA-48, KPC-2 and CTX-M-14 β-lactamases was the cause of an outbreak of CRKP. To the best of our knowledge, a single strain harbouring A-, B- and D-class carbapenemase genes has not previously been identified. There is a high prevalence of plasmid-encoded KPC-2- and OXA-48-producing CRKP in our hospital; most isolates were members of ST11, which may be representative of a high-risk CRKP clone disseminating in central Taiwan.

Assessment of Airborne Bacterial and Fungal Communities in Selected Areas of Teaching Hospital, Kandy, Sri Lanka

Nosocomial infections, in lay term known as hospital acquired infections, are caused mainly by airborne pathogens found in healthcare facilities and their surroundings. The aim of this study was to quantify and identify bacteria and fungi in a hospital, which is an understudied area of air quality in Sri Lanka. Air samples were collected in agar medium and petri plates containing sterile filter papers. The number of culturable and total airborne microorganisms was estimated by manual counting and fluorescent microscopy, respectively. The morphologically distant bacteria and fungi were identified by DNA sequencing. The statistical analysis revealed significant variances between studied sites (p < 0.05) where Outpatients Department and Respiratory Unit showed higher levels of airborne microbial load. Culturable microbial count was higher at noon (hospital visiting hours) compared to other sampling periods (after hospital visiting hours) within the hospital. Total count of airborne microbes was found to be the highest during the afternoon. The most sensitive zones such as Operating Theatre and Intensive Care Unit showed considerably higher counts of airborne microbes. Identification by molecular means revealed the presence of human pathogens in the hospital air including Bacillus sp, Micrococcus sp, Pseudomonas sp, Staphylococcu ssp, Exiguobacterium sp, Enterobacter sp, Escherichia sp, Sphingomonas sp, Massilia sp, Kocuria sp, Fusarium sp, and Aspergillus sp. In conclusion, the results from this study indicate that the hospital air was generally contaminated. Therefore, the implementation of proactive policies and strategies are needed to monitor hospital air quality in sensitive zones as well as other areas of the hospitals.

Isolation, characterization and efficacy of phage MJ2 against biofilm forming multi-drug resistant Enterobacter cloacae

Biofilm is involved in a variety of infections, playing a critical role in the chronicity of infections. Enterobacter cloacae is a biofilm-forming and multi-drug-resistant (MDR) nosocomial pathogen leading to significant morbidity and mortality. This study aimed at isolation of a bacteriophage against MDR clinical strain of E. cloacae and its efficacy against bacterial planktonic cells and biofilm. A bacteriophage MJ2 was successfully isolated from wastewater and was characterized. The phage exhibited a wide range of thermal and pH stability and demonstrated considerable adsorption to host bacteria in the presence of CaCl₂ or MgCl₂. Transmission electron microscopy (TEM) showed MJ2 head as approximately 62 and 54 nm width and length, respectively. It had a short non-contractile tail and was characterized as a member of the family Podoviridae [order Caudovirales]. The phage MJ2 was found to possess 11 structural proteins (12-150 kDa) and a double-stranded DNA genome with an approximate size of 40 kb. The log-phase growth of E. cloacae both in biofilm and suspension was significantly reduced by the phage. The E. cloacae biofilm was formed under different conditions to evaluate the efficacy of MJ2 phage. Variable reduction pattern of E. cloacae biofilm was observed while treating it for 4 h with MJ2, i.e., biofilm under static conditions. The renewed media with intervals of 24, 72, and 120 h showed biomass decline of 2.8-, 3-, and 3.5-log, respectively. Whereas, the bacterial biofilm formed with dynamic conditions with refreshing media after 24, 72, and 120 h demonstrated decline in growth at 2.5-, 2.6-, and 3.3-log, respectively. It was, therefore, concluded that phage MJ2 possessed considerable inhibitory effects on MDR E. cloacae both in planktonic and biofilm forms.

Characterization of the population structure, drug resistance mechanisms and plasmids of the community-associated Enterobacter cloacae complex in China

Objectives

To investigate the population structure, drug resistance mechanisms and plasmids of community-associated Enterobacter cloacae complex (CA-ECC) isolates in China.

Methods

Sixty-two CA-ECC isolates collected from 31 hospitals across China were typed by hsp60 typing and MLST. ESBL and AmpC-overexpression phenotype was determined by double-disc synergy test. Replicon typing and conjugation were performed for plasmid analysis. All ESBL-positive isolates and representative conjugants were subjected to detailed characterization by WGS.

Results

Enterobacter hormaechei and Enterobacter kobei were predominant in our collections. MLST distinguished 46 STs with a polyclonal structure. ST591 was the most prevalent clone detected in northern China. Twenty-two isolates (35.5%) were ESBL positive and half of them were E. kobei. ESBL positivity was related to ESBL production (15/22) and to AmpC overexpression (18/22). Core-genome phylogenetic analysis identified intra- and inter-regional dissemination of ESBL-producing E. kobei clones. ESBL producers were exclusively classified as E. hormaechei and E. kobei, and blaCTX-M-3 was the most prevalent ESBL genotype (10/15) detected in four different environments. In the ESBL-positive population, the ESBL producers encoded more drug resistance genes (8-24 genes) by carrying more plasmids (1-3 plasmids) than the non-ESBL-producing isolates, resulting in an inter-group difference in drug susceptibilities. IncHI-type plasmids were prevalent in the ESBL producers (12/15). All IncHI2-type plasmids (n = 11) carried ESBL genes and shared a similar backbone to p09-036813-1A_261 recovered from Salmonella enterica in Canada.

Conclusions

The species-specific distribution, species-dependent ESBL mechanism and endemic plasmids identified in our study highlight the necessity for tailored surveillance of CA-ECC in the future.

Multiple brain abscesses due to Enterobacter cloacae in an immune-competent child

Brain abscesses due to Enterobacteriaceae in immune-competent children are rare, and those due to Enterobacter cloacae are even rarer. We report an interesting case of community-acquired E. cloacae neuroinfection resulting in multiple brain abscesses in a young child with no underlying risk-factors. A 10 year-old-boy presented with low-grade fever, headache, neck pain and progressive deterioration of sensorium. On examination, he was conscious but drowsy with photophobia, normal fundii, meningeal signs, mild hypertonia, brisk muscle stretch reflexes and extensor plantar responses. Magnetic resonance imaging of brain showed bilateral, multiple pyogenic abscesses. Culture of the abscess material aspirated at the time of surgical drainage showed growth of E. cloacae. He received intravenous imipenem for 18 weeks guided by clinical and radiological response. A pragmatic approach combining early surgical drainage, targeted antimicrobial therapy and patient-tailored duration based on the clinico-radiological response is needed in such difficult cases.

Characterization of IS26-composite transposons and multidrug resistance in conjugative plasmids from Enterobacter cloacae

SHV-12 is the most widespread resistance determinant of Enterobacter cloacae in Taiwan; however, blaSHV-12 has rarely been mobilized. Six multidrug-resistant E. cloacae isolates were collected. After conjugal transfer, plasmid profiling and analysis of incompatibility groups was performed to characterize the genetic context of blaSHV-12 -containing fragments. The presence of mobile genetic elements was demonstrated by PCR, cloning, sequencing and bioinformatics analyses. Four different β-lactamase genes (blaTEM-1 , blaSHV-12 , blaCTX-M-3 and/or blaCTX-M-14 ) were observed in the conjugative plasmids belonging to the IncHI2 (n = 4), IncI1 or IncP incompatibility groups. The IS26-blaSHV-12 -IS26 locus was located in five different genetic environments. A novel structural organization of a class 1 integron with the aac(6')-IIc cassette truncated by IS26 was identified in one isolate. Thus, blaSHV-12 was obtained from different plasmids through IS26-mediated homologous recombination. IS26 plays a vital role in the distribution of mobile resistance elements between different plasmids found in multidrug-resistant E. cloacae isolates.

Association of antibiotic resistance with SHV-12 extended-spectrum β-lactamase in Enterobacter cloacae

The association between antibiotic resistance and SHV-12 extended-spectrum β-lactamase (ESBL) in Enterobacter cloacae remains unknown. The aim of the present study was to investigate the prevalence of both chromosome- and plasmid-borne SHV-12 ESBL genes in Enterobacter cloacae. Transmission of the SHV-12 ESBL gene was explored, and the risk factors for antibiotic resistance in E. cloacae were analyzed. Polymerase chain reaction (PCR) results showed that 58 out of the 100 isolates carried the SHV-12 ESBL gene: 34.48% of them occurred in the chromosome, 48.28% were plasmid-borne and 17.24% appeared in both. Enterobacterial repetitive intergenic consensus-PCR tests detected 82 chromosomal genotypes. Conjugation assays showed that 70.00% of plasmid-borne SHV-12 ESBL genes were successfully transconjugated into E. coli C600 and that the antibiotic resistance phenotype of E. cloacae was partially (84%) or completely (10%) transferred. A significantly higher SHV-12 ESBL detection rate was found in patients with underlying conditions and/or complications compared with those without (P<0.05). The detection of SHV-12 ESBL-producing E. cloacae from vertical transmission varied significantly across clinical departments and age groups (P<0.05), with the highest rates in the intensive care unit and the group of patients aged ≥60 years. The present results indicate that the location and transmission efficiency of SHV-12 ESBL are closely correlated with the antibiotic resistance of E. cloacae.

Multidrug-resistant phenotype and isolation of a novel SHV- beta-Lactamase variant in a clinical isolate of Enterobacter cloacae

Background

ESBL-producing bacteria are a clinical problem in the management of diseases caused by these pathogens. Worldwide, systemic infections with BL enzymes are evolving by mutations from classical bla genes in an intensified manner and they continue to be transferred across species.

Results

E.cloacae BF1417 isolate and its transconjugants gave positive results with the DDST, suggesting the presence of ESBL. Sequence analysis revealed a bla_SHV-ESBL-type gene that differs from the gene encoding SHV-1 by five point mutations resulting in three amino acid substitutions in the coding region: C123R, I282T and L286P. This novel SHV-type enzyme was designated SHV-128. The conjugation tests and plasmid characterization showed that the bla_SHV-128 is located on a conjugative plasmid IncFII type. Expression studies demonstrated that the above mutations participated in drug resistance, hydrolysis of extended spectrum β-lactam and the change of the isoelectric point of the protein.

Conclusion

These findings underscore the diversity by which antibiotic resistance can arise and the evolutionary potential of the clinically important ESBL enzymes. In addition, this study highlights the need for systematic surveillance of ESBL-mediated resistance as well as in clinical areas and communities.

Clinical and microbiological characteristics of bloodstream infections due to AmpC β-lactamase producing Enterobacteriaceae: an active surveillance cohort in a large centralized Canadian region

Background

The objective of this study was to describe the clinical and microbiological characteristics of bloodstream infections (BSIs) due to AmpC producing Enterobacteriaceae (AE) in a large centralized Canadian region over a 9-year period.

Methods

An active surveillance cohort design in Calgary, Canada.

Results

A cohort of 458 episodes of BSIs caused by AE was assembled for analysis. The majority of infections were of nosocomial origin with unknown sources. Enterobacter spp. was the most common species while BSIs due to Serratia spp. had a significant higher mortality when compared to other AE. Delays in empiric or definitive antibiotic therapy were not associated with a difference in outcome. However, patients that did not receive any empiric antimicrobial therapy had increased mortality (3/5; 60% vs. 57/453; 13%; p = 0.018) as did those that did not receive definitive therapy (6/17; 35% vs. 54/441; 12%; p = 0.015).

Conclusions

Delays in therapy were not associated with adverse outcomes although lack of active therapy was associated with increased mortality. A strategy for BSIs due to AE where β-lactam antibiotics (including oxyimino-cephalosporins) are used initially followed by a switch to non-β-lactam antibiotics once susceptibility results are available is effective.

Risk factor analysis for extended-spectrum β-lactamase-producing Enterobacter cloacae bloodstream infections in central Taiwan

BACKGROUND

Enterobacter cloacae (E.cloacae) bloodstream infection (EcBSI) is an important cause of morbidity and mortality, with an increasing incidence in our hospital. We wanted to elucidate the risk factors of mortality among patients with ESBL-positive EcBSI in central Taiwan.

METHODS

We ordered the clinical and microbiological data of cases with diagnosis of EcBSI, and analyzed the isolates by using antibiotyping, detection of ESBL, detection of class 1 integron and genomic fingerprinting by pulsed-field gel electrophoresis (PFGE).

RESULTS

Seventy episodes of EcBSI from 70 patients (56 hospital-acquired infections) were enrolled. Significant differences were found between ESBL-positive and ESBL-negative isolates with regard to risk factors, including the diseases severity (p = 0.03), category of health care-associated infection (p = 0.04), prior use of antibiotics (p = 0.023), and prior use of a ventilator (p = 0.037). A significant difference in mortality between two groups (p = 0.004) was determined using the chi-square test, and a trend in mortality between two groups (p = 0.006, OR = 4.750, 95% C.I.=1.573-14.344) was determined using univariate logistic regression analysis. The predominant clone in ESBL-positive strains was associated with a higher mortality rate but not with the presence of the integron.

CONCLUSIONS

The study disclosed four types of clinical characteristics to obtain ESBL-positive EcBSI, and there was a trend in mortality too. We suggested the need to review antibiotic prescription practices, and the possible need to consider ESBL-positive strains in empirical treatment of bloodstream infection.

Relationship between the distribution of cefepime minimum inhibitory concentrations and detection of extended-spectrum β-lactamase production among clinically important Enterobacteriaceae isolates obtained from patients in intensive care units in Taiwan: results from the Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART) in 2007

BACKGROUND

The data on susceptibility of important cephalosporins against four Enterobacteriaceae members producing potential extended-spectrum β-lactamase (ESBL) collected from Taiwanese intensive care units are lacking.

METHODS

Minimum inhibitory concentrations (MICs) of cefotaxime, ceftazidime, and cefepime were determined using agar dilution method, against Escherichia coli (n = 344), Klebsiella pneumoniae (n = 359), Enterobacter cloacae (n = 103), and Proteus mirabilis (n = 78). Susceptibilities of these isolates to three cephalosporins were assessed according to MIC breakpoints recommended by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in 2013. The double-disk synergy test using disks containing cefepime (30 μg) with or without clavulanate (10 μg) was applied to confirm production of ESBL for isolates with cephalosporin MIC ≥ 2 μg/mL.

RESULTS

A total of 175 isolates were verified as ESBL producers. The rates of cefepime susceptibility among the ESBL-producing isolates, according to CLSI (EUCAST) criteria, were 56.7% (22.4%) for E. coli, 61.3% (12.0%) for K. pneumoniae, 57.9% (31.6%) for E. cloacae, and 71.4% (7.1%) for P. mirabilis. Using different cefepime MIC breakpoints (MICs ≥ 16 μg/mL recommended by CLSI criteria and ≥ 2 μg/mL by EUCAST criteria) to define nonsusceptibility, we found that both criteria were poorer at predicting ESBL producers among K. pneumoniae and E. cloacae than among the other two species. In addition, we also found that the cefepime MIC level of 1.0 μg/mL best distinguished non-ESBL- from ESBL-producing K. pneumoniae and E. cloacae.

CONCLUSION

To detect ESBLs, CLSI should revise the cefepime MIC breakpoint against Enterobacteriaceae.

Clinical analysis of Enterobacter bacteremia in pediatric patients: a 10-year study

BACKGROUND

Enterobacter species has emerged as an important pathogen of nosocomial bacteremia. The purpose of this study is to review the clinical characteristics of bacteremia in pediatric patients.

MATERIALS AND METHODS

We reviewed retrospectively the medical records of patients (under the age of 18 years) having Enterobacter bacteremia who were treated at Taipei the Veterans General Hospital from January 2001 to June 2011.

RESULTS

In total, 853 positive blood cultures were obtained from 620 patients during the study period. Among them, 96 episodes of Enterobacter bacteremia were found in 83 patients, accounting for 11.3% of all bacteremia. Eighty-two cases (98.8%) were nosocomial infections. Most of the cases were neonates (62 cases, 74.7%) and premature infants (51 cases, 61.5%). The common sources of bacteremia were the respiratory tract (53.0%), followed by intravascular catheter (10.8%), multiple sources (10.8%), and the gastrointestinal tract (8.4%). The overall case fatality rate was 18.1%, with the highest rate being reported among premature infants. The factors responsible for the deaths were leukocytosis and a higher median number of underlying diseases.

CONCLUSION

Based on the findings of the present study, it can be concluded that Enterobacter species are probably an important pathogen of nosocomial bacteremia in premature neonates. The number of underlying diseases should be considered a major factor influencing the prognosis.

In vitro synergistic antimicrobial effect of imipenem and colistin against an isolate of multidrug-resistant Enterobacter cloacae

BACKGROUND/PURPOSE

Enterobacter cloacae is an important nosocomial pathogen responsible for various infections. Little is known about the synergistic effects of imipenem and colistin against multidrug-resistant E. cloacae. Therefore, we investigated the in vitro effects of imipenem and colistin against a clinical isolate of multidrug-resistant E. cloacae.

METHODS

A strain of E. cloacae, designed Ent 831, was isolated from the sputum of a woman who developed severe pneumonia in a medical intensive care unit. Minimal inhibitory concentrations (MICs) of imipenem and colistin were determined by the agar dilution method. The synergistic effects were investigated using the time-kill method.

RESULTS

MICs of imipenem and colistin for E. cloacae strain Ent 831 were 0.5 microg/mL and 1.0 microg/mL, respectively. Using a standard inoculum (5 x 10(5)) CFU/mL), synergism was shown with a concentration of two times the MICs of imipenem and colistin. Furthermore, four times the MIC of imipenem completely inhibited bacterial growth for more than 48 hours, but four times the MICs of colistin resulted in re-growth after 4 hours. There was no synergism between imipenem and colistin at two times the MICs against a high concentration inoculum (6.24 x 10(6)) CFU/mL). Nevertheless, imipenem, with or without colistin, at a concentration of four times MICs could inhibit the growth of bacteria for more than 48 hours.

CONCLUSION

High-dose imipenem, alone or in combination with colistin, is effective against multidrug-resistant E. cloacae. Colistin alone, even at a high dose, is not effective. However, in vitro susceptibility to antimicrobial compounds does not always correlate with clinical success. Thus further testing of these antibiotic combinations in animal models is needed in order to predict their suitability for clinical use.

Enterobacter cloacae: an "ICU bug" causing community acquired necrotizing meningo-encephalitis

Enterobacter cloacae is a gram negative bacillus that is ubiquitous as a contaminant and a pathogen in adult, paediatric, and neonatal ICUs. Its transmission is almost exclusively nosocomial with community acquired infection reported rarely. We report a case of community acquired, rapidly progressive E. cloacae meningo-encephalitis in a neonate. A three-week-old term infant presented from home, having been discharged from hospital within two days of delivery. She rapidly progressed to multi-organ dysfunction. Initial CT of her brain showed evidence of severe hypoxic changes and herniation of the frontal lobes through the anterior fontanelle. Care was withdrawn 72 hours after admission. Post mortem examination confirmed E.cloacae meningo-encephalitis as a cause of her death. The baby had not been in a critical care environment at any time before admission, making it highly likely to have been a community acquired infection. Transmission of the organism may have been vertical as maternal transmission with intestinal colonization of neonates with E. cloacae has previously been reported. This case confirms that infection with E. cloacae should be included in the differential diagnosis of any severely ill neonate presenting from the community, and antimicrobial therapy should be optimized accordingly.

Clinical and molecular epidemiology of community-onset, extended-spectrum beta-lactamase-producing Escherichia coli infections in Thailand: a case-case-control study

BACKGROUND

Extended-spectrum beta-lactamase (ESBL)-producing organisms, first identified in Germany in 1983, are now widely recognized as clinically relevant causes of infections in community.

METHODS

Our objective was to evaluate the clinical and molecular epidemiology of community-onset, extended-spectrum beta-lactamase (CO-ESBL)-producing Escherichia coli infections. We used a case-case-control study undertaken in a 450-bed, tertiary care hospital. Patients included case group (CG) I, which had confirmed CO-ESBL-producing E coli infections (n=46). Case group (CG) II (n=46) included patients with CO-non-ESBL-producing E coli infections. Controls (n=138) were patients without infections.

RESULTS

By multivariate analysis, diabetes (95% confidence interval [CI]: 1.9-13.2, P< .001), prior ESBL E coli colonization (<90 days) (95% CI: 1.2-67.8, P< .001), recent receipt of antibiotics (<90 days) (95% CI: 4.2-44.2, P= .004), and previous exposure to third-generation cephalosporins (95% CI: 2.2-16.4, P= .001) and fluoroquinolones (95% CI: 1.4-18.3; P= .003) were associated risks among CG I. Diabetes (95% CI: 1.6-15.4, P= .005), stroke (95% CI: 1.5-17.1, P= .001), and diarrhea (95% CI: 3.8-65.8, P= .001) were risks among CG II. Patients with CO-ESBL in CG I versus controls were more likely to die (30% vs 0%, respectively; P< .001), had prolonged hospital length of stay (8 vs 5 days, respectively; P< .001), and had higher hospitalization costs (median, US $528 vs $108, respectively; P< .001). The plasmid carrying the CTX-M-15 gene was identified in 13 of 25 (52%) available CO-ESBL-producing E coli isolates.

CONCLUSION

CO-ESBL-producing E coli is an emerging multidrug-resistant microorganism in Thailand. Patients with prior ESBL colonization and recent antibiotic exposures, especially to third-generation cephalosporins and fluoroquinolones, were at risk for CO-ESBL-producing E coli infection.

Characterisation and molecular epidemiology of extended-spectrum beta-lactamase-producing Enterobacter cloacae isolated from a district teaching hospital in Taiwan

Enterobacter cloacae (n = 110) isolates from a district hospital in Taiwan were screened for extended-spectrum beta-lactamases (ESBLs). In total, 17 ESBL-producers were identified, based on the combination-disk synergy test using cefotaxime and ceftazidime +/- clavulanic acid. Investigation of ESBL genes in 33 ceftazidime-resistant isolates revealed the SHV-12 gene in the same 17 ESBL-producers. In addition, one isolate also carried the CTX-M-3 gene, and two isolates also carried the CTX-M-9 gene. No major epidemic clone of ESBL-producers was identified by pulsed-field gel electrophoresis. Routine screening for the ESBL phenotype, focusing on ceftazidime-resistant E. cloacae, should be undertaken in this area.

Cefotaxime-resistant Citrobacter freundii in isolates from blood in a tertiary teaching hospital in Northern Taiwan

From January 2002 to December 2003, 12 patients in a tertiary teaching hospital in northern Taiwan had bloodstream infections caused by Citrobacter freundii. Seven of the 12 isolates were resistant to cefotaxime. Using polymerase chain reaction and DNA sequencing, 3 of the 7 cefotaxime-resistant C. freundii isolates were found to carry extended-spectrum beta-lactamase (ESBL). AmpC beta-lactamase genes were also detected in all strains of C. freundii. All strains of C. freundii with MICs >or=4 mg/L for cefepime were positive for ESBL. Rather than performing PCR on all cefotaxime-resistant C. freundii isolates, assessment of the MIC for cefepime might be a practical way to choose between treatment with cefepime or with carbapenems.

The continuing challenge of ESBLs

Since their first description more than 20 years ago, Escherichia coli and Klebsiella pneumoniae possessing extended-spectrum class A beta-lactamases (ESBLs) continue to thwart our best clinical efforts. In the 'early years' the most common beta-lactamases were of the TEM and SHV varieties. Now, CTX-M enzymes are being discovered throughout the world and are becoming the most prevalent beta-lactamases found in clinical isolates. The K. pneumoniae carbapenemases (KPC) (ESBL-type enzymes that confer resistance to extended-spectrum cephalosporins and carbapenems) present the most significant challenge to date. Structural studies of ESBLs indicate that active site expansion and remodeling are responsible for this extended hydrolytic activity. Continuing questions still exist regarding the optimal detection method for ESBLs. Most relevant are the increasing concerns regarding the status of carbapenems as 'best therapy' for ESBL-producing bacteria in light of the emergence of carbapenemases.

Identification of plasmid-mediated extended-spectrum and AmpC β-lactamases in Enterobacter spp. isolated from dogs

The genetic determinants involved in reduced susceptibility to third-generation cephalosporins and aztreonam were identified in ten canine Enterobacter isolates associated with opportunistic infections in three veterinary hospitals in Brisbane, Australia. All isolates were evaluated by a combination of phenotypic (broth microdilution and disc susceptibility, modified disc diffusion and IEF) and genotypic (PFGE, plasmid analysis, Southern blot hybridization, bacterial conjugation, PCR and sequencing) methods to investigate genetic relatedness and to identify plasmid-mediated resistance genes, in particular beta-lactamase genes responsible for extended-spectrum cephalosporin resistance. The ten canine isolates were genotypically diverse based on PFGE and belonged to either Enterobacter cloacae or Enterobacter hormaechei on the basis of 16S rRNA gene sequence analysis. Plasmid profiles were also diverse. Nine isolates contained a transmissible blaSHV-12-carrying plasmid (approximately 140 kb) that also conferred resistance to chloramphenicol, gentamicin, spectinomycin, tetracycline, trimethoprim and sulfonamides. In all plasmid-mediated extended-spectrum beta-lactamase (ESBL)-producing isolates including transconjugants, blaSHV-12 was shown to reside in a approximately 6.5 kb plasmid fragment. The remaining isolate that was not an ESBL producer possessed an AmpC beta-lactamase gene (blaCMY-2) on a approximately 93 kb transmissible plasmid. This plasmid did not contain any other antimicrobial resistance genes. Additional plasmid-mediated beta-lactamases identified in some isolates included bla(TEM) and blaOXA-10. This is the first report of canine Enterobacter isolates containing transmissible plasmid-mediated blaSHV-12 and blaCMY-2 resistance genes. Therefore, Enterobacter isolated from opportunistic infections in dogs may be an important reservoir of plasmid-mediated resistance genes, which could potentially be spread to other members of the Enterobacteriaceae.

Failure to control an outbreak of qnrA1-positive multidrug-resistant Enterobacter cloacae infection despite adequate implementation of recommended infection control measures

A large outbreak with an aminoglycoside-resistant Enterobacter cloacae (AREC) clone occurred at the University Medical Center Utrecht beginning in 2001 and continued up through the time that this study was completed. This clone (genotype I) contains a conjugative R plasmid carrying the qnrA1, bla(CTX-M-9), and aadB genes, encoding resistance to quinolones, extended-spectrum beta-lactamases, and aminoglycosides, respectively. The aim of this study was to determine whether this clone was more transmissible than other AREC strains. Therefore, the dissemination of this genotype and of other E. cloacae strains was studied. In addition, infection control measures taken were evaluated. Pulsed-field gel electrophoresis analysis divided the 191 AREC strains into 42 different genotypes, of which 5 (12%) involved at least three patients. Aside from this outbreak (133 patients), only two other small outbreaks occurred, showing that the infection control measures were successful for all strains but one. Among 324 aminoglycoside-susceptible E. cloacae strains, 34/166 (20%) genotypes were identified from at least three patients, but only 4 involved small outbreaks. The outbreak strain was also detected in 11 of 15 other Dutch hospitals and caused outbreaks in at least 4. Evaluation of infection control measures showed that the outbreak strain disseminated throughout the hospital despite adequate implementation of internationally accepted guidelines on the control of multidrug-resistant Enterobacteriaceae (MRE). In conclusion, some MRE strains are better able to spread than others, and these strains may not be controlled by the current infection control guidelines. Strategies to identify such strains in an early phase and adapted guidelines for such "superbugs" are needed to prevent these clones from becoming endemic.

Molecular characterization of extended-spectrum beta-lactamases in Enterobacteriaceae from patients of two hospitals in Saxony, Germany

Between January and September 2003, 39 isolates of the family Enterobacteriaceae with phenotypically positive Vitek 1 extended-spectrum beta-lactamase (ESBL) test results were collected, originating from patients of two hospitals in Saxony, Germany. Plasmid DNA was isolated and screened by PCR for the presence of genes encoding beta-lactamases of SHV, TEM and CTX-M types. To differentiate ESBL and non-ESBL among SHV and TEM genes, detailed analysis of PCR products was performed. Twenty-four strains carried SHV-2, SHV-5 or SHV-12 genes. In a further 11 strains a CTX-M gene was detected. The CTX-M genes could be affiliated to the CTX-M-1 and CTX-M-9 cluster by RFLP analysis. In the case of four Klebsiella oxytoca isolates, hyperproduction of the chromosomal beta-lactamase K1 was inferred, because genes of the above-mentioned types were not detected. The strains contained plasmid DNA between 45 and 160 kb in size. Common plasmid restriction patterns among SHV-5 producers provided evidence of horizontal spread. Twenty strains had a MIC for cefotaxime of ⩽4 mg l−1, 18 strains had the same MIC for ceftazidime, and nine strains had this MIC of >4 mg l−1 for both antibiotics. The ESBL phenotypes often coincided with ciprofloxacin or gentamicin resistance.

Dissemination of extended-spectrum beta-lactamase-producing Enterobacteriaceae in intensive care units of a medical center in Taiwan

The prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in a tertiary hospital in Taiwan was assessed over a 16-month period. A total of 125 nonrepetitive ESBL-producing isolates of Enterobacter cloacae, Escherichia coli, and Klebsiella pneumoniae were available for investigation using molecular methods. Four predominant intensive care units (ICUs) were identified, and SHV-12 (59%), CTX-M- 3 (36%), and CTX-M-14 (14%) were the three most frequent ESBLs. SHV-12 was predominant among E. cloacae in the burn unit and K. pneumoniae in the other three chest medicine-related ICUs. CTX-M-3 was predominant among E. coli and K. pneumoniae in three other ICUs. The dissemination of ESBL-producing Enterobacteriaceae in four ICUs of a medical center in Taiwan is a consequence of the clonal dissemination of a few epidemic strains along with the horizontal transmission of resistance genes-carrying plasmids among bacterial organisms.

Clinical and molecular analysis of extended-spectrum {beta}-lactamase-producing enterobacteria in the community setting

During a previous survey, five extended-spectrum beta-lactamase (ESBL)-producing enterobacteria (ESBLE) (two Enterobacter aerogenes isolates expressing TEM-24 b, two Escherichia coli isolates expressing TEM-21 or TEM-24 b, and one Klebsiella pneumoniae isolate expressing SHV-4/TEM-15) responsible for urinary tract infections (UTIs) were found among 1,584 strains collected from community patients. The aim of the present study was to elucidate the route of emergence of these typically nosocomial organisms in the community. Thus, the files of the five patients were analyzed over at least a decade, and potentially related ESBLE from hospitals or clinics were examined. Their enzymes were characterized at a molecular level, and the strains were typed by amplified-primed PCR, enterobacterial repetitive intergenic consensus PCR, and restriction plasmid profile. All patients (C1 to C5) had risk factors for ESBLE acquisition, including past history of hospitalization (2.5 to 23 months before). Four (C1 and C3 to C5) had previously received antibiotics (concomitantly to 35 months earlier), two (C1 and C3) had indwelling urinary catheters and recurrent UTIs, and three (C2, C3, and C5) formerly experienced ESBLE-induced UTIs (2 to 11 months before). The same ESBLE and/or an identical or similar ESBL-encoding plasmid was identified in the hospital ward (C1 to C4) or in a clinic (C5) where the patients had previously resided. Patients C1 and C4, infected with different ESBLE carrying a closely related plasmid, were hospitalized in the same unit. Persistence of ESBLE over at least a 5-year period was demonstrated for patient C3. Thus, community-acquired UTIs in these patients likely resulted from nosocomially acquired ESBLE or an ESBL-encoding plasmid followed by a prolonged digestive carriage.

Ceftriaxone resistance of nontyphoidal Salmonella enterica isolates in Northern Taiwan attributable to production of CTX-M-14 and CMY-2 beta-lactamases

Among 3,027 nontyphoidal Salmonella enterica isolates identified between January 1999 and December 2002 in a medical center in northern Taiwan, 31 were resistant to the extended-spectrum cephalosporin ceftriaxone (1.02% [31/3,027]), including 2 in 1999 (0.36% [2/549]), 13 in 2000 (1.49% [13/870]), 7 in 2001 (0.78% [7/893]), and 9 in 2002 (1.26% [9/715]). Sixteen of these isolates belonged to Salmonella serogroup B, nine belonged to serogroup C, four belonged to serogroup D, and two belonged to serogroup E. The majority were from stool cultures. The mechanism of resistance was investigated for eight isolates, including three S. enterica serovar Typhimurium, one S. enterica serovar Wagenia, one S. enterica serovar Senftenberg, one S. enterica serovar Derby, one S. enterica serovar Panama, and one S. enterica serovar Duesseldorf isolate. All eight patients from whom these isolates were recovered had community-acquired infections. All eight isolates were resistant to ampicillin, ceftriaxone, and cefotaxime but susceptible to imipenem and ciprofloxacin. Ceftriaxone resistance was due to the production of the CMY-2 AmpC beta-lactamase by seven isolates and the CTX-M-14 beta-lactamase by the remaining isolate. Both beta-lactamase genes were carried on conjugative plasmids. In a 2.5-kb region encompassing the bla(CMY-2) gene, at nucleotide 49 upstream of the start codon of bla(CMY-2), three of the seven bla(CMY-2)-positive isolates had an A nucleotide and four had a G nucleotide. In conclusion, the ceftriaxone resistance of nontyphoidal Salmonella isolates in our hospital was attributed to the CTX-M-14 and CMY-2 beta-lactamases.