Enterobacter spp.: pathogens poised to flourish at the turn of the century

Microbial diversity similarities in periodontal pockets and atheromatous plaques of cardiovascular disease patients

Background and Objective

The immune and infectious alterations occurring in periodontitis have been shown to alter the development and severity of cardiovascular disease. One of these relationships is the translocation of oral bacteria to atheroma plaques, thereby promoting plaque development. Thus, the aim of this study was to assess, by 16s cloning and sequencing, the microbial diversity of the subgingival environment and atheroma plaques of patients concomitantly suffering from periodontitis and obstructive coronary artery atherosclerosis (OCAA).

Methods

Subgingival biofilm and coronary balloons used in percutaneous transluminal coronary angioplasty were collected from 18 subjects presenting with generalized moderate to severe periodontitis and OCAA. DNA was extracted and the gene 16S was amplified, cloned and sequenced.

Results

Significant differences in microbial diversity were observed between both environments. While subgingival samples mostly contained the phylum Firmicutes, in coronary balloons, Proteobacteria (p<0.05) was predominant. In addition, the most commonly detected genera in coronary balloons were Acinetobacter, Alloprevotella, Pseudomonas, Enterobacter, Sphingomonas and Moraxella, while in subgingival samples Porphyromonas, Filifactor, Veillonella, Aggregatibacter and Treponema (p<0.05) were found. Interestingly, 17 identical phylotypes were found in atheroma and subgingival samples, indicating possible bacterial translocation between periodontal pockets and coronary arteries.

Conclusion

Periodontal pockets and atheromatous plaques of cardiovascular disease patients can present similarities in the microbial diversity.

MLST reveals potentially high-risk international clones of Enterobacter cloacae

OBJECTIVES

To perform the first multinational Enterobacter cloacae clonality study, using the MLST scheme newly developed in Japan.

METHODS

The analysis included 195 rectal carriage E. cloacae isolates resistant to expanded-spectrum cephalosporins (ESCs), collected from patients in 12 hospital units across Europe and Israel. All of the isolates were typed by PFGE and 173 isolates were subjected to MLST. ESC resistance was analysed phenotypically; genes encoding ESBLs and carbapenemases were identified by PCR and sequencing.

RESULTS

MLST distinguished 88 STs, which correlated with the PFGE data. PFGE was more discriminatory, producing 129 pulsotypes (169 patterns). Numerous STs were observed in several countries each. The most widespread were ST66, ST78, ST108 and ST114, each having at least 10 isolates from three to five countries, diversified into multiple pulsotypes, with clusters of related isolates in one or more centres. Analysis of the STs against the MLST database revealed several epidemic clonal complexes, such as those with central genotypes ST74 (including ST78) or ST114 (including ST66). ESC resistance was equally related to overexpression of the AmpC cephalosporinase and to ESBL production. Among ESBL producers some spreading subclones were identified, including specific ST66, ST78 and ST114 pulsotypes, associated with CTX-M-15 production. Several isolates produced carbapenemase VIM-1 or KPC-2.

CONCLUSIONS

Together with the information available in the MLST database, our results suggest that, like Escherichia coli and Klebsiella pneumoniae, E. cloacae harbours clonal lineages of increased epidemic potential that may be associated with resistance spread.

Prevalence and impact of extended-spectrum β-lactamase production on clinical outcomes in cancer patients with Enterobacter species bacteremia

BACKGROUND/AIMS

We examined the prevalence of extended-spectrum β-lactamase (ESBL) production and the impact of ESBL on clinical outcomes in cancer patients with Enterobacter spp. bacteremia.

METHODS

Using prospective cohort data on Enterobacter bacteremia obtained between January 2005 and November 2008 from a tertiary care center, the prevalence and clinical impact of ESBL production were evaluated.

RESULTS

Two-hundred and three episodes of Enterobacter spp. bacteremia were identified. Thirty-one blood isolates (15.3%, 31/203) scored positive by the double-disk synergy test. Among 17 isolates in which ESBL genes were detected by polymerase chain reaction and sequencing, CTX-M (n = 12), SHV-12 (n = 11), and TEM (n = 4) were the most prevalent ESBL types. Prior usage of antimicrobial agents (77.4% vs. 54.0%, p = 0.02) and inappropriate empirical antimicrobial therapy (22.6% vs. 3.0%, p < 0.001) were more commonly encountered in the ESBL-positive group than in the extended-spectrum cephalosporin-susceptible ESBL-negative group, respectively. Clinical outcomes did not differ significantly between the two groups (30-day mortality rate, 19.4% vs. 17.0%, p = 0.76; median length of hospital stay, 24.0 days vs. 30.5 days, p = 0.97). Initial presentation of severe sepsis/septic shock, pneumonia, and intra-abdominal infection were independently associated with 30-day mortality.

CONCLUSIONS

The prevalence of ESBL-producing isolates was 15.3% in cancer patients with Enterobacter bacteremia. Although inappropriate empirical therapy was more common in the ESBL-positive group, ESBL production was not associated with poorer outcomes.

Enterobacter cloacae complex: clinical impact and emerging antibiotic resistance

Species of the Enterobacter cloacae complex are widely encountered in nature, but they can act as pathogens. The biochemical and molecular studies on E. cloacae have shown genomic heterogeneity, comprising six species: Enterobacter cloacae, Enterobacter asburiae, Enterobacter hormaechei, Enterobacter kobei, Enterobacter ludwigii and Enterobacter nimipressuralis, E. cloacae and E. hormaechei are the most frequently isolated in human clinical specimens. Phenotypic identification of all species belonging to this taxon is usually difficult and not always reliable; therefore, molecular methods are often used. Although the E. cloacae complex strains are among the most common Enterobacter spp. causing nosocomial bloodstream infections in the last decade, little is known about their virulence-associated properties. By contrast, much has been published on the antibiotic-resistance features of these microorganisms. In fact, they are capable of overproducing AmpC β-lactamases by derepression of a chromosomal gene or by the acquisition of a transferable ampC gene on plasmids conferring the antibiotic resistance. Many other resistance determinants that are able to render ineffective almost all antibiotic families have been recently acquired. Most studies on antimicrobial susceptibility are focused on E. cloacae, E. hormaechei and E. asburiae; these studies reported small variations between the species, and the only significant differences had no discriminating features.

Detection of Salmonella bacterium in drinking water using microring resonator

A new microring resonator system is proposed for the detection of the Salmonella bacterium in drinking water, which is made up of SiO2-TiO2 waveguide embedded inside thin film layer of the flagellin. The change in refractive index due to the binding of the Salmonella bacterium with flagellin layer causes a shift in the output signal wavelength and the variation in through and drop port's intensities, which leads to the detection of Salmonella bacterium in drinking water. The sensitivity of proposed sensor for detecting of Salmonella bacterium in water solution is 149 nm/RIU and the limit of detection is 7 × 10(-4)RIU.

Colistin heteroresistance in Enterobacter cloacae is associated with cross-resistance to the host antimicrobial lysozyme

Here, we describe the first identification of colistin-heteroresistant Enterobacter cloacae in the United States. Treatment of this isolate with colistin increased the frequency of the resistant subpopulation and induced cross-resistance to the host antimicrobial lysozyme. This is the first description of heteroresistance conferring cross-resistance to a host antimicrobial and suggests that clinical treatment with colistin may inadvertently select for bacteria that are resistant to components of the host innate immune system.

Multiple antibiotic-resistant bacteria on fluted pumpkin leaves, a herb of therapeutic value

Fluted pumpkin (Telfairia occidentalis) is a minimally-processed green leafy vegetable traditionally used for its antianaemic properties in the form of leaf juice without a heating or inactivation step before consumption. The aim of the study was to assess the presence of surface microbiota on T. occidentalis leaves and also to determine the antimicrobial susceptibility of isolated organisms. Bacterial contaminants on 50 samples of T. occidentalis leaves were isolated and characterized using standard biochemical methods and the antimicrobial susceptibility of isolated organisms was determined using the antibiotic disc diffusion assay. The results obtained show that the leaves of T. occidentalis is contaminated with organisms which included Enterobacter agglomerans (25.9%), Proteus vulgaris (24.9%), Klebsiella spp. (2.6%), and Serratia liquefaciens (2.1%). Other bacterial isolates recovered in order of frequency included: Staphylococcus spp. (33.7%), Bacillus spp. (8.3%), and Pseudomonas fluorescens (2.6%). Of the 193 bacterial isolates from the leaves of T. occidentalis samples tested for antimicrobial resistance, all (100%) were found to be resistant to ampicillin, cloxacillin, augmentin, erythromycin, and tetracycline while 96% of the isolates were resistant to cephalothin. Resistance to trimethoprim (93%) and gentamicin (83%) was also observed. Approximately, 22% of the isolates were resistant to ciprofloxacin; however, only 11 (5.8%) were resistant to ofloxacin. Thus, uncooked T. occidentalis is a potential source of highly-resistant epiphytic bacteria which could be opportunistic pathogens in consumers.

Antibiotic resistance in the intensive care unit setting

Antibiotic resistance is an important factor influencing clinical outcome for patients in intensive care units. It is also associated with increased healthcare costs resulting from prolonged patient stays. The problem of antibiotic resistance is particularly acute in intensive care units because they house seriously ill patients who are predisposed to infection, as a result of which, antibiotic use is extremely common. Strategies for controlling resistance in intensive care units have focused on attempting to reduce unnecessary antibiotic use, while at the same time ensuring adequate antibiotic cover is provided. The formulation of policies for the effective use of antibiotics in individual intensive care units requires a multidisciplinary approach, entailing regular epidemiological surveillance, together with input from critical care specialists, infectious disease specialists and pharmacists.

Phenotypic characterization of ESBL producing Enterobacter cloacae among children

Objective: The emergence of ESBL producing Enterobacter cloacae in clinical isolates is posing a serious threat for treating nosocomial infections. The aim of the study was to determine the frequency of extended spectrum β-lactamase (ESBL) producing Enterobacter cloacae and to compare the phenotypic methods used for the characterization of ESBL producing strains.

Methodology: This cross sectional observational study was conducted during April 2011 to March 2012 at Microbiology department of The Children’s Hospital and Institute of Child Health, Lahore. A total number of 20,257 various clinical samples were analyzed during the study period. Enterobacter cloacae were identified using API 20E system and ESBL detection was carried out using double-disk synergy test (DDST) and CLSI confirmatory test.

Results:Enterobacter cloacae were isolated from 221 samples, out of which 33 (14.93%) were ESBL producers and 188 (85.07%) were non-ESBL producers. The gender distribution of ESBL producing Enterobacter cloacae was 21 (63.6%) in males and 12 (36.4%) in females. Highest frequency (63%) of ESBL producing Enterobacter cloacae was detected in blood samples. Comparison of DDST and CLSI confirmatory test showed that 25 (75.75%) isolates were characterized by DDST and 33 (100%) using CLSI confirmatory test.

Conclusion: The present study shows moderately high frequency of ESBL producing Enterobacter cloacae among children. DDST was found to be less efficient in ESBL detection as compared to CLSI confirmatory test.

Early aetiological agent identification of osteomyelitis with the Light Cycler SeptiFast test from peripheral blood

The commercial real-time PCR SeptiFast test allows identification of 25 bacterial and fungal species directly from peripheral blood in patients with bloodstream infections. A 22-year-old Caucasian woman reported an open femur fracture requiring a two step surgical procedure. After the second procedure the patient manifested sepsis and Enterobacter cloacae/aerogenes DNA was detected in the peripheral blood with the SeptiFast. Thereafter, femur osteomyelitis was diagnosed and E cloacae was cultured from intraoperative bone samples. The patient completed a 3-month course of antimicrobial therapy. Five months after therapy was discontinued, the patient remained symptom free, but delayed bone consolidation occurs. Molecular methods to identify aetiological agents in blood, in addition to conventional cultures, could represent an advantageous tool in clinical practice also in patients with post-traumatic bone infections.

Isolation, identification and antimicrobial susceptibility of Pantoea (Enterobacter) agglomerans isolated from consumed powdered infant formula milk (PIF) in NICU ward: First report from Iran

BACKGROUND AND OBJECTIVES

Pantoea agglomerans is a Gram-negative rod in the Enterobacteriaceae family. It is reported as both commensal and opportunistic pathogen of animals and humans. This organism is potential candidates as powdered infant milk formula-borne opportunistic pathogen. The aim of our study was to perform isolation, identification and antimicrobial susceptibility pattern of Pantoea (Enterobacter) agglomerans strains isolated from consumed powdered infant formula milk (PIF) in NICU ward.

MATERIALS AND METHODS

A of total 125 powdered infant formula milk (PIF) samples were purchased from hospital drug stores between June 2011 to March 2012. P. agglomerans was isolated according to FDA method. For final confirmation, biochemical tests embedded in the API-20E system were used. The drug susceptibility test was performed using the disc diffusion method according to CLSI guidelines.

RESULTS

Out of the 125 samples investigated, 8 (6.4%) samples were positive for P. agglomerans and these were uniformly susceptible to tigecycline, chloramphenicol, cefepime, levofloxacin, minocycline and colistin. Fifty percent of isolates were resistant to cefotaxime, moxifloxacin, cotrimoxazole and ticarcillin.

CONCLUSION

Controlling the primary populations of P. agglomerans during the PIF production process and preventing post processing contamination, by using suitable microbiological guidelines, is accessible. Sanitary practices for the preparation of infant formula in both the home and hospitals should be carefully controlled.

Development of quorum-based anti-virulence therapeutics targeting Gram-negative bacterial pathogens

Quorum sensing is a cell density-dependent signaling phenomenon used by bacteria for coordination of population-wide phenotypes, such as expression of virulence genes, antibiotic resistance and biofilm formation. Lately, disruption of bacterial communication has emerged as an anti-virulence strategy with enormous therapeutic potential given the increasing incidences of drug resistance in pathogenic bacteria. The quorum quenching therapeutic approach promises a lower risk of resistance development, since interference with virulence generally does not affect the growth and fitness of the bacteria and, hence, does not exert an associated selection pressure for drug-resistant strains. With better understanding of bacterial communication networks and mechanisms, many quorum quenching methods have been developed against various clinically significant bacterial pathogens. In particular, Gram-negative bacteria are an important group of pathogens, because, collectively, they are responsible for the majority of hospital-acquired infections. Here, we discuss the current understanding of existing quorum sensing mechanisms and present important inhibitory strategies that have been developed against this group of pathogenic bacteria.

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.

Multilocus sequence typing (MLST) for characterization of Enterobacter cloacae

Enterobacter cloacae is an important emerging pathogen, which sometime causes respiratory infection, surgical site infection, urinary infection, sepsis, and outbreaks at neonatal units. We have developed a multilocus sequence typing (MLST) scheme utilizing seven housekeeping genes and evaluated the performance in 101 clinical isolates. The MLST scheme yielded 83 sequence types (ST) including 78 novel STs found in the clinical isolates. These findings supported the robustness of the MLST scheme developed in this study.

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.

Emergence of extended-spectrum β-lactamase producing Enterobacter spp. in patients with bacteremia in a tertiary hospital in southern Brazil

BACKGROUND

Extended-spectrum β-lactamases (ESBLs) are increasingly prevalent in Enterobacter spp., posing a challenge to the treatment of infections caused by this microorganism. The purpose of this retrospective study was to evaluate the prevalence, risk factors, and clinical outcomes of inpatients with bacteremia caused by ESBL and non ESBL-producing Enterobacter spp. in a tertiary hospital over the period 2004-2008.

METHODS

The presence of blaCTX-M, blaTEM, blaSHV, and blaPER genes was detected by polymerase chain reaction (PCR) and nucleotide sequence analysis. Genetic similarity between strains was defined by pulsed-field gel electrophoresis (PFGE).

RESULTS

Enterobacter spp. was identified in 205 of 4907 of the patients who had positive blood cultures during hospitalization. Of those cases, 41 (20%) were ESBL-producing Enterobacter spp. Nosocomial pneumonia was the main source of bacteremia caused by ESBL-producing Enterobacter spp. The presence of this microorganism was associated with longer hospital stays. The ESBL genes detected were: CTX-M-2 (23), CTX-M-59 (10), CTX-M-15 (1), SHV-12 (5), and PER-2 (2). While Enterobacter aerogenes strains showed mainly a clonal profile, Enterobacter cloacae strains were polyclonal.

CONCLUSION

Although no difference in clinical outcomes was observed between patients with infections by ESBL-producing and non-ESBL-producing strains, the detection of ESBL in Enterobacter spp. resulted in the change of antimicrobials in 75% of cases, having important implications in the decision-making regarding adequate antimicrobial therapy.

Prevalence and characterization of multidrug-resistant zoonotic Enterobacter spp. in poultry of Bangladesh

Poultry and poultry products are major contributors of zoonotic pathogens. Limited data are available on Enterobacter spp. as a potent zoonotic pathogen in poultry. The present study is a first endeavor on the emergence of multidrug-resistant zoonotic Enterobacter spp. and its prevalence arising from poultry in Bangladesh. Cloacal swabs from poultry samples of five different farms at Savar, Dhaka, Bangladesh were collected and from 106 isolates, 18 presumptive Enterobacter spp. were obtained. Antibiogram using 19 used antibiotics belonging to 15 major groups revealed that all of the 18 isolates were completely resistant to penicillin and rifampicin, but differed in their drug resistance pattern against ampicillin (94.4%), clindamycin (94.4%), erythromycin (94.4%), vancomycin (88.9%), sulfonamides (72.2%), imipenem (66.6%), streptomycin (55.6%), nitrofurantoin (33.3%), doxycycline (33.3%), tetracyclines (33.3%), cefepime (11.1%), and gentamicin (5.6%). All Enterobacter spp. were found to be plasmid free, implying that multidrug-resistant properties are chromosomal borne. The vanA and sulI were detected by polymerase chain reaction assay in 17 and 13 isolates, respectively. Amplified ribosomal DNA restriction analysis and randomly amplified polymorphic DNA distributed the 18 multidrug-resistant Enterobacter spp. into three genotypes. Phylogenetic analysis of the representatives of the three genotypes using partial 16S rRNA gene sequence (approximately 900 bp) showed that the genotypically diverse groups belonged to Enterobacter hormaechei, E. cloacae, and E. cancerogenus, respectively. The clinical significance of the close relative Enterobacter spp. is indicative of their zoonotic potential. Therefore, urgent intervention is required to limit the emergence and spread of these bacteria in poultry feed as well as prudent use of antibiotics among poultry farmers in Bangladesh.

An assessment of fecal indicator and other bacteria from an urbanized coastal lagoon in the City of Los Angeles, California, USA

A study was performed in Del Rey Lagoon, City of Los Angeles, to determine if the lagoon was as a source or sink for fecal indicator bacteria (FIB: total coliforms, Escherichia coli, enterococci) and to screen for the presence of other potentially pathogenic bacteria. The lagoon receives tidal flows from the adjacent Ballona Estuary whose water usually is contaminated with FIB originating from the highly urbanized Ballona Creek Watershed. During 16 sampling events from February 2008 through March 2009, replicate water samples (n = 3) were collected 1 h prior to the high tide and 1 h prior to the following low tide. FIB concentrations were measured by the defined substrate method (IDEXX, Westbrook, Me) followed by culturing of bacterial isolates sampled from positive IDEXX Quanti-Tray wells and were identified using the Vitek 2 Compact (bioMérieux, Durham, NC). Mean concentrations of FIB often differed by an order of magnitude from flood to ebb flow conditions. The lagoon tended to act as a sink for total coliforms based on the ratio of mean flood to ebb densities (R (F/E)) >1.0 during 56 % of the sampling events and during ebb flows, as a source for E. coli and enterococci (R (F/E) <1.69 % of events). Approximately 54 species were identified from 277 isolates cultured from the IDEXX Quanti-Trays. Of these, 54 % were species known to include pathogenic strains that can be naturally occurring, introduced in runoff, or originated from other sources. Diversity and cluster analyses indicated a dynamic assemblage that changes in species composition with day-to-day fluctuations as well as tidal action. The concept of monitoring the lagoon and estuary as a sentinel habitat for pathogenic assemblages is discussed.

Characterisation and clinical features of Enterobacter cloacae bloodstream infections occurring at a tertiary care university hospital in Switzerland: is cefepime adequate therapy?

Despite many years of clinical experience with cefepime, data regarding the outcome of patients suffering from bloodstream infections (BSIs) due to Enterobacter cloacae (Ecl) are scarce. To address the gap in our knowledge, 57 Ecl responsible for 51 BSIs were analysed implementing phenotypic and molecular methods (microarrays, PCRs for bla and other genes, rep-PCR to analyse clonality). Only two E. cloacae (3.5%) were ESBL-producers, whereas 34 (59.6%) and 18 (31.6%) possessed inducible (Ind-Ecl) or derepressed (Der-Ecl) AmpC enzymes, respectively. All isolates were susceptible to imipenem, meropenem, gentamicin and ciprofloxacin. Der-Ecl were highly resistant to ceftazidime and piperacillin/tazobactam (both MIC₉₀≥256 μg/mL), whereas cefepime retained its activity (MIC₉₀ of 3 μg/mL). rep-PCR indicated that the isolates were sporadic, but Ecl collected from the same patients were indistinguishable. In particular, three BSIs initially due to Ind-Ecl evolved (under ceftriaxone or piperacillin/tazobactam treatment) into Der-Ecl because of mutations or a deletion in ampD or insertion of IS4321 in the promoter. These last two mechanisms have never been described in Ecl. Mortality was higher for BSIs due to Der-Ecl than Ind-Ecl (3.8% vs. 29.4%; P=0.028) and was associated with the Charlson co-morbidity index (P=0.046). Using the following directed treatments, patients with BSI showed a favourable treatment outcome: cefepime (16/18; 88.9%); carbapenems (12/13; 92.3%); ceftriaxone (4/7; 57.1%); piperacillin/tazobactam (5/7; 71.4%); and ciprofloxacin (6/6; 100%). Cefepime represents a safe therapeutic option and an alternative to carbapenems to treat BSIs due to Ecl when the prevalence of ESBL-producers is low.

An opportunistic pathogen isolated from the gut of an obese human causes obesity in germfree mice

Lipopolysaccharide endotoxin is the only known bacterial product which, when subcutaneously infused into mice in its purified form, can induce obesity and insulin resistance via an inflammation-mediated pathway. Here we show that one endotoxin-producing bacterium isolated from a morbidly obese human's gut induced obesity and insulin resistance in germfree mice. The endotoxin-producing Enterobacter decreased in relative abundance from 35% of the volunteer's gut bacteria to non-detectable, during which time the volunteer lost 51.4 kg of 174.8 kg initial weight and recovered from hyperglycemia and hypertension after 23 weeks on a diet of whole grains, traditional Chinese medicinal foods and prebiotics. A decreased abundance of endotoxin biosynthetic genes in the gut of the volunteer was correlated with a decreased circulating endotoxin load and alleviated inflammation. Mono-association of germfree C57BL/6J mice with strain Enterobacter cloacae B29 isolated from the volunteer's gut induced fully developed obesity and insulin resistance on a high-fat diet but not on normal chow diet, whereas the germfree control mice on a high-fat diet did not exhibit the same disease phenotypes. The Enterobacter-induced obese mice showed increased serum endotoxin load and aggravated inflammatory conditions. The obesity-inducing capacity of this human-derived endotoxin producer in gnotobiotic mice suggests that it may causatively contribute to the development of obesity in its human host.

Effect of long-term freezing and freeze-thaw cycles on indigenous and inoculated microorganisms in dewatered blackwater

Wastewater treatment in many Arctic regions is inadequate, even nonexisting. Natural freezing of wastewater in those areas may be beneficial for reduction of microorganisms. The aim of this study was to investigate the effect of long-term freezing, and repeated freezing and thawing, on indigenous coliforms, fecal streptococci, and antibiotic-resistant (AR) bacteria, and inoculated Salmonella Enteriditis and E. coli bacteriophage ΦX174 in dewatered blackwater. At the end of the long-term freezing experiment (10 months), an MPN recovery study was done, including the microbial groups that had shown the largest reduction, using tryptone soy broth at incubation temperatures of 10 and 20 °C overnight for the coliforms and AR bacteria, and buffered peptone water at incubation temperature of 37 °C for 18-20 h for Salmonella. Fecal streptococci were more resistant to long-term freezing than the coliform group. Total number of AR bacteria decreased slowly but constantly over the 10-month freezing period. Salmonella rapidly decreased and were nondetectable within a week but exhibited some recovery after 10 months of freezing, whereas limited or no recovery of coliforms and AR-bacteria was detected. Bacteriophages showed limited reduction during the long-term freezing. Repeated freezing and thawing increased the reduction of all tested microbial groups markedly.

Effects of Postharvest Onion Curing Parameters on the Development of Sour Skin and Slippery Skin in Storage

The influence of postharvest curing temperature and duration on development of slippery skin (caused by Burkholderia gladioli pv. alliicola) and sour skin (caused by B. cepacia) in onion (Allium cepa) bulbs during storage was evaluated by inoculating bulbs of the storage cultivars 'Redwing' and 'Vaquero' with each of the pathogens after harvest, curing the bulbs at 25, 30, 35, or 40°C for 2 or 14 days, and storing the bulbs at 5°C for 1, 2, or 3 months. Noninoculated bulbs and bulbs injected with sterile water served as control treatments. The onion bulbs were from drip-irrigated, commercial onion crops grown in the semiarid Columbia Basin of central Washington in 2009 and 2010. Each bulb was cut through the point of inoculation from the neck to the basal plate to assess severity of bulb rot (percentage of cut bulb surface area with bacterial rot symptoms) after 1, 2, or 3 months of storage. Bulb rot severity in the 2009-10 and 2010-11 trials was negligible for noninoculated bulbs (mean of 4.0 and 4.5%, respectively) and bulbs injected with water (6.2 and 10.1%, respectively) compared with bulbs inoculated with B. cepacia (34.6 and 39.8%, respectively) and B. gladioli pv. alliicola (20.7 and 27.4%, respectively). Bulbs inoculated with B. cepacia developed significantly more severe rot than those inoculated with B. gladioli pv. alliicola, even though a 10-fold greater inoculum concentration was used for B. gladioli pv. alliicola, demonstrating the more aggressive nature of B. cepacia compared with B. gladioli pv. alliicola. Severity of bulb decay caused by B. cepacia or B. gladioli pv. alliicola was affected significantly (P < 0.05) by season (trial), cultivar, curing temperature, curing duration, and storage duration, with significant interactions among these factors. In both trials and for both pathogens, bulb rot was significantly more severe the greater the curing temperature and the severity of bulb rot was significantly greater when bulbs were cured for 14 versus 2 days prior to cold storage. Overall, the severity of bulb rot was greater with a longer duration of storage after curing. This increase in bulb rot severity, which resulted from an increase in curing temperature and duration, was significantly greater for Vaquero than Redwing and significantly greater for bulbs inoculated with B. cepacia than B. gladioli pv. alliicola. The results suggest that postharvest curing at temperatures <35°C for a limited duration can significantly reduce the severity of sour skin or slippery skin in storage.

Effect of transcriptional activators SoxS, RobA, and RamA on expression of multidrug efflux pump AcrAB-TolC in Enterobacter cloacae

Control of membrane permeability is a key step in regulating the intracellular concentration of antibiotics. Efflux pumps confer innate resistance to a wide range of toxic compounds such as antibiotics, dyes, detergents, and disinfectants in members of the Enterobacteriaceae. The AcrAB-TolC efflux pump is involved in multidrug resistance in Enterobacter cloacae. However, the underlying mechanism that regulates the system in this microorganism remains unknown. In Escherichia coli, the transcription of acrAB is upregulated under global stress conditions by proteins such as MarA, SoxS, and Rob. In the present study, two clinical isolates of E. cloacae, EcDC64 (a multidrug-resistant strain overexpressing the AcrAB-TolC efflux pump) and Jc194 (a strain with a basal AcrAB-TolC expression level), were used to determine whether similar global stress responses operate in E. cloacae and also to establish the molecular mechanisms underlying this response. A decrease in susceptibility to erythromycin, tetracycline, telithromycin, ciprofloxacin, and chloramphenicol was observed in clinical isolate Jc194 and, to a lesser extent in EcDC64, in the presence of salicylate, decanoate, tetracycline, and paraquat. Increased expression of the acrAB promoter in the presence of the above-described conditions was observed by flow cytometry and reverse transcription-PCR, by using a reporter fusion protein (green fluorescent protein). The expression level of the AcrAB promoter decreased in E. cloacae EcDC64 derivates deficient in SoxS, RobA, and RamA. Accordingly, the expression level of the AcrAB promoter was higher in E. cloacae Jc194 strains overproducing SoxS, RobA, and RamA. Overall, the data showed that SoxS, RobA, and RamA regulators were associated with the upregulation of acrAB, thus conferring antimicrobial resistance as well as a stress response in E. cloacae. In summary, the regulatory proteins SoxS, RobA, and RamA were cloned and sequenced for the first time in this species. The involvement of these proteins in conferring antimicrobial resistance through upregulation of acrAB was demonstrated in E. cloacae.

AiiA quorum-sensing quenching controls proteolytic activity and biofilm formation by Enterobacter cloacae

The aim of this work was to evaluate a quorum-quenching approach to identify functions regulated by quorum sensing in Enterobacter cloacae. We employed an aiiA transconjugant strain of E. cloacae that synthesizes a lactonase enzyme that hydrolyzes N-acyl homoserine lactone signaling molecules to compare bacterial phenotypes in the presence and absence of quorum signals. The aiiA-expressing strain displayed increased proteolytic activity and intensity of a milk-clotting reaction when compared to the wild-type strain. Although both strains growing on polystyrene plates in rich media and a minimal medium of salts formed biofilms, the wild-type strain exhibited a higher number of adhered cells. On the surface of stainless steel coupons that were submerged in culture media, the number of adhered cells of the wild type contained up to one log more cells compared with the aiiA transconjugant. However, after 48 h of incubation, there was no significant difference between the strains. The results demonstrated that the quorum-sensing system negatively regulates proteolytic activity and is likely involved in the early steps of biofilm formation by E. cloacae 067.

Direct Real-Time PCR with Ethidium Monoazide: A Method for the Rapid Detection of Viable Cronobacter sakazakii in Powdered Infant Formula

The goal of this study was to establish a rapid assay for the specific detection of viable Cronobacter sakazakii in powdered infant formula (PIF). Samples were subjected to treatment multiple times with ethidium monoazide with a concentration gradient (gEMA) prior to PCR to discriminate viable from dead C. sakazakii cells. To improve the current detection limits, we developed a new buffer for direct quantitative real-time PCR (DqPCR) without DNA isolation. Using 17 PIF samples, our rapid assay was compared with the new U.S. Food and Drug Administration (FDA) method published in the Bacteriological Analytical Manual in 2012. Although both the new FDA method and our rapid assay, which consists of DqPCR combined with gEMA (gEMADqPCR), produced negative results for all 17 PIF samples, 5 of the 17 PIFs were positive by DqPCR when they were not treated with EMA. Furthermore, for PIF samples artificially contaminated with viable C. sakazakii, gEMA-DqPCR successfully detected between 1 and 9 CFU of viable C. sakazakii in 300 g of PIF within 9 h, including a 6-h preincubation. Our results indicate that multiple EMA treatments are required to avoid false-positive results due to the contamination of commercial PIF with dead or injured C. sakazakii cells. Our rapid assay may also improve the sensitivity of the screening portion required by the new FDA method published in the Bacteriological Analytical Manual in 2012.

Antibiotic therapy for inducible AmpC β-lactamase-producing Gram-negative bacilli: what are the alternatives to carbapenems, quinolones and aminoglycosides?

Some bacteria that possess chromosomally determined AmpC β-lactamases may express these enzymes at a high level following exposure to β-lactams, either by induction or selection for derepressed mutants. This may lead to clinical failure even if an isolate initially tests susceptible in vitro, a phenomenon best characterised by third-generation cephalosporin therapy for Enterobacter bacteraemia or meningitis. Several other Enterobacteriaceae, such as Serratia marcescens, Citrobacter freundii, Providencia spp. and Morganella morganii (often termed the 'ESCPM' group), may also express high levels of AmpC. However, the risk of clinical failure with β-lactams that test susceptible in vitro is less clear in these species than for Enterobacter. Laboratories frequently do not report β-lactam or β-lactamase inhibitor combination drug susceptibilities for ESCPM organisms, encouraging alternative therapy with quinolones, aminoglycosides or carbapenems. However, quinolones and carbapenems present problems with selective pressure for multiresistant organisms, and aminoglycosides with potential toxicity. The risk of emergent AmpC-mediated resistance for non-Enterobacter spp. appears rare in clinical studies. Piperacillin/tazobactam may remain effective and may be less selective for AmpC derepressed mutants than cephalosporins. The potential roles for agents such as cefepime or trimethoprim/sulfamethoxazole are also discussed. Clinical studies that better define optimal treatment for this group of bacteria are required.

Prevalences of the Enterobacter cloacae complex and its phylogenetic derivatives in the nosocomial environment

Despite the importance of the Enterobacter cloacae complex as a nosocomial pathogen, little is known about the relative contribution of its single species and genotypes to its pathogenicity. We studied here the relationship between phylogenetically related strains and clinical infection sites. A total of 196 prospectively collected isolates of the E. cloacae complex were included in the study, comprising 67 blood culture isolates. Isolates were analyzed for clonality by pulsed-field gel electrophoresis (PFGE) and genetically assigned to their genotypes by partial hsp60 sequencing. Most isolates belonged in phylogenetic clade 1, with E. hormaechei being the most prevalent species. Notably, some genotypes and species, indeed, showed predilections to certain clinical specimens, whereas clinical outbreaks with members of the E. cloacae complex were rare. Our study stresses the need to identify alleged E. cloacae isolates on the subspecies level in clinical routine in order to obtain more insight into their distinct infectious potentials.

Involvement of the AcrAB-TolC efflux pump in the resistance, fitness, and virulence of Enterobacter cloacae

Multidrug efflux pumps have emerged as important mechanisms of antimicrobial resistance in bacterial pathogens. In order to cause infection, pathogenic bacteria require mechanisms to avoid the effects of host-produced compounds, and express efflux pumps may accomplish this task. In this study, we evaluated the effect of the inactivation of AcrAB-TolC on antimicrobial resistance, fitness, and virulence in Enterobacter cloacae, an opportunistic pathogen usually involved in nosocomial infections. Two different clinical isolates of E. cloacae were used, EcDC64 (multidrug resistance overexpressing the AcrAB-TolC efflux pump) and Jc194 (basal AcrAB-TolC expression). The acrA and tolC genes were deleted in strains EcDC64 and Jc194 to produce, respectively, EcΔacrA and EcΔtolC and JcΔacrA and JcΔtolC knockout (KO) derivatives. Antibiotic susceptibility testing was performed with all isolates, and we discovered that these mechanisms are involved in the resistance of E. cloacae to several antibiotics. Competition experiments were also performed with wild-type and isogenic KO strains. The competition index (CI), defined as the mutant/wild-type ratio, revealed that the acrA and tolC genes both affect the fitness of E. cloacae, as fitness was clearly reduced in the acrA and tolC KO strains. The median CI values obtained in vitro and in vivo were, respectively, 0.42 and 0.3 for EcDC64/EcΔacrA, 0.24 and 0.38 for EcDC64/EcΔtolC, 0.15 and 0.11 for Jc194/JcΔacrA, and 0.38 and 0.39 for Jc194/JcΔtolC. Use of an intraperitoneal mouse model of systemic infection revealed reduced virulence in both E. cloacae clinical strains when either the acrA or tolC gene was inactivated. In conclusion, the structural components of the AcrAB-TolC efflux pump appear to play a role in antibiotic resistance as well as environmental adaptation and host virulence in clinical isolates of E. cloacae.

Characterization of ertapenem-resistant Enterobacter cloacae in a Taiwanese university hospital

The emergence of carbapenem resistance in Enterobacteriaceae has become a great concern. The aim of this study was to characterize ertapenem-resistant Enterobacter cloacae isolates from a Taiwanese university hospital. A total of 355 nonduplicated E. cloacae isolates collected in 2007 were analyzed by antimicrobial susceptibility testing with and without an inhibitor of efflux pumps and AmpC β-lactamase. The phenotype of extended-spectrum β-lactamase (ESBL), profile of outer membrane proteins (OMPs), and clonal relatedness were investigated by the double-disk synergy test, urea/SDS-PAGE, and pulsed-field gel electrophoresis (PFGE), respectively. β-Lactamase genes were examined by PCR and sequencing, and the expression of efflux pump gene acrB was evaluated by reverse transcription-PCR. The contribution of porin deficiency to resistance was investigated by restoring functional porin genes on plasmids. We demonstrated that ertapenem resistance was prevalent (53/355; 14.9%) in E. cloacae. Among the strains, IMP-8, SHV-12, and TEM-1 β-lactamases were identified in 3 (5.7%), 40 (75.5%), and 46 (86.8%) isolates, respectively. PFGE showed clonal diversity among these isolates. Phenotypes of ESBL, AmpC β-lactamase overproduction, an active efflux pump, and change in the expression of OMPs were found in 18 (34%), 11 (20.8%), 51 (96.2%), and 23 (43.4%) of ertapenem-resistant strains, respectively. Ertapenem MICs were restored in strains with OmpC and OmpF expression plasmids. This study suggests that ESBL, AmpC β-lactamase overproduction, and decreased OMP expression combined with an active efflux pump contribute to the ertapenem resistance of E. cloacae. The presence of IMP-8 may also play a partial role in ertapenem resistance in Taiwan.

An Enterobacter plasmid as a new genetic background for the transposon Tn1331

Background

Genus Enterobacter includes important opportunistic nosocomial pathogens that could infect complex wounds. The presence of antibiotic resistance genes in these microorganisms represents a challenging clinical problem in the treatment of these wounds. In the authors’ screening of antibiotic-resistant bacteria from complex wounds, an Enterobacter species was isolated that harbors antibiotic-resistant plasmids conferring resistance to Escherichia coli. The aim of this study was to identify the resistance genes carried by one of these plasmids.

Methods

The plasmids from the Enterobacter isolate were propagated in E. coli and one of the plasmids, designated as pR23, was sequenced by the Sanger method using fluorescent dyeterminator chemistry on a genetic analyzer. The assembled sequence was annotated by search of the GenBank database.

Results

Plasmid pR23 is composed of the transposon Tn1331 and a backbone plasmid that is identical to the plasmid pPIGDM1 from Enterobacter agglomerans. The multidrug-resistance transposon Tn1331, which confers resistance to aminoglycoside and beta lactam antibiotics, has been previously isolated only from Klebsiella. The Enterobacter plasmid pPIGDM1, which carries a ColE1-like origin of replication and has no apparent selective marker, appears to provide a backbone for propagation of Tn1331 in Enterobacter. The recognition sequence of Tn1331 transposase for insertion into pPIGDM1 is the pentanucleotide TATTA, which occurs only once throughout the length of this plasmid.

Conclusion

Transposition of Tn1331 into the Enterobacter plasmid pPIGDM1 enables this transposon to propagate in this Enterobacter. Since Tn1331 was previously isolated only from Klebsiella, this report suggests horizontal transfer of this transposon between the two bacterial genera.

Growth inhibition of various Enterobacteriaceae species by the yeast Hansenula anomala during storage of moist cereal grain

Eleven of 13 Enterobacteriaceae species tested grew in moist stored wheat, highlighting a potential risk of this energy-saving airtight storage method. When Hansenula anomala was coinoculated, all Enterobacteriaceae species were significantly inhibited after 2 months of storage, six of them to below the detection limit.

Distribution of extended-spectrum beta-lactamase genes using a commercial DNA micro-array system

Extended-spectrum beta-lactamase (ESBL) genes are distributed worldwide and their epidemiology is complex. Using the Check-ESBL assay, the distribution of class A ESBL genes in clinical isolates of aerobic Gram-negative bacilli from three laboratories in the East of The Netherlands was determined. Four patient categories were distinguished: (i) patients admitted to an intensive care unit (ICU); (ii) non-ICU inpatients; (iii) outpatients admitted less than a year before collection of the isolate, (<1); (iv) outpatients admitted more than one-year prior to isolate collection or who had never been hospitalized (>1). From February 2009 until March 2010, out of 491 putative ESBL-positive isolates detected by the Vitek2 or Phoenix automated sensitivity testing systems, ESBL genes were detected in 247 (50.3%) by the Check-ESBL assay. Of these, 116 were from hospitalized patients (35 ICU, 81 non-ICU) and 131 were from outpatients (43 <1, 88 >1). In all, 274 ESBL genes were identified in these 247 isolates: 153 CTX-M-1 group (predominantly in E. coli and K. pneumoniae, 70.4% and 51.6% respectively), 67 CTX-M-9 group (predominantly in E. cloacae, 57.9%), 32 SHV, 14 TEM and 8 CTX-M-2 group. ESBL-producing E. cloacae were significantly more common in hospitalized patients than in outpatients, 20.7% and 3.8% respectively (P=0.001). CTX-M-9 group ESBLs were significantly more prevalent in ICU patients (P=0.003), whereas SHV ESBLs were more common in hospitalized patients than in outpatients (P<0.001). There was no significant difference in distribution of ESBL genes between the two outpatient groups.

Resistance patterns and integron cassette arrays of Enterobacter cloacae complex strains of human origin

The aim of this research was to analyse the resistance patterns and characterize the distribution and genetic content of resistance integrons within Enterobacter cloacae complex strains originating from hospitalized patients. The strains were included in the E. cloacae complex study following sequence analysis of the hsp60 gene. The determination of resistance towards eight classes of antimicrobials was followed by PCR detection of integrons and analyses of the size and sequences of their variable parts. The majority of 69 clinical strains of the E. cloacae complex were identified as Enterobacter hormaechei. They were isolated from a variety of samples, including urine, wounds, blood and stools. The remaining isolates belonged to E. cloacae clusters III and IV, E. cloacae subsp. cloacae and Enterobacter kobei. Fifty-two isolates (75.4 %) were resistant to more than three unrelated antibiotics. The resistance for each antibiotic, except imipenem, was significantly associated with the presence of integrons. Class 1 integrons were detected in 55 % of isolates: 63.3 % of 'E. hormaechei subsp. steigerwaltii', 50 % of E. cloacae cluster III, 40 % of 'E. hormaechei subsp. oharae', 33 % belonging to E. cloacae cluster IV and 20 % of 'E. hormaechei subsp. hormaechei' were intI1-positive. All of the integrons were located on transferable genetic elements. The transferred resistance primarily included that to aminoglycosides, ticarcillin, piperacillin, sulfamethoxazole, trimethoprim and tetracycline. Sequence analysis of the variable regions of integrons identified two groups of genes: those encoding aminoglycoside adenylotransferases responsible for resistance to aminoglycosides, and dfr cassettes conferring resistance to trimethoprim. Integrons of the E. cloacae complex showed limited variability of genes encoding resistance to therapeutics and were stable in structure with the following cassette arrays: dfrA12-orfF-aadA2, aadB-aadA2, dfrA1-aadA1 and aacA4-aadA1. Hospital-dependent differences in type and arrays of gene cassettes were observed, which seemed to be conserved and not liable to changes.

Emergence in Spain of a multidrug-resistant Enterobacter cloacae clinical isolate producing SFO-1 extended-spectrum beta-lactamase

Between February 2006 and October 2009, 38 patients in different wards at the A Coruña University Hospital (northwest Spain) were either infected with or colonized by an epidemic, multidrug-resistant (MDR), and extended-spectrum-β-lactamase (ESBL)-producing strain of Enterobacter cloacae (EbSF), which was susceptible only to carbapenems. Semiautomated repetitive extragenic palindromic sequence-based PCR (rep-PCR) and pulsed-field gel electrophoresis (PFGE) analysis revealed that all of the E. cloacae isolates belonged to the same clone. Cloning and sequencing enabled the detection of the SFO-1 ESBL in the epidemic strain and the description of its genetic environment. The presence of the ampR gene was detected upstream of bla(SFO-1), and two complete sequences of IS26 surrounding ampR and ampA were detected. These IS26 sequences are bordered by complete left and right inverted repeats (IRL and IRR, respectively), which suggested that they were functional. The whole segment flanked by two IS26 copies may be considered a putative large composite transposon. A gene coding for aminoglycoside acetyltransferase (gentamicin resistance gene [aac3]) was found downstream of the 3' IS26. Despite the implementation of strict infection control measures, strain EbSF spread through different areas of the hospital. A case-control study was performed to assess risk factors for EbSF acquisition. A multivariate analysis revealed that the prior administration of β-lactam antibiotics, chronic renal failure, tracheostomy, and prior hospitalization were statistically associated with SFO-1-producing E. cloacae acquisition. This study describes for the first time an outbreak in which an SFO-1-producing E. cloacae strain was involved. Note that so far, this β-lactamase has previously been isolated in only a single case of E. cloacae infection in Japan.

Biodegradation of acrylamide by Enterobacter aerogenes isolated from wastewater in Thailand

A widespread use of acrylamide, probably a neurotoxicant and carcinogen, in various industrial processes has led to environmental contamination. Fortunately, some microorganisms are able to derive energy from acrylamide. In the present work, we reported the isolation and characterization of a novel acrylamide-degrading bacterium from domestic wastewater in Chonburi, Thailand. The strain grew well in the presence of acrylamide as 0.5% (W/V), at pH 6.0 to 9.0 and 25 degrees C. Identification based on biochemical characteristics and 16S rRNA gene sequence identified the strain as Enterobacter aerogenes. Degradation of acrylamide to acrylic acid started in the late logarithmic growth phase as a biomass-dependent pattern. Specificity of cell-free supernatant towards amides completely degraded butyramide and urea and 86% of lactamide. Moderate degradation took place in other amides with that by formamide > benzamide > acetamide > cyanoacetamide > propionamide. No degradation was detected in the reactions of N,N-methylene bisacrylamide, sodium azide, thioacetamide, and iodoacetamide. These results highlighted the potential of this bacterium in the cleanup of acrylamide/amide in the environment.

Effects of Postharvest Onion Curing Parameters on Enterobacter Bulb Decay in Storage

Enterobacter bulb decay is a recently described storage disease of onion (Allium cepa) bulbs caused by Enterobacter cloacae. The disease is generally considered minor but, on occasion, can cause significant losses for onion producers. The impact of postharvest curing temperature and duration on Enterobacter bulb decay of onion was evaluated by inoculating bulbs of the cultivars Redwing and Vaquero with E. cloacae after harvest, curing the bulbs at 25, 30, 35, or 40°C for 2 or 14 days, and storing the bulbs at 5°C for 1, 2, or 3 months. Noninoculated bulbs and bulbs injected with sterile water served as control treatments. The trial was completed using bulbs harvested from commercial onion crops grown in the semi-arid Columbia Basin of central Washington in each of 2008-09 (center-pivot irrigated crop) and 2009-10 (drip irrigated crop). Severity of bulb rot was assessed by cutting each bulb down the center from the neck to the basal plate, and rating the percentage of cut surface area with bacterial rot symptoms. Bulb rot severity was negligible for noninoculated bulbs (mean of 0.3% in the 2008-09 storage trial and 1.0% in the 2009-10 storage trial) and bulbs injected with water (0.8% in the 2008-09 trial and 1.3% in the 2009-10 trial) compared to bulbs inoculated with E. cloacae (15.3% in 2008-09 and 23.3% in 2009-10). Severity of Enterobacter bulb decay was affected significantly (P < 0.05) by season (trial), cultivar, curing temperature, curing duration, and storage duration, with significant interactions among these factors. Enterobacter bulb decay was significantly more severe for bulbs cured at 40°C than for bulbs cured at 25, 30, or 35°C. This effect was even greater when bulbs were cured for 14 days versus 2 days prior to cold storage, and in bulbs stored for 2 or 3 months after curing compared to bulbs stored for 1 month. The increase in bulb rot severity caused by curing bulbs at 40°C for 14 days compared to lower temperatures and shorter durations was greater for Vaquero than Redwing, particularly in the 2008-09 trial. The results suggest that curing temperatures ≤35°C should significantly reduce the risk of Enterobacter bulb decay in storage for these cultivars. If higher curing temperatures are used in order to dry onion necks for long-term storage and reduce the risk of fungal diseases such as neck rot (caused by Botrytis spp.), a shorter curing duration may be necessary to minimize the risk of Enterobacter bulb decay in storage.