High prevalence of extended-spectrum beta-lactamase-producing strains among blood isolates of Enterobacter spp. collected in a tertiary hospital during an 8-year period and their antimicrobial susceptibility patterns

Detection of expanded-spectrum β-lactamases in Gram-negative bacteria in the 21st century

Emerging β-lactamase-producing-bacteria (ESBL, AmpC and carbapenemases) have become a serious problem in our community due to their startling spread worldwide and their ability to cause infections which are difficult to treat. Diagnosis of these β-lactamases is of clinical and epidemiological interest. Over the past 10 years, several methods have been developed aiming to rapidly detect these emerging enzymes, thus preventing their rapid spread. In this review, we describe the range of screening and detection methods (phenotypic, molecular and other) for detecting these β-lactamases but also whole genome sequencing as a tool for detecting the genes encoding these enzymes.

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.

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.

Ceftazidime for respiratory infections

INTRODUCTION

Ceftazidime is a third-generation cephalosporin that has activity against Gram-negative bacilli, including Pseudomonas aeruginosa. The increasing prevalence of antimicrobial resistance and the limited number of antimicrobial agents in development have necessitated a review of the current status of treatments involving ceftazidime.

AREAS COVERED

This review focuses on studies examining the in vitro antibacterial activity of ceftazidime against recent clinical isolates and recent randomized controlled trials studying the clinical efficacy of ceftazidime, and discusses strategies for the optimal use of ceftazidime for treating respiratory tract infections, mainly hospital-acquired pneumonia (HAP).

EXPERT OPINION

Although ceftazidime remains an important option for HAP treatment, its role as an effective antimicrobial agent has been compromised by the sharp increase in resistance rates over the last decade, especially in P. aeruginosa and Acinetobacter baumannii. To maintain or improve the clinical use of ceftazidime in patients with severe HAP, it will be essential to gain a thorough understanding of local resistance patterns, reserve ceftazidime use when pathogens are susceptible to other third-generation cephalosporins, optimize ceftazidime therapy using prolonged or continuous infusion, determine the effectiveness of the combination of ceftazidime with inhibitors of broad-spectrum β-lactamases and role of combination therapy for P. aeruginosa infections, and judiciously use antimicrobial agents through individualization of antimicrobial therapy for HAP.

Treatment outcomes in patients with third-generation cephalosporin-resistant Enterobacter bacteremia

BACKGROUND

Infections with resistant Enterobacter spp. are increasingly described, yet data on outcomes associated with these infections are limited.

METHODS

A retrospective cohort study was conducted to investigate outcomes of hospitalized patients with third-generation cephalosporin-resistant (CR) Enterobacter bacteremia. Cephalosporin resistance was detected using cefotaxime and cefpodoxime. Patients with Enterobacter spp. bacteremia from January 2006 through February 2008 defined the population. We defined cases as those with CR isolates; controls were patients with bacteremia due to non-CR isolates. Treatment failure was defined as persistence of the presenting signs of infection 72 h after initial culture collection.

RESULTS

Of the 95 Enterobacter cases identified, 31 (33%) were CR. CR cases were significantly associated with treatment failure (odds ratio (OR) 2.81, 95% confidence interval (CI) 1.14-6.94). This association was not seen after adjustment for age, simplified acute physiology score (SAPS II), and inappropriate empiric antibiotic therapy. Inappropriate empiric therapy (adjusted OR 3.86, 95% CI 1.32-11.31) and SAPS II score (adjusted OR 1.09, 95% CI 1.02-1.16) were significantly associated with treatment failure in the multivariate analysis.

CONCLUSIONS

Third-generation cephalosporin-resistant Enterobacter bacteremia is associated with treatment failure due to receipt of inappropriate empiric antibiotic therapy and severity of illness.

Clinical significance of infections caused by extended-spectrum β-lactamase-producing Enterobacteriaceae blood isolates with inducible AmpC β-lactamase

Few studies have investigated the clinical features and outcomes for extended-spectrum β-lactamase (ESBL)-producing Enterobacter spp., Citrobacter spp., Serratia spp., and Morganella morganii (ECSM) bloodstream infections. This study was performed to investigate the clinical features and outcomes for ESBL-producing ECSM bloodstream infections. Patients with ECSM bloodstream infection were enrolled from October 2006 to March 2008. Of 124 patients with ECSM bacteremia, 30 cases (24.2%) were ESBL-producing isolates. Immunosuppressive drugs use within 30 days (p=0.028), indwelling device at the time of bacteremia (p=0.042) and antibiotics use within 3 months (p=0.022) were independently associated with ESBL production in multivariate analysis. Overall 30-day mortality rate was 19.4% (24/124). When the 30-day mortality rate was evaluated, no significant difference was found between the ESBL group (16.6%; 5/30) and non-ESBL group (20.2%; 19/94). Hospitalization was longer in the ESBL group than in the non-ESBL group (65.4±92.8 vs. 32.9±37.8 days, respectively; p=0.007). The recent use of antibiotics (especially broad-spectrum cephalosporins and other β-lactam antibiotics) was an important risk factor for ESBL among ECSM bacteremia. ESBL production of ECSM isolates was not significantly associated with mortality but ESBL-producing organisms have an important impact on the duration of hospital stay and subsequent medical cost.

Characterization and molecular epidemiology of extended spectrum beta-lactamase producing Enterobacter cloacae isolated from a Tunisian hospital

In 2009, out of the 66 nonrepetitive Enterobacter cloacae collected at Charles Nicolle hospital in Tunisia, 44 were extended spectrum β-lactamase (ESBL) producers. The aim of the current study was to detect and characterize the genes encoding the ESBLs including blaTEM, blaSHV, and blaCTX-M groups by polymerase chain reaction and sequencing. Pulsed-field gel electrophoresis (PFGE) analysis was used to determine the genetic relatedness between isolates. All strains were susceptible to carbapenems. They were resistant to fluoroquinolones, gentamicin, tobramycin, and trimethoprim+sulfamethoxazole but variably resistant to netilmicin, amikacin, and tetracyclines. Sequence analysis of the polymerase chain reaction products revealed the presence of blaCTX-M-15 (39 strains), blaSHV-12 (6 strains), and blaSHV-27 (1 strain). The coexistence of two ESBLs was observed in two isolates harboring, respectively, SHV-12+CTX-M-15 and SHV-27+CTX-M-15. PFGE revealed 36 unrelated profiles. Diffusion of E. cloacae producing CTX-M-15 ESBL in our hospital is the consequence of dissemination of identical or related plasmids harboring the CTX-M-15 gene.

Bacteremia due to extended-spectrum-beta-lactamase-producing Enterobacter cloacae: role of carbapenem therapy

Enterobacter cloacae is an important nosocomial pathogen. However, few studies specifically dealing with the clinical characteristics and outcome of extended-spectrum beta-lactamase (ESBL)-producing E. cloacae infections have been published. During an 8-year period in a medical center, of 610 E. cloacae bacteremic isolates, 138 (22.6%) with ESBL genes were designated the ESBL group, and 120 (19.6%) cefotaxime-nonsusceptible isolates without the ESBL phenotype and genes were designated the control group. Of the former group of isolates, 133 (96.3%) carried the bla(SHV-12) gene, 3 (2.1%) had bla(CTX-M3), and 2 (1.4%) had both the bla(SHV-12) and bla(CTX-M3) genes. After patients under the age of 18 years were excluded, there were 206 adults with E. cloacae bacteremia, and these consisted of 121 patients in the ESBL group and 85 in the control group. More episodes of hospital-onset and polymicrobial bacteremia, increased severity of illness, more cases of bacteremia onset in intensive care units (ICUs), and longer stays in the hospital and ICU after bacteremia onset were noted in the ESBL group. However, the crude and sepsis-related mortality rates in two groups were similar. Of the ESBL group, the in-hospital sepsis-related mortality rate of patients definitively treated by a carbapenem was lower than that of those treated by noncarbapenem beta-lactams (5/53, or 9.4%, versus 13/44, or 29.5%; P = 0.01) though the difference was not significant in the hierarchical multivariate analysis (P = 0.46). Among 62 patients with follow-up blood cultures within 14 days of bacteremia onset, breakthrough bacteremia was more common in those treated by a noncarbapenem beta-lactam agent than in those treated by a carbapenem (18/31, or 58.0%, versus 3/31, or 9.6%; P < 0.001). Thus, carbapenem therapy for ESBL-producing E. cloacae that cause bacteremia may provide therapeutic benefits.

Emergence of antibiotic resistance during therapy for infections caused by Enterobacteriaceae producing AmpC beta-lactamase: implications for antibiotic use

Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii are characterized by chromosomally encoded AmpC beta-lactamases and possess the ability to develop resistance upon exposure to broad-spectrum cephalosporins. To determine the incidences of the emergence of resistance during antimicrobial therapy for infections caused by these organisms and the effect of the emergence of resistance on patient outcomes, all patients who were admitted to the Asan Medical Center (Seoul, Republic of Korea) from January 2005 to June 2006 and whose clinical specimens yielded Enterobacter spp., S. marcescens, C. freundii, or M. morganii were monitored prospectively. The main end point was the emergence of resistance during antimicrobial therapy. A total of 732 patients with infections were included for analysis. The overall incidence of the emergence of antimicrobial resistance during antimicrobial therapy was 1.9% (14/732). Resistance to broad-spectrum cephalosporins, cefepime, extended-spectrum penicillin, carbapenem, fluoroquinolones, and aminoglycosides emerged during treatment in 5.0% (11/218), 0% (0/20), 2.0% (2/100), 0% (0/226), 0% (0/153), and 1.1% (1/89) of patients, respectively. The emergence of resistance to broad-spectrum cephalosporins occurred more often in Enterobacter spp. (8.3%, 10/121) than in C. freundii (2.6%, 1/39), S. marcescens (0%, 0/37), or M. morganii (0%, 0/21). Biliary tract infection associated with malignant bile duct invasion was significantly associated with the emergence of resistance to broad-spectrum cephalosporins (P = 0.024 at a significance level of 0.042, by use of the Bonferroni correction). Only 1 of the 14 patients whose isolates developed resistance during antimicrobial therapy died. The emergence of resistance was more frequently associated with broad-spectrum cephalosporins than with the other antimicrobial agents tested, especially in Enterobacter spp. However, the emergence of resistance was associated with a low risk of mortality.

Prevalence of clinical isolates of Escherichia coli and Klebsiella spp. producing multiple extended-spectrum β-lactamases

Eleven thousand two hundred seventy-two Escherichia coli, 1109 Klebsiella pneumoniae, 1124 Salmonella enterica, and 602 Klebsiella oxytoca unrelated clinical isolates were obtained between 2001 and 2004 in a university hospital in Salamanca, Spain. One hundred thirteen E. coli (1%), 32 K. pneumoniae (2.9%), 4 K. oxytoca (0.66%), and 5 S. enterica (0.44%) isolates produced extended-spectrum beta-lactamases (ESBLs). We obtained 42.2% of the ESBL-producing isolates from outpatients and 57.8% from inpatients. The most commonly detected ESBLs were CTX-M 14 (43.5% of ESBL-producing isolates), TEM-116 (22.1%), and SHV-2 (15.6%). A CTX-M 27-producing E. coli is 1st reported in Spain in this study. Two (20 isolates, 13%) or 3 (7 isolates, 4.5%) ESBLs were produced by 17.5% of ESBL-producing isolates (27 isolates). The most frequent combinations were CTX-M 14 + TEM-116 (5.7%), SHV-12 + TEM-116 (2.6%), and SHV-2 + CTX-M 14 + TEM-116 (2.6%). Clonal diversity was high even between isolates producing the same combinations of 2 or 3 beta-lactamases.

Prevalence, microbiology, and clinical characteristics of extended-spectrum beta-lactamase-producing Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii in Korea

We examined the prevalence and characteristics of extended-spectrum beta-lactamase (ESBL)-producing clinical isolates among Enterobacter spp., Serratia marcescens, Citrobacter freundii, and Morganella morganii, and evaluated screening criteria, clinical characteristics and outcomes of infections caused by ESBL-producing organisms. Between January and June 2005, a total of 493 nonduplicate consecutive isolates were collected at Asan Medical Center, a 2,300-bed tertiary hospital in Seoul, Republic of Korea. Fifty isolates (10.1%) were positive for phenotypical ESBL-test. The positive rate of phenotypical ESBL-test in Enterobacter spp., S. marcescens, C. freundii, and M. morganii was 12.8%, 12.4%, 4.9%, and 0% respectively. SHV-12 (18 isolates), CTX-M-9 (17 isolates), and TEM-52 (five isolates) were the most prevalent ESBL types. The ESBL in 17 strains could not be identified. As an ESBL screening criterion, the cefepime MIC >or=1 microg/ml had the highest sensitivity (0.84) and specificity (0.87). Half of the ESBL-producing isolates (25/50) were judged as pathogens. Cholangitis (ten cases), and pneumonia (six cases) were the most common infections. The overall mortality was 12.0%.

Extended double disc synergy testing reveals a low prevalence of extended-spectrum β-lactamases in Enterobacter spp. in Vienna, Austria

OBJECTIVES

The aims of this study were to determine the prevalence of extended-spectrum beta-lactamases (ESBLs) in AmpC-carrying Enterobacter spp. in a tertiary care university hospital in Vienna, Austria, and to implement a cost-effective strategy to detect ESBLs in this particular genus on a routine basis.

METHODS

Clinical Enterobacter isolates (n=208) were investigated by means of (i) an inhibitor-potentiated diffusion test using cefpodoxime, (ii) an expanded double disc diffusion synergy test (discs of cefotaxime, ceftazidime, cefpodoxime and cefepime placed around amoxicillin/clavulanic acid), (iii) the Etest ESBL screening method and (iv) the cefoxitin-cefotaxime antagonist test. Cefepime MICs were determined by separate Etests.

RESULTS

Of 208 isolates, 76 (37%), 18 (9%) and 92 (44%) were derepressed, partially derepressed and inducible AmpC producers, respectively. Eight (4%) ESBL-producing Enterobacter strains could be detected, all of which would have been detected using disc-based tests. Six out of eight strains were genetically not related, as assessed by random amplification of polymorphic DNA. Typing results were confirmed by means of enterobacterial repetitive intergenic consensus PCR. The MIC(90) of cefepime was not different in ESBL carriers (range 2-4 mg/L), and was especially low in inducible AmpC producers (0.125 mg/L). More than half of all Enterobacter isolates (n=110; 53%) were partly derepressed or fully inducible AmpC producers. In the absence of cefoxitin, they appeared susceptible or intermediately susceptible to cefazolin (n=8; 9%), cefuroxime (n=75; 81.5%), ceftazidime (n=91; 99%), cefotaxime (n=92; 100%), cefpodoxime (n=75; 81.5%) and cefepime (n=91; 99%).

CONCLUSIONS

Susceptibility to third-generation cephalosporins would have been falsely assumed in more than half of all Enterobacter isolates, but ESBL in Enterobacter is currently rare in our institution. Integration of multiple double disc tests into the routine antibiogram seems a reliable approach to screen for emerging resistance mechanisms. Etests did not provide additional information in this study.

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.

Prevalence of newer beta-lactamases in gram-negative clinical isolates collected in the United States from 2001 to 2002

Newer beta-lactamases such as extended-spectrum beta-lactamases (ESBLs), transferable AmpC beta-lactamases, and carbapenemases are associated with laboratory testing problems of false susceptibility that can lead to inappropriate therapy for infected patients. Because there appears to be a lack of awareness of these enzymes, a study was conducted during 2001 to 2002 in which 6,421 consecutive, nonduplicate clinical isolates of aerobically growing gram-negative bacilli from patients at 42 intensive care unit (ICU) and 21 non-ICU sites across the United States were tested on-site for antibiotic susceptibility. From these isolates, 746 screen-positive isolates (11.6%) were referred to a research facility and investigated to determine the prevalence of ESBLs in all gram-negative isolates, transferable AmpC beta-lactamases in Klebsiella pneumoniae, and carbapenemases in Enterobacteriaceae. The investigations involved phenotypic tests, isoelectric focusing, beta-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular analyses. ESBLs were detected only in Enterobacteriaceae (4.9% of all Enterobacteriaceae) and were found in species other than those currently recommended for ESBL testing by the CLSI (formerly NCCLS). These isolates occurred at 74% of the ICU sites and 43% of the non-ICU sites. Transferable AmpC beta-lactamases were detected in 3.3% of K. pneumoniae isolates and at 16 of the 63 sites (25%) with no difference between ICU and non-ICU sites. Three sites submitted isolates that produced class A carbapenemases. No class B or D carbapenemases were detected. In conclusion, organisms producing ESBLs and transferable AmpC beta-lactamases were widespread. Clinical laboratories must be able to detect important beta-lactamases to ensure optimal patient care and infection control.

Resistance in gram-negative bacteria: Enterobacteriaceae

The emergence and spread of resistance in Enterobacteriaceae are complicating the treatment of serious nosocomial infections and threatening to create species resistant to all currently available agents. Approximately 20% of Klebsiella pneumoniae infections and 31% of Enterobacter spp infections in intensive care units in the United States now involve strains not susceptible to third-generation cephalosporins. Such resistance in K pneumoniae to third-generation cephalosporins is typically caused by the acquisition of plasmids containing genes that encode for extended-spectrum beta-lactamases (ESBLs), and these plasmids often carry other resistance genes as well. ESBL-producing K pneumoniae and Escherichia coli are now relatively common in healthcare settings and often exhibit multidrug resistance. ESBL-producing Enterobacteriaceae have now emerged in the community as well. Salmonella and other Enterobacteriaceae that cause gastroenteritis may also be ESBL producers, which is of relevance when children require treatment for invasive infections. Resistance of Enterobacter spp to third-generation cephalosporins is most typically caused by overproduction of AmpC beta-lactamases, and treatment with third-generation cephalosporins may select for AmpC-overproducing mutants. Some Enterobacter cloacae strains are now ESBL and AmpC producers, conferring resistance to both third- and fourth-generation cephalosporins. Quinolone resistance in Enterobacteriaceae is usually the result of chromosomal mutations leading to alterations in target enzymes or drug accumulation. More recently, however, plasmid-mediated quinolone resistance has been reported in K pneumoniae and E coli, associated with acquisition of the qnr gene. The vast majority of Enterobacteriaceae, including ESBL producers, remain susceptible to carbapenems, and these agents are considered preferred empiric therapy for serious Enterobacteriaceae infections. Carbapenem resistance, although rare, appears to be increasing. Particularly troublesome is the emergence of KPC-type carbapenemases in New York City. Better antibiotic stewardship and infection control are needed to prevent further spread of ESBLs and other forms of resistance in Enterobacteriaceae throughout the world.

Resistance in gram-negative bacteria: enterobacteriaceae

The emergence and spread of resistance in Enterobacteriaceae are complicating the treatment of serious nosocomial infections and threatening to create species resistant to all currently available agents. Approximately 20% of Klebsiella pneumoniae infections and 31% of Enterobacter spp infections in intensive care units in the United States now involve strains not susceptible to third-generation cephalosporins. Such resistance in K pneumoniae to third-generation cephalosporins is typically caused by the acquisition of plasmids containing genes that encode for extended-spectrum beta-lactamases (ESBLs), and these plasmids often carry other resistance genes as well. ESBL-producing K pneumoniae and Escherichia coli are now relatively common in healthcare settings and often exhibit multidrug resistance. ESBL-producing Enterobacteriaceae have now emerged in the community as well. Salmonella and other Enterobacteriaceae that cause gastroenteritis may also be ESBL producers, which is of relevance when children require treatment for invasive infections. Resistance of Enterobacter spp to third-generation cephalosporins is most typically caused by overproduction of AmpC beta-lactamases, and treatment with third-generation cephalosporins may select for AmpC-overproducing mutants. Some Enterobacter cloacae strains are now ESBL and AmpC producers, conferring resistance to both third- and fourth-generation cephalosporins. Quinolone resistance in Enterobacteriaceae is usually the result of chromosomal mutations leading to alterations in target enzymes or drug accumulation. More recently, however, plasmid-mediated quinolone resistance has been reported in K pneumoniae and E coli, associated with acquisition of the qnr gene. The vast majority of Enterobacteriaceae, including ESBL producers, remain susceptible to carbapenems, and these agents are considered preferred empiric therapy for serious Enterobacteriaceae infections. Carbapenem resistance, although rare, appears to be increasing. Particularly troublesome is the emergence of KPC-type carbapenemases in New York City. Better antibiotic stewardship and infection control are needed to prevent further spread of ESBLs and other forms of resistance in Enterobacteriaceae throughout the world.

SHV-type extended-spectrum beta-lactamase production is associated with Reduced cefepime susceptibility in Enterobacter cloacae

Cefepime is a potentially useful antibiotic for treatment of infections with Enterobacter cloacae. However, in our institution the MIC(90) for E. cloacae bloodstream isolates is 16 microg/ml. PCR amplification of bla genes revealed that one-third (15/45) of E. cloacae bloodstream isolates produced SHV-type extended-spectrum beta-lactamases (ESBLs) in addition to hyperproduction of AmpC-type beta-lactamases. The majority (11/15) of ESBL producers also produced the TEM-1 beta-lactamase. The SHV types included SHV-2, -5, -7, -12, -14, and -30. All but two of the ESBL-producing E. cloacae isolates, but none of the non-ESBL-producing strains, had MICs of cefepime of >or=2 microg/ml. The MIC(90) for cefepime for ESBL-producing strains was 64 mug/ml, while for non-ESBL producers it was 0.5 microg/ml. Using current Clinical and Laboratory Standards Institute breakpoints for cefepime, two thirds (10/15) of ESBL-producing isolates would have been regarded as susceptible to cefepime. Phenotypic ESBL detection methods were generally unreliable with these E. cloacae isolates. Based on these results, pharmacokinetic, pharmacodynamic, and clinical reevaluation of cefepime breakpoints for E. cloacae may be prudent.

Prevalence of derepressed ampC mutants and extended-spectrum beta-lactamase producers among clinical isolates of Citrobacter freundii, Enterobacter spp., and Serratia marcescens in Korea: dissemination of CTX-M-3, TEM-52, and SHV-12

The resistance mechanism of extended-spectrum cephalosporins in clinical isolates of Citrobacter freundii, Enterobacter spp., and Serratia marcescens was studied. Of 152 isolates, 45 isolates (29.6%) were derepressed AmpC mutants and 39 isolates (25.7%) produced extended-spectrum beta-lactamase (ESBLs). The most prevalent ESBLs were CTX-M enzymes, followed by TEM-52 and SHV-12.

Detection and characterization of extended-spectrum β-lactamases among bloodstream isolates of Enterobacter spp. in Hong Kong, 2000–2002

OBJECTIVES

A total of 139 consecutive and non-duplicate bloodstream isolates of Enterobacter spp. collected from inpatients in Hong Kong during 2000-2002 were studied for production of extended-spectrum beta-lactamases (ESBLs).

METHODS

All isolates were evaluated by the modified double-disc synergy test (m-DDST), the combined disc method (CDM) and the three-dimensional (3D) test. The m-DDST and CDM were modified by the use of cefepime discs. beta-Lactamases were characterized by isoelectric focusing and PCR sequencing using specific primers.

RESULTS

ESBLs were identified in nine isolates (overall 6.5%), including seven of 39 (17.9%) Enterobacter hormaechei, one of 27 (3.7%) Enterobacter aerogenes and the only Enterobacter intermedius strain. The E. intermedius strain was positive only in the 3D test but not in the other two tests. The other eight strains were positive in all three tests. No ESBL was detected in the other species, including non-hormaechei members of the Enterobacter cloacae complex (n=61), Enterobacter agglomerans (n=7), Enterobacter gergoviae (n=4) and Enterobacter sakazakii (n=1). The ESBL content included five different CTX-M enzymes (CTX-M-9, CTX-M-13, CTX-M-14, CTX-M-24 and a novel CTX-M-2-like beta-lactamase), SHV-12 (n=2) and unidentifiable ESBLs with a pI of 7.7 or 7.9 in two strains. The seven ESBL-producing E. hormaechei were genotyped by pulsed-field gel electrophoresis and were found to be unrelated to each other. In three of the CTX-M-producing strains, ISEcp1-like elements, including promoters for the beta-lactamase gene, were found.

CONCLUSIONS

Our data underscore the diversity of CTX-M enzymes among Enterobacter spp. in Hong Kong.