First report of the emergence of CTX-M-type extended-spectrum beta-lactamases (ESBLs) as the predominant ESBL isolated in a U.S. health care system

Clinical and microbiologic characteristics of cephalosporin-resistant Escherichia coli at three centers in the United States

We investigated the clinical and microbiologic features of 300 cases of cephalosporin-resistant Escherichia coli producing extended-spectrum β-lactamase (ESBL) or plasmid-mediated AmpC β-lactamase (pAmpC) at three medical centers in the United States. Solid-organ malignancy, connective tissue disease, and a recent history of surgery were more common among pAmpC-producing cases (n = 49), whereas urinary catheter at enrollment, diabetes, and hospitalization in the past year were more common among ESBL-producing cases (n = 233). The factors independently associated with clinical outcome were the following: the presence of cardiovascular disease (odds ratio [OR], 2.88; 95% confidence interval [CI], 1.29 to 6.43), intra-abdominal infection (OR, 6.35; 95% CI, 1.51 to 26.7), other or multiples sources of infection (OR, 8.12; 95% CI, 2.3 to 28.6), age of 65 years or greater (OR, 0.43; 95% CI, 0.2 to 0.95), favorable baseline health status (OR, 0.39; 95% CI, 0.16 to 0.95), and appropriate empirical antimicrobial therapy given in the first 72 h (OR, 0.42; 95% CI, 0.20 to 0.88). β-Lactamase genes responsible for cephalosporin resistance were identified in 291 cases. CTX-M-type ESBLs accounted for 72.0%. Of those, 88.0% were CTX-M-15. The next most common type was CMY-type pAmpC (16.7%), followed by SHV- and TEM-type ESBLs (6.3 and 1.3%, respectively). Seven cases (2.3%) had KPC-type β-lactamase. Ertapenem, imipenem, meropenem, doripenem, piperacillin-tazobactam, amikacin, nitrofurantoin, and tigecycline were highly active, with greater than 90% of the isolates being susceptible. Cefepime was less active, with only 74.2% being susceptible due to the predominance of CTX-M-15. These findings have implications in the selection of appropriate empirical therapy when infection due to cephalosporin-resistant E. coli is suspected.

Molecular characterization of CTX-Mβ-lactamases among Klebsiella pneumoniae isolated from patients at Tehran hospitals

PURPOSE

Plasmid-encoded CTX-M-group of extended-spectrum β-lactamases (ESBLs) represent a significant and rapidly emerging problem in most part of the world. The aim of the present study was to describe the prevalence of CTX-M producing Klebsiella pneumoniae at Tehran hospitals.

MATERIALS AND METHODS

Clinical isolates of K. pneumoniae (n=250) were collected from 10 hospitals of Tehran. Susceptibility to antimicrobial agents, MIC of cefotaxime and ESBLs production of collected isolates were detected. All ESBL-producing isolates were screened for bla CTX-M genes using PCR and DNA sequencing. Molecular typing of bla(CTX-M) harboring isolates was performed by Pulsed-field gel electrophoresis assay.

RESULTS

Of 250 K. pneumoniae clinical isolates, 102 isolates revealed ESBLs - phenotype. PCR assay and sequencing detected bla(CTX-M) genes in 71.5% (n= 73) of ESBL-producing isolates. The prevalence of CTX-M -I and CTX-M-III clusters among these isolates was 35.61% (n=26) and 21.9 % (n=16) respectively. Coexistence of CTX-M -I and CTX-M-III clusters was found among 42.5% (n= 31) of isolates. Of 102 isolates that were positive in the phenotypic confirmatory test (PCT), 29 isolates (28.4%) did not produce any amplicons in PCR for bla(CTX-M) gene. The results of PCR for CTX-M -II and CTX-M-IV clusters were also negative. Analysis of the 31 CTX-M producing K. pneumoniae isolates by PFGE typing showed 26 distinct patterns.

CONCLUSIONS

The bla CTX-M genes are widespread among Iranian isolates of K. pneumoniae. PFGE demonstrated the high diversity of K. pneumoniae harboring bla(CTX-M) in our study.

Detection of favorable oral cephalosporin-clavulanate interactions by in vitro disk approximation susceptibility testing of extended-spectrum-Beta-lactamase-producing members of the enterobacteriaceae

Extended-spectrum-beta-lactamase (ESBL)-producing members of the Enterobacteriaceae are often resistant to multiple drug classes, making therapy of urinary infections with oral antibiotics difficult. Previously it was shown that amoxicillin-clavulanate can provide clavulanate inhibition of ESBLs and protect an oral cephalosporin present in combination when tested by broth microdilution. This study has shown that disk approximation testing could detect favorable cephalosporin-clavulanate interactions among a group of 101 previously characterized members of the Enterobacteriaceae with CTX-M, SHV, or TEM ESBLs.

Antimicrobial susceptibility of global inpatient urinary tract isolates of Escherichia coli: results from the Study for Monitoring Antimicrobial Resistance Trends (SMART) program: 2009-2010

Escherichia coli is the most important uropathogen. The Study for Monitoring Antimicrobial Resistance Trends program collected 1643 E. coli isolates in 2009-2010 from urinary tract infection (UTI) specimens of hospitalized patients in countries worldwide. Ertapenem and imipenem were the most active agents tested, inhibiting >98% of all E. coli phenotypes. Overall, 17.9% of isolates were extended-spectrum beta-lactamase (ESBL) producers. The highest ESBL rate was from the Asia/Pacific region (27.7%). Amikacin and piperacillin-tazobactam achieved 90% inhibition levels only for ESBL-negative isolates. Ciprofloxacin and levofloxacin were not effective for ESBL-positive isolates, with only 14.6% and 15.9% susceptible, respectively. These observations highlight the need for continued monitoring of susceptibility of E. coli isolated from hospitalized patients with UTIs.

Clinical characteristics of bacteraemia caused by extended-spectrum β-lactamase-producing Enterobacteriaceae in the era of CTX-M-type and KPC-type β-lactamases

Clin Microbiol Infect 2012; 18: 887-893 ABSTRACT: A multicentre, case-control study was conducted to assess risk factors and patient outcomes of bacteraemia caused by Enterobacteriaceae producing extended-spectrum β-lactamases (ESBLs) and Klebsiella pneumoniae carbapenemases (KPCs). One hundred and five and 20 patients with bacteraemia caused by ESBL-producing and KPC-producing organisms were matched to controls who had bacteraemia caused by non-ESBL/KPC-producing organisms, respectively. Independent risk factors for ESBL production included admission from a nursing home (OR 4.64; 95% CI 2.64-8.16), chronic renal failure (OR 2.09; 95% CI 1.11-3.92), the presence of a gastrostomy tube (OR 3.36; 95% CI 1.38-8.18), length of hospital stay before infection (OR 1.02; 95% CI 1.01-1.03), transplant receipt (OR 2.48; 95% CI 1.24-4.95), and receipt of antibiotics with Gram-negative activity in the preceding 30 days (OR 1.76; 95% CI 1.00-3.08). Twenty-eight-day crude mortality rates for patients infected with ESBL-producing or KPC-producing organisms and controls were 29.1% (34/117) and 19.5% (53/272), respectively (OR 1.70; 95% CI 1.04-2.80). On multivariate analysis, inadequate empirical therapy (OR 2.26; 95% CI 1.18-4.34), onset of bacteraemia while in the intensive-care unit (OR 2.74; 95% CI 1.47-5.11), Apache II score (OR 1.17; 95% CI 1.12-1.23) and malignancy (OR 2.66; 95% CI 1.31-5.41) were independent risk factors for mortality. CTX-M was the most common ESBL type in Escherichia coli, whereas SHV predominated in Klebsiella spp. and Enterobacter spp.

High rates of susceptibility to ceftazidime among globally prevalent CTX-M-producing Escherichia coli: potential clinical implications of the revised CLSI interpretive criteria

The CTX-M family of extended-spectrum β-lactamases (ESBLs) is a significant global public health threat. The prevalence of specific bla (CTX-M) genes varies geographically, but bla (CTX-M-15) and bla (CTX-M-14) dominate in most countries. We applied the latest Clinical Laboratory Standards Institute (CLSI) interpretive criteria (M100-S20) to a diverse collection of ESBL-producing Escherichia coli strains obtained from clinical specimens in our laboratory. Whereas under previous CLSI recommendations all isolates in this strain collection would have been reported as ceftazidime-resistant, under the new recommendations, approximately 11% of CTX-M-15-producing E. coli and 93% of CTX-M-14-producing E. coli respectively tested as ceftazidime-susceptible. We also found that, whilst many CTX-M-14-producers had minimum inhibitory concentrations (MICs) less than the breakpoint of 4 mg/L, the MIC distribution for these strains was higher than that of wild-type E. coli, with one CTX-M-14-producing isolate having an MIC of >64 mg/L. Although the new CLSI recommendations imply that ceftazidime can be safely used to treat serious infections due to CTX-M-producing E. coli, clinical outcome data are lacking. Consequently, the widespread use of ceftazidime in this setting could have profound clinical implications.

Emergence of community-acquired extended-spectrum beta-lactamase Escherichia coli (ESBLEC) in Honolulu: a case series of three individuals with community-acquired ESBLEC bacteriuria

Community-acquired extended-spectrum beta-lactamase E coli (ESBLEC) have not been previously described in Honolulu. Its emergence as a community-acquired pathogen is concerning. This case series describes three patients who were diagnosed with community-acquired ESBLEC bacteriuria in 2010.

Nosocomial infection and characterization of extended-spectrum β-lactamases-producing Enterobacteriaceae in Northeast Brazil

INTRODUCTION: Extended spectrum β-lactamases (ESBLs) are enzymes that degrade β-lactam antibiotics and have been reported to be an important cause of nosocomial infection in worldwide. METHODS: During 2009, 659 enterobacteria strains were isolated from different clinical specimens and tested for ESBL production. The disk approximation test, combined disk method and addition of clavulanic acid were used for phenotypic detection of the ESBL-producing strains and PCR for detection of the blaTEM and blaCTX-M genes. RESULTS: Among the isolates, 125 were ESBL producers. The blaCTX-M and blaTEM genes were detected in 90.4% and 75% of the strains, respectively. Most strains were isolated from urine. Klebsiella pneumoniae was the most prevalent organism. Microorganisms presented high resistance to the antibiotics. CONCLUSIONS: These results support the need for extending ESBL detection methods to different pathogens of the Enterobacteriaceae family because these methods are only currently standardized by the CLSI for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca and Proteus mirabilis. Carbapenems were the antibiotic class of choice for the treatment of infections caused by ESBL-producing Enterobacteriaceae.

ESBLs: A Clear and Present Danger?

Extended spectrum β-lactamases (ESBLs) are enzymes produced by a variety of Gram negative bacteria which confer an increased resistance to commonly used antibiotics. They are a worrying global public health issue as infections caused by such enzyme-producing organisms are associated with a higher morbidity and mortality and greater fiscal burden. Coupled with increasing prevalence rates worldwide and an ever diminishing supply in the antibiotic armamentarium, these enzymes represent a clear and present danger to public health. This article aims to give an overview of the current situation regarding ESBLs, with a focus on the epidemiology and management of such infections.

Molecular and phenotypic characterization of Escherichia coli and Klebsiella pneumoniae producing extended-spectrum β-lactamases with focus on CTX-M in a low-endemic area in Sweden

During the last decade increasing prevalence of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae has been detected worldwide, mainly due to dissemination of Escherichia coli and Klebsiella pneumoniae producing CTX-M-type ESBLs. CTX-M-15 is the most widespread CTX-M type, and the predominant type in various countries. Dissemination of ESBL-producing organisms is caused not only by horizontal transfer of plasmids, but also by clonal spread of ESBL-producing strains. In this study, the molecular epidemiology of class A ESBL (ESBL(A))-producing E. coli and K. pneumoniae isolated in Örebro County, Sweden, was investigated. Out of 200 ESBL(A) -producing E. coli and K. pneumoniae isolates, collected over a 10-year period, 87% were producing CTX-M, belonging to subgroup CTX-M-1 (64%), CTX-M-9 (34%), or CTX-M-2 (2%). The remaining isolates were producing variants of SHV and TEM. Sequencing of the bla(CTX-M) genes revealed 10 different CTX-M types, with a dominance of CTX-M-15 (E. coli 54%, K. pneumoniae 50%) followed by CTX-M-14 (E. coli 28%, K. pneumoniae 27%). Phenotypic characterization of the CTX-M-producing isolates was performed using the PhenePlate system. Although a few minor clusters of CTX-M-15 and CTX-M-14 producers were identified, the majority of the isolates did not appear to be clonally related.

Rapid identification of gram-negative bacteria with and without CTX-M extended-spectrum β-lactamase from positive blood culture bottles by PCR followed by microchip gel electrophoresis

We evaluated the usefulness of PCR analysis of the 16S-23S rRNA gene internal transcribed spacer (ITS) and the CTX-M extended-spectrum β-lactamase (ESBL) followed by microchip gel electrophoresis (MGE) for direct identification and CTX-M detection of Gram-negative bacteria (GNB) from positive blood culture bottles. Of 251 GNB isolated from blood cultures containing a single bacterium, 225 (90%) were correctly identified at the species level directly from positive blood culture bottles by comparing the ITS-PCR patterns of the sample strain with those of the control strains. There were no cases of incorrect identification. Limitations encountered included the inability to detect mixed cultures (four bottles) as well as some species (Enterobacter species and Klebsiella oxytoca) demonstrating identical ITS-PCR patterns. A total of 109 ESBL-producing isolates from various clinical materials obtained between January 2005 and December 2008 were examined for bla(CTX-M), bla(SHV), and bla(TEM) genes by PCR and sequences of PCR products. CTX-M ESBL was detected in 105 isolates, and SHV ESBL was detected in two isolates. The remaining two isolates (K. oxytoca) were shown to harbor bla(OXY.) Twenty (19%) of 104 Escherichia coli isolates from blood cultures were suspected to produce ESBL by the combination disk method, and these isolates were shown to harbor CTX-M ESBL by PCR-MGE. The results were obtained within 1.5 h at a calculated cost of $6.50 per specimen. In conclusion, simultaneous detection of ITS length polymorphisms and bla(CTX)-(M) by single PCR followed by MGE is useful for rapid, cost-effective, and reliable species-level identification of CTX-M ESBL-producing GNB responsible for bloodstream infections.

CTX-M-producing non-Typhi Salmonella spp. isolated from humans, United States

CTX-M-type beta-lactamases are increasing among US Enterobacteriaceae isolates. Of 2,165 non-Typhi Salmonella isolates submitted in 2007 to the National Antimicrobial Resistance Monitoring System, 100 (4.6%) displayed elevated MICs (≥2 mg/L) of ceftriaxone or ceftiofur. Three isolates (serotypes Typhimurium, Concord, and I 4,5,12:i:-) contained bla(CTX-M-5), bla(CTX-M-15), and bla(CTX-M-55/57), respectively.

Prevalence of antimicrobial-resistant pathogens in Canadian hospitals: results of the Canadian Ward Surveillance Study (CANWARD 2008)

A total of 5,282 bacterial isolates obtained between 1 January and 31 December 31 2008, inclusive, from patients in 10 hospitals across Canada as part of the Canadian Ward Surveillance Study (CANWARD 2008) underwent susceptibility testing. The 10 most common organisms, representing 78.8% of all clinical specimens, were as follows: Escherichia coli (21.4%), methicillin-susceptible Staphylococcus aureus (MSSA; 13.9%), Streptococcus pneumoniae (10.3%), Pseudomonas aeruginosa (7.1%), Klebsiella pneumoniae (6.0%), coagulase-negative staphylococci/Staphylococcus epidermidis (5.4%), methicillin-resistant S. aureus (MRSA; 5.1%), Haemophilus influenzae (4.1%), Enterococcus spp. (3.3%), Enterobacter cloacae (2.2%). MRSA comprised 27.0% (272/1,007) of all S. aureus isolates (genotypically, 68.8% of MRSA were health care associated [HA-MRSA] and 27.6% were community associated [CA-MRSA]). Extended-spectrum β-lactamase (ESBL)-producing E. coli occurred in 4.9% of E. coli isolates. The CTX-M type was the predominant ESBL, with CTX-M-15 the most prevalent genotype. MRSA demonstrated no resistance to ceftobiprole, daptomycin, linezolid, telavancin, tigecycline, or vancomycin (0.4% intermediate intermediate resistance). E. coli demonstrated no resistance to ertapenem, meropenem, or tigecycline. Resistance rates with P. aeruginosa were as follows: colistin (polymyxin E), 0.8%; amikacin, 3.5%; cefepime, 7.2%; gentamicin, 12.3%; fluoroquinolones, 19.0 to 24.1%; meropenem, 5.6%; piperacillin-tazobactam, 8.0%. A multidrug-resistant (MDR) phenotype occurred frequently in P. aeruginosa (5.9%) but uncommonly in E. coli (1.2%) and K. pneumoniae (0.9%). In conclusion, E. coli, S. aureus (MSSA and MRSA), P. aeruginosa, S. pneumoniae, K. pneumoniae, H. influenzae, and Enterococcus spp. are the most common isolates recovered from clinical specimens in Canadian hospitals. The prevalence of MRSA was 27.0% (of which genotypically 27.6% were CA-MRSA), while ESBL-producing E. coli occurred in 4.9% of isolates. An MDR phenotype was common in P. aeruginosa.

Antibiotic-resistant Escherichia coli bacteria, including strains with genes encoding the extended-spectrum beta-lactamase and QnrS, in waterbirds on the Baltic Sea Coast of Poland

Individual cloacal swabs of mallards (Anas platyrhynchos) and of herring gulls (Larus argentatus), as well as samples of waterbird feces obtained in 2008 and 2009, were cultivated for Escherichia coli. Isolates of E. coli were tested for susceptibilities to 12 antimicrobial agents by the disk diffusion method. Moreover, the samples were subcultivated on MacConkey agar (MCA) containing cefotaxime (2 mg liter(-1)) to detect E. coli with extended-spectrum beta-lactamase (ESBL) and subsequently on MCA supplemented with ciprofloxacin (0.05 mg liter(-1)) and MCA with nalidixic acid (20 mg liter(-1)) to isolate fluoroquinolone-resistant E. coli. PCR was used to detect specific antibiotic resistance genes. We found 9 E. coli isolates producing ESBL with bla genes: bla(CTX-M-1) (6 isolates), bla(CTX-M-9) plus bla(TEM-1b) (1 isolate), bla(CTX-M-15) plus bla(OXA-1) (1 isolate), and bla(SHV-12) (1 isolate). In the isolate with bla(CTX-M-15), the gene aac(6)-Ib-cr was also detected. The bla genes were harbored by transferable plasmids of the IncN and IncI1 groups. Nine quinolone-resistant E. coli isolates with qnrS genes were found and characterized. The gene qnrS was associated with a Tn3-like transposon on the IncX1 plasmid together with bla(TEM-1) in two isolates. The gene qnrS was also harbored by conjugative plasmids of the IncN and IncX2 groups. Even if populations of wild birds are not directly influenced by antibiotic practice, we have demonstrated that antibiotic-resistant E. coli strains, including strains with various ESBL and qnrS genes, are found in the feces of wild birds on the coast of the Baltic Sea in Poland.

High prevalence of bla(CTX-M) extended spectrum beta-lactamase genes in Klebsiella pneumoniae isolates from a tertiary care hospital: first report of bla(SHV-12), bla(SHV-31), bla(SHV-38), and bla(CTX-M-15) in Brazil

The aim of this study was to investigate the presence and prevalence of bla(TEM), bla(SHV), and bla(CTX-M) and bla(GES)-like genes, responsible for extended spectrum beta-lactamases (ESBLs) production in clinical isolates of Klebsiella pneumoniae collected from a Brazilian tertiary care hospital. Sixty-five ESBL producing K. pneumoniae isolates, collected between 2005 and 2007, were screened by polymerase chain reaction (PCR). Identification of bla genes was achieved by sequencing. Genotyping of ESBL producing K. pneumoniae was performed by the enterobacterial repetitive intergenic consensus-PCR with cluster analysis by the Dice coefficient. The presence of genes encoding ESBLs was confirmed in 59/65 (90.8%) isolates, comprising 20 bla(CTX-M-2), 14 bla(CTX-M-59), 12 bla(CTX-M-15), 9 bla(SHV-12), 1 bla(SHV-2), 1 bla(SHV-2a), 1 bla(SHV-5), and 1 bla(SHV-31) genes. The ESBL genes bla(SHV-12), bla(SHV-31), and bla(CTX-M-15), and the chromosome-encoded SHV-type beta-lactamase capable of hydrolyzing imipenem were detected in Brazil for the first time. The analysis of the enterobacterial repetitive intergenic consensus-PCR band patterns revealed a high rate of multiclonal bla(CTX-M) carrying K. pneumoniae isolates (70.8%), suggesting that dissemination of encoding plasmids is likely to be the major cause of the high prevalence of these genes among the K. pneumoniae isolates considered in this study.

Outbreak of CTX-M-15-producing Klebsiella pneumoniae in the intensive care unit of a French hospital

The CTX-M-15 extended spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates were identified in 36 patients hospitalized from December 2006 to September 2007 in the medical intensive care unit (ICU) of the Bicêtre hospital, South Paris, France. The incidence of colonization and/or infection was 4.8%. Eighty-nine percent of the ESBL-producing K. pneumoniae isolates were acquired in the ICU, and only 8.3% of the patients were infected. Pulsed field gel electrophoresis (PFGE) analysis of the isolates showed that 32 isolates were clonally related and contained a 160-kb plasmid carrying the bla(CTX-M-15), bla(OXA-1), bla(TEM-1), and aac6'-Ib-cr genes. CTX-M-15-producing Escherichia coli isolates collected in the ward during the same period of time contained distinct plasmids and were not clonally related. This study highlights the possible occurrence of outbreaks due to CTX-M-producing K. pneumoniae within hospital settings, whereas CTX-Ms are mostly reported in E. coli in community-acquired infections.

OAK-based cochleates as a novel approach to overcome multidrug resistance in bacteria

Antibiotic resistance has become a worldwide medical problem. To find new ways of overcoming this phenomenon, we investigated the role of the membrane-active oligo-acyl-lysyl (OAK) sequence C(12)K-7α(8), in combination with essentially ineffective antibiotics. Determination of minimal inhibitory concentration (MIC) against gram-negative multidrug-resistant strains of Escherichia coli revealed combinations with sub-MIC OAK levels that acted synergistically with several antibiotics, thus lowering their MICs by several orders of magnitude. To shed light into the molecular basis for this synergism, we used both mutant strains and biochemical assays. Our results suggest that bacterial sensitization to antibiotics was derived mainly from the OAK's capacity to overcome the efflux-enhanced resistance mechanism, by promoting backdoor entry of otherwise excluded antibiotics. To facilitate simultaneous delivery of the pooled drugs to an infection site, we developed a novel OAK-based cochleate system with demonstrable stability in whole blood. To assess the potential therapeutic use of such cochleates, we performed preliminary experiments that imitate systemic treatment of neutropenic mice infected with lethal inoculums of multidrug resistance E. coli. Single-dose administration of erythromycin coencapsulated in OAK-based cochleates has decreased drug toxicity and increased therapeutic efficacy in a dose-dependent manner. Collectively, our findings suggest a potentially useful approach for fighting efflux-enhanced resistance mechanisms.

OAK-based cochleates as a novel approach to overcome multidrug resistance in bacteria

Antibiotic resistance has become a worldwide medical problem. To find new ways of overcoming this phenomenon, we investigated the role of the membrane-active oligo-acyl-lysyl (OAK) sequence C(12)K-7α(8), in combination with essentially ineffective antibiotics. Determination of minimal inhibitory concentration (MIC) against gram-negative multidrug-resistant strains of Escherichia coli revealed combinations with sub-MIC OAK levels that acted synergistically with several antibiotics, thus lowering their MICs by several orders of magnitude. To shed light into the molecular basis for this synergism, we used both mutant strains and biochemical assays. Our results suggest that bacterial sensitization to antibiotics was derived mainly from the OAK's capacity to overcome the efflux-enhanced resistance mechanism, by promoting backdoor entry of otherwise excluded antibiotics. To facilitate simultaneous delivery of the pooled drugs to an infection site, we developed a novel OAK-based cochleate system with demonstrable stability in whole blood. To assess the potential therapeutic use of such cochleates, we performed preliminary experiments that imitate systemic treatment of neutropenic mice infected with lethal inoculums of multidrug resistance E. coli. Single-dose administration of erythromycin coencapsulated in OAK-based cochleates has decreased drug toxicity and increased therapeutic efficacy in a dose-dependent manner. Collectively, our findings suggest a potentially useful approach for fighting efflux-enhanced resistance mechanisms.

Bench-to-bedside review: The role of beta-lactamases in antibiotic-resistant Gram-negative infections

Multidrug resistance has been increasing among Gram-negative bacteria and is strongly associated with the production of both chromosomal- and plasmid-encoded β-lactamases, whose number now exceeds 890. Many of the newer enzymes exhibit broad-spectrum hydrolytic activity against most classes of β-lactams. The most important plasmid-encoded β-lactamases include (a) AmpC cephalosporinases produced in high quantities, (b) the expanding families of extended-spectrum β-lactamases such as the CTX-M enzymes that can hydrolyze the advanced-spectrum cephalosporins and monobactams, and (c) carbapenemases from multiple molecular classes that are responsible for resistance to almost all β-lactams, including the carbapenems. Important plasmid-encoded carbapenemases include (a) the KPC β-lactamases originating in Klebsiella pneumoniae isolates and now appearing worldwide in pan-resistant Gram-negative pathogens and (b) metallo-β-lactamases that are produced in organisms with other deleterious β-lactamases, causing resistance to all β-lactams except aztreonam. β-Lactamase genes encoding these enzymes are often carried on plasmids that bear additional resistance determinants for other antibiotic classes. As a result, some infections caused by Gram-negative pathogens can now be treated with only a limited number, if any, antibiotics. Because multidrug resistance in Gram-negative bacteria is observed in both nosocomial and community isolates, eradication of these resistant strains is becoming more difficult.

Evaluation of a DNA microarray, the check-points ESBL/KPC array, for rapid detection of TEM, SHV, and CTX-M extended-spectrum beta-lactamases and KPC carbapenemases

Extended-spectrum beta-lactamases (ESBLs) and Klebsiella pneumoniae carbapenemases (KPC carbepenemases) have rapidly emerged worldwide and require rapid identification. The Check-Points ESBL/KPC array, a new commercial system based on genetic profiling for the direct identification of ESBL producers (SHV, TEM, and CTX-M) and of KPC producers, was evaluated. Well-characterized Gram-negative rods (Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii) expressing various ss-lactamases (KPC-2, SHV, TEM, and CTX-M types) were used as well as wild-type reference strains and isolates harboring ss-lactamase genes not detected by the assay. In addition, phenotypically confirmed ESBL producers isolated in clinical samples over a 3-month period at the Bicetre hospital were analyzed using the Check-Points ESBL/KPC array and by standard PCR. The Check-Points ESBL/KPC array allowed fast detection of all TEM, SHV, and CTX-M ESBL genes and of the KPC-2 gene. The assay allowed easy differentiation between non-ESBL TEM and SHV and their ESBL derivatives. None of the other tested ss-lactamase genes were detected, underlining its high specificity. The technique is suited for Enterobacteriaceae but also for P. aeruginosa and A. baumannii. However, for nonfermenters, especially P. aeruginosa, a 1:10 dilution of the total DNA was necessary to detect KPC-2 and SHV-2a genes reliably. The Check-Points ESBL/KPC array is a powerful high-throughput tool for rapid identification of ESBLs and KPC producers in cultures. It provided definitive results within the same working day, allowing rapid implementation of isolation measures and appropriate antibiotic treatment. It showed an interesting potential for routine laboratory testing.

Antimicrobial susceptibility patterns of KPC-producing or CTX-M-producing Enterobacteriaceae

Enterobacteriaceae clinical isolates harboring KPC-(178 strains) or CTX-M-encoding (67 strains) genes were collected during surveillance programs in the 2000-2007 period; and susceptibility was tested by broth microdilution methods. Organisms were dominantly collected in U.S. hospitals (93%). CTX-M-15 and -14 were the most prevalent CTX-M types (97%), all collected from the United States. KPC producers were isolated in the United States (160/178), Israel, China, and Argentina. bla(CTX-M)-carrying isolates were 95.5 and 98.5%, susceptible to Imipenem and meropenem respectively, and were all susceptible to tigecycline, whereas KPC-producing isolates were highly resistant to all antimicrobials tested except polymyxin B and tigecycline (90.6% and 99.4% susceptibility, respectively). The occurrence of KPC-producing and CTX-M-producing isolates has rapidly increased especially in U.S. hospitals, and expanded therapeutic options are needed to treat infections caused by these emerging organisms.

Identification of CTX-M beta-lactamases in Escherichia coli from hospitalized patients and residents of long-term care facilities

Bacteria harboring CTX-M extended-spectrum beta-lactamases (ESBLs) have been identified worldwide, with most reports coming from regions outside North America. We have identified CTX-M enzymes in 31% of ESBL-positive Escherichia coli isolates from our hospital and more than half (53%) of the isolates from associated long-term care facilities. Approximately 3/4 of all CTX-M-bearing isolates were from urine specimens, with a predominance of CTX-M-15. A large proportion of such isolates were nonsusceptible to levofloxacin, trimethoprim/sulfamethoxazole, and all beta-lactam antimicrobials with the exception of the carbapenems, requiring carbapenem therapy for acute urinary tract infection or urinary tract-related sepsis. CTX-M beta-lactamases have emerged within our location, and detection of bacteria harboring these enzymes in the clinical microbiology laboratory remains problematic because molecular methods are needed for their identification.

First detection of CTX-M and SHV extended-spectrum beta-lactamases in Escherichia coli urinary tract isolates from dogs and cats in the United States

One hundred fifty canine and feline Escherichia coli isolates associated with urinary tract infections were screened for the presence of extended-spectrum beta-lactamase (ESBL) genes. Out of 60 isolates suspected to be ESBL positive based on antimicrobial susceptibility testing, 11 ESBLs were identified, including one SHV-12 gene, one CTX-M-14 gene, and nine CTX-M-15 genes. This study provides the first report of CTX-M- and SHV-type ESBLs in dogs and cats in the United States.

Susceptibility of gram-negative pathogens isolated from patients with complicated intra-abdominal infections in the United States, 2007-2008: results of the Study for Monitoring Antimicrobial Resistance Trends (SMART)

During 2007-2008, 1,036 gram-negative bacilli were isolated from patients with complicated intra-abdominal infections in the United States. Against members of the family Enterobacteriaceae, the most active agents in vitro were ertapenem, imipenem, and amikacin, while the least active agent was ampicillin-sulbactam. Ertapenem and imipenem were active against all extended-spectrum-beta-lactamase (ESBL)-positive Escherichia coli. Antimicrobial resistance in gram-negative bacilli isolated from patients with complicated intra-abdominal infections in the United States continues to increase.

Molecular characteristics of extended-spectrum beta-lactamase-producing Escherichia coli from the Chicago area: high prevalence of ST131 producing CTX-M-15 in community hospitals

This study was designed to characterise 30 non-duplicate extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli clinical isolates from the community in the Chicago metropolitan area collected during 2008. The majority of isolates (n=28) were recovered from urine and 2 isolates were from blood. Molecular characterisation was done using the following techniques: isoelectric focusing; polymerase chain reaction (PCR) and sequencing of bla(ESBL); PCR for plasmid-mediated quinolone resistance determinants; identification of ST131; phylogenetic grouping; and replicon typing. Genetic relatedness was determined by pulsed-field gel electrophoresis (PFGE) with XbaI and repetitive sequence-based PCR (rep-PCR) typing. Twenty-six (87%) of the ESBL-producing E. coli were positive for bla(CTX-M) genes (22 CTX-M-15 and 4 CTX-M-14), whilst the remaining 4 isolates produced SHV-2. Twenty-eight isolates (93%) were non-susceptible to ciprofloxacin and 16 (53%) were positive for aac(6')-Ib-cr. Overall, 16 (53%) of the ESBL-producers belonged to clonal complex ST131 that produced CTX-M-15 or CTX-M-14. Molecular characteristics of ST131 showed that it belonged to three distinct but related PFGE clones, was derived from phylogenetic group B2 and contained IncFII type plasmids. These results illustrate that E. coli clonal complex ST131 producing CTX-M-15, CTX-M-14, OXA-1, TEM-1 and aac(6')-Ib-cr has emerged as an important cause of community-onset urinary tract infections caused by ESBL-producing E. coli isolates in the Chicago area.

Changing prevalence of Escherichia coli with CTX-M-type extended-spectrum beta-lactamases in outpatient urinary E. coli between 2003 and 2008

One hundred ninety-three single-patient isolates of Escherichia coli harboring extended-spectrum beta-lactamases (ESBL) were identified among 11 407 E. coli urine isolates recovered from single-patient outpatient urine cultures from 2003 to 2008. The percentage of ESBL-producing E. coli among community-onset E. coli urine isolates increased from 0.21% in 2003 to 2.99% in 2008. One hundred seven of the ESBL producers were positive for the presence of bla(CTX-M) genes. The percentage of CTX-M-producing E. coli rose from 0.07% in 2003 to 1.66% in 2008. The annual percentage of ESBL E. coli producing CTX-Ms changed from 35% in 2003 to 64% in 2008. Genes belonging to 3 bla(CTX-M) groups: bla(CTX-M-1) group, bla(CTX-M-2) group, and bla(CTX-M)(-9) group, were detected. In addition, resistance to commonly used antimicrobial agents for community-acquired urinary tract infections was found common among CTX-M-producing E. coli isolates. Ertapenem and nitrofurantoin showed good in vitro activity against CTX-M producers.

Detection of SHV-type extended-spectrum beta-lactamase in Enterobacter isolates

One hundred four Enterobacter isolates were tested by standard CLSI disk diffusion methods for detecting extended-spectrum beta-lactamases (ESBLs) and with cefepime-clavulanate disk combinations. SHV-12 was produced by 8.7% of isolates. The cefepime-clavulanate combination provided 88% sensitivity and 91% specificity for the detection of SHV-12 ESBL.

Recent changes in the epidemiology and management of extended-spectrum β-lactamase-producing Enterobacteriaceae

Since 2000, Escherichia coli producing CTX-M enzymes (especially CTX-M-15) have emerged worldwide as important causes of community-onset urinary tract and blood stream infections due to extended-spectrum β-lactamase (ESBL) producing bacteria. Studies suggest that the sudden worldwide increase of CTX-M-15-producing E. coli is mostly due to a single clone named ST131 and that foreign travel to high-risk areas, such as the Indian subcontinent, play in part a role in the spread of this clone across different continents. Empiric antibiotic coverage for these resistant organisms should be considered in community patients presenting with sepsis involving the urinary tract, especially if a patient recently traveled to a high-risk area. If this emerging public health threat is ignored, it is possible that the medical community may be forced in the near future to use carbapenems as the first choice for the empirical treatment of serious infections associated with urinary tract infections originating in the community.

Detection of CTX-M-type extended-spectrum beta-lactamase (ESBLs) by testing with MicroScan overnight and ESBL confirmation panels

CTX-M extended-spectrum beta-lactamases (ESBLs) have emerged as the most common type of ESBL globally, their incidence easily surpassing those of SHV and TEM ESBLs in most locales. This study compared the performance of two MicroScan dried panels with CLSI reference broth microdilution and disk diffusion methods on a collection of genetically characterized ESBL-producing isolates. These included 64 Enterobacteriaceae isolates that produced CTX-M8, -14, -15, or -16 according to PCR and sequencing of the bla gene, 17 isolates that produced a SHV or TEM ESBL, and 19 that produced both CTX-M and SHV ESBLs. Each isolate was tested by a frozen reference microdilution panel, the MicroScan ESbetaL plus confirmation panel, and a routine dried panel containing streamlined ESBL confirmation dilutions (MicroScan Neg MIC panel type 32) that included cefotaxime and ceftazidime tested alone or with a fixed concentration of 4 microg/ml of clavulanate. Each isolate was also tested by the standard CLSI double-disk confirmation tests. The disk diffusion method detected all ESBL-producing isolates, the frozen reference panel detected 90% of isolates (10 out of 100 could not be analyzed because of off-scale MICs that exceeded the clavulanate combination concentrations in the panel), the ESbetaL plus panel detected 98% (1 missed and 1 off scale), and the streamlined ESBL panel detected 95% (5 off scale). Very high MICs for a few strains that produced SHV or both CTX-M and SHV ESBLs precluded noting the required three twofold-dilution differences with clavulanate needed to confirm an ESBL primarily in the reference panel and the Neg type 32 panel.

The clinical consequences of antimicrobial resistance

The continued evolution of antimicrobial resistance in the hospital and more recently in the community threatens to seriously compromise our ability to treat serious infections. The major success of the seven-valent Streptococcus pneumoniae vaccine at reducing both infection and resistance has been followed by the emergence of previously minor serotypes that express multiresistance. The almost universal activity of cephalosporins and fluoroquinolones against community Escherichia coli strains has been compromised by the spread of CTX-M beta-lactamase-producing, fluoroquinolone-resistant strains, and the emergence of community-onset methicillin-resistant Staphylococcus aureus, particularly in the United States, has forced us to re-think our empirical treatment guidelines for skin and soft-tissue infections. Finally, our most potent and reliable class of antibiotics, the carbapenems, is compromised by the growth, primarily in intensive care units, of multiresistant Klebsiella pneumoniae, Acinetobacter baumanni, and Pseudomonas aeruginosa. The lack of a robust pipeline of new agents, particularly against resistant Gram-negative bacteria, emphasizes the importance of optimizing our use of current antimicrobials and promoting strict adherence to established infection control practices.

Molecular epidemiology of CTX-M-producing Escherichia coli isolates at a tertiary medical center in western Pennsylvania

A combination of phenotypic and genotypic methods was used to investigate 70 unique Escherichia coli clinical isolates identified as producing extended-spectrum beta-lactamases (ESBLs) at a medical center in Pittsburgh, PA, between 2007 and 2008. Fifty-seven isolates (81%) produced CTX-M-type ESBLs, among which CTX-M-15 was predominant (n = 46). Isolates producing CTX-M-2, -9, -14, and -65 were also identified. One CTX-M-producing isolate coproduced CMY-2 cephalosporinase. Ten isolates (14%) produced SHV-type ESBLs, either SHV-5 or SHV-7. Two isolates produced only CMY-2 or -32. Pulsed-field gel electrophoresis revealed the presence of two major clusters of CTX-M-15-producing E. coli isolates, one in phylotype B2 (n = 15) and the other in phylotype A (n = 19). Of four phylotype B2 isolates that were able to transfer the bla(CTX-M-15)-carrying plasmids, three showed fingerprints related (>60%) to those of plasmids from phylotype A isolates. In phylotype B2, all CTX-M-15-producing isolates, as well as three isolates producing CTX-M-14, two producing SHV-5, and one producing SHV-7, belonged to the international epidemic clone defined by serotype O25:H4 and sequence type 131. The plasmids from eight of nine CTX-M-15-producing E. coli isolates of phylotype A that were examined were highly related to each other and were also found in two isolates belonging to phylotype D, suggesting horizontal transfer of this bla(CTX-M-15)-carrying plasmid between phylotypes. Our findings underscore the need to further investigate the epidemiology and virulence of CTX-M-producing E. coli in the United States.

Spread of CTX-M-type extended-spectrum beta-lactamases among bloodstream isolates of Escherichia coli and Klebsiella pneumoniae from a Korean hospital

This study was to determine the prevalence and characteristics of CTX-M-type extended-spectrum beta-lactamases (ESBLs) in nonduplicate Escherichia coli (n=760) and Klebsiella pneumoniae (n=379) bloodstream isolates collected during January 2005 to October 2007 at a university hospital (2000 beds) in Seoul, Korea. Antimicrobial susceptibilities were determined by disk diffusion and agar dilution methods. The double-disk synergy test detected ESBLs in 8.7% (66/760) of E. coli and 11.3% (43/379) of K. pneumoniae isolates. Polymerase chain reaction detected bla(CTX-M) in 60/66 (90.9%) E. coli and 9/43 (20.9%) K. pneumoniae isolates with the ESBL phenotype. CTX-M-14 was the most common type of CTX-M ESBLs in both E. coli (n=32) and K. pneumoniae (n=6). CTX-M-15 was the 2nd most common type of CTX-M ESBLs in E. coli (n=22), but it was not detected in K. pneumoniae. In addition, CTX-M-24 (n=2), CTX-M-65 (n=2), CTX-M-27 (n=1), and CTX-M-32 (n=1) were detected for the 1st time in Korea.

A 7-year surveillance for ESBL-producing Escherichia coli and Klebsiella pneumoniae at a university hospital in Taiwan: the increase of CTX-M-15 in the ICU

To monitor the changing trend of extended-spectrum beta-lactamase (ESBL)-producing bacteria, a 7-year continuous study was launched in 2001 at the largest tertiary hospital in Taiwan. A significant increase over the study period was evident for ESBL-producing isolates of Escherichia coli (4.8-10.0%) and Klebsiella pneumoniae (15.0-23.4%). Molecular investigation conducted in three separate periods revealed the prevalent ESBL types and their genetic relatedness. CTX-M-producing isolates (73.8%) were more prevalent than SHV-type ESBLs (37.0%), the most frequent being CTX-M-14 (34.3%), CTX-M-3 (25.9%), and SHV-12 (25.7%). However, a marked increase of CTX-M-15-producing isolates from 2.1% in 2002 to 29.6% in 2007 was also noted. The increase of ESBL-producing isolates in both species may be mainly due to the horizontal transmission of resistance plasmids, while clonal expansion of some epidemic strains further added to the dispersion of ESBL-producing K. pneumoniae.

Extended-spectrum beta-lactamase-producing organisms

Extended-spectrum beta-lactamases (ESBLs), which hydrolyse extended-spectrum cephalosporins and are inhibited by clavulanic acid, are spreading among Enterobacteriaceae. The CTX-M enzymes are replacing SHV and TEM enzymes as the prevalent type of ESBLs, principally in community-acquired infections caused by Escherichia coli. Associated infectious syndromes include mainly urinary tract infections, and secondly bloodstream and intra-abdominal infections, and may be serious enough to warrant hospitalisation. Affected patients commonly have various underlying risk factors. This is also observed in hospital-acquired infections. The rates of ESBL-expression among nosocomial Enterobacteriaceae isolates, particularly Klebsiella pneumoniae, have risen substantially in several countries. The hospital epidemiology of these infections is often complex; multiple clonal strains causing focal outbreaks may co-exist with sporadic ones. Relevant infection-control measures should focus on reducing patient-to-patient transmission via the inanimate environment, hospital personnel, and medical equipment. Wise use of antibiotics is also essential. The available therapeutic options for the treatment of ESBL-associated infections are limited by drug resistance conferred by the ESBLs, along with frequently observed co-resistance to various antibiotic classes, including cephamycins, fluoroquinolones, aminoglycosides, tetracyclines, and trimethoprim/sulfamethoxazole. Relevant clinical data regarding the effectiveness of different regimens for ESBL-associated infections are limited. Although certain cephalosporins may appear active in vitro, associated clinical outcomes are often suboptimal. beta-Lactam/beta-lactamase inhibitor combinations may be of value, but the supporting evidence is weak. Carbapenems are regarded as the agents of choice, and may be more effective than fluoroquinolones for serious infections. Tigecycline and polymyxins have substantial antimicrobial activity against ESBL-producing Enterobacteriaceae, and, along with fosfomycin, merit further evaluation.

Prevalence of CTX-M beta-lactamases in Philadelphia, Pennsylvania

CTX-M beta-lactamases were thought to be rare in the United States, but a recent study in Texas showed that up to 70% of extended-spectrum beta-lactamase (ESBL)-containing members of the Enterobacteriaceae family were CTX-M positive (J. S. Lewis, M. Herrera, B. Wickes, J. E. Patterson, and J. H. Jorgensen, Antimicrob. Agents Chemother. 51:4015-4021, 2007). We used PCR to detect CTX-M in all 291 extended-spectrum cephalosporin-resistant gram-negative bacteria isolated in our laboratory during 2007. Thirty (48%) Escherichia coli isolates, 6 (3%) Klebsiella sp. isolates, and 7 (100%) Proteus mirabilis isolates tested were CTX-M positive, with 15% of all Enterobacteriaceae tested being positive. The E. coli CTX-M groups were I (57%), IV (37%), II (3%), and not groupable (3%); three of the group IV isolates were positive for CTX-M-18, and three of the group I isolates were positive for CTX-M-15. One of seven positive P. mirabilis isolates was in group II, with the remainder being positive for a CTX-M-25-like beta-lactamase; and 33% of the Klebsiella sp. isolates were in group I or IV, with the remainder not being in groups I to IV. CTX-M-producing bacteria were isolated from urine (n = 13), blood (n = 13), wounds (n = 12), and the respiratory tract (n = 4). All 31 CTX-M-positive isolates tested for the presence of ESBL were confirmed to produce ESBLs by the use of tests recommended by the CLSI. Pulsed-field gel electrophoresis of the CTX-M-positive isolates showed that six P. mirabilis isolates were clonal and that there were seven different E. coli clusters. Five of seven P. mirabilis isolates were from blood cultures. The CLSI tests for the confirmation of ESBL production reliably detect these isolates if both cefotaxime and ceftazidime are tested, but only about half would be classified as a possible CTX-M producers on the basis of the antibiogram alone. A new panprimer set increases the ability to detect CTX-M-producing strains. CTX-M-positive bacteria are common in our geographic region, are often invasive, and, with the exception of P. mirabilis, are multiclonal.

Impact of therapeutic treatment with beta-lactam on transfer of the bla(CTX-M-9) resistance gene from Salmonella enterica serovar Virchow to Escherichia coli in gnotobiotic rats

The conjugative transfer of the plasmid carrying the bla(CTX-M-9) gene from Salmonella enterica serovar Virchow isolated from a chicken farm to a recipient Escherichia coli strain was evaluated in vitro and in axenic rats inoculated with both strains, with or without selective pressure due to therapeutic doses of cefixime. The transfer of the bla(CTX-M-9) gene of S. enterica serovar Virchow to E. coli was confirmed in vitro, at a low frequency of 5.9 x 10(-8) transconjugants/donors. This transfer rate was higher in gnotobiotic rats and reached approximately 10(-5) transconjugants/donors without selective pressure. This frequency was not affected by the addition of therapeutic doses of cefixime. Thus, estimates of in vitro transfer underestimated potential transfer in the digestive tract, and therapeutic doses of cefixime did not increase the selection for transconjugants.