Effects of inoculum and beta-lactamase activity in AmpC- and extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae clinical isolates tested by using NCCLS ESBL methodology

Escherichia coli and Klebsiella pneumoniae isolates with extended-spectrum beta-lactamases (ESBLs) or AmpC cephalosporinases generally respond as predicted to NCCLS tests for ESBL production. However, inoculum size may affect MICs. The effect of inoculum level in clinical isolates expressing beta-lactamases were studied at inocula within 0.5 log unit of the standard inoculum, using broth microdilution methodology with ceftazidime, cefotaxime, cefepime, cefpodoxime, and aztreonam. Strains with TEM-1 or no beta-lactamases gave consistent MIC results with inocula of 10(5) and 10(6) CFU/ml. When the bacteria were screened for ESBL production and the lower inoculum was used, several strains with ESBLs, including CTX-M-10, TEM-3, TEM-10, TEM-12, TEM-6, SHV-18, and K1, gave false-negative results for one or more antimicrobial agents (MICs below the NCCLS screening concentration for detecting suspected ESBLs). When the higher inoculum was used, MICs of at least one antimicrobial agent increased at least fourfold in strains producing TEM-3, TEM-10, TEM-28, TEM-43, SHV-5, SHV-18, and K1. All antimicrobial agents showed an inoculum effect with at least one ESBL producer. Confirmatory clavulanate effects were seen for both inocula for all ESBL-producing strains with all antimicrobial agents tested, except for the CTX-M-10-producing E. coli with ceftazidime and the SHV-18-producing K. pneumoniae with cefotaxime. In kinetic studies, cefpodoxime and cefepime were hydrolyzed by ESBLs in a manner similar to that of cefotaxime. When total beta-lactamase activity and hydrolysis parameters were evaluated, however, no single factor was predictive of inoculum effects. These results indicate that the NCCLS screening and confirmation tests are generally predictive of ESBL production, but false-negative results can arise when a lower inoculum is used in testing.     

Clonal dissemination of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates in a Korean hospital

In this study, we investigated the molecular characteristics of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates that were recovered from an outbreak in a Korean hospital. A new multilocus sequence typing (MLST) scheme for K. pneumoniae based on five housekeeping genes was developed and was evaluated for 43 ESBL-producing isolates from an outbreak as well as 38 surveillance isolates from Korea and also a reference strain. Overall, a total of 37 sequence types (STs) and six clonal complexes (CCs) were identified among the 82 K. pneumoniae isolates. The result of MLST analysis was concordant with that of pulsedfield gel electrophoresis. Most of the outbreak isolates belonged to a certain clone (ST2), and they produced SHV-1 and CTX-M14 enzymes, which was a different feature from that of the K. pneumoniae isolates from other Korean hospitals (ST20 and SHV-12). We also found a different distribution of CCs between ESBL-producing and -nonproducing K. pneumoniae isolates. The MLST method we developed in this study could provide unambiguous and well-resolved data for the epidemiologic study of K. pneumoniae. The outbreak isolates showed different molecular characteristics from the other K. pneumoniae isolates from other Korean hospitals.     

Prevalence of extended-spectrum beta-lactamases among Escherichia coli and Klebsiella pneumoniae isolates in a tertiary care hospital

Extended-spectrum beta-lactamases (ESBLs) continue to be a major problem in clinical setups the world over, conferring resistance to the expanded-spectrum cephalosporins. Knowledge about their prevalence is essential to guide towards appropriate antibiotic treatment. The aim of the present study is to determine the prevalence of ESBL producers among Escherichia coli and Klebsiella pneumoniae isolates at a tertiary care institution. A total of 357 clinical isolates comprising E. coli (n = 181) and K. pneumoniae (n = 176) were recovered from various clinical samples over a period of six months from April to September 2006. Antibiogram profile of these isolates was determined to commonly used antibiotics, along with screening for ESBL production by the screening test as recommended by the Clinical Laboratory Standards Institute (CLSI). Isolates which showed positive results with screening test were shortlisted for confirmatory tests of ESBL production. Two tests were performed: phenotypic confirmatory test with combination disk and the minimum inhibitory concentration (MIC) reduction test. Out of 357 isolates of E. coli and K. pneumoniae screened for ESBL production, 120 were found to be potential ESBL producers. Of these, 80 isolates were confirmed to be ESBL producers. Thus the prevalence of ESBL-producing isolates of E. coli and K. pneumoniae was found to be 22% (80 out of 357). This was significantly lower than the data available from other hospitals.     

Prevalence and characterisation of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates in healthy volunteers in Tunisia

The objective of this investigation was to analyse the carriage rate of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli in faecal samples of healthy humans in Tunisia and to characterise the recovered isolates. One hundred and fifty samples were inoculated on MacConkey agar plates supplemented with cefotaxime (2 μg/ml) for ESBL-positive E. coli recovery. The characterisation of ESBL genes and their genetic environments, detection of associated resistance genes, multilocus sequence typing (MLST) and phylogroup typing were performed by polymerase chain reaction (PCR) and sequencing. The presence and characterisation of integrons and virulence factors were studied by PCR and sequencing. ESBL-positive E. coli isolates were detected in 11 of 150 faecal samples (7.3%) and one isolate/sample was further characterised. These isolates contained the blaCTX-M-1 (ten isolates) and blaTEM-52c genes (one isolate). The ISEcp1 (truncated by IS10 in four strains) and orf477 sequences were found upstream and downstream, respectively, of all bla (CTX-M-1) genes. Seven different sequence types (STs) and three phylogroups were identified among CTX-M-1-producing isolates [ST/phylogroup (number of isolates)]: ST58/B1 (3), ST57/D (2), ST165/A (1), ST155/B1 (1), ST10/A (1), ST398/A (1) and ST48/B1 (1). The TEM-52-producing isolate was typed as ST219 and phylogroup B2. Six ESBL isolates contained class 1 integrons with the gene cassettes dfrA17-aadA5 (five isolates) and dfrA1-aadA1 (one). Healthy humans in the studied country could be a reservoir of CTX-M-1-producing E. coli.     

Detection of extended-spectrum beta-lactamases in clinical isolates of Klebsiella pneumoniae and Escherichia coli.

Forty clinical isolates of Escherichia coli and 141 isolates of Klebsiella pneumoniae that either transferred ceftazidime resistance or showed sulbactam enhancement of oxyimino-beta-lactam susceptibility were tested by disk diffusion methodology for susceptibility to aztreonam, cefotaxime, ceftazidime, and cefoxitin. With standard 30 micrograms antibiotic disks, the fraction of these extended-spectrum beta-lactamase (ESBL)-producing isolates testing resistant by National Committee for Clinical Laboratory Standards criteria was lowest (24%) with cefotaxime disks. Forty percent of the E. coli and 29% of the K. pneumoniae isolates appeared susceptible with at least one oxyimino-beta-lactam disk. Ceftazidime and aztreonam disks were equivalent in differentiating ESBL production, and both were superior to cefotaxime disks. Over half the E. Coli and 29% of the K. pneumoniae isolates tested cefoxitin resistant. In 30 isolates, cefoxitin resistance was transmissible and due to a plasmid-mediated AmpC-type beta-lactamase. With a 5-micrograms ceftazidime disk, a breakpoint could be chosen with high sensitivity and specificity for ESBL-producing organisms. Present disk diffusion criteria underestimate the prevalence of ESBL-producing strains.     

Identification of CTX-M-14 extended-spectrum beta-lactamase in clinical isolates of Shigella sonnei, Escherichia coli, and Klebsiella pneumoniae in Korea

CTX-M-14 beta-lactamase was identified in a stool isolate of Shigella sonnei and in blood isolates of Escherichia coli (one isolate) and Klebsiella pneumoniae (two isolates) from different parts of Korea. The amino acid sequence differed by one amino acid from CTX-M-9 (Ala-231--> Val) and was identical to that of beta-lactamases recently found in China and Japan.     

Extended spectrum b lactamases (ESBL) in clinical isolates of Klebsiella pneumoniae and Escherichia coli

The present study was conducted to find the prevalence of Extended spectrum b Lactamase (ESBL) producing strains of Klebsiella pneumoniae (K. pneumoniae) and Escherichia coli (E. Coli) in different clinical samples received at the Department of Microbiology, Medical College Baroda. A total of 187 clinical isolates (106 of K. pneumoniae and 81 of E. Coli) were tested for resistance to any one of the three Third generation cephalosporins (3GC) namely cefotaxime, ceftazidime and ceftriaxone. 100 isolates (57 of K. pneumoniae and 43 of E. Coli) were found to be resistant to at least one of the 3GC tested. These were then tested for ESBL production by Double Disc Diffusion Synergy Test (DDST) using Ceftriaxone, Ceftazidime, and Cefotaxime along with Augmentin as well as by the MIC reduction test. ESBL was detected in 53 isolates (33 K. pneumoniae and 20 E. coli). Using the interpretative guidelines of the NCCLS, 24% to 27% of the ESBL isolates would have been reported to be susceptible to the 3GC by routine antimicrobial susceptibility methods. DDST was found to be a useful, simple and cost effective test for the detection of ESBL producing strains.     

Modified double-disc test for detection of extended-spectrum beta-lactamases in Escherichia coli and Klebsiella pneumoniae

This study evaluates the performance of a modified double-disc test (MDDT) for the detection of extended-spectrum beta-lactamases (ESBLs) in clinical isolates of Escherichia coli and Klebsiella pneumoniae. Ninety-six isolates of E. coli and 40 K. pneumoniae are studied for ESBL production by the National Committee for Clinical Laboratory Standards (NCCLS) combination disc tests and MDDT A total of 112 (82%) isolates (80 [83%] E. coli, 32 [80%] K. pneumoniae) were positive for ESBL by MDDT compared to 102 (75%; 72 [75%] E. coli and 30 [75%] K. pneumoniae) by the NCCLS method. In 10 (7.4%) isolates, ESBLs were detected only by MDDT Twenty-four (17.6%) isolates were negative for ESBL by both methods. The protocol described in this study provides a more sensitive approach than does the NCCLS method for ESBL detection in E. coli and K. pneumoniae.     

Molecular characterization of extended-spectrum beta-lactamases produced by clinical isolates of Klebsiella pneumoniae and Escherichia coli from a Korean nationwide survey

To determine the prevalence and genotypes of extended-spectrum beta-lactamases (ESBLs) among clinical isolates of Klebsiella pneumoniae and Escherichia coli, we performed antibiotic susceptibility testing, pI determination, induction testing, transconjugation, and DNA sequencing analysis. Among the 509 isolates collected from 13 university hospitals in Korea, 39.2% produced ESBLs. ESBL-producing isolates were detected in every region in Korea. A total of 44.6% of the isolates produced both TEM- and SHV-type ESBLs, and 52% of ESBL-producing isolates transferred resistance to ceftazidime by transconjugation. The ESBLs were TEM-19, TEM-20, TEM-52, SHV-2a, SHV-12, and one new variant identified for the first time in Korea, namely, TEM-116. TEM-1 and SHV-12 were by far the most common variants. TEM-1, TEM-116, and SHV-12 showed a high prevalence in K. pneumoniae. Two isolates (E. coli SH16 and K. pneumoniae SV3) produced CMY-1-like beta-lactamases, which play a decisive role in resistance to cefoxitin and cefotetan, as well as TEM-type enzymes (TEM-20 and TEM-52, respectively). Using MIC patterns and DNA sequencing analysis, we postulated a possible evolution scheme among TEM-type beta-lactamases in Korea: from TEM-1 to TEM-19, from TEM-19 to TEM-20, and from TEM-20 to TEM-52.     

产AmpC酶大肠埃希菌和肺炎克雷伯菌中整合子与多重耐药的研究

目的探讨整合子介导的耐药机制在产AmpC酶大肠埃希菌和肺炎克雷伯菌多重耐药中的作用.方法5株产AmpC酶大肠埃希菌和肺炎克雷伯菌分离自2002年1月-2004年5月间我院呼吸科住院的患者,采用E-test试验条进行药敏试验、电转化试验,筛选、分离耐药质粒.PCR扩增Ⅰ型整合子基因盒插入序列,分子克隆和序列分析.结果所有产酶菌株通过电转化试验可将头孢西丁耐药性传递给受体菌,5个产AmpC酶耐药质粒中,有4个检出整合酶序列,其中3个携带2种抗药性基因盒,包括氨基糖苷乙酰转移酶基因aacA4;氨基糖苷腺苷转移酶基因aadA5;二氢叶酸还原酶基因dfrA17;氯霉素外排蛋白编码基因cmL44.结论整合子介导的抗药性基因盒参与了产质粒AmpC酶大肠埃希菌和肺炎克雷伯菌多重耐药的形成,应引起高度重视.     

Prevalence and risk factors of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in an Israeli long-term care facility

The purpose of this study was to ascertain the prevalence of extended-spectrum beta-lactamases (ESBLs) among Escherichia coli and Klebsiella pneumoniae strains obtained from urine samples of residents of a long-term care facility and to determine the risk factors for acquisition of ESBL-producing strains. All urine samples collected from January 2003 to October 2003 that were positive for E. coli or K. pneumoniae were tested for the presence of ESBL. Records of patients with ESBL-positive (ESBL-P) samples were analyzed for clinical and demographic data. The records of a matched control group of patients whose urine samples were positive for E. coli or K. pneumoniae but were ESBL-negative (ESBL-N) were also analyzed. The overall rate of ESBLs among the E. coli and K. pneumoniae samples was 25.6%. Of 350 urine samples that grew E. coli, 77 (22%) were positive for ESBL; 34 of 84 (40.5%) samples that grew K. pneumoniae were ESBL-P. Male sex, treatment in the subacute care unit, recent antimicrobial treatment, pressure sores, (percutaneous endoscopic gastrostomy) PEG tube, anemia, hypoalbuminemia, permanent urinary catheter, and any recent invasive procedure were all associated with ESBL-P bacteria in the univariate analysis. The multivariate analysis revealed three independent risk factors for the presence of an ESBL-producing strain: anemia, permanent urinary catheter, and previous antibiotic use. Fluoroquinolones were most strongly associated with the development of ESBL-producing bacteria. The prevalence of ESBL-producing E. coli and K. pneumoniae in the long-term care facility investigated was unexpectedly high and corroborates the notion that long-term care facilities could be important reservoirs of resistant bacteria. Identification of the risk factors for ESBLs is the first step in formulating an effective strategy to curtail the spread of ESBL resistance in long-term care facilities.     

Long-term study of the frequency of Escherichia coli and Klebsiella pneumoniae isolates producing extended-spectrum β-lactamases

In total, 438 (1.7%) Escherichia coli and 125 (3.98%) Klebsiella pneumoniae isolates were found to be producers of extended-spectrum beta-lactamase (ESBL) during 1995-2003 in southern Spain. There was a significant increase in the frequency of ESBL-producing E. coli isolates, from < 0.36% before 1999 to 4.8% in 2003, while the frequency of ESBL-producing K. pneumoniae isolates decreased during the same period. The most common ESBLs detected in K. pneumoniae were SHV type, whereas both CTX-M and SHV types were detected in E. coli. In addition, E. coli isolates showed greater clonal diversity (84 distinct REP-PCR patterns, compared with five in K. pneumoniae), fewer enzymes per isolate, and a higher number of isolates recovered from outpatients. These differences may have implications for the control measures that should be used for these two microorganisms.     

Aminoglycoside resistance in clinical Escherichia coli and Klebsiella pneumoniae isolates from Western Norway

Resistance to gentamicin in Escherichia coli from blood culture has shown an increase over the past decade in Norway. This study was done to investigate aminoglycoside resistance in Escherichia coli and Klebsiella pneumoniae in Western Norway. The material included 49 blood culture isolates which had shown aminoglycoside resistance collected during 2000-2009. To investigate co-resistance to alternative antibiotics and dynamics involved in aminoglycoside resistance 67 isolates (mostly from urine) exhibiting resistance to both aminoglycosides and extended spectrum beta-lactam antibiotics were also included. MIC values were obtained for amikacin, gentamicin, kanamycin, netilmicin, streptomycin and tobramycin and all isolates were screened using PCR for aac(3)-II and aac(6')-Ib, encoding aminoglycoside modifying enzymes. Resistance to ≥3 aminoglycosides was found in 92% of the isolates and 60.3% showed resistance to gentamicin, netilmicin, tobramycin and kanamycin. Amikacin resistance was low. Co-resistance to ciprofloxacin was found in 88% of the isolates with gentamicin resistance. aac(3)-IIa/c was found in 79.3% and aac(6')-Ib in 37.9% of the isolates and 28.4% harboured both genes. aac(6')-Ib-cr, possibly contributing to ciprofloxacin resistance was found mostly in extended spectrum beta-lactamase producers. The aminoglycoside resistance patterns indicate co-existence of multiple resistance mechanisms. The use of ciprofloxacin and third generation cephalosporins is likely to have contributed to the increase in aminoglycoside resistance in Norway.     

Evaluation of efficiency of screening extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in hospitals where the bacteria are increasingly prevalent

The disk screening methods for extended-spectrum beta-lactamase-producing strains were evaluated. The confirmatory work is reduced significantly in settings such as those in this study, by changing the cefpodoxime breakpoint to < or =20 mm and by not testing cefoxitin-resistant isolates. Cefotaxime and ceftazidime disk screening is reliable, and the laboratory-prepared cefotaxime- and ceftazidime-clavulanic acid disks are stable at -20 degrees C for 12 weeks.     

Prevalence and antimicrobial susceptibility of extended-spectrum beta lactamases-producing Escherichia coli and Klebsiella pneumoniae isolated in selected hospitals of Anyigba,Nigeria

BackgroundEscherichia coli and Klebsiella pneumoniae are commonly implicated in urinary tract infections accounting for majority of the antimicrobial resistance encountered in hospitals.ObjectivesTo determine the prevalence and antimicrobial susceptibility of extended-spectrum beta-lactamases (ESBLs) producing E. coli and K. pneumoniae among patients in Anyigba, Nigeria.MethodsThis hospital-based cross-sectional study was conducted using urine samples from 200 patients of Grimmard Catholic hospital and Maria Goretti hospital. Urine samples were processed to identify ESBL-producing E. coli and K. pneumoniae using standard microbiological techniques. Isolates were then tested against antimicrobial agents.ResultsA total of 156 bacterial isolates were recovered consisting 128 of E. coli and 28 of K. pneumoniae. Extended spectrum beta-lactamases production was observed in 69% of E. coli and 31% of K. pneumoniae. These pathogens were resistant to 3 or more antibiotics. Of the antimicrobials tested, cefotaxime demonstrated the highest rates of resistance (100%) for both ESBL-producing E. coli and K. pneumoniae. Fifty-four isolates of ESBL-producing E. coli showed a high level of resistance to amoxicillin clavulanic acid (83.3%), ciprofloxacin (83.3%), and ceftazidime (79.6%). ESBL-positive K. pneumoniae isolates were highly resistant to ciprofloxacin (75%), and amoxicillin clavulanic acid (83.3%). Cefoxitin (62.5%) and gentamicin (66.7%) showed substantially higher rates of resistance against these isolates while all 24 strains were resistant to imipenem.ConclusionThis study indicated the prevalence of ESBL-positive Gram-negative pathogens in these study sites and also demonstrated their resistance to a few antibiotics. This highlights the need for new antimicrobials that are potent and improved policy on use of antibiotics.     

Detection of extended-spectrum beta-lactamases by using boronic acid as an AmpC beta-lactamase inhibitor in clinical isolates of Klebsiella spp. and Escherichia coli

We evaluated highly sensitive methods using boronic acid (BA) to detect extended-spectrum beta-lactamase (ESBL) production. A total of 182 clinical isolates of Klebsiella spp. (n = 118) and Escherichia coli (n = 64) were analyzed: 62 harbored only ESBLs, 80 harbored both ESBLs and plasmid-mediated AmpC beta-lactamases (pAmpCs), and 40 harbored only pAmpCs. The CLSI confirmatory test detected all isolates that produce only ESBLs but detected 85% of isolates that produce both enzymes. When a >/=5-mm increase in the zone diameter of either the cefotaxime (CTX) or the ceftazidime (CAZ) disk in the presence of both clavulanic acid (CA) and BA was considered to be a positive result, the test detected all isolates that harbor ESBLs (+/- pAmpCs) but showed frequent false-positive results (50%) for isolates that produce only pAmpCs. Meanwhile, when a >/=3-mm increase in the zone diameter of either the CTX/BA or the CAZ/BA disk in the presence of CA was considered to be a positive result, the test also detected all isolates that harbor ESBLs (+/- pAmpCs) and showed less frequent false-positive results (5%) in isolates that produce only pAmpCs. The latter new interpretive guideline has enhanced detection of ESBLs in clinical isolates of Klebsiella spp. and Escherichia coli and allowed detection of an ESBL even when potentially masked by a pAmpC.     

Molecular characterisation of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella spp. isolates at a tertiary-care centre in Lebanon.

The prevalence of bla CTX-M, bla TEM and bla SHV genes among extended-spectrum beta-lactamase (ESBL)-producing clinical isolates of Escherichia coli (n = 50) and Klebsiella spp. (n = 50) from Lebanon was 96%, 57% and 67%, and 40%, 82% and 84%, respectively. Genotyping revealed that the clonal diversity was unrelated to the presence of bla genes. Sequence analysis of 16 selected isolates identified the bla CTX-M-15, bla TEM-1, bla OXA-1 and six bla SHV genes, as well as the gene encoding the quinolone-modifying enzyme AAC(6')-Ib-cr. The genes encoding CTX-M-15 and AAC(6')-Ib-cr were carried on a 90-kb plasmid of the pC15-1a or pCTX-15 type, which transferred both ESBL production and quinolone resistance from donors to transconjugants.     

Prevalence and diversity of extended-spectrum β-lactamases in faecal Escherichia coli isolates from healthy humans in Spain

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates were detected in seven of 105 faecal samples from healthy humans, from two Spanish cities, during 2007. In these isolates, five ESBLs were detected, CTX-M-14 ( n  = 2), CTX-M-1 ( n  = 2), CTX-M-32 ( n  = 1), CTX-M-8 ( n  = 1) and TEM-52 ( n  = 1). Both bla _CTX-M-14a (surrounded by IS Ecp1 -IS 903 ) and bla _CTX-M-14b variants (included in an integron structure) were identified in this study. This is the first time that the bla _CTX-M-8 gene and ESBLs of the CTX-M-8 group have been found in Europe and Spain, respectively. Faecal E. coli of healthy humans therefore constitute a reservoir of bla _CTX-M genes with different surrounding genetic elements.     

In vitro activities of 16 antimicrobial agents against clinical isolates of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in two regional hospitals in Taiwan.

BACKGROUND AND PURPOSE: Infections due to extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae (ESBL-EC and ESBL-KP) have become an important clinical problem. Local knowledge of antimicrobial susceptibilities of these organisms is important for implementation of effective hospital anti-infective policies. METHODS: We analyzed the activities of various antimicrobial agents against recent isolates of ESBL-EC and ESBL-KP from 2 regional hospitals using the agar dilution method to determine minimal inhibitory concentrations (MICs). A total of 80 strains of ESBL-EC and 101 strains of ESBL-KP collected during 2003 and 2004 were included in the study. RESULTS: The MICs of all carbapenems were relatively low, with almost all isolates being susceptible. In contrast, only 30.0% of ESBL-EC and 36.6% of ESBL-KP were susceptible to ciprofloxacin. Flomoxef and cefmetazole were the most active cephamycins (88.8% and 90.0% ESBL-EC and 93.1% and 87.1% ESBL-KP susceptible, respectively), followed by ceftibuten (85.0% and 80.2%) and cefoxitin (42.5% and 49.5%). A cefepime MIC < or = 8 mg/L was found in 77.5% of ESBL-EC and 73.3% of ESBL-KP isolates. The susceptible rates to amikacin and isepamicin were both 81.3% for ESBL-EC; 72.3% and 73.3% for ESBL-KP. Inter-hospital differences in susceptibilities were demonstrated for several antimicrobials. CONCLUSIONS: The inter-hospital variation of these data emphasizes the need for monitoring of antimicrobial susceptibility profiles at the individual hospital level and to establish rationales supporting policy for treating infections caused by ESBL-producing bacteria.     

A simple and reliable method to screen isolates of Escherichia coli and Klebsiella pneumoniae for the production of TEM- and SHV-derived extended-spectrum β-lactamases

Objective: To evaluate which of 24 β-lactams used in susceptibility tests best discriminated between strains of Klebsiella pneumoniae and Escherichia coli that produce extended spectrum β-lactamases (ESBLs) from strains that produce older, more familiar, plasmid-mediated β-lactamases such as TEM-1 and SHV-1.
Methods: Susceptibility to the 24 β-lactam agents was determined by agar dilution and disk diffusion methodologies, using 27 strains of K. pneumoniae and E. coli that produced 22 different older plasmid-mediated β-lactamases and 28 strains that produced 17 different ESBLs.
Results: In general, strains that produced ESBLs were intermediate or resistant to cefpodoxime, whereas those that produced other β-lactamases were susceptible to this agent. The agar dilution test exhibited 96% sensitivity and 100% specificity in discriminating these two groups of organisms. The disk diffusion test exhibited 100% sensitivity and 96% specificity. All other β-lactam agents tested were inferior discriminators between the two groups of organisms.
Conclusions: Agar dilution and disk diffusion tests with cefpodoxime can be used to discriminate strains of K. pneumoniae and E. coli that produce ESBLs from those that produce older, plasmid-mediated β-lactamases.