Detection Of Β-lactamases Research Articles

English

Enterobacteriaceae are the main etiological agents of environmental bovine mastitis and are often resistant to antimicrobials, especially β-lactam class due to the production of β-lactamases. These can be classified into several groups according to the molecular structure and substrate activity. The present study evaluated the profile of pheno-genotypic resistance to β-lactams, with emphasis on the functional detection of β-lactamases. The isolates were obtained from milk samples from farms located in the interior region of the state of Rio de Janeiro. 47.6% (20/42) of the bacterial isolates producing enzymes classified as Group 1 (AmpC type) were detected, and in disk approximation test, 30% were classified as the inducible type and 70% as not inducible. To the best of the authors’ knowledge, this is the first report on AmpC β-lactamase production in enterobacteria involved in mastitis etiology in Brazil. Key words: Raw milk, environmental mastitis, dairy cattle, antimicrobial resistance.

Detection and genetic characterization of β-lactamases in Prevotella intermedia and Prevotella nigrescens isolated from oral cavity infections and peritonsillar abscesses

A prospective analysis on β-lactam resistance mechanisms and β-lactamase prevalence was conducted on Prevotella intermedia and Prevotella nigrescens recovered from patients with chronic periodontitis and peritonsillar abscesses. Both phenotypic and genotypic methods were performed to characterize the β-lactamases, their coding genes and their genetic contexts. Overall, β-lactamase production was observed in 64% (16/25) P. intermedia and 23.8% (5/21) P. nigrescens (p < 0.01). Besides higher β-lactamase production rates were observed in P. intermedia (8/16) than in P. nigrescens (2/16) recovered from chronic periodontitis, almost all isolates from peritonsillar abscesses were producers (8/9 and 3/3, respectively). cfxA, but not cepA and cblA, was detected in those isolates, which were previously categorized as β-lactamase producers. CfxA producing isolates displayed higher β-lactam MICs than non-producers in both species. The most frequent allele was cfxA2, followed by cfxA3 and a new allelic variant named cfxA6. The analysis of the downstream flanking region in the three cfxA variants revealed the association with mobA of Tn4555, suggesting their localization in a mobilizable element. β-lactam resistance and cfxA carriage prevalence seems to be not only related to the bacterial species but also to the infection site.

A prospective study on aetiological agents of acute and chronic suppurative otitis media

Otitis media is a persistent, insidious, and dangerous disease because of multiple aetiology and serious complications. Hence, a study was conducted to find out the bacterial and fungal aetiology of suppurative otitis media. Aim: The aim was to find the prevalence of bacterial and fungal pathogens in acute and chronic otitis media. Materials and Methods: A total of 260 patients having otitis media belonging to all age groups and both sexes who attended the ENT outpatient department were selected for study for a period of 1-year. Ear discharge was collected under aseptic precautions using sterile cotton swabs. Both bacterial and fungal culture were done. The antimicrobial susceptibility of bacterial isolates was done including detection of extended-spectrum β-lactamase and detection of metallo β-lactamase for resistant strains. Results: In acute suppurative otitis media, Gram-positive organisms 48 (55.18%) were predominant compared to Gram-negative organisms 37 (42.52%). No fungal isolates were obtained in the present study. In the case of chronic suppurative otitis media (CSOM), bacteria were isolated in 129 (74.57%) cases and fungus in 41 (23.7%) cases. Polymicrobial infection was found only in 14 (10.85%) cases. Among the bacterial isolates in CSOM, Gram-negative organisms (65.35%) were more compared to Gram-positive organisms (35.65%).

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the detection of extended spectrum β-lactamases and carbapenemases among Gram-negative bacilli

In the last few years, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has become the new gold standard method for the identification of microorganisms. Nevertheless, other useful applications of mass spectrometry have recently been demonstrated including the detection of resistance mechanisms. The MALDI-TOF-MS hydrolysis assay allows rapid detection of β-lactamase activity with results available within a few hours. Rapid detection of β-lactamases is important since β-lactam antibiotics remains as the mainstay of the treatment of several community-acquired and nosocomial infections, and a steady increase has been observed of resistant microorganisms associated with the production of extended spectrum β-lactamases (ESBLs) and carbapenemases. Several studies have reported the high sensitivity and specificity of the MALDI-TOF-MS antibiotic hydrolysis assay for the detection of ESBLs - or carbapenemase-producing Gram-negative bacilli. In addition, this technique can be performed directly from positive blood culture, significantly shortening the time of resistance detection. However, the standardization of assay conditions as well as automatic analysis of the spectra obtained is required. The aim of this review was to summarize the currently available data regarding the accuracy of the detection of β-lactamase activity using the MALDI-TOF-MS antibiotic hydrolysis assay.

Amperometric detection of extended-spectrum β-lactamase activity: application to the characterization of resistant E. coli strains.

The amperometric detection of extended-spectrum β-lactamase (ESBL) with carbon screen-printed sensors was investigated in the presence of the Nitrocefin, a commercially-available β-lactamase chromogenic cephalosporin substrate. Using an ESBL isolated from a clinical sample, it was shown for the first time that the intensity of a specific anodic pic current (EP = ∼+0.3 V vs. Ag/AgCl) resulting from the catalytic hydrolysis of the β-lactam ring was proportional to the amount of ESBL. The proof-of-principle of a novel susceptibility assay for the rapid and accurate identification of ESBL- producing bacteria was then demonstrated. The detection scheme relied on (i) the culture of the sample in a medium containing the cefotaxime supplemented or not with the clavulanic acid inhibitor to allow the specific determination of ESBL producers (ii) followed by the incubation of the bacteria with the Nitrocefin and (iii) the measurement of the enzyme product by cyclic voltammetry. The amperometric assay was further applied to the characterization of E. coli strains and to the quantification of the ESBL producers. A detection limit of 5 × 10(4) cfu mL(-1) ESBL-producing E. coli was achieved after a 10 min incubation time. In contrast to the approved routine assays, the electrochemical approach, which did not require isolated colonies to be performed, provided quantified results regarding ESBL activity within a few hours. Finally, owing to its cost-effectiveness, portability and simplicity, this test holds great promise for clinical and environmental applications.

Antimicrobial-Resistant and Extended-Spectrum β-Lactamase–Producing Escherichia coli in Raw Cow's Milk

The occurrence of antimicrobial-resistant bacteria is an important public health issue. The aim of this study was the monitoring of resistant Escherichia coli in raw cow's milk with a focus on the detection of extended-spectrum β-lactamase (ESBL)–producing strains. In total, 263 samples of raw milk from 40 farms were collected and investigated in 2010 to 2013 in the Czech Republic. Detection of E. coli was performed and evaluated according to ISO 16649-2, and antibiotic resistance was screened by the disk diffusion method. The presence of E. coli was detected in 243 (92.4%) samples. In total, 270 isolates were obtained. Resistance to β-lactam (31.8%) and tetracycline (13.0%) antibiotics was detected most often and also multiresistant strains (5.5%) were observed. E. coli isolates found to be resistant to β-lactam, tetracycline, and quinolone antibiotics were assayed by PCR to detect selected genes encoding those resistance mechanisms. In isolates in which any bla genes were detected, a double-disk synergy test was performed. ESBL production was confirmed in 2 (0.7%) isolates. The genetic analysis identified the presence of the blaCTX-M gene and other resistance genes (tet(B) and qnrB). Both ESBL-positive isolates originated from the same farm and had an identical pulsed-field gel electrophoresis profile. The findings of our study indicate that milk can be a reservoir of bacteria carrying resistance genes with a potential for spreading through the food chain.

A five-year experience of carbapenem resistance in Enterobacteriaceae causing neonatal septicaemia: predominance of NDM-1.

Treatment of neonatal sepsis has become a challenge with the emergence of carbapenemase-producing bacteria. This study documents the trend of carbapenem susceptibility in Enterobacteriaceae that caused septicaemia in neonates over a five year period (2007–2011) and the molecular characterisation of Enterobacteriaceae resistant to carbapenems and cephalosporins. Hundred and five Enterobacteriaceae including Escherichia coli (n = 27), Klebsiella pneumoniae (n = 68) and Enterobacter spp. (n = 10) were isolated from blood of septicaemic neonates followed by antibiotic susceptibility tests, determination of MIC values, phenotypic and genotypic detection of β-lactamases. Carbapenem was the most active antimicrobial tested after tigecycline. CTX-M type was the most prevalent ESBL throughout the period (82%). New Delhi Metallo-β-lactamase-1 (NDM-1), which is a recent addition to the carbapenemase list, was the only carbapenemase identified in our setting. Fourteen percent of the isolates possessed bla NDM-1. Carbapenem non-susceptibility was first observed in 2007 and it was due to loss of Omp F/Ompk36 in combination with the presence of ESBLs/AmpCs. NDM-1 first emerged in E. coli during 2008; later in 2010, the resistance was detected in K. pneumoniae and E. cloacae isolates. NDM-1-producing isolates were resistant to other broad-spectrum antibiotics and possessed ESBLs, AmpCs, 16S-rRNA methylases, AAC(6′)-Ib-cr, bleomycin resistant gene and class 1 integron. Pulsed field gel electrophoresis of the NDM-1-producing isolates indicated that the isolates were clonally diverse. The study also showed that there was a significantly higher incidence of sepsis caused by NDM-1-harbouring isolates in the male sex, in neonates with low birth weight and neonates born at an extramural centre. However, sepsis with NDM-1-harbouring isolates did not result in a higher mortality rate. The study is the first to review the carbapenem resistance patterns in neonatal sepsis over an extended period of time. The study highlights the persistence of ESBLs (CTX-Ms) and the emergence of NDM-1 in Enterobacteriaceae in the unit.

Detection of extended-spectrum β-lactamases (blaCTX-M-1 and blaTEM) in Escherichia coli, Salmonella spp., and Klebsiella pneumoniae isolated from poultry in North Eastern India

Detection of extended-spectrum β-lactamases (blaCTX-M-1 and blaTEM) in Escherichia coli, Salmonella spp., and Klebsiella pneumoniae isolated from poultry in North Eastern India

Phenotypic and genotypic detection of extended-spectrum β-lactamase (ESBL) producing Escherichia coli isolated from urinary tract infections in Zabol, Iran

Phenotypic and genotypic detection of extended-spectrum β-lactamase (ESBL) producing Escherichia coli isolated from urinary tract infections in Zabol, Iran

Rapid optical determination of β-lactamase and antibiotic activity

BackgroundThe absence of rapid tests evaluating antibiotic susceptibility results in the empirical prescription of antibiotics. This can lead to treatment failures due to escalating antibiotic resistance, and also furthers the emergence of drug-resistant bacteria. This study reports a rapid optical method to detect β-lactamase and thereby assess activity of β-lactam antibiotics, which could provide an approach for targeted prescription of antibiotics. The methodology is centred on a fluorescence quenching based probe (β-LEAF – β-Lactamase Enzyme Activated Fluorophore) that mimics the structure of β-lactam antibiotics.ResultsThe β-LEAF assay was performed for rapid determination of β-lactamase production and activity of β-lactam antibiotic (cefazolin) on a panel of Staphylococcus aureus ATCC strains and clinical isolates. Four of the clinical isolates were determined to be lactamase producers, with the capacity to inactivate cefazolin, out of the twenty-five isolates tested. These results were compared against gold standard methods, nitrocefin disk test for β-lactamase detection and disk diffusion for antibiotic susceptibility, showing results to be largely consistent. Furthermore, in the sub-set of β-lactamase producers, it was demonstrated and validated that multiple antibiotics (cefazolin, cefoxitin, cefepime) could be assessed simultaneously to predict the antibiotic that would be most active for a given bacterial isolate.ConclusionsThe study establishes the rapid β-LEAF assay for β-lactamase detection and prediction of antibiotic activity using S. aureus clinical isolates. Although the focus in the current study is β-lactamase-based resistance, the overall approach represents a broad diagnostic platform. In the long-term, these studies form the basis for the development of assays utilizing a broader variety of targets, pathogens and drugs.

Modified CLSI Extended-Spectrum β-Lactamase (ESBL) Confirmatory Test for Phenotypic Detection of ESBLs among Enterobacteriaceae Producing Various β-Lactamases

The worldwide dissemination of Enterobacteriaceae producing AmpC β-lactamases and carbapenemases makes difficult the phenotypic detection of extended-spectrum β-lactamases (ESBLs), as they may be masked by these additional enzymes. A modification of the CLSI ESBL confirmatory test was developed and evaluated in a comparative study for its ability to successfully detect ESBLs among Enterobacteriaceae producing various carbapenemases (Klebsiella pneumoniae carbapenemase [KPC], VIM, NDM, and OXA-48) and plasmidic or derepressed AmpCs. The modified CLSI ESBL confirmatory test was performed with cefotaxime and ceftazidime disks with and without clavulanate, on which both boronic acid (BA) and EDTA were dispensed. A total of 162 genotypically confirmed ESBL-positive Enterobacteriaceae isolates (83 carbapenemase/ESBL producers, 25 AmpC/ESBL producers, and 54 ESBL-only producers) were examined. For comparison, 139 genotypically confirmed ESBL-negative Enterobacteriaceae isolates (94 of them possessed carbapenemases and 20 possessed AmpCs) were also tested. The standard CLSI ESBL confirmatory test was positive for 106 of the 162 ESBL producers (sensitivity, 65.4%) and showed false-positive results for 4 of the 139 non-ESBL producers (specificity, 97.1%). The modified CLSI ESBL confirmatory test detected 158 of 162 ESBL producers (sensitivity, 97.5%) and showed no false-positive results for non-ESBL producers (specificity, 100%). The findings of the study demonstrate that the modified CLSI ESBL confirmatory test using antibiotic disks containing both BA and EDTA accurately detects ESBLs in Enterobacteriaceae regardless of the coexistence of additional β-lactam resistance mechanisms.

Status of detection of Extended-spectrum β-lactamase (ESBL)-producing bacteria isolated from blood and urine in four medium-size hospitals

Status of detection of Extended-spectrum β-lactamase (ESBL)-producing bacteria isolated from blood and urine in four medium-size hospitals

Phenotypic and molecular characterization of plasmid mediated AmpC β-lactamases among Escherichia coli, Klebsiella spp., and Proteus mirabilis isolated from urinary tract infections in Egyptian hospitals.

The incidence of resistance by Enterobacteriaceae to β-lactam/β-lactamase inhibitors combination is increasing in Egypt. Three phenotypic techniques, comprising AmpC disk diffusion and inhibition dependent methods using phenylboronic acid (PBA) and cloxacillin, were compared to PCR based method for detection of plasmid mediated AmpC β-lactamase in common urinary tract isolates. A total of 143 isolates, including E. coli, Klebsiella pneumonia, and Proteus mirabilis, were collected from urinary tract infections cases in Egyptian hospitals. Plasmid encoded AmpC genes were detected by PCR in 88.46% of cefoxitin resistant isolates. The most prevalent AmpC gene family was CIT including CMY-2, CMY-4, and two CMY-2 variants. The second prevalent gene was DHA-1 which was detected in E. coli and Klebsiella pneumonia. The genes EBC, FOX, and MOX were also detected but in small percentage. Some isolates were identified as having more than one pAmpC gene. The overall sensitivity and specificity of phenotypic tests for detection of AmpC β-lactamase showed that AmpC disk diffusion and inhibition dependent method by cloxacillin were the most sensitive and the most specific disk tests. PCR remains the gold standard for detection of AmpC β-lactamases. This study represents the first report of CMY-2 variants of CMY-42 and CMY-102 β-lactamase-producing E. coli, Klebsiella pneumonia, and Proteus mirabilis isolates in Egypt.

The frequency of BRO β-lactamase and its relationship to antimicrobial susceptibility and serum resistance in Moraxella catarrhalis

We investigated the frequency of BRO β-lactamase and its relationship to antibiotic susceptibility profiles and serum susceptibility. Moraxella catarrhalis clinical isolates (n=197) were collected from patients with respiratory tract infections in Tokyo between November 2004 and April 2005. Phenotypic and genotypic detection of β-lactamases was performed. The MICs of 6 antibiotics were determined by Etest, and the serum bactericidal assay was conducted by using the culture-and-spot test. Nearly all (192; 97%) of the clinical isolates were β-lactamase producers; of these, 182 (95%) were bro-1 and 10 (5%) were bro-2 positive. MIC50, MIC90, and geometric mean MICs of penicillin, amoxicillin, cefixime, and clarithromycin for BRO-1 isolates were significantly higher than for BRO-2 isolates. The frequency of intermediate and full serum resistance was significantly higher in BRO-1 isolates than in BRO-2 isolates (P=0.0056), but not BRO-negative isolates (P=0.1333). We provide the first evidence that the presence of BRO-1 in M.catarrhalis is associated with reduced susceptibility to clarithromycin and β-lactam antibiotics, as well as serum non-sensitive (intermediate and resistant).

Phenotypic detection of extended spectrum ?-lactamase and AmpC ?-lactamase in urinary isolates of Escherichia coli at a tertiary care referral hospital in Northeast India

Objective Urinary tract infections (UTIs) are the most prevalent infections worldwide, mostly caused by Escherichia coli. Emerging antibiotic resistance due to extended spectrum â-lactamase (ESBL) and AmpC β- lactamase production limit the use of β-lactam antibiotics against the infections caused by E. coli. We detected the production of ESBL and AmpC β-lactamase in urinary isolates of E. coli, recovered from a tertiary care referral hospital in Northeast India. Materials and Methods A total of 140 E. coli urinary isolates were recovered during October 2008 to January 2009. Antibiotic susceptibility testing and ESBL detection were carried out according to Clinical Laboratory and Standards Institute (CLSI) guidelines. Phenotypic detection of AmpC β-lactamase was carried out by AmpC disc method. Results Among the 140 urinary isolates, 112 isolates (80%) were multi-drug resistance (MDR). ESBL was detected in 67.14% (94/140) of E. coli isolates. AmpC β-lactamase was detected in 22.34% of ESBL producing E. coli isolates. Conclusions Routine testing for ESBL and AmpC β-lactamase in E. coli urinary isolates with conventional antibiogram would be useful for strict antibiotic policy implementation in hospitals, to estimate the impact of increased drug resistance and to take steps for reducing their resistance. Journal of College of Medical Sciences-Nepal, 2012, Vol-8, No-3, 22-29 DOI: http://dx.doi.org/10.3126/jcmsn.v8i3.8682

Evaluation of the AID ESBL line probe assay for rapid detection of extended-spectrum β-lactamase (ESBL) and KPC carbapenemase genes in Enterobacteriaceae

This study aimed at evaluating the AID ESBL line probe assay for the detection of extended-spectrum β-lactamase (ESBL) and KPC carbapenemase genes in Enterobacteriaceae. The AID ESBL line probe assay was verified for accuracy of its probes using PCR products from clinical ESBL Enterobacteriaceae strains harbouring TEM, SHV and CTX-M ESBL genes and KPC genes and mutant fusion PCR products generated from Enterobacteriaceae strains containing wild-type (wt) TEM and wt SHV. Sensitivity and specificity was determined testing a set of 424 clinical Enterobacteriaceae strains (including 170 strains negative for TEM, SHV, CTX-M and KPC to evaluate the possibility of false positive signals). The line probe assay was shown to detect with 100% accuracy ESBL genes for which oligonucleotide probes are present in the assay. Testing a set of 424 clinical Enterobacteriaceae strains showed 100% sensitivity and specificity for the detection and differentiation of TEM, SHV and CTX-M ESBL genes present in that group. In addition, the line probe assay detected KPC genes accurately. The AID ESBL line probe assay is an accurate and easy-to-use test for the detection of ESBL and KPC genes, which can readily be implemented in the diagnostic laboratory.

Prevalence of multi drug resistant Acinetobacter baumannii in the clinical samples from Tertiary Care Hospital in Islamabad, Pakistan

Acinetobacter baumannii can cause a wide range of infections, including bacteremia, pneumonia, urinary tract infection, peritonitis, etc. This organism is becoming resistant to a large group of antibiotics, especially β-lactam antibiotics. The reason for multi-drug resistance may be the production of extended- spectrum β-lactamses (ESBLs), carbapenemases/metallo β-lactamases or AmpC β-lactamases. The aim of the present study was to determine the prevalence of multi-drug resistant Acinetobacter baumannii isolated from the patients in Surgical Intensive Care Units (SICUs) of Pakistan Institute of Medical Sciences (PIMS), Islamabad, Pakistan. A total of 91 A. baumanni isolates were collected from PIMS during the period from February 2011 to December 2011. The antibiotic susceptibility testing was performed by standard disc diffusion method as recommended by CLSI. Combination disc method, Modified Hodge test, EDTA disc synergy test and AmpC disc test were performed for detection of ESBLs, carbapenemases, metallo β-lactamases, and AmpC β-lactamases, respectively. The prevalence of MDRs was reported 100% among A. baumannii. The antibiotic susceptibility profile showed that minocycline and tigecycline were the most effective drugs against A. baumannii. Almost all of A. baumannii isolates were carbapenemase and metallo β-lactamase producers. AmpC prevalence was observed in 41.76%, while none of the isolates was ESBL producer. Antibiogram and minimal inhibitory concentrations (MICs) indicated tetracycline is relatively effective against A. baumanii. Increased frequency of multi-drug resistance supports the need for continuous surveillance to determine prevalence and evolution of these enzymes in Pakistan.

National Surveillance Study on Carbapenem Non-Susceptible Klebsiella pneumoniae in Taiwan: The Emergence and Rapid Dissemination of KPC-2 Carbapenemase

ObjectivesThe global spread and increasing incidence of carbapenem non-susceptible Klebsiella pneumoniae (CnSKP) has made its treatment difficult, increasing the mortality. To establish nationwide data on CnSKP spread and carbapenem-resistance mechanisms, we conducted a national surveillance study in Taiwanese hospitals.MethodsWe collected 100 and 247 CnSKP isolates in 2010 and 2012, respectively. The tests performed included antibiotic susceptibility tests; detection of carbapenemase, extended-spectrum β-lactamases (ESBL), and AmpC β-lactamases genes; outer membrane porin profiles; and genetic relationship with pulsed-field gel electrophoresis and multilocus sequence type.ResultsThe resistance rate of CnSKP isolates to cefazolin, cefotaxime, cefoxitin, ceftazidime, and ciprofloxacin was over 90%. Susceptibility rate to tigecycline and colistin in 2010 was 91.0% and 83.0%, respectively; in 2012, it was 91.9% and 87.9%, respectively. In 2010, carbapenemase genes were detected in only 6.0% of isolates (4 bla IMP-8 and 2 bla VIM-1). In 2012, carbapenemase genes were detected in 22.3% of isolates (41 bla KPC-2, 7 bla VIM-1, 6 bla IMP-8, and 1 bla NDM-1). More than 95% of isolates exhibited either OmpK35 or OmpK36 porin loss or both. Impermeability due to porin mutation coupled with AmpC β-lactamases or ESBLs were major carbapenem-resistance mechanisms. Among 41 KPC-2-producing K. pneumoniae isolates, all were ST11 with 1 major pulsotype.ConclusionsIn 2010 and 2012, the major mechanisms of CnSKP in Taiwan were the concomitance of AmpC with OmpK35/36 loss. KPC-2-KP dissemination with the same ST11 were observed in 2012. The emergence and rapid spread of KPC-2-KP is becoming an endemic problem in Taiwan. The identification of NDM-1 K. pneumoniae case is alarming.

Co-existence of Pseudomonas-derived cephalosporinase among plasmid encoded CMY-2 harbouring isolates of Pseudomonas aeruginosa in north India

Context: In Pseudomonas aeruginosa, AmpC β-lactamases are often responsible for high-level resistance to β-lactam antibiotics. The co-production of plasmid-mediated AmpC along with chromosomal Pseudomonas-derived cephalosporinases thus remain a serious clinical concern owing to high resistance spectrum towards antibiotics. Aim: The present study was performed to investigate the co-existence of both chromosomally-encoded and plasmid-mediated AmpC β-lactamase among clinical isolates of P. aeruginosa. Setting and Design: It is a cross-sectional study carried out in the Department of Microbiology in a tertiary referral hospital of northern India. Methods and Methods: A total of 329 consecutive, non-duplicate clinical isolates of P. aeruginosa, were selected for the detection of AmpC β-lactamases and confirmed for AmpC production by modified three dimensional (M3D) test. Ceftazidime -imipenem antagonism test was used to detect inducible AmpC producers. Molecular characterisation of chromosomally-encoded blaPDC and plasmid-mediated AmpC gene was studied by performing polymerase chain reaction (PCR). Result: A total of 214 (65%) isolates were confirmed for AmpC production by M3D test. On performing multiplex PCR, 27 isolates were detected posessing blaCMY type of plasmid-mediated AmpC gene. While 48 isolates were found to harbour chromosomally-encoded blaPDC gene co-production of both chromosomal and plasmid-encoded AmpC was reported in eleven isolates. Conclusions: Although these chromosomally-encoded cephalosporinases might spread more slowly than mobilised AmpC, but it is likely that in the present scenario of intense antibiotic pressure, this will become an increasing problem and may further limit our antibiotic choices.

Detection of ESBLs or AmpC β-lactamase in Escherichia coli and drug resistance

Objective To investigate extended-spectrum β-lactamases (ESBLs),AmpC β-lactamase and drug resistance in Escherichia coli (E.coli) for instructing rational medication uses.Methods 287 E.coli strains were isolated in our hospital from January 2011 to June 2012.ESBLs were detected by the double-disk method; AmpC were detected by the three dimensional extract test; and the drug sensitivity was tested by the KB method.Results Of the 287 E.coli strains,119 (41.5％) strains produced ESBLs and 47 (16.4％) strains produced AmpC,and ESBLs and AmpC were simultaneously detectable in 16 strains (accounting for 5.6％).ESBLs-or AmpC-producing strains had a higher drug resistance; ESBLs-and AmpC-producing strains had multiple drug resistance.All the strains had susceptibility to imipenem.Conclusions The rates of isolation and drug resistance are higher for ESBLs-or AmpC-producing E.coli; ESBLs-and AmpC-producing strains have multiple drug resistance.Imipenem has good antibacterial activity.Detection of ESBLs and AmpC and monitoring of drug resistance should be strengthened clinically and effective measures must be taken to prevent resistant strains. Key words: Escherichia coli; Extended spectrum β-lactamase; AmpC; Drug resistance