Phenotypic and genotypic characterization of plasmid-mediated AmpC beta-lactamases in enteric Gram-negative bacteria from patients with lower respiratory tract infections in a tertiary hospital, southwest Nigeria

Background: AmpC or class C or group 1 beta lactamases are class C cephalosporinases that hydrolyse a wide variety of beta-lactam antibiotics including alpha methoxy beta-lactams (cefoxitin), narrow and broad spectrum cephalosporins. This study was conducted to characterize plasmid-mediated AmpC producing enteric Gram- negative bacteria from patients with lower respiratory tract infections in Obafemi Awolowo University Teaching Hospital Complex (OAUTHC) Ile Ife, Osun State, Nigeria Methodology: A total of 149 patients with clinical features of lower respiratory tract infections (LRTI) were selected by simple random sampling for the study. All Gram-negative isolates recovered from standard microbiological cultures of respiratory specimens of these patients were tested against cefoxitin, third generation cephalosporins (3GCs), and other antibiotics using the disc diffusion AST method, and also screened for production of AmpC beta-lactamases phenotypically by the CLSI method. Plasmid DNA extraction was carried out on twenty-nine cefoxitin-resistant selected isolates using the Kado and Lin method, while genotypic detection of plasmid-mediated AmpC gene was carried out by the polymerase chain reaction (PCR) assay. Results: The results showed that 204 (43.3%) of 471 isolates recovered from the 149 selected patients were resistant to 3GC in the AST assay, among which 121 (59.3%) were resistant to cefoxitin, and 189 of the 471 isolates (40.1%) were AmpC producers. The AmpC producers concurrently showed multiple resistance pattern to other antibiotics tested in this study. Ninety six percent of the 29 selected isolates for plasmid analysis contained plasmids, 45% of which amplified positive on PCR for CMY, 38% for FOX, and 31% for ACC types of AmpC genes. Conclusion: This study showed a high degree of antibiotic resistance among enteric Gram-negative bacteria recovered from patients with LRTIs, as well as high degree of plasmid-encoded AmpC genes responsible for this high antibiotic resistance among the isolates. Proper antibiotic policy and regulation are required to limit the spread of plasmid mediated AmpC ß-lactamase

Clinico-microbiological study of Citrobacter isolates from various clinical specimens and detection of β-lactamase production.

Citrobacter species have been reported to cause a wide spectrum of infections in humans and invasive infections are associated with a high mortality rate, with 33 to 48% of patients succumbing to Citrobacter bacteraemia. The high mortality rate associated with Citrobacter infections may be due in part to ineffective empirical antibiotic therapy. Citrobacter has been found to produce SHV and TEM derived Extended spectrum beta lactamases in addition to chromosomal inducible AmpC beta - lactamases which could be contributing to increasing drug resistance. The aims of the study were to detect the prevalence of Citrobacter infections with its associated risk factors, antibiotic susceptibility patterns and determination of beta-lactamase activity- both extended spectrum beta - lactamase and AmpC beta-lactamase activity among Citrobacter isolates. The isolates were identified by standard microbiological procedures. ESBL detection was by double disc diffusion method and AmpC beta-lactamase detection was done using Cefotaxime and Cefoxitin discs. C. braakii (33.3%) was the commonest genomospecies identified followed by C. freundii (21.3%) and C. amalonaticus (16.66 %) among 150 Citrobacter isolates. Diabetes mellitus was the major risk factor. Imipenem (100%)was most effective whereas 98% showed resistance to Ampicillin; carbapenems and fourth generation Cefipime showed better sensitivity than third generation cephalosporins. The study highlights the need for informed antibiotic treatment guided by routine antimicrobial susceptibility and knowledge of the ESBL status of the isolate, the outcome of which undoubtedly will be better patient care.

AmpC-BETA Lactamases among Enterobacteriaceae Isolated at a Tertiary Hospital, South Western Uganda.

Aim: To characterize AmpC-beta lactamases among Enterobacteriaceae isolates from clinical samples at Mbarara Regional Referral Hospital. Study Design: Laboratory-based descriptive cross-sectional study Place and Duration of Study: Microbiology Department, Mbarara Regional Hospital and MBN clinical Laboratories, between May to September 2013. Methodology: This study included 293 Enterobacteriaceae isolates recovered from clinical specimens that included blood, urine, stool and aspirates. AmpC Beta lactamase production was determined using disc placement method for cefoxitin at a break point of <18mm. Common AmpC plasmid mediated genes were EBC, ACC, FOX, DHA, CIT and MOX were; was determined by Multiplex PCR as described by Hanson and Perez-Perez. Results: Plasmid mediated AmpC phenotype was confirmed in 107 of the 293 (36.5%) cefoxitin resistant isolates with 30 isolates having more than one gene coding for resistance. The commonest source that harbored AmpC beta lactamases was urine and E. coli was the most common AmpC producer (59.5%). The genotypes detected in this study, included EBC (n=36), FOX (n=18), ACC (n=11), CIT (n=10), DHA (n=07) and MOX (n=1). Conclusion: Our findings showed that prevalence of AmpC beta- lactamase at MRRH was high (39.6), with EBC as the commonest genotype among Enterobacteriaceae Urine and E. coli were the commonest source and organism respectively that harbored AmpC beta-lactamases. There‘s rational antimicrobial therapy and antibiotic susceptibility tests should be requested by health workers especially patients presenting with urinary tract infections and bacteraemias.

A Korean Nationwide Surveillance Study for Non-Typhoidal Salmonella Isolated in Humans and Food Animals from 2006 to 2008: Extended-Spectrum beta-Lactamase, Plasmid-Mediated AmpC beta-Lactamase, and Plasmid-Mediated Quinolone Resistance qnr Genes / 대한임상미생물학회지

BACKGROUND: The emergence of non-typhoidal Salmonella (NTS) with decreased susceptibilities to fluoroquinolone, ampicillin, or ceftriaxone has been reported worldwide. However, current surveillance studies of resistance among NTS in Korea are limited. Thus, the antimicrobial susceptibilities; resistance mechanisms such as extended-spectrum beta-lactamase (ESBL), plasmid-mediated AmpC beta-lactamase (PABL), and plasmid-mediated quinolone resistance (PMQR); and molecular epidemiologic characteristics were investigated in the present study. METHODS: National Institute of Health and National Veterinary Research and Quarantine Service collected NTS strains from 219 clinical and 293 non-clinical specimens from 2006 to 2008. The antimicrobial susceptibilities were determined using the Clinical and Laboratory Standards Institute disk diffusion test. ESBL, PABL, and qnr genotyping were performed using PCR and nucleotide sequencing. Pulsed-field gel electrophoresis was used for the molecular epidemiologic study. RESULTS: The resistance to ampicillin in clinical and non-clinical NTS was 49% and 18 to 47%, respectively. The resistance rates to trimethoprim-sulfamethoxazole in clinical and non-clinical NTS were 8% and 0 to 41%, respectively. The rates to extended-spectrum cephalosporin were 0 to 1%. One CTX-M-15-producing isolate and four CMY-2-producing isolates were detected. Notably, PFGE analysis showed four isolates carrying bla CMY-2, including one non-clinical strain had high clonality. Although the rate of ciprofloxacin resistance was very low, two qnrS1-carrying NTS strains were detected in non-clinical specimens. CONCLUSION: The resistance rates to ampicillin in both clinical and non-clinical NTS were high, while those to trimethoprim-sulfamethoxazole varied depending on the specimen. NTS strains harboring CTX-M-15-type ESBL or CMY-2-type PABL were detected even though the resistance rates to cephalosporins were very low. Four NTS strains carrying the blaCMY-2-gene implied zoonotic infection. Continuous effort to minimize transfer of resistance genes in NTS is necessary.

Emergence and control of multidrug resistant organisms in small cities in India: A wake up call.

Context: Urinary tract infections (UTIs) is one of the most common bacterial infections in general practice. Antimicrobial resistance in urinary pathogens, particularly the most common being Escherichia coli, is directly associated with prescribing in primary care. Diagnosis of UTI requires laboratory examination of urine sample in addition to clinical evaluation, which may lead to higher cost of treatment, but the proper treatment of the case that will lead to complete recovery with no recurrence episodes far outweigh the cost issue of microbiological investigation. Even though UTIs are a very common diagnosis, management of this condition is not consistent in general practice. This study was conducted in an effort to see the extent of presence of multi drug resistant organisms in local set up . Aims: To describe the common urine isolates observed in the small cities of India and also to test for drug resistance among them with simple manageable tests in small-scale laboratories. Materials and Methods: A retrospective review was conducted of Gram negative bacilli and Gram positive cocci isolated from the clinical urine samples collected from various hospitals and private practitioners in Shimoga City, Karnataka and Jamshedpur City, Jharkhand. The study period was between November 2011 to January 2012. Results: A total of 788 urine samples were included in the study. It was seen that 55.8% of the total isolated organisms were multidrug resistant (MDR) in Shimoga city, Karnataka and 38.8% of the total isolated organisms were MDR in Jamshedpur city, Jharkhand. Conclusions: Only with the combined efforts of the local laboratories and clinicians, the looming threat of the pandrug resistant organisms in small cities can be avoided. However, more such studies are required from both clinicians and laboratory health care professionals in order to arrive at a common consensus, and uniformity can be brought about in the community regarding prescription practices.

Prevalence of Extended-spectrum beta-lactamase among Enterobacteriacae Blood Isolates with Inducible AmpC beta-lactamase / 감염과화학요법

BACKGROUND: Among the inducible AmpC beta-lactamase-producing members of the family Enterobacteriaceae such as Enterobacter spp., Citrobacter spp., Serratia spp., and Morganella morganii (ECSM), the prevalence of ESBL-producing isolates are increasing. However, there have been only a limited number of studies that have investigated the prevalence for ESBL-production in blood isolates of these organisms. MATERIALS AND METHODS: We performed a prospective observational study to evaluate the prevalence for ESBL production among ECSM blood isolates. All consecutive blood isolates in the Samsung Medical Center were included from Oct 2006 to Mar 2008. Antimicrobial susceptibility test was performed by broth microdilution method. ESBLs were confirmed by double-disk synergy test and ESBL phenotypes were determined by PCR. RESULTS: The 124 isolates (94 Enterobacter spp., 18 Citrobacter spp., 8 Serratia spp. and 4 Morganella spp.) were investigated. Among 124 ESCM isolates, 30 isolates (24.2%) showed ESBL-producing activity. Derepressed or partially derepressed AmpC mutants and derepressed AmpC mutants with ESBL production accounted for 36.3% (45/124) and 16.9% (21/124), respectively. Of ESBL producers, the most prevalent ESBL was SHV-12 (5/24, 20.8%). CONCLUSIONS: The prevalence of ESBL-producing isolates is high in Enterobacter spp., Serratia marcescens and Citrobacter spp. clinical isolates. It suggested that routine screening test for ESBLs among Enterobacteriacae blood isolates with inducible AmpC beta-lactamase should be needed.

Comparison of 3 Phenotypic-detection Methods for Identifying Plasmid-mediated AmpC beta-lactamase-producing Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis Strains / 대한진단검사의학회지

BACKGROUND: Plasmid-mediated AmpC beta-lactamases (PABLs) have been detected in the strains of Escherichia coli, Klebsiella spp., Proteus mirabilis, and Salmonella spp. PABLs may be difficult to detect and might interfere in the therapeutic and infection-control processes. Although several PABL-detection methods based on phenotypes have been reported, the Clinical and Laboratory Standards Institute currently does not recommend a routine detection method for PABLs. The aim of this study is to compare the performances of 3 phenotypic PABL detection methods. METHODS: Total 276 non-duplicated clinical isolates of E. coli (N=97), K. pneumoniae (N=136), and P. mirabilis (N=43) were collected from 14 hospitals in Korea between April and June 2007 in a non-consecutive and non-random manner. Multiplex PCR was performed to detect the PABL genes. Further, 3 phenotypic detection methods-cephamycin-Hodge test, Tris-EDTA (TE) disk test, and combination-disk test with 3-aminophenylboronic acid (BA)-were performed using cefoxitin and cefotetan disks. RESULTS: PABL genes were detected by multiplex PCR in 122/276 isolates, including 14/97 E. coli, 105/136 K. pneumoniae, and 3/43 P. mirabilis isolates. The combination-disk test with BA showed higher sensitivity (98.4%), specificity (92.2%), and efficiency (96.3%) than the cephamycin-Hodge (76.2%, 96.1%, and 88.6%, respectively) and the TE-disk (80.3%, 91.6%, and 87.9%, respectively) tests. CONCLUSIONS: The combination-disk test with BA is a simple, efficient, and interpretable test that can be applicable in clinical laboratories involved in the detection of PABLs in clinical isolates of E. coli, K. pneumoniae, and P. mirabilis.

Use of Boronic Acid Disks for the Detection of Extended-spectrum beta-lactamase and AmpC beta-lactamase in Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca and Proteus mirabilis / 대한임상미생물학회지

BACKGROUND: Accurate detection of organisms producing extended-spectrum beta-lactamase (ESBL) and AmpC beta-lactamase is very important for treatment of patients. However, unlike the ESBL confirmatory test, there are no guidelines for detection of organisms producing AmpC beta-lactamase. We evaluated a detection method using boronic acid (BA) for ESBL and AmpC beta-lactamase. METHODS: Clinical isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis showing intermediate resistance or resistance to cefoxitin (FOX) or positive for ESBL were tested. A > or =5 mm increase in zone diameter of ceftazidime/clavulanic acid/BA (CAZ/CA/BA) and/or cefotaxime/clavulanic acid/BA (CTX/CA/BA) versus CAZ/BA and/or CTX /BA was considered positive for ESBL. Likewise, a > or =5 mm increase in zone diameter of FOX/BA and/or cefotetan/BA (CTT/BA) versus FOX and/or CTT alone was considered positive for AmpC beta-lactamase. RESULTS: Among 622 clinical isolates, ESBL positive rates by the CLSI ESBL confirmatory test or by the BA method were 18.1% or 18.4% for E. coli, 38.3% or 40.4% for K. pneumoniae, 8.7% or 8.7% for K. oxytoca, and 14.8% or 14.8% for P. mirabilis, respectively. AmpC beta-lactamase positive rates using the BA method were 3.7% for E. coli, 33.3% for K. pneumoniae, 0% for K. oxytoca, and 7.4% for P. mirabilis. The detection rates of coproducing ESBL and AmpC beta-lactamase were 2.4% in E. coli 27.1% in K. pneumoniae, and 3.7% in P. mirabilis. CONCLUSION: The ESBL confirmatory method using BA was found to enhance the detection of ESBLs, even when potentially masked by AmpC beta-lactamase.

First Outbreak of Multidrug-Resistant Klebsiella pneumoniae Producing both SHV-12-Type Extended-Spectrum beta-Lactamase and DHA-1-Type AmpC beta-Lactamase at a Korean Hospital

PURPOSE: Coexistence of different classes of beta-lactamases in a single bacterial isolate may pose diagnostic and therapeutic challenges. We investigated a spread of Klebsiella pneumoniae isolates co-producing an AmpC beta-lactamase and an extended-spectrum beta-lactamase (ESBL) in a university hospital. MATERIALS AND METHODS: Over a three-month period, a total of 11 K. pneumoniae isolates, which exhibited resistance to cefotaxime, aztreonam, and cefoxitin, were isolated. These isolates showed positive to ESBLs by double disk tests. Minimal inhibitory concentrations (MICs) were determined by broth microdilution testing. All isolates were examined by isoelectric focusing, PCR and sequence analysis to identify bla(SHV) and bla(DHA), and molecular typing by pulsed-field gel electrophoresis (PFGE). RESULTS: All 11 isolates were highly resistant (MIC, > or = 128microngram/ml) to ceftazidime, aztreonam, and cefoxitin, while they were susceptible (MIC, < or = 2microngram/ml) to imipenem. The bla(SHV-12) and bla(DHA-1) genes were detected by PCR and sequence analysis. PFGE revealed a similar pattern in 10 of the 11 strains tested. CONCLUSION: This is the first outbreak report of K. pneumoniae in Korea which co-produced SHV-12 and DHA-1 beta-lactamase, and we suggest a clonal spread of multidrug-resistant K. pneumoniae at a hospital.

Epidemiology of Plasmid-Mediated AmpC beta-Lactamase Produced by Clinical Isolates of Klebsiella pneumoniae from Four University Hospitals in Korea / 병원감염관리

BACKGROUND: Plasmid-mediated AmpC beta-lactamases (PABLs) are cephalosporinases that confer resistance to a wide variety of beta-lactam drugs and that may thereby create serious therapeutic problems. The PABL-producing organisms are a major concern in nosocomial infections and should therefore be monitored in surveillance studies. METHODS: During the period of May to July 2004, 27 cefoxitin non-susceptible isolates of Klebsiella pneumoniae from four university hospitals (Seoul 2, Daejeon 1, and Choongju 1) were tested for antimicrobial susceptibility by the broth microdilution method. The cefoxitin non-susceptible isolates were further investigated by the double disk synergy test for extended-spectrum beta-lactamases, multiplex AmpC PCR, DNA sequencing, and pulsed-field gel electrophoresis (PFGE). RESULTS: PABL-producing K. pneumoniae were found in all the four hospitals. Eight (32%) of 25 PABL producers were also tested positive by double disk synergy tests. Susceptibilities of the PABL producers were as follows: ceftazidime, 4%; aztreonam, 36%; cefepime, 76%; and imipenem, 100%. Among the 25 K. pneumoniae isolates were 24 DHA-1 and 1 CMY-1 beta-lactamase producers. The PFGE patterns of the DHA-1-producing K. pneumoniae showed variable as well as identical patterns. CONCLUSION: PABL-producing K. pneumoniae is widespread among medical institutions in Korea. A DHA-1 type in K. pneumoniae was the predominant enzyme detected. Overall, despite many different PFGE patterns of the PABL producers, some outbreak and epidemic clones appear to be prevalent in some hospitals in Korea. For the prevention of the spread of PABL-producing K. pneumoniae, it should be identified accurately by the clinical laboratory.

Purification of AmpC beta-lactamase in Enterobacter cloacae / 临床检验杂志

Objective To purify AmpC beta-lactamase from Enterobacter cloacae and study its physical and chemical characteristics.Methods The bacteria were fragmentized by ultrasonication and AmpC beta-lactamase was purified by ion-exchange.The properties of the purified enzyme,such as molecular weight and isoelectric point were determined by electrophoresis.Results The purified AmpC beta-lactamase was obtained and its specificity to substrate was sufficient for classification of class C cephalosporinase.Conclusion AmpC can be successfully purified from Enterobacter cloacae and is effective for application.

Genes of Extended Spectrum ?-Lactamases and AmpC ?-Lactamase from Klebsiella pneumoniae and Klebsiella oxytoca / 中华医院感染学杂志

OBJECTIVE To study the phenotypic existence,genetic type and gene transfer of extended spectrum beta-lactamases(ESBLs) and AmpC beta-lactamase from Klebsiella pneumoniae and K.oxytoca. METHODS Disk confirmation test and 3-aminophenylboronic acid(APB) disk potentiation test were used to detect ESBLs and AmpC beta-lactamase.The genetic types of these two kinds of beta-lactamases were examined by gene chip technology and sequence analysis.The transfer of resistance genes was conducted by conjugation. RESULTS From 72 strains of K.pneumoniae and 20 strains of K.oxytoca which were not susceptible to cefoxitin,coexistence of AmpC(beta-lactamase) with ESBLs together was very common,accounted for 54.2% and 75.0%,single ESBLs accounted for 22.2% and 25.0%,respectively.There were 12.5% single AmpC in(K.pneumoniae).DHA type ampC gene and SHV type ESBLs gene were the main molecular types.These genes could be transferred from clinical isolates to recipient E.coli J53. CONCLUSIONS ESBLs as well as AmpC(beta-lactamase) are the most important resistance mechanism in K.pneumoniae and K.oxytoca.The resistance could be transferred through the bacterial conjugation.

Emergence of Plasmid-Mediated CMY-2 beta -Lactamase Produced by Clinical Isolates of Escherichia coli in Korea / 대한진단검사의학회지

BACKGROUND: Of the plasmid-mediated AmpC beta-lactamases (ABLs), CMY-2 is the most prevalent and is distributed in many countries. However, little is known about the emergence and characteristics of CMY-2 among Escherichia coli isolates in Korea. The aims of this study were to detect the emergence of the CMY-2 beta-lactamase in clinical isolates of E. coli from various regions in Korea. METHODS: Eighteen cefoxitin non-susceptible isolates of 1, 130 consecutive, nonrepeat isolates of E. coli at five university hospitals were tested for antimicrobial susceptibility by the broth microdilution method. The cefoxitin non-susceptible isolates were further investigated by AmpC disk tests, double disk synergy (DDS) tests, isoelectric focusing, CMY-2-specific PCR, DNA sequencing, and plasmid analysis. RESULTS: Seven (0.6%) isolates of plasmid-mediated ABL-producing E. coli were found at three of the five hospitals; all seven isolates produced CMY-2 beta-lactamase and one of the isolates was also tested positive by the DDS test. All isolates demonstrated different plasmid patterns by plasmid analysis. CONCLUSIONS: Our data indicate that CMY-2-producing E. coli has emerged and is prevalent in the medical institution in Korea. Therefore, constant surveillance is needed to prevent its further spread.

Emergence and Wide Dissemination of CTX-M-type ESBLs, and CMY-2- and DHA-1-type AmpC beta-Lactamases in Korean Respiratory Isolates of Klebsiella pneumoniae

Respiratory isolates of Klebsiella pneumoniae in Korea during 2002-2003 were studied to determine the prevalence and types of extended-spectrum beta-lactamases (ESBLs) and plasmid-mediated AmpC beta-lactamases (PABLs). ESBL-production was tested by double-disk synergy, and genotypes of beta-lactamases were determined by PCR and sequencing. ESBLs were detected in 28.4% of 373 isolates, and the most prevalent types were SHV-12 (63 isolates) and CTX-M-14 (9 isolates). Forty of 75 ESBL-producers (53.5%) also had PABLs: 21 isolates with CMY-2-like, 17 with DHA-1-like. Pulsed-field gel electrophoresis showed 19 types and 25 of 74 isolates had an identical pattern, indicating nosocomial spread. Dissemination of ESBL- and PABL-producing K. pneumoniae strains in Korea is a particular concern, as it limits the choice of antimicrobial agents for treatment of infections.

Antimicrobial Resistance of Clinically Important Bacteria Isolated from 12 Hospitals in Korea in 2004 / 대한임상미생물학회지

BACKGROUND: A rapid increase in antimicrobial-resistant bacteria has become a serious problem in many countries including Korea, but the rate and pattern of antimicrobial resistance may vary significantly depending on countries and even on hospitals. The aim of this study was to determine the nationwide prevalence of resistance among frequently isolated bacterial pathogens in Korea. METHODS: Routine susceptibility data for medically important bacterial pathogens from 12 university hospital and general hospital laboratories in Korea were analysed by patient group. These pathogens had been isolated during the period from April to November in 2004. RESULTS: The proportion of methicillin-resistant Staphylococcus aureus (MRSA) was 67%. Van-comycin-resistance rate of Enterococcus faecalis was 1% and that of E.faecium was 20%. The resistance rates of Streptococcus pneumoniae to penicillin and Haemophilus influenzae to ampicillin were 70% and 54%, respectively. The resistant rates of Escherichia coli and Klebsiella pneumoniae were 7-10% and 26-31% to the 3rd generation cephalosporin, respectively. The resistance rates to 3rd generation cephalosporin were 22-30% in Citrobacter freundii, 35-44% in Enterobacter cloacae and 15-22 % in Serratia marcescens. Imipenem resistance rates of Pseudomonas aeruginosa and Acinetobacter baumannii were 26% and 17%. Cotrimoxazole and levofloxacin resistance rates of Stenotrophomonas maltophilia were 46% and 44%, respectively. CONCLUSION: Antimicrobial resistance rates of clinically important pathogens in Korea were still high and were generally higher among the bacteria isolated from the intensive care unit patients. Strict infection control and continuous nationwide surveillance program will be required to manage the antimicrobial resistance problem.

Isolation of Klebsiella Oxytoca Clinical Isolate Producing AmpC beta-lactamase, DHA-1 / 대한임상미생물학회지

BACKGROUND: Klebsiella oxytoca strain exhibiting an unusual inducible beta-lactam resistance phenotype was isolated from a wound specimen of a patient at a university hospital in August 2002. The isolate was resistant to ampicillin, ampicillin-sulbactam, cephalothin, cefoxitin, and demonstrated reduced inhibition zone diameters for ceftazidime in combination with clavulanate versus those for ceftazidime when tested alone. METHODS: Antimicrobial susceptibilities were tested using the Etest and disk diffusion method. AmpC beta-lactamase production was determined by modified Hodge test. The disk antagonism method was used to detect inducibility of beta-lactamase. Conjugation experiments were performed by the filter mating method using the recipient Escherichia coli J53 Azir strain. PCR and DNA sequencing of DHA-specific PCR products were tested. RESULTS: The double disk synergy test was negative and the modified Hodge test was positive for the K. oxytoca isolate. Antagonism was observed between cefoxitin and oxyimino-cephalosporins. Sequence analysis of the DHA-specific PCR products revealed that they were identical to the amino acid sequence of the DHA-1 beta-lactamase. Transfer of the resistance by conjugation experiments was successful. CONCLUSIONS: We found a plasmid-mediated DHA-1 beta-lactamase-producing K. oxytoca possessing an unusual inducible beta-lactam resistance phenotype was found in a university hospital in Korea. The resistance phenotype was conferred by DHA-1 encoded by a self-transferable plasmid.

Antimicrobial Resistance of Clinically Important Bacteria Isolated from 12 Hospitals in Korea / 대한임상미생물학회지

BACKGROUND: A rapid increase in antimicrobial-resistant bacteria has become a serious problem in Korea. Moreover, the antibiotic resistance problem has worsened noticeably during the past several years. The aim of this study was to determine the prevalence of resistance among frequently isolated gram-positive and -negative bacteria in Korea. METHODS: Routine susceptibility data for medically important bacteria isolated during 6 months of 2003 were collected from 12 university and general hospital laboratories in Korea. RESULTS: The proportion of methicillin-resistant Staphylococcus aureus (MRSA) was 66%; however, vancomycin-resistant strains were not detected. The rates of vancomycin-resistant Enterococcus faecium and penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) were 22% and 73%, respectively. The resistance rates to 3rd generation cephalosporins and monobactam were: Escherichia coli 8-12%, Klebsiella pneumoniae 18-22%, Citrobacter freundii 22-32%, Enterobacter cloacae 34-37%, and Serratia marcescens 12-21%, respectively. Imipenem resistance rates of Acinetobacter baumannii and Pseudomonas aeruginosa were 23% and 25%, respectively. CONCLUSIONS: Antimicrobial resistant strains were already prevalent among the clinically important isolates, especially, MRSA, PNSP, and extended-spectrum cephalosporin resistant gram-negative bacilli in Korea. The imipenem-resistant rates of A. baumannii and P. aeruginosa increased, respectively, from 13% and 20% in 2002 to 23% and 25% in 2003. The results of this study will provide a basis for proper treatment of bacterial infections and prevention of spread of resistant bacteria. A continuous nationwide surveillance of antimicrobial resistance is very important and should be performed.

Isolation Trend of Enterobacter, Citrobacter, and Serratia for the Recent Five Years and Antimicrobial Susceptibility of Derepressed AmpC beta-lactamase Producing Strains / 감염

BACKGROUND: Derepressed AmpC beta-lactamase producing Enterobacter cloacae, Citrobacter f reundii, and Serratia marcescens are important nosocomial pathogens and the infections are difficult to treat, because they are multi-drug resistant. The aim of this study was to determine the isolation rate and trend, and antimicrobial susceptibility of derepressed strains isolated from clinical specimens. METHODS: E. cloacae, S. marcescens, and C. f reundii isolated from 1996 through 2000 were enrolled in the study. Antimicrobial susceptibility was tested by NCCLS disk diffusion method. Derepressed strain was defined as strain non-susceptible to third generation cephalosporin. The isolation patterns of important gram-negative bacilli with the derepressed strains were analyzed with respect to years, patient's locations and specimens. RESULTS: Among the clinical isolates, the derepressed strains of E. cloacae, S. marcescens, and C. f reundii were 65%, 70%, and 56%. The proportion of the derepressed strains : E. cloacae increased from 68% in 1996 to 71% in 1998, however, decreased to 59% in 2000, S. marcescens increased from 68% in 1996 to 73% in 2000, C. f reundii decreased from 69% in 1996 to 41% in 2000. The proportion of the derepressed strains were high among the isolates from blood and respiratory specimens of inpatient and intensive care patient. The resistance rates of the depressed strains were 47~62% to third generation cephalosporin and aztreonam, 15~85% to aminoglycoside, 68% to cotrimoxazole, and 31% to levofloxacin. CONCLUSION: Among the clinical isolates of E. cloacae, S. marcescens, and C. f reundii, the derepressed strains were as high as 56~70%, and they were commonly isolated from blood and sputum specimens of inpatient and intensive care patient, and showed high resistance rates to the most antimicrobial agents.

Detection of Genotypes of Plasmid-mediated AmpC ?-Lactamase and Analysis of Antimicrobial Resistance of Klebsiella pneumoniae in Harbin / 中华医院感染学杂志

OBJECTIVE To determine the drug resistance phenotype and genotype of plasmid-mediated AmpC ?-lactamase in Klebsiella pneumoniae isolated from Harbin.METHODS Isolates of K.pneumoniae with an inhibition ring to cefoxitin of ≤18 mm diameter were used.Antimicrobial susceptibilities were determined by disc diffusion method.AmpC genes were detected by PCR with six pairs of primers.RESULTS Sixty-three isolates had an inhibition ring to cefoxitin of ≤18 mm diameter and 26(11.3%)were detected to be AmpC-producing in a total of 231 clinical isolates of K.pneumoniae.Seventy-six percent,70.2%,53.8%,50.5%,57.7%,38.5% and 7.7% of AmpC-producers were resistant to cefoxitin,cefotaxime,ceftazidime,amoxicillin/clavulanic cid,ciprofloxacin,amikacin and imipenem,respectively.ACT,DHA and CIT types of AmpC beta-lactamase were detected in 13,8 and 5 isolates,respectively.No ACC,MOX and FOX were detected.CONCLUSIONS The AmpC ?-lactamase in Harbin is mainly in the types of ACT,DHA and CIT.AmpC-producing K.pneumoniae shows decreased susceptibilities to cefoxitin and third generation cephalosporins.