AmpC-producing Enterobacteriaceae Research Articles

Retraction: Plagiarism in Detection of ESBL among ampc producing enterobacteriaceae using inhibitor-based method (Pan Afr Med J. 2013;14:28)

We, editors of The Pan African Medical Journal hereby notify readers of the retraction of the article "Detection of ESBL among ampc producing enterobacteriaceae using inhibitor-based method" by Bakthavatchalu S et al. [1] published in 2013. It has come to the attention of the editorial team that this article shares striking similarities with the article “Comparison of the boronic acid disk potentiation test and cefepime-clavulanic acid method for the detection of ESBL among AmpC-producing Enterobacteriaceae.” by Shoorashetty RM et al.[2], published in the Indian Journal of Medical Microbioly in 2011. An internal investigation has raised sufficient evidence of plagiarism; as such, we retract this article from the literature in accordance with guidelines and best editorial practices from the Committee on Publication Ethics. We apologize to our audience about this unfortunate situation.

Risk factors of community-onset urinary tract infections caused by plasmid-mediated AmpC β-lactamase-producing Enterobacteriaceae

The AmpC β-lactamase (AmpC)-producing Enterobacteriaceae emerged worldwide. This study was conducted to determine the risk factors of community-onset urinary tract infections (UTIs) caused by plasmid-mediated AmpC-producing Enterobacteriaceae. Patients who were diagnosed as community-onset UTIs caused by Enterobacteriaceae in a tertiary-care teaching hospital from December 2010 to January 2012 were included. Extended-spectrum β-lactamase (ESBL)-producing isolates were excluded. We identified plasmid-mediated AmpC-producing Enterobacteriaceae both phenotypically (by disk potentiation test and double-disk synergy test) and genotypically (by Multiplex polymerase chain reaction (PCR) assay). The demographic data, clinical characteristics, and risk factors of acquisition were described. Among the 323 non-ESBL-producing Enterobacteriaceae identified in community-onset UTIs, 50 isolates were phenotypically positive for AmpC. Escherichia coli was the most common AmpC-producing organism (60%), followed by Klebsiella pneumonia (8%), and Enterobacter cloacae and Proteus mirabilis (6% for each species). The independent risk factors for acquisition of AmpC-producing Enterobacteriaceae included prior history of cerebral vascular accident [odds ratio (OR) = 2.014; 95% confidence interval (CI) = 1.007-4.031; p = 0.0048], and prior use of fluoroquinolones (OR = 4.049; 95% CI = 1.759-9.319; p = 0.001) and cephamycin (OR = 9.683; 95% CI = 2.007-45.135; p = 0.004). AmpC-producing isolates were multidrug resistant. Carbapenems, cefepime, and piperacillin/tazobactam had the best in vitro efficacy. The most commonly identified plasmid-mediated AmpC gene was bla(CIT), followed by bla(DHA)/bla(EBC), and bla(MOx). For community-onset UTIs, AmpC-producing Enterobacteriaceae should be suspected in those with prior history of cerebral vascular accident and prior use of antimicrobials. To treat these multiple-resistant isolates, carbapenems, cefepime, and piperacillin/tazobactam may be considered.

Extended spectrum ß-lactamase- and constitutively AmpC-producing Enterobacteriaceae on fresh produce and in the agricultural environment

The attribution of fresh produce to the overall community-associated exposure of humans to ESBL- or AmpC-producing bacteria is currently unknown. To address this issue, the prevalence of ESBL- and AmpC-producing Enterobacteriaceae on fresh produce produced in the Netherlands was determined. Seven vegetable types that are consumed raw were selected: blanched celery, bunched carrots, chicory, endive, iceberg lettuce, mushrooms, and radish. The vegetables were mostly obtained from supermarkets. To determine whether the agricultural environment is the source of ESBL-producing Enterobacteriaceae on fresh produce, iceberg lettuce was also obtained directly from three farms, in conjunction with soil and irrigation water. ESBL-producing Enterobacteriaceae isolated from vegetables and environment were all environmental species: Rahnella aquatilis (n=119), Serratia fonticola (n=45) and Pantoea agglomerans (n=1). ESBL genes of R. aquatilis and S. fonticola were identified as blaRAHN-1 and blaRAHN-2 and blaFONA-1, blaFONA-2, blaFONA-3/6 and blaFONA-5, respectively. For R. aquatilis and S. fonticola, different prevalence numbers were observed using different isolation methods, which could at least partially be explained by an inverse correlation between the level of cefotaxime resistance of these species and incubation temperature. R. aquatilis was isolated from 0 to 46% of soil samples and 11 to 83% of vegetable samples, and S. fonticola from 2 to 60% of soil samples and 0 to 1.3% of vegetable samples. Third generation cephalosporin-resistant faecal Enterobacteriaceae were isolated from 2.7%, 1.3% and 1.1% of supermarket vegetables, iceberg lettuce from farms, and agricultural soil respectively. Faecal Enterobacteriaceae were all identified as Citrobacter and Enterobacter species and, with the exception of one Citrobacter koseri strain, all had phenotypes indicative of constitutive AmpC production. Comparison of fresh produce and its agricultural environment indicates that the Enterobacteriaceae population on fresh produce reflects that of the soil it is grown in.Public health risks associated with exposure to ESBL- and AmpC-producing bacteria through consumption of uncooked fresh produce are diverse. They range from occasional ingestion of 3GC-resistant opportunistic pathogens which may result in difficult-to-treat infections, to frequent ingestion of relatively harmless ESBL-producing environmental bacteria that may therewith constitute a continuously replenished intestinal reservoir facilitating dissemination of ESBL genes to (opportunistic) pathogens.

Molecular epidemiology, resistance profiles and clinical features in clinical plasmid-mediated AmpC-producing Enterobacteriaceae

During the 30 months of surveillance period, 85 pAmpC-producing isolates were detected (prevalence 0.56% overall): blaCMY-2 gene in 70 E. coli, 2 K. pneumoniae and 6 P. mirabilis isolates; and the blaDHA-1 gene in 4 E. coli and 3 K. pneumoniae. In 8.23% of them, other β-lactamases (predominantly OXA-1) were identified. All pAmpC-producing isolates were susceptible to carbapenems, whereas high resistance to nalidixic acid, ciprofloxacin and trimethoprim-sulfamethoxazole was observed among pAmpC-producing isolates (80%, 60%, and 44.7%, respectively). In hospital patients, predisposing factors such as prior antibiotic use, previous hospitalization, presence of an indwelling device, invasive urinary tract procedures and mechanical ventilation were observed. In the community setting, urinary tract infection was the most common type of infection related to pAmpC-producing isolates. A wide heterogeneity of clones was found among our E. coli isolates by PFGE, suggesting that this mechanism of resistance is not due to the dissemination of a clonal strain. Surveillance of these resistance mechanisms in the community is thus needed. Awareness of pAmpC dynamic is required to prevent introduction into hospitals and to control the spread of this emerging resistance within the community.

Detection of ESBL among ampc producing enterobacteriaceae using inhibitor-based method

IntroductionThe occurrence of multiple β-lactamases among bacteria only limits the therapeutic options but also poses a challenge. A study using boronic acid (BA), an AmpC enzyme inhibitor, was designed to detect the combined expression of AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs) in bacterial isolates further different phenotypic methods are compared to detect ESBL and AmpC.MethodsA total of 259 clinical isolates of Enterobacteriaceae were isolated and screened for ESBL production by (i) CLSI double-disk diffusion method (ii) cefepime- clavulanic acid method (iii) boronic disk potentiation method. AmpC production was detected using cefoxitin alone and in combination with boronic acid and confirmation was done by three dimensional disk methods. Isolates were also subjected to detailed antibiotic susceptibility test.ResultsAmong 259 isolates, 20.46% were coproducers of ESBL and AmpC, 26.45% were ESBL and 5.40% were AmpC. All of the 53 AmpC and ESBL coproducers were accurately detected by boronic acid disk potentiation method.ConclusionThe BA disk test using Clinical and Laboratory Standards Institute methodology is simple and very efficient method that accurately detects the isolates that harbor both AmpCs and ESBLs.

Impact of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry on the Clinical Management of Patients With Gram-negative Bacteremia: A Prospective Observational Study

Early identification of pathogens from blood cultures using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry may optimize the choice of empirical antibiotic therapy in the setting of bloodstream infections. We aimed to assess the impact of this new technology on the use of antibiotic treatment in patients with gram-negative bacteremia. We conducted a prospective observational study from January to December 2010 to evaluate the sequential and separate impacts of Gram stain reporting and MALDI-TOF bacterial identification performed on blood culture pellets in patients with gram-negative bacteremia. The primary outcome was the impact of MALDI-TOF on empirical antibiotic choice. Among 202 episodes of gram-negative bacteremia, Gram stain reporting had an impact in 42 cases (20.8%). MALDI-TOF identification led to a modification of empirical therapy in 71 of all 202 cases (35.1%), and in 16 of 27 cases (59.3%) of monomicrobial bacteremia caused by AmpC-producing Enterobacteriaceae. The most frequently observed impact was an early appropriate broadening of the antibiotic spectrum in 31 of 71 cases (43.7%). In total, 143 of 165 episodes (86.7%) of monomicrobial bacteremia were correctly identified at genus level by MALDI-TOF. In a low prevalence area for extended spectrum betalactamases (ESBL) and multiresistant gram-negative bacteria, MALDI-TOF performed on blood culture pellets had an impact on the clinical management of 35.1% of all gram-negative bacteremia cases, demonstrating a greater impact than Gram stain reporting. Thus, MALDI-TOF could become a vital second step beside Gram stain in guiding the empirical treatment of patients with bloodstream infection.

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Introduction: Anecdotally, an increase in early isolates of Serratia, Pseudomonas, Acinetobacter, Citrobacter and Enterobacter (SPACE) species from respiratory specimens was noted in patients admitted to our trauma-orthopedics-vascular (TOV) intensive care unit (ICU). Given the guideline-recommended empiric anti-infective therapy for early pneumonia may not provide sufficient coverage for SPACE organisms, specifically Pseudomonas and AmpC-producing Enterobacteriaceae, patients may receive inadequate initial anti-infective therapy. Hypothesis: We hypothesize that SPACE respiratory isolates are being identified early, defined < 5 days following admission, in our TOV ICU patients. Methods: Medical records of 212 patients with gram negative respiratory isolates (GNRI) and admitted to TOV ICU from November 1st, 2009 to May 31st, 2012 were retrospectively reviewed. The primary aim of the study is to evaluate the number of GNRI with SPACE species. The secondary aim is to determine the times between admission, intubation, and respiratory cultures with SPACE organisms. Results: Cultures from 83% of patients grew at least one SPACE organism. In approximately 1/3 of patients with GNRI, a SPACE organism was isolated < 5 days following admission. The median times between first GNRI positive for a SPACE organism and hospital and ICU admissions were 7.3 days and 6.6 days, respectively. The median time between first intubation and GNRI positive for SPACE organism was 6.4 days. Conclusions: Of TOV ICU patients with GNRI, the majority were SPACE organisms. Although the median time from admission to SPACE respiratory isolate was > 5 days, about 1/3 of patients with GNRI yielded a SPACE organism < 5 days, which remains concerning given current anti-infective recommendations for early pneumonia. Patient specific characteristics of these patients with early pulmonary SPACE isolates will be collated for trends or risk factors. These data will facilitate both the use of targeted anti-infective therapy in our ICU setting as well as the development of quality improvement initiatives that may optimize anti-infective utilization.

Comparison of different phenotypic assays for the detection of extended-spectrum β-lactamase production by inducible AmpC-producing Gram-negative bacilli

Routine detection of extended-spectrum β-lactamase (ESBL) production by AmpC-producing Enterobacteriaceae in microbiology laboratories is still a problem. The aim of this study was to compare the performance of four different phenotypic ESBL confirmation assays within this group of Enterobacteriaceae. A total of 83 AmpC-inducible Enterobacteriaceae were included in this study (58 clinical isolates with presumptive ESBL production and 25 molecularly characterized ESBL-producing isolates). Each isolate was tested for the presence of an ESBL enzyme by four phenotypic ESBL confirmation assays: ESBL Etests and combined double-disk synergy tests (CDDST), both on Mueller-Hinton (MH) agar with and without the use of cloxacillin, an AmpC inhibitor. Our study showed that performing a CDDST on MH agar with cefotaxime as the only indicator cephalosporin is not a reliable way to detect ESBL-encoding genes among chromosomal AmpC-producing Enterobacteriaceae due to its low sensitivity (52 %). The use of cloxacillin in this CDDST could only significantly increase the specificity of the CDDST when used with ceftazidime as the indicator [sensitivity (SN), 92 %; specificity (SP), 93 %]. Regarding ESBL Etest® strips, the sensitivity of the cefepime strip (80 %) was significantly higher compared to the cefotaxime and ceftazidime strips (16 % and 32 %, respectively). Adding cloxacillin to the MH agar improved the ESBL detection of each of these strips. We recommend the CDDST on MH agar supplemented with cloxacillin and ceftazidime or cefepime as the indicator cephalosporin as the most cost-efficient strategy to confirm ESBL production in inducible AmpC-producing Enterobacteriaceae.

Molecular Characteristics of Extended-Spectrum Beta-Lactamases and qnr Determinants in Enterobacter Species from Japan

The incidence of extended-spectrum β-lactamases (ESBLs) has been increasing worldwide, but screening criteria for detection of ESBLs are not standardized for AmpC-producing Enterobacteriaceae such as Enterobacter species. In this study, we investigated the prevalence of ESBLs and/or AmpC β-lactamases in Japanese clinical isolates of Enterobacter spp. and the association of plasmid-mediated quinolone resistance (PMQR) determinants with ESBL producers. A total of 364 clinical isolates of Enterobacter spp. collected throughout Japan between November 2009 and January 2010 were studied. ESBL-producing strains were assessed by the CLSI confirmatory test and the boronic acid disk test. PCR and sequencing were performed to detect CTX-M, TEM, and SHV type ESBLs and PMQR determinants. For ESBL-producing Enterobacter spp., pulsed-field gel electrophoresis (PFGE) was performed using XbaI restriction enzyme. Of the 364 isolates, 22 (6.0%) were ESBL producers. Seven isolates of Enterobacter cloacae produced CTX-M-3, followed by two isolates producing SHV-12. Two isolates of Enterobacter aerogenes produced CTX-M-2. Of the 22 ESBL producers, 21 had the AmpC enzyme, and six met the criteria for ESBL production in the boronic acid test. We found a significant association of qnrS with CTX-M-3-producing E. cloacae. The 11 ESBL-producing Enterobacter spp. possessing bla CTX-M, bla SHV, or bla TEM were divided into six unique PFGE types. This is the first report about the prevalence of qnr determinants among ESBL-producing Enterobacter spp. from Japan. Our results suggest that ESBL-producing Enterobacter spp. with qnr determinants are spreading in Japan.

An evaluation of the Mast D69C AmpC Detection Disc Set for the detection of inducible and derepressed AmpC -lactamases

Sir, The emergence of Enterobacteriaceae that can produce AmpC b-lactamases is a major worldwide concern. They have arisen through acquisition of a plasmid-mediated ampC gene or hyperproduction of an inducible chromosomal AmpC enzyme, either by induction or derepression. These organisms are resistant to penicillins, first-, secondand third-generation cephalosporins and b-lactamase inhibitor/b-lactam combinations. Therapeutic options to treat these infections are severely limited and often not included in empirical therapy guidelines for serious infections. Rapid detection of AmpC-producing Enterobacteriaceae is therefore essential in order that patients can be optimally managed at an early stage without indiscriminate use of broad-spectrum antibiotics. Methods available for the detection of AmpC producers are relatively unsatisfactory and there are no established guidelines, as there are for the detection of extended-spectrum b-lactamase (ESBL)-producing organisms. We evaluated the commercial D69C AmpC Detection Disc Set (Mast Group Ltd, UK). This system is based on a combination disc method that incorporates cefpodoxime (CPD10) as the screening agent in the presence of AmpC-inducing or -inhibiting agents (exact formulations undisclosed), enabling the detection of both plasmid-mediated and chromosomal AmpC, whether inducible or derepressed. An ESBL inhibitor is additionally included to unmask and minimize interference from any ESBL that may be present on the AmpC detection system. Three discs are used: A (CPD10+AmpC inducer), B (CPD10+AmpC inducer+ESBL inhibitor) and C (CPD10+AmpC inducer+ESBL inhibitor+AmpC inhibitors). A total of 103 previously characterized isolates (comprising 80 AmpC+, 15 AmpC2/ESBL+, 1 AmpC2/KPC+ and 7 AmpC2/ ESBL2 strains) were blindly tested using the detection kit. These isolates were a combination of reference strains and clinical isolates that had been characterized by genotypic or disc diffusion methods, and included strains with chromosomal derepressed, inducible and plasmid-mediated AmpC resistance mechanisms. The Enterobacteriaceae represented were Escherichia coli, Klebsiella pneumoniae, Morganella morganii, Citrobacter freundii, Enterobacter cloacae, Enterobacter aerogenes and Serratia marcescens. Testing and interpretation were performed according to the manufacturer’s instructions. Isolates were sub-cultured onto Mueller–Hinton agar to achieve semi-confluent growth. The three discs were placed on the plate as far apart as possible, and the plate was incubated at 378C in air for 18–24 h. The organisms were interpreted as ‘AmpC negative’ if all zone sizes differed by ≤3 mm and as ‘AmpC positive’ if the zone size of disc C exceeded those of both discs A and B by at least 5 mm. If zone sizes of both discs B and C exceeded that of disc A by at least 5 mm and the zone sizes of discs B and C had a difference of ,5 mm, the isolate was classified as ‘AmpC negative, but exhibits a different resistance mechanism’. As shown in Table 1, The D69C kit correctly determined the AmpC status of all 80 AmpC+ and 23 AmpC2 isolates tested. Amongst the 23 AmpC2 isolates, 12 out of the 15 AmpC2/ ESBL+ isolates and the 1 AmpC2/KPC+ isolate were correctly classified as ‘AmpC negative, but exhibits a different resistance mechanism’. All seven AmpC2/ESBL2 isolates were correctly identified as ‘AmpC negative’. The kit failed to detect the presence of a different resistance mechanism in 3 out of 15 AmpC2/ESBL+ isolates—they were an SHV ESBL+ K. pneumoniae, a TEM/CTX-M ESBL+ E. coli and a TEM/SHV+ ESBL+ E. coli. There is no immediate explanation for these results, particularly since several other TEM, SHV and CTX-M ESBL+ isolates were correctly identified as ‘exhibiting another resistance mechanism’. The ESBL activity might have been masked by the AmpC inducer (incorporated into all three discs), and hence these results highlight an important limitation of the D69C kit, i.e. it is solely a method for AmpC detection, and its use cannot be extrapolated to ESBL detection. The ESBL inhibi-

Occurrence and characteristics of extended-spectrum-β-lactamase- and AmpC-producing clinical isolates derived from companion animals and horses

To investigate the occurrence and characteristics of extended-spectrum β-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae isolates in clinical samples of companion animals and horses and compare the results with ESBL/AmpC-producing isolates described in humans. Between October 2007 and August 2009, 2700 Enterobacteriaceae derived from clinical infections in companion animals and horses were collected. Isolates displaying inhibition zones of ≤ 25 mm for ceftiofur and/or cefquinome by disc diffusion were included. ESBL/AmpC production was confirmed by combination disc tests. The presence of resistance genes was identified by microarray, PCR and sequencing, Escherichia coli genotypes by multilocus sequence typing and antimicrobial susceptibility by broth microdilution. Sixty-five isolates from dogs (n = 38), cats (n = 14), horses (n = 12) and a turtle were included. Six Enterobacteriaceae species were observed, mostly derived from urinary tract infections (n = 32). All except 10 isolates tested resistant to cefotaxime and ceftazidime by broth microdilution using clinical breakpoints. ESBL/AmpC genes observed were bla(CTX-M-1, -2, -9, -14, -15,) bla(TEM-52), bla(CMY-2) and bla(CMY-)(39). bla(CTX-M-1) was predominant (n = 17). bla(CTX-M-9) occurred in combination with qnrA1 in 3 of the 11 Enterobacter cloacae isolates. Twenty-eight different E. coli sequence types (STs) were found. E. coli carrying bla(CTX-M-1) belonged to 13 STs of which 3 were previously described in Dutch poultry and patients. This is the first study among a large collection of Dutch companion animals and horses characterizing ESBL/AmpC-producing isolates. A similarity in resistance genes and E. coli STs among these isolates and isolates from Dutch poultry and humans may suggest exchange of resistance between different reservoirs.

Escherichia coli Producing CMY-2 β-Lactamase in Bovine Mastitis Milk

An Escherichia coli isolate producing the CMY-2 β-lactamase was found in the milk of a cow with recurrent subclinical mastitis. The isolate was resistant to the antibiotics commonly used for intramammary mastitis treatment, such as penicillins, cephalosporins, β-lactam/β-lactamase inhibitor combinations, aminoglycosides, tetracyclines, and sulfonamides. This is the first report of a plasmid-mediated AmpC-producing Enterobacteriaceae in bovine milk.

High prevalence of extended-spectrum -lactamases and qnr determinants in Citrobacter species from Japan: dissemination of CTX-M-2

Extended-spectrum β-lactamases (ESBLs) have become a problem among AmpC-producing Enterobacteriaceae and the emergence of concomitant quinolone resistance in β-lactamase-producing isolates poses a global threat. In this study we investigated the prevalence and regional variation of ESBLs in Japanese clinical isolates of Citrobacter spp. and analysed plasmid-mediated quinolone resistance (PMQR) determinants in ESBL-producing Citrobacter spp. A total of 348 clinical isolates of Citrobacter spp. collected throughout Japan were studied. Screening and the boronic acid disc test were performed to detect ESBLs in Citrobacter spp. with chromosomal AmpC β-lactamases. PCR and sequencing were done to identify ESBL and PMQR genes. For ESBL-producing Citrobacter spp., PFGE was performed using the SfiI restriction enzyme. The number of ESBL-producing isolates confirmed phenotypically was 67 (19.3%). The prevalence of ESBL-producing Citrobacter koseri was significantly higher (32.1%) than that of ESBL-producing Citrobacter freundii (4.6%) (P < 0.01). Moreover, the prevalence of ESBLs was notably higher among C. koseri from southern Japan (60.0%). CTX-M-2 was predominant in C. koseri. Of the ESBL-producing C. koseri analysed, 23.2% possessed PMQR determinants, and there was a significant association between qnrB4 and bla(SHV-12). The 57 ESBL-producing Citrobacter spp. possessing bla(CTX-M), bla(SHV) or bla(TEM) were divided into 18 unique PFGE types. This is the first report about the prevalence of PMQR determinants among ESBL-producing Citrobacter spp. from Japan. Our data suggest that ESBLs and PMQR determinants are spreading among C. koseri in Japan.

Comparison of the boronic acid disk potentiation test and cefepime–clavulanic acid method for the detection of ESBL among AmpC-producing Enterobacteriaceae

Purpose: Extended spectrum β-lactamase (ESBL) and AmpC β-lactamase are important mechanisms of betalactam resistance among Enterobacteriaceae. The ESBL confirmation test described by Clinical Laboratory Standards Institute (CLSI) is in routine use. This method fails to detect ESBL in the presence of AmpC. Therefore, we compared two different ESBL detection methods against the CLSI confirmatory test. Materials and Methods: A total 200 consecutive clinical isolates of Enterobacteriaceae from various clinical samples were tested for ESBL production using (i) CLSI described phenotypic confirmatory test (PCT), (ii) boronic acid disk potentiation test and (iii) cefepime–CA disk potentiation method. AmpC confirmation was done by a modified three-dimensional test. Results: Among total 200 Enterobacteriaceae isolates, 82 were only ESBL producers, 12 were only AmpC producers, 55 were combined ESBL and AmpC producers, 14 were inducible AmpC producers and 37 isolates did not harboured any enzymes. The CLSI described PCT detected ESBL-producing organisms correctly but failed to detect 36.3% of ESBLs among combined enzyme producers. The boronic acid disk potentiation test reliably detected all ESBL, AmpC, and combined enzyme producers correctly. The cefepime–CA method detected all ESBLs correctly but another method of AmpC detection has to be adopted. Conclusion: The use of boronic acid in disk diffusion testing along with the CLSI described PCT enhances ESBL detection in the presence of AmpC betalactamases.

Risk factors and clinical features of infections caused by plasmid-mediated AmpC β-lactamase-producing Enterobacteriaceae

A case–control study was performed with the objective of analysing risk factors and clinical features of infections caused by plasmid-mediated AmpC β-lactamase (plasmid AmpC)-producing Enterobacteriaceae. All patients infected with plasmid AmpC-producing Enterobacteriaceae in two tertiary care hospitals from December 2006 to August 2007 were included. Plasmid AmpC enzymes were characterised by isoelectric focusing, enzyme inhibition assay and enzyme-specific polymerase chain reaction. A total of 30 patients (20 with Klebsiella pneumoniae and 10 with Escherichia coli) were recruited prospectively. CMY-2 and DHA-1 were the most common plasmid AmpC in E. coli and K. pneumoniae, respectively. An independent risk factor for infection with plasmid AmpC-producing Enterobacteriaceae was the use of an oxyimino-cephalosporin within 1 month of plasmid AmpC infection [adjusted odds ratio (aOR), 10.8, 95% confidence interval (CI), 1.6–75.4; P = 0.016], with the use of a urinary catheter showing borderline significance (aOR, 6, 95% CI 0.93–38.4; P = 0.06). An independent risk factor for treatment failure at 72 h was infection due to plasmid AmpC-producing Enterobacteriaceae (aOR, 9.78, 95% CI 1.34–71.17; P = 0.02). These results suggest that infections caused by plasmid AmpC-producing isolates significantly increase treatment failure at 72 h and that prior use of an oxyimino-cephalosporin is a risk factor for infections caused by plasmid AmpC-producing Enterobacteriaceae.

Prevalence and characteristics of aac(6′)-Ib-cr in AmpC-producing Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens: a multicenter study from Korea

We investigated the prevalence of aac(6′)-Ib-cr and its association with other resistance genes in AmpC-producing Enterobacteriaceae without any selection criteria. A total of 479 clinical isolates of Enterobacter cloacae (179), Citrobacter freundii (134), and Serratia marcescens (166) from 12 laboratories between March and July 2005 were examined. We performed polymerase chain reaction for aac(6′)-Ib, bla OXA-1, IS Ecp1, and class 1 integron. The aac(6′)-Ib-cr was further identified by digestion with BstF5I and sequencing. The aac(6′)-Ib was detected in 110 (23%) of 479 isolates, and 15 isolates (3.1%) were cr variants (8 E. cloacae, 5 C. freundii, and 2 S. marcescens). The aac(6′)-Ib-cr was significantly associated with various resistance genes ( bla OXA-1, qnrS, qnrA, bla CTX-M-3, and bla CTX-M-14), mobile elements (IS Ecp1, IS CR1, and class 1 integron), and quinolone resistance. Eleven of 15 aac(6′)-Ib-cr producers coharbored qnr genes. Although aac(6′)-Ib-cr was uncommon in Korean AmpC producers, its association with various resistance genes and mobile elements would facilitate the dissemination of this variant.

Characterization of TEM-, SHV- and AmpC-type β-lactamases from cephalosporin-resistant Enterobacteriaceae isolated from swine

Extended-spectrum β-lactamase (ESBL) and AmpC-producing Enterobacteriaceae are an increasing problem in human medicine and an emerging problem in the veterinary field. Our study, therefore, focused on assessing the prevalence of β-lactamases isolated from swine. Sixty-six Salmonella enterica serovar Typhimurium ( S. Typhimurium), 33 Salmonella enterica serovar Enteritidis ( S. Enteritidis), 26 Klebsiella pneumonia ( K. pneumoniae) and 130 Escherichia coli ( E. coli) pig isolates collected from 1999–2006 were screened for β-lactam resistance by the disk diffusion test (DDT) and micro-broth dilution. Among the isolates, five E. coli and five K. pneumoniae exhibited reduced susceptibility to the cephalosporins tested. PCR, plasmid profiling and Southern blot hybridization showed the presence of multiple β-lactamases in these isolates of animal origin. Hybridization patterns of the DHA-1 specific probe indicated that dissemination of DHA-1 related β-lactamases could be attributed to plasmids of one common size among the enteric microbes of animal origin. To the best of our knowledge, this study reports the first identification of SHV-28 and DHA-1 from microbes of animal origin.

Doripenem

Doripenem, a parenteral, broad-spectrum antibacterial agent of the carbapenem family, is indicated as empirical therapy in serious bacterial infections in adults. Doripenem is indicated in Japan for use as a single agent in intra-abdominal infections (IAIs), lower respiratory tract infections (including nosocomial pneumonia), complicated urinary tract infections (cUTIs) and a variety of other bacterial infections, such as complicated skin and skin structure infections (cSSSIs), obstetric and gynaecological infections, serious ear, nose and throat infections, sepsis and endocarditis, dental and oral surgical infection, and ophthalmic infection caused by various susceptible strains of Gram-negative, Gram-positive or anaerobic bacteria. Doripenem is indicated in the US for the treatment of complicated IAIs (cIAIs) or cUTIs, including pyelonephritis, caused by susceptible strains of designated pathogens, and in the EU for the treatment of nosocomial pneumonia (including ventilator-associated pneumonia [VAP]), cIAIs or cUTIs.Doripenem has a broad spectrum of in vitro activity against Gram-positive and Gram-negative bacteria, including extended-spectrum beta-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae, and anaerobic pathogens. The drug also has a low propensity to select for resistance and is suitable for the prolonged infusions that may be required to achieve pharmacodynamic/pharmacokinetic targets for bactericidal activity (and therefore efficacy) against pathogens with increased MICs (minimum concentrations required to inhibit the pathogens). Doripenem is no less effective than other antibacterial agents, including meropenem, imipenem/cilastin, piperacillin/tazobactam or levofloxacin in a wide range of serious bacterial infections, such as complicated lower respiratory infections, nosocomial pneumonia (including VAP), cIAIs and cUTIs, and is well tolerated. Thus, doripenem is a valuable addition to the options available for the empirical treatment of serious bacterial infections in hospitalized patients.

Meropenem

Meropenem (Merrem, Meronem) is a broad-spectrum antibacterial agent of the carbapenem family, indicated as empirical therapy prior to the identification of causative organisms, or for disease caused by single or multiple susceptible bacteria in both adults and children with a broad range of serious infections. Meropenem is approved for use in complicated intra-abdominal infection (cIAI), complicated skin and skin structure infection (cSSSI) and bacterial meningitis (in paediatric patients aged > or = 3 months) in the US, and in most other countries for nosocomial pneumonia, cIAI, septicaemia, febrile neutropenia, cSSSI, bacterial meningitis, complicated urinary tract infection (UTI), obstetric and gynaecological infections, in cystic fibrosis patients with pulmonary exacerbations, and for the treatment of severe community-acquired pneumonia (CAP). Meropenem has a broad spectrum of in vitro activity against Gram-positive and Gram-negative pathogens, including extended-spectrum beta-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae. It has similar efficacy to comparator antibacterial agents, including: imipenem/cilastatin in cIAI, cSSSI, febrile neutropenia, complicated UTI, obstetric or gynaecological infections and severe CAP; clindamycin plus tobramycin or gentamicin in cIAI or obstetric/gynaecological infections; cefotaxime plus metronidazole in cIAI; cefepime and ceftazidime plus amikacin in septicaemia or febrile neutropenia; and ceftazidime, clarithromycin plus ceftriaxone or amikacin in severe CAP. Meropenem has also shown similar efficacy to cefotaxime in paediatric and adult patients with bacterial meningitis, and to ceftazidime when both agents were administered with or without tobramycin in patients with cystic fibrosis experiencing acute pulmonary exacerbations. Meropenem showed greater efficacy than ceftazidime or piperacillin/tazobactam in febrile neutropenia, and greater efficacy than ceftazidime plus amikacin or tobramycin in patients with nosocomial pneumonia. Meropenem is well tolerated and has the advantage of being suitable for administration as an intravenous bolus or infusion. Its low propensity for inducing seizures means that it is suitable for treating bacterial meningitis and is the only carbapenem approved in this indication. Thus, meropenem continues to be an important option for the empirical treatment of serious bacterial infections in hospitalized patients.

Prevalence and diversity of qnr alleles in AmpC-producing Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii and Serratia marcescens: a multicentre study from Korea

To investigate the prevalence of qnr determinants, their influence on quinolone susceptibility and their association with other plasmid-mediated genes in AmpC-producing Enterobacteriaceae without any selection criteria. A total of 644 consecutive, non-duplicate isolates of Enterobacter cloacae (186), Enterobacter aerogenes (154), Citrobacter freundii (138) and Serratia marcescens (166) were examined. We performed antimicrobial susceptibility testing and PCR for qnr determinants (qnrA, qnrB and qnrS), extended-spectrum beta-lactamase (ESBL) (bla(TEM), bla(SHV) and bla(CTX-M)), orf513, orf1005 and bla(DHA-1.) To differentiate qnr subtypes, restriction enzyme analysis and sequencing was performed. The prevalence of qnr determinants was high in C. freundii (38.4%) and E. cloacae (28.5%), but low in E. aerogenes (3.2%) and S. marcescens (2.4%). qnrA1 was most frequent in E. cloacae, and qnrB was prevalent in C. freundii. All the qnrA- and qnrB4-positive isolates showed ciprofloxacin MICs > or = 0.5 mg/L and nalidixic acid MICs > or = 16 mg/L. However, the B1 and B2 subtypes showed a wide range of quinolone MICs. In relation to ESBLs, we found that qnrA1, qnrB2 and qnrB4 producers were significantly more frequent among ESBL producers (P < 0.05). Twelve of 13 qnrB4 producers harboured bla(DHA-1). orf513 was detected in 43 isolates of the 47 isolates with co-resident qnr and ESBL genes. None of the qnr producers harboured orf1005. The prevalence of qnrA and qnrB was high among C. freundii and E. cloacae in Korea and there were characteristics unique to the qnr subtypes. Quinolones should be used cautiously in these species, especially when they are ESBL producers.