First Detection of the Ambler Class C 1 AmpC β-Lactamase in
            <i>Citrobacter freundii</i>
            by a New, Simple Double-Disk Synergy Test

Ruppé, Étienne; Bidet, Philippe; Verdet, Charlotte; Arlet, Guillaume; Bingen, Édouard

doi:10.1128/jcm.00918-06

Cited by 45 publications

(42 citation statements)

References 38 publications

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“…Otherwise, ACCtype enzymes are characteristically inhibited by cefoxitin visible as enhancement of the inhibition zones (synergy phenomena) of expanded-spectrum cephalosporins and cefoxitin. With this strategy, the detection of ACC-type AmpC enzymes is possible, although ACC enzymes appear to be cefoxitin susceptible (1,22). In contrast, cefoxitin screening by MIC alone would miss ACC types.…”

Section: Discussionmentioning

confidence: 99%

Practical Approach for Reliable Detection of AmpC Beta-Lactamase-Producing Enterobacteriaceae

et al. 2011

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In this prospective study all Enterobacteriaceae isolates (n ‫؍‬ 2,129) recovered in the clinical microbiology laboratory during October 2009 to April 2010 were analyzed for AmpC production. Clinical and Laboratory Standards Institute (CLSI) cefoxitin and cefotetan susceptibility breakpoints and CLSI critical ESBL diameters were used to screen for potential AmpC producers. In total, 305 isolates (211 potential AmpC producers and 94 AmpC screen-negative isolates as a control group) were further analyzed by multiplex PCR for the detection of plasmid-encoded ampC beta-lactamase genes and by ampC promoter sequence analysis (considered as the gold standard). Cefoxitin and cefotetan were assessed as primary screening markers. The sensitivities of cefoxitin and cefotetan for the detection of AmpC production were 97.4 and 52.6%, respectively, and the specificities were 78.7 and 99.3%, respectively. As a phenotypic confirmation test, the Etest AmpC and the cefoxitin-cloxacillin double-disk synergy method (CC-DDS) were compared. The sensitivities for the Etest AmpC and the CC-DDS method were 77.4 and 97.2%, respectively, and the specificity was 100% for both methods. The results of the Etest AmpC were inconclusive for 10 isolates. With the CC-DDS method 2 inconclusive results were observed. Based on this study, we propose a comprehensive diagnostic flow chart for the detection of AmpC production consisting of a simple phenotypic screening and a single phenotypic confirmation test with inconclusive results being resolved by molecular analysis. For the proposed flow chart using (i) cefoxitin as a screening marker for AmpC production, (ii) the CC-DDS method as phenotypic confirmation, and (iii) molecular methods in case of inconclusive results, the sensitivity and specificity for AmpC detection would have been 97.4 and 100%, respectively, with respect to the studied isolates. The phenotypic methods used in the AmpC algorithm are simple to perform and easy to implement in the diagnostic laboratory.

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Section: Discussionmentioning

confidence: 99%

Practical Approach for Reliable Detection of AmpC Beta-Lactamase-Producing Enterobacteriaceae

et al. 2011

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“…ACC-1 itself is inhibited by cefoxitin, and thus strains carrying it may appear cefoxitin susceptible (1,16,32). ACC-1 was first isolated in Germany and in several other European countries (1,25,30,32). Recently, the AmpC betalactamase ACC-4 was identified in E. coli, conferring increased MICs for oxyimino-cephalosporins, with low MICs for cefoxitin and cefepime (28).…”

Section: Discussionmentioning

confidence: 99%

“…However, the use of cefoxitin as a screening marker is compromised by isolates producing plasmid-encoded AmpC beta-lactamases of the ACC family. ACC-1 itself is inhibited by cefoxitin, and thus strains carrying it may appear cefoxitin susceptible (1,16,32). ACC-1 was first isolated in Germany and in several other European countries (1,25,30,32).…”

Section: Discussionmentioning

confidence: 99%

Detection of AmpC Beta-Lactamase in Escherichia coli: Comparison of Three Phenotypic Confirmation Assays and Genetic Analysis

et al. 2011

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Two mechanisms account for AmpC activity in Escherichia coli, namely, mutations in the ampC promoter and attenuator regions resulting in ampC overexpression and acquisition of plasmid-carried ampC genes. In this study, we analyzed 51 clinical E. coli isolates with reduced susceptibility to amoxicillin-clavulanic acid, piperacillin-tazobactam, or extended-spectrum cephalosporins for the presence of AmpC production. Three phenotypic AmpC confirmation assays (cefoxitin-cloxacillin disk diffusion test, cefoxitin-EDTA disk diffusion test, and AmpC Etest) were compared for the detection of AmpC activity. All 51 isolates were characterized genetically by mutational analysis of the chromosomal ampC promoter/attenuator region and by PCR detection of plasmid-carried ampC genes. Altogether, 21/51 (41%) E. coli isolates were considered true AmpC producers. AmpC activity due to chromosomal ampC promoter/attenuator mutations was found in 12/21 strains, and plasmid-carried ampC genes were detected in 8/21 isolates. One strain contained both ampC promoter mutations and a plasmid-carried ampC gene. All three phenotypic tests were able to detect the majority (>90%) of AmpC-positive strains correctly. Cefoxitin resistance was found to be a discriminative parameter, detecting 20/21 AmpC-producing strains. Susceptibility to extended-spectrum cephalosporins, e.g., ceftriaxone, ceftazidime, and cefotaxime, was found in 9 of the 21 AmpC-positive strains. Considering the elevated zone diameter breakpoints of the 2010 CLSI guidelines, 2/21 AmpC-positive strains were categorized as susceptible to extended-spectrum cephalosporins.

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“…Strain K-12, MG1655, was used as a colicin-sensitive strain. Strain J53, with natural rifampin (rifampicin) resistance, was used for conjugal transfer of plasmids as previously described (51).…”

Section: Methodsmentioning

confidence: 99%

The Plasmid of Escherichia coli Strain S88 (O45:K1:H7) That Causes Neonatal Meningitis Is Closely Related to Avian Pathogenic E. coli Plasmids and Is Associated with High-Level Bacteremia in a Neonatal Rat Meningitis Model

et al. 2009

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A new Escherichia coli virulent clonal group, O45:K1, belonging to the highly virulent subgroup B2 1 was recently identified in France, where it accounts for one-third of E. coli neonatal meningitis cases. Here we describe the sequence, epidemiology and function of the large plasmid harbored by strain S88, which is representative of the O45:K1 clonal group. Plasmid pS88 is 133,853 bp long and contains 144 protein-coding genes. It harbors three different iron uptake systems (aerobactin, salmochelin, and the sitABCD genes) and other putative virulence genes (iss, etsABC, ompT P , and hlyF). The pS88 sequence is composed of several gene blocks homologous to avian pathogenic E. coli plasmids pAPEC-O2-ColV and pAPEC-O1-ColBM. PCR amplification of 11 open reading frames scattered throughout the plasmid was used to investigate the distribution of pS88 and showed that a pS88-like plasmid is present in other meningitis clonal groups such as O18:K1, O1:K1, and O83:K1. A pS88-like plasmid was also found in avian pathogenic strains and human urosepsis strains belonging to subgroup B2 1 . A variant of S88 cured of its plasmid displayed a marked loss of virulence relative to the wild-type strain in a neonatal rat model, with bacteremia more than 2 log CFU/ml lower. The salmochelin siderophore, a known meningovirulence factor, could not alone explain the plasmid's contribution to virulence, as a salmochelin mutant displayed only a minor fall in bacteremia (0.9 log CFU/ml). Thus, pS88 is a major virulence determinant related to avian pathogenic plasmids that has spread not only through meningitis clonal groups but also human urosepsis and avian pathogenic strains.Escherichia coli is the second cause of neonatal bacterial meningitis in industrialized countries, after group B streptococci. Despite advances in neonatal care, E. coli neonatal meningitis (ECNM) remains a potentially devastating illness, with a mortality rate of 10 to 15% and neurological sequelae in 30 to 50% of cases (8,20,28,29,62). Like most extraintestinal pathogenic E. coli (ExPEC) strains, ECNM strains mainly belong to phylogenetic group B2 and compose a small number of

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First Detection of the Ambler Class C 1 AmpC β-Lactamase in Citrobacter freundii by a New, Simple Double-Disk Synergy Test

Cited by 45 publications

References 38 publications

Practical Approach for Reliable Detection of AmpC Beta-Lactamase-Producing Enterobacteriaceae

Practical Approach for Reliable Detection of AmpC Beta-Lactamase-Producing Enterobacteriaceae

Detection of AmpC Beta-Lactamase in Escherichia coli: Comparison of Three Phenotypic Confirmation Assays and Genetic Analysis

The Plasmid of Escherichia coli Strain S88 (O45:K1:H7) That Causes Neonatal Meningitis Is Closely Related to Avian Pathogenic E. coli Plasmids and Is Associated with High-Level Bacteremia in a Neonatal Rat Meningitis Model

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