[Recent evolution and characterization of extended-spectrum beta-lactamase producing enterobacteria in the CHU of Nice (2005-2007)]. / Evolution récente et caractérisation des entérobactéries productrices de BLSE au CHU de Nice (2005-2007).

AIM OF THE STUDY: ESBL producing enterobacteria (E-ESBL+) are always a public health concern, mainly due to increase of CTX-M beta-lactamase. So, 542 new strains were isolated in the CHU de Nice during the 2005-2007 period. The aim of this work was to characterize the ESBL and to type isolates suspected to be implicated in outbreaks. METHODS: Every first E-ESBL+ was studied, the antibiotype was defined by the agar diffusion technique. Type of ESBL was determined by PCR, followed by sequencing for CTX-M and SHV enzymes. Typing was performed when several strains of one species had same antibiotype and beta-lactamase. RESULTS: CTX-M type ESBL are predominant (45% of all E-ESBL+), mainly in Escherichia coli (34.5%). The TEM24 ESBL was the second predominant type (34.5%), mainly in Enterobacter aerogenes (18.6%) and Klebsiella pneumoniae (9.4%). SHV5/12 ESBL was found mainly in Enterobacter cloacae (7.5%). Several epidemic situations were identified, with CTX-M15 in Escherichia coli (2005/2006: 27 patients), SHV5/12 in Enterobacter cloacae (2006: 10 patients) and TEM in Proteus mirabilis (2007: nine patients). Enterobacter aerogenes is still endemic (101 patients) while an epidemic clone of TEM24 producing K. pneumoniae persists especially in an intensive care unit (26 patients during the three years). CONCLUSION: Caracterization of E-ESBL+ is essential to better understand their mode of dissemination, monitor the emergence of new enzymes and adapt the efforts against BMR cross transmission.

[Phenotypes of beta-lactam resistance in the genus Aeromonas]. / Phénotypes de résistance aux beta-lactamines dans le genre Aeromonas.

This work aimed to investigate resistance profiles towards beta-lactam antibiotics in correlation with beta-lactamases production in the genus Aeromonas. In a series of 417 wild-type strains, biochemical identification and testing with 11 beta-lactams by the disk-diffusion method revealed 5 predominant phenotypes: A. hydrophila complex/class B, C and D beta-lactamases; A. caviae complex/class C and D beta-lactamases; A. veronii complex/class B and D beta-lactamases; A. schubertii spp./class D beta-lactamase; A. trota spp./class C beta-lactamase. A subgroup of 64 representative strains was submitted to MIC determination with 8 beta-lactam compounds alone and in combination with 3 beta-lactamase inhibitors (clavulanic acid, tazobactam and BRL 42715). Visualisation of beta-lactamases and pI determination were performed in all these 64 isolates by isoelectric focusing from crude extracts. The different Aeromonas species produced 1 to 3 of the following inducible enzymes: an imipenemase with low expression, which is difficult to detect with routine phenotype studies (class B, pI 8, imipenem MIC > 2 micrograms/ml), a cephalosporinase (class C, pI > 7 +/- 0.5, cephalothin MIC > 256 micrograms/ml), and an oxacillinase widely produced in the genus Aeromonas (class D, pI > 8.5, ticarcillin MIC > 256 micrograms/ml). In Aeromonas spp. resistance profile to beta-lactam antibiotics is correlated with naturally occurring phenotypes of beta-lactamases production. As a conclusion, the characterisation of these different enzymes is of therapeutic and taxonomic interest, in species notoriously difficult to identify.

A seven-year survey of Klebsiella pneumoniae producing TEM-24 extended-spectrum beta-lactamase in Nice University Hospital (1994-2000).

The aim of this study was to investigate TEM-24-producing isolates of Klebsiella pneumoniae, and their clonal dissemination in Nice University Hospital. During the 1994-2000 period, a total of 263 non-repetitive isolates of ESBL-producing K. pneumoniae were collected. Most of these isolates were highly resistant in vitro to ceftazidime, cefotaxime and aztreonam, but susceptible to cefoxitin and imipenem. Resistance profile analysis revealed seven predominant antibiotypes (P1 to P7). Isoelectric focusing evidenced beta-lactamase activity, with a chromosomal penicillinase (pl 7.7), and one or two additional enzymes with pls ranging from 5.4 to 8.2 identified as presumed TEM-1 pl 5.4, TEM-3 pl 6.3, TEM-24 pl 6.5, SHV-3 pl 7.0, SHV-4 pl 7.8, SHV-5 pl 8.2, or other unidentified beta-lactamases. Among these K. pneumoniae, 130 isolates produced TEM-24, and 115 of them were highly resistant in vitro to quinolones (antibiotype P1). This phenotype was responsible for an outbreak in a medical intensive care unit from March to September 2000. Four isolates submitted were genetical sequenced, and shared 99.9% homology with tem-24 (GenBank no. X 65253). Pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus polymerase chain reaction (PCR) (ERIC2-PCR) applied to 28 non-epidemic and six epidemic isolates yielded concordant results. Molecular typing revealed the persistence and dissemination of a single clone of TEM-24 producing K. pneumoniae in Nice Hospital during the seven-year study period.

Induced colistin resistance as an identifying marker for Aeromonas phenospecies groups.

AIMS: To investigate the taxonomic interest of colistin resistance as an identifying marker for Aeromonas phenospecies groups. METHODS AND RESULTS: Colistin resistance was investigated in 387 Aeromonas isolates identified at species level using a 14-test format protocol with miniaturized tests combined with determination of urocanic acid utilization whenever necessary. Colistin resistance, determined by the disc diffusion method, was unreliable when compared with minimum inhibitory concentration (MIC) determination. In some strains, the MIC values and resistance rates of colistin could be increased after overnight induction with a 50- microg colistin disc in 20 ml of Mueller-Hinton broth (2.5 mg l(-1)). Colistin-induced resistance level was raised to 85.8% in the Aeromonas hydrophila complex, 2.1% in the A. caviae complex and 2.5% in the A. veronii complex except for A. jandaei (100% colistin resistant). This new marker allowed the identification of 96.2 and 93.6% of Aeromonas isolates to phenospecies and species level, respectively. CONCLUSIONS: Colistin-induced colistin resistance is a new phenotypic marker for Aeromonas isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: With the present protocol, colistin resistance determination may improve the identification of Aeromonas isolates to phenogroup level, when results obtained by conventional biochemical methods are ambiguous.

High prevalence of cfxA beta-lactamase in aminopenicillin-resistant Prevotella strains isolated from periodontal pockets.

This prospective study was designed to investigate amoxicillin-resistant oral anaerobes, and to identify their beta-lactamase-encoding genes. Three subgingival bacterial samples were collected from 12 patients suffering from periodontitis. One to seven beta-lactamase-producing strains were obtained from each patient, mostly belonging to the Prevotella genus (Bacteroides eggerthii, 2/35 strains; Prevotella sp., 33/35 strains). PCR assays were used to detect cfxA and cepA/cblA, the genes encoding class A/group2e beta-lactamases previously described in the Bacteroides fragilis group. The present investigation confirmed the role of Prevotella species as beta-lactamase producers in periodontal pockets. Additionally, this PCR screening showed (1): the high prevalence of CfxA beta-lactamase production by aminopenicillin-resistant Prevotella (32/33: 97.0% positive strains) vs. cepA/cblA (1/33: 3.0% positive strains), and (2) the presence of cfxA in the periodontal reservoir in the absence of antimicrobial therapy during the previous 6 months.