β-lactam-resistance phenotypes in the genus 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 I 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 mug/ml), a cephalosporinase (class C, pI >7 +/- 0.5, cephalothin MIC >256 mug/ml), and an oxacillinase widely produced in the genus Aeromonas (class D, pI >8.5, ticarcillin MIC >256 mug/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. (C) 2003 Editions scientifiques et medicales Elsevier SAS. Tous droits reserves.