[Carbenicillin resistance of gram-negative bacteria: incidence, biochemical and genetic determinism]

Of nine hundred ampicillin resistant (Amp-R) enterobacteria strains, isolated in hospital between July and December 1981, 73,7% are also carbenicillin-resistant (Carb-R). This particular double resistance varies depending upon the species considered: indole positive Proteus (23%), Enterobacter cloacae (64%), Citrobacter freundii (67%), Acinetobacter calcoaceticus (73%), Proteus mirabilis (75%), Serratia marcescens (90%), Escherichia coli (91%), Providencia stuartii (96%) and Klebsiella pneumoniae (100%). The biochemical and genetic basis of resistance to beta-lactamines was studied in 27 strains belonging to these 9 species. A constitutive beta-lactamase was found in all the strains. These enzymes were identified by determination of the isoelectric point on crude sonic extracts, the enzymic activity profile, the inhibition by clavulanic acid and cloxacillin of enzyme activity. Two types of enzymes were predominant: TEM-1 (20 strains) and TEM-2 (7 strains); two strains of Klebsiella pneumoniae produced both SHV-1 and TEM-1. The transfer by conjugation to E. coli K12 of ampicillin and carbenicillin resistance was obtained with 14 strains: (E. coli: 9, C. freundii: 1, K. pneumoniae: 1, E. cloacae: 2, P. stuartii: 1). In all strains but one E. coli we noted the co-transfer of other antibiotic resistance markers.