Jean-Louis Martel

Plasmid-Mediated Florfenicol Resistance Encoded by the floR Gene in Escherichia coli Isolated from Cattle

ABSTRACT A florfenicol resistance gene almost identical to floRof Salmonella enterica serovar Typhimurium DT104 was detected on 110- to 125-kb plasmids in Escherichia coliisolates of animal origin. Analysis of the floR gene flanking regions of one of the plasmids showed that they were different from those encountered in S. enterica serovar Typhimurium DT104.

Emergence of aminoglycoside 3-N-acetyltransferase IV in Escherichia coli and Salmonella typhimurium isolated from animals in France.

We studied two outbreaks of calf salmonellosis caused by apramycin and gentamicin-resistant Salmonella typhimurium strains. In both cases, the responsible strains were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, tetracycline, and trimethoprim; one strain was also resistant to nalidixic acid in one outbreak. A systematic survey of the intestinal Escherichia coli strains of calves from the two affected flocks showed that 11 of 24 animals sampled were also colonized by apramycin- and gentamicin-resistant E. coli strains. These isolates belonged to four biotypes and were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, tetracycline, trimethoprim, and nalidixic acid. All of the strains were resistant to high levels of apramycin (MICs, 512 to 1,024 micrograms/ml) and to gentamicin (MICs, 8 to 32 micrograms/ml), and these resistances were always transferred en bloc. In S. typhimurium, this coresistance was borne by plasmids that were approximately 39 kilobases long (outbreak 1) or 90 kilobases long (outbreak 2), whereas in E. coli, the coresistance was due to plasmids that were approximately 110 kilobases long in both outbreaks. The two plasmids of Salmonella and four plasmids of E. coli encoded type IV aminoglycoside 3-N-acetyltransferases. The intensive use of curative and preventive treatments in calf production could be responsible for the emergence of enzymic resistance to apramycin and gentamicin. Images

Evolution of chloramphenicol resistance, with emergence of cross-resistance to florfenicol, in bovine Salmonella Typhimurium strains implicates definitive phage type (DT) 104.

The prevalence of resistance to florfenicol, a phenicol drug newly introduced in veterinary therapy, was determined in 86 chloramphenicol-resistant Salmonella Typhimurium isolates from cattle collected during 1985-1995. All were highly resistant to chloramphenicol (MICs > or = 128 mg/L) and 38 were simultaneously resistant to florfenicol (MICs >16 mg/L) and to beta-lactam agents, spectinomycin, streptomycin, sulphonamides and tetracyclines. The isolates susceptible to florfenicol harboured the chloramphenicol acetyl transferase gene, cat of type I. All the florfenicol-resistant isolates harboured the floR resistance gene and the characteristic multiple resistance genetic locus, previously characterised in a S. Typhimurium DT104 strain and identified by a multiplex PCR. Plasmid profiles and ribotype patterns were determined for all the isolates. The florfenicol-resistant isolates were grouped into the same ribotyping pattern and presented similar plasmid profiles, whereas the florfenicol-susceptible isolates showed a wider genetic diversity that is usual for S. Typhimurium. Thus, the florfenicol-resistant isolates could represent a clonal cluster, closely related to, if not of DT104 phage type, which appeared in 1989 and is now predominant within chloramphenicol-resistant S. Typhimurium. The multiplex PCR provided a useful tool to survey further evolution of multiresistant S. Typhimurium strains.

The French antibiotic resistance monitoring programs

Surveillance of antimicrobial resistance in bacteria from animal origin in France is organised by the French Agency for Food Safety (Agence Française de Sécurité Sanitaire des Aliments, AFSSA) through two types of networks. The first collects non-human zoonotic Salmonella strains in one centre (AFSSA, Paris) where they are tested for their antimicrobial susceptibility. The others, managed by AFSSA Lyon, deal with bovine pathogenic strains and are multicentric, that is they collecting antibiotic sensitivity and other data from the local public veterinary diagnostic laboratories. This requires standardisation of the methods used in each partner laboratory. Statistical analysis of any change in French resistance patterns can be monitored by these three networks either as a function of strain pathogenicity and/or of the ecological origin of the isolate. The system also encourages efficient collaboration between veterinarians and the laboratory. Such collaboration improves both the quality of routine antibiotic testing and understanding of the molecular mechanisms underlying resistance.

Detection of a second mechanism of resistance to gentamicin in animal strains of Escherichia coli.

One mechanism of plasmid-mediated resistance to gentamicin in Escherichia coli strains isolated from animals is due to the synthesis of the aminoglycoside 3-N-acetyltransferase type IV. A second mechanism of plasmid-mediated resistance to gentamicin was detected in animal strains of E. coli in France and is due to the production of the aminoglycoside 3-N-acetyltransferase type II. The molecular relationships among plasmids encoding this enzyme were studied. Images