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

Abstract

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 >128 mg=L) and 38 were simultaneously resistant to florfenicol (MICs >16 mg=L) and to â-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 florfenicolresistant isolates could represent a clonal cluster, closely related to, if not of DT104 phage type, which appeared in 1989 and is now predominant within chloramphenicolresistant S. Typhimurium. The multiplex PCR provided a useful tool to survey further evolution of multiresistant S. Typhimurium strains.

Molecular Epidemiology of Ceftiofur-Resistant Escherichia coli Isolates from Dairy Calves

“…Similar cross-resistance has also been reported for Salmonella spp. (2,4). All E. coli strains were sensitive to the fluoroquinolone antibiotic Eno.…”

Molecular characterization, spread and evolution of multidrug resistance in Salmonella enterica Typhimurium DT104

“…Multiplex PCR based on the surrounding genes of the antibiotic resistance gene cluster has also been proposed for the identification of S. enterica Typhimurium DT104 strains [5,12,26]. In the light of evidence of horizontal transfer of the DT104 antibiotic resistance gene cluster to other Typhimurium phage types or other S. enterica serovars [18], these methods appear to be no longer suitable for the specific detection of multidrug-resistant S. enterica Typhimurium DT104.…”

Epidemiology, Clinical Presentation, Laboratory Diagnosis, Antimicrobial Resistance, and Antimicrobial Management of Invasive Salmonella Infections

“…Resistance to ampicillin is often mediated through ␤-lactamases (e.g., bla PSE and bla TEM ), whereas several mechanisms may be associated with chloramphenicol resistance. Three types of chloramphenicol acetyltransferases (CATs) (types I to III) have been described in Gram-negative bacteria, but resistance due to the production of CAT of type I has been encountered most frequently in Enterobacteriaceae (411). Genes involving nonenzymatic resistance mechanisms, such as cmlA and floR, have also been found in Salmonella enterica (411,412).…”

“…Three types of chloramphenicol acetyltransferases (CATs) (types I to III) have been described in Gram-negative bacteria, but resistance due to the production of CAT of type I has been encountered most frequently in Enterobacteriaceae (411). Genes involving nonenzymatic resistance mechanisms, such as cmlA and floR, have also been found in Salmonella enterica (411,412). Both trimethoprim and sulfamethoxazole are folate pathway inhibitors that prevent the synthesis of DNA.…”