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CAT III chloramphenicol resistance in Pasteurella haemolytica and Pasteurella multocida isolated from calves
C Vassort-Bruneau1, M C Lesage-Descauses, J L Martel
1Institut National de la Recherche Agronomique, Centre de Tours-Nouzilly, Monnaie, France.
Abstract:
Chloramphenicol, which had been used extensively for antimicrobial veterinary therapy, was prohibited in Europe in 1994. Soon after it became available, resistance to this drug was detected, generally conferred by plasmids encoding inactivating enzymes, the chloramphenicol acetyltransferases (CAT), in Gram-negative as well as in Gram-positive bacteria. In the last few years, resistance to antibiotics emerged in Pasteurella strains from breeding herds and this evolution was followed by a national surveillance network. Chloramphenicol-resistance was more recently detected in multiresistant strains. We studied 25 strains of Pasteurella, selected for their resistance to chloramphenicol. Production of a CAT was demonstrated in all these strains. PCR amplification indicated that the CAT produced was of type III for 23 of them. In these strains, chloramphenicol-resistance was mediated by plasmids of about 5.1 kb. Southern blots on restriction fragments suggested a high degree of homology between these 5.1 kb plasmids. In the two other strains, production of a CAT type I was demonstrated, and the corresponding genes were either shown on a plasmid of 17 or 5.5 kb.
Insights
Chloramphenicol resistance in Pasteurella strains is linked to specific chloramphenicol acetyltransferase (CAT) enzymes, primarily type III, often carried on plasmids. This finding is crucial for understanding antibiotic resistance in veterinary pathogens.
Area of Science:
- Microbiology
- Veterinary Medicine
- Molecular Biology
- Antimicrobial Resistance
Background:
- Chloramphenicol, once widely used in veterinary therapy, was banned in Europe in 1994 due to emerging resistance.
- Resistance is often plasmid-mediated, involving chloramphenicol acetyltransferases (CAT) enzymes in both Gram-negative and Gram-positive bacteria.
- Recent antibiotic resistance in Pasteurella strains from breeding herds has been monitored by a national surveillance network.
Purpose of the Study:
- To investigate the mechanisms of chloramphenicol resistance in 25 selected Pasteurella strains.
- To characterize the specific chloramphenicol acetyltransferase (CAT) types and associated genetic elements involved in resistance.
Main Methods:
- Phenotypic detection of CAT enzyme production in resistant Pasteurella strains.
- Polymerase Chain Reaction (PCR) amplification to identify the specific type of CAT enzyme.
- Plasmid analysis, including size determination and Southern blotting, to investigate the genetic basis of resistance.
Main Results:
- All 25 studied Pasteurella strains demonstrated chloramphenicol resistance due to CAT production.
- CAT type III was identified in 23 strains, with resistance mediated by approximately 5.1 kb plasmids showing high homology.
- The remaining two strains produced CAT type I, with resistance genes located on plasmids of 17 kb or 5.5 kb.
Conclusions:
- Chloramphenicol resistance in these Pasteurella strains is primarily mediated by plasmid-borne chloramphenicol acetyltransferase enzymes, predominantly type III.
- The high homology among the 5.1 kb plasmids carrying CAT type III suggests a common origin or efficient spread mechanism.
- Understanding these resistance mechanisms is vital for managing antimicrobial use in veterinary settings and preventing further spread.