Comparison of gyrA mutations, cyclohexane resistance, and the presence of class I integrons in Salmonella enterica from farm animals in England and Wales.
This study is focused on real-time detection of gyrA mutations and of the presence of class I integrons in a panel of 100 veterinary isolates of Salmonella enterica from farm animals. The isolates were selected on the basis of resistance to nalidixic acid, representing a variety of the most prevalent serotypes in England and Wales. In addition, organic solvent (cyclohexane) resistance in these isolates was investigated in an attempt to elucidate the presence of efflux pump mechanisms. The most prevalent mutation among the isolates studied was Asp87-Asn (n = 42), followed by Ser83-Phe (n = 38), Ser83-Tyr (n = 12), Asp87-Tyr (n = 4), and Asp87-Gly (n = 3). Two distinct subpopulations were identified, separated at the 1-mg/liter breakpoint for ciprofloxacin: 86% of isolates with mutations in codon 83 showed MICs of >or=1 mg/liter, while 89.8% of isolates with mutations in codon 87 presented MICs of <or=0.5 mg/liter. Cyclohexane resistance was more prevalent among Ser83 mutants than among Asp87 mutants (34.7 and 4%, respectively), and in 79% of isolates that presented both gyrA mutations and cyclohexane resistance, the level of ciprofloxacin resistance was >or=2.0 mg/liter. Thirty-four isolates contained class I integrons, with 71% of the S. enterica serovar Typhimurium isolates and 6.9% of isolates belonging to other serotypes containing such elements. The methods used represent sensitive ways of investigating the presence of gyrA mutations and of detecting class-I integrons in Salmonella isolates. The results can be obtained in less than 1 h from single colonies without the need for purifying DNA.
Liebana
Ernesto
E
Department of Bacterial Diseases, Veterinary Laboratories Agency-Weybridge, Addlestone, Surrey KT15 3NB, UK. E.liebana@VLA.DEFRA.gsi.gov.UK
Clouting
Carol
C
Cassar
Claire A
CA
Randall
Luke P
LP
Walker
Rachel A
RA
Threlfall
E John
EJ
Clifton-Hadley
Felicity A
FA
Ridley
Anne M
AM
Davies
Robert H
RH
D000818:Animals; D000829:Animals, Domestic; D000890:Anti-Infective Agents / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D003510:Cyclohexanes / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D004739:England; D019426:Integrases / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D019779:Salmonella enterica / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D014852:Wales
D000890:Anti-Infective Agents; D003510:Cyclohexanes; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D019426:Integrases; C115006:integron integrase IntI1; D027081:DNA Gyrase