Susceptibility of Campylobacter hyointestinalis subsp. hyointestinalis to antimicrobial agents and characterization of quinolone-resistant strains.
OBJECTIVE
To study the susceptibility of Campylobacter hyointestinalis subsp. hyointestinalis to several antimicrobial agents and to investigate the mechanisms of nalidixic acid and ciprofloxacin resistance.


METHODS
The disc diffusion method was employed to study the susceptibility of 49 C. hyointestinalis subsp. hyointestinalis strains of reindeer and bovine origin to 12 different antimicrobial agents. In addition, the MICs of nalidixic acid and ciprofloxacin were determined. The nucleotide sequence of a 270 bp fragment of the gyrA gene was determined in ciprofloxacin-susceptible and -resistant strains. The effect of a multidrug efflux pump inhibitor Phe-Arg-beta-naphthylamide (PA beta N) on the MICs of ciprofloxacin and nalidixic acid was also studied.


RESULTS
The only decreased susceptibility for antimicrobial agents of this study was observed for sulphonamide compound and streptomycin (24% and 32% of the strains, respectively), and this phenomenon was observed exclusively in the bovine strains. In sequence studies, a Thr-86-->Ile change was found in strains with MICs of ciprofloxacin of > or = 64 mg/L, but this mutation was absent in strains with lower resistance levels. The use of PA beta N did not affect the MIC of ciprofloxacin but decreased the MIC of nalidixic acid 2-4-fold.


CONCLUSIONS
The Finnish C. hyointestinalis subsp. hyointestinalis strains are susceptible to a majority of the antimicrobials of veterinary importance. The mechanism of ciprofloxacin resistance at lower levels (< or = 32 mg/L) is not associated with a specific mutation in the quinolone resistance-determining region of the gyrA gene. Finally, there are distinct differences in the mechanisms of ciprofloxacin resistance compared with nalidixic acid resistance within the studied species.
Laatu
Minna
M
Department of Food and Environmental Hygiene, Faculty of Veterinary Medicine, PO Box 57, FIN-00014 University of Helsinki, Finland. minna.laatu@helsinki.fi
Rautelin
Hilpi
H
Hänninen
Marja-Liisa
ML
D000818:Animals; D044862:Campylobacter hyointestinalis / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology; D002417:Cattle; D002939:Ciprofloxacin / Q000494:pharmacology*; D004352:Drug Resistance, Microbial / Q000502:physiology*; D008826:Microbial Sensitivity Tests / Q000706:statistics & numerical data; D009268:Nalidixic Acid / Q000494:pharmacology*; D015363:Quinolones / Q000494:pharmacology; D012053:Reindeer
D015363:Quinolones; D009268:Nalidixic Acid; D002939:Ciprofloxacin