Acquisition of quinolone resistance and point mutation of the gyrA gene in Campylobacter jejuni isolated from broilers and in vitro-induced resistant strains

Two distinct mutations in gyrA lead to ciprofloxacin and nalidixic acid resistance in Campylobacter coli and Campylobacter jejuni isolated from chickens and beef cattle

AIMS

The aim of this study was to identify point mutations in the gyrA quinolone resistance determining region (QRDR) of Campylobacter coli (n = 27) and Campylobacter jejuni (n = 26) that confer nalidixic acid (NAL) resistance without conferring resistance to ciprofloxacin (CIP).

METHODS AND RESULTS

Point mutations in the QRDR of gyrA from C. coli and C. jejuni isolates were identified by direct sequencing. All isolates (n = 14) with minimum inhibitory concentrations (MICs) >or=4 microg ml(-1) for CIP and >or=32 microg ml(-1) for NAL possessed a missense mutation leading to substitution of Ile for Thr at codon 86. Three isolates with a missense mutation leading to a Thr86Ala substitution had MICs <4 mug ml(-1) for CIP and >or=32 microg ml(-1) for NAL.

CONCLUSIONS

These data confirm previous findings that Thr86Ile mutations confer resistance to both CIP and NAL. However, resistance to NAL alone was conferred by a single Thr86Ala mutation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Resistance to NAL alone arises independently from CIP resistance. In addition, the role of other previously described point mutations in quinolone resistance is discussed.

Emergence of Fluoroquinolone Resistance in Campylobacter jejuni in Chickens Exposed to Enrofloxacin Treatment at the Inherent Dosage Licensed in Japan

The objective of the present study was to determine whether selection of fluoroquinolone resistance could be easily induced in Campylobacter jejuni-colonized chickens by treatment with enrofloxacin of representative fluoroquinolones at the inherent dosage licensed in Japan (50 ppm in drinking water for 3 days). In the case of isolates from chickens of study 1, an increase in the population of susceptible isolates appeared after the cessation of treatment and maintained throughout the experiments. On the contrary, our results of study 2 demonstrated that administration of enrofloxacin generated a rapid increase of fluoroquinolone resistance in C. jejuni showing the mutation of Asp-90-Asn in the gyrA gene. Present results indicate that the enrofloxacin treatment for broilers at the inherent dosage is able to select fluoroquinolone resistance in C. jejuni. We conclude that whatever enrofloxacin dosage is used, an emergence of fluoroquinolone resistant of C. jejuni occurs.