The drug resistance and molecular mechanisms of human Campylobacter jejuni

Abstract

Objective To analyze the characteristics of drug resistance to quinolones and erythromycin of clinical Campylobacter jejuni (C.jejuni) strains and to further investigate its molecular mechanisms. Methods A total of 193 clinical C. jejuni strains were isolated from feces of patients with diarrhea. Drug susceptibilities to ciprofloxacin (CIP), gentamycin (GEN), azithromycin (AZI), erythromycin (ERY), chloromycetin (CHL), doxycycline (DOX) and tetracycline (TET) were tested using standard agar dilution method. gyrA, gyrB and parC genes were amplified by polymerase chain reaction (RCR) and analyzed for molecular mechanisms of quinolones resistance, and 23S rRNA, rplD and rplV genes for erythromycin resistance. Chi-square test or Fisher′s exact two-tailed tests were used to perform the statistical analysis. Results A total of 193 clinical C. jejuni strains were isolated during 1994—2010, among which 43 C. jejuni strains were isolated in 1994—1999, 80 in 2000—2005 and 70 in 2006—2010. The drug resistance rates for CIP increased significantly from 55.8% in 1994—1999 to 95.0% in 2000—2005 and 94.3% in 2005—2010 (χ2=41.94, P<0.01). The drug resistance rates for GEN were 0 in 1994—1999, 11.3% in 2000—2005 and 10.0% in 2006—2010, but with no statistic difference (χ2=5.078, P=0.08). The drug resistance rates for AZI were 0 in 1994—1999, 3.8% in 2000—2005 and 4.3% in 2006—2010 (χ2=1.81, P=0.40). The drug resistance rates for ERY were 0 in 1994—1999, 1.3% in 2000—2005 and 4.3% in 2006—2010 (χ2=2.87, P=0.24). The drug resistance rates for CHL were 2.3% in 1994—1999, 11.3% in 2000—2005 and 20.0% in 2006—2010 (χ2=7.82, P=0.02). The drug resistance rates for DOX were 60.5% in 1994-1999, 86.3% in 2000—2005 and 82.9% in 2006—2010 (χ2=12.18, P<0.01). The drug resistance rates for TET were 74.4% in 1994—1999, 95.0% in 2000—2005 and 94.3% in 2006—2010 (χ2=15.46, P<0.01). The drug resistance rates for CIP-DOX-TET were 37.2% in 1994—1999, 83.8% in 2000—2005 and 80.0% in 2006—2010 (χ2=33.53, P<0.01). The drug resistance rates for CHL-CIP-DOX-TET were 0 in 1994—1999, 7.5% in 2000—2005 and 20.0% in 2006—2010 (χ2=12.68, P<0.01). The drug resistance rates for GEN-CIP-DOX-TET were 0 in 1994—1999, 7.5% in 2000—2005 and 8.6% in 2006—2010 (χ2=3.74, P=0.15). All 163 CIP-resistant C. jejuni strains had C257T mutation on gyrA gene. Mutations on gyrB gene were silent. ParC gene was absent in C. jejuni. Four ERY resistant C. jejuni strains had no mutation on rplD and rplV genes, but 3 of them had A2075G mutation on 23S rRNA gene. Conclusions The antimicrobial resistance rates for C. jejuni increase remarkably over the periods. C257T mutation on gyrA gene and A2075G mutation on 23S rRNA gene are main mechanisms for quinolones resistance and erythromycin resistance, respectively. Key words: Campylobacter jejuni; Drug resistance, microbial; Ciprofloxacin; Erythromycin; Resistance mechanisms