Quinolone Resistance Of Avian Escherchia Coli And Salmonella Spp. Isolates

Escherichia coli (E. coli) and Salmonella are important pathogens that cause gastrointestinal infections and septicemia in humans and animals as well as a range of secondary conditions, including respiratory tract infections in animals. Collectively, infections caused by E. coli and Salmonella are responsible for significant economic losses to the poultry industry in many parts of the world. Quinolones are broad-spectrum antibacterial agents used in human and veterinary medicine. The extensive use of quinolones has been associated with an increase in the level of quinolone resistance.This study was conducted in order to compare the quinolone resistance and prevalence of plasmid-mediated quinolone resistance genes among E. coli and Salmonella spp. Strains, which were isolated from avian samples obtained between 1993 and 2008 from 14 provinces of China.1. Quinolone resistance of avian E. coli and Salmonella spp. isolatesA total of 361 E. coli and 224 Salmonella spp. field isolates were derived from clinically affected chickens in 14 provinces (Jiangsu, Shanghai, Shandong, Shanxi, Henan, Guangdong, Zhejiang, Hubei, Beijing, Anhui, Sichuan, Guizhou, Shanxi and Guangxi) of China between 1993 and 2008. All E. coli and Salmonella spp. strains were isolated from diseased chickens for which sufficient amounts of bacteria could be obtained from systemic lesions (heart, liver, spleen, brain, and blood) for culturing. The samples were cultured directly on MacConkey agar (Difco) and were identified as E. coli and Salmonella spp. using biochemical procedures.Quinolone resistance of E. coli was increased more than two fold in recent 20 years. Among the 361 avian E. coli isolates, more than 40% isolates were resistant to 9 quinolone antibiotics, except gatifloxacin(22.44%). Resistance to quinolone antibiotics from 1993~1999 was much lower than that of the isolates obtained during 2000~2008. Resistance of the isolates obtained during 1990~1999 to 8 antibiotics was only approximately half of that of the isolates obtained during 2000~2008. More than 60% of the isolates obtained during 1993~1999 exhibited resistance to only Nalicixic acid, while more than 60% of the isolates obtained during 2000~2008 demonstrated resistance to 9 antibiotics (nalidixic acid, pipemidic acid, fleroxacin, enrofloxacin, enoxacin, lomefloxacin, ciprofloxacin, norfloxacin, and ofloxacin). Among the 4 common serogroups, more than 50% of O78 serogroup isolates were resistance to 7 antibiotics, more than 50% of O18 serogroup isolates were resistance to 5 antibiotics, and more than 50% of O1 and O2 serogroup isolates were resistance to 3 antibioticsAll the Salmonella spp. isolates obtained during 1993~1999 were susceptible to quinolones, and a nalidixic acid-resistant isolate of Salmonella spp. were first observed in the year 2000. Among the Salmonella spp. isolates obtained during 2000~2008, more than 50% of the strains were found to be resistant to only nalidixic acid (83.74%) while more than 50% of the E. coli isolates collected during the period exhibited resistance to 9 antibiotics. Less than 10% strains were resistant to other antibiotics such as enrofloxacin, lomefloxacin, ciprofloxacin, norfloxacin, ofloxacin, and gatifloxacin, i.e., resistant strains were 6.5%, 0.81%, 0.81%, 1.62%, 0.81%, and 0%, respectively.2. Screening and analysis of plasmid-mediated quinolone resistant genes of avian E. coli and Salmonella spp. IsolatesAll quinolones have the same mechanism of action, namely, the inhibition of DNA replication, regardless of whether they are used in clinical or veterinary medicine. Until 1998, it was believed that quinolone resistance could be acquired only through chromosomal mutation. Later, it became clear that quinolone resistance may be associated with plasmid-mediated resistance genes. Thus far, the following 3 mechanisms have been reported to be involved in plasmid-encoded quinolone resistance: a quinolone-protective mechanism encoded by the qnr gene, a double class antibiotic-modifying enzyme encoded by aac(6′)-ib-cr, a two-point mutation allele of aac(6′)-ib that is involved in the acetylation of ciprofloxacin and norfloxacin, and the qepA gene, which encodes an efflux pump belonging to the major facilitator subfamily.Among the 361 avian E. coli isolates, plasmid-mediated quinolone resistant genes aac(6′)-ib-cr, qepA, and qnrB were detected in 9 (2.5%), 3 (0.8%), and 1 (0.3%) of the isolates, respectively. In our study, aac(6′)-ib-cr was first observed in 2007. Seven aac(6′)-ib-cr positive isolates were detected in 2008, while only 2 were detected in 2007. No plasmid-mediated quinolone resistant gene was detected in 224 Salmonella spp. isolates. In order to determine if quinolone resistance was transferable in the strains with plasmids, conjugation experiments were carried out in on filters with E. coli J53AziR as the recipient. Transconjugants were selected with several antimicrobial agents but not with quinolones to avoid spontaneous quinolone resistance mutations in the recipient. The transconjugants exhibited a 2-16 fold range of MICs of 10 quinolone antimicrobials.