犊牛腹泻大肠杆菌临床症状及分子流行病学

Clinical symptoms and molecular epidemiology of diarrhea caused by Escherichia coli in calves

摘要:

【背景】腹泻是导致新生犊牛死亡的主要原因之一，而大肠杆菌(Escherichia coli)作为机会性致病菌是新生犊牛肠道感染的主要病原。尽管常用抗生素对其进行治疗，但大肠杆菌的多血清型及多种抗生素耐药性的增加给治疗带来了极大的困难。【目的】探究吉林省地区牛场犊牛腹泻中大肠杆菌感染的临床症状、毒力基因、血清型、耐药性及系统进化群等流行特征。【方法】采用PCR、药敏试验等方法对大肠杆菌的血清型、毒力因子和耐药性、系统发育进行检测。【结果】从150份病料中分离出92株大肠杆菌，检出率为61.3%；肠道内致病性大肠杆菌主要毒力基因为K88 (10%)、K99 (48%)、F17 (85%)、F41 (20%)、fimH (20%)、csgA (87%)、eaeA (4.5%)、bfpA (5%)、hlyA (4.5%)、hlyE (61.8%)、stx1 (22%)、stx2 (34%)、fyuA (3%)、Sta (15%)、STb (92%)，未检出F6和F18。O血清检测中，86% (79/92)的毒株确定了O抗原血清型，其中O101 (32%)为优势血清型；其次为O103 (15%)。分离菌株多数具有多重耐药性，对氨苄西林、四环素、庆大霉素和链霉素耐药率分别为52.7%、53.3%、40.7%和50%。菌株携带β-内酰胺类ampC (45.21%)、bla_CTX (42.47%)、bla_TEM (56.85%)，四环素类tetA (55.48%)，氨基糖苷类addA (55.48%)、aph(3')-Ia (43.15%)和aphA3 (30.22%)基因。菌株中36株为A1群(24%)，27株为B1群(18%)，6株为B2群(4%)，20株为D群(13.3%)。【结论】吉林省牛场犊牛腹泻大肠杆菌感染率较为严重，多属于A1和B1群，O101为优势血清型，分离株携带多种毒力基因和耐药基因，多重耐药严重。应加强犊牛饲养管理及疫苗免疫，减少抗生素使用。

关键词:犊牛腹泻;肠道内致病性大肠杆菌;毒力基因;耐药性

Abstract:

[Background] Diarrhea is one of the main causes of death in newborn calves, and Escherichia coli, as an opportunistic pathogen, is the main pathogen of intestinal infection in newborn calves. Although antibiotics are commonly used to treat this pathogen, the multiple serotypes of E. coli and the enhancing resistance to multiple antibiotics have brought great difficulties to treatment. [Objective] To investigate the clinical symptoms of E. coli-induced diarrhea and the virulence genes, serotypes, drug resistance, and phylogenetic characteristics of E. coli in calves in Jilin Province. [Methods] PCR, drug sensitivity test, and other methods were employed to determine the serotypes, phylogeny, virulence factors, and drug resistance of E. coli. [Results] A total of 92 strains of E. coli were isolated from 150 samples, with the detection rate of 61.3%. The main virulence genes of intestinal pathogenic E. coli were K88 (10%), K99 (48%), F17 (85%), F41 (20%), fimH (20%), csgA (87%), eaeA (4.5%), bfpA (5%), hlyA (4.5%), hlyE (61.8%), stx1 (22%), stx2 (34%), fyuA (3%), STa (15%), and STb (92%), while F6 and F18 were not detected. Among the isolates, 86% (79/92) were of O-antigen serotypes, among which O101 (32%) was the dominant serotype, followed by O103 (15%). Most of the isolates had multidrug resistance, with the resistance rates to ampicillin, tetracycline, gentamicin, and streptomycin being 52.7%, 53.3%, 40.7%, and 50%, respectively. The strains carried ampC (45.21%), bla_CTX (42.47%), bla_TEM (56.85%) of β-lactams, tetA (55.48%) of tetracyclines, and addA (55.48%), aph(3')-Ia (43.15%), and aphA3 (30.22%) of aminoglycosides. Among the strains, 36 (24%), 27 (18%), 6 (4%), and 20 (13.3%) strains belonged to groups A1, B1, B2, and D, respectively. [Conclusion] The infection rate of E. coli causing diarrhea in calves in Jilin Province is serious, and most of the pathogen strains belonged to A1 and B1 groups. O101 was the dominant serotype, and the isolates carried a variety of virulence genes and drug resistance genes, demonstrating serious multidrug resistance. Feeding management and vaccine immunization should be strengthened for calves, and the use of antibiotics should be reduced.

Key words:calf diarrhea;intestinal pathogenic Escherichia coli;virulence gene;drug resistance