Sawant Ashish A, Hegde Narasimha V, Straley Beth A, Donaldson Sarah C, Love Brenda C, Knabel Stephen J, Jayarao Bhushan M
Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, PA 16802, USA.
Appl Environ Microbiol. 2007 Jan;73(1):156-63. doi: 10.1128/AEM.01551-06. Epub 2006 Nov 10.
A study was conducted to understand the descriptive and molecular epidemiology of antimicrobial-resistant gram-negative enteric bacteria in the feces of healthy lactating dairy cattle. Gram-negative enteric bacteria resistant to ampicillin, florfenicol, spectinomycin, and tetracycline were isolated from the feces of 35, 8, 5, and 42% of 213 lactating cattle on 74, 39, 9, 26, and 82% of 23 farms surveyed, respectively. Antimicrobial-resistant gram-negative bacteria accounted for 5 (florfenicol) to 14% (tetracycline) of total gram-negative enteric microflora. Nine bacterial species were isolated, of which Escherichia coli (87%) was the most predominant species. MICs showing reduced susceptibility to ampicillin, ceftiofur, chloramphenicol, florfenicol, spectinomycin, streptomycin, and tetracycline were observed in E. coli isolates. Isolates exhibited resistance to ampicillin (48%), ceftiofur (11%), chloramphenicol (20%), florfenicol (78%), spectinomycin (18%), and tetracycline (93%). Multidrug resistance (> or =3 to 6 antimicrobials) was seen in 40% of E. coli isolates from healthy lactating cattle. Of 113 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 93% of isolates, while the remaining 7% isolates carried the tet(A) determinant. DNA-DNA hybridization assays revealed that tet determinants were located on the chromosome. Pulsed-field gel electrophoresis revealed that tetracycline-resistant E. coli isolates (n = 99 isolates) belonged to 60 subtypes, which is suggestive of a highly diverse population of tetracycline-resistant organisms. On most occasions, E. coli subtypes, although shared between cows within the herd, were confined mostly to a dairy herd. The findings of this study suggest that commensal enteric E. coli from healthy lactating cattle can be an important reservoir for tetracycline and perhaps other antimicrobial resistance determinants.
开展了一项研究，以了解健康泌乳奶牛粪便中耐抗菌药物革兰氏阴性肠道细菌的描述性和分子流行病学情况。分别从213头泌乳奶牛中35%、8%、5%和42%的粪便中分离出对氨苄西林、氟苯尼考、壮观霉素和四环素耐药的革兰氏阴性肠道细菌，这些奶牛分别来自所调查的23个养殖场中的74%、39%、9%、26%和82%。耐抗菌药物革兰氏阴性细菌占革兰氏阴性肠道微生物群落总数的5%（氟苯尼考）至14%（四环素）。分离出9种细菌，其中大肠杆菌最为常见（87%）。在大肠杆菌分离株中观察到对氨苄西林、头孢噻呋、氯霉素、氟苯尼考、壮观霉素、链霉素和四环素敏感性降低的最低抑菌浓度。分离株对氨苄西林（48%）、头孢噻呋（11%）、氯霉素（20%）、氟苯尼考（78%）、壮观霉素（18%）和四环素（93%）表现出耐药性。在健康泌乳奶牛的大肠杆菌分离株中，40%表现出多重耐药性（对3至6种抗菌药物耐药）。在113株耐四环素大肠杆菌分离株中，tet(B)是主要的耐药决定因素，在93%的分离株中检测到，其余7%的分离株携带tet(A)决定因素。DNA-DNA杂交试验表明，tet决定因素位于染色体上。脉冲场凝胶电泳显示，耐四环素大肠杆菌分离株（共99株）属于60个亚型，这表明耐四环素微生物群体高度多样化。在大多数情况下，大肠杆菌亚型虽然在牛群中的奶牛之间有共享，但大多局限于一个奶牛场。本研究结果表明，健康泌乳奶牛的共生肠道大肠杆菌可能是四环素及其他抗菌药物耐药决定因素的重要储存库。
