禽畜养殖粪便中多重抗生素抗性细菌研究

通过对新乡地区8家养猪场和11家养鸡场饲喂抗生素情况的调研,发现头孢氨苄、阿莫西林、卡那霉素、庆大霉素等4种抗生素是该地区被普遍使用的兽药抗生素。通过多点取样法和微生物培养技术对3家养鸡场和3家养猪场不同养殖时期的粪便进行单一抗生素和多重抗生素抗性细菌的检测,结果表明养鸡场堆置1周的粪便中抗头孢氨苄的细菌比例最高,达到65.90%,对所研究的3种和4种抗生素同时抗性的比例高达8.60%—12.51%和9.73%,明显高于饲喂中药的对照养鸡场样本检测结果(0.02%—2.73%和0.12%)。养猪场堆置1周的粪便中检测到抗头孢氨苄的细菌比例也是最高,达到49.12%上,但养猪场粪便中多重抗生素抗性细菌的比例明显低于养鸡场。同时研究发现,在两种养殖场中,幼龄期粪便中检测到的多重抗性细菌比例明显高于成熟期粪便,这可能与养殖过程中鸡、猪在幼龄期由于防病和促生长等因素而同时大剂量使用多种抗生素有关。

Multidrug-resistant bacteria in livestock feces

The increase in the prevalence of bacteria resistant to multiple antibiotics (i.e., multidrug-resistant bacteria), especially "super bacteria," has received considerable attention around the world. In addition to the effects on human health, these bacterial strains can have a considerable impact on agriculture. The feces of livestock have become a reservoir for antibiotic-resistant bacteria because of the wide use of various antibiotics in animal production. However, there are only a few systematic studies that have reported on the development of multidrug-resistant bacteria in livestock feces and its relationship with antibiotics in feed. In this study, we evaluated the use of antibiotics on 8 pig farms and 11 chicken farms. The survey investigated several factors, such as breeding scale, commonly used antibiotics, antibiotic usage and dosage, feces scale of everyday and destination of feces, among other factors. Our survey results indicated that cefalexin, amoxicillin, kanamycin, and gentamycin were the main antibiotics used, and the antibiotics were almost always used at levels exceeding the recommended dosage. Bacteria isolated from feces specimens collected during different feeding periods from 3 chicken farms and 3 pig farms were analyzed using multi-sampling and microbial culture enumeration techniques to identify bacteria resistant to one or multiple antibiotics. In chicken manure, microbial enumeration results revealed 2.37×10¹² to 3.91×10¹² CFU/g cultivable bacteria, 2.03×10¹⁰ to 1.85×10¹¹ CFU/g Actinomyces, and 1.72×10⁷ to 1.42×10⁸ CFU/g fungi. A greater percentage of bacteria was resistant to cefalexin (65.90%) than to the other four antibiotics tested. Moreover, 8.60% to 12.51% of cultivable bacteria were resistant to three of the antibiotics tested, and 9.73% were resistant to all four antibiotics. These rates were significantly higher than rates observed on chicken farms using traditional Chinese medicines (0.02% to 2.73% and 0.12%, respectively). In pig manure, microbial enumeration results revealed 4.85×10¹¹ to 1.90×10¹² CFU/g cultivable bacteria, 3.04×10¹⁰ to 6.26×10¹⁰ CFU/g Actinomyces, and 1.89×10⁷ to 5.89×10⁷ CFU/g fungi. Similar to the results observed on chicken farms, more bacteria were resistant to cefalexin (49.12%) than the other antibiotics tested; however, fewer multidrug-resistant bacteria were found in pig manure (<1% total cultivable bacteria) compared with chicken manure. The different distributions of multidrug-resistant bacteria between chicken and pig farms may be the result of differences in factors such as the antibiotic dosages used, drug metabolism, or breeding cycles. The rates of bacteria resistant to two or more antibiotics isolated from the feces of newborn chickens and pigs (chickens, 3.00%-25.20%; pigs, 0.15%-9.35%) were significantly higher than the rates in mature animals (chickens, 4.45%-13.71%; pigs, 0.01%-6.40%). This difference is likely related to the relatively common practice of simultaneous use of high concentrations of more than one antibiotic in young animals to prevent disease and promote growth. These high rates of multidrug-resistant bacteria in livestock feces indicate that regulating the standard use of antibiotics in the livestock farming process is imperative to control the prevalence of bacteria resistant to multiple antibiotics. Further research to identify the genes associated with multidrug-resistance as well as the underlying modes of action of the gene products is currently underway.