Abstract: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.