Animal-derived Proteus mirabilis ( P. mirabilis) is an important food-borne zoonotic bacillus and widely exists in the broiler-breeding industry. The present study was designed to explore the P. mirabilis prevalence and antimicrobial resistance characteristics in 6 conventional broiler-fattening farms in Shandong Province, China. The overall isolation rate of P. mirabilis was 7.07% (50/707). Antimicrobial resistance was very common in the P. mirabilis isolated from these farms and varied for different antibacterial drugs, with chloramphenicol, ciprofloxacin, and trimethoprim-sulfamethoxazole having the highest resistance rate (98%) and aztreonam the lowest (0%). Multidrug resistance was as high as 100%. The majority of the MDR isolates were resistant to between 9 and 12 of the antibiotics, with these accounting for 76% (38/50) of multidrug resistant strains. These P. mirabilis isolates carried 24 drug-resistance genes in 6 types, with stcM having the highest rate (96%) and cmlA, bla_TEM, and qnrC the lowest (2%). Superdrug resistance gene bla_NDM-1 was found in 10% (5/50) of isolates from poultry farms in Shandong. All the P. mirabilis isolates carried at least 6 virulence genes, with 100% detection rates of the ireA and hpmA genes. Our study revealed that the P. mirabilis strains isolated in the Shandong area all showed the MDR phenotype and the poultry-derived carbapenem-resistant MDR P. mirabilis strains may pose a potential risk to humans. Surveillance findings presented herein will be conducive to our understanding of the prevalence and characteristics of carbapenem-resistant P. mirabilis strains in Shandong, China.

Klebsiella pneumoniae (K. pneumoniae) is a conditionally pathogenic bacterium present in the intestinal or the respiratory tract of animals, and it is a common factor in acquired infections and a major threat to public health. Increased production of extended-spectrum β-lactamases (ESBLs) has become a serious issue in the treatment of K. pneumoniae infections. In this study, we examined the serotypes and antibiotic resistance profiles of K. pneumoniae isolated from broiler chickens on farms in Shandong Province, China. The K. pneumoniae isolation rate was 4.67% (33/707), and the serotype Capsular K54 (42.42%, 14/33) was the most prevalent serotype in broilers in Shandong. The antimicrobial susceptibility assay revealed that the 33 isolates were resistant to 28 antimicrobial drugs to varying degrees; among these, the highest resistance rate was observed for tetracyclines (90.91%), and the lowest rate of resistance was observed for moxifloxacin and fosfomycin (0%). The multidrug resistance (MDR) rate was 87.88% (29/33). The carrying rate of β-lactam-resistance genes was as high as 100%, with bla_SHV having the highest rate (93.94%). It is worth noting that one carbapenem-resistant K. pneumoniae (CRKP) isolate carrying bla_NDM-1 and one colistin-resistant K. pneumoniae (COLR-KP) isolate carrying mcr-3 were found in broiler chickens. This study indicates that ESBL-producing CRKP isolates and COLR-KP isolates have emerged on poultry farms in Shandong and could be a potential threat to food safety and public health.

Colibacillosis, caused by Escherichia coli, is one of the most common bacterial diseases of chickens. The high incidence and considerable economic losses associated with colibacillosis make it a significant concern worldwide. In recent years, the efficacy of colistin has been severely impacted by the emergence of plasmid-mediated colistin resistance genes, especially mcr-1. Therefore, monitoring of antibiotic resistance, particularly colistin resistance, amongst E. coli strains is vitally important to the future growth and sustainability of the poultry industry. In this study, a total of 130 E. coli strains were isolated from the livers of chickens displaying symptoms of colibacillosis in Tai'an, China. Isolates were screened for their susceptibility to various antibiotics and for the presence of mobile colistin resistance genes and other antibiotic resistance genes. Overall, 75 (57.7%) isolates showed resistance to colistin and were positive for mcr-1. The mobile colistin resistance genes, mcr-2, -3, and -4, were not detected in this study. Of the 75 mcr-1-positive isolates, all (100%) also carried tetracycline resistance genes, 71 (94.7%) also contained genes associated with β-lactam resistance, 59 (78.7%) contained aminoglycoside resistance genes, and 57 (76%) contained sulfonamide resistance genes. This high prevalence of multidrug resistance among mcr-1-positive E. coli isolates, including the production of extended-spectrum β-lactamases, is highly concerning. The surveillance findings presented here will be conducive to our understanding of the prevalence and characteristics of multidrug-resistance in E. coli in the Tai'an area and will provide a better scientific basis for the clinical treatment of colibacillosis in chickens.

The extensive use of antibiotics has, in recent years, caused antimicrobial resistance and multidrug resistance in Escherichia coli to gradually develop into a worldwide problem. These resistant E. coli could be transmitted to humans through animal products and animal feces in the environment, thereby creating a problem for bacterial treatment for humans and animals and resulting in a public health issue. Monitoring the resistance of E. coli throughout the broiler fattening period is therefore of great significance for both the poultry industry and public health. In this longitudinal study, samples were taken from 6 conventional broiler fattening farms in Shandong Province, China, at 3 different times within 1 fattening period. The overall isolation rate of E. coli was 53.04% (375/707). Antibiotic resistance was very common in the E. coli isolated from these farms, and differed for different antibiotics, with ampicillin having the highest rate (92.86%) and cefoxitin the lowest (10.12%). Multidrug resistance was as high as 91.07%. More importantly, both the resistance rate of E. coli to the different drugs and the detection rate of drug resistance genes increased over time. The mobile colistin resistance (mcr-1) gene was detected in 24.40% of the strains, and these strains often carried other drug resistance genes, such as those conferring aminoglycoside, β-lactamase, tetracycline, and sulfonamide resistance. Antimicrobial resistance and drug resistance genes in E. coli were least common in the early fattening stage. The individual detection rates of sul1, sul3, aacC4, aphA3, and mcr-1 were significantly lower (P < 0.05) for the early fattening stage than for the middle and late stages. The rational use of antibiotics, in conjunction with the improvement of the breeding environment during the entire broiler fattening cycle, will be helpful in the development of the poultry industry and the protection of public health.