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The objective of this study was to evaluate the prevalence and characteristics of avian-origin mcr -1-harbouring Escherichia coli in Shandong Province, China. During 2017—2018, a total of 668 non-duplicate E. coli isolates were separately collected from 8eight large intensive poultry farms in Shandong Province. Antimicrobial susceptibility testing for 10 antimicrobial agents commonly used in farms was performed on all E. coli isolates by the agar dilution method; the mobile colistin resistance gene (mcr -1) gene was screened by PCR, and mcr -1 positive isolates were PCR-screened for antimicrobial resistance genes and typed by multi-locus sequence typing (MLST). Among the 668 E. coli , 102 (15.3%) harbored the mcr -1 gene; high antimicrobial resistance rates were observed for ampicillin (100/102, 98.0%), followed by amoxicillin (99/102, 97.1%) and florfenicol (97/102, 95.1%), and a low level of resistance was found for amoxicillin/clavulanic acid (24/102, 23.5%). Five ESBL genes were detected, and all isolates carried bla TEM (102/102, 100%), followed by bla CTX–M (90/102, 88.2%). Four PMQR genes were detected; aac(6)-Ib-cr (40/102, 39.2%) was the most commonly isolated PMQR gene, followed by qnrA (10/102, 9.8%). Thirty-eight different kinds of STs were identified, and the dominant ST was ST93 (19/102, 18.6%), followed by ST48 (9/102, 8.8%). In summary, E. coli from poultry in Shandong could be a reservoir for the mcr -1 gene, which could pose serious risks to human public health. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus (S. aureus) is one of the most common pathogens that cause mastitis in dairy cows. The emergence of methicillin-resistant S. aureus (MRSA) constitutes a serious public health concern due to its ability to colonize and infect humans and animals. In this study, the prevalence and antimicrobial resistance of S. aureus and MRSA were investigated from bulk tank milk (BTM) in Shandong dairy farms. A total of 418 pooled BTM samples from 418 different dairy farms were collected. The prevalence of S. aureus was 28.9% (121/418), while the MRSA prevalence was 0.7% (3/418). The strains exhibited high percentages of resistance to penicillin (74.4%) and erythromycin (58.7%), and 91.7% of the isolates were found to be resistant to at least one antimicrobial agent. Moreover, 55.4% (67/121) of isolates were multidrug-resistant (MDR). The most predominant virulence genes were sed (13.2%, 16/121) and sec (8.3%, 10/121), which encode Staphylococcal enterotoxins (sed and sec). Multilocus sequence typing (MLST) was employed to identify 18 different sequence types (STs). The predominant STs were ST50 (13.2%, 16/121) and ST398 (12.4%, 15/121), while ST97, ST2779, and ST3191 were observed in MRSA isolates. Staphylococcal protein A gene (spa) typing identified spa types t034 (12.4%, 15/121) and t189 (9.9%, 12/121) most frequently among S. aureus isolates, while t002, t267, and t437 were observed in MRSA isolates. The results of this study indicated that S. aureus isolates had a relatively high prevalence rate in BTM, and these isolates harbored multiple virulence and exhibited multiple antimicrobial resistance. Meanwhile, our results confirm the lurking threat of MRSA in raw milk and suggest the need for surveillance programs starting at the farm level. • The S. aureus from BTM showed high genetic diversity (spa, MLST). • Three MRSA isolates were identified from BTM. • MDR phenotype detected in 55.4% of the isolates from BTM. • Limited data about the prevalence and characterization of S. aureus , including MRSA, in BTM in China are available. [ABSTRACT FROM AUTHOR]