AUTHOR=Liu Huimin , Meng Lu , Dong Lei , Zhang Yangdong , Wang Jiaqi , Zheng Nan 

TITLE=Prevalence, Antimicrobial Susceptibility, and Molecular Characterization of Escherichia coli Isolated From Raw Milk in Dairy Herds in Northern China

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.730656

DOI=10.3389/fmicb.2021.730656

ISSN=1664-302X

ABSTRACT=<p><italic>Escherichia coli</italic> is a common bacterium in the intestines of animals, and it is also the major important cause of toxic mastitis, which is an acute or peracute disease that causes a higher incidence of death and culling of cattle. The purpose of this study was to investigate <italic>E. coli</italic> strains isolated from the raw milk of dairy cattle in Northern China, and the antibacterial susceptibility of these strains and essential virulence genes. From May to September 2015, 195 raw milk samples were collected from 195 dairy farms located in Northern China. Among the samples, 67 (34.4%) samples were positive for <italic>E. coli</italic>. About 67 <italic>E. coli</italic> strains were isolated from these 67 samples. The prevalence of Shiga toxin-producing <italic>E. coli</italic> (STEC), enterotoxigenic <italic>E. coli</italic> (ETEC), enteropathogenic <italic>E. coli</italic> (EPEC), and enteroinvasive <italic>E. coli</italic> (EIEC) were 9, 6, 4.5, and 1.5%, respectively. Among the virulence genes detected, <italic>stx</italic>1 was the most prevalent (6/67, 9%) gene, followed by <italic>eae</italic> (3/67, 4.5%), and <italic>est</italic>B (2/67, 3%). Moreover, the strains exhibited different resistance levels to ampicillin (46.3%), amoxicillin-clavulanic acid (16.4%), trimethoprim-sulfamethoxazole (13.4%), tetracycline (13.4%), cefoxitin (11.9%), chloramphenicol (7.5%), kanamycin (7.5%), streptomycin (6.0%), tobramycin (4.5%), azithromycin (4.5%), and ciprofloxacin (1.5%). All of the <italic>E. coli</italic> isolates were susceptible to gentamicin. The prevalence of β-lactamase-encoding genes was 34.3% in 67 <italic>E. coli</italic> isolates and 45% in 40 β-lactam-resistance <italic>E. coli</italic> isolates. The overall prevalence of <italic>bla</italic><sub>SHV</sub>, <italic>bla</italic><sub>TEM</sub>, <italic>bla</italic><sub>CMY</sub>, and <italic>bla</italic><sub>CTX-M</sub> genes were 1.5, 20.9, 10.4, and 1.5%, respectively. Nine non-pathogenic <italic>E. coli</italic> isolates also carried β-lactamase resistance genes, which may transfer to other pathogenic <italic>E. coli</italic> and pose a threat to the farm’s mastitis management projects. Our results showed that most of <italic>E. coli</italic> were multidrug resistant and possessed multiple virulence genes, which may have a huge potential hazard with public health, and antibiotic resistance of <italic>E. coli</italic> was prevalent in dairy herds in Northern China, and ampicillin should be used cautiously for mastitis caused by <italic>E. coli</italic> in Northern China.</p>