Contamination and molecular characteristics of Staphylococcus aureus in raw milk in Urumqi,Xinjiang
Objective To investigate the contamination of Staphylococcus aureus in bulk raw milk in Urumqi,and analyze the molecular characteristics of isolated strains,including molecular typing,resistance genes and virulence genes.Methods A total of 108 bulk raw milk samples were collected from markets in Urumqi.All samples were subjected to qualitative and quantitative analysis for Staphylococcus aureus according to national standard GB4789.10-2016.All isolates were subjected to multilocus sequence typing(MLST)based on whole genome sequencing analysis,as well as analysis of resistance and virulence genes.Results In total of 108 samples,52.8％(57/108)were positive for Staphylococcus aureus,59.6％(34/57)of the samples were ≥110 MPN/ml in quantitative analysis.In addition,15 sequence types were obtained by multilocus sequence typing,and ST50 was the main genotype,followed by ST5405.24 drug-resistant genes were detected in 57 strains of bacteria,among which the carrying rates of norA_l,tet(38),mgrA,arlR,arlS,sav1866,mepR and mepA were higher.The overall carriage rate of staphylococcal enterotoxin genes was 28.1％(16/57),among which sec-sell had the highest carriage rate of 12.3％(7/57),followed by seb being 10.5％(6/57).In addition,the carriage rates of toxic shock syndrome toxin coding gene(tsst-1)and leukocytocin encoding genes(lukF-PV and lukS-PV)were 12.3％(7/57)and 5.3％(3/57),respectively.Conclusion There was risk of contamination by Staphylococcus aureus in bulk sold raw milk in Urumqi,Xinjiang.The isolated strains all carried multiple drug resistance genes,and multiple pathogenic virulence factors such as enterotoxins had been detected positive.We should strengthen the supervision of raw milk sold in bulk to ensure its quality and safety.
Raw milkStaphylococcus aureusFood safetyWhole genome sequencingMolecular characteristic
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