Antimicrobial resistance and virulence characteristics in 3 collections of staphylococci from bovine milk samples

摘要

Mastitis is a prevalent disease in dairy cattle, andstaphylococci are among the most common causativepathogens. Staphylococci can express resistance to arange of antimicrobials, of which methicillin resistanceis of particular public health concern. Additionally,Staphylococcus aureus carries a variety of virulence factors,although less is understood about the virulence ofnon-aureus staphylococci (NAS). The aim of our studywas to identify and characterize 3 collections of staphylococcalisolates from bovine milk samples regardingantimicrobial resistance, with emphasis on methicillinresistance, and their carriage of virulence genes typicallydisplayed by Staph. aureus. A total of 272 staphylococcalisolates collected in Norway and Belgium in 2016were included, distributed as follows: group 1, Norway,100 isolates; group 2, Flanders, Belgium, 64 isolates;group 3, Wallonia, Belgium, 108 isolates. Species identificationwas performed by use of MALDI-TOF massspectrometry. Phenotypic resistance was determinedvia disk diffusion, and PCR was used for detectionof methicillin resistance genes, mecA and mecC, andvirulence genes. Antimicrobial resistance was commonin Staphylococcus epidermidis and Staphylococcushaemolyticus from all different groups, with resistanceto trimethoprim-sulfonamide frequently occurring inStaph. epidermidis and Staph. haemolyticus as wellas in Staph. aureus. Resistance to penicillin was mostfrequently observed in group 1. Ten Belgian isolates (1from group 2, 9 from group 3) carried the methicillinresistance determinant mecA: 5 Staph. aureus from 2different farms and 5 NAS from 3 different farms. Almostall Staph. aureus isolates were positive for at least3 of the screened virulence genes, whereas, in total, only8 NAS isolates harbored any of the same genes. Ourstudy contributes to the continuous need for knowledgeregarding staphylococci from food-producing animalsas a basis for better understanding of occurrence ofresistance and virulence traits in these bacteria.