Abstract :
[en] Mastitis is a prevalent disease in dairy cattle, and
staphylococci are among the most common causative
pathogens. Staphylococci can express resistance to a
range of antimicrobials, of which methicillin resistance
is of particular public health concern. Additionally,
Staphylococcus aureus carries a variety of virulence factors, although less is understood about the virulence of
non-aureus staphylococci (NAS). The aim of our study
was to identify and characterize 3 collections of staphylococcal isolates from bovine milk samples regarding
antimicrobial resistance, with emphasis on methicillin
resistance, and their carriage of virulence genes typically
displayed by Staph. aureus. A total of 272 staphylococcal isolates collected in Norway and Belgium in 2016
were included, distributed as follows: group 1, Norway,
100 isolates; group 2, Flanders, Belgium, 64 isolates;
group 3, Wallonia, Belgium, 108 isolates. Species identification was performed by use of MALDI-TOF mass
spectrometry. Phenotypic resistance was determined
via disk diffusion, and PCR was used for detection
of methicillin resistance genes, mecA and mecC, and
virulence genes. Antimicrobial resistance was common in Staphylococcus epidermidis and Staphylococcus
haemolyticus from all different groups, with resistance
to trimethoprim-sulfonamide frequently occurring in
Staph. epidermidis and Staph. haemolyticus as well
as in Staph. aureus. Resistance to penicillin was most
frequently observed in group 1. Ten Belgian isolates (1
from group 2, 9 from group 3) carried the methicillin
resistance determinant mecA: 5 Staph. aureus from 2
different farms and 5 NAS from 3 different farms. Almost all Staph. aureus isolates were positive for at least
3 of the screened virulence genes, whereas, in total, only
8 NAS isolates harbored any of the same genes. Our
study contributes to the continuous need for knowledge
regarding staphylococci from food-producing animals
as a basis for better understanding of occurrence of
resistance and virulence traits in these bacteria.
Key words: Staphylococcus aureus, non-aureus
staphylococci, antimicrobial resistance, virulence genes,
bovine mastitis
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