Phenotypic and genotypic antimicrobial resistance of staphylococci from bovine milk

Abstract

The aim of this study was to examine phenotypic and genotypic antimicrobial resistance of staphylococci from milk samples from cows with subclinical and clinical mastitis and from cows without mastitis symptoms to methicillin, tetracyclines, macrolides and lincosamides (ML). Of 207 strains, including 34 S. aureus and 173 coagulase-negative staphylococci (CNS), 11 (6.4%) CNS strains were phenotypically resistant to methicillin. The mecA gene was detected by PCR only in two S. xylosus strains and one strain of S. epidermidis and S. simulans. No methicillin-resistant S. aureus strains were observed. In methicillin-resistant strains with mecA, gene resistance to other investigated antibiotics was not observed. Phenotypic resistance to tetracycline was detected in 11.0% of CNS strains and 47.4% of them carried the tetK gene. Of 173 CNS strains studied, 27 (15.6%) were resistant to at least one ML antibiotic. The resistance gene ermC was detected in 55.5% of the 27 ML-resistant strains. The ermA and ermB genes were detected in 14.8% and 11.1% of ML-resistant CNS strains, respectively. Antimicrobial resistance to methicillin, tetracyclines and macrolides was detected more frequently in staphylococcal strains from clinical mastitis compared to animals with subclinical symptoms and without mastitis, while the resistance to lincosamides showed a similar frequency in all groups of cows. In conclusion, CNS species from bovine milk differ in phenotypic and genotypic antimicrobial resistance profiles, and the use of PCR technique alone for the detection of methicillin, macrolide, lincosamide and tetyracycline resistance in CNS from cattle is not reliable.

Molecular identification of coagulase-negative staphylococci isolated from bovine mastitis and detection of β-lactam resistance

“…With respect to the third species most frequently identified in our study, our percentages agree with those reported in Switzerland [14], S. haemolyticus was reported as the most frequently isolated species in Turkey [17]. Among the least common species identified, they were the same as those reported in other countries [9,11,16,18]. The S. devriesei species was identified using the ClaI restriction enzyme; we could not identify this species before, staying only within a group.…”

Molecular types and antimicrobial resistance profile of Staphylococcus aureus isolated from dairy cows and farm environments

“…Genotypic resistance to tetK was recorded in 16 (32.69%) isolates, out of which 15 (93.75%) were resistant to oxytetracycline. Such variations in phenotypic and genotypic AMR patterns in the staphylococci from bovine mastitis milk have been documented earlier (23), whereby 47.4% of coagulasenegative staphylococci (CNS) harbored the tetK gene and 11.1% of macrolide-resistant CNS strains harbored the ermB gene.…”

Characterization of antimicrobial resistance in Staphylococcus aureus isolated from bovine mastitis in Central Ethiopia

“…It has been known that, isolates harbor erm genes (erythromycin resistance rRNA methylase) code for the protein called methyl transferase which induces N6dimethylation of an adenine residue of 23S rRNA. This process produces conformational changes in the phosphate site of the rRNA and prevents the macrolide binding at the peptidyl transferase center, hence the protein production will proceed and the bacteria will survive (Kot et al, 2012;Westh et al, 1995). Expression of the three related factors; ermA, ermB, and ermC, are responsible to make the bacteria resistance to macrolides and other related antibiotic groups (Ojo et al, 2006;Westh et al, 1995).…”