Phenotypic antimicrobial susceptibility and occurrence of selected resistance genes in gram-positive mastitis pathogens isolated from Wisconsin dairy cows

Abstract

In the United States, few intramammary antimicrobials exist that are approved for treatment of bovine mastitis; thus, ensuring judicious use of these products is a priority. The objectives of this study were to determine phenotypic susceptibility and presence of selected antimicrobial resistance genes from staphylococci, streptococci, and streptococcal-like organisms recovered from cases of clinical mastitis occurring in cows on large Wisconsin farms. Staphylococcus aureus (n=35 from 19 herds), coagulase-negative staphylococci (n=51 from 30 herds), Streptococcus spp. (n=78 from 36 herds), and streptococcal-like organisms (n=31 from 19 herds) were used in this study. All Staphylococcus spp. were susceptible to ceftiofur, cephalothin, and the combination of penicillin and novobiocin. Of all staphylococci, only a single Staphylococcus epidermidis exhibited phenotypic resistance to oxacillin. Phenotypic susceptibility to erythromycin was observed in only 8.6 and 15.7% of Staphylococcus aureus and coagulase-negative staphylococci, respectively. Approximately 20% of staphylococci and 13 to 22% of streptococci and streptococcal-like organisms exhibited phenotypic resistance to pirlimycin. All Streptococcus spp. exhibited phenotypic susceptibility to ceftiofur, cephalothin, and oxacillin. The proportion of isolates exhibiting phenotypic susceptibility to pirlimycin and sulfadimethoxine differed among Streptococcus dysgalactiae and Streptococcus uberis. All streptococcal-like organisms exhibited phenotypic susceptibility to ceftiofur, cephalothin, oxacillin, penicillin, and the combination of penicillin and novobiocin. Of all organisms tested, 36.9% did not carry any of the resistance genes (ermC, blaZ, tetK, or tetM), 35.4% carried 1 gene, and 27.7% carried multiple genes (usually blaZ in combination with a tet gene). Eighteen (51.4%) Staph. aureus and 12 (48.0%) Staphylococcus chromogenes carried multiple resistance genes. Six (12.2%) Strep. dysgalactiae and no Strep. uberis carried multiple resistance genes. Results indicate that most gram-positive mastitis organisms were susceptible to most antimicrobials used for intramammary administration, but some resistance to drugs used for systemic treatment of mastitis was noted. The presence of selected resistance genes was not proportional to the occurrence of phenotypic resistance.

Molecular epidemiology and distribution of antimicrobial resistance genes of Staphylococcus species isolated from Chinese dairy cows with clinical mastitis

“…Likewise, mecA gene (resistance to β-lactam antibiotics; Wendlandt et al, 2013) was identified in >15 and 70% of S. aureus and NAS isolates, respectively. Prevalence of mecA among Staphylococcus isolates in this study was higher on these Chinese dairy farms than in CM isolates from other studies (Frey et al, 2013;Ruegg et al, 2015). This high prevalence of blaZ and mecA and potential resistance to β-lactam antibiotics in Chinese bovine Staphylococcus isolates highlighted a decisive point in the use of these antimicrobials, commonly used in mastitis treatment, in the dairy industry in China and other countries.…”

Whole-Genome Sequence Analysis of Antimicrobial Resistance Genes in Streptococcus uberis and Streptococcus dysgalactiae Isolates from Canadian Dairy Herds

“…The presence of both genes has been previously reported in bovine and human Streptococcus spp. isolates (53, 70). In general, associations between the phenotypic and genotypic characteristics were observed for a limited number of antibiotics for both pathogens (Table 3; Table S3 in Supplementary Material; P  < 0.10).…”

Mastitis treatment—Reduction in antibiotic usage in dairy cows

“…To date, the issue of resistant or multiresistant MCP such as methicillin‐resistant S. aureus (MRSA) seems to play a subordinate role in dairy industry (Erskine et al., ; Kreausukon et al., ; Oliver, Murinda, & Jayarao, ; Pol & Ruegg, ; Schröder, Hoedemaker, & Klein, ; Tenhagen et al., ). However, the number of studies reporting of enhanced emergence of AMR increases (da Costa Krewer et al., ; Ding et al., ; Fairbrother et al., ; Jagielski et al., ; Petrovski et al., ; Ruegg, Oliveira, Jin, & Okwumabua, ; Saini, McClure, Scholl, DeVries, & Barkema, ; Spohr et al., ).…”