Antimicrobial Susceptibility Patterns of Environmental Streptococci Recovered from Bovine Milk Samples in the Maritime Provinces of Canada

Abstract

Determination of antimicrobial susceptibility of bovine mastitis pathogens is important for guiding antimicrobial treatment decisions and for the detection of emerging resistance. Environmental streptococci are ubiquitous in the farm environment and are a frequent cause of mastitis in dairy cows. The aim of the study was to determine patterns of antimicrobial susceptibility among species of environmental streptococci isolated from dairy cows in the Maritime Provinces of Canada. The collection consisted of 192 isolates identified in milk samples collected from 177 cows originating from 18 dairy herds. Results were aggregated into: (1) Streptococcus uberis (n = 70), (2) Streptococcus dysgalactiae (n = 28), (3) other Streptococci spp. (n = 35), (4), Lactococcus spp. (n = 32), and (5) Enterococcus spp. (n = 27). Minimum inhibitory concentrations (MICs) were determined using the Sensititre microdilution system and mastitis plate format. Multilevel logistic regression models were used to analyze the data, with antimicrobial susceptibility as the outcome. The proportion of susceptible S. uberis ranged from 23% (for penicillin) to 99% (for penicillin/novobiocin), with a median of 82%. All S. dysgalactiae were susceptible to all antimicrobials except for penicillin (93% susceptible) and tetracycline (18% susceptible). The range of susceptibility for other Streptococcus spp. was 43% (for tetracycline) to 100%, with a median percent susceptibility of 92%. Lactococcus spp. isolates displayed percent susceptibilities ranging from 0% (for penicillin) to 97% (for erythromycin), median 75%. For the antimicrobials tested, the minimum inhibitory concentrations were higher for Enterococcus spp. than for the other species. According to the multilevel models, there was a significant interaction between antimicrobial and bacterial species, indicating that susceptibility against a particular antimicrobial varied among the species of environmental streptococci and vice versa. Generally, susceptibility decreased with increasing within-herd average somatic cell count, isolates recovered in mid-lactation were more susceptible than isolates recovered in early lactation, and isolates recovered in samples collected post-clinical mastitis were more susceptible than isolates recovered from non-clinical lactating quarters. The results of this research support continued susceptibility of environmental streptococci to beta-lactam antimicrobials. A departure from the expected susceptibility to beta-lactams was the apparent reduced susceptibility of S. uberis to penicillin.

Effect of recycled manure solids as bedding on bulk tank milk and implications for cheese microbiological quality

“…Therefore, higher levels in RMS-milk samples could be linked to their presence in the bedding. This could be an issue since environmental streptococci other than S. uberis and S. dysgalactiae, such as S. gallolyticus and S. lutetiensis, can cause mastitis in dairy cows (Cameron et al, 2016). This infection increases the number of somatic cells in raw milk.…”

“…The occurrence of the genera Enterococcus and Streptococcus in milk and cheese is also important. Indeed, environmental streptococci, including Streptococcus uberis, Streptococcus dysgalactiae, and enterococci such as Enterococcus spp., can cause mastitis in dairy cows (Cameron et al, 2016). Enterococcus spp.…”

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

“…From this national cohort, 98 isolates included in the Cameron et al’s (1) study were initially considered for WGS, based on their resistant and pan susceptibility characteristics. Seven isolates were excluded, from the initial number due to low DNA quality.…”

“…The mastitis plates were read automatically, as described in the study by Cameron et al (1). The MIC and the susceptibility status were interpreted according to the Clinical Laboratory and Standards Institute guidelines for each of the antimicrobials (CLSI 2013).…”

Biofilm formation on different pH conditions byStreptococcus agalactiaeisolated from bovine mastitic milk

“…Bovine mastitis is the commonest reason for antimicrobial use in lactating cows. Antimicrobial resistance patterns of mastitis pathogens have received much interest in recent years (Cameron et al 2016). Biofilm provides a protective structure that enhances bacteria survival and proliferation in the host environment (Ebrahimi et al 2013).…”