Short communication: Genotypic and phenotypic identification of environmental streptococci and association of Lactococcus lactis ssp. lactis with intramammary infections among different dairy farms

Abstract

Lactococcus species are counted among a large and closely related group of environmental streptococci and streptococci-like bacteria that include bovine mastitis pathogenic Streptococcus, Enterococcus, and Aerococcus species. Phenotypic and biochemical identification methods can be inaccurate and unreliable for species within this group, particularly for Lactococcus spp. As a result, the incidence of Lactococcus spp. on the farm may have been historically underreported and consequently little is known about the clinical importance of this genus as a mastitis pathogen. We used molecular genetic identification methods to accurately differentiate 60 environmental streptococci and streptococci-like bacteria isolated from cows with high somatic cell count and chronic intramammary infection (IMI; >2 somatic cell scores above 4) among 5 geographically distinct farms in New York and Minnesota that exhibited an observed increase in IMI. These isolates were phenotypically identified as Streptococcus uberis and Streptococcus spp. Genetic methods identified 42 isolates (70%) as Lactococcus lactis ssp. lactis, including all 10 isolates originally phenotypically identified as Streptococcus uberis. Antibiotic inhibition testing of all Lc. lactis ssp. lactis showed that 7 isolates were resistant to tetracycline. In the present study, a predominance of Lc. lactis ssp. lactis was identified in association with chronic, clinical bovine IMI among all 5 farms and characterized antimicrobial resistance for treatment therapies. Routine use by mastitis testing labs of molecular identification methods for environmental streptococci and streptococci-like bacteria can further define the role and prevalence of Lc. lactis ssp. lactis in association with bovine IMI and may lead to more targeted therapies.

<b>Etiological and molecular profile of pathogens causing clinical mastitis, and antimicrobial use in dairy herds</b>

“…Because Strep. uberis identification by conventional culturing method could be subject to misidentification (WERNER et al, 2014), all Strep. uberis isolates were also identified using MALDI-TOF MS as described previously (Chapter 4).…”

Molecular characterization of bacterial isolates and microbiome: study of mastitic milk, bulk tank milk, and cheese processing plants

“…For example, species within Lactococcus genus, widely used in the dairy industry (CASALTA; MONTEL, 2008) are now being considered as potential mastitis pathogens (PLUMED-FERRER et al, 2013;PLUMED-FERRER et al, 2015;WERNER et al, 2014). Lactococcus are very close to environmental streptococci and streptococci-like bacterial groups that include classical mastitis pathogens (WERNER et al, 2014).…”

“…Lactococcus are very close to environmental streptococci and streptococci-like bacterial groups that include classical mastitis pathogens (WERNER et al, 2014). Many phenotypic and biochemical methods typically used for identification of species can be inaccurate and unreliable particularly for some closely related species (WERNER et al, 2014).…”

“…as pathogens may have been underreported and consequently there is lack of information about their clinical importance in bovine mastitis (WERNER et al, 2014). Moreover, advancements in available technologies, predominately DNA sequencing, will greatly support the identification and characterization of bacteria.…”

“…Moreover, advancements in available technologies, predominately DNA sequencing, will greatly support the identification and characterization of bacteria. A recent study using DNA sequencing, described that 70% of isolates identified as streptococci by conventional microbiological assays were in fact lactococci, the majority of which were L. lactis (WERNER et al, 2014). Thus, applying new methods to identify bacteria has yielded increased reports on Lactococcus spp.…”