Non-aureus Staphylococci and Bovine Udder Health: Current Understanding and Knowledge Gaps

Abstract

Despite considerable efforts to control bovine mastitis and explain its causes, it remains the most costly and common disease of dairy cattle worldwide. The role and impact of non-aureus staphylococci (NAS) in udder health are not entirely understood. These Gram-positive bacteria have become the most frequently isolated group of bacteria in milk samples of dairy cows and are associated with (mild) clinical and subclinical mastitis. Different species and strains of NAS differ in their epidemiology, pathogenicity, virulence, ecology and host adaptation, and antimicrobial resistance profiles. They have distinct relationships with the microbiome composition of the udder and may also have protective effects against other mastitis pathogens. Some appear to persist on the skin and in the teat canal and udder, while others seem to be transient residents of the udder from the environment. Analyzing genotypic and phenotypic differences in individual species may also hold clues to why some appear more successful than others in colonizing the udder. Understanding species-level interactions within the microbiome and its interactions with host genetics will clarify the role of NAS in bovine mastitis and udder health.

Spatio-Temporal Variation in the Prevalence of Major Mastitis Pathogens Isolated From Bovine Milk Samples Between 2008 and 2017 in Ontario, Canada

“…This study also showed that over the years NAS have increasingly been isolated from the milk samples. At the species level, S. chromogenes was the dominant NAS species similar to what was noted in a Canada wide study, the US study and some European studies, however regional variation in the type of NAS species prevalence was noted ( 27 – 29 ). Understanding of the prevalence of NAS at species level is necessary from a disease control and management point of view as infection by some of these species of NAS has been known to be persistent and hence a source of infection to other animals in the herd.…”

“…Understanding of the prevalence of NAS at species level is necessary from a disease control and management point of view as infection by some of these species of NAS has been known to be persistent and hence a source of infection to other animals in the herd. Whereas, other species like S. simulans are more of an environmental pathogen ( 29 , 30 ).…”

Whole Genome Sequencing of Staphylococci Isolated From Bovine Milk Samples

“…Considering the apparent complexity of virulence and the limited knowledge on the subject in bovine NAS, further studies on the association between virulence and clinical impact of these species is important. As several studies indicates that S. chromogenes could have a greater impact on udder health ( Supré et al, 2011 ; Fry et al, 2014 ; Valckenier et al, 2019 ) and both this study and Naushad et al (2019) found S. chromogenes among those with the highest virulence potential, further studies of the virulence and pathogenesis of this species should be emphasized ( De Buck et al, 2021 ).…”

“…The genus Staphylococcus includes a range of different species ( De Buck et al, 2021 ) some of which are among the most commonly isolated bacteria causing intramammary infections in bovines ( Pitkälä et al, 2004 ; Reksen et al, 2006 ; Olde Riekerink et al, 2008 ). For a long time, Staphylococcus aureus has been the most recognized staphylococcal species causing both clinical and subclinical mastitis ( Østerås et al, 2006 ; Olde Riekerink et al, 2008 ).…”

“…All these factors contribute to bacterial survival, -spread and nutrient acquisition ( Tam and Torres, 2019 ). However, in recent years, non- aureus staphylococci (NAS) have emerged as the most frequently isolated bacterial group from bovine milk in many countries and they are increasingly associated with intramammary infections ( Pyörälä and Taponen, 2009 ; De Vliegher et al, 2012 ; Condas et al, 2017 ; De Buck et al, 2021 ).…”