Non-aureus staphylococci and mammaliicocci as a cause of mastitis in domestic ruminants: current knowledge, advances, biomedical applications, and future perspectives – a systematic review

Abstract

Non-aureus staphylococci and mammaliicocci (NASM) are one of the most common causes of subclinical mastitis in dairy animals and the extent of damage by intramammary infections (IMI) caused by NASM is still under debate. The different effects of NASM on the mammary gland may be associated with differences between bacterial species. NASM are normal and abundant colonizers of humans and animals and become pathogenic only in certain situations. The veterinary interest in NASM has been intense for the last 25 years, due to the strongly increasing rate of opportunistic infections. Therefore, the objective of this review is to provide a general background of the NASM as a cause of mastitis and the most recent advances that exist to prevent and fight the biofilm formation of this group of bacteria, introduce new biomedical applications that could be used in dairy herds to reduce the risk of chronic and recurrent infections, potentially responsible for economic losses due to reduced milk production and quality. Effective treatment of biofilm infection requires a dual approach through a combination of antibiofilm and antimicrobial agents. Even though research on the development of biofilms is mainly focused on human medicine, this technology must be developed at the same time in veterinary medicine, especially in the dairy industry where IMI are extremely common.

Staphylococcal mastitis in dairy cows

“…NAS are increasingly reported as the most frequent isolates from lactating dairy cows ( 6 , 20 , 25 , 92 ). Some NAS are frequently reported as etiology of subclinical mastitis in dairy ruminants ( 6–9 , 93 , 94 ), while others occasionally cause mastitis in dairy cows as well as other diseases in animals ( 10–15 ). Some studies reported S. chromogenes, S. simulans , S. epidermidis, and S. xylosus as major isolates from teat skin and teat tips, whereas other studies identified S. chromogenes , S. haemolyticus , and S. xylosus as major isolates from milk samples ( 95–98 ).…”

“…NAS species induce only mild inflammatory response with mild to moderate increase in SCC in the infected quarter, reducing milk quality and price, and low bulk tank milk SCC may discourage producers from intervening in IMI, allowing these pathogens to cause continuous loss of productivity ( 124 , 143 , 146 ). In dairy cows with subclinical infection with these groups of pathogens at peak lactation can result in approximately 1.8 kg/d reduction in milk production ( 94 , 146 ). Because of a modest increase in milk SCC, the IMI due to NAS may not account for increased SCC in dairy farms that already have high SCC due to major mastitis pathogens.…”

“…Similarly, under in vivo conditions, the udder, pre-colonized by some strains of NAS, was shown to resist colonization by major bacterial mastitis pathogens ( 157–160 ). However, even though pre-colonization of the udder by some members of NAS species seems protective against colonization by major mastitis pathogens, some NAS species themselves were isolated and identified as the etiology of mastitis and shown to be responsible for milk production losses ( 94 , 142 , 146 ). It has also been shown that priming the murine mammary glands with S. chromogenes induced innate responses that reduced the growth of S. uberis ( 161 ).…”

“…MRSA infection is zoonotic ( 168 ), and continuous antimicrobial susceptibility surveillance is crucial to control the transmission of this strain from animal production to humans and vice versa ( 169 ). They may transfer resistance traits to S. aureus or other bacteria, resulting in the emergence of multidrug-resistant strains ( 94 , 135 ). The prevalence of infection by these groups of bacteria is on the rise mainly due to the spread of resistance to antimicrobial drugs among these groups ( 135 ).…”

Coagulase-Negative Staphylococci as an Etiologic Agent of Ovine Mastitis, with a Focus on Subclinical Forms

“…Coagulase-negative Staphylococci (CoNS) are opportunistic pathogens regularly associated with intramammary infection (IMI) in ruminants, and mostly in subclinical cases. During the last years, this group has become a main etiologic agent of ruminant mastitis [6]. Furthermore, recent studies indicate that these species are capable of causing more severe tissue damage in the mammary gland than was previously considered [7].…”