Pathogens Associated with Bovine Mastitis: The Experience of Bosnia and Herzegovina

Simple Summary Mastitis is defined as the inflammation of the mammary gland and is one of the most widespread and economically important diseases of dairy cows. Bacteria are the most reported mastitis-causative agents, while other pathogens are often overlooked because they are not routinely investigated. Incomplete diagnosis may result in inappropriate antimicrobial therapy, treatment failure, antimicrobial resistance, dissemination of pathogens, and mastitis recurrences. Thus, this study aimed to investigate the presence of not only bacteria but also other microorganisms associated with cattle mastitis on dairy farms in Bosnia and Herzegovina, a country that lacks an effective mastitis control programme and bacteriological analysis of mastitic milk. The current study revealed Mycoplasma bovis as the main pathogen and a variety of other mastitis-causing agents in cattle: bacteria (Escherichia coli, Staphylococcus aureus, coagulase negative staphylococci, Streptococcus agalactiae, Streptococcus uberis, and others), fungi (Candida spp.), and algae (Prototheca zopfii). The finding of mastitis cases requiring currently unavailable treatment and vaccines emerges in the broader scope of etiological agents in routine mastitis diagnosis. These measures applied at the herd and national levels are crucial for more effective mastitis control, animal health and welfare, the dairy industry, and public health. Abstract To obtain improved insights into the complex microbial aetiology of bovine mastitis, this study investigated the pathogens involved in cattle mastitis in Bosnia and Herzegovina. A total of 179 milk samples from cows with clinical mastitis (CM) and subclinical mastitis (SCM), as well as eight bulk tank milk (BTM) samples from 48 dairy farms, were analysed by standard bacteriological and mycological methods. Mycoplasma detection and identification were performed using culture techniques and real-time polymerase chain reaction (PCR). A total of 88 (49.2%) mastitis samples were positive for known mastitis pathogens at 32 of 47 farms (68.1%). Mycoplasma bovis was a predominant pathogen (25/187; 13.4%) in the majority of herds (14/48; 29.2%) and accounted for 48.9% of positive CM samples. Escherichia coli was the second most dominant CM pathogen (34%), followed by Streptococcus agalactiae (10.6%), whereas Staphylococcus aureus and coagulase-negative staphylococci were the most common in SCM samples (17.1%). Other mastitis pathogens included Candida spp. and Prototheca zopfii. Two BTM samples were positive for M. bovis only, and one was positive for a mixed culture of S. aureus and Streptococcus uberis. The finding of various causative agents of bovine mastitis, with M. bovis emerging as the main pathogen, emphasizes the significance of comprehensive testing that includes not only common mastitis pathogens but also mycoplasmas, fungi, and algae.