The aim of this review was to describe the importance of coryneform bacteria in bovine mastitis and human diseases, as well as laboratory examinations applied in their case. The coryneform group comprises Gram- -positive, non-sporeforming and irregularly shaped rods. Within this group there is a lot of species that are part of the normal flora of skin and mucous membranes of humans and animals. Under favourable conditions opportunistic infections are caused by these microorganisms in immunocompromised hosts. They also occur in bovine mastitic milk and cause differentiated clinical symptoms. The most frequently isolated bacteria from this group are Corynebacterium bovis, which is considered as contagious but less pathogenic for cows’ mammary gland; Arcanobacterium pyogenes, which belongs to major pathogens; and Corynebacterium ulcerans. While Arc. pyogenes causes an acute suppurative mastitis, termed summer mastitis, C. bovis and C. ulcerans may cause subclinical forms of mammary gland inflammation. Summer mastitis is associated with abscesses within the udder and milk losses in the affected quarter, and may even lead to the death of the animal. Conversely, C. bovis mastitis often manifests itself in only slight increases of somatic cell counts in milk. Moreover, C. bovis may protect quarters against infection with e.g. Staphylococcus aureus. Unpasteurized milk and raw dairy products derived from infected cows and direct contact with animals constitute potential sources of coryneform bacteria infections in humans. Arc. pyogenes has been reported to cause ear infections, endocarditis, cystitis and cutaneous abscesses as well. Patients infected with C. bovis exhibited signs of septicaemia and purulent conjunctivitis. Toxigenic C. ulcerans strains may cause pharyngeal infections mimicking classical diphtheria, ulcers and sinusitis in humans. Non-toxigenic strains cause pulmonary nodules and necrotizing granulomas. Bacteriological examination of the coryneform includes phenotypic methods (Gram stain, biochemical reactions) as well as molecular methods (PCR, 16S rRNA sequencing). Considering the increasing proportion of coryneform bacteria in hospital infections and the transmission of infections from animals to humans, in cases of mastitis there is a need for a permanent control of the occurrence of microorganisms that are dangerous for human health.
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