Slime production by bovine milk Staphylococcus aureus and identification of coagulase-negative staphylococcal isolates

Abstract

Staphylococcus aureus isolates from bovine milk were assessed for capsule or slime production. When pure S. aureus cultures in milk were inoculated directly into serum-soft agar constituted with a modified staphylococcus 110 medium, 100% of the isolates grew with diffuse colony morphology. Diffuse colony morphology was rapidly lost on subculture and was more rapidly lost in brain heart infusion-serum-soft agar. No evidence was seen for encapsulation in India ink preparations or by the clumping factor test. It was concluded that freshly isolated S. aureus strains produce slime, not true capsules. During examination of the 84 milk samples that grew staphylococci in addition to S. aureus (27.4%), a significant number of coagulase-negative staphylococcal species were encountered and identified by conventional tests as S. simulans (41.7%), S. xylosus (11.9%), S. epidermidis (3.6%), S. saprophyticus (3.6%), S. hyicus (2.9%), S. cohnii (1.2%), S. haemolyticus (1.2%), and S. warneri (1.2%). Five isolates (6.0%) were not identified. Attempts were also made to identify the isolates by the API Staph-Ident system, which gave an overall accuracy of 45.2%. The susceptibilities of the isolates to a variety of antibiotics were determined, and they appeared to be less resistant than human clinical isolates.

Prevalence of capsular polysaccharide types 5 and 8 among Staphylococcus aureus isolates from cow, goat, and ewe milk

“…By comparison of the growth in SSA and India ink staining, Anderson (1) rejected the conclusions of these previous reports, claiming that strains from cases of mastitis are not encapsulated and that growth as diffuse colonies in SSA is not a reliable test of encapsulation. Recently, Rather et al (14) confirmed both the results of Norcross and Opdebeeck and those of Anderson and concluded that fresh bovine milk isolates of S. aureus produce slime, not true capsules. These authors suggested that capsule, as defined as a covering, thick polysaccharide layer outside the cell wall, demonstrable by light microscopy, occurs in very few strains.…”

Coagulase‐negative Staphylococci and Mammary Gland Infections in Cows

“…The negative selection for Staphylococcus aureus by culling infected cows, has resulted in more frequently isolated CNS from mastitic cases . Several reports showed that CNS could be associated with subclinical mastitis and elevated somatic cell count (SCC), ranging from 200 000 to 620 000/ml (Watts et al, 1984;Rather et al, 1986;Pyörälä and Syväjärvi, 1987;Matthews et al, 1990;Chaffer et al, 1998) or clinical mastitis (Jarp, 1991) with severe local clinical signs in the affected quarter as well as general systemic effects. Mastitis caused by CNS appears to be a disease of young cows .…”

Staphylococcus aureus exopolysaccharide in vivo demonstrated by immunomagnetic separation and electron microscopy

“…Although encapsulation in S. aureus from bovine mastitis is controversial (25), recent evidence indicates that capsular polysaccharide production is a predominant feature of mastitis pathogenic S. aureus (19). The present study provides a direct demonstration of abundant capsular polysaccharide of S. aureus in situ in bovine mastitis milk.…”