Differential Abilities of Capsulated and Noncapsulated Staphylococcus aureus Isolates from Diverse agr Groups To Invade Mammary Epithelial Cells

Abstract

Staphylococcus aureus is the bacterium most frequently isolated from milk of bovines with mastitis. Four allelic groups, which interfere with the regulatory activities among the different groups, have been identified in the accessory gene regulator (agr) system. The aim of this study was to ascertain the prevalence of the different agr groups in capsulated and noncapsulated S. aureus bacteria isolated from mastitic bovines in Argentina and whether a given agr group was associated with MAC-T cell invasion and in vivo persistence. Eighty-eight percent of the bovine S. aureus strains were classified in agr group I. The remainder belonged in agr groups II, III, and IV (2, 8, and 2%, respectively). By restriction fragment length polymorphism analysis after PCR amplification of the agr locus variable region, six agr restriction types were identified. All agr group I strains presented a unique allele (A/1), whereas strains from groups II, III, and IV exhibited more diversity. Bovine S. aureus strains defined as being in agr group I (capsulated or noncapsulated) showed significantly increased abilities to be internalized within MAC-T cells, compared with isolates from agr groups II, III, and IV. agr group II or IV S. aureus strains were cleared more efficiently than agr group I strains from the murine mammary gland. The results suggest that agr group I S. aureus strains are more efficiently internalized within epithelial cells and can persist in higher numbers in mammary gland tissue than S. aureus strains classified in agr group II, III, or IV.

SpA, ClfA, and FnbA Genetic Variations Lead to Staphaurex Test-Negative Phenotypes in Bovine Mastitis Staphylococcus aureus Isolates

“…The dominance of agr types I and II in bovine S. aureus isolates was also shown previously by Gilot et al (12). Buzzola et al (7) demonstrated that agr type II S. aureus isolates displayed a significantly decreased level of internalization into MAC-T (bovine mammary epithelial cell line) cells in vitro. One plausible hypothesis would be that this might be linked to a higher degree of suppression of spa and fnbA and -B expression by agr type II than by agr type I isolates, but this remains to be investigated.…”

“…Moreover, S. aureus is able to invade epithelial and endothelial cells as well as fibroblasts via binding of FnpA and -B to fibronectin, which provides a bridge to the ␣5␤1 integrin of host cells (34). The role of the fibronectin-binding proteins in adhesion and invasion of cells has also been shown for bovine mammary gland cells (25), but strain-associated differences were observed (7,18).…”

Screening of virulence genes in Staphylococcus aureus isolates from rabbits

“…Vancraeynest et al (2006) also reported that the most frequent agr subgroup was type IV (100%). However, these results disagree with studies in human and bovine species, determining that the most frequent agr subgroup was type I (Buzzola et al, 2007;Vautor et al, 2009). …”

Existence of two groups of Staphylococcus aureus strains isolated from bovine mastitis based on biofilm formation, intracellular survival, capsular profile and agr-typing

“…In addition, S. aureus bacteria that do not express capsule induce chronic mastitis in mice, suggesting that the absence of capsule synthesis may help the bacteria to persist in the mammary glands (Tuchscherr et al, 2005). Finally, agr group I is associated with a persistence or with features that help the bacteria to persist in the udder: strains belonging to agr group I are more likely to be internalised in epithelial cells, to persist in murine mammary glands (Buzzola et al, 2007) and to be associated with penicillin resistance (Melchior et al, 2011) than the strains belonging to the other groups.…”

“…Therefore, the bacteria are not only protected from the action of commonly used antibiotics in mastitis treatment (mainly b-lactams), and also able to persist in the host without causing any apparent inflammation (Boulanger et al, 2003;Garzoni and Kelley, 2009). The absence of capsular expression enhance the adherence to and the invasion of eukaryotic cells by S. aureus (PohlmannDietze et al, 2000;Buzzola et al, 2007;Tuchscherr et al, 2005). In addition, S. aureus bacteria that do not express capsule induce chronic mastitis in mice, suggesting that the absence of capsule synthesis may help the bacteria to persist in the mammary glands (Tuchscherr et al, 2005).…”