Anti-S. aureus Hla monoclonal antibody, clone 7D23

Staphylococcus aureus is a common cause of bovine mastitis and foodborne and other diseases in humans. This study tested the hypothesis that small colony variants (SCVs) of S. aureus are implicated in chronic bovine mastitis. Six S. am-ens isolates from foremilk samples from 11 chronically infected cows were investigated. Five isolates had typical morphology and were hemolytic and coagulase positive; one was a heterogeneous Population of typical and SCV phenotype (tiny nonhemolytic colonies). In the presence of gentamicin, three of the previously typical S. aureus developed SCVs that were confirmed as S. aureus by biochemical and genetic analyses; these SCVs reverted to the typical form on antibiotic-free medium. The SCV isolate (Heba3231) from the heterogeneous population had a slow growth rate and prolonged lag phase and did not revert during 10 h of incubation. Transcriptional analysis showed that SCV Heba3231. had reduced expression of agr, hla, and con and increased expression of indicators of fermentation pathways compared to the parent strain. Invasion of and persistence in a primary culture of bovine aortic endothelial cells (BAEC) showed that SCV Heba3231. had minimal deleterious effects, whereas the parent strain or the Newbould 305 strain caused severe damage. Recovery of the parent strain from BAEC yielded a mixture of the parent and SCV phenotypes. This study reports for the first time the isolation of S. aureus SCV from persistent bovine mastitis and suggests that SCV may be an important contributor to the prolonged survival of S. aureus in some cases of mastitis.

The production of cytokines in monocytes/macrophages is regulated by several different cytokines that have activating or inhibitory effects. Interleukin (IL)-10, IL-4, IL-13, and transforming growth factor (TGF)-beta are usually considered to be the most important macrophage-deactivating factors, with inhibitory effects on cytokine production. Unlike IL-10 and TGF-beta, which appear to act as downmodulators of many phagocytic cell functions, the mode of action of IL-4 and IL-13 is more complex. Addition of IL-4 and IL-13 to peripheral blood mononuclear cell (PBMC) cultures inhibited production of IL-12, tumor necrosis factor (TNF)-alpha, IL-10, and IL-1 beta induced by lipopolysaccharide (LPS) or Staphylococcus aureus trs added simultaneously with the cytokines. However, pretreatment of PBMC with IL-4 or IL-13 for greater than or equal to 20 h enhanced the production of IL-12 and TNF-alpha in response to LPS or S. aureus several fold in these cells; this IL-4-induced priming for the two cytokines was inhibited by anti-IL-4 neutralizing antibodies. IL-4 priming also enhanced the accumulation of IL-12 and TNF-alpha mRNA induced by LPS and S. aureus. The enhanced accumulation of transcripts for the IL-12 p35 and p40 chains by IL-4 priming was reflected in enhanced secretion of both the IL-12 free p40 chain and the p70 heterodimer. These results suggest an unexpected complexity in the regulatory role of IL-4 and IL-13 in immune responses.