Staphylococcus aureus secretes two cysteine proteases, Staphopain A (scpA) and Staphopain B (sspB). We hypothesized that ScpA will exhibit a distinct activation mechanism, and a different or complementary substrate specificity compared to SspB. A Cys>Ala active site substitution led to the accumulation of unprocessed 40-kDa proScpA, confirming that ScpA undergoes autocatalytic activation. A temporal analysis of ScpA expression revealed that activation was initiated by processing at Lys171 and Glu176, producing an intermediate that was rapidly converted to several isoforms of mature protease by processing after Thr202, Lys209, Thr214 and Asn216. Consistent with broad specificity, mature ScpA was sensitive to autocatalytic degradation. ScpA demonstrated activity towards elastin, fibrinogen and indicated evidence for binding to heparin. Elastinolytic activity was uniquely associated with strains belonging to CC30, and was correlated with ScpA expression. Therefore, although ScpA and SspB share both sequence and structural similarity, they exhibited very different substrate specificities and activation mechanisms.

Mastitis is a syndrome manifested by mammary gland inflammation which is thought to cause between $300 and $400 million in annual losses to the Canadian Dairy Industry. Studies have indicated that <i>S. aureus</i> may cause the production of anti-inflammatory cytokines which may enhance its survival within the bovine mammary gland. However, other studies have reported differing results following S. aureus intramammary infection (IMI). This thesis tested the hypothesis that S. aureus generated anti-inflammatory cytokine responses at the site of infection. In the first objective, different S. aureus isolates were screened for their effects on cytokine production (IFN-γ, TNF-α, IL-4 and IL-10) by bovine peripheral blood mononuclear cells (PBMCs) in vitro. Nine S. aureus isolates were co-cultured with PBMCs from lactating dairy cattle. Cattle used in the study had recall immune responses to <i>S. aureus</i>. The majority (6/9) of S. aureus isolates had minor effectors on cytokine production. The three remaining isolates generated large cytokine responses with both pro-inflammatory (IFN-γ and TNF-α) and anti-inflammatory (IL-4 and IL-10) characteristics. Two of these three isolates were tested in vivo by experimentally infecting lactating ewes. Cytokine production was characterized in the teat end, the mammary parenchyma and the supramammary lymph nodes (SMLNs). One isolate generated anti-inflammatory responses <i>in vivo</i> (IL-4 and IL-10) whilst the other generated both pro-inflammatory (IFN-γ) and anti-inflammatory (IL-10) responses in vivo. Given that some studies have suggested a role of staphylococcal enterotoxin C (sec) in the generation of anti-inflammatory responses, the role of sec was also investigated using bovine PBMCs. When purified SEC protein was co-cultured with PBMCs from beef steers, anti-inflammatory cytokines were produced. However, a <i>S. aureus</i> strain which was transformed for the sec gene did not affect cytokine production when co-cultured with PBMCs from lactating dairy cattle. The results of this thesis suggest that <i>S. aureus</i> infection can cause anti-inflammatory cytokine production but the response depends on the isolate causing the infection. Furthermore, the role of sec appears to be minimal.

Staphylococcus aureus secretes two cysteine proteases, Staphopain A (scpA) and Staphopain B (sspB). We hypothesized that ScpA will exhibit a distinct activation mechanism, and a different or complementary substrate specificity compared to SspB. A Cys>Ala active site substitution led to the accumulation of unprocessed 40-kDa proScpA, confirming that ScpA undergoes autocatalytic activation. A temporal analysis of ScpA expression revealed that activation was initiated by processing at Lys171 and Glu176, producing an intermediate that was rapidly converted to several isoforms of mature protease by processing after Thr202, Lys209, Thr214 and Asn216. Consistent with broad specificity, mature ScpA was sensitive to autocatalytic degradation. ScpA demonstrated activity towards elastin, fibrinogen and indicated evidence for binding to heparin. Elastinolytic activity was uniquely associated with strains belonging to CC30, and was correlated with ScpA expression. Therefore, although ScpA and SspB share both sequence and structural similarity, they exhibited very different substrate specificities and activation mechanisms.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Toxicology." Includes bibliographical references (p. 158-173).

published_or_final_version / Public Health / Master / Master of Public Health

published_or_final_version / Public Health / Master / Master of Public Health

No description available.

Staphylococcus aureus (S. aureus) is a medically important bacterial pathogen associated with many diseases and infections of the respiratory system, wound sites, surgical incisions, and other portals of entry and exit. S. aureus is able to invade cells via mechanisms that have yet to be fully characterized. Vimentin, a protein filament of the animal cell cytoskeleton, and phosphoinositide 3-kinase (PI3K), a family of kinases responsible for initiating several cell signaling events, were found to be associated with S. aureus invasion. Confocal microscopy revealed that the vimentin network in human umbilical vein endothelial cells (HUVECs) undergoes dynamic rearrangement in steady state under control conditions. However, cells infected with S. aureus demonstrated peri-nuclear collapse of the vimentin network. Pre-treatment with LY294002, a drug that inhibits PI3K activity, decreased invasion of S. aureus and paralyzed the vimentin network. These data suggest that PI3K mediates S. aureus infection and vimentin rearrangement. / Department of Biology

The growing threat of drug- resistant Staphylococcus aureus (S. aureus) infections mandates the need to develop novel, effective and alternative antibacterial therapeutics. Despite infection prevention and control measures, methicillin resistant S. aureus (MRSA)-associated deaths reached 11,285 in 2011 in the USA (CDC, 2013). To counteract the threat of drug resistant S. aureus, we sought to construct and characterize a novel therapeutic based on the display of lytic antibacterial enzymes, termed endolysins. These endolysins were displayed on the surface of a specific bacterial virus, bacteriophage (phage), to generate lytic antibacterial nanoparticles. Endolysins are encoded individually by a variety of double-stranded DNA phage and act to direct host lysis and escape. These lytic enzymes confer a high degree of host specificity that could potentially substitute for, or be combined with, antibiotics in the treatment of gram-positive drug resistant bacterial infections such as MRSA. In this study, modular domains of the phage-encoded endolysin K enzyme, specific to S. aureus, were displayed on the capsid surface of phage lambda () via fusion with the λ major head (capsid) protein, gpD. The constructs of displayed endolysins were prepared in various combinations to maximize the functional display of gpD::X fusions on the phage. Phage lysates were generated, collected and purified and lysis was investigated by adding to fresh lawns of MRSA, vancomycin resistant S. aureus (VRSA) and bovine S. aureus. Phage preparations did not readily confer cell lysis, likely due to poor incorporation of the fusions onto the functional phage capsid. We purified the fusion proteins (gpD::X) and tested them for their lytic activity. We noted that the activity of the gpD::LysK protein was not impaired by the fusion and demonstrated lysis on live and dead (autoclaved) bovine S. aureus. In contrast to gpD::LysK, the gpD::CHAP protein fusion, expressing only the CHAP catalytic domain of endolysin K showed variable results in the lysis assays that we performed. In the zymogram assay, gpD::CHAP did not elicit any observable lysis on live bovine S. aureus cells, but did effectively lyse dead cells of the same S. aureus species; however, it was highly lytic in the inhibition assay on bovine S. aureus. The CHAP::gpD protein fusion, which is the CHAP domain fused to the N terminus of gpD only showed its ability to inhibit bovine S. aureus growth on the inhibition assay. The fusion of endolysin K or its CHAP domain to gpD protein does not seem to interfere with lytic activity, but may result in recalcitrant gpD fusions that compromise the ability to efficiently decorate the phage capsid. Suggestions for improved fusion capsid integration are discussed.

Staphylococcus aureus is the most clinically important Staphylococcus species and is associated with high mortality in patients with positive blood cultures. S. aureus bacteria may cause a variety of disease manifestations ranging from minor skin infections to life-threatening conditions such as pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock syndrome (TSS) and sepsis. This microorganism belonging to the gram positive cocci may also be part of the normal flora. In Sweden, penicillinase-stable penicillins are the primary alternatives to treat S. aureus infection. Mutations in genes encoding the penicillin binding proteins (PBP2) in the bacteria which lead to a lower affinity for the  beta-lactam antibiotics define  methicillin resistant S. aureus (MRSA) which is a significant global health problem. Other resistance mechanisms of S. aureus are present, and one of these is penicillinase production which is associated with resistance to penicillin G. In order to detect penicillinase production in S. aureus, there are several methods but the European guidelines recommend disc diffusion and the clover-leaf test for follow-up if the zone diameter for benzylpenicillin (PcG) is 26 mm or more. There are no modern Swedish studies on the prevalence of S. aureus susceptible to PcG and this has recently attained interest from infectious disease physicans. Thus, the purpose of this study was to investigate the frequency of S. aureus susceptible to PcG from blood cultures isolated during 2012 from the Kalmar county.    Disc diffusion testing showed that 32% of 90 unique isolates tested had an inhibition zone diameter of PcG that was ≥ 26 mm in diameter. All of these isolates were confirmed as PcG sensitive with clover-leaf test. Internal controls showed little variation and external control isolates showed full agreement with the results obtained from a Danish study, suggesting that PcG zone diameter of ≥ 26 mm in combination with cloverleaf test can be used to detect penicillin susceptibility of S. aureus.    In conclusion, this study shows that nearly 1 /3 of the blood culture isolates of S. aureus from Kalmar are sensitive to benzylpenicillin.