Pathogenesis of MRSA infections

Human Palatine Tonsils Are Linked to Alzheimer’s Disease through Function of Reservoir of Amyloid Beta Protein Associated with Bacterial Infection

Amyloid-β (Aβ)-peptide production or deposition in the neuropathology of Alzheimer’s disease (AD) was shown to be caused by chronic inflammation that may be induced by infection, but the role of pathogenic-bacteria-related AD-associated Aβ is not yet clearly understood. In this study, we validated the hypothesis that there is a correlation between the Aβ-protein load and bacterial infection and that there are effects of bacteria, Staphylococcus aureus (S. aureus), on the Aβ load in the inflammatory environment of human tonsils. Here, we detected Aβ-peptide deposits in human tonsil tissue as well as tissue similar to tonsilloliths found in the olfactory cleft. Interestingly, we demonstrated for the first time the presence of Staphylococcus aureus (S. aureus) clustered around or embedded in the Aβ deposits. Notably, we showed that treatment with S. aureus upregulated the Aβ-protein load in cultures of human tonsil organoids and brain organoids, showing the new role of S. aureus in Aβ-protein aggregation. These findings suggest that a reservoir of Aβ and pathogenic bacteria may be a possible therapeutic target in human tonsils, supporting the treatment of antibiotics to prevent the deposition of Aβ peptides via the removal of pathogens in the intervention of AD pathogenesis.

Construction of A New Dose-Response Model for Staphylococcus aureus Considering Growth and Decay Kinetics on Skin

In order to determine the relationship between an exposure dose of Staphylococcus aureus (S. aureus) on the skin and the risk of infection, an understanding of the bacterial growth and decay kinetics is very important. Models are essential tools for understanding and predicting bacterial kinetics and are necessary to predict the dose of organisms post-exposure that results in a skin infection. One of the challenges in modeling bacterial kinetics is the estimation of model parameters, which can be addressed using an inverse problem approach. The objective of this study is to construct a microbial kinetic model of S. aureus on human skin and use the model to predict concentrations of S. aureus that result in human infection. In order to model the growth and decay of S. aureus on skin, a Gompertz inactivation model was coupled with a Gompertz growth model. A series of analyses, including ordinary least squares regression, scaled sensitivity coefficient analysis, residual analysis, and parameter correlation analysis were conducted to estimate the parameters and to describe the model uncertainty. Based on these analyses, the proposed model parameters were estimated with high accuracy. The model was then used to develop a new dose-response model for S. aureus using the exponential dose–response model. The new S. aureus model has an optimized k parameter equivalent to 8.05 × 10⁻⁸ with 95^th percentile confidence intervals between 6.46 × 10⁻⁸ and 1.00 × 10⁻⁷.

Penetration of the blood-brain barrier by Staphylococcus aureus: contribution of membrane-anchored lipoteichoic acid

Staphylococcus aureus is one of the most prevalent organisms responsible for nosocomial infections, and cases of community-acquired S. aureus infection have continued to increase despite widespread preventative measures. Pathologies attributed to S. aureus infection are diverse; ranging from dermal lesions to bacteremia, abscesses, and endocarditis. Reported cases of S. aureus-associated meningitis and brain abscesses have also increased in recent years, however, the precise mechanism whereby S. aureus leave the bloodstream and gain access to the central nervous system (CNS) are not known. Here we demonstrate for the first time that S. aureus efficiently adheres to and invades human brain microvascular endothelial cells (hBMEC), the single-cell layer which constitutes the blood-brain barrier (BBB). The addition of cytochalasin D, an actin microfilament aggregation inhibitor, strongly reduced bacterial invasion, suggesting an active hBMEC process is required for efficient staphylococcal uptake. Furthermore, mice injected with S. aureus exhibited significant levels of brain bacterial counts and histopathologic evidence of meningeal inflammation and brain abscess formation, indicating that S. aureus was able to breech the BBB in an experimental model of hematogenous meningitis. We found that a YpfP-deficient mutant, defective in lipoteichoic acid (LTA) membrane anchoring, exhibited a decreased ability to invade hBMEC and correlated to a reduced risk for the development of meningitis in vivo. Our results demonstrate that LTA-mediated penetration of the BBB may be a primary step in the pathogenesis of staphylococcal CNS disease.

Risk factors and outcomes of methicillin-resistant Staphylococcus aureus bacteraemia in critically ill patients: a case control study

Methicillin-resistant Staphylococcus aureus (MRSA) infection is an increasing threat to critically ill patients in many intensive care units. MRSA bacteraemia is an extreme form of MRSA infection and is a significant cause of morbidity and mortality. This case control study aimed to assess the risk factors and outcomes of MRSA bacteraemia compared to methicillin-susceptible Staphylococcus aureus (MSSA) bacteraemia. A total of 21 MRSA bacteraemia and 60 randomly selected MSSA bacteraemia episodes, admitted to the intensive care unit at Royal Perth Hospital between 1997 and 2007, were considered. There was a suggestion that hospitalisation within the preceding six months (P = 0.087) and residence in a long-term care facility (P = 0.065) were associated with a higher risk of MRSA bacteraemia. MRSA bacteraemia was more often treated with antibiotics to which the pathogen was not susceptible in vitro (38.1% vs 0%, P = 0.001), resulting in a longer duration of fever (median 7.0 vs 2.0 days, P= 0.009) and bacteraemia (mean 3.2 vs 0.6 days, P = 0.005) and a higher incidence of metastatic seeding of infection (52.4% vs 21.7%, P = 0.012) as compared to MSSA bacteraemia. While in-hospital mortality between MRSA and MSSA was similarly high (47.6% vs 38.3% for MRSA and MSSA respectively, P = 0.607), a significant proportion of the patients who had MRSA bacteraemia died within five years of hospital discharge (36.4%, hazard ratio 26.0, 95% confidence interval 1.90 to 356.7, P = 0.015). Infections contributed to 75% of the deaths after hospital discharge in patients who had an episode of MRSA bacteraemia. MRSA bacteraemia carries a much worse long-term prognosis than MSSA bacteraemia and that could be explained by recurrent MRSA infections and residual confounding.