Pathological profiles of systemic infections by Panton-Valentine leukocidin-positive, methicillin-resistant Staphylococcus aureus strains in a murine model

AIMS

Staphylococcus aureus is one of the most common pathogens in hospital environment and community. Panton-Valentine leukocidin (PVL) production is clinically associated with skin abscesses, soft tissues infections, bacteraemia and sepsis. This study aimed to investigate the effects of the presence of genes lukF/S-PV coding for PVL, in histological and haematological features during systemic infection, using a Swiss mice experimental model.

METHODS AND RESULTS

Experiments were performed using 25 mice distributed into five experimental groups, intravenously inoculated with 50 µl suspensions at density 1·0 × 10⁷  CFU per ml of strains: methicillin-susceptible (MSSA) and pvl-negative strains isolated from nasal colonization; MSSA pvl-positive strains isolated from nasal colonization; methicillin-resistant (MRSA) and pvl-positive strains isolated from peripheral blood of a patient with severe pulmonary infection; and a MRSA pvl-positive strains isolated from a peripheral blood culture of a patient with bacteraemia. Haematological analysis was performed at 24, 48, 72 and 96 h post-infection. Morphoanatomy and histopathological analyses were performed at 96 h post-infection. For all S. aureus strains tested, the capability of intravenous dissemination and survival into mice tissues was demonstrated. Inflammatory processes at different levels were related to the presence of pvl genes, and included alterations in the format, size and colour of the organs. Staphylococcus aureus pvl-positive strains were detected in greater numbers in the organs of the infected animals.

CONCLUSIONS

The pvl-positive strains isolated from blood cultures were capable to induce the greatest modifications in both haematological and histopathological profiles, and seemed to aggravate the systemic infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings are valuable in characterizing infections caused by S. aureus in humans and murine.

A case report and literature overview: Abiotrophia defectiva aortic valve endocarditis in developing countries

A fatal case of aortic valve endocarditis due to Abiotrophia defectiva was reported in Brazil. An overview of cases of endocarditis and other human infections related to A. defectiva in developing countries was also accomplished.

Surface vesicles: a possible function in commensal relations of Bacteroides fragilis

Surface vesicles (SV) defined by electron microscopy as outer membrane (OM) extrusions were detected in Bacteroides fragilis strains from distinct sources. A partial identity between SV and OM electrophoretic protein profiles, in addition to the microscopic analysis, may suggest the designation of OMSV. Sialidase activity, a virulence determinant, was associated with these sub-cellular structures in all the strains, but in an inverse relation to the vesicle quantity per cell. A commensal strain, previously defined as avirulent in an animal model, presented the lowest vesicle-associated sialidase activity and the greatest SV expression as opposed to what happened with clinical and environmental strains. These results seem to suggest that these surface components have a function in commensal stages of B. fragilis.

Bacteroides fragilis: an exogenous pathogen?

Thirteen strains of Bacteroides fragilis isolated from contaminated water or from cases of intestinal and non-intestinal infections were comparatively analyzed in order to detect a possible biological relationship among them. The observation of similar profiles among the two groups, regarding the capacity of inducing abscesses and some surface properties, may support the hypothesis that the species could also act as an exogenous pathogen.