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

Abstract

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. Experiments were performed using 25 mice distributed into five experimental groups, intravenously inoculated with 50µl 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 96h post-infection. Morphoanatomy and histopathological analyses were performed at 96h 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. 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. These findings are valuable in characterizing infections caused by S. aureus in humans and murine.