Phagocytosis and killing of epidemic methicillin-resistant Staphylococcus aureus by human neutrophils and monocytes

Abstract

Staphylococcus aureus is a pathogen that has been associated with nosocomial infections since the preantibiotic era. Since the introduction of antibiotics in medical practice in the 1940's, methicillin-resistant S. aureus (MRSA) strains have been emerging in various parts of the world. In view of the important role of the phagocytic system in the defense against this bacteria, we decided to study phagocytosis by neutrophils and monocytes of an epidemic MRSA strain in São Paulo, Brazil, in comparison with methicillin-sensitive strains. Complement system opsonins are fundamental for efficient ingestion of the resistant and sensitive strains by both types of phagocytes. We found no association of the opsonic requirement of the MRSA strain with the multiresistance phenotype. On the other hand, the MRSA strain was found to be more resistant to the effector mechanisms of neutrophils than both sensitive strains when opsonized with fresh serum, despite the phagocytosis results. This fact suggests that the intracellular killing of S. aureus is an additional parameter of bacterial virulence, but new approaches must be implemented to study the interactions of this MRSA strain with phagocytes in order to investigate the possible factors involved in its behavior in response to neutrophil effector mechanisms.

"Non-Antibiotics": Alternative Therapy for the Management of MDRTB and MRSA in Economically Disadvantaged Countries

“…The inability of the beta-lactam to follow the organism into the macrophage resulted in recurrent S. aureus infections at sites where such macrophages were common, i.e., bone marrow, etc [12]. Since the 1980's, clinical isolates of S. aureus have become more frequently resistant and shown to have their origins within the hospital itself [13] and more recently, they have been acquired from community sources [14]. At this time, the percentage of beta-lactam resistant clinical isolates of S. aureus (MRSA) has been noted to increase significantly in some hospitals of Denmark, a country known to have the lowest frequency of MRSA, and has reached levels as high as 63% in South Africa [15].…”

Is MRSA more virulent than MSSA?

“…Comparative in‐vitro studies of heteroresistant MRSA and non‐heteroresistant MSSA clinical isolates have investigated protein A‐, fibrinogen‐, fibronectin‐, collagen‐ and vitronectin‐binding proteins. The results were not consistent with respect to the frequency and content of these adhesins, either in the MRSA or in the MSSA strains [7–10]. Similarly, the magnitude of binding to epithelial cells and plastic surfaces did not differ significantly between MRSA and MSSA strains [7].…”

Surveillance programs for detection and characterization of emergent pathogens and antimicrobial resistance: results from the Division of Infectious Diseases, UNIFESP

“…We observed a high lethality rate, increasing of costs and time of hospitalization associated with blood stream infections due to this particular pathogen when compared to infections caused by methicillin susceptible strains (Moreira et al 1998). In addition, we detected in a MRSA-BEC strain a decrease in its phagocytosis and killing by neutrophils and monocytes when compared with the susceptible isolates (Salgado et al 2004). …”