Community-Acquired Pneumonia: March 2006

John G. Bartlett, MD


March 08, 2006

In This Article

Methicillin-Resistant Staphylococcus aureus

Micek ST, Dunne M, Kolleff MH. Pleuropulmonary complications of Panton-Valentine leukocidin-positive community-acquired methicillin-resistant Staphylococcus aureus: importance of treatment with antimicrobials inhibiting exotoxin production. Chest. 2005;128:2732-2738. Four patients were seen at Barnes-Jewish Hospital, St. Louis, Missouri, with severe necrotizing pneumonia, empyema, and/or adult respiratory distress syndrome (ARDS) complicating pneumonia. Patients had positive cultures of blood (3), respiratory secretions (3), or empyema fluid (1) for methicillin-resistant Staphylococcus aureus (MRSA) that were positive for Panton-Valentine leukocidin (PVL). Details of the cases are provided in Table 6 .

With regard to treatment, all patients received vancomycin treatment initially, but 3 failed to respond, including 2 who had persistent bacteremia despite at least 48 hours of vancomycin. Substitution with linezolid or clindamycin yielded good results in these cases.

Conclusion: Pulmonary infections involving PVL-positive MRSA should be treated with antibiotics that inhibit exotoxin production.

Comment: The study authors point out that the PVL-producing strains of MRSA (primarily USA 300 and 400 strains, according to the US Centers for Disease Control and Prevention [CDC] classification) should be treated with antimicrobial agents that inhibit protein synthesis, including PVL. They also point out that alpha toxin, which is encoded by the human leukocyte antigen (HLA) gene, is a major virulence factor of S. aureus.[12] Prior studies show that vancomycin has no effect on this gene in subinhibitory doses, but low concentrations of clindamycin reduced HLA expression by 98%.[13] Other studies showed that clindamycin inhibits the production of toxic shock syndrome toxin 1 (TSST-1).[14] There is justifiable concern about the "disassociated cross-resistance" of clindamycin when S aureus strains are resistant to macrolides, but this can easily be determined by the disk-diffusion test ("D-test") in the laboratory. Thus, the recommendation for serious infections involving PVL-positive S aureus is clindamycin or linezolid; linezolid would be preferred in cases in which there is resistance in vitro to clindamycin or inducible resistance according to the D-test. The potential of linezolid to inhibit the toxin production of S aureus in subinhibitory concentrations has been well demonstrated in vitro.[15]


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.