Variation and persistence of methicillin-resistantStaphylococcus aureus strains among individual patients over extended periods of time

Abstract

To determine the strain variation and persistence among isolates of methicillin-resistant Staphylococcus aureus (MRSA) cultured from patients with colonization over extended time spans, pulsed-field gel electrophoresis was used to analyze the isolates from 47 patients for whom at least two mecA-positive isolates collected a minimum of six months apart were available. For 22 (47%) patients, the isolates represented multiple distinct strains of Staphylococcus aureus, while 20 (43%) patients had only a single strain detected; five (11%) patients had similar, genetically related isolates. MRSA were frequently associated with mucocutaneous abnormalities; 29 (62%) patients had focal cutaneous defects, and ten (21%) had chronic dermatitis. Multiple strains of MRSA were detected more frequently than single strains among patients in whom the initial focus of MRSA resolved clinically and another mucocutaneous defect subsequently developed compared to patients with clinically persistent foci (11/15 versus 9/23, respectively; p = 0.05, Fisher's exact test). Among the 21 patients in this series for whom isolates cultured within a two-month time span were available, there were seven (33%) patients with multiple strains of MRSA, including one patient with polyclonal bacteremia. In summary, patients with long-term MRSA colonization often have several different strains of MRSA, which typically change overtime in association with removal or resolution of a colonized focus and the recurrence of mucocutaneous defects.

A type III-like restriction endonuclease functions as a major barrier to horizontal gene transfer in clinical Staphylococcus aureus strains

“…antibiotic resistance | transformation | targetron T he opportunistic pathogen Staphylococcus aureus colonizes 20-50% of the human population (1,2) and is responsible for a broad spectrum of human and animal diseases, ranging from benign skin infections to such severe diseases as osteomyelitis, endocarditis, and sepsis (3,4). A major issue in the treatment of S. aureus infections is the presence of methicillin-resistant strains (MRSA) responsible for hospital-acquired infections and, more recently, highly virulent community-acquired infections.…”

Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus Isolates from Patients Newly Identified as Nasal Carriers

“…However, changes in the colonizing strain may occur during acute hospitalization, where patients are exposed to antibiotics and the competing flora of other patients and health care workers (15,16). Documenting persistence of carriage of the index strain or a change or loss of the index strain could be useful for evaluating the utility of repeated assessments in MRSA-positive patients.…”

Altered Growth, Pigmentation, and Antimicrobial Susceptibility Properties of Staphylococcus aureus Due to Loss of the Major Cold Shock Gene cspB

“…The emergence of methicillin-resistant S. aureus (MRSA) in the hospital and community settings, coupled with the increasing number of persistent MRSA infections (25) and multidrugresistant strains, is a growing problem not just for immunocompromised patients but also for otherwise healthy individuals. The virulence of S. aureus strains is multifactorial and involves the production of extracellular toxins, surface structures that mediate interaction with host cells and resistance to host defenses, transcriptional regulatory processes that control virulence gene expression, and metabolic schemes that allow for adaptation to stresses imposed by the local environment within and outside the human or animal host.…”