The co-existence of multiple genotypes in colonization by Staphylococcus aureus has not been fully investigated. The aim of this study was to evaluate the heterogeneity of S. aureus carriage in children. We evaluated 125 nasal and perianal swab samples that were positive for S. aureus from 76 children scheduled for elective surgery. For each sample, at least four colonies with the same or different morphotypes were selected for analysis. Multiple-locus variable-number tandem-repeat fingerprinting was used to determine the genetic relatedness and to characterize the clonality of the S. aureus strains. Of the 125 swabs, 91 (73 %) contained meticillin-sensitive S. aureus (MSSA), 8 (6 %) contained meticillin-resistant S. aureus (MRSA), and 26 (21 %) contained MSSA and MRSA simultaneously. A total of 738 S. aureus strains were evaluated with a mean of 6 colonies (range 4-15) picked from each culture. Of the 125 swabs, 32 (26 %) samples contained two genetically distinct S. aureus strains and 6 (5 %) contained three different genotypes. Multiple S. aureus strains simultaneously carried by individual children were genetically unrelated to each other. We concluded that the co-existence of multiple genotypes of S. aureus was common. The significance of multiple carriage is yet to be determined, but this intraspecies interplay could be important to pathogenicity and virulence in S. aureus. INTRODUCTIONStaphylococcus aureus is an important pathogen responsible for a wide range of clinical entities from asymptomatic colonization to invasive and life-threatening infections. Carriage of S. aureus has been associated with subsequent infections, especially surgical site infections (Herwaldt, 2003;Wenzel & Perl, 1995), and a variety of other clinical conditions (Keene et al., 2005;Niven et al., 2009;Von Eiff et al., 2001). Studies have revealed that among individuals with S. aureus infections, the infecting strains were indeed genetically identical or related to the carriage strains (Keene et al., 2005;Kreft et al., 2001;Von Eiff et al., 2001).Two studies have reported the carriage of multiple subtypes of meticillin-resistant S. aureus (MRSA) in sequential cultures from adult patients during their stay in an intensive care unit (Bloemendaal et al., 2009;Lim et al., 2006). However, Bloemendaal et al. (2009) did not look at multiple colonies within the same S. aureus positive swabs. Therefore, it was uncertain whether these episodes were polyclonal as a result of multiple clones simultaneously colonizing patients, or acquisition of different MRSA strains over time. Lim et al. (2006) studied MRSA carriage at various body sites and found that multiple subtypes can be carried simultaneously at different sites by a single patient. Simultaneous carriage of more than one genetically distinct S. aureus isolate was also reported in groups of paediatric patients with certain medical conditions, such as cystic fibrosis and atopic dermatitis (Goerke et al., 2007;Lomholt et al., 2005). However, the frequency of concurrent colonization with m...

BackgroundThe nation-wide concern over methicillin-resistant Staphylococcus aureus (MRSA) has prompted many clinicians to use vancomycin when approaching patients with suspected staphylococcal infections. We sought to characterize the epidemiology of community-onset S. aureus infections in hospitalized children to assist local clinicians in providing appropriate empiric antimicrobial therapy.MethodsFrom January 2005–June 2008, children (0–18 years old) admitted to the Children's Hospital of Illinois with community-onset S. aureus infections were identified by a computer-assisted laboratory-based surveillance and medical record review.ResultsOf 199 patients, 67 (34%) had invasive infections, and 132 (66%) had skin and soft tissue infections (SSTIs). Among patients with invasive infections, S. aureus isolates were more likely to be susceptible to methicillin (MSSA 63% vs. MRSA 37%), whereas patients with SSTIs, S. aureus isolates were more likely to be resistant to methicillin (MRSA 64% vs. MSSA 36%). Bacteremia and musculoskeletal infections were the most common invasive infections in both groups of S. aureus. Pneumonia with empyema was more likely to be caused by MRSA (P = 0.02). The majority (~90%) of MRSA isolates were non-multidrug resistant, even in the presence of healthcare-associated risk factors.ConclusionEpidemiological data at the local level is important for antimicrobial decision-making. MSSA remains an important pathogen causing invasive community-onset S. aureus infections among hospitalized children. In our hospital, nafcillin in combination with vancomycin is recommended empiric therapy in critically ill patients with suspected invasive staphylococcal infections. Because up to 25% of MSSA circulating in our area are clindamycin-resistant, clindamycin should be used cautiously as empiric monotherapy in patients with suspected invasive staphylococcal infections.