Comparison of Genetic Backgrounds of Methicillin-Resistant and -Susceptible Staphylococcus aureus Isolates from Portuguese Hospitals and the Community

Abstract

In order to understand the origins of the dominant methicillin-resistant Staphylococcus aureus (MRSA) clones in Portuguese hospitals, we compared the genetic backgrounds of nosocomial MRSA with methicillinsusceptible S. aureus (MSSA) isolates from the same hospitals (n ‫؍‬ 155) and from the community (n ‫؍‬ 157) where they were located. Pulsed-field gel electrophoresis, spa typing, multilocus sequence typing, and agr type analysis revealed that the genetic backgrounds correspondent to the dominant MRSA clones in Portuguese hospitals during the last 15 years (Iberian ST247, Brazilian ST239, and EMRSA-15 ST22) were scarcely or not found among the present MSSA collection. The four major MSSA clones encountered (A-ST30, B-ST34, C-ST5, and H-ST45) correspond, or are very similar, to the background of other international MRSA pandemic clones, i.e., EMRSA-16, New York/Japan, Pediatric, and Berlin clones. However, with the exception of the Pediatric clone, none of these MRSA clones has been detected in Portugal. Our findings suggest the three major MRSA clones identified in Portuguese hospitals have not originated from the introduction of SCCmec into dominant MSSA backgrounds present in the Portuguese nosocomial or community environment but were probably imported from abroad. In contrast, the MRSA Pediatric clone might have originated in our country by the acquisition of SCCmec type IV into MSSA clone C. Furthermore, we provide evidence that the introduction of SCCmec into sensitive clones is most likely a relatively infrequent event that seems to depend not exclusively on the presence of a successful MSSA lineage.

Transcriptional profiling of a Staphylococcus aureus clinical isolate and its isogenic agr and sarA mutants reveals global differences in comparison to the laboratory strain RN6390

“…The results of this comparison confirmed that the UAMS isolates are closely related to each other and to (Cassat et al, 2005), which is a prominent clinical isolate found in diverse geographical areas worldwide (Aires de Sousa et al, 2005;Johnson et al, 2005;Nimmo et al, 2006;Udo et al, 2006). Our analysis also confirmed that the cluster containing UAMS-1, UAMS-601 and EMRSA-16 is the most distantly related, among the strains we examined, to the prototype laboratory strains NCTC 8325 and RN6390 (Cassat et al, 2005).…”

High prevalence of ST121 in community-associated methicillin-susceptible Staphylococcus aureus lineages responsible for skin and soft tissue infections in Portuguese children

“…Retrospectively, all STs found in the present study (with the exception of ST152) have already been described in carriage among the Portuguese community in 1996, although with a different prevalence [6]. Despite the small size of the collection, the major CA-MSSA clones described in Europe, ST1, ST5, ST30, and ST45 [29], were found in the pediatric Portuguese community (Table 1).…”

“…The staphylococcal cassette chromosome mec (SCCmec) type and the accessory gene regulator (agr) alleles are also differentially distributed: SCCmec types IV or V and agr type III are more commonly present in CA-MRSA, while SCCmec types I-III and agr type II are more typical of HA-MRSA [1]. In contrast, community-acquired methicillinsusceptible S. aureus (CA-MSSA) isolates, responsible for a significant number of mild SSTI, do not differ from HA-MSSA [6,7].…”

“…Previous studies dated from 1996 to 2009, including isolates from nasal swabs of young healthy individuals and nasopharyngeal swabs of children attending day care centers, reported an MRSA prevalence lower than 0.25% in the Portuguese healthy community (0.24% in 1996-1998 and 0.13% in [2006][2007][2008][2009] [6,9,10].…”

Epidemiological and molecular biological studies of multi-resistant methicillin-susceptible Staphylococcus aureus

“…The emergence of MRSA is due to the acquisition of SCCmec into the chromosome of MSSA [63][64][65][66][67]. Studies have shown that SCC and mecA originally existed as individual genetic components, and it is suggested that SCCmec may have been acquired from multi-resistant coagulase-negative staphylococci such as S. sciuri [68][69][70].…”