Clonal associations among Staphylococcus aureus isolates from various sites of infection

Abstract

A molecular epidemiological analysis was undertaken to identify lineages of Staphylococcus aureus that may be disproportionately associated with infection. Pulsed-field gel electrophoresis analysis of 405 S. aureus clinical isolates collected from various infection types and geographic locations was performed. Five distinct S. aureus lineages (SALs 1, 2, 4, 5, and 6) were identified, which accounted for 19.01, 9.14, 22.72, 10.12, and 4.69% of isolates, respectively. In addition, 85 lineages which occurred with frequencies of <2.5% were identified and were termed "sporadic." The most prevalent lineage was methicillin-resistant S. aureus (SAL 4). The second most prevalent lineage, SAL 1, was also isolated at a high frequency from the anterior nares of healthy volunteers, suggesting that its prevalence among clinical isolates may be a consequence of high carriage rates in humans. Gene-specific PCR was carried out to detect genes for a number of staphylococcal virulence traits. tst and cna were found to be significantly associated with prevalent lineages compared to sporadic lineages. When specific infection sites were examined, SAL 4 was significantly associated with respiratory tract infection, while SAL 2 was enriched among blood isolates. SAL 1 and SAL 5 were clonally related to SALs shown by others to be widespread in the clinical isolate population. We conclude from this study that at least five phylogenetic lineages of S. aureus are highly prevalent and widely distributed among clinical isolates. The traits that confer on these lineages a propensity to infect may suggest novel approaches to antistaphylococcal therapy.

FIG. 1

Relative distribution of SALs identified following PFGE analysis of S. aureus clinical isolates from various sources. Sporadic SALs were those which occurred at a frequency of <2.5% of all isolates.

FIG. 2

Genomic DNA fingerprint patterns of SAL 1 clinical isolates analyzed by PFGE following SmaI digestion of chromosomal DNA. Lanes 1 and 13, lambda ladder; lanes 2 and 3, respiratory tract isolates; lanes 4 and 5, blood isolates; lanes 6 and 7, catheter tip isolates; lanes 8 and 9, bone or joint isolates; lanes 10 and 11, ET41 strains KD₂22 and Minn 8, respectively; lane 12, agr group III isolate (16, 27).

FIG. 3

Genomic DNA fingerprint patterns of SAL 4 clinical isolates analyzed by PFGE following SmaI digestion of chromosomal DNA. Lanes 1, lambda ladder; lanes 2 and 4, respiratory tract isolates; lane 3, bone or joint isolates; lanes 5 and 6, blood isolates; lane 7, ocular isolate; lanes 8 and 9, catheter tip isolates.

FIG. 4

Genomic DNA fingerprint patterns of SAL 5 clinical isolates analyzed by PFGE following SmaI digestion of chromosomal DNA. Lanes 1 and 11, lambda ladder; lanes 2 and 5, bone or joint isolates; lane 3, ocular isolate; lanes 4 and 6, respiratory tract isolates; lane 7, blood isolate; lane 8, catheter tip isolate; lanes 9 and 10, phage type 95 isolates 145A-259 and 896A-SC-02, respectively.

FIG. 5

Genomic DNA fingerprint patterns of SAL 2 (lanes 7 to 10) and SAL 6 (lanes 2 to 6) clinical isolates analyzed by PFGE following SmaI digestion of chromosomal DNA. Lanes 1 and 11, lambda ladder; lanes 2 and 5, bone or joint isolates; lane 3, respiratory tract isolate; lane 4, blood isolate; lane 6, cellulitis isolate; lane 7, bone or joint isolate; lane 8, blood isolate; lane 9, catheter tip isolate; lane 10, respiratory tract isolate.

FIG. 6

Relative distributions of prevalent and sporadic SALs at anatomical sites frequently associated with S. aureus infection and at all sites. Resp., respiratory.

FIG. 7

Frequency and distribution of SALs most commonly associated with normal flora isolates compared with their frequency and distribution among all clinical isolates.