Clonal análisis of selected genes and assessment of selected virulence factors showed that Staphylococcus aureus isolates carrying the cap5 allele may have an increased fitness to the human host compared with those carrying the cap8 allele.

LATTAR SM, TUCHSCHERR L, CENTRON D, BUZZOLA FR AND SORDELLI DO.

Waterville Valley, USA

Conferencia; Gordon Research Conference Satphylococcal Diseases; 2009

            Most S. aureus isolates from humans produce capsular polysaccharide (CP) of serotypes 5 (CP5) or 8 (CP8).  Previous reports from our laboratory have linked the loss of CP expression to long exposure to the in vivo environment.  In a previous study conducted on 99 S. aureus isolates from 66 patients with chronic and 33 with acute osteomyelitis from 7 hospitals in Argentina, we described a significantly higher prevalence of staphylococci that do not express CP in patients with chronic osteomyelitis, compared with those with acute osteomyelitis. The present study was conducted using those 99 isolates to ascertain the presence of selected genes (pvl, agr, mecA, agr, hla, hlb), slime production and the disease course in the search for particular clones associated to chronicity.  Twenty-seven SmaI PFGE types were defined arbitrarily (85% similitude).  All isolates bearing the cap5 and cap8 alleles were distributed into two SmaI PFGE clusters.  Isolates with pulsotypes A through M carried the cap5 allele whereas isolates of pulsotypes M through AA carried the cap8 allele. A significantly (p=0.0005) higher proportion of MRSA isolates bearing the cap5 allele (37/47) was found, compared with those bearing the cap8 allele (n=10/47).  The presence of the hla and the lukS-PV/lukF-PV genes was also significantly (p<0.0001 and p= 0.0001, respectively) associated to the presence of the cap5 allele.  No significant association was found between disease course and pulsotype, meticilin-resistance, agr type or presence of the lukS-PV/lukF-PV, hla or hlb genes. Whereas agr I isolates were evenly distributed among strains bearing cap5 and cap8, most agr group II isolates carried the cap5 allele and most agr group III isolates carried the cap8 allele. No agr IV isolates were found among the 99 S. aureus isolates tested.  In conclusion, we demonstrated that loss of CP expression remains the single factor among those so far investigated associated with chronic osteomyelitis. Our results are consistent with an increased fitness of S. aureus bearing the cap5 allele in patients with osteomyelitis. Many S. aureus factors may be responsible for this increased fitness and á-haemolysin and PVL and meticilin resistance are among them. The definition of two S. aureus genomovars, namely Cap5 and Cap8, is suggested.