Evolution of genotypes of Group A streptococci from colonization and infection

Dissertação para obtenção do Grau de Doutor em Biologia

Streptococcus pyogenes is one pathogenic bacterium of humans and is associated with a wide variety of infections and disease states, ranging from uncomplicated but highly prevalent pharyngitis to extremely severe infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome. This work aimed to study important and unexplored aspects of the epidemiology, transmission and evolution of S. pyogenes causing colonization and a wide range of diseases. Our sample included 1,629 nonduplicated S. pyogenes isolates associated with colonization and infections. Out of the 1,629 isolates, 1,026 were recovered from 10,578 throat swabs of asymptomatic populations (children and adults) during 2000-2007 and 603 isolates were from patients diagnosed with clinical infections: 487 with tonsillitis/pharyngitis in 2000-2006, 72 with skin/soft tissue infections in 1999-2005, and 44 with invasive diseases in 1999-2005. This study demonstrated that a very heterogeneous population of S. pyogenes colonized healthy carriers. The mean carrier rate was higher among pre-school children (0-6 years) than among school-aged children (7-16 years) and colonization frequency was higher during Winter periods, which suggests that the crowding of children in day-care centers may possibly increase the carrier rate in healthy pre-school children. Moreover, it was also found that a high diversity of S. pyogenes strains was associated with long-term colonization, and it was detected co-colonization of the oropharynx by multiple S. pyogenes strains. In this work, it was reported the long term persistence among carriers of the low-level bacitracin-resistant emm28/ST52 lineage, which is prevalent in Europe. It was also reported for the first time a high-level bacitracin-resistant isolate of the emm74/ST120 lineage, which was not previously known to include bacitracin-resistant isolates. In this study were also reported for the first time temporal inversions of macrolide resistance phenotypes among colonization isolates, reinforcing the importance of surveillance of carriers, as they may be indicators of the pool of isolates circulating in the community that may cause infections. The high prevalence (>20%) of virulence genes speC, prtF1 and ssa was probably caused either by clonal dissemination (speC), or to horizontal gene transfer events (prtF1 and ssa). In this work it was observed that ciprofloxacin-nonsusceptibility rate was slightly lower among colonization isolates (4.3%) than among the clinical isolates (6.0%). All but one ciprofloxacin-nonsusceptible isolates had parC-QRDR mutations generating the aminoacid substitutions S79A (n=63) and D83G (n=2); the ParC-D83G substitution was found for the first time in this study and emm1 association with fluoroquinolone-nonsusceptibility was also first detected in this work. It was observed a higher frequency of virulence genes among isolates from disease, such as tonsillitis/pharyngitis, skin/soft tissue infections or invasive disease, than among colonization. In particular, this study contributed to a better knowledge of S. pyogenes virulence factors that circulate in this country. Among the 1,629 isolates, novel genotypes were discovered, such as emm-subtypes 6.63, 28.9, 53.10, st4040.0 and stMrp6.0, as well as sequence types ST380, ST397, ST398, ST401, ST402, ST427, ST428, ST429, ST430, ST431 and ST581. In conclusion, the results from this dissertation extend our knowledge about the carrier state, the susceptibility to antimicrobial agents, molecular epidemiology and virulence of S. pyogenes isolates from oropharyngeal colonization and symptomatic infections.

Fundação para a Ciência e a Tecnologia (FCT)- (SFRH/BD/32374/2006)