AbstractsBiology & Animal Science

Lancefield group C and G streptococci in human infection:molecular typing, virulence and antimicrobial susceptibility

by Marcos Daniel Pinho

Institution: Universidade de Lisboa
Year: 2014
Keywords: Teses de doutoramento - 2014; Estreptococos Viridans; Recombinação genética; Infecção; Tipagem molecular; Virulência
Record ID: 1323831
Full text PDF: http://www.rcaap.pt/detail.jsp?id=oai:repositorio.ul.pt:10451/11436


Tese de doutoramento, Ciências e Tecnologias da Saúde (Microbiologia), Universidade de Lisboa, Faculdade de Medicina, 2014 Beta-hemolytic, large-colony-forming (diameter greater than 0.5 mm) Lancefield group C and group G streptococci (GCGS) is a group within the Streptococcus genus which includes several species recognized as either colonizers or pathogens in humans and animals. Streptococcus dysgalactiae subsp. equisimilis (SDE), which can express any of these two Lancefield group antigens, is the GCGS species most commonly reported in human infection worldwide and may cause a number of potentially life-threatening infections. SDE is increasingly regarded as an emerging global pathogen and is able to colonize and infect humans, while other GCGS species, such as Streptococcus canis, are mainly animal pathogens that occasionally infect the human host. The rising number of human infections reported to be caused by GCGS warrants a better study of their epidemiology, in order to establish the relevance of each species, and clarifying the clonal dynamics and the intra-specific factors influencing the virulence of the strains. This work aimed at determining the GCGS species responsible for human infection in Portugal and, by assessing the genetic diversity of the isolates recovered, to define the clonal structure of this population. Thus, a special emphasis on molecular typing techniques was given, including those more commonly used to type these streptococci: pulsed-field gel electrophoresis (PFGE), emm typing and multilocus sequence typing (MLST). The application of these techniques to characterize collections of SDE and S. canis isolates recovered from other geographic locations and, for the latter species, from animal hosts, allowed to elucidate their respective population structures and provided new insights into the biology and evolution of GCGS. Initially, the speciation and characterization of GCGS isolates recovered from human infections in Portugal identified the central role of SDE. Not only was there a weak correlation between emm typing and PFGE results, but the polyclonal origin of the SDE population in this region was revealed by each of the methods used that generated multiple partitions. Furthermore, a correlation between emm type and invasive disease potential was suggested. A more global snapshot of the clonal architecture of this pathogen population was achieved by developing a MLST scheme which was applied to an expanded collection of SDE isolates recovered from distinct continents. An association of Lancefield groups with distinct MLST partitions was found and the high prevalence of a small number of widely distributed MLST sequence types (STs) suggested that a few genetic lineages dominate among SDE causing human infection worldwide. The occurrence of intra-specific and inter-specific recombination with Streptococcus pyogenes (Lancefield group A streptococcus, [GAS]), involving the housekeeping genes used in MLST was detected. The poor correlation between emm typing and either PFGE or MLST…