Abstract
BackgroundMultilocus sequence typing (MLST) is currently the reference method for genotyping Streptococcus agalactiae strains, the leading cause of infectious disease in newborns and a major cause of disease in immunocompromised children and adults. We describe here a genotyping method based on multiple locus variable number of tandem repeat (VNTR) analysis (MLVA) applied to a population of S. agalactiae strains of various origins characterized by MLST and serotyping.ResultsWe studied a collection of 186 strains isolated from humans and cattle and three reference strains (A909, NEM316 and 2603 V/R). Among 34 VNTRs, 6 polymorphic VNTRs loci were selected for use in genotyping of the bacterial population. The MLVA profile consists of a series of allele numbers, corresponding to the number of repeats at each VNTR locus. 98 MLVA genotypes were obtained compared to 51 sequences types generated by MLST. The MLVA scheme generated clusters which corresponded well to the main clonal complexes obtained by MLST. However it provided a higher discriminatory power. The diversity index obtained with MLVA was 0.960 compared to 0.881 with MLST for this population of strains.ConclusionsThe MLVA scheme proposed here is a rapid, cheap and easy genotyping method generating results suitable for exchange and comparison between different laboratories and for the epidemiologic surveillance of S. agalactiae and analyses of outbreaks.
Highlights
Multilocus sequence typing (MLST) is currently the reference method for genotyping Streptococcus agalactiae strains, the leading cause of infectious disease in newborns and a major cause of disease in immunocompromised children and adults
Eburst analysis clustered the sequence type (ST) into five clonal complexes (CC17, CC19, CC10, CC23 and CC7), two groups with only two STs and six singletons (Table 3)
The various serotypes of S. agalactiae were distributed between multiple CCs and singleton STs
Summary
Multilocus sequence typing (MLST) is currently the reference method for genotyping Streptococcus agalactiae strains, the leading cause of infectious disease in newborns and a major cause of disease in immunocompromised children and adults. We describe here a genotyping method based on multiple locus variable number of tandem repeat (VNTR) analysis (MLVA) applied to a population of S. agalactiae strains of various origins characterized by MLST and serotyping. Streptococcus agalactiae, one of the group B streptococci (GBS), is a leading cause of bovine mastitis [1] and has been implicated in cases of invasive disease in humans since the 1960s and 1970s [2]. Analyses of fully sequenced bacterial genomes have revealed the existence of tandemly repeated sequences varying in size, location and the type of repetition [19]. Variation in the number of repeats at particular loci is used by some bacteria as a means of rapid genomic and phenotypic adaptation to the environment [20]
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