Abstract
BackgroundGroup B streptococci (GBS), or Streptococcus agalactiae, are the leading bacterial cause of meningitis and bacterial sepsis in newborns. Here we compared different culture media for GBS detection and we compared the occurrence of different genotypes and serotypes of GBS isolates from the vagina and rectum.MethodsStreptococcus agalactiae was cultured separately from both rectum and vagina, for a total of 150 pregnant women, i) directly onto Columbia CNA agar, or indirectly onto ii) Granada agar resp. iii) Columbia CNA agar, after overnight incubation in Lim broth.ResultsThirty six women (24%) were colonized by GBS. Of these, 19 harbored GBS in both rectum and vagina, 9 only in the vagina and 8 exclusively in the rectum. The combination of Lim broth and subculture on Granada agar was the only culture method that detected all GBS positive women. Using RAPD-analysis, a total of 66 genotypes could be established among the 118 isolates from 32 women for which fingerprinting was carried out. Up to 4 different genotypes in total (rectal + vaginal) were found for 4 women, one woman carried 3 different genotypes vaginally and 14 women carried two 2 different genotypes vaginally. Only two subjects were found to carry strains with the same genotype, although the serotype of both of these strains was different.Eighteen of the 19 subjects with GBS at both sites had at least one vaginal and one rectal isolate with the same genotype.We report the presence of two to four different genotypes in 22 (61%) of the 36 GBS positive women and the presence of identical genotypes in both sites for all women but one.ConclusionThe combination of Lim broth and subculture on Granada medium provide high sensitivity for GBS detection from vaginal and rectal swabs from pregnant women. We established a higher genotypic diversity per individual than other studies, with up to four different genotypes among a maximum of 6 isolates per individual picked. Still, 18 of the 19 women with GBS from both rectum and vagina had at least one isolate from each sampling site with the same genotype.
Highlights
Group B streptococci (GBS), or Streptococcus agalactiae, are the leading bacterial cause of meningitis and bacterial sepsis in newborns
Several molecular techniques have been applied to study the genetic diversity of GBS, such as restriction fragment length polymorphism analysis (RFLP) [10], ribotyping [10,11], pulsed-field gel electrophoresis (PFGE) [3,12,13,14,15,16,17] multilocus enzyme electrophoresis (MLEE) [18] randomly amplification of polymorphic DNA-analysis (RAPD) [9,19,20], amplified cps restriction polymorphism analysis [21] and multilocus sequence typing (MLST) [13,22,23,24,25]
The culture of rectal specimens, direct plating onto Columbia CNA agar was significantly less sensitive than culture in Lim broth with subculture on Granada agar (p < 0.0001), which was more sensitive than culture on Lim broth with subculture on Columbia CNA agar (p = 0.0313)
Summary
Group B streptococci (GBS), or Streptococcus agalactiae, are the leading bacterial cause of meningitis and bacterial sepsis in newborns. We compared different culture media for GBS detection and we compared the occurrence of different genotypes and serotypes of GBS isolates from the vagina and rectum. Streptococcus agalactiae, group B Streptococcus (GBS), is a leading cause of neonatal morbidity and mortality in the US, Western Europe and Australia. Motherto-child transmission may lead to neonatal infection in 1 to 2 infants per 1,000 live births [5] with mortality rates ranging from 10 to 20% [6]. Screening consists of obtaining vaginal and rectal specimens for culture at 35 to 37 weeks of gestation. Several molecular techniques have been applied to study the genetic diversity of GBS, such as restriction fragment length polymorphism analysis (RFLP) [10], ribotyping [10,11], pulsed-field gel electrophoresis (PFGE) [3,12,13,14,15,16,17] multilocus enzyme electrophoresis (MLEE) [18] randomly amplification of polymorphic DNA-analysis (RAPD) [9,19,20], amplified cps restriction polymorphism analysis [21] and multilocus sequence typing (MLST) [13,22,23,24,25]
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