Abstract
Clustered regularly interspaced short palindromic repeats (CRISPR) and Cas (CRISPR-associated proteins) play a critical role in adaptive immunity against mobile genetic elements, especially phages, through their ability to acquire novel spacer sequences. Polarized spacer acquisition results in spacer polymorphism and temporal organization of CRISPR loci, making them attractive epidemiological markers. Group B Streptococcus (GBS), a genital commensal for 10 to 30% of healthy women and a major neonatal pathogen, possesses a ubiquitous and functional CRISPR1 locus. Our aim was to assess the CRISPR1 locus as an epidemiological marker to follow vaginal carriage of GBS in women. This study also allowed us to observe the evolution of the CRISPR1 locus in response to probable phage infection occurring in vivo. We followed carriage of GBS among 100 women over an 11-year period, with a median duration of approximately 2 years. The CRISPR1 locus was highly conserved over time. The isolates that show the same CRISPR1 genotype were collected from 83% of women. There was an agreement between CRISPR genotyping and other typing methods [MLVA (multilocus variable number of tandem repeat Analysis) and MLST (multilocus sequence typing)] for 94% of the cases. The CRISPR1 locus of the isolates from 18 women showed modifications, four of which acquired polarized spacer, highlighting the in vivo functionality of the system. The novel spacer of one isolate had sequence similarity with phage, suggesting that phage infection occurred during carriage. These findings improve our understanding of CRISPR-Cas evolution in GBS and provide a glimpse of host-phage dynamics in vivo.
Highlights
Streptococcus agalactiae, or Group B Streptococcus (GBS), is a major pathogen in humans and is the leading cause of neonatal infections in industrialized countries (Stoll et al, 2011; Edmond et al, 2012)
As spacer acquisition events occurred in vivo in multiple and independent cases during carriage, notably in response to a probable phage infection, our results strongly suggest that the CRISPR1-Cas system is functionally active for adaptation
We explored the in vivo dynamics of human colonization by GBS over several years by comparing the CRISPR1 loci of 205 isolates collected from 100 women over an
Summary
Streptococcus agalactiae, or Group B Streptococcus (GBS), is a major pathogen in humans and is the leading cause of neonatal infections in industrialized countries (Stoll et al, 2011; Edmond et al, 2012). It is universal practice to screen pregnant women for vaginal and/or rectal colonization with GBS to prevent early-onset infection (ANAES, 2001; Verani et al, 2010; Di Renzo et al, 2015). The aim of this screening strategy is to limit bacterial transmission and prevent EOD by the administration of intrapartum antibiotic prophylaxis. Screening for pathogenic bacteria, including GBS, must be performed in cases of imminent delivery risk (suspicion of chorioamnionitis, prolonged membrane rupture, or preterm labor) (ANAES, 2001)
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