Serotype IV group B (GBS) is emerging in Canada and america with rates as high as 5% of the total burden of adult invasive GBS disease. genomes of the GBS strains and confirmed the genes with manual inspection of the sequences. All serotype IV GBS strains were tested by agar dilution for susceptibility to tetracycline, ampicillin, clindamycin, erythromycin, cefotaxime, penicillin, and vancomycin following Clinical and Laboratory Standards Institute guidelines (34). Technicians performing the phenotypic tests were blind to the genetic results. Short-read whole-genome sequencing data accession number. Data have been deposited at NCBI’s Sequence Read Archive under accession number PRJNA286872. RESULTS High prevalence of serotype IV strains among adult invasive GBS disease in Manitoba and Saskatchewan. We first serotyped all 549 strains recovered from adult GBS invasive infections in Manitoba and Saskatchewan between 2010 and 2014 (see Table S3 in the supplemental material). In Manitoba, the three most common serotypes were V (73/355, 21%), IV (57/355, 16%), and Ib (56/355, 16%) (Fig. 1A). In Saskatchewan, serotype V was the most prevalent 755038-65-4 (39/194, 20%) and was followed by serotype IV (36/194, 19%) and serotypes II and III (each 25/194, 13%) (Fig. 1B). Thus, the overall prevalence of serotype IV strains among cases of GBS in adult invasive disease was 16.9% (93/549) during the period under consideration. Although the frequency of isolation of serotype IV GBS strains was relatively constant during each of the 5 years studied, the overall serotype IV GBS prevalence in Manitoba and Saskatchewan was higher than that previously reported elsewhere in North America PPP3CC (2, 4, 11, 18) and greatly exceeded the 6% prevalence recently reported in Toronto, Ontario, over a time period (2010 to 2012) that partially overlaps with the current data set (19). The median age of patients with invasive GBS infection was 60 years in Saskatchewan and Manitoba. The percentage of invasive serotype IV GBS disease in adults aged 18 to 59 was 19.1% (34/178) in Manitoba and 19.1% (18/94) in Saskatchewan, while in older adults (aged 60) serotype IV strains represented 13.0% (23/177) of the Manitoba cases and 18% (18/100) of the Saskatchewan cases. FIG 1 Distribution of group B (GBS) serotypes among cases of adult invasive disease in the provinces 755038-65-4 of Manitoba (A) and Saskatchewan 755038-65-4 (B) during the years 2010 to 2014. Serotype V GBS strains were the most frequently isolated in the two provinces … The vast majority of serotype IV GBS isolates causing adult invasive disease in Manitoba and Saskatchewan are ST459. We used Illumina short-reads and the read-mapping-based tool SRST2 (24) to derive MLST information for each isolate directly from WGS data (STs are presented in Table S1 in the supplemental material). The vast majority of isolates belonged to CC1 ST459 (87% or 47/54 serotype IV isolates in Manitoba and 94% or 29/31 in Saskatchewan) (Fig. 2). The remaining isolates included five CC1 strains: two ST3, one ST711 (a novel single locus variant of ST3), one ST196, and one ST710 (a novel single locus variant of ST459). We also identified four CC23 ST452 isolates. Table S4 in the 755038-65-4 supplemental material lists the number of locus variants between the different STs identified. The proportion of ST459 isolates among invasive serotype IV GBS in the two provinces (89%) was significantly higher than that recently described in Toronto, Ontario, where approximately half of serotype IV isolates were ST459 (19/37 or 51%, < 0.001) (20). FIG 2 Inferred genetic relationships between strains of serotype IV group B (GBS) causing invasive disease in adults in Manitoba and Saskatchewan. A neighbor-joining phylogenetic tree was constructed using the concatenated sequences of the 7 genes ... Antibiotic susceptibility in serotype IV GBS strains. All serotype IV GBS strains were.