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Population Structure and Antimicrobial Resistance of Invasive Serotype IV Group B Streptococcus, Toronto, Ontario, Canada - Volume 21, Number 4—April 2015 - Emerging Infectious Disease journal - CDC


Population Structure and Antimicrobial Resistance of Invasive Serotype IV Group B Streptococcus, Toronto, Ontario, Canada - Volume 21, Number 4—April 2015 - Emerging Infectious Disease journal - CDC

Volume 21, Number 4—April 2015


Population Structure and Antimicrobial Resistance of Invasive Serotype IV Group BStreptococcus, Toronto, Ontario, Canada

Sarah Teatero, Allison McGeer, Aimin Li, Janice Gomes, Christine Seah, Walter Demczuk, Irene Martin, Jessica Wasserscheid, Ken Dewar, Roberto G. Melano, and Nahuel FittipaldiComments to Author 
Author affiliations: Public Health Ontario, Toronto, Ontario, Canada (S. Teatero, A. Li, J. Gomes, C. Seah, R.G. Melano, N. Fittipaldi)University of Toronto, Toronto (A. McGeer, R.G. Melano, N. Fittipaldi)Mount Sinai Hospital, Toronto (A. McGeer, R.G. Melano)Public Health Agency of Canada, Winnipeg, Manitoba, Canada (W. Demczuk, I. Martin)McGill University, Montreal, Quebec, Canada (J. Wasserscheid, K. Dewar)Genome Quebec Innovation Centre, Montreal (J. Wasserscheid, K. Dewar)


We recently showed that 37/600 (6.2%) invasive infections with group B Streptococcus (GBS) in Toronto, Ontario, Canada, were caused by serotype IV strains. We report a relatively high level of genetic diversity in 37 invasive strains of this emerging GBS serotype. Multilocus sequence typing identified 6 sequence types (STs) that belonged to 3 clonal complexes. Most isolates were ST-459 (19/37, 51%) and ST-452 (11/37, 30%), but we also identified ST-291, ST-3, ST-196, and a novel ST-682. We detected further diversity by performing whole-genome single-nucleotide polymorphism analysis and found evidence of recombination events contributing to variation in some serotype IV GBS strains. We also evaluated antimicrobial drug resistance and found that ST-459 strains were resistant to clindamycin and erythromycin, whereas strains of other STs were, for the most part, susceptible to these antimicrobial drugs.
Group B Streptococcus (GBS), also known as Streptococcus agalactiae, are a major cause of neonatal sepsis and meningitis and are increasingly being associated with invasive infections in nonpregnant adults (13). For instance, in 2011, adult cases accounted for nearly 90% of the burden of GBS disease in the United States (4). Elderly persons and those with preexisting conditions (e.g., diabetes mellitus, cirrhosis, cancer, and compromised immunity) are most at risk (5). The clinical features of GBS disease in adults range from localized tissue infection to severe bacteremia with shock (1). Less common clinical syndromes, such as endocarditis and meningitis, are associated with considerable illness and death (1).
GBS are classified into 10 serotypes (Ia, Ib, and II–IX) on the basis of a serologic reaction against capsular polysaccharide. The most common GBS serotypes causing invasive disease in the United States and Canada in adults and neonates are Ia, III, and V (2,3,69). However, recent reports have shown that serotype IV GBS is emerging in pregnant carriers and causing infections in neonates and adults in North America and several other regions (1014). This emergence is of concern because GBS conjugate vaccines that are being developed to prevent invasive disease may protect only against serotypes Ia, Ib, II, III, and V, or combinations thereof (15,16).
Ferrieri et al. reported different genetic backgrounds among serotype IV GBS strains, which have been shown to include sequence types (STs) ST-452 and ST-459 (11). Horizontal gene transfer occurs frequently in GBS. For example, capsular switching from serotype III to IV has been recently reported and found to be the result of recombination involving the entire cps locus (8,17,18). GBS are considered to be universally susceptible to penicillins; therefore, these are the primary drugs used for prophylaxis and treatment of GBS disease (19,20). However, macrolide and lincosamide antimicrobial drugs, such as erythromycin and clindamycin, are often used to treat GBS infections in patients allergic or suspected to be allergic to β-lactam drugs. Acquisition of resistance against these drugs by horizontal gene transfer has been frequently described in GBS (2,21).

We recently reported a relatively high prevalence (6.2%) of serotype IV strains among GBS causing invasive infections in Toronto, Ontario, Canada (8). In the current study, we used whole-genome sequencing (WGS) to characterize the population structure of serotype IV GBS isolates. We describe a genetically heterogeneous population of isolates that differ in their antimicrobial drug resistance profiles.

Ms. Teatero is a research technician at Public Health Ontario, Toronto, Ontario, Canada. Her primary research interest is the molecular epidemiology of GBS.


We thank Taryn B.T. Athey for assistance with bioinformatics analysis and genome annotations and Dax Torti for performing Illumina sequencing of our strains. During this study, we used the S. agalactiae MLST website (http://pubmist.org/sagalactiae/), which was developed by Keith Jolley and is sited at the University of Oxford.
This study was supported by Public Health Ontario. The MLST website is supported by the Wellcome Trust.


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Technical Appendix

Suggested citation for this article: Teatero S, McGeer A, Li A, Gomes J, Seah C, Demczuk W, et al. Population structure and antimicrobial resistance of invasive serotype IV group B Streptococcus, Toronto, Ontario, Canada. Emerg Infect Dis. 2015 Apr [date cited].http://dx.doi.org/10.3201/eid2104.140759
DOI: 10.3201/eid2104.140759

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