A multilocus sequence typing (MLST) system was developed for group B streptococcus (GBS). The system was used to characterize a collection (n ‫؍‬ 152) of globally and ecologically diverse human strains of GBS that included representatives of capsular serotypes Ia, Ib, II, III, V, VI, and VIII. Fragments (459 to 519 bp) of seven housekeeping genes were amplified by PCR for each strain and sequenced. The combination of alleles at the seven loci provided an allelic profile or sequence type (ST) for each strain. A subset of the strains were characterized by restriction digest patterning, and these results were highly congruent with those obtained with MLST. There were 29 STs, but 66% of isolates were assigned to four major STs. ST-1 and ST-19 were significantly associated with asymptomatic carriage, whereas ST-23 included both carried and invasive strains. All 44 isolates of ST-17 were serotype III clones, and this ST appeared to define a homogeneous clone that was strongly associated with neonatal invasive infections. The finding that isolates with different capsular serotypes had the same ST suggests that recombination occurs at the capsular locus. A web site for GBS MLST was set up and can be accessed at http://sagalactiae.mlst.net. The GBS MLST system offers investigators a valuable typing tool that will promote further investigation of the population biology of this organism.Streptococcus agalactiae, group B streptococcus (GBS), is an important human pathogen. It is the leading cause of neonatal sepsis in the United Kingdom (18) and the United States (23). It is regarded as an emerging pathogen in the elderly (13) and is a frequent cause of maternal sepsis. However, GBS is usually a commensal organism and can be isolated from the genitourinary and gastrointestinal tracts of up to 35% of healthy adults (1).Capsular serotyping has been one of the mainstays in the descriptive epidemiology of GBS. Nine capsular serotypes have been described (Ia, Ib, and II to VIII). Serotype III GBS strains are of particular importance, as they are responsible for the majority of infections, including meningitis, in neonates worldwide (22). Diverse lineages of serotype III strains can be distinguished with multilocus enzyme electrophoresis (12, 19), pulsed-field gel electrophoresis (20), and restriction digest pattern (RDP) analysis (2), and the lineages appear to vary in pathogenic potential.Multilocus sequence typing (MLST) is an unambiguous sequence-based typing method that involves sequencing approximately 500-bp fragments of seven housekeeping genes and has been used successfully to type strains and investigate the population structure of a number of human bacterial pathogens, including Neisseria meningitidis (16) and Streptococcus pneumoniae (9). MLST is particularly suitable for epidemiological studies because it provides data that can easily be compared between laboratories over the Internet.The primary aim of this study was to develop an MLST system for GBS. Secondary aims were to show that the system could be used on a di...

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The genetic relatedness and evolutionary relationships between group B streptococcus (GBS) isolates from humans and those from bovines were investigated by phylogenetic analysis of multilocus sequence typing data. The collection of isolates consisted of 111 GBS isolates from cows with mastitis and a diverse global collection of GBS isolates from patients with invasive disease (n ‫؍‬ 83) and carriers (n ‫؍‬ 69). Cluster analysis showed that the majority of the bovine isolates (93%) grouped into one phylogenetic cluster. The human isolates showed greater diversity and clustered separately from the bovine population. However, the homogeneous human sequence type 17 (ST-17) complex, known to be significantly associated with invasive neonatal disease, was the only human lineage found to be clustered within the bovine population and was distinct from all the other human lineages. Split decomposition analysis revealed that the human isolate ST-17 complex, the major hyperinvasive neonatal clone, has recently arisen from a bovine lineage.

Listeria monocytogenes, an uncommon foodborne pathogen, is increasingly recognized as a cause of life-threatening disease. A marked increase in reported cases of listeriosis during 1998 motivated a retrospective nationwide survey of the infection in Israel. From 1995 to 1999, 161 cases were identified; 70 (43%) were perinatal infections, with a fetal mortality rate of 45%. Most (74%) of the 91 nonperinatal infections involved immunocompromised patients with malignancies, chronic liver disease, chronic renal failure, or diabetes mellitus. The common clinical syndromes in these patients were primary bacteremia (47%) and meningitis (28%). The crude case-fatality rate in this group was 38%, with a higher death rate in immunocompromised patients.