Phylogenetic relationships among Streptococcus agalactiae isolated from piscine, dolphin, bovine and human sources: a dolphin and piscine lineage associated with a fish epidemic in Kuwait is also associated with human neonatal infections in Japan.

Streptococcus agalactiae, commonly known as group B streptococcus (GBS), is a cause of infectious disease in numerous animal species. This study examined the genetic relatedness of piscine, dolphin and human GBS isolates and bovine GBS reference strains from different geographical regions using serological and molecular serotyping and multilocus sequence typing (MLST) techniques. Piscine isolates originating from Kuwait, Brazil, Israel and the USA were capsular serotype Ia, a serotype previously unreported in GBS isolated from fish. Sequence typing of piscine isolates produced six sequence types (ST-7, ST-257, ST-258, ST-259, ST-260 and ST-261), the latter five representing allelic designations and allelic combinations not previously reported in the S. agalactiae MLST database. Genomic diversity existed between dolphin and piscine GBS isolates from Kuwait and other geographical areas. Piscine GBS isolates from Brazil, Israel, Honduras and the USA appeared to represent a distinct genetic population of strains that were largely unrelated to human and bovine GBS. The Kuwait dolphin and piscine lineage (ST-7, Ia) was also associated with human neonatal infections in Japan. Comparative genomics of piscine, human and bovine GBS could help clarify those genes important for host tropism, the emergence of unique pathogenic clones and whether these hosts act as reservoirs of one another's pathogenic lineages.

A unique serine-rich repeat protein (Srr-2) and novel surface antigen (epsilon) associated with a virulent lineage of serotype III Streptococcus agalactiae.

Group B streptococci (GBS) are pathogens of both neonates and adults, with serotype III strains in particular being associated with invasive disease and meningitis. In this study, a novel GBS surface antigen, epsilon, was found to be co-expressed with the previously reported delta antigen on an identical subset of serotype III GBS. Expression of delta/epsilon on the surface of serotype III GBS was shown to distinguish the restriction digest pattern (RDP) III-3 and multilocus sequence typing (ST)-17 lineage. epsilon-Specific antibodies were reactive with a unique, high-molecular-mass, serine-rich repeat protein (Srr-2) found exclusively in RDP III-3 strains. The gene encoding Srr-2 was located within a putative accessory secretory locus that included secY2 and secA2 homologues and had a genetic organization similar to that of the secY2/A2 locus of staphylococci. In contrast, serotype III delta/epsilon-negative strains and strains representative of serotypes Ia, Ib, Ic and II shared a common Srr-encoding gene, srr-1, and an organization of the secY2/A2 locus similar to that of previously reported serotype Ic, delta/epsilon-negative serotype III and serotype V GBS strains. Representative serotype III delta/epsilon-positive strains had LD(90) values 3-4 logs less than those of serotype III delta/epsilon-negative strains in a neonatal mouse model of infection. These results indicate that the RDP III-3/ST-17 lineage expresses Srr-2 and is highly virulent in an in vivo model of neonatal sepsis.

Serotype III Streptococcus agalactiae from bovine milk and human neonatal infections.

Streptococcus agalactiae (group B streptococcus [GBS]) causes invasive human infections and bovine mastitis. This study examined the genetic relationship between bovine and human serotype III GBS by using molecular techniques that classify human serotype III GBS into four distinct phylogenetic lineages. Bovine serotype III GBS were largely contained in two lineages, which are distinct from the two major lineages (restriction digest types III-2 and III-3) that infect human neonates. One of the bovine lineages closely resembles the human III-1 lineage, whose members occasionally cause human neonatal infections. The bovine strains in the other lineage characteristically have an initiation factor IF2 gene (infB) H allele and multilocus sequence types that are not found in human GBS strains. Evidence suggests that this "H allele" lineage is related to the human III-3 lineage. These results support the assertion that human and bovine GBS are largely unrelated and provide further insight into the genetic relation between human and bovine GBS.

Correlation of phylogenetic lineages of group B Streptococci, identified by analysis of restriction-digestion patterns of genomic DNA, with infB alleles and mobile genetic elements.

Phylogenetic lineages of pathogenic Streptococcus agalactiae (group B streptococci [GBS]) can be identified by analysis of restriction-digestion patterns (RDPs) of chromosomal DNA. The purpose of the present study was to correlate GBS RDP types and (1) alleles of the highly conserved gene encoding translation-initiation factor IF2, infB, and/or (2) the inserted elements IS1548 and GBSi1. Only 1 combination of serotype and infB allele was found within each RDP type. Strains within a particular RDP type also tend to have the same inserted elements in each of 3 loci examined. A novel insertion sequence, designated "IS1563," was found within all RDP type II-2 strains. Most RDP types could be identified by a combination of serotype, infB allele, and inserted elements at each of the loci. These molecular markers can be used to identify GBS populations and to correlate RDP types and phylogenetic lineages identified by different methods.

Long-range mapping of the Streptococcus agalactiae phylogenetic lineage restriction digest pattern type III-3 reveals clustering of virulence genes.

Human isolates of serotype III Streptococcus agalactiae (group B streptococcus [GBS]) can be divided into three separate phylogenetic lineages based on analysis of the restriction digest patterns (RDPs) of chromosomal DNA. Nine DNA sequences that are present in all isolates of the RDP III-3 phylogenetic lineage, but not in the other lineages, were identified by genomic subtractive hybridization. A complete physical map of a III-3 chromosome was constructed. Six of the nine III-3-specific sequences mapped to a 340-kb Sse8387I fragment which contains or is located close to known GBS virulence genes. One of the III-3-specific probes, AW-10, encodes part of GBSi1, a group II intron that is inserted at two sites within the GBS genome. The second chromosomal site for GBSi1 was isolated, sequenced, and mapped to a location near the locus responsible for hemolysin production. These findings suggest that the genetic variation that distinguishes the RDP type III-3 strains from other serotype III strains occurs largely within localized areas of the genome containing known or putative virulence genes.