the same group as a junior synonym of S. iniae. Phylogenetic analyses based on 16S ribosomal DNA suggest that S. iniae is closely related to other streptococcal pathogens of humans and animals. Specifically, it is clustered in the pyogenic group, along with other pathogenic streptococci such as S. pyogenes, S. agalactiae, S. uberis, S. canis, S. porcinus, S. phocae, and S. intestinalis. Of these related species, it is most closely related to S. porcinus. Genomic restriction fragment analysis of diverse host and geographical panels of S. iniae isolates has shown common profiles between virulent fish and human strains, though multiple pulsed field gel electrophoresis patterns have been identified among human isolates. Identification S. iniae may be easily misidentified (or not identified at all) by conventional automated microbiology systems. Molecular genetics methods, such as DNA sequencing and DNA-DNA hybridization, can be useful for correct identification, although work by the U.S. Centers for Disease Control and Prevention has suggested they are unnecessary in most cases. Several groups have used 16S rDNA sequencing to identify S. iniae isolates, and while it can differentiate this species from other related species, such as S. porcinus and S. uberis, 16S sequencing cannot be used to differentiate between strains of S. iniae. Ribotyping is a similar method, by which 16S and 23S rRNA genes are digested with restriction endonucleases and Southern blotted using species-specific oligonucleotide probes. This method is more sensitive than 16S rDNA sequencing, as in addition to species differentiation, it can be used to differentiate between strains. Ribotyping was used in 1997 to differentiate between Israeli and American strains, thus ruling out the possibility of an epidemiological link between outbreaks in the two countries. S. iniae is beta-hemolytic when incubated in anaerobic conditions, although it may be misidentified as alpha-hemolytic because, in some strains, zones of beta-hemolysis (complete destruction of red blood cells in the blood agar culture medium) are surrounded by large zones of alpha-hemolysis (incomplete destruction of red blood cells with a greenish discoloration due to breakdown of hemoglobin). The bacterium is catalase-negative and LAP-positive (like all streptococci), PYR-test and CAMP-test-positive, does not hydrolyze sodium hippurate, and does not grow in bile esculin agar. It does not express any of the known Lancefield antigens. Serotypes Two serotypes of S. iniae are established. The ATCC 29178 type strain first characterized in 1976 by Pier and Madin is representative of serotype I isolates. Serotype II