All seal isolates included in the current study (n = 6) had serot

All seal isolates included in the current study (n = 6) had serotype Ia, suggesting buy Target Selective Inhibitor Library a human origin. In humans, ST23 is common as vaginal-rectal carrier strain in adults although it may also cause neonatal invasive disease [1, 13]. Given the predominant niche of ST23 in humans, it is conceivable that its presence in seals is due to microbial contamination of surface water. ST23 probably has the broadest known host range of all S. agalactiae STs. Both homeothermic and poikilothermic

species can be affected, including humans, cattle, dogs, crocodiles and seals [6, 14, 15]. Despite the high prevalence of ST23 in humans, its wide host range and its ability to affect aquatic mammals and semi-aquatic reptiles, there are no reports on occurrence of ST23 in fish. This may reflect the relatively small number of fish isolates characterized to date or it may indicate true biological differences, e.g. an inability to infect fish. Challenge studies using ST23 are required to assess its ability to cause disease in fish. If ST-associated differences in virulence are confirmed, comparative genomic analysis of human,

fish, seal and bovine isolates may help to identify molecular correlates of virulence. S. agalactiae ST260 and ST261 are associated with fish but not with humans The final subpopulation in our collection consisted of non-haemolytic strains of S. agalactiae. Non-haemolytic S. agalactiae may cause invasive disease such as endocarditis in adult humans [42] but no MLST data on non-haemolytic human isolates could be found. The prevalence of non-haemolytic S. agalactiae among carriage isolates has been estimated at 5 to 8%, although this

value may be underestimated in studies that use β-haemolyis as a diagnostic criterion for identification of the organism [43]. All 4��8C non-haemolytic isolates in our collection belonged to serotype Ib, a serotype that has been associated with β-haemolytic and non-haemolytic human isolates [1, 37]. The subpopulation of non-haemolytic serotype Ib isolates in our study encompassed all fish isolates that did not originate from Southeast Asia, suggesting an association between geographic origin and strain. The association with host species and geographic origin is not absolute, as β-haemolytic serotype Ib isolates and ST261 have also been reported from frogs [37, 44] and ST261 has been reported in fish from Indonesia [45]. This is the first report of ST261 in aquarium fish, which originated from Australia. Outbreaks of streptococcosis in wild fish have occurred repeatedly in Australia in the past few years [21]. The isolates causing disease in Queensland grouper and other reef fish were non-haemolytic with serotype Ib, suggesting that they belong to the fish-associated subpopulation of S. agalactiae.

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