Abstract
BackgroundIn humans, Streptococcus agalactiae or group B streptococcus (GBS) is a frequent coloniser of the rectovaginal tract, a major cause of neonatal infectious disease and an emerging cause of disease in non-pregnant adults. In addition, Streptococcus agalactiae causes invasive disease in fish, compromising food security and posing a zoonotic hazard. We studied the molecular epidemiology of S. agalactiae in fish and other aquatic species to assess potential for pathogen transmission between aquatic species and humans.MethodsIsolates from fish (n = 26), seals (n = 6), a dolphin and a frog were characterized by pulsed-field gel electrophoresis, multilocus sequence typing and standardized 3-set genotyping, i.e. molecular serotyping and profiling of surface protein genes and mobile genetic elements.ResultsFour subpopulations of S. agalactiae were identified among aquatic isolates. Sequence type (ST) 283 serotype III-4 and its novel single locus variant ST491 were detected in fish from Southeast Asia and shared a 3-set genotype identical to that of an emerging ST283 clone associated with invasive disease of adult humans in Asia. The human pathogenic strain ST7 serotype Ia was also detected in fish from Asia. ST23 serotype Ia, a subpopulation that is normally associated with human carriage, was found in all grey seals, suggesting that human effluent may contribute to microbial pollution of surface water and exposure of sea mammals to human pathogens. The final subpopulation consisted of non-haemolytic ST260 and ST261 serotype Ib isolates, which belong to a fish-associated clonal complex that has never been reported from humans.ConclusionsThe apparent association of the four subpopulations of S. agalactiae with specific groups of host species suggests that some strains of aquatic S. agalactiae may present a zoonotic or anthroponotic hazard. Furthermore, it provides a rational framework for exploration of pathogenesis and host-associated genome content of S. agalactiae strains.
Highlights
In humans, Streptococcus agalactiae or group B streptococcus (GBS) is a frequent coloniser of the rectovaginal tract, a major cause of neonatal infectious disease and an emerging cause of disease in non-pregnant adults
The aim of the current paper is to enhance our knowledge of the molecular epidemiology of S. agalactiae in fish and other aquatic species, with emphasis on use of standardized typing systems that cover housekeeping genes as well as virulence genes and that allow for assessment of transmission potential between aquatic species and humans based on comparison with existing databases
Pulsotypes were indistinguishable for isolates from different host species or countries, e.g. for bullfrog and tilapia isolates from Thailand or for tilapia isolates from Honduras, Colombia and Costa Rica (Figure 1)
Summary
Streptococcus agalactiae or group B streptococcus (GBS) is a frequent coloniser of the rectovaginal tract, a major cause of neonatal infectious disease and an emerging cause of disease in non-pregnant adults. We studied the molecular epidemiology of S. agalactiae in fish and other aquatic species to assess potential for pathogen transmission between aquatic species and humans. The. To study the epidemiology of S. agalactiae, numerous molecular methods have been used. ST17 is more prevalent among isolates from invasive disease in infants than among carriage isolates from pregnant adults [1,13]. Three-set genotyping encompasses molecular serotyping (MS) and profiling of surface protein genes and mobile genetic elements (MGE), and allows for further differentiation of isolates belonging to the same ST [11]. ST283 isolates with molecular serotype III-4, C-α protein and C-α protein repeating units and the MGEs IS1381, ISSag, and ISSag are associated with the emergence of GBS meningitis in adults in Southeast Asia [7,8]
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