base composition determinations showed this organism to be more 

 closely related to Vibrio than Aeromonas species. Further 

 characterization showed the bacterium to be indistinguishable 

 from group F organisms isolated from cases of human diarrhea in 

 Indonesia and Bangladesh. Nine of 16 group F strains from the 

 New York Bight showed responses for virulence in both the Y-l 

 adrenal cell and the rabbit ileal loop assays. Group F vibros, 

 therefore, represent yet another potential human pathogen in 

 coastal waters. 



Aeromonas 



Aeromonads are ubiquitous waterborne microorganisms. 

 Several studies have been undertaken to determine the 

 distribution of Aeromonas spp. in the Chesapeake Bay and its 

 tributaries ( Kaper et al . , 1981; Seidler et al . , 1979; Seidler et 

 al., 1980a; Cavari et al., 1981a). In each study, it was 

 demonstrated that counts of Aeromonas increased with increasing 

 temperature and were highest during the summer months, dropping 

 off with declining temperatures in the fall and winter. From 

 studies of heterotrophic activity Cavari et al . (1981a; 1981b) 

 determined that one reason Aeromonas counts drop off in cold 

 weather is that they are physiologically unable to compete with 

 other microorganisms under such conditions. Furthermore, Seidler 

 et al. (1980a) showed that Aeromonas counts tended to be higher 

 in sediment than in the water column reaching 300 cells/ml in 

 the water column, compared with 4x10^ cell/g sediment in the 

 Anacostia River in August. Numbers of Aeromonas spp. also 

 exhibit an inverse correlation with salinity and dissolved 

 oxygen, (Kaper et al . , 1981; Seidler et al . , 1980a) and are, 

 thus, more prevalent in hypoxic waters of medium to low salinity. 



Kaper et al. (1981) and Seidler et al . (1980a) have shown 

 that counts of Aeromonas in the Chesapeake Bay and Anacostia 

 River demonstrate significant correlation with total and fecal 

 conforms. However, Kaper also cites cases whereby A. hydrophila 

 was isolated from samples devoid of fecal coliforms, providing 

 further evidence that traditional coliform counts are 

 insufficient indicators of microbial pollution. 



Regarding toxicity of environmental isolates of Aeromonas , 

 Kaper et al . (1981) cite positive Y-l adrenal cell assays for 

 71% of 116 isolates tested. In addition, the strains which were 

 cytotoxic also produced fluid accumulation in ligated loops, 

 albeit in low concentrations. Similarly, Seidler et al. (1980a) 

 reported that 39% of A. hydrophila strains and 37% of A. sobria 

 strains isolated from polluted waters produced cytotoxin. 

 Investigating the question of whether a particular subpopulation 

 or biotype of Aeromonas is more likely to be virulent, Daily et 

 al . (1981b) determined that A. sobria is a human pathogen of 

 significance. Furthermore, subpopulations of Aeromonas in the 

 environment may be distinguished on the basis of virulence 



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