Characterization and significance of Aeromonas spp. isolated from diarrhoeic stools in Nigeria.

During a 12-month study period (January-December 1986), 12 Aeromonas strains (eight A. hydrophila and four A. sobria) were isolated from the 400 diarrhoeic and 200 non-diarrhoeic stools examined. Isolates were characterized for frequency of phenotypic properties associated with virulence using the suckling mouse test for enterotoxin assay; haemolysis of rabbit erythrocytes for haemolysin production, and haemagglutination of human group A cells (HA) for presence of colonization factor antigens (CFA). All seven A. hydrophila and three A. sobria strains isolated from diarrhoeic stools produced enterotoxin. All, except one A. sobria strain from a diarrhoeic stool, produced haemolysin in titres greater than 4. Fifty per cent of strains from diarrhoeic stools and 100% of strains from non-diarrhoeic stools were HA positive. All HA reactions were sensitive to mannose and galactose. The frequency of enterotoxin-producing aeromonads was significantly higher (P less than 0.05) in diarrhoeic patients than in non-diarrhoeic controls. There was no significant difference (P greater than 0.05) in the frequency of haemolysin and HA production between diarrhoeic and non-diarrhoeic strains.