Production of an enterotoxin by a gastro-enteritis-associated Aeromonas strain.

The potential of motile Aeromonas species to cause human gastrointestinal infections has been recognised recently. Considerable worldwide epidemiological, microbiological and clinical investigations have shown that some strains of the different motile aeromonads are of increasing enteropathogenic significance, especially in children, the elderly and in immunocompromised individuals. Some of the diarrhoeal symptoms of Aeromonas-associated gastro-enteritis have been attributed to enterotoxins. In this study, 15 Aeromonas isolates from clinical and non-clinical sources, representing the three motile aeromonads commonly associated with gastro-enteritis (A. caviae, A. hydrophila and A. veronii biovar sobria), were tested for their ability to cause fluid accumulation in infant mice by the suckling mouse technique. Eight isolates were found to produce enterotoxin. Of these, an A. veronii biovar sobria strain (AS15), isolated from lamb kidney, was found to produce the highest enterotoxin score. An enterotoxin of c. 40 kDa produced by A. veronii biovar sobria AS15 was purified by Sephacryl S-100 gel filtration and high-performance liquid chromatography. This enterotoxin caused marked fluid accumulation in infant mice by the suckling mouse technique. The purified enterotoxin cross-reacted with cholera toxin antibodies and was readily inactivated by heating at 56 degrees C for 10 min. The production of a 'cholera-like' enterotoxin by Aeromonas isolates from samples of animal origin suggests that these organisms could be of public health significance in food products.

Growth and exotoxin production at low temperatures by Aeromonas strains in meat slurries.

The ability of enterotoxigenic strains of Aeromonas hydrophila and Aeromonas sobria to produce exotoxins (haemolysin and enterotoxin) and exoenzymes (protease and lipase), as well as their growth in meat slurries stored at low temperatures (5 and 12 degrees C) was investigated. The results showed that Aeromonas grew well in meat slurries stored at low temperatures in the presence of background flora. Exotoxins and exoenzymes were not detected in filtrates from meat slurries inoculated with enterotoxigenic Aeromonas strains after 5 and 8 days incubation at both incubation temperatures. The significance of the competitive growth of aeromonads in foods at refrigeration temperatures is discussed.

Cytotoxic and haemagglutinating activities of motile Aeromonas species.

Cytotoxic and haemagglutinating properties were determined in 114 Aeromonas strains isolated from various sites in slaughtered lambs and from processed lamb meat. Cytotoxic activity on Vero cells was observed in 48 (42%) of the strains. It was more common in A. sobria and A. hydrophila isolates than with A. caviae isolates. Haemagglutination (HA) activity was found frequently in motile aeromonads irrespective of species; it was present in 50% of A. sobria strains, 51% of A. hydrophila strains and 48% of A. caviae strains. HA was inhibited by fucose, galactose and mannose at low concentration, and in most cases, two or three of these sugars were inhibitory. A significant association was found between certain HA-inhibition patterns and the production of cytotoxin by Aeromonas spp.

Experimental evidence for toxin production by Aeromonas hydrophila and Aeromonas sobria in a meat extract at low temperatures.

The ability of enterotoxigenic strains of Aeromonas hydrophila and Aeromonas sobria to produce exotoxins (enterotoxin and haemolysin) in a meat extract at low temperatures (5 and 12 degrees C) was investigated. All three strains incubated at 12 degrees C were enterotoxigenic and haemolytic in the meat extract after 5 days. At 5 degrees C, five of the six strains tested were able to produce these exotoxins after 8 days incubation while one strain was neither enterotoxigenic nor haemolytic after 5, 8 and 11 days. The possible involvement of performed toxin(s) in Aeromonas gastroenteritis is also discussed.

Production of exotoxins by Aeromonas spp. at 5 degrees C.

The ability of 60 strains of Aeromonas to produce enterotoxin and haemolysin after cultivation at 5 degrees C for 7-10 d was investigated. The strains were isolated from lamb meat, offal, carcasses and faeces, and had previously been tested for their ability to produce these exotoxins at 37 degrees C. The results showed that some strains of Aeromonas hydrophila and A. sobria were capable of producing enterotoxin and haemolysin at 5 degrees C, but none of the A. caviae strains tested produced these two factors. Of the 30 A. hydrophila strains investigated 25 and 27 were enterotoxigenic and haemolytic respectively. Likewise, of the 24 A. sobria strains investigated 16 and 18 were enterotoxigenic and haemolytic respectively. The results indicate that certain strains of Aeromonas species, in particular A. hydrophila and A. sobria, are of potential public health significance in meats stored at refrigeration temperature.

Incidence of aeromonads in samples from an abattoir processing lambs.

Two hundred and thirty three samples of lamb carcasses, livers, kidneys and faeces, collected at a local abattoir, were examined to determine the incidence of motile Aeromonas spp. Wash water from the abattoir was also tested. Direct plating on starch ampicillin agar and enrichment in alkaline peptone water were used. The incidence of aeromonads was low. They were detected only after enrichment in 5/47 faecal samples and 11/50 carcass samples. The 41 strains of Aeromonas isolated were identified to species level and 93% of them were able to grow at 5 degrees C. The ability to produce both haemolysin and enterotoxin was species-related and was more common in Aeromonas hydrophila and A. sobria strains than in A. caviae strains.