Enrichment in alkaline peptone water was compared with the direct plating method for the isolation of Aeromonas spp. from lamb meat and offal samples. The enrichment method significantly increased the isolation rate of aeromonads. Motile Aeromonas species (A. hydrophila, A. sobria and A. caviae) were present in all kinds of samples investigated. Seventy-three Aeromonas strains isolated in this survey were characterized to species level and examined for their ability to produce virulence factors. Strains identified as A. sobria were the strongest producers of haemolysin and enterotoxin, whereas A. caviae strains were consistently non-haemolytic and non-enterotoxigenic. Thus it is likely that lamb meat and offal are potentially significant sources of virulent Aeromonas species and may play an important role in the aetiology of Aeromonas-associated gastro-enteritis.
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.
Summary. Cytotoxic and haemagglutinating properties were determined in 1 14 Aeromonas strains isolated from various sites in slaughtered lambs and from processed lamb meat. Cytotoxic activity on Vero cells was observed in 48 (42 YO) 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 YO of A . sobria strains, 51 YO of A. hydrophila strains and 48 YO 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.
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