Search

The occurrence of Clostridium botulinum in fresh (67) and cured fish (278) samples in retail trade in Cochin was studied. An overall prevalence of 19% (13/67) was found in fresh retail fish and types A to D were detected in the positive samples. In pelagic fish, incidence of C. botulinum was 18% (7/39) whereas in demersal fish, 21% (5/24) of the samples harboured C. botulinum. Incidence of C. botulinum in shrimp was 25% (1/4) and type D was found in the positive sample. Of 257 cured fish in retail trade tested for the presence of C. botulinum, the overall contamination level was 10% (25/257). Among the C. botulinum types A to D prevalent in fresh fish, types C and D were the predominant types found in cured products. In salt-dried shrimp, of the 21 samples analysed, 10 samples (48%) harboured C. botulinum.

The effect of sodium chloride concentration (3, 4, 5, 6, 8, 10 and 12%) and storage temperatures (4°C, 10°C, 15°C and 30°C) on toxin production by Clostridium, botulinum isolated from tropical fish was studied in anaerobic cooked meat medium. The combined effect of sodium chloride (3, 5%), low pH (5.5) and low temperature (15°C) on toxin production by C. botulinum was also examined. The toxicity was tested by mouse bioassay. An increase in lag phase was noticed by increasing the salt concentration. At 30°C, spores of C. botulinum type E were able to grow and produce toxin up to 3% salt (aw = 0.976), whereas for types C and D the limiting salt concentration was 4-5% (aw = 0.97-0.974) and for types A and B it was 8% (aw = 0.952). By lowering the storage temperature, an increase in lag phase and time to toxicity was noticed for type Eat 3% salt and for types A, C and D at 5% salt level. The probability of growth and toxin production at 5% salt decreased as the pH and storage temperature (combined stress) was decreased. [ABSTRACT FROM AUTHOR]

This study was undertaken to determine the influence of temperature and pH on growth and time to toxicity of spores of Clostridium botulinum types isolated from tropical fish. Anaerobic meat medium with varying temperatures (4-30°C) and pH values (4.5 to 7.0) were used and toxicity was tested by mouse bioassay. An increase in lag phase was noticed by lowering the growth temperature from 30°C to 4°C and the pH from 7.0 to 4.6. The probability of toxin production increased with storage time, but decreased as either the pH or storage temperature and pH (combined stress) was decreased. The results indicated the effect of pH in controlling toxin production by C. botulinum spores in refrigerated foods with pH 5.0 or < 5.0. [ABSTRACT FROM AUTHOR]