Contaminating Microflora Research Articles

Incidence and growth potential of Bacillus cereus in poultrymeat products

A total of 102 retail samples of poultrymeat products was examined for Bacillus cereus, using PEMBA as a selective isolation medium. The products included various raw and cooked items, either fresh or frozen. Only 6·9% of samples contained detectable levels of B. cereus, with counts ranging from log10 1·4 to 3·5 g−1, but large numbers of other organisms, up to log10 7·7, were sometimes observed on the plates and may have masked the presence of B. cereus or inhibited growth. The latter possibility was confirmed in an experiment involving three selective media, three standard strains of B. cereus and the contaminating microflora of a chicken product. On each of the media, recovery of B. cereus was adversely affected by equivalent numbers of the other organisms. Growth of B. cereus in cooked chicken breast and leg meat was studied at 10, 15, 22 and 37°C. Mean generation times for four strains varied from 0·4 to 0·5 h at 37°C, from 1·1 to 1·5 h at 22°C and from 2·6 to 4·1 h at 15°C. At 15°C, two of the strains multiplied faster in leg than in breast meat. Little or no growth occurred at 10°C within five days.

Estimation of chicken microbial load using the growth curve parameters of chicken microflora.

Chicken microbial loads, estimated through absorbance increase of culture medium inoculated with the contaminant microflora of the carcasses, were compared with total plate counts and psychrotrophic counts obtained on the same carcasses using the pour plate method after 0, 48, 96, and 144 hr stored chicken at 4 to 5 C. For estimating microbial loads on the carcasses, the mathematical relation 1n AO = 1nA1 - R - Kt was used, which was developed by combining the growth and R equations (described in Materials and Methods) and using growth data at 28 C. The values obtained by this method, when compared with those of plating, give correlation coefficients of .94, .91, .88, and .64 for total plate counts after 0, 48, 96, and 144 hr of storage and .94, .83, .82, and .86 for psychrotrophics counts after 0, 48, 96, and 144 hr of cold storage. The method proposed in the present work permits the estimation of psychrotrophics and total counts in no more than 11 hr, which is very promising for industrial applications.