1984 Volume 25 Issue 4 Pages 322-328_1
Taxonomic studies were carried out on 2, 842 strains of gram-negative, facultatively anaerobic, fermentative rods isolated from foods and environmental materials by means of a probabilistic method using a computer. Although coliforms included only a few species in the classification proposed by the Coli-Aerogenes Subcommittee in 1956, the 2, 842 strains studied were divided into 51 species.
Strains showing an IMViC pattern on Escherichia coli included authentic E. coli and eight other species that probably originated from the environment. The majority of strains of E. coli were easily differentiated from other coliform organisms by their ability to grow at 44.5°, but 17% of lactose-fermenting and 16% of lactose-nonfermenting strains of E. coli failed to grow at this temperature. In addition, 13.3% of 188 E. coli strains were non- or late lactose-fermenters and 10.4% of 163 lactose-fermenting E. coli produced no gas, so that these strains did not serve as indicator organisms of fecal contamination. Thus, enterobacteria found in foods may not always indicate direct fecal contamination, but may often originate from environmental sources.
It is discussed whether enterobacterial species other than E. coli should also be included in the indicator organisms of microbial standards for processed foods. Although the species found in foods in this study would be harmless to healthy persons, they have often been observed as opportunistic pathogens in hospitalized patients with some underlying diseases. It seems desirable, therefore, that separate microbial standards from those for public health should be applied to foods served to hospitalized patients.
