The Microflora of Milking Equipment Cleansed by Chemical Methods

S ummary : The incidence of the main types of bacteria among 2,856 isolated on Yeastrel-milk agar incubated at 30° from 121 rinses of dairy equipment cleansed by chemical methods, showed that micrococci were dominant in low colony count (<10⁴/ft²) rinses of equipment treated by immersion cleaning in caustic soda or cleansed in detergent-hypochlorite solutions, whereas nonpigmented Gram-negative rods were dominant in low count rinses of equipment cleansed with detergent-sterilizers containing quaternary ammonium compounds. Gram-negative rods were dominant and streptococci frequent in high count (<2·5 × 10⁵/ft²) rinses irrespective of the chemical used. A high proportion of the streptococci and coli-aerogenes organisms gave acid reactions in litmus milk after 72 h at 22°, many of the anaerogenic Gram-negative rods and several of the aerobic sporeformers gave proteolytic reactions, whereas the majority of the micrococci, corynebacteria and other asporogenous Gram-positive rods showed no change. Bacteria isolated from high count rinses were more active in producing milk spoilage reactions at 22° than those isolated from low count rinses.