THE DETERMINATION OF THE COLI-AEROGENES CONTENT OF MILK AND DAIRY EQUIPMENT BY PLATING ON VIOLET RED BILE AGAR INCUBATED AT 30°

SUMMARY: Violet red bile agar (VRB) incubated at 30° for 20–24 hr was as good an indicator of coli-aerogenes bacteria in milk as MacConkey's broth. A high proportion (82%) of the large, deep red colonies considered to be formed by coli-aerogenes bacteria were confirmed as such. A British brand of dehydrated VRB agar was as suitable as an American brand of this medium for determining the coli-aerogenes content of milk. All the strains of typical coli-aerogenes bacteria tested formed red colonies. In a small proportion of cases the diameter was less than 0·5 mm. The only other milk bacteria which formed colonies resembling those of coli-aerogenes organisms were some acid forming strains of Gram-negative rods. Coli-aerogenes bacteria, determined on VRB agar at 30°, generally constituted only a small proportion of the microflora of fresh raw milk and of farm dairy equipment.