CHARACTERIZATION OF BACTERIA WHICH PRODUCE COLONIES ATYPICAL OF THE COLIFORM GROUP ON VIOLET RED BILE AGAR1

Abstract

Summary Thirty-three strains of bacteria were isolated during routine analysis of dairy products at two Canadian centers from colonies on violet red bile agar VRB which measured less than 0.5 mm in diameter after incubation at 35 C for 24 hr. All isolates showed typical coli-form morphology and Gram reaction and from the results of biochemical test were identified as coliform biotypes. No strain survived laboratory pasteurization at 145 F for 30 min. Strains of presumptive intestinal orgin (E. coli) were typed serologically and one strain was found to be of serotype 026:B6, an important etiological agent of infantile diarrhoea. It is concluded that size of colony is not a valid criterion for discriminating between colonies of coliform and non-coliform bacteria on VRB.