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

Abstract
Thirty-three strains of bacteria were isolated during routine analysis of dairy products at 2 Canadian centers from colonies on violet red bile agar (VRB) which measured less than 5 mm in diameter after incubation at 35 C for 24 hr. All isolates showed typical coliform 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 origin (Escherichia coli) were typed serologically and one strain was found to be of serotype 025: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.

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