Biochemical and Antigenic Relationships of the Paracolon Bacteria

Abstract

In the bacteriological laboratories of Brown University and the Connecticut State Department of Health, Bureau of Laboratories, we have been engaged in a systematic study of the biochemical and serological relationships of the coliform and related bacteria since April 1937. During this time over 12,000 normal and aberrant coliform cultures have been isolated. The IMViC reactions and in addition cellobiose fermentation were determined for all these cultures. A wide variety of biochemical types were encountered ranging from those positive in all five tests to a few weakly positive in only one of the IMViC tests. The ability of more than 3,500 of these cultures to ferment glucose, lactose, sucrose, salicin, maltose and mannitol was determined. Normal coliform cultures negative in sucrose or salicin or both were commonly found. Strains failing to ferment maltose were not anticipated but several were isolated from widely different sources. Mannitol fermentation appeared to be a constant characteristic of normal coliforms but among the last 500 isolations two, otherwise normal, mannitol-negative strains were obtained. Coliform cultures fermenting lactose slowly or not at all, but normal in other respects, were frequently encountered. We have obtained from both rapid and slow lactose-fermenting coliforms variants which were anaerogenic in lactose only or in all carbohydrates. Some of these variants have remained constant for 2 years, one for more than 3 years. In addition motile and nonmotile, indole-positive cultures were found which produced no gas from carbohydrates when originally isolated. Many such cultures would be classed as Eberthella or Shigella, particularly when the fermentation of lactose, sucrose or salicin was slow or absent. After varying periods of laboratory cultivation many of these strains produced gas. Cultures that appeared to be non-gas-forming but which could not be identified as known Eberthella or Shigella have been included in the paracolon group since they could be anaerogenic variants of coliforms. These exceptions and others are a serious handicap to the practical bacteriologist because strains not infrequently defy classification in any of the recognized sections of the coliform group. The tendency to disregard such exceptions for the most part is justifiable but occasionally this might be a mistake. Stuart, Mickle and Borman (1940) proposed the term "aberrant" coliforms for cultures not fermenting lactose, producing acid only, or requiring more than 48 hours for the production of 20 per cent gas when the unusual fermenting characteristics of such strains are relatively stable. Aberrant coliforms are frequently isolated from such sources as water with an excellent sanitary survey, soils from rigidly 101