Abstract
The enormous numbers of anaerobic non-spore forming, gramnegative rods reported in the intestinal contents of man (Sanborn 1 and Eggerth and Gagnon 2 ) have not been considered in the routine isolation of pathogenic bacteria, or in the false presumptive tests in water analyses. Bacteroides are small gram-negative or gram-positive rods, some of the gram-negative forms being indistinguishable morphologically from the gram-negative pathogenic bacteria. Although they are strict anaerobes, the possibility that they might find conditions favorable for multiplication in mixed cultures with aerobes was considered in this investigation.
Bacterium typhosum (Rawlings) and 2 strains of Bacteroides, one isolated from a colon specimen from man and the other from a monkey colon, were studied. The biochemical reactions of the 2 strains of Bacteroides are listed in Table I.
A mixed suspension of these Bacteroides strains and Bacterium typhosum produced acid without gas in lactose broth incubated aerobically. An experiment was performed with the human Bacteroides strain in mixture with Bacterium typhosum. This suspension was plated on endo and eosine-methylene blue agar media and incubated aerobically for 24 hours, after which colonies were picked and put into lactose broth. Bacteroides was demonstrated in a few of these colonies by the production of acid in the lactose broth after 36 hours' incubation. All of the colonies on the plates were colorless and identical with those of a pure culture of the typhoid bacillus, although plates prepared in a similar manner, incubated aerobically for 48 hours and then placed in an anaerobic jar and incubated for 3 days longer, contained some isolated colonies of Bacteroides and some which appeared to be superimposed on the typhoid colonies.
A mixed suspension of Bacteroides (monkey strain) and Bacterium typhosum was used for inoculation of 12 freshly prepared veal infusion agar slants.
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