SHORT ARTICLES

SOME bacteria isolated at the hospital laboratory in Hexham grew on a medium containing Oxoid Peptone L37 (OP), but not on blood agar containing home-made tryptic digest of meat. This was confirmed at the Regional Public Health Laboratory in Newcastle, where other organisms behaving similarly were later isolated. It was noted that the strains showed satellitism with other bacterial species. Seven of these recently isolated strains were then examined at the Public Health Laboratory in Sunderland. All grew badly on blood agar made with home-made extract of heart and Evans Peptone, batch no. N89900 (HME), and better or much better on a medium containing Oxoid Blood Agar Base (OBA). Of the seven strains subcultured at Sunderland five were Escherichia coli and two were streptococci. The colonies of the former in early subcultures were less than 0.2 mm in diameter after 24 hr at 37°C on HME but 2-3 mm on OBA; in smears stained by Gram's method the bacteria were pleomorphic, fusiform, irregularly stained, and up to 15 pm long from HME but alike, parallel sided, uniformly stained, and only 5 pm long from OBA. The two strains of streptococci grew slightly better on OBA, their action on the blood in the two media was different, but the Gram-stained smears were not distinguishable. The cause of these phenomena could have been a toxic substance in some of the media. But the original observation at Hexham had been that the demanding strains grew on MacConkey agar containing OP, and not on blood agar with tryptic digest of meat. Toxicity, which one might expect to be reduced by blood, therefore seemed unlikely to account for the failure of the tryptic digest. Nor did charcoal improve the growth on a medium made with Evans Peptone (EP), but this medium if layered on OBA allowed growth as luxuriant as on OBA itself. It seemed likely that OP contained some nutrient that the other media lacked and this was sought in eight other nitrogen-containing nutrients {Yeastrel; Oxoid peptone (old batch)