Contrasting Growth On Different Peptones

Abstract

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); Lab-Lemco (Oxoid) ; tryptone (Oxoid) ; enzymic hydrolysate of lactalbumin ; acid hydrolysate of casein (Oxoid); Oxoid peptone (batch no. 460); Difco Proteose Peptone no. 3 (control 513512)). Of these, only OP (batch no. 460) and Difco Proteose Peptone no. 3 enhanced the growth of the demanding strains. Both peptones contained aerobic sporebearing bacilli and it could be shown that these bacilli alonc, without the peptone, produced satellitism of the demanding strains. Failure of the Yeastrel to enhance growth showed that the essential nutrient was not V-factor. It remained only to show that these organisms modify EP to make it suitable for the growth of the demanding strains. The numerical yield of bacterial cells, more easily measured than the diameter of colonies and more constant after repeated subculture, was used to contrast the behaviour of the peptones and their modifications.Media. Peptone water was made by dissolving 1 g of peptone in 100 ml demineralised water. The pH was adjusted to 7.0-7-2 and the medium sterilised at 115-5"C for...

Quality Control of Solid Culture Media: A Comparison of the Classic and the So‐called Ecometric Technique

“…First and foremost the so-called intrinsic attributes play an important role. Numerous reports have been published illustrating failures of 'non-selective' media (OMeara & McSween 1937;Buchbinder et al 1954;Schwarz et al 1954;Barnes 1955;Stamer et al 1964, Thomas et al 1966Williams 1970;Bovallius & Zacharias 1971;Johnson et al 1971;Laws et al 1971;Schubert & Schleidt 1975;Then 1977;Babu et al 1978;Wallen & Walker 1979). during excessive heating.…”