No abstract

SUMMARY The effects of various environmental conditions on the viability and growth of normal Escherichia coli and Staphylococcus aureus cells, and of cells of these species which had been damaged by exposure to phenol, o‐cresol and p‐chloro‐m‐cresol, have been examined. With normal cells none of the conditions tried had any effect on the initial counts, but sometimes, more often with Staph. aureus, the bulk of growth eventually obtained in broth media was larger, especially when the medium had been made with pyridine extracted peptone, or when it had been treated with 0·1% of Norit charcoal or 0·02% of FeCl3. In contrast, damaged cells of both species were very sensitive to their environment. At room temperature, 0·1% of Norit added to tap water adsorbed more than 80% of the cells and the initial count was increased. Nevertheless the cells died thereafter. Damaged cells inoculated into broth also died, but when Norit was present both the rate and the extent of death were markedly reduced, though few cells were adsorbed. The addition of FeCl3 (0·02 or 0·03%) had no effect. At 37° damaged cells died faster than at room temperature, but the protective effect of Norit was still evident. In nephelometric studies of cultures growing in Norit treated broth the times to turbidity were shorter than those of control cultures in untreated broth, but broth treated with FeCl3 often gave longer times than the controls. In a comparison of broths prepared with peptone and/or Lab‐Lemco which had been extracted with pyridine to remove suspected toxic substances, the initial counts of treated cells were highest when only the peptone had been extracted. With media containing extracted Lab‐Lemco, or with both ingredients extracted, the counts were smaller but were still generally higher than in normal broth. The results of nephelometric studies were consonant with these findings: broths prepared with extracted ingredients generally gave shorter turbidity times than normal broth, especially with E. coli. The addition to broth of cations, especially Mg2+ (10–3 M), favoured the survival of damaged E. coli but did not influence that of Staph. aureus. But with both species, five times that concentration of Mg2+ was as effective as 0·1% of Norit, which was shown to adsorb lead, tin, copper, zinc, silver and cobalt from broth. Temperatures above 37° were unfavourable to the survival of damaged cells of both species, 44° often being completely inhibitory for Staph. aureus, but this effect was not due to traces of phenol in the inoculum. At 25° damaged E. coli recovered less well than at 30° and 37°, but damaged Staph. aureus did better at 25° and 30° than at 37°.

Summary The inclusion of 0·1 per cent, of activated charcoal or 0·03 per cent. of ferric chloride in subculture media had no consistent influence on the extinction times of Bact. coli exposed to 1 per cent, phenol, but the overall responses in experiments made with several batches of media were positive. On the whole, individual batches of medium consistently gave the same kind of response, positive or null. Activated charcoal (0·1 per cent.) adsorbed about 80 per cent, of the phenol from solution in water at a concentration of 0·005 per cent. In the presence of broth much less was adsorbed; Norit adsorbed only about 9 per cent, and Darco G 60 about 25 per cent. The ferric chloride‐nutrient broth precipitate did not adsorb phenol from either water or broth. In the concentration range 0·001 to 0·020 per cent., phenol in the subculture medium did not appear to influence the extinction times of bacterial populations exposed to that substance.

SUMMARY Bacteriological agar has been shown to be toxic towards Escherichia coli and Staphylococcus aureus. The effect was observed when nutrient agar was treated with Norit or ferric chloride and when the agar component alone was treated similarly. With both agents, larger colonies from untreated suspensions of Staph. aureus and higher counts from phenol treated suspensions of both species, were produced. Aluminium and chromium gave effects similar to those of iron, but iron gave the largest colonies of Staph. aureus. Magnesium also was especially successful in inducing high counts of damaged cells. A batch of Japanese agar, although apparently of poor quality, was superior by both the above criteria to two batches of New Zealand agar; but all three batches of agar were toxic to some degree.

Suspensions of Escherichia coli and Staphylococcus aureus, untreated and treated by exposure to phenol, o‐cresol or p‐chloro‐m‐cresol, were counted on various types of media. While the counts from untreated suspensions were not affected by the nature of the medium, those from treated suspensions were influenced markedly. There was no correlation between the nutritional status of a medium and its suitability for the cultivation of the treated organisms. Although both bacterial species gave similar patterns of response and ranked the media in roughly the same order of suitability, E. coli was the more responsive species. Generally, the order of suitability was: meat extracts, yeast extracts, meat extract‐peptone broth, peptones (all the single ingredients 1 per cent, pH 7; media solidified with New Zealand agar). Although supplementation of the meat extract‐peptone control medium, especially with yeast extracts, led to higher counts from treated suspensions, dilution of the extract broth also gave similar results. Further, a fresh infusion broth was superior both to the extract broth and to a digest medium, for counting treated bacteria. The deficiencies of the extract broth were due partly to the phosphate precipitation procedure used in its preparation. The results indicate that when media suitable for the growth of damaged bacteria are required, they should be selected without recourse to preconceived ideas about composition, concentration or method of preparation.

No abstract

No abstract

SUMMARY: Counts of Escherichia coli were done on nutrient agar (control), on membrane filters on nutrient agar and on membrane filters on filter paper pads. With untreated bacteria counts were similar under all conditions, though membrane filters on nutrient agar tended to give slightly low counts. Phenol treated bacteria gave much lower counts when membrane filters were used: the mean counts for 3 strains of the test organism with filters on nutrient agar varied from 35–65% of the control, while counts with filters on filter paper pads were somewhat lower, varying from 30–47% of the control. The low counts on membrane filters on filter paper pads were not due to adsorption of phenol by the filters or to a low concentration of nutrients in the growth medium.