ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb04641.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:The addition to 32 samples of freshly produced milk from 16 farms of 0.25, 0.5 and 1.0 unit/ml. of penicillin tended to increase the methylene blue reduction time at 37—38°, and to improve the keeping quality at 22°, irrespective of season. In no case was the reduction time decreased or the keeping quality made worse. In general, the effects were almost as marked with 0.25 unit as with the higher concentrations. The increases in the reduction time ranged from 0 to over 3 hr. in winter and from 0 to 2.5 hr. in summer. The delay in reaching the end‐point of the keeping quality test ranged from 0 to 15 hr. in winter and from 0 to over 18 hr. in summer. The response to penicillin differed with the two tests in individual samples. In some cases the methylene blue reduction time was markedly increased but keeping quality was little affected: in others, the reverse was observed.In both winter and summer streptococci predominated in the control samples at the keeping quality end‐point, but with penicillin added Gram‐negative rods often gained the ascendancy. At the time of reduction of methylene blue the flora of the winter control samples consisted mainly of streptococci and micrococci, but in the presence of penicillin the proportion of Gram‐negative rods generally increased: in summer Gram‐negative rods predominated in the control samples and in the presence of penicillin.Practically all the Gram‐negative rods were resistant to penicillin. All the micrococci and most of the streptococci were sensitive to penicillin; the resistant streptococci were strains ofStr. faecalis. The variable distribution of resistant and sensitive organisms. coupled with the possible production of penicillinase, probably accounts for the variable effect of penicillin on the methylene blue and keeping quality tests in di

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01989.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:In order to design and apply microbiological standards for manufactured foods, it is necessary to obtain a reliable count of significant types of organism. Methods of counting, and the choice of types of organism to be counted, are discussed.

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01990.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:In collaboration with the National Physical Laboratory temperature distribution in an in‐bottle pasteurization plant was studied by means of thermocouples, and the coolest point in the coolest bottles located. A simple method is given for assessing the heat‐treatment in comparison with orthodox holder pasteurization. The results of bacteriological and phosphatase activity tests of in‐bottle pasteurized milk compared very favourably with those of the holder and H.T.S.T. processes. The safety margin is similar to that of the holder process and the efficiency of destruction of tubercle bacilli in milk has been calculated to be over 100%. The heating curve follows a straight line on inverted semi‐logarithmic paper, and linear relationships are shown to exist between the ‘slope’of this line, the maximum milk temperature reached in the coolest part of the coolest bottles and the heating equivalent. It is suggested that the process can be controlled by knowing this maximum

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01991.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:The addition of certain carbohydrates, notably glucose, lactose and sucrose, to penicillin gives rise to inhibition zones of increased size and, consequently, to apparently increased potencies, when assayed by the cylinder‐plate method. On the other hand, glucose in the assay medium leads to smaller zones. The accuracy of the assay is reduced in the former case, but not in the latter. Accuracy can be restored by using 0.2% glucose agar instead of nutrient agar in the assa

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01992.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:The methods suggested in the Report of the Coliform Sub‐Committee of the Society for Applied Bacteriology (Report, 1949) have been used in isolating and studying the coli‐aerogenes content of 142 samples of farm water supplies in two distinctive areas of Britain. The Gram‐negative cultures were grouped into typical, anaerogenic, non‐lactose‐fermenting and ‘unclassifiable’types, forming 54.2, 2.9, 10.9 and 32.0% of the 384 cultures respectively. Among the 261 coli‐aerogenes cultures,Bact. coli, intermediate and aerogenes‐cloacae organisms were found with frequencies of 32.2, 19.5 and 48.3% respectively. The majority of anaerogenic coli‐aerogenes organisms resembledBact. colitype II while the predominant non‐lactose‐fermenters resembledBact. cloacaeandBact. aerogenestype I. The reactions of 123 ‘unclassifiable'strains were such that very few could be regarded asBact. colitypes owing to the high incidence of gelatin liquefaction an

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01993.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:The effect of acidity on the growth ofCl. botulinumwas studied by following changes in the viable count of cultures in acid buffered broths containing bread crumbs, after inoculation with about 104vegetative cells or spores/ml. In 9 out of 10 experiments growth did not occur below pH 5.0; in the tenth it took place at pH 4.8. There was no significant difference between vegetative cells and spores.

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01994.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01995.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:Seventy‐three comparative tests of dairy plant were made using swabs of ribbon gauze and calcium alginate wool, the latter being dissolved before plating in dilute sodium hexametaphosphate solution. The colony counts obtained with alginate swabs were in the great majority of cases much higher than those with gauze. When both types of swab were inoculated with known numbers ofBact. coli, the recovery was again much greater with alginate woo

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01996.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Summary:Forty strains ofA. chroococcumfrom Danish soils showed a rather uniform power of nitrogen fixation in mannitol solution where the mean gain of nitrogen after 12 days corresponded to 17.1 mg./g. of mannitol, with a standard deviation of ±9.1%. In agreement with the statement of Fischer (1949) the strains could be divided into two groups with different rates of nitrogen fixation. Ten strains fixed in 3 days less than 30% and 30 strains from 45 to 100% of the final amount of nitrogen after 12 days, which was almost the same in both groups. In glucose medium a rapid nitrogen fixation was shown by some of the strains that grew slowly with mannitol. Strains which fixed rapidly with mannitol did so with glucose also.Ten strains ofA. beijerinckiigrew slowly with glucose as well as mannitol, and two strains apparently failed to utilize the latter compound.In media sterilized by autoclaving, the gain of nitrogen was approximately one‐third higher with mannitol than with glucose, owing to deterioration of the glucose on heating. When glucose and mannitol were sterilized by filtration, the difference in nitrogen fixation corresponded closely to the difference in heat of combustion of the two compounds.Some strains of bothA. chroococcumandA. beijerinkiicould grow on nitrogen‐free agar containing sodium benzoate as the sole source of carbon, while others could

ISSN:0370-1778    

DOI:10.1111/j.1365-2672.1951.tb01997.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY