- Volume 5, Issue 5, 1951

Summary: The familiar resazurin test used in milk testing has been adapted to the estimation of nisin, using a fast-growing strain of Streptococcus cremoris as test organism. The reproducibility and accuracy of this test compares favourably with the many other assay methods for nisin which use Strep. agalactiae as test organism. Results may be obtained in less than an hour as compared with 15–48 hr. in the other tests and are a measure of bactericidal power only. Aseptic technique during the actual assay procedure is unnecessary. Methods were devised to ensure a suitable standard inoculum, which is imperative for this test. As little as 0·5 unit nisin ml, may be estimated.

Summary: The bacteria of the upper reaches of a chalk stream (Hobson’s Brook) were studied as part of an inquiry into their association with ciliate protozoa. The bacteria studied were primarily those found in the current core at 2-month intervals as revealed by plating at 22°. The waters of the stream flow from chalk springs through arable land and are swift, cold, alkaline and usually rich in dissolved oxygen. These physical characters generally restricted the microfiora to psychrophilic aerobes; but once, when turbulence was lost by damming of the water by a growth of Nasturtium officinale, micro-aerophilic and anaerobic bacteria tended to predominate. Near plants, especially blue-green algae, bacterial numbers were always much higher than in the current core.

The natural indigenous water flora was supplanted, after floods, continued heavy rain, or periods of drought, by a foreign microflora apparently coming from the adjacent soil. The latter flora was apparently modified by agricultural operations on the surrounding arable land and was partly recruited from the rhizospheres of cereal crops thereon.

A tributary stream contaminated by farmyard and domestic waste opens into the Brook but true Escherichia coli were only isolated from its mouth. It is suggested that the topography and turbulence of the Brook combine with protozoan activity to remove polluting bacteria rapidly.

Two strains of Gram-positive micrococci isolated from the Brook induced fission in ciliate protozoa. An unusual type of nitrogen-fixing bacterium was isolated on several occasions.

Summary: Sulphanilamide inhibition of the growth of certain yeasts and yeastlike organisms was overcome in a non-competitive manner by methionine, adenine and histidine, which are therefore regarded as end-products of enzyme systems for which p-aminobenzoic acid is essential. The methionine system was the most sensitive to sulphanilamide, followed in order by those of adenine and histidine.

In the presence of methionine, adenine and histidine together, the test organisms were still sensitive to sulphanilamide, implying that p-aminobenzoic acid is concerned in still another system, or systems. The nature of these systems is obscure, but the inhibition is not overcome by purines, pyrimidines or pteroylglutamic acid, nor by single amino-acids, except in one case when dl-cysteine showed some effect. In another case, a low concentration of choline chloride was effective.

Summary: Two strains of Ruminococcus flavefaciens, an important cellulose-decomposing bacterium, were isolated, one from the rumen of a sheep, the other from the rumen of a cow. Pure cultures were obtained by using the dilution method in agar media containing a strip of filter-paper. These strictly anaerobic, Gram-positive streptococci attack cellulose and cellobiose, but not starch, maltose, lactose or xylose. Only one strain could use glucose. Colonies on cellulose media were characterized by the formation of a yellow pigment; in cellobiose media the colonies were white. Growth on cellulose was favoured by addition of Clostridium sporogencs or a certain amount of sterilized medium in which Cl. sporogenes had previously grown.

Estimations of the end-products of fermentation of cellulose and cellobiose showed that at least 25% of the carbon could be recovered as succinic acid, c. 23% as acetic acid and c. 10% as formic acid; ethanol was absent and gas formation very limited. A description of the genus and the species is given.

Summary: A strain of Bacterium coli capable of growth in broth and in an ammonium + glucose + salts medium at 37° and in broth at 44°, died in the defined medium at 44°. The addition of glutamic acid to this medium allowed the growth temperature to be raised slightly; the further addition of nicotinamide allowed a further increase in growth temperature.

Summary: A yeast hybrid heterozygous for many alleles produces an occasional ascus in which instead of the expected 2 dominant:2 recessive segregations one finds 4 dominant:0 recessive ratios for most of the characters. The single ascospore cultures are often incapable of copulating with either mating type. Genetical analysis has revealed that such asci contain ascospores which are diploid and heterozygous for the mating type alleles and other characters. The single ascospore cultures, heterozygous for mating type, may sporulate and by characterization of their progeny the genotype of the ascospore can be determined. Other diploid cultures originating from single ascospores are homozygous for mating type. Cells from these cultures (unlike the diploid cells heterozygous for mating type) are capable of mating, and when mated with similar cells of complementary mating type produced tetraploid yeasts. Triploids were produced by mating diploids with haploids. The tetraploid segregates to produce the expected tetrad types and gametic ratios. Some sporulating cultures produced unexpected types of asci for characters controlling sugar fermentation but interpretation of their significance is not feasible since our customary control of breeding procedure does not apply in the analysis of diploid cultures which sporulate on ordinary agar slants.

Summary: Twenty strains of aerobic, facultatively anaerobic, chitinoclastic bacteria have been isolated from marine mud by enrichment cultures. Each was able to derive its full carbon and nitrogen requirements from chitin. None was an obligate chitinovor.

These cultures comprised four new species of Acnromobacter, two new species of Pseudomonas, one new species of Flavobacterium and one new species of Micrococcus. Detailed descriptions for each species are appended.

Each organism was able to liberate ammonia and reducing sugar from the chitin molecule. Glucosamine and acetic acid were not detected in the cultures, possibly because of their ready availability as supplementary nutrients.

SUMMARY: The titre of streptococcal polysaccharidase was increased by incubation with β-alanine, serine, tyrosine, cystine, cysteine or methionine. Dextrinogenic amylase and hyaluronidase measured by a turbidity end-point were both activated by cysteine, cystine, serine or methionine. Polysaccharidase activity also increased after incubation with hyaluronic acid, starch, pectin or dextran. Pantothenic acid suppressed activity of SH-activated enzymes, and the rise of titre observed during incubation with substrate was decreased twofold or fourfold by addition of valine. The activation of streptococcal proteinase by cysteine was also prevented or retarded by pantothenic acid or valine. Pantothenyl alcohol was more active than either pantothenate (dl-calcium salt)ordl-valine.

Summary: By the use of six phages, 294 (94%) of 306 strains of Salmonella dublin were classified into eleven types. The remaining twelve strains were insusceptible to all phages. Unfortunately, for the purposes of distinguishing strains of epidemiological interest, 66·9% of the strains belonged to the same type. Acquired phage resistance was responsible for many of the strains being regarded as different phage types.

The phages were also active on S. rostock, S. gallinarum and on a small proportion of S. pullorum strains tested. They were not active on S. enteritidis. Three phages possessed a different range of lytic activity despite the fact that Bail's cross-resistance tests suggested that they were identical.

The ability to type a species of Salmonella satisfactorily by means of anti-O phages appears to depend mainly on a large proportion of the strains having acquired resistance to different phages.

Summary: The zygospores of several species of Chlamydomonas present in dry soil are very resistant to dehydrating agents. Based on this resistance a method for the isolation of sexual strains has been developed, and two homothallic and three heterothallic species of Chlamydomonas have been obtained in pure culture.

Summary: All of 43 strains of Protcus vulgaris. 75 strains of P. mirabilis and 10 strains of P. morganii when grown in an acid-hydrolysed casein or nutrient broth medium produced isobutylamine and two other amines tentatively identified as isoamylamine and β-methylbutylamine. These amines were not produced by any of 239 strains representative of other species in the family Enterobacteriaceae grown under the same conditions. This character is sufficiently constant to be included in the generic description. Ten strains of P. rettgeri did not produce these amines, and for this and other reasons it is proposed that this species be excluded from the genus Proteus.

Summary: The species Pseudomonas aeruginosa is defined more precisely, and a method is presented whereby apyocyanogenic strains of this species can be correctly identified. This method depends upon the correlated characteristics: (1) ability to grow at 41° ± 1; (2) ability to oxidize potassium gluconate, in shaken culture, to a reducing compound presumed to be potassium 2-ketogluconate; (3) production of slime in static culture in a medium containing potassium gluconate as the principal carbon source.

All strains of P. aeruginosa tested, regardless of their pigment-forming capacity or their stage of growth, could be converted to a type of growth characterized by profuse sliminess in liquid potassium gluconate medium.

Detection of pyocyanogenic capacity is shown to be equally reliable in Gessard’s glycerol peptone agar and in Burton’s defined medium when negative results in one or the other medium are rechecked in both, and when the observation period in Burton’s medium is lengthened.

Summary: Washed suspensions of a laboratory strain of Haemophilus pertussis did not take up oxygen with, or ferment, five carbohydrates, nor did the same strain produce detectable acid from fourteen carbohydrates during growth. Of twenty-one amino-acids tested only proline, serine, alanine, aspartic and glutamic acids were oxidized by washed suspensions at an approciable rate. The first four of these were oxidized to completion but with glutamic acid only 80% of the theoretical uptake of oxygen occurred; however, in the presence of dinitrophenol it, too, was oxidized to completion. Cells oxidizing glutamic acid in the presence of arsenite produced α-ketoglutaric acid.

During the logarithmic growth of H. pertussis glutamic acid disappeared from Cohen & Wheeler’s medium. The organism grew in a Cohen & Wheeler’s medium in which the Casamino acids had been replaced by glutamic acid. These results suggest that glutamic acid can serve as energy, carbon and nitrogen source for H. pertussis

Some of the findings were confirmed with freshly isolated strains.

Summary: The ribonucleic acid fraction of Micrococcus pyogenes var. aureus (strain Duncan), separated by the method of Schmidt & Thannhauser (1945), contains organic phosphate in excess of that which can be accounted for by a polynucleotide nucleic acid structure. This ‘excess phosphate’ can be separated from the other phospho-compounds after fractional extraction of M. pyogenes in dilute acid or in dilute alkali. Four polyolphosphate compounds occur in the extracts. The main components are α-and β-glycerophosphate, the two other polyolphosphates (giving water-insoluble barium salts; separable chromatographically) occurring in smaller amount. The yields of glycerophosphate show that at least 75% of the excess phosphate is present in an easily hydrolysed glyccrophospho-compound which may also be the origin of the unidentified polyolphosphates. The glycerophospho-compound of M. pyogenes accounts for more than one-quarter of the total organic phosphate of the organism. The presence of ‘excess phosphate’ in a number of Gram-positive organisms suggests that a glycerophospho-compound similar to that of M. pyogenes may be of general occurrence in Gram-positive bacteria and in yeasts.

Summary: The glycerophospho-compound which has been shown to account for more than one-quarter of the total organic phosphate of Micrococcus pyogenes is present almost exclusively in the particulate fractions of mechanically disintegrated cell suspensions.

The main particulate fraction corresponds to the cell envelope material of Dawson (1949). Three-quarters of the weight of this material is made up of a glycerophospho-protein complex of which the protein moiety resembles silk fibrom in amino-acid composition and in its general properties. The amount of hydroxylamino-acid in the protein of the envelope would be sufficient to bind the polyolphosphoric acids covalently, but the possibility that the polyolphosphoric acids form a polymer which is adsorbed on to a protein matrix is not excluded.

A subsidiary particulate fraction, made up of very small particles containing a high proportion of phospholipid, was found to be otherwise similar in composition to the envelope fraction. It is suggested that in the intact cell, the material of the small particle fraction may form a continuous layer (lipid membrane?) lying beneath the glycerophospho-protein complex envelope (cell wall?).

Summary: A strain of Bacillus megathcrium has been isolated which requires glucose specifically for optimal spore germination. Cyanide, fluoride, iodoacetate, citrate, oxalate, azide, and 2:4-dinitrophenol were ineffective as inhibitors of germination in glucose, while 8-hydroxyquinoline inhibited completely at 10 mm. The inhibitory effect of glucose on sporulation of the organism in liquid and solid media is described.

Summary: Antisera, prepared against smooth variants of the Flexner, Boyd and Sonne types of Shigella, were investigated for their agglutinin and precipitin content. The precipitation reactions, employing formamide extracts of the organisms, showed a marked degree of specificity which was lacking in the agglutianation reactions except with the Boyd and Sonne types. Cross-precipitation reactions occurred with Boyd’s Flexner IV (103) and Flexner Y and also with Boyd’s Flexner V(P110) and Flexner X. Absorption tests, however, revealed each of these four organisms to have a predominant specific precipitinogen.

The biochemical and fermentation reactions of 432 strains of aerobic, catalase-positive. Gram-positive cocci were examined in an attempt to produce an orderly classification of the group. The subdivision into Staphylococcus, Micrococcus, Gaffkya and Sarcina could not be justified, and, as Micrococcus is regarded as an invalid generic name, all acrobic species are placed in the genus Staphylococcus with the type species Staph. aureus Rosenbach.

The primary subdivision was made on the coagulase reaction, with secondary subdivisions of the coagulase-negative strains based on the production of acid and acetoin from glucose. The characterization of the subdivisions is presented in a quantitative way.

SUMMARY: Ageing, chilling, and media containing suitable concentrations of glycine were found to stimulate the production of L-forms in cultures of Haemophilus pertussis. Stained with Giemsa these L-forms are morphologically similar to the L-forms of many other bacilli produced by similar stimuli. Serologically the L-and bacillary forms appearto be related. The suggestion is put forward that the small round red form is a ‘resistant’ form of H. pertussis and reverts to the rod by passing through the stages characteristic of the L-cycle.