KINETICS OF MATING OF FP+ AND FP- STRAINS OF PSEUDOMONAS AERUGINOSA

Loutit, J. S. (University of Otago, Dunedin, N.Z.), and L. E. Pearce. Kinetics of mating of FP(+) and FP(-) strains of Pseudomonas aeruginosa. J. Bacteriol. 90:425-430. 1965.-Recently, we reported the variability of the FP(+) x FP(-) mating in Pseudomonas aeruginosa, and the increase in efficiency when the cells were mated after dilution. The present work shows that when standardized cells were mated after a dilution of 10(-2) for FP(-) and 2 x 10(-3) for FP(+), there was less variability in the system. Investigation of pairing between FP(+) and FP(-) cells, as measured by genetic transfer, revealed that none took place during 24 hr in liquid media in which growth of both parents was possible. Transfer in liquid minimal medium was not investigated, because the single marker in the male was insufficient to control back mutation in 24 hr. No transfer occurred on solid media which allowed full growth of both FP(+) and FP(-) cells. Transfer took place very slowly on minimal agar, requiring 19 to 20 hr. It is thought that this represents growth of microcolonies with eventual transfer when internal nutrients were exhausted.

STREPTOMYCIN AS AN ANTIVIRAL AGENT: MODE OF ACTION

In host bacteria resistant to the antibiotic, streptomycin inhibits phage replication by inhibiting the process of injection. This effect is competitively reversed by certain divalent cations, polyamines, and streptidine. It is proposed that streptomycin inhibits injection by attaching to the phage DNA while it is still folded within the phage head, and in this way it prevents the unfolding which is essential for the injection process. The reversal agents probably function by displacing the antibiotic from the phage, but they also promote injection themselves.

GASEOUS ENVIRONMENT AND GROWTH OF MICROAEROPHILIC VIBRIOS

Fletcher, R. D. (University of Connecticut, Storrs), and W. N. Plastridge. Gaseous environment and growth of microaerophilic vibrios. J. Bacteriol. 87:352-355. 1964.-Strains of microaerophilic vibrios from cattle, chickens, man, and sheep were placed in four groups on the basis of catalase and H(2)S production and glycine tolerance. By these tests group I was + - -, group II was + - +, group III was + + +, and group IV was - + +. On yeast extract-agar, the optimal oxygen level was 2.5% for group I, and 5.0% for the other three groups; the optimal carbon dioxide level was 10% for all four groups; the group I strains from man and sheep and the group II strains differed from the group I strains from cattle, by tolerating higher levels of both oxygen and carbon dioxide. On a chemically defined medium, the optimal oxygen level was 1.0%, and the optimal carbon dioxide level was 10% for groups I and II; the group II strains were more sensitive to high levels of carbon dioxide than were group I strains from cattle.

CHEMICALLY DEFINED MEDIUM FOR SOME MICROAEROPHILIC VIBRIOS

Fletcher, R. D. (University of Connecticut, Storrs) and W. N. Plastridge. Chemically defined medium for some microaerophilic vibrios. J. Bacteriol. 85:992-995. 1963.-The medium described supported growth of 22 of 26 catalase-positive, H(2)S-negative vibrios (Vibrio fetus). The strains used were isolated from cattle, chickens, man, sheep, and swine; 10 failed to grow in thiol medium plus 1% glycine (group I), and 16 were glycine-tolerant (group II). Growth on the defined medium was compared with growth on yeast extract agar, blood agar, and thiol agar. Four of the group I strains failed to grow on the defined medium, and growth of seven of the group II strains equaled or exceeded growth obtained on the compared media. Use of synthetic media for determining growth requirements and for possible classification of vibrios is discussed.

A NEW SELECTIVE BLOOD AGAR MEDIUM FOR STREPTOCOCCUS PYOGENES AND OTHER HAEMOLYTIC STREPTOCOCCI

Horse blood agar containing polymyxin B sulphate, neomycin sulphate, and fusidic acid inhibited the growth of Staph. aureus, Ps. pyocyanea, Proteus mirabilis, E. coli, and Klebsiella pneumoniae but allowed good growth of, and haemolysis by, Str. pyogenes. In a comparison with blood agar, blood 4% agar, and gentian violet blood agar, the selective medium (P.N.F.) yielded a significantly higher proportion of streptococci than the other media, both by aerobic and by anaerobic culture, from burn swab extracts deliberately contaminated with Str. pyogenes; P.N.F. culture was more effective with dilute than with heavy inocula of Str. pyogenes, allowing from three to seven times as many recoveries of Str. pyogenes from swabs contaminated with 10(-3) dilution of streptococcal cultures than cultures of the same material on the other media. Haemolytic streptococci of groups A, C, D, G, and others were isolated by aerobic culture from burns in a consecutive series of 1,277 swabs more often on P.N.F. medium than on blood 4% agar. Viable counts of 12 strains (including 11 different serological types) of Str. pyogenes showed some reduction in the numbers of colonies compared with counts on blood agar, and some strains grew more slowly on P.N.F. medium. These limitations, however, were offset and outweighed by the higher final yield of streptococci on the selective medium.

INFLUENCE OF GROWTH MEDIUM ON ASSIMILATORY ACTIVITIES OF ESCHERICHIA COLI

Clifton, C. E. (Stanford University, Stanford, Calif.). Influence of growth medium on assimilatory activities of Escherichia coli. J. Bacteriol. 85:1371-1377. 1963.-Nutrient agargrown cells assimilate about 50% of the glucose added to washed suspensions (phosphate buffer, pH 7.2, 30 C), as indicated by O(2) consumption or C(14)-uptake from uniformly labeled glucose. Most of the nonassimilated glucose is oxidized, but a small portion remains in forms other than glucose in the suspension medium. Cells from glucose agar, however, assimilate only about 20 to 30% of the U-glucose and ferment a considerable portion of the remainder, the extent of each being determined in part at least by growth conditions. Evidence is presented that this behavior is the result of metabolic controls induced during growth. C(14) from U-glucose appeared in all fractions of either agar- or glucose agar-grown cells, the highest percentage being present in cellular matter insoluble in hot 5% trichloroacetic acid. Data on the distribution of C(14) from 1-, 2-, and 6-glucose, and from acetate and pyruvate, are also presented.

COMPARATIVE EVALUATION OF FIVE SELECTIVE AND DIFFERENTIAL MEDIA FOR THE DETECTION AND ENUMERATION OF COAGULASE-POSITIVE STAPHYLOCOCCI IN FOODS

Five selective media for the detection and enumeration of coagulase-positive staphylococci were evaluated for their efficiency in the recovery of 17 strains of coagulase-positive staphylococci from foods. They were Staphylococcus Medium 110 (SM-110), tellurite-glycine-agar (TGA), egg-tellurite-glycine-pyruvate-agar (ETGPA), tellurite-egg-agar (TEA), and tellurite-polymyxin-egg yolk-agar (TPEY). Statistical analysis by the rank correlation method of the efficiency with which these media recovered staphylococci from pure 24-hr Brain Heart Infusion cultures revealed the following efficiencies in descending order: (i) TPEY, (ii) ETGPA, (iii) TGA, (iv) TEA, (v) SM-110. Growth of 17 strains of coagulase-negative cocci on these media showed the following approximate descending order of inhibition to these organisms: (i) ETGPA, (ii) TEA, (iii) SM-110, (iv) TGA, (v) TPEY. The appearance of colonies of the various coagulase-negative strains on each medium was studied for the degree to which they could be confused with colonies of coagulase-positive strains. Nineteen food contaminants, including Proteus vulgaris, Bacillus sp., Escherichia coli, Erwinia sp., fecal streptococci, and others, were also studied for similarities in appearance to staphylococci and for ability to grow on the selective media. The influence of five sterile food homogenates (frozen chicken and tuna pies, custard, smoked ham, and raw whole egg) on recovery of 1,500 enterotoxigenic staphylococci (three strains) per milliliter was determined by statistical analysis. Three main effects (culture, media, and food) and three interactions (media with food, food with cultures, and media with culture) were found to be significant. Recovery on TPEY was influenced less by food than the other selective media and showed optimal recovery ability from sterile custard, eggs, and ham. TGA recovered well from sterile chicken pie and custard, SM-110 from sterile custard, and TEA from sterile ham. None of the media was outstanding in recovering staphylococci from tuna pie. The ability of the five selective media to recover 1,500 enterotoxigenic staphylococci (three strains) per ml from three sterile foods in the presence of 10 strains of contaminating bacteria added at the 0, 10(5), and 10(6) levels per milliliter was also studied and analyzed statistically. Only three factors were significant under these conditions-cultures, foods, and the interaction of media with the level of added contamination. Efficiency of recovery of TGA, SM-110, and ETGPA was found not to be dependent upon the level of contamination. Recovery on TPEY decreased with increases in the number of contaminants. TEA increased in efficiency at the 10(5) level, but decreased at the 10(6) level. When recovery on Trypticase Soy Agar was considered to be 100%, the average percentage of recovery by each of the selective media under all experimental conditions was determined.

MEDIUM FOR DIFFERENTIATING THE GRAM-NEGATIVE, NONFERMENTING BACILLI OF MEDICAL INTEREST

Sellers, Walter (U.S. Air Force School of Aerospace Medicine, Brooks Air Force Base, Tex.). Medium for differentiating the gram-negative, nonfermenting bacilli of medical interest. J. Bacteriol. 87:46-48. 1964.-An agar-slant medium is described for differentiating gram-negative, nonfermenting bacilli of medical interest. Differences in the ability of bacilli to grow anaerobically in the presence of nitrate, to produce pH changes, to produce N(2) from nitrite and nitrate (singly and in combination), to fluoresce, and to oxidize a drop of glucose solution to acid in the presence of high peptone concentrations were used in the development of the medium. Organisms differentiated by the medium include Pseudomonas aeruginosa, Bacterium anitratum, Mima polymorpha, and Vibrio alcaligenes or Alcaligenes faecalis.

EFFECT OF PHENOL ON BACILLUS SUBTILIS SPORES AT ELEVATED TEMPERATURES

The nature of the recovery medium is shown to influence the number of Bacillus subtilis spores which, after exposure to 2.5 or 5% phenol at high temperatures, can produce a visible colony. Higher survivor counts were obtained in nutrient agar containing L-alanine and D-glucose than in plain nutrient agar.

EFFECT OF PH ON HUMAN MYCOPLASMA STRAINS

Shepard, Maurice C. (U.S. Naval Medical Field Research Laboratory, Camp Lejeune, N.C.), and Carl D. Lunceford. Effect of pH on human Mycoplasma strains. J. Bacteriol. 89:265-270. 1965.-The optimal reaction of culture media for the cultivation of T-strain Mycoplasma of human origin was investigated. By use of a recently modified tryptic digest medium, the optimal reaction in either agar or fluid medium was found to be pH 6.0. In contrast, human classic (large-colony) Mycoplasma could be cultivated in agar or fluid medium over a rather broad pH range, and the influence of the reaction of the medium appeared to be primarily species-dependent. M. salivarium, for example, grew best in agar from pH 5.5 through 6.5. M. pneumoniae (Easton's agent) yielded largest colony numbers in agar and highest titers in broth at pH 8.0. In the case of T-strain Mycoplasma, both maximal colony numbers in agar and highest titers in fluid media were achieved at a reaction of pH 6.0. In addition, largest colony size of T-strain Mycoplasma was also achieved in agar at pH 6.0, and averaged 50 to 100% larger than that obtained by cultivation at pH 8.0 with the same medium. Although T-strains will develop in agar media over a pH range of from 5.0 through 10.0, the extremely small colony size and poor staining properties resulting from growth in an alkaline medium make their recognition in agar cultures difficult. Aerobic cultivation of T-strains was first achieved in agar adjusted to pH 5.5 to 6.0. In fluid medium, multiplication of T-strains occurred only within the limits of pH 5.0 through 8.0, with highest titers being reached at pH 6.0. Greater attention to the reaction of complete Mycoplasma media is stressed.

SEX-ASSOCIATED DIFFERENCES IN SERUM PROTEINS OF MICE

Agar electrophoresis of serum from mice of C57BL/10-H-2(d), B10.Sn, A.SW, A.CA, R III, and P1 inbred strains shows that the females have a lower concentration of alpha-1 serum globulin than the males and, in some strains, the females also have a lower concentration of alpha-2 and, beta-serum globulin. Females of the A.SW strain have a higher serum albumin concentration than males, and females of the C57BL/10-H-2(d) strain have a higher gamma-globulin concentration than males. Two-dimensional (agar and hydrolyzed-starch) electrophoresis gives a typical sex-associated pattern for alpha-1 and alpha-2 globulins which clearly permits recognition of male and female serums.

INVESTIGATION OF A QUANTITATIVE ANOMALY ENCOUNTERED IN THE ASSAY OF FIBRINOGEN BY IMMUNO-DIFFUSION

When diluted platelet-poor normal plasma is allowed to react with a specific antifibrinogen antiserum by double diffusion in agar the fibrinogen content of the plasma, as estimated immunologically, is less than would be expected from chemical estimation.

This discrepancy is even more marked in plasma exposed to procedures bringing about increased coagulability: such as storage of platelet-rich plasma, glass contact or pre-treatment of the blood with traces of thrombin insufficient to cause coagulation. On the other hand, full development of immune precipitation occurs with purified fibrinogen and is often almost complete in plasmas with severe coagulation defects. Full development of immune precipitation is restored when chelating agents such as sodium citrate or sequestrene are added to both the agar medium and the diluting fluid in re-testing plasmas initially showing the anomaly in saline—agar.

Investigation of this phenomenon suggests that it is not mediated by any one of the plasma factors concerned in thromboplastin generation, but that the anomaly is closely concerned with thrombin evolution. Evidence is presented that the quantitatively anomalous immune behaviour of plasma fibrinogen in saline—agar may be due to fibrin deposition in the agar consequent upon lowered citrate concentration in the plasma and the formation of traces of thrombin during diffusion.

Antifibrinogen—antibody interaction with the products of plasmin lysis of fibrinogen also shows a quantitative anomaly in saline—agar, but this is only demonstrable early in the digestion process. In conformity with other workers it is suggested that the early digestion products (fibrino-peptides) formed as a result of the proteolytic action of thrombin compete with the digestion products of plasmin for interaction with antibody.

The practical implications of this anomaly are discussed in relation to (i) immunological estimation of the fibrinogen content of plasma and (ii) the development of a screening test for plasma coagulation defects.