FIBRINOGEN MEDIA FOR STUDIES ON STAPHYLOCOCCI

LIMITATIONS OF FIBRINOGEN-POLYMYXIN MEDIUM IN DETECTING COAGULASE-POSITIVE STAPHYLOCOCCI IN RAW MILK

A fibrinogen-polymyxin medium and Staphylococcus Medium 110 were used in the isolation of coagulase-positive staphylococci in raw milk. Results indicated that both media allow the growth of some rods and of many coagulase-negative cocci. A significantly greater number of coagulase-positive staphylococci were identified by the tube test than were revealed by halo formation on fibrinogen-polymyxin medium.

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.

The identification of staphylococci in clinical and food microbiology laboratories

A comprehensive review of the methods which have been utilized for the identification of staphylococci is presented. Biochemical characteristics which have assisted in the primary isolation of staphylococci, such as pigmentation, hemolytic activity, the egg yolk phenomenon, and deoxyribonuclease and coagulase production, are also analyzed. The potential applicability of advanced techniques to identify staphylococci, such as the detection of enterotoxin production, base ratio analysis, cell wall analysis, phage typing, and serology, is discussed. The following procedures are recommended for routine use: Idnetification of Staphylococcus sp. (clinical laboratories): microscopic observation, catalase activity, coagulase production, lysostaphin sensitivity, and (optional) facultative growth in thioglycolate medium. Identification of Staphylococcus aureus (food laboratories): microscopic observation, catalase activity, coagulase production, thermonuclease production, and (optional) lysostaphin sensitivity.

Hemolytic behavior of staphylococci isolated from cows' milk

Patterns of hemolysis produced by staphylococci isolated from milk were investigated on media prepared with bovine, sheep, horse, and rabbit erythrocytes under a variety of cultural circumstances. Hemolytic patterns were sharper and easier to interpret on erythrocyte agar plates when incubated at 37 degrees C in an atmosphere containing 30% CO(2.) Alpha-hemolysin production was greatly enhanced in this environment and was not detected at times when cultures were grown in air only. This was also true of deltahemolysin but to a lesser extent. Very satisfactory identification of alpha, beta- and delta-hemolysins was obtained by streaking BEA plates with the unknown strains perpendicularly to a strain producing beta-hemolysin and incubating in 30% CO(2.) This procedure avoided use of erythrocytes of different species of origin and use of staphylococcal alpha-antitoxin. Prior action of the beta-hemolysin on bovine cells was found to completely inhibit hemolysis from alpha-hemolysin but the reverse was not true. A strain inhibiting beta-hemolysis in air failed to exhibit its antihemolytic properties for 24 hours when incubated in 30% CO(2.) Patterns of hemolysis within areas subject to multiple hemolysins were found to reflect the nature and relative strength of contributing hemolysins or antihemolysins and could be modified by the time sequence of exposure to certain hemolysins or antihemolysins.

SOME CULTURAL CHARACTERISTICS OF STAPHYLOCOCCI ISOLATED FROM MILK

Observations were made on the value of certain selective media for isolation and identification of staphylococci from milk obtained from individual quarters and farm bulk tanks Aerobic fermentation of mannitol salt was unreliable for identification of coagulase positive strains. Coagulase positive strains tended to clump when grown in tryptose serum broth. Tellurite glycine agar plates were not entirely reliable for the selection of coagulase positive strains. Fibrinogen-tellurite-glycine plates were very useful for the isolation of staphylococci from milk in the presence of other microorganisms and for the simultaneous identification of coagulase positive strains. Plate coagulase tests utilizing fibrinogen tellurite glycine agar corresponded almost perfectly with conventional tube tests. Fibrinolytic strains were not uncommon and were found also among beta hemolysin producing coagulase positive strains.

COMPARISON OF SEVERAL SELECTIVE MEDIA FOR ISOLATION AND DIFFERENTIATION OF COAGULASE-POSITIVE STRAINS OF STAPHYLOCOCCUS AUREUS

Six coagulase-positive strains of Staphylococcus aureus which had been cultivated in Brain Heart Infusion broth, milk, and brine were plated on seven isolation media. A significant difference in the growth patterns of the individual strains was found as well as a significant effect resulting from the previous cultivation history before plating. Brine and, to a lesser extent, milk were found to reduce maximal cell concentrations attained, but strains grown in brine and milk showed greater ability to withstand the selective action of the isolation media. Fibrinogen applied to the surface of five of the media allowed the formation of characteristic halos by coagulase-positive strains of S. aureus. Only half of the strains studied produced a zone of precipitation on SM110-Egg Yolk agar. The isolation medium containing cycloheximide and a high level of polymxin B was most inhibitory to the organisms.

COAGULASE-NEGATIVE MUTANTS OF STAPHYLOCOCCUS AUREUS: GENETIC STUDIES

Korman, Ruth Z. (Cornell University, Ithaca, N.Y.). Coagulase-negative mutants of Staphylococcus aureus: genetic studies. J. Bacteriol. 86:363-369. 1963.-The behavior in mutation and transduction of pleiotropic coagulase-negative mutants of Staphylococcus aureus PS 53 (NCTC 8511) was analyzed. Coagulase-positive colonies were recovered, as well as a novel phenotype resistant to some cell-wall inhibitors and differing in sugar fermentation pattern. The hypothesis that the coagulase-negative strains differ from the original propagating strain in the structure or organization of the cell wall is discussed.

GENETIC TRANSDUCTION WITH STAPHYLOPHAGE

Korman, Ruth Z. (Elmira College, Elmira, N.Y.) and David T. Berman . Genetic transduction with staphylophage. J. Bacteriol. 84: 228–236. 1962.—Transduction by crude lysates obtained by ultraviolet-light induction of phage 53 lysogenic derivatives of Staphylococcus aureus NCTC 8511 has been confirmed. A defined medium and sugar-differential medium were developed, permitting demonstration of transmission of sugar-fermentation loci. The range of transmissible markers has been extended to include free-coagulase production as well as antibiotic-resistance markers. A rare class of heterogeneous streptomycin-resistant transformed clones was obtained. These were assumed to be heterogenotic.