Showing papers on "Agar plate published in 1971"
TL;DR: Advantages of mesophyll protoplasts as the source of clones as well as implication of the plating technique for genetical studies are discussed.
Abstract: A technique was developed to derive cell and plant clones from isolated mesophyll protoplasts of tobacco. The protoplasts, plated on a fully defined agar medium, divided and grew actively forming visible colonies after one month of culture. Efficiency of colony formation depended on cell density and light condition during incubation. Under standard conditions, 60% of plated protoplasts formed colonies. Upon transfer onto suitable media, these colonies differentiated shoots and roots, and eventually regenerated whole plants. Advantages of mesophyll protoplasts as the source of clones as well as implication of the plating technique for genetical studies are discussed.
468 citations
TL;DR: An improved solid agar medium (MP medium) has been developed which allows detection of pectolytic activity in bacteria and has successfully been used to detect pECTolytic organisms in soil, forest litter, and rotting vegetable samples.
Abstract: An improved solid agar medium (MP medium) has been developed which allows detection of pectolytic activity in bacteria. Organisms tested exhibited a variety of regulatory controls governing pectate lyase synthesis. The medium contains mineral salts, pectin, and yeast extract. After growth of the organisms, the agar plate is flooded with a polysaccharide precipitant, and pectolytic activity is shown by clear zones around active colonies. High concentrations of phosphate are shown to be necessary for pectic enzyme formation on solid media. The medium has successfully been used to detect pectolytic organisms in soil, forest litter, and rotting vegetable samples.
175 citations
TL;DR: The demonstration of several different species of bacteria in normal individuals possessing cross-reacting antigens may provide an explanation for the development of the "natural" immunity to H. influenzœ type b observed in most adults.
122 citations
TL;DR: This article corrects the article on p. 501 in vol.
Abstract: A selective and differential medium, Shahidi-Ferguson Perfringens agar (SFP agar), and a confirmatory medium, lactose-motility agar (LM agar), were developed for the enumeration and identification of Clostridium perfringens in foods These media provide a rapid, specific, and direct diagnosis of C perfringens SFP agar contains sodium metabisulfite and ferric ammonium citrate to demonstrate H(2)S production and egg yolk to demonstrate lecithinase production by C perfringens On SFP agar, C perfringens produces black colonies, 2 to 3 mm in diameter, surrounded by zones of opaque precipitate The typical colonies are confirmed on LM agar Enumeration and identification are completed within 48 hr All of the ingredients of SFP agar are stable to heat and storage conditions SFP agar also contains two antibiotics, kanamycin and polymyxin B, which are inhibitory to many bacteria commonly occurring in foods A comparative study of SFP agar and noninhibitory media showed that SFP agar did not inhibit any of the 16 strains of C perfringens tested Recovery of C perfringens added to foods averaged 906% for SFP agar as compared with 698% for sulfite polymyxin-sulfadiazine (SPS) agar (BBL) and 602% for SPS agar (Difco) The colonies on the SFP agar, were much larger and were consistently black Of 464 food samples tested, C perfringens was found in 27 samples with SFP agar and in 5 samples with SPS agar (Difco), with a recovery ratio considerably higher on SFP agar SFP agar is a more specific presumptive medium for the enumeration of C perfringens and in conjunction with LM agar should save considerable time, effort, and materials toward the final identification of the species
76 citations
TL;DR: Two strains of Escherichia coli sublethally treated in acidic environments showed an increased sensitivity to violet red bile agar, suggesting that unreliable results may occur if selective media are used for the detection and enumeration of Enterobacteriaceae in acid foods.
Abstract: Two strains of Escherichia coli sublethally treated in acidic environments showed an increased sensitivity to violet red bile agar. The death of cells, treated in tryptic soy broth which had been a...
60 citations
TL;DR: To produce an immunologically and enzymologically new type of l-asparaginase, 108 strains of bacteria were screened for enzyme production and 13 bacteria belonging to the genera Alcaligenes, Bacterium, and Proteus were found to produce l- asparaginases in high levels.
Abstract: To produce an immunologically and enzymologically new type of l-asparaginase, 108 strains of bacteria were screened for enzyme production. As a result, 13 bacteria belonging to the genera Alcaligenes, Bacterium, and Proteus were found to produce l-asparaginases in high levels. Among these l-asparaginases, partially purified l-asparaginases from B. cadaveris and P. vulgaris showed antitumor activity. A partially purified l-asparaginase preparation of P. vulgaris did not react with the antibody of Escherichia colil-asparaginase on the Ouchterlony agar plate. Culture conditions for the production of l-asparaginase by P. vulgaris were investigated in detail. The enzyme was produced in high yields when cells were grown aerobically in a medium containing sodium fumarate and corn steep liquor. The addition of glucose or ammonium ion to the medium, however, resulted in depressed production of l-asparaginase. Under the optimum conditions, 3,700 international units of l-asparaginase was obtained from 1 liter of culture medium.
50 citations
TL;DR: SFP agar, which was the least selective of the media, allowed growth to some extent of nearly all of the facultative anaerobes tested, and gave significantly higher recoveries of spores than SPS and TSN agar.
Abstract: For the enumeration of viable vegetative cells and spores of Clostridium perfringens, noncommercial (laboratory prepared) sulfite-polymyxin-sulfadiazine (SPS) agar, tryptone-sulfite-neomycin (TSN) agar, and Shahidi-Ferguson-perfringens (SFP) agar were statistically compared to SPS agar without antibiotics. The selectivities of these four media were also evaluated on the basis of their ability to inhibit the growth of pure cultures of a variety of other organisms. The average recovery of vegetative cells of 10 strains of C. perfringens with SFP agar was not significantly higher than with SPS agar with 10(4) organisms per g, but with 10(6) organisms per g it yielded significantly higher recoveries than SPS agar. TSN agar yielded significantly lower recoveries at both inoculum levels. SFP agar gave significantly higher recoveries of spores than SPS and TSN agars. Average plate counts of spores in SFP agar were 75% as high as in SPS agar without antibiotics, but only 45% of the spores grew in SPS agar and 25% in TSN agar. TSN agar was the most selective of the three media, but the selectivity of SPS agar approached that of TSN agar under the test conditions. SFP agar, which was the least selective of the media, allowed growth to some extent of nearly all of the facultative anaerobes tested.
41 citations
TL;DR: The present authors succeeded repeatedly in isolating the causative bacterium in pure culture from lesions of spleen and kidney of affected fish which were obtained on the occasions of outbreaks of the disease in Miyazaki, Oita and Ehime Prefectures during the period from 1969 to 1970.
Abstract: For the past several years “bacterial tuberculoioidosis” has caused severe losses among young fishes of Seriola quinqueradiata and S. purpurascens cultured in various parts of Japan. The name “bacterial tuberculoidosis” was proposed by KUBOTA et al (1970) on th basis of the symptomatology and histopathology of the disease, though the causative agent responsible for it was not isolated.The present authors succeeded repeatedly in isolating the causative bacterium in pure culture from lesions of spleen and kidney of affected fish which were obtained on the occasions of outbreaks of the disease in Miyazaki, Oita and Ehime Prefectures during the period from 1969 to 1970. The bacterium when inolulated into Seriola caused the same pathological features as seen in naturally affected fish and killed them. The bacterium grew well on Brain heart infusion agar containing fresh human or rabbit blood and Brain heart infusion broth containing rabbit serum, both with 3% NaCl, but very poorly on ordinary nutrient agar or broth with 3% NaCl.In 2-day old cultures, grown on blood agar, cells were straight or slightly curved rods of 0.6 by 1.6 microns in the average size and arranged singly, in pairs or in chains. They were Gram-positive in young cultures but changed into Gram-negative after about 18 hours generally. Cells exhibited pleomorphism and had metachromatic granulus at the both ends of the cells. They did not form spores and were non-motile in semisolid agar madia. Capsules were absent.The bacerium was a facultative anaerobe. Nitrates were not reduced and neither indole (Kovac's method) nor hydrogen sulfide was produced. The oxydase test, methyl red test and catalass test were all positive, and the Voges-Proskauer test was negative. Gelatin was not liquefied. Agar Plates containing rabbit erythrocytes showed alpha-hemolysis. Acid was produced from glucose, mannose, levurose and galactose, but other sugars tested were not fermented. The bacterium was definitely sensitive to penicillin.On the basis of these observations, it is assumed that this organism is more closely related to the genus Corynebacterium than to any other known genera.
37 citations
TL;DR: The index of validity, which equates successful isolation of pathogens with total pickings, favored XLD and gram-negative broth as the media of choice, with direct streaking the poorest method by all counts.
Abstract: Two enrichment broths and four plating media were compared for efficiency of detection of enteric pathogens from 1,597 stool specimens. Of 170 salmonellae isolated from the composite of all methods, direct streaking yielded but 54%, whereas enrichment in gram-negative broth found 87% and Selenite-F broth 97%. By contrast, gram-negative broth produced 100% of the 17 shigellae, Selenite-F broth but 77%, and direct streaking only 59%. Thus, enrichment methods produced almost twice the number of both pathogens as direct streaking. Comparison of the plating media revealed xylose lysine deoxycholate agar (XLD) and Hektoen enteric agar to be equal in their abilities to find both pathogens. Both were moderately better than Salmonella-Shigella agar and markedly superior to eosin methylene blue agar. XLD fround 83% of salmonellae produced by the composite of four media and 90% of the shigellae. Hektoen enteric agar found 80% of both. Salmonella-Shigella agar detected 74 and 68%, respectively, and eosin methylene blue agar only 42 and 63%. The numbers of false positives accruing to each medium, however, showed Hektoen enteric and Salmonella-Shigella agars to produce more than twice as many false-positive plates as XLD. Similarly, Selenite-F broth resulted in many more false-positives for all plating media than did gram-negative broth. Consequently, the index of validity, which equates successful isolation of pathogens with total pickings, favored XLD and gram-negative broth as the media of choice, with direct streaking the poorest method by all counts.
37 citations
TL;DR: L-forms of a strain of Pseudomonas aeruginosa produced by serial subculture of the bacterial form on agar medium containing sucrose as an osmotic stabilizer and carbenicillin eventually became stable, i.e., would not revert in the absence of antibiotic, and were adapted to grow well in broth with the osmosis stabilizer.
Abstract: L-forms of a strain of Pseudomonas aeruginosa were produced by serial subculture of the bacterial form on agar medium containing sucrose as an osmotic stabilizer and carbenicillin. L-forms eventually became stable, i.e., would not revert in the absence of antibiotic, and were adapted to grow well in broth with the osmotic stabilizer. Gross morphology and light microscopic colony morphology were typical of an L-form. L-form cells were approximately spherical and bounded in part by a plasma membrane; they lacked the triple-layer cell wall structure and coarse, electron-dense nucleoidal granules of the parent bacterial form. The L-form, but not the bacterial form, contained cores, organelles previously reported only in group D streptococci. Antibiotic disc-sensitivity studies showed the stable L-form to be as sensitive as, or more sensitive than, the bacterial form to most antibiotics. Exceptions were polymyxin B, colimycin sulfate, and gentamicin, which were more active against the bacterial form. The remainder of the aminoglycosides and cell wall-active antibiotics showed no inhibition of either form. The L-form was more susceptible to cidal activity of normal human serum than the parent form. The L-form exhibited fewer biochemical activities than the parent bacteria or bacterial forms derived by reversion at a time when the L-form was still unstable. L-form colonies appeared colorless, and chemical analysis demonstrated that, if the L-form produces pigment at all, which was not demonstrated, it could not have been more than 3.6% of that produced by the bacterial form.
30 citations
TL;DR: The bacteriocin, boticin E, was produced by only a few strains of those clostridia which are nontoxigenic but otherwise identical to Clostridium botulinum type E and killed those of all other strains whose spores were sensitive.
Abstract: The bacteriocin, boticin E, was produced by only a few strains of those clostridia which are nontoxigenic but otherwise identical to Clostridium botulinum type E. Boticin preparations from four different strains had identical spectra against indicator cultures. Experiments with bacterial lawns showed boticin to be sporostatic for all tested nonproteolytic C. botulinum (types B, E, and F) and nontoxigenic type E-related strains which included the producing strains as well as those different from type E in the fermentation of one to three carbohydrates. Boticin had no detectable effect on vegetative cells of boticinogenic strains but killed those of all other strains whose spores were sensitive. Cultures that were growing in an agar medium were more sensitive to the bacteriocin than those growing in broth. Vegetative cells of indicator strains adsorbed boticin, but cells of a boticin-resistant mutant did not. Boticin did not lyse suspensions of vegetative cells which had been killed previously by exposure to air but lysed actively growing protoplasts and L-forms of a strain whose normal vegetative cells are susceptible to lysis. Sporostasis resulted from inhibition of germination rather than of outgrowth. Proteolytic strains of C. botulinum (types A, B, and F) were resistant to boticin E.
TL;DR: Mouse hemolytic 19S antibodies can be quantitatively measured if they are allowed to radially diffuse in an agar plate containing the erythrocyte antigen and a linear relationship can be seen between the area of lysis and the square root of the antibody dilution.
Patent•
02 Jun 1971
TL;DR: In this paper, the authors describe a machine for finding a VARYING AMOUNT of baceria solutions on the surface of a solidified AGAR plate in the CONFIGURATION of an archerses spire.
Abstract: A MACHINE FOR DEPOSITING A VARYING AMOUNT OF BACTERIA SOLUTION ON THE SURFACE OF A SOLIDIFIED AGAR PLATE IN THE CONFIGURATION OF AN ARCHIMEDES SPIRAL. THE AMOUNT OF SOLUTION DEPOSITED ON THE AGAR IS CONTINUOUSLY DECREASED, RESULTING IN A HIGHER CONCENTRATION OF BACTERIA PER UNIT LENGTH AT THE CENTER OF THE SPIRAL AND A DECREASING CONCENTRATION PER UNIT LENGTH AT THE EDGE OF THE PLATE. AFTER AN INCUBATION PERIOD THE BACTERIA BECOMES VISIBLE, AND ARE COUNTED BY INTERRUPTING A LIGHT BEAM INCIDENT TO A PHOTODIODE. THE CONCENTRATION OF AN UNKNOWN SOLUTION MAY BE DETERMINED BY VISUALLY COUNTING THE NUMBER OF COLONIES ON A DISCRETE AREA OF THE PLATE.
TL;DR: Cells of nine amphibian permanent cell lines grew in or on agar with plating efficiencies of 10–85%.
TL;DR: M extracted from BCG or H(37)Rv cells neutralized serum tuberculostasis as effectively for the homologous as for heterologous strains, however, the extract of virulent bacilli was much more active in the neutralization than similar extract prepared from attenuated cells.
Abstract: Mycobactin (M), an iron-chelating product of tubercle bacilli, neutralized serum tuberculostasis by removing growth-essential iron from transferrin (Tr) and supplying the metal to the bacteria. The competition for iron between Tr and M has been demonstrated by the agar-plate diffusion test. This test is suitable not only for the study of Tr-iron-M interplay but also for the evaluation of serum tuberculostasis. Extremely poor solubility of M in water and consequently its association with lipoidal cell wall of tubercle bacillus was overcome by the use of water-dispersible and surface-active Tween 80. The addition of Tween 80 to culture media insured the presence of M in spent media; otherwise M was extracted from bacillary cells with a solution of Tween 80 or a mixture of ethanol and Tween 80. Although M was produced irrespective of the amount of iron present in culture medium, its production in iron-poor medium was more prolific than in iron-rich medium. M extracted from BCG or H37Rv cells neutralized serum tuberculostasis as effectively for the homologous as for heterologous strains. However, the extract of virulent bacilli was much more active in the neutralization than similar extract prepared from attenuated cells; whether this difference is of quantitative or qualitative nature remains to be determined.
TL;DR: The genusErwinia contained two groups; an anaerogenic group which produced aggregates of bacteria (symplasmata) in the syneresis water of slant cultures and biconvex bodies in colonies on agar medium, and an aerogenic groupwhich lacked these characteristics.
Abstract: Sixty-five strains of gram-negative, yellow-pigmented bacilli, including four chromogenicEnterobacter strains and 55 anaerogenic and six aerogenicErwinia strains, were isolated from human sources. The genusErwinia contained two groups; an anaerogenic group which produced aggregates of bacteria (symplasmata) in the syneresis water of slant cultures and biconvex bodies in colonies on agar medium, and an aerogenic group which lacked these characteristics.Erwinia was differentiated fromEnterobacter, since the latter possessed dihydrolase and decarboxylase activity and demonstrated resistance to cephalothin.
TL;DR: The polysaccharide levan was synthesized in a solidified agar medium containing sucrose as a source of fructose and observed as circular white areas, the size of which was dependent on the time of incubation and the concentration of enzyme used.
Abstract: The polysaccharide levan was synthesized in a solidified agar medium containing sucrose as a source of fructose. The biosynthesis was achieved by the enzyme levansucrase (2,6-fructan–d-glucose 6-fructosyltransferase, EC 2.4.1.10), a small quantity of which was placed in circular wells cut in the agar gel. The enzyme slowly diffused through the agar–sucrose medium and the synthesis of levan was observed as circular white areas, the size of which was dependent on the time of incubation and the concentration of enzyme used. Images
TL;DR: A selective medium which allows detection of relatively small numbers of Fusobacterium varium in fecal specimens is described and should be useful with other kinds of specimens where mixtures of organisms are common.
Abstract: A selective medium which allows detection of relatively small numbers of Fusobacterium varium in fecal specimens is described. Blood-agar containing 50 μg of rifampin per ml inhibits the growth of many species of Bacteriodes and of F. fusi-forme/nucleatum but allows good growth of F. varium and most strains of F. mortiferum. Quantitative cultures of 11 fecal specimens were done on rifampin and other selective and nonselective media. F. varium was recovered in counts of 106 and 107 per gram from two specimens on rifampin only. A third specimen yielded 1010F. varium on several media, including rifampin. Some Eubacterium and Clostridium species also grew on rifampin, and these ordinarily were distinguished from the Fusobacterium by colony morphology. This medium is of value in fecal flora studies and should be useful with other kinds of specimens where mixtures of organisms are common.
TL;DR: In this article, the precipitation of peptide- and protein-lignosulphonic acid complexes can be demonstrated and studied in agar plates in the form of precipitation zones, and the effects on the precipitates caused by variations in incubation temperature, incubation time, concentration of the reagents and in pH in the mixture of reagents, are described.
Abstract: The precipitation of peptide- and protein-lignosulphonic acid complexes can be demonstrated and studied in agar plates in the form of precipitation zones. The effects on the precipitates caused by variations in incubation temperature, incubation time, concentration of the reagents and in pH in the mixture of reagents, are described, and the nature of the peptide-lignosulphonic acid bond is discussed. The central lysis zones which appeared in some precipitation zones were found to be probably caused by excess of lignosulphonic acids. The possibility of developing the agar precipitation method described as a direct micro quantitative procedure for the determination of certain lignosulphonic acids in aqueous solution is suggested.
TL;DR: An agar plate method has been developed for determination of lysosyme activity and was found suitable for determining the lysozyme activity in human saliva.
Abstract: – An agar plate method has been developed for determination of lysosyme activity. Micrococcus lysodeikticus cell walls were used as substrate. The method was found suitable for determining the lysozyme activity in human saliva.
TL;DR: Of 120 Staphylococcus epidermidis strains tested, 25.8% were of the compact type in serum-soft agar, and compact variants showed higher production of metabolites than counterpart diffuse variants.
Abstract: Of 120 Staphylococcus epidermidis strains tested, 25.8% were of the compact type in serum-soft agar. Compact variants showed higher production of metabolites than counterpart diffuse variants.
TL;DR: A composite agar medium is described for the characterization of Pseudomonas aeruginosa and other Gram negative bacilli and glucose oxidation and the production of ammonia by the arginine dihydrolase system are demonstrable in one tube.
Abstract: SUMMARY: A composite agar medium is described for the characterization of Pseudomonas aeruginosa and other Gram negative bacilli. Glucose oxidation and the production of ammonia by the arginine dihydrolase system are demonstrable in one tube. This arginine glucose (AG) medium also indicates the evolution of gas by glucose fermenting Gram negative bacilli.
TL;DR: In this paper, an account is given of simple procedures by which Trypanosoma theileri -like trypanosomes of cattle may be isolated, cultured and stored.
TL;DR: It was possible to type both laboratory and freshly isolated strains of Mycoplasma hyorhinis using the disk growth inhibition test and the combination of fresh horse serum in the agar medium and M. hyorHinis antiserum-impregnated disks appeared to have a synergistic effect and inhibited the growth of all M. Hyorhini cultures on agarmedium.
TL;DR: In this article, it was shown that various microbial and animal proteinases, with the exception of pepsin, have a lytic effect on peptide and protein-lignosulphonic acid complexes in agar gel, and that this effect is characteristically inhibited by specific antiproteinases and naturally occurring serum inhibitors.
Abstract: It is shown that various microbial and animal proteinases, with the exception of pepsin, have a lytic effect on peptide- and protein-lignosulphonic acid complexes in agar gel, and that this effect is characteristically inhibited by specific antiproteinases and naturally occurring serum inhibitors. The activity of the enzymes is studied at various concentrations of peptides and proteins, and at various pH values in the agar. The lysis phenomenon is seen in relation to the precipitation theory of peptide- and protein-lignosulphonic acid complexes, and to biochemical reactions taking place in certain natural ecosystems. Activity caused by different microbial proteinases is demonstrated in agar plates at pH 3.6. The possibility of using the method for studies on proteolytic enzymes at low pH values is suggested.
TL;DR: Submicroscopic, viable L- phase elements produced during colony formation were capable of passing through membrane filters with pore channels as small as 0.22 mum; these elements required transfer from underneath the filters to fresh agar medium in order to develop into L-phase colonies.
Abstract: Membrane filters (Millipore Corp.; pore sizes 1.2 to 0.22 μm) were placed on the surface of L-phase growth medium solidified with agar. The filter and the surrounding medium were inoculated with either protoplasts or stable broth-grown L-phase variants obtained from Streptococcus faecium strain F24. The L-phase inoculum gave rise to viable L-colonies on the filters and on the medium, whereas protoplasts gave colony formation only on the medium. However, when the Millipore filters were covered by a layer of solid L-phase medium, 75 μm or greater in depth, before inoculation with protoplasts, colony formation resulted but with atypical morphology. In contrast, inoculation of protoplasts on Nuclepore and Sartorius membrane filters did give rise to L-colonies on the surface and underneath the filters after 2 days of incubation at 37 C. Submicroscopic, viable L-phase elements produced during colony formation were capable of passing through membrane filters with pore channels as small as 0.22 μm; these elements required transfer from underneath the filters to fresh agar medium in order to develop into L-phase colonies. Membrane filters were also placed on the surface of L-phase growth medium solidified with gelatin. Inoculation of the filters and surrounding medium with a lysozyme-prepared protoplast suspension gave rise to streptococci on the surface of the filters and on the medium. However, inoculation with the stable broth-grown L-phase variants gave rise to atypical colonies on the medium and only small patches of abortive growth on the filters. Images
TL;DR: A method was developed for identification of Bacillus anthracis based on elaboration of protective antigen by individual colonies and its detection by double-diffusion precipitation in agar plates.
Abstract: A method was developed for identification of Bacillus anthracis based on elaboration of protective antigen by individual colonies and its detection by double-diffusion precipitation in agar plates.
TL;DR: A system for the identification of non-fermentative gram-negative rods from clinical specimens is proposed, which uses blood agar and MacConkey agar for their isolation, and divides them into oxidase-positive and oxid enzyme-negative groups.
Abstract: A system for the identification of non-fermentative gram-negative rods from clinical specimens is proposed. It uses blood agar and MacConkey agar for their isolation, and divides them into oxidase-positive and oxidase-negative groups. A few sensitivity tests and a maximum of eight media are used for the diagnosis which can be obtained within 24–48 hours.
TL;DR: Results indicate that this assay method should be a useful adjunct to the Bratton-Marshall colorimetric procedure, by permitting the direct measurement of antibacterially active drug in clinical specimens.
Abstract: A reasonably precise, reproducible, and sensitive microbiological procedure for directly assaying sulfacytine and other sulfonamides as antibacterially active drugs has been developed by appropriately modifying the standard disc-agar diffusion technique. Blood and urine levels as low as 3 mug/ml may be determined through the use of a strain of Escherichia coli and a chemically defined agar medium devoid of sulfonamide antagonists. Results indicate that this assay method should be a useful adjunct to the Bratton-Marshall colorimetric procedure, by permitting the direct measurement of antibacterially active drug in clinical specimens.
TL;DR: Growth of all the porcine mycoplasma serotypes was inhibited by fresh sheep serum and the addition of fresh horse serum to specific M. hyorhinis rabbit antiserum-impregnated disks appeared to have a synergistic effect.
Abstract: When fresh animal serum was dropped onto seeded mycoplasma agar plates, inhibition of growth frequently occurred. This effect was dependent on the mycoplasma serotype and on the animal species from which the fresh serum came. This activity of fresh animal serum was heat-labile and would not diffuse through the agar medium. Growth of all the porcine mycoplasma serotypes was inhibited by fresh sheep serum. M. hyorhinis, M. hyopneumoniae, B 3 and the P 45 strains were insensitive to fresh horse serum. The addition of fresh horse serum to specific M. hyorhinis rabbit antiserum-impregnated disks appeared to have a synergistic effect and the combination of M. hyorhinis antiserum-impregnated disk and fresh horse serum always inhibited the growth of M. hyorhinis strains.