Showing papers on "Agar plate published in 1989"

Fractal Growth of Bacillus subtilis on Agar Plates

Abstract: Bacteria have been shown to grow with various morphologies under different conditions on agar plates. A Bacillus subtilis strain was inoculated on the plate surface and incubated at 35°C. Colonies grew two-dimensionally with random branches, similar to clusters of the diffusion-limited aggregation (DLA) model. The colony patterns were analyzed and found to be self-similar with a fractal dimension of 1.716±0.008, in excellent agreement with the expected value of the DLA model. Interior branches were observed to stop growing in spite of their open neighborhood during the incubation period, implying the existence of a screening effect. These results clearly suggest that the colony pattern of the organism was formed through the DLA process. Moreover, the colonies were found to grow radially with almost regular branches on agar plates with moist surfaces, reminiscent of “dense radial” morphology.

Development of a differential medium for bile salt hydrolase-active Lactobacillus spp.

Abstract: An agar plate assay was developed to detect bile salt hydrolase activity in lactobacilli. On Lactobacillus-selective MRS or Rogosa SL medium supplemented with taurodeoxycholic, taurocholic, or taurochenodeoxycholic acids, bile salt hydrolysis was manifested at two intensities: (i) the formation of precipitate halos around colonies or (ii) the formation of opaque granular white colonies. Sixty-six lactobacilli were tested for bile salt hydrolase activity by both the plate assay and a sensitive radiochemical assay. No false-positive or false-negative results were detected by the plate assay. Based on results of experiments with Eubacterium lentum and Bacteroides species, the plate assay was dependent on two factors: (i) the presence of bile salt hydrolytic activity and (ii) the ability of the organism to sufficiently acidify the medium to protonate free bile acids. The availability of a differential medium for determination of bile salt hydrolase activity will provide a rapid method for determining shifts in a specific functional activity of intestinal Lactobacillus species and provide a rapid screening capability for identifying bile salt hydrolase-deficient mutants. The latter application should allow bile salt hydrolase activity to be used as a marker enzyme in genetic experiments.

Detection of pathogenic Yersinia enterocolitica by using congo red-magnesium oxalate agar medium.

Abstract: A Congo red-magnesium oxalate agar medium was developed to detect expression of virulence-associated calcium dependency and Congo red absorption in Yersinia enterocolitica. Of the 157 pathogenic serotypes tested, 119 (75.8%) were positive; 98% of nonpathogenic serotypes and strains of three other Yersinia species were negative.

A New Method for the Intensive Isolation of Actinomycetes from Soil

Abstract: A new method was developed to isolate actinomycetes from soil more selectively and more thoroughly.Elements of the procedure are (1) treatment of soil suspension with a solution containing yeast extract (YE) 6% and sodium dodecyl sulfate (SDS) 0.05%, at 40°C for 20 min, (2) subsequent dilution with water and (3) a few week’s incubation on HV agar plates containing nalidixic acid (n.a.) 20 mg/L.The YE and the heat shock at 40°C activated spore germination of a variety of actinomycete strains, the SDS acted as a germicide only on bacterial cells with rare exception, and the n.a. suppressed growth of bacterial spore formers without any effect on the actinomycetes, under the conditions used.By the treatment of soil suspension with YE and SDS, the count of actinomycete cfu per g. of various soils (10 samples) was increased by 40% and the count of bacteria was decreased to 20%, on the averages. The bacterial count was further decreased to less than 10% by addition of n.a. into the isolation medium.

Distribution of chitinase and chitobiase in bacillus

Abstract: Sixty strains representing 29 taxospecies ofBacillus were assayed for their ability to hydrolyze colloidal chitin. A qualitative estimation of chitinolysis was made from the clear zone produced around colonies in the conventional agar plate method and chitobiase activity by use of the fluorescence of 4-methylumbelliferyl-N-acetyl-β-d-glucosaminide.

Staphylococcus aureus exopolysaccharide in vivo demonstrated by immunomagnetic separation and electron microscopy.

Abstract: Staphylococcus aureus strains were separated from mastitis milk samples without cultivation by using monodisperse magnetic polymer particles coated with polyclonal antiserum against an encapsulated S. aureus strain. Exopolysaccharide was verified by transmission electron microscopy and the serum soft-agar culture technique. Capsular polysaccharide was found on virtually all clinical isolates. Surface protein A and S. aureus-specific cell wall components were masked when the strains were cultured on an exopolysaccharide-promoting medium. Masking of surface determinants was dependent on their concentration on the bacterial surface as well as on exopolysaccharide abundance. The polysaccharide layer on in vivo bacteria was reduced markedly after just one transfer from milk to blood agar plates but was reexpressed after culturing was done on a capsule-generating medium.

Antagonistic effect of pediococcus spp. against listeria monocytogenes

Abstract: A total of 37 strains of Pediococcus were screened for antagonistic effect against the growth of eight strains of Listeria monocvtoaenes (CA, V7, Scott A, 19111, 19113, 19115, F5027, F5069). Using an agar plate diffusion method, 28% of the 296 pairings were positive with distinct, clear zones of inhibition evident. The positive reactions were primarily seen with Pediococcus acidilactici strains isolated from or associated with meat fermentations and from abdominal related sites in humans. Strains of Pediococcus pentosaceus and Pediococcus damnosus also showed an inhibitory effect against Listeria. Studies employing growth extracts of P. acidilactici PO2 versus growth of L. monocvtoaenes 19113 showed that the inhibitory substance was retained by a molecular sieve with a pore size of 12,000 daltons, that P02 growth extract in late stationary phase (48 hour culture) was most effective, and that apparent resistant sub‐populations of L. monocytoaenes 19113 eventually arose after continued exposure to ...

A semiselective medium for the isolation of Pseudomonas syringae pv. savastanoi.

Abstract: A new medium, designated as PVF-1 agar, was developed and tested for isolating Pseudomonas syringae pv. savastanoi from olive plants under field conditions. It was compared with other conventionally used media, including nutrient-sucrose agar medium (NSA), King's B medium, and the NPC medium of Sands and Rovira. The new medium, a modification of Kado and Heskett's D4, allowed growth of P.s savastanoi, but retained its selectivity against saprophytic bacteria. (...)

Use of the Chrome Azurol S Agar Plate Technique To Differentiate Strains and Field Isolates of Rhizobium leguminosarum biovar trifolii.

Abstract: Identification of Rhizobium and Bradyrhizobium strains and especially of indigenous isolates continues to be one of the major difficulties associated with competition studies. Because there is no universally accepted method, the method of choice depends on preference, experience, and equipment. Here, an agar plate technique was used to distinguish strains and field isolates of Rhizobium leguminosarum biovar trifolii to provide a basis for identifying nodule occupants in further competition studies. A rapid plate technique, based on differential growth characteristics, complements other techniques such as serological reactions, particularly when antisera cross-react with nonhomologous strains. The technique involves culturing strains and isolates on chrome azurol S agar. Although similar responses were observed among some strains, the response was highly reproducible and was considered an ideal complementary technique used in conjunction with serological procedures. Strains with similar responses could often be differentiated by varying media components, such as the source of carbon.

Identification of W-type and R-type isolates of Pseudocercosporella herpotrichoides

Abstract: W-type isolates of Pseudocercosporella herpotrichoides grown on a maize-based agar and exposed to near- ultra-violet radiation at c 13°C produced a greenish black colour, whilst R-type isolates produced a pink or pale brown colour in the agar medium More colonies from directly plated lesions or from spore suspensions could be recognized as P herpotrichoides and could be more easily differentiated as W-type or R-type or as mixtures of both by colour production on maize agar (MA) than by colony morphology on potato dextrose agar (PDA), despite the presence of other fungi Isolates with intermediate morphology on PDA were positively identified as W-type or R-type on MA; their pathogenicities to wheat and rye seedlings were usually similar to those of W-type or R-type isolates with typical colony morphology, confirming their identification on MA Drops of mixed suspensions of W-type and R-type spores on PDA formed fast-growing colonies with smooth margins which sometimes had slow-growing sectors with feathery margins Drops of the same mixtures on MA formed greenish black colonies which sometimes had pink or pale brown sectors However, when these mixtures were spread onto MA, W-type and R-type colonies could easily be differentiated by colour

Direct isolation of atypical thermophilic Campylobacter species from human feces on selective agar medium.

Abstract: Campylobacter upsaliensis is the name which has been proposed for a new group of thermophilic campylobacter strains which differ from C. jejuni and C. coli in having a negative or weak catalase reaction. Primary isolation of these strains from human feces has been achieved only by use of filtration techniques. We report here direct isolation of strains corresponding to C. upsaliensis from stools of six children. The strains were isolated on a newly described campylobacter-selective medium. The strains were oxidase positive, hippurate negative, nitrate positive, negative for H2S in triple sugar iron, and susceptible to cephalothin (30-micrograms disk) and nalidixic acid (30-micrograms disk), and they grew at 37 and 43 degrees C, but not at 25 degrees C. The selective medium used was a blood-free, charcoal-based medium consisting of Columbia agar base, activated charcoal, cefoperazone (32 micrograms/ml), vancomycin (20 micrograms/ml), and cycloheximide (100 micrograms/ml). The medium supported the growth of the weakly reacting or catalase-negative strains, with colony counts equivalent to those obtained on antibiotic-free horse blood agar. These strains could not be isolated directly from stool on Skirrow medium, and colony counts confirmed that this medium could not support a low inoculum of these organisms. The clinical significance of these strains is unknown. We conclude that C. upsaliensis can be isolated directly from stool by using a selective medium, without the need for filtration.

Grouping of soil bacteria by analysis of colony formation on agar plates

Abstract: The colony formation of soil bacteria was studied in relation to incubation time. The process was simulated by a colony-forming curve (CFC) which was a superposition of several component curves (cCFC) given theoretically by the first-order reaction (FOR) model. This model had been previously proposed to define the colony formation of cells of a single culture. Soil bacteria were divided into several groups by these cCFC, as different types of bacteria produced their own colonies. Bacteria belonging to a single group grew at a similar rate on the plating medium and each group was characterized by a different growth rate. Most copiotrophic bacteria were fast growers and most oligotrophic bacteria slow growers.

Growth of Leuconostoc oenos under Anaerobic Conditions

Abstract: Malolactic fermentation acts to reduce acidity levels in wine and is most commonly initiated by the lactic acid bacterium Leuconostoc oenos . We examined the growth of reference strains and New Zealand isolates of L. oenos using pre-reduced broth and agar media, and found that anaerobic conditions facilitated the growth of this organism, especially on agar plates. Growth did not appear to be stimulated specifically by carbon dioxide. Anaerobic media were used to examine the temperature optima and carbohydrate utilization patterns of L. oenos strains. These tests demonstrated that there was considerable heterogeneity among strains of L. oenos .

Optimum conditions for growth of cyanobacteria on solid media

Abstract: The colony forming ability of single cells or very short filaments of 7 strains of cyanobacteria was tested on media solidified by agar or by agar substitutes (Gel Gro or Gel Rite). In addition, the effect of various methods for preparation of agar media on colony forming ability was measured. High efficiency colony formation for most of the strains required that the agar be autoclaved separately from the salts in the medium. The addition of thiosulfate, but not buffer, significantly increased the plating efficiency of most strains.

An increase in the antimicrobial activity in vitro of fosfomycin under anaerobic conditions

Abstract: Fosfomycin showed lower MIC values under anaerobic culture conditions than those under aerobic conditions for four Gram-positive and 18 Gram-negative bacterial isolates The degree of change in MICs was dependent on the culture media and strains tested The growth-inhibitory diameter in the paper disc assay increased in parallel with the decrease in the redox potential of the agar medium Bacteriolytic activity was also potentiated in anaerobiosis The increase of the bio-activity of fosfomycin in anaerobic culture was neither due to the change of medium pH nor to the change of mobility of drug in agar However it is possible that the uptake of fosfomycin through the cell membrane increased in anaerobiosis The anaerobic MICs of fosfomycin were better correlated than the aerobic MICs with the ED50 values in a mouse systemic infection model

Effect of propiconazole on growth and sterol biosynthesis by Sclerotium rolfsii

Abstract: Germination of sclerotia ofSclerotium rolfsii on agar nutrient medium was delayed or slightly inhibited by concentrations of propiconazole between 0.4 and 4.0 μg ml−1, but was strongly inhibited by 8 μg ml−1 and completely inhibited by 16 μg ml−1. On the other hand, growth of hyphae from the germinated sclerotia was strongly inhibited by propiconazole at 1 μg ml−1 or greater. Hyphal growth from agar discs on agar medium was about 8 times less sensitive than hyphal growth from the sclerotia or from hyphal inoculum in liquid media. Propiconazole at 0.25 and 1.0 μg ml−1 strongly inhibited ergosterol biosynthesis, but this was not associated with large accumulations of C-14 methyl sterols. The ratio of eburicol to ergosterol in hyphae grown in the presence of 0.25 μg ml−1 propiconazole for 16, 30 or 45 h was 0.11, 0.13 and 0.04, respectively, for the three intervals while for hyphae grown in the presence of 1 μg ml−1, the ratios were 0.29, 0.36 and 0.30, respectively, for the same intervals. In view of a ratio of 23.5 for14C-acetate incorporation into the two sterols during the initial 6 h growth period in the presence of propiconazole, it is believed that the lack of large accumulation of C-14 methyl sterols is due to the feedback inhibition by eburicol or to cell lysis when the content of ergosterol becomes too low in the actively growing cells.

Chlamydospore formation by Paracoccidioides brasiliensis mycelial form

Abstract: To investigate the role of some adverse environmental conditions in chlamy-dospore formation by the mycelial form of P brasiliensis, we cultured four P brasiliensis isolates (18, Bt4, 1183, Pb9) at 25°C within solid agar medium either rich or poor in nutrients Isolates 18 and 1183 were also cultured under anaerobiosis in a nitrogen atmosphere Isolate 18 produced great number of terminal and intercalary chlamydospore after 7-10 days of culture in a medium poor in nutrients (2% agar with 01% dextrose and polypepton) The three other isolates also produced chlamydospores under the same conditions, but in lower numbers Chlamydospore production by isolate 18 was abolished when the fungus was cultured in two agar media rich in nutrients (brain heart infusion and potato dextrose agar) Anaerobic incubation of isolate 18 under an atmosphere of N2 showed small mycelial outgrowth with numerous chlamydospores At the electron microscopical level, the chlamydospores showed one or various nuclei and numerous mitochondria, indicating great potential for further development Accordingly, chlamydospores produced multiple budding after only 24 h incubation at 35°C The results demonstrate that under adverse environmental conditions P brasiliensis mycelial form produces chlamydospores within a short period of time

Comparison of four commercial brucella agar media for growth of anaerobic organisms.

Abstract: Four different commercial brucella blood agar plating media (Anaerobe Systems, BBL Microbiology Systems, Remel, and Scott Laboratories) were compared for the abilities to recover anaerobic organisms from clinical specimens and to support the growth of American Type Culture Collection anaerobic stock cultures. Following 24 h of incubation in an anaerobe chamber, Anaerobe Systems prereduced, anaerobically sterilized brucella plates yielded 63% of the total clinical anaerobe isolates, the Scott medium yielded 51%, the Remel medium yielded 42%, and the BBL medium yielded 37%. Poor growth of Peptostreptococcus magnus, P. anaerobius, Fusobacterium necrophorum, F. nucleatum, and pigmented Bacteroides spp. was observed on brucella media obtained from BBL, Remel, and Scott. Data obtained with stock anaerobic cultures showed that Anaerobe Systems plates yielded good growth and produced a larger colony size with all of the strains tested in 1 day, whereas poor growth of Peptostreptococcus spp., B. melaninogenicus, and Fusobacterium spp. was noted on brucella media from BBL, Remel, and Scott.

Evaluation of four qualitative methods for detection of beta-lactamase production in Staphylococcus and Micrococcus species.

Abstract: Four qualitative methods for the detection of beta-lactamase production in Staphylococcus and Micrococcus species were evaluated and compared with a quantitative macroiodometric reference method The disc diffusion test with penicillin G and the cloverleaf method could not separate beta-lactamase-positive from beta-lactamase-negative strains Two applications of the chromogenic cephalosporin test, using uninduced strains and strains grown on blood agar plates, gave a large number of false negative and false positive results False negative reactions were most common among uninduced strains, while the false positive reactions were most often recorded for Staphylococcus saprophyticus A high degree of efficiency was recorded for the nitrocefin spot test, using induced strains grown on antibiotic susceptibility agar, and for the starch-iodine plate method The starch-iodine plate with methicillin as inducer gave the most reliable results

Production of Purplish-red Pigment in Mixed Culture of Streptomyces propurpuratus ATCC 21630 and Bacillus sp. R-89

Abstract: The purplish-red pigment was formed on agar plate by superimposed streaking of Streptomyces propurpuratus ATCC 21630 and strain R-89, The strain No.89 was ascribable to the genus Bacillus and designated as Bacillus sp. R-89. Both strain did not produced such pigment when cultivated independently. For hyperpigment production, we selected the mutant S.P-6 from Streptomyces propurpuratus ATCC 21630 by MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) treatment. Maximum purplish-red pigment 1420 mg/ were produced, when the mutant of R-16 and Bacillus sp. R-89 were mixed cultured at 3 for 72 hr.

Production of bacteriocin-like antagonism by clinical isolates of Yersinia enterocolitica.

Abstract: Fourteen clinical isolates of Yersinia enterocolitica serotype O:3 and four well-documented virulent strains of serotypes O:3, O:8, and O:9 were biotyped and examined for plasmid-associated autoagglutination and calcium dependency and for epithelial cell adherence. These strains were tested for the production of bacteriocin-like antagonism by using tryptone soya blood agar at room temperature and at 37 degrees C. By using the cross-streaking method, three clinical isolates produced inhibitory substances at room temperature. These substances were active against a variety of clinical isolates and their plasmid-cured derivatives at both room temperature and 37 degrees C. The inhibition was easier to read after incubation of the cross-streaked plate at 37 degrees C. The inhibition patterns indicate that two of the three producer strains appear to recognize potentially virulent O:3 strains, with or without the virulence plasmid.

Comparison of Y1 mouse adrenal cell and coagglutination assays for detection of Escherichia coli heat labile enterotoxin.

Abstract: A commercial coagglutination assay (COA; Phadebact LT-ETEC) was compared with a Y1 mouse adrenal cell assay for detecting the heat labile enterotoxin of Escherichia coli. Of four different media evaluated for use with the COA, only one (modified blood agar) gave a positive result with all strains known to produce heat labile enterotoxin. With modified blood agar, the COA detected 74 (85%) of 87 such strains. Eighty six strains negative by cell culture assay were also negative by COA, and one strain positive by COA could not be confirmed by cell culture. The Phadebact LT-ETEC kit provides a simple, sensitive, and economical method for detecting E coli heat labile enterotoxin.

The suitability of four media for enumerating Aeromonas spp. from environmental samples

Abstract: Starch ampicillin agar (SA), dextrin fuchsin sulphite agar (DFS) and blood agar with 10 mg (BA-10) and 30 mg (BA-30) ampicillin/l, respectively, were evaluated for enumeration of Aeromonas spp from environmental samples Recovery from pure cultures was excellent on all media except for ampicillin-sensitive strains on the ampicillin-containing media With natural samples, the ability to differentiate Aeromonas from the background microflora was best on SA agar where 85% presumptive Aeromonas colonies were confirmed, compared with 18% on DFS, 36% on BA-10 and 40% on BA-30 Prolonged incubation caused a decrease in the differentiating ability

Inoculation of cowpea and wheat with strains of Bradyrhizobium sp. that differ in their production of indole acetic acid

Abstract: Sufficient indole acetic acid (IAA) was produced in yeast extract-mannitol (YM) medium by each of two isolates of indigenous Bradyrhizobium sp., to inhibit primary root growth of cowpea. Similar inoculation of cowpea with YM-cultivated strains from a culture collection or with washed cell suspensions of the two IAA-producing isolates had no apparent inhibiting effect on primary root growth. YM-cultivated cultures of each of the two high IAA-producing strains did not prevent nodulation of secondary roots and did not affect plant growth. In tests on agar plates a Bradyrhizobium sp. strain, CB756, frequently used for commercial inoculant production, stimulated root growth of cowpea and wheat seedlings, but when used to inoculate wheat in sand culture, neither strain CB756 nor the IAA-producing isolates measurably affected wheat growth. Production of IAA by the isolates and strains was strongly influenced by growth medium; all required tryptophan to excrete at least 0,5 μg IAA cm−3. Nine 5-methyl-tryptophan-r...