Inhibitory effect of oregano and thyme essential oils on moulds and foodborne bacteria

The essential oil of oregano ('origanum oil'; thymol type oil from Origanum vulgare) inhibited completely the mycelial growth of Aspergillus niger and A. flaous at 400 μg/ml, while A. ochraceus was inhibited at 600 μg/ml. At 700 μg/ml, thyme oil inhibited the mycelial growth of A. flavus and A. niger but not that of A. ochraceus . Fungal spore germination was inhibited by 600 μg/ml of origanum oil and (with the exception of A. ochraceus) by 700 μg/ml of thyme oil. Under aerobic conditions, the essential oils of oregano (250 μg/ml) and thyme (350 μg/ml) inhibited to some extent the growth of Staphylococcus aureus and Salmonella typhimurium. Pseudomonas aeruginosa was not affected by either oregano or thyme oil at concentrations up to 500 μg/ml. The origanum oil was very effective against Campylohacter jejuni and Clostridiurn sporogenes and thyme oil was very effective against C. jejuni. The antagonistic effect of the two oils on Staph. aureus and Salm. typhimuriutn was greatly enhanced when those organisms were incubated in atmospheres of low oxygen tensions     

Effect of bisabolangelone on development ofCydia pomonella larvae and oviposition of the females

The effects of bisabolangelone on the development of codling moth larvae,Cydia pomonella L., and on ovipositional behaviour of the females were studied under laboratory conditions. Entry of the neonate larvae into apples and their development on a semi-synthetic medium were completely inhibited when the larvae were exposed respectively to 10 μg a.i./cm² and 20 μg a.i./ml of this compound. While concentrations of 1.25 to 5.0 μg a.i./ml bisabolangelone in the medium did not significantly affect larval development, exposure of the larvae to a higher rate (10 μg a.i./ml) resulted in 80% mortality during the first week. Nevertheless, the larvae which survived the treatments underwent further development until emergence of the adults. No significant changes in duration of larval or pupal periods were recorded. Oviposition of the females in plastic beakers, whose inner surfaces were partially painted with two concentrations of bisabolangelone (1.25 to 5.0 μg a.i./cm²), was significantly reduced and the eggs were mainly laid on the parts painted with the ethanol solvent alone. When the inner surface of the cups was completely treated (i.e. top, bottom, and side) with similar concentrations of bisabolangelone, a dramatic reduction in oviposition occurred and the eggs were mostly laid on the bottom of the beakers. While this compound did not significantly influence egg hatch, it inhibited the normal upward movement of the adults in the cups and migration of the newly hatched larvae through perforations of the lids.     

Susceptibility of Neisseria gonorrhoeae to seven antibiotics in vitro

One hundred consecutive isolates of N. gonorrhoeae were tested for susceptibility to penicillin, ampicillin, tetracycline, erythromycin, kanamycin, cephaloridine and cephalexin by an agar dilution method. Relative resistance to penicillin was frequent. For 39% of isolates the minimum inhibitory concentration (MIC) of penicillin was 0.05 U./ml. or less; in 55% the MIC was 0.5 to 2.0 U./ml. Ampicillin was slightly more active than penicillin G: all isolates were inhibited by 0.5μg./ml. or less. Resistance to tetracycline and erythromycin was frequent with MIC of 1 μg./ml. or greater observed in 32 and 24% of isolates respectively. The MIC of kanamycin for all gonococci was 8 μg./ml. or greater. Cephalexin was slightly more active than cephaloridine, though each drug exhibited a wide range of MIC values. Gonococcus isolates resistant to penicillin (MIC of 1.0 U./ml. or greater) tended to be resistant to the other antibiotics tested.     

The effects of Tunicamycin and 2-deoxy-D-glucose on the development ofXenopus laevis embryos

Summary Tunicamycin and 2-deoxy-D-glucose were applied toXenopus laevis embryos in the first cleavage furrow, blastula and early gastrula stages. No effect was observed with 2-deoxy-D-glucose up to the concentration 0.1 M. The effect of Tunicamycin is dose- and stage-dependent. At the concentration of 5 g/ml cleaving embryos are arrested at the onset of gastrulation and their cells exhibit decreased intercellular adhesivity, while embryos treated in the blastula and early gastrula stages may develop up to the late neurula and tail-bud stage, respectively. Higher concentrations (up to 20 g/ml) drastically affect cleavage. Concentrations of 4 to 1 g/ml allow embryos to develop up to more advanced stages; however, developmental defects are the rule. Concentrations of less than 1 g/ml do not affect development.     

In vitro activity of a new triazole antifungal agent,Sch 56592, against clinical isolates of filamentous fungi

Sch 56592 is a new triazole derivative that possesses potent, broad-spectrum antifungal activity. We evaluated the in vitroactivity of Sch 56592 compared with that of itraconazole, amphotericin B and 5-fluorocytosine against 51 clinical isolates of filamentous fungi, including Aspergillus flavus(10), A. fumigatus(12), Fusariumspp. (13), Rhizopus spp. (6), Pseudallescheria boydii(5), and one isolate each of Acremoniumspp., A. niger, A. terreus, Paecilomycesspp., and Trichodermaspp. In vitrosusceptibility testing was performed using the microdilution broth method outlined in the NCCLS 27-A document. Sch 56592 was highly active against A. flavus(MIC₉₀, 0.25 μg/ml), A. fumigatus(MIC₉₀, 0.12 μg/ml), P. boydii(MIC₅₀, 1 μ/ml) and Rhizopusspp (M1C₅₀, 1 μg/ml). By comparison with itraconazole, Sch 56592 was four- to eight-fold more active against isolates of Aspergillusand both compounds showed equipotent in vitroactivity against P. boydiiand Rhizopusspp. Sch 56592 was four- to 16-fold more active than amphotericin B against Aspergillusspp. and P. boydiiand both antifungal drugs displayed similar activity against Rhizopusspp. Overall, Sch 56592 showed good in vitroactivity against all isolates tested (MIC, ≤ 2 μg/ml) except isolates of Fusarium(MIC range, 1–>4 μg/ml). On the basis of these data Sch 56592 has promising activity against Aspergillus spp. and other species of filamentous fungi that are likely to be encountered clinically. Additional in vitroand in vivostudies are warranted. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rifampin-resistant RNA polymerase in spirochetes

Abstract Various free-living and host-associated spirochetes isolated by methods not involving rifampin were resistant to relatively high concentrations of this antibiotic. The lowest concentrations of rifampin that were inhibitory for the spirochetes ranged from 50 to more than 200 μ g/ml, depending on the species. The spirochete strains examined were at least 10-fold more resistant to rifampin than Escherichia coli and 10 000-fold more resistant than Staphylococcus aureus . The results support the conclusion that rifampin resistance is a general characteristic of spirochetes. Resistance of Spirochaeta aurantia to rifampin was not the result of detoxification of the antibiotic in the culture medium. The activity of spirochete DNA-dependent RNA polymerase in vitro was completely resistant to 10 μg of rifampin per ml, a concentration that totally inhibited E. coli RNA polymerase. Higher concentrations decreased the spirochetal activity. Thus, rifampin resistance may be due to a low affinity of spirochete RNA polymerase for the antibiotic.     

Fungicidal effect of hydrogen peroxide on fungal infection of rainbow trout eggs

Exposure to 1,500 μg/ml of hydrogen peroxide (H₂O₂) for 60 min at 13°C was found to be injurious to rainbow trout eggs. On the other hand, the concentration which effectively inhibited pathogenic fungi in vitro was substantially less than this toxic dosage; specifically, 500 μg/ml for 60 min at 20°C to inhibit the zoosporic stage and 1,000 μg/ml for 60 min at 20°C to inhibit the vegetative stage. From in vivo tests, treatment with 1,000 μg/ml of H₂O₂ for 60 min at 13°C was found to be the most effective procedure to control fungal infection and increase the hatching rate of rainbow trout eggs.     

The Effect of Monensin on Pure and Mixed Cultures of Rumen Bacteria

The antibiotic monensin was added to pure cultures of Bacteroides ruminicola, Selenomonas ruminantium, Anaerovibrio lipolytica and Megasphaera elsdenii. These organisms, representing succinate- and propionate-producing rumen bacteria, were not affected by monensin up to 10 μg/ml. Methanobacterium ruminantium was slightly inhibited by monensin, Butyrivibrio fibrisolvens, Ruminococcus albus and Streptococcus bovis were inhibited to differing extents by monensin at concentrations between 0.1 and 10 μg/ml. Bacteroides succinogenes was inhibited at first by monensin at >0.5 μg/ml but after a prolonged lag phase adapted to grow in the presence of monensin at concentrations below 5 μg/ml.
Monensin (1 μg/ml) almost completely stopped the digestion of chopped straw and dewaxed cotton fibres by rumen contents incubated in vitro. The digestion of grass and powdered filter paper was not significantly reduced under these conditions, but when the concentration of monensin was increased to between 3 and 5 μg/ml, the digestion of these substrates was reduced.     

Effect of chlorhexidine on a chlorhexidine-sensitive and a chlorhexidine-resistant strain of Providencia stuartii

The sensitivity and resistance of three strains of Providencia stuartii to various antibacterial agents, and especially to chlorhexidine, are described. Providencia stuartii Pv 2 was the most sensitive, and Pv 67 the most resistant, to chlorhexidine and to polymyxin B. These two strains took up approximately equal amounts of chlorhexidine from solution, but the biguanide had a considerably greater effect on the electrophoretic mobility of cells of strain Pv 2. Greater inner membrane damage (determined by the leakage of K⁺ and of pentoses) occurred with Pv 2. Chlorhexidine at 20 μg/ml achieved a 2-log reduction and 50 μg/ml a > 7-log reduction in viable numbers in strain Pv 2 over a 120 min contact period at 20C. In contrast, these concentrations induced < 0.5 log reduction in strain Pv 67.     

Changes in the faecal enterococcal population of young chickens and its effect on the incidence of resistance to certain antibiotics

The faecal enterococcal population of chickens, fed a ration containing no coc-cidiostat or growth-promoting antibiotic, was monitored during the first 23 d after purchase as day-old birds. The proportion of Enterococcus faecalis , the majority of which were resistant to streptomycin (60μg/ml) and tetracycline (30 μg/ml), fell during the first week while there was a corresponding increase in the proportion of Ent. gallinarum. Enterococcus faecium , half of which were resistant to cephalothin (30 μg/ml), increased during the first week but thereafter rarely exceeded a quarter of the enterococcal isolates. The changes in the relative proportion of these three bacterial species was reflected by changes in the incidence of resistance to these antibiotics in the enterococcal population as a whole.     

Antifungal effect of gaseous nitric oxide on mycelium growth, sporulation and spore germination of the postharvest horticulture pathogens, Aspergillus niger, Monilinia fructicola and Penicillium italicum

Aim:  To evaluate the antifungal activity of nitric oxide (NO) against the growth of the postharvest horticulture pathogens Aspergillus niger , Monilinia fructicola and Penicillium italicum under in vitro conditions.
Methods and Results:  Different volumes of NO gas were injected into the Petri dish headspace to obtain the desired concentrations of 50–500  μ l l⁻¹ . The growth of the fungi was measured for 8 days of incubation in air at 25°C . All concentrations of NO were found to produce an antifungal effect on spore germination, sporulation and mycelial growth of the three fungi, with the most effective concentration for A. niger and P. italicum being 100 and 500  μ l l⁻¹ for M. fructicola .
Conclusions:  Short-term exposure to a low concentration of NO gas was able to inhibit the subsequent growth of A. niger , M. fructicola and P. italicum .
Significance and Impact of the Study:  NO gas has potential use as a natural fungicide to inhibit microbial growth on postharvest fruit and vegetables.     

Antivibrio compounds produced by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. W3: characterisation and assessment of their safety to shrimps

In order to explore compounds naturallly inhibitory to shrimp pathogenic vibrios, a culture filtrate of Pseudomonas sp. W3 at a pH of 2 was extracted with ethyl acetate (EtOAc) to produce 82.15 mg/l of a yellow–brown extract (EtOAc-W3) that had MIC values of 225-450 μg/ml against the growth of 18 shrimp pathogenic Vibrio harveyi strains. The MIC of EtOAc-W3 against the most pathogenic strain PSU 2015 was 450 μg/ml and this strain had the lowest LD₅₀ (50% lethal dose) to pacific white shrimp (Litopenaeus vannamei, PL 21). At this MIC value, EtOAc-W3 in artificial sea water (ASW) killed strain PSU 2015; however in natural sea water, only a partial growth inhibition was observed. The toxicity to pacific white shrimp and antivibrio activity of the EtOAc-W3 were investigated by conducting an experiment with 4 sets; native control (commercial ASW), EtOAc-W3 control (MIC/10, 45 μg/ml), challenge (inoculation 6.0 × 10⁶ c.f.u./ml PSU 2015) and treatment (6.0 × 10⁶ c.f.u./ml PSU 2015 + 45 μg/ml EtOAc-W3). The same experiment was repeated by increasing the dose of EtOAc-W3 to 90 μg/ml (MIC/5). Both concentrations of EtOAc-W3 tested had no toxicity to postlarval shrimps. A significant decrease in shrimp mortality was observed over a 72 h period as approximately 80% of the shrimps died in each challenge set but only 63 and 23% died in the presence of 45 and 90 μg/ml EtOAc-W3. The major component of EtOAc-W3 was supposed to be 2-heptyl-4-quinolone (HHQ) by FAB-MS and ¹H-NMR analyses of the purified fraction.     

Biosorption of Ni, Cr and Cd by metal tolerant Aspergillus niger and Penicillium sp. using single and multi-metal solution

Fungi including Aspergillus and Penicillium, resistant to Ni2+, Cd2+, and Cr6+ were isolated from soil receiving long-term application of municipal wastewater mix with untreated industrial effluents of Aligarh, India. Metal tolerance in term of minimum inhibitory concentration (MIC) was 125-550 microg/ml for Cd, 300-850 microg/ml for Ni and 300-600 microg/ml for Cr against test fungi. Two isolates, Aspergillus niger and Penicillium sp. were tested for their Cr, Ni and Cd biosorption potential using alkali treated, dried and powdered mycelium. Biosorption experiment was conducted in 100 ml of solution at three initial metal concentrations i.e., 2, 4 and 6 mM with contact time (18 hr) and pretreated fungal biomass (0.1g) at 25 degrees C. Biosorption of all metals was found higher at 4 mM initial metal concentration as compared to biosorption at 2 and 6 mM concentrations. At 4 mM initial metal concentration, chromium biosorption was 18.05 and 19.3 mg/g of Aspergillus and Penicillium biomasses, respectively. Similarly, biosorption of Cd and Ni ions was also maximum at 4 mM initial metal concentration by Aspergillus (19.4 mg/g for Cd and 25.05 mg/g of biomass for Ni) and Penicillium (18.6 mg/g for Cd and 17.9 mg/g of biomass for Ni). In general, biosorption of metal was influenced by initial metal concentration and type of the test fungi. The results indicated that fungi of metal contaminated soil have high level of metal tolerance and biosorption properties.     

Susceptibility to Phosphomycin as a Differential Character for Gram Negative Anaerobic Bacilli

On the basis of their sensitivity to phosphomycin, various species of anaerobic Gram negative bacilli examined fell into one of two groups. All strains of Bacteroides were resistant to 500 umg/ml whereas strains of Fusobacterium were uniformly sensitive to 62.5 μg/ml. Disc sensitivity testing to phosphomycin at concentrations of 200–500 μg/ml provides a reliable and rapid means of distinguishing fusobacteria from bacteroides.     

Fermentation studies on roselle (Hibiscus sabdariffa) calyx neutralized with trona (sodium sesquicarbonate) at different concentrations

The effect of trona at different concentrations on the fermentation of roselle (Hibiscus sabdariffa) calyx was studied. Mixed flora of bacteria and fungi were isolated and identified from the fermenting calyx. The isolates were Micrococcus luteus, Staphylococcus aureus, Echerichia coli, Bacillus subtilis, Saccharomyces cerevisiae, Aspergillus niger and A. flavus. The addition of trona to the samples raised the initial pH which affected the terminal pH. There was an increase in microbial population with increases in the concentration of trona, especially for bacterial population which ranged from 5.18 to 5.59 log10 c.f.u./ml. The changes in total titratable acidity level were inconsistent. Fermentation enhanced the protein content of the samples but significantly decreased (P < 0.05) the content of antinutritional factors (phytic acid and tannin).     

Efficacy of Novel Antimicrobials Against Clinical Isolates of Opportunistic Amebas

ABSTRACT We examined the effects of the macrolide antimicrobial agent azithromycin and phenothiazine compounds against clinical isolates of Acanthamoeba spp. and Balamuthia mandrillaris , opportunistic pathogens of human beings and other animals. Acanthamoeba growth was inhibited in vitro at 1,5, and 10 μg/ml of azithromycin, but not the macrolides, erythromycin, and clarithromycin. In experiments attempting to simulate in vivo conditions, azithromycin protected monolayers of rat glioma cells from destruction by Acanthamoeba at a concentration of 0.1 μg/ml, and delayed destruction at concentrations of 0.001 and 0.01 μg/ml. We concluded that the minimal inhibitory concentration of azithromycin was 0.1 μg/ml. Our results, however, suggested that the drug was amebastatic but not amebicidal, since ameba growth eventually resumed after drug removal. The phenothiazines (chlorpromazine, chlorprothixene, and triflupromazine) inhibited Acanthamoeba growth by 70-90% at 5 and 10 μg/ml, but some of these compounds were toxic for rat glioma cells at 10 μg/ml. Azithromycin was not very effective against B. mandrillaris in an in vitro setting, but was amebastatic in tissue culture monolayers at concentrations of 0.1 μg/ml and higher. Balamuthia amebas showed in vitro sensitivity to phenothiazines. Ameba growth was inhibited 30-45% at 5 μg/ml in vitro, but completely at 5 μg/ml in the rat glioma model. In spite of their potential as antiamebic drugs in Balamuthia infections, toxicity of phenothiazines limits their use in clinical settings.     

Antibiotics and the Oral Streptococci of Man

The effects of 3 antibiotics, phenoxymethylpenicillin, cephalexin and clindamycin on the normal oral streptococcal flora in the region of the gingival crevice were investigated because these organisms are able to cause subacute bacterial endocarditis. Secretion of these antibiotics into the oral cavity was also examined. Penicillin and clindamycin exerted marked effects on the normal oral streptococci, whereas cephalexin did not cause any obvious change in the total flora. Following penicillin therapy, streptococci resistant to 1.5 μg/ml penicillin were observed and these organisms could be detected at least 8 weeks after the last dose of the antibiotic. They probably arose by selection from the mixed flora. Following cephalexin therapy, a much lower proportion of streptococci resistant to 15 μg/ml was found. The proportion of resistant strains fluctuated appreciably, however, probably due to their transient nature. Streptococci resistant to 1 μg/ml clindamycin were not observed in 10 out of 11 treated subjects.
Penicillin and clindamycin could be detected in the pooled saliva and gingival fluid after administering single doses of 500 mg and 300 mg, respectively. The peak levels were obtained between half and 1 h. The concentration of penicillin dropped rapidly within 3 h but clindamycin could be detected at significant levels for at least 6 h. No cephalexin could be detected in the pooled saliva or gingival fluid after a 500 mg dose. The implications of these findings in the prevention of subacute bacterial endocarditis are discussed.     

Tunicamycin-resistant mutants of Bacillus amyloliquefaciens are deficient in amylase, protease and penicillinase synthesis and have altered sensitivity to antibiotics and autolysis

Mutants of Bacillus amyloliquefaciens resistant to at least 10 μg/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile.     

A carbon source-dependent antimetabolite sensitivity test in Bacillus megaterium B71 for isolation of ethionine resistant mutants

Alteration of carbon sources significantly altered the analogue sensitivity of Bacillus megaterium B71. DL-Ethionine (ETN) was highly inhibitory with glucose, mannitol, sucrose, citrate, glycerol and arabinose. DL-Norleucine, L-homoserine and S(2'-aminoethyl)-L-cysteine were either highly inhibitory, slightly inhibitory or non-inhibitory depending on the carbon sources used. Maltose markedly overcame the inhibitory effect of ETN in liquid culture. Uninhibited growth was poor on citrate and arabinose when compared with other carbon sources. Six carbon sources showing comparable growth were used to determine minimum inhibitory concentrations (MIC) of the analogues. The MIC of ETN was highest (450 μg/ml) with maltose and lowest (4 μg/ml) with mannitol. ETN sensitivity was inversely related to the endogenous L-methionine pool size, and was relatively low with mannitol which was used to isolate ETN resistant mutants of B. megaterium B71. The best mutant BUE-118 produced 435 μg/ml of L-methionine.     

Resistance of Pseudomonas aeruginosa to gentamicin

The resistance to gentamicin 4 μg./ml. of 250 Pseudomonas aeruginosa isolates was measured by a proportion method. Twenty-eight (11.2%) of the cultures fell into the most resistant group, in whose populations between 10 and 100% of the organisms were resistant. A relatively high percentage of urinary isolates and a comparatively low percentage of isolates from respiratory sources occurred in this group. Three of the 28 were resistant to carbenicillin 150 μg./ml. and 6 of 18 tested were as resistant to gentamicin 8 μg./ml. as they were to 4 μg./ml. The distribution of Ps. aeruginosa isolates between the different grades of resistance did not change significantly during the 10 months in which the survey was performed.