D. V. Vadehra

Susceptibility of multidrug-resistant isolates of Klebsiella pneumoniae to silver nitrate

Multidrug-resistant (MDR) clinical isolates ofKlebsiella pneumoniae were checked for their sensitivity toward silver nitrate by the tube-dilution method. Nearly 75% of MDR strains clould be successfully inhibited by 5 mg/L of silver nitrate. A significant correlation was observed between incidence of silver and trimoxazole resistance and silver and kanamycin resistance in these isolates. The genetic linkage of these two properties could not be proved since simultaneous curing and co-transfer studies gave negative results.

Effect of metal ions on aflatoxin production by Aspergillus parasiticus

The effect of iron, copper, cobalt, cadmium, zinc, molybdenum, magnesium and manganese salts was studied on aflatoxin production in relation to mycelial mass. Iron, copper and cadmium salts decreased the aflatoxin production to different levels but a mixed trend was observed depending on salt concentration, with molybdenum, magnesium and manganese. Cobalt and zinc salts stimulated aflatoxin production at all concentrations studied. The maximum increase in aflatoxin production, 655 % and 519 % was observed in the presence of zinc sulfate and sodium molybdate, respectively. A negative correlation was observed between aflatoxin production and vegetative growth of fungus.

Mechanism of action of aflatoxin B1

The inhibitory effects of aflatoxin B1 were found to be related to the gram character in procaryotes, used in this study. Ethylene diamine tetra chloroacetic acid (0.05% w/v) or Tween-80 (0.05 % v/v) addition accentuated the aflatoxin B1 growth inhibition inSalmonella typhi andEscherichia coli at different pH values. The inhibition of lipase production was only 5–20 % inPseudomonas fluorescence ca. 25–48% inStaphylococcus aureus andBacillus cereus at different aflatoxin B1 concentrations (4–16μg/ml).However, inhibition of α-amylase induction was complete in1Bacillus megaterium whereas the inhibition was partial inPseudomonas fluorescence (27–40%) at 32μg aflatoxin B1 concentration. An increase in leakage of cell contents and decreased inulin uptake were observed in toxin incubated sheep red blood cell suspension (1 %) with increased aflatoxin B1 concentration

Factors affecting intra-and extracellular phospholipase A1 production by salmonella newport

The effect of various physico-chemical factors on production of intra- and extracellular phospholipase A1 bySalmonella newport was investigated. Maximum intracellular enzyme levels were observed when cells were grown in brain heart infusion broth, after 12 h of incubation at 37°C. Highest level of extracellular phospholipase A1, however, was seen in synthetic medium (pH 7.0) after 24 h of incubation at 37°C. Agitation during incubation had no effect on the intracellular enzyme synthesis but enhanced extracellular enzyme levels. Addition of surfactants to the growth media significantly decreased both intra- and extracellular phospholipase A1 production.

Effect of various inducing agents on bacteriocin (klebocin) production by Klebsiella pneumoniae

The influence of various inducing agents on growth, synthesis and release of klebocin byKlebsiella pneumoniae was studied. A significant level of klebocin was detected only after induction. The highest level of klebocin was achieved with mitomycin C followed by rifampicin and polymyxin B. Chloramphenicol and UV irradiation did not show any effect on klebocin production. Maximum klebocin release occurred after 8 h of induction with all the agents. Concentration of mitomycin C did not show any significant effect on klebocin production.

Drug Resistance Patterns and Susceptibility to Aflatoxin B1 of Strains of Escherichia Coli and Staphylococcus Aureus

The antibacterial properties of aflatoxin B1 have been evaluated against antibiotic-resistant clinical isolates of Escherichia coli and Staphylococcus aureus. The inhibition of growth ranged from 11.5 to 60.0% and 4.5 to 18.5% in the strains of S. aureus and E. coli, depending on the extent of drug resistance. Aflatoxin-B1 binding varied with toxin concentration, the presence of surfactants (Tween-80 or EDTA) as well as with the antibiotic-resistance pattern; binding was maximal in antibiotic-sensitive strains and least in the most resistant strains. Binding of aflatoxin B1, correlated with growth inhibition. Aflatoxin B1 also caused leakage of cell contents and decrease in inulin uptake, effects which were also concentration dependent.

Evidence for a chromosomally determined bacteriocin production byKlebsiella pneumoniae

Location of the genes responsible for pneumocin production inKlebsiella pneumoniae was examined by classical procedures. Conjugal intrageneric transfers, elimination experiments with various curing agents, high temperature and plasmid isolation procedures showed that this strain did not harbour any plasmid. Hence chromosomal location of the genetic determinants is suggested.

Effect of medium on the bacteriocin production byKlebsiella pneumoniae

The influence of growth media and media constituents on bacteriocin production byKlebsiella pneumoniae was studied. Among the standard laboratory media used trypticase soy broth (TSB) showed the maximum production and poor yields resulted from growth in peptone water and nutrient broth. A number of peptones differed in their bacteriocin production. Best yields were observed in tryptone and proteose peptone water. Addition of 1 % yeast extract to TSB further stimulated bacteriocin production. However, activity was low when glucose, glycine, sodium mercaptoacetate or bile salt mixture were added to the medium. Supression of synthesis by certain agents as well as inhibition of formed bacteriocin by the others appears to affect the bacteriocin yield. No proteinase activity was detected during the entire incubation period.

Effect of nutritional factors on aflatoxin B1 inhibition of growth inEscherichia coli andSalmonella typhi

The extent of growth inhibition by aflatoxin B1 inS. typhi andE. coli was greater in the presence of sodium citrate or sodium phosphate, palmitic and stearic acid than aflatoxin B1 alone. The addition of amino acids (glycine or glutamic acid) stimulated growth inE. coli and inhibited inS. typhi in the presence of aflatoxin B1. Other nutrients, such as yeast extract, lactose, or salt addition did not alter aflatoxin B1 antibacterial activity but decreased growth was observed in the presence of peptone.