effect of organic acids and nisin at sub-minimum inhibitory concentrations on growth of a strain of bacillus cereus isolated from cheese

One of the methods for preserving foods is decontamination by using food preservatives. Food preservatives exert antagonistic effects on microorganisms through interference with the structure and function of their cell membrane, enzyme action, or genetic structure. The effects of different preservatives on the growth of Bacillus cereus isolated from cheese were determined. First the growth curve of the bacteria was studied without addition of the preservatives. Then the curve was re-drawn after adding acetic acid and nisin as a chemical and a natural preservative, respectively, at sub-minimum inhibitory concentrations [sub-MIC]. Finally growth curves were drawn in the presence of both citric acid and potassium sorbate at different concentrations, the pH changes being determined. Bacillus cereus did not grow well in acetic acid at a concentration of half-MIC, and the pH was 5 and did not change. However, it caused changes in the pH at 1/4-MIC and 1/8-MIC of acetic acid and grew. Furthermore, it could increase the pH in the presence of nisin and grow after a lag phase of 12 hours. The simultaneous use of citric acid and potassium sorbate showed a synergistic preservative effect. Bacillus cereus isolated from cheese is resistant to sub-MIC concentrations of different preservatives. Therefore, it is recommended not to use preservatives at such concentrations

[Study of pseudomonas aeruginosa from nosocomial infection with multi resistance]

Background and Objective: The incorrect and unsuitable use of antibiotics affects on the transfer of antibiotic resistance. Since, pseudomonas aeruginosa is one of the most serious pathogenic bacteria in hospitals and it is resistant to different antibiotics and it has created therapeutic problems for physicians, this study was done to determine the multiple resistance in pseudomonas aeruginosa against antibiotics, arsenate and metals

Methods: In this study, 23 strains of P.aeruginosa isolated from clinical samples. They were tested against the antibiotics penicillin groups by Kirby-Bauer test. MIC and MBC of antibiotics and heavy metals [Cadmium, mercury] and arsenate were measured respectively by broth and agar dilution and grown on agar plate methods

Findings: In this method, the most and less MIC against heavy metals were cadmium [0.6, 4.9 microg/ml], mercury [<0.12, 4 microg/ml] and arsenate [8×10[3], 256×10[3] microg/ml]. Of 23 strains of P.aeruginosa, 84% were resistant against antibiotics carbenicillin, 63% to piperacillin and 100% to metals cadmium and arsenate. 82.6% of these strains were resistant to mercury

Conclusion: So our results showed that these strains are generally multi-resistant to antibiotics carbenicillin, piperacillin, arsenate and metals