ABSTRACT
The response of the antimicrobial compounds sulfamethoxazole (SMX) and trimethoprim (TMP) - individually and in mixtures - to ionizing radiation was investigated using laboratory prepared mixtures and a commercial pharmaceutical formulation. The residual antibacterial activity of the solutions was monitored using Staphylococcus aureus and Escherichia coli test strains. Based on antibacterial activity, SMX was more susceptible to ionizing radiation as compared to TMP. The antibacterial activity of SMX and TMP was completely eliminated at 0.2 kGy and 0.8 kGy, respectively. However, when SMX and TMP were in a mixture, the dose required to eliminate the antibacterial activity was 10 kGy, implying a synergistic antibacterial activity when these are present in mixtures. Only when the antibiotic concentration was below the Minimum Inhibitory Concentration of TMP (i.e., 2 µmol dm-3) did the antibacterial activity of the SMX and TMP mixture disappear. These results imply that the synergistic antimicrobial activity of antimicrobial compounds in pharmaceutical waste streams is a strong possibility. Therefore, antimicrobial activity assays should be included when evaluating the use of ionizing radiation technology for the remediation of pharmaceutical or municipal waste streams.
Subject(s)
Bacteria/drug effects , Bacteria/radiation effects , Radiation, Ionizing , Sulfamethoxazole/pharmacology , Trimethoprim/pharmacology , Anti-Bacterial Agents/pharmacology , Anti-Bacterial Agents/radiation effects , Anti-Infective Agents/pharmacology , Anti-Infective Agents/radiation effects , Bacteria/growth & development , Biological Oxygen Demand Analysis , Escherichia coli/drug effects , Escherichia coli/radiation effects , Humans , Microbial Sensitivity Tests , Staphylococcus aureus/drug effects , Staphylococcus aureus/radiation effects , Sulfamethoxazole/radiation effects , Trimethoprim/radiation effects , Trimethoprim, Sulfamethoxazole Drug CombinationABSTRACT
Heat resistance of Lactobacillus bulgaricus in skimmed milk at 62 degrees, 64 degrees, 65 degrees and 66 degrees C was studied. The response to increasing temperatures in this range was not linear, with temperatures at 65 degrees C and above giving a lower survival rate than would be predicted from experiments at lower temperatures. To identify sites of injury at these temperatures, chemical markers were used. Heating at 64 degrees C and below resulted in damage to the cytoplasmic membrane. At temperatures of 65 degrees C and above chemical markers also indicated damage in the cell wall and proteins. Using differential scanning calorimetry analysis of whole cells of Lact. bulgaricus seven main peaks were observed (1-51, m1-61, m2-73, n-80, p-89, q-100, r-112 degrees C). Three of these peaks (l(r), m(r) and p(r)) were the result of reversible reactions. Analysis of cell fractions identified the cell structure involved in giving rise to each of the three reversible peaks; l(r), cell membrane lipids, m(r), ribosomes, and p(r), DNA. The evidence presented in this paper shows that irreversible reactions in the cell ribosomes are a critical site of damage in Lact. bulgaricus during heat stress in liquid media at 65 degrees C and above.
Subject(s)
Lactobacillus/growth & development , Lactobacillus/metabolism , Milk/microbiology , Animals , Bacteriological Techniques , Fermentation , Hot Temperature , Hydrogen-Ion Concentration , Stress, Physiological/physiopathologyABSTRACT
Heat destruction of seven foodborne microorganisms (Lactobacillus plantarum, Lactobacillus brevis, Saccharomyces cerevisiae, Zygosaccharomyces bailii, Yarrowia lipolytica, Paecilomyces varioti and Neosartoria fischeri) as a function of the temperature, pH, redox potential and water activity was studied in synthetic heating media. Several mathematical models were developed for describing the heat destruction rate, most of them resulted in a good correlation between the fitted and measured values. The determination coefficients of the model-fitting were the best in case of lactobacilli and moulds (0.96-0.99) and the worst in case of the yeasts (0.81-0.88).
