Effect of short HV pulses on bacteria and fungi

The survival of three kinds of microorganisms under strongpulse electric field conditions was investigated with a possible application of the electric pulse method for sterilization of consumable liquids. The results of the investigations of survival ratio of Gram-negative (Escherichia coli, Yersinia enterocolitica) and Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacteria and yeastlike fungi (Candida albicans) are presented. The HV pulses with peak voltage U = 0 to 100 kV and rise time t, = 0.5 to 1.2 ps were applied. The microorganisms were suspended in an NaCl solution with 7 = 6 to 13 mS/cm conductivity and pH = 7.2. The experimental setup and the dependency of the microorganism survival ratio on the rise time, peak voltage and on the number of pulses applied, are presented. It has been found that the lethal effect on microorganisms caused by HV pulses depends on the pulse parameters as well as on the kind of microorganism being treated

Adhesion of Malassezia pachydermatis of different growth type to canine epithelial cells

A total of 100 Malassezia pachydermatis strains recovered from skin and mucosal membranes of dogs were evaluated for their adhesive properties. Two types of growth, related to colony morphology on Sabouraud agar, were observed (type I and II). The mean number of fungal cells attaching to canine buccal epithelial cells was found to be 17. The number of adhered cells was greater (statistically significant at the level of p < 0.01) in strains belonging to the type I

Inactivation of Yersinia enterocolitica Gram-negative bacteria using high voltage technique

High voltage pulses of peak voltages U=5-75 kV and rise times tp=500-1300 ns were applied with repetition frequency f=lHz in order to cause the irreversible electroporation of Gram negative bacteria Yersinia enterocolitica. The bacteria were suspended in NaCl solution of pH=7.2 and conductivity y ~0.8-1.3 S/m. The suspension was placed in glass tube immersed in the cylindrical electrode system gap filled with distilled water. Such an electrode system will protect the bacteria suspension from the chemical processes at the electrode-liquid interface due to conduction and pre-breakdown phenomena. The current chopping electrode system was connected in parallel to the sample in order to avoid heat generation from direct discharge of the pulse through the suspension. The dependence of the survival ratio s=N/No (the number of bacteria per cm3 after pulse treatment, N, divided by the number of bacteria per cm3 before treatment, NJ of Y. enterocolitica on peak voltage of the pulse, number of pulses applied and on various rise times of pulses have been measured. The reduction by 6 orders of magnitude of Y. enterocolitica living cells per cm3 was achieved. The results show that considerable inactivation of microbes can be achieved by the application of short (tp 4000 ns) high voltage pulses for bacteria suspension without directly exposing the bacteria suspension to the electrodes. It is therefore possible to use the electrode system proposed as a means for sterilization of liquid foods

Invasiveness of Listeria monocytogenes strains isolated from animals in Poland

Animals are important reservoir of Listeria monocytogenes, a pathogen causing serious infections in both humans and livestock. However, data on invasiveness of L. monocytogenes strains of animal origin is very scarce. Ability of 18 L. monocytogenes strains of animal origin to invade HT- 9 cells was investigated. Plaque forming assay was used to assess invasiveness and ability of the pathogen to spread in the cell line. Almost 40% of L. monocytogenes strains were weakly invasive. It was shown that strains from serogroup 4b exhibited the highest invasiveness, whereas serogroup 1/2b consisted of strains of invasiveness below 0.0001%. Analysis of translated inlA and inlB gene sequences revealed no premature stop codons. Lineage-specific mutations in low invasive strains were identified within inlA and inlB sequences. Our results demonstrate high incidence of low invasive animal L. Monocytogenes strains, which may be at least partly explained by unique point mutations in the InlA and InlB