Journal of microorganism control最新文献

Earlobes, nasal cavities, and fingers of 145 healthcare workers in convalescent and rehabilitation hospital (60 nurses and 85 rehabilitation healthcare workers) were sampled. Of the 3 sites sampled, Staphylococcus aureus was detected in one or more sites in 25 nurses and 27 rehabilitation workers. S. aureus was detected in all 3 sites in 2 (8.0%) nurses and 2 (7.4%) rehabilitation workers, and the S. aureus isolates in each case showed related PFGE pattern. S. aureus was detected in both the fingers and nasal cavities of 5 (18.5%) of the rehabilitation healthcare workers; in all 5 cases, the PFGE patterns of the S. aureus isolates from each site belonged to same cluster based on PFGE. Of the 2 cases in which methicillinresistant S. aureus (MRSA) was recovered from earlobes, fingers, and nasal cavities, in both cases, MRSA isolates from the 3 sites were the same clone according to PFGE analysis and SCCmec type IV. As S. aureus was detected in pierced earlobes of nurses, hand hygiene must be practiced after touching pierced earlobes and before patient contact. The same S. aureus clone in the nasal cavity and earlobes indicates that the route of transmission is through the fingers.

Bacillary necrosis of pangasius (BNP) is a disease caused by Edwardsiella ictaluri bacteria in striped catfish Pangasianodon hypophthalmus that results in high mortality rates. To control this disease, bacteriophages have been considered as alternatives to antibiotics. In this study, we applied the lytic bacteriophage PVN06 in striped catfish fingerlings to prevent E. ictaluri infection. In an experimental trial, the phage was administered to fish by feeding phage-coated feed with doses of 7.17±0.09, 8.17±0.09 and 9.17±0.09 log PFU/g feed per day before bacterial infection. Fish were infected by bacteria once with concentrations ranging from 3.01 to 7.01 log CFU/ml tank water. A day after infection, phage treatment resumed at a rate of once per day until the end of the trial. The results of the trial show that bacterial infection caused typical symptoms of BNP in fish with the cumulative fish death rate of 36.7±2.9 to 75.0±5.0%, depending on the bacterial concentration used for infection. Phage treatment with 9.17±0.09 log PFU/g significantly reduced the mortality rate, while treatments with 8.17±0.09 and 7.17±0.09 log PFU/g did not. This phage dose resulted in a 61.7-fold reduction in the toxicity of the bacterial pathogen and the survival rate of 15-23.3% in fish. Our study has demonstrated that the bacteriophage PVN06 protected striped catfish from BNP.

Many gram-negative pathogens can activate virulence factors under the control of N-acylhomoserine lactone (AHL）-mediated quorum sensing. AHL-degrading enzymes have been investigated for their application in disease control. Trichoderma is a genus of fungi inhabiting various types of soil and are widely used as biocontrol agents for plant pathogens. When the AHL-degrading activity of 33 strains belonging to Trichoderma species was investigated, most strains can degrade AHL. AHL lactonase catalyzes AHL ring opening by hydrolyzing lactone. Two model strains, Trichoderma atroviride MAFF 242473 and MAFF 242475, degrade AHL using their AHL lactonase activity and rapidly metabolize ring-opening AHL. Moreover, co-inoculation with MAFF 242473 and MAFF 242475 effectively inhibited AHL production by the plant pathogens, Pantoea ananatis and Pectobacterium carotovorum subsp. carotovorum. Our study suggested that Trichoderma might be an effective biocontrol agent to inhibit the expression of virulence factors via AHL-mediated quorum sensing.

Shredded cabbage treated with either tap water or electrolyzed water was stored in an active modified atmosphere packaging (MAP) of 10% CO₂ for 5 d at 10℃, 7 d at 5℃, and 8 d at 1℃ to evaluate the occurrence and viability of sublethally injured coliform bacteria. The CO₂ and O₂ concentrations in the packages approached an equilibrium of 10% CO₂ and 10% O₂ during storage at all temperatures tested. Coliforms in shredded cabbage increased during storage at all three temperatures, with the increase being greater at 10℃. Sublethal injury at 65% to 69% for the coliforms was detected only on cabbage samples treated with electrolyzed water and stored at 5℃ for 4 and 7 d. Enterobacter cloacae was one of the injured species of coliform bacteria in shredded cabbage. Shredded cabbage was inoculated with chlorine-injured Escherichia coli O157:H7 and stored at 5℃ for 6 d in an active MAP of 10% CO₂. Counts of E. coli O157:H7 remained almost constant during storage, and injured E. coli O157:H7 ranging from 50% to 70% were found on shredded cabbage throughout the storage period. These results indicate that sublethally injured indicator and pathogenic bacteria would be found on fresh-cut cabbage in the realistic MAP storage at 5℃.

The inactivation of Vibrio parahaemolyticus cells attached to a polyethylene terephthalate (PET) disc in a sodium chlorite (NaClO₂) solution was kinetically studied in a weakly acidic pH range of 4.0 - 6.5. The logarithmic reduction in the survival ratio depended on the concentration-time product. All inactivation curves showed a linear reduction phase, and the reduction in viable cells was greater than 4-log. No significant desorption of attached cells was observed during the inactivation treatment. The first-order inactivation rate constant (k) increased by approximately 4.5-fold for every 1.0 unit fall in pH. At all pH values, the k values calculated for the attached cells were approximately half of those for the unattached cells. These findings indicate that a weakly acidic NaClO₂ solution is effective in inactivating bacteria attached to hard surfaces.

Fatalities caused by pneumonia and underlying diseases from COVID-19 infection show the highest relative frequency among elderly people. Long-term care facilities for elderly people have continued to be the areas most vulnerable to COVID-19. We examined the effectiveness of training for infection control and COVID-19 at elderly care facilities. After sending questionnaires to all long-term elderly care facilities in Ibaraki prefecture, Japan during January 18-29, 2022, we received useful responses from 98 facilities. Using logistic regression, we regressed a dummy variable for outbreak experience to dummy variables representing routine but partial training, routine training for all staff members, long-term care facilities for elderly people, numbers of nurses, and numbers of residents. Outbreak experiences of two types were inferred, as represented by a dummy variable for a COVID-19 outbreak at the facility, and by a dummy variable for outbreak experience at the facility before COVID-19 was found. Multivariate analysis indicated routine training for all staff members as the most effective, in fact the only effective, countermeasure against COVID-19 outbreak.

Various combination treatments are used for microorganism control in food, medicine, and the environment. Especially in food, combination treatments have been studied using antimicrobial compounds in pasteurization and sterilization but comprehensive quantitative evaluation methods, have not yet been established to evaluate their effectiveness. This review introduces the author's recently published methods for evaluating the effects of combination treatments on the control of harmful microorganisms in food. Particularly important items are 1) the type of action of the control treatment and the mode of the combined method, 2) the choice of endpoint method and growth delay method for analytical evaluation, 3) the construction of extended isobolography that allows the application of conventional isobologram (IBo) for chemicals to various control methods, 4) the extended use of combined index (CI）, and 5) the introduction of synergistic parameter (SP) for quantitative evaluation of synergistic effects. In addition, I describe the characteristics of the action of antimicrobial compounds and disinfectants in their combined effects with heating, and insist on the advantages of using combined treatments and their evaluation methods in the food industry.

This study aimed to clarify how the phenolic monoterpene carvacrol and its structural isomer thymol both as essential oil components (EOCs) inhibit the germination of Bacillus subtilis spore. Germination was evaluated by the OD₆₀₀ reduction rate in a growth medium and phosphate buffer containing either l-alanine (l-Ala) system or l-asparagine, d-glucose, d-fructose plus KCl (AGFK) system. The germination of the wild-type spores in the Trypticase Soy broth (TSB) was found to be greatly inhibited by thymol than by carvacrol. Such a difference in the germination inhibition was confirmed by the dipicolinic acid (DPA) release from germinating spores in the AGFK buffer system, but not in the l-Ala system. Similar to the wild-type spores, no difference in the inhibitory activity between the EOCs was also indicated with the gerB, gerK-deletion mutant spores in the l-Ala buffer system and the above substantial difference was also done with the gerA-deleted mutant spores in the AGFK. Fructose was found to release spores from the EOC inhibition and inversely even stimulated. Increased concentrations of glucose and fructose partially suppressed the germination inhibition by carvacrol. The results obtained should contribute to the elucidation of the control effects of these EOCs on bacterial spores in foods.

The concentration of the indoor gaseous hypochlorous acid (HOCl _(g)) varied significantly during disinfection. The kinetics of self-decomposition of HOCl _(g) was studied at temperatures within the range of 10℃ to 40℃ and relative humidity between 30% RH and 90% RH in a lab-scale confined polyvinylidene fluoride gas bag space. The decay curve of HOCl _(g) , obtained by plotting the logarithm of the HOCl _(g) concentration against time, was analyzed using an integrated model that showed two simultaneous first-order processes. One process was assumed to be the adsorption of HOCl _(g) onto the gas bag surface, whereas the other was the self-decomposition of HOCl ^_(g) in the gas space. The decay curve is reduced to the sum of two independent and simultaneous first-order processes. The decay rate constant for self-decomposition depended on temperature and relative humidity. The half-life time of HOCl _(g) was estimated to be between 76.9 h and 116 h depending on the temperature and relative humidity conditions.