Journal of microorganism control最新文献

For microbiological management of water quality, it is important to identify bacteria and to understand the community structure. To analyze the community structure during water purification and distribution, we selected a distribution system in which water from other water treatment facilities was not mixed with the target water. Changes in the bacterial community structure during treatment and distribution processes in a slow filtration water treatment facility were analyzed using 16S rRNA gene amplicon sequencing with a portable sequencer MinION. The microbial diversity was reduced by chlorination. The genus level diversity increased during distribution and this diversity was maintained through to the terminal tap water. Yersinia and Aeromonas were dominant in the intake water, and Legionella was dominant in the slow sand filtered water. Chlorination greatly reduced the relative abundance of Yersinia, Aeromonas, and Legionella, and these bacteria were not detected in the terminal tap water. Sphingomonas, Starkeya and Methylobacterium became dominant in the water after chlorination. These bacteria could be used as important indicator bacteria to provide useful information for microbiological control in drinking water distribution systems.

Hypochlorous acid (HOCl) is an active species in the chlorination process. Hypochlorite salts that release hypochlorite ion (OCl^-) have been used for more than 200 years as disinfecting, cleaning, deodorizing, and decolorizing agents in various technological fields. In the food industry, sodium hypochlorite is the most widely used among chlorine compounds. The antimicrobial activity of a dilute hypochlorite solution is attributed largely to HOCl because of its cell membrane permeability. OCl^- exhibits an excellent cleaning action for organic soils on solid surfaces. HOCl has been used as an aqueous solution, and its objects to be treated are things. In hypochlorite solution, HOCl is volatile and easily volatilized by stirring, bubbling, atomizing, or forced-air vaporization. On the other hand, OCl^- is non-volatile and stays in the solution. Recently, the scope of objects to be treated with hypochlorite solution has been expanded to indoor spaces, and the use of gaseous hypochlorous acid (HOCl_（g) ) has been studied intensively. This review describes the mechanisms of actions of hypochlorous acid as liquid-based and gaseous disinfectants and provides the evidence for the safety and effectiveness of HOCl_（g) for controlling microorganisms in indoor spaces.

The comparison of the inactivation rate of SARS-CoV-2 by ozone in water with that in gas, based on data from references and experiments, has indicated the inactivation rate of the former is remarkably higher than that of the latter. To investigate the reason for this difference, we analyzed the reaction rate using a diffusional reaction model, in which ozone is carried by micro spherical viruses to inactivate the target viruses. Using this model, we can evaluate the amount of ozone required to inactivate a virus based on the ct value. We found that inactivation in gas phase requires 10¹⁴-10¹⁵ ozone molecules per virus virion, while the inactivation in aqueous phase requires 5×10¹⁰ to 5×10¹¹ ozone molecules. This implies that the efficiency in gas phase is 200-20,000 times lower than that in aqueous phase. This is not attributed to the lower probability of collision in gas phase than in aqueous phase. Rather, it may be due to the fact that the ozone and radicals generated by ozone react and subsequently dissipate. We proposed the diffusion of ozone into a spherical virus at a steady state and the decomposition reaction model through radicals.

A new concept of injured population assessment is proposed, in which the size of the injured population in stressed mold spores is evaluated by analyzing the colony formation process on a solid agar medium. In this method, a small paper disc containing mold spores is placed on a subculture agar plate, and the linear increase in the radius of the colony formed by development from the spore is measured over time. Then, the principle of the previously reported growth delay analysis (GDA) method originally using a liquid medium is applied to obtain the integrated viable ratio (IV) of the stressed population from the delay time relative to the growth of the unstressed population. On the other hand, the viable ratio (V) to the initial value as the colony count obtained with the stressed culture is obtained; the difference between the logarithms of V and IV is determined as the log number of the injured population. Applying this analysis method to heated spores of Cladosporium sphaerospermum, we determined the size of the injured population that occurred. This method was considered to be effective as a new method for quantifying injured populations using a solid medium.

The transmission of potentially life-threatening plasmid-mediated antibiotic-resistant bacteria poses a major threat to public health. This study aimed to determine the presence of commonly observed plasmids encoding plasmid-mediated antibiotic-resistance genes in Salmonella and Escherichia coli isolates from fishery products. Eighty river fishes were purchased from retail stores and supermarkets in Vietnam. Only Salmonella-positive fishes were used for antibiotic-resistant E. coli isolation. Salmonella serotyping was performed using Salmonella antisera. Isolated bacterial DNA was extracted, and antibiotic susceptibility, resistance genes, and replicon typing were determined. Our results showed that Salmonella was isolated from 12.5% (10/80) of the river fishes. Cefotaxime-resistant Salmonella was isolated from 3.8% (3/80) of the fishes and colistin-resistant Salmonella from 1.3% (1/80) . Salmonella serotyping revealed Potsdam, Schwarzengrund, Bardo/Newport, Give, Infantis, Kentucky, and Typhimurium. Multiplex polymerase chain reaction revealed the presence of extended-spectrum β-lactamase-related genes bla_CTX-M-55 and bla_CTX-M-65 and the colistin resistance gene mcr-1. To date, no study has reported an antibiotic-resistance plasmid present in multiple bacteria collected from the same food. Thus, horizontal transmission of antibiotic-resistance plasmids may occur at the food level.

Bedside dialysis monitoring equipment for hemodialysis are located in the bioburden section upstream of the endotoxin-retentive filter for dialysis fluid sterilization. We observed 26 equipment at our institution for bacterial contamination at least once every 4 weeks for 5 years with another ultrafiltration membrane upstream to prevent bacterial contamination. Bacterial contamination levels were highest and most diverse at the time of the first flush. During subsequent initial cleanng, the contamination level decreased, and bacterial species converged almost exclusively to one genus, namely Methylobacterium spp. During clinical use, the equipment were cleaned and disinfected daily after dialysis, and daily operations and maintenance were performed using aseptic techniques. Although the frequency of bacterial detection decreased annually, the same bacterial genotypes observed at the first flush were isolated even after long time periods and were thought to persist in the equipment possibly by forming biofilm. Pseudomonas aeruginosa was newly detected after the replacement of parts during breakdown maintenance, indicating the need to sterilize replacement parts. Thus, the bioburden should be assessed regularly as part of the management of in-house-produced dialysis fluid.

Considering the lack of detailed research on the antibacterial mechanism of polyoxometalates, we examined the synergistic effect of novel bulky mixed Ti/W hetero-polyoxometalates (K_9.5H_2.5 ［α-Ge₂Ti₄W₂₀O₇₈］・ 29H₂O; αTi4, K₉H₅ ［α-Ge₂Ti₆W₁₈O₇₇］・16H₂O; αTi6, K₂₃H₅［α-Ge₄Ti₁₂W₃₆O₁₅₄］・39H₂O; αTi12, K₉H₅ ［β-Ge₂Ti₆W₁₈O₇₇］・ 45H₂O; βTi6) with the antibiotic oxacillin against vancomycin intermediate-resistant Staphylococcus aureus (VISA) using fractional inhibitory concentration (FIC) index and growth curve in this study. All polyoxometalates used in this study showed remarkable synergistic effects with oxacillin. Its synergistic antibacterial mechanism was examined using reverse transcription PCR (RT-PCR) and penicillin binding protein-2' (PBP2') latex agglutination test. The results suggested that these polyoxometalates did not inhibit mecA gene transcription but resulted in PBP2' protein malfunction. From these results, we concluded that the substances producing resistance in VISA were affected by polyoxometalates depending on their molecular size, facilitating a synergistic antibacterial effect with oxacillin.

Respiratory infectious diseases have potential of aerosol transmission such as COVID-19. The development of new technologies for infection control against airborne viruses are further required. It is necessary for effective development to evaluate properly the effect and role of these technologies in indoor environment. Here, the author provided essential knowledge for infection control of viral aerosols, i.e., basic concept of infection control, features of COVID-19 and Influenza including the entry receptor in body of each virus, behavior of the viral aerosols released from patient bodies, and Wells-Riley model as a traditional quantitative assessment of the infection risk by aerosol transmission. Previous evaluation studies on airborne viruses were categorized into three types of experiments, namely, in vitro, in vivo, and in humans and real indoor environments. Some prospects were described, including standard evaluation methods for air cleaners, the research group to formulate guidelines for evaluating the hygienic effects of chemical substances on microbes in real indoor space, and personal opinions on evaluation concept linked to three types of experiments. This minireview may help to correctly evaluate the hygienic effects of control technologies against airborne viruses in indoor environment and to contribute development of technologies with required performance according to infection risk.

Bacterial stresses can occur from the production to the distribution environments of produce, and these stresses can lead to nonlethal bacterial damage that is an injured state called sublethally injured bacteria. The damage is mainly due to the disruption of the surface structure and cytoplasmic membrane of the cells. Sublethally sanitizer-injured indicator coliform bacteria injured by chlorine, ethanol, and/or fungicide stress could exhibit on vegetables during production and harvest. Chlorine stress and cold stress could induce sublethally injured indicator and pathogenic coliform bacteria on fresh-cut vegetables during processing and subsequent storage. Enterobacter kobei and Pantoea ananatis injurd by chlorine stress, E. amnigenus, E. asburiae, and E. kobei injured by ethanol stress, and Rahnella aquatilis, Yersinia mollaretii, and Escherichia coli injured by fungicide stress could be amongst the injured cells in the coliforms detected in the produce environments. To ensure the microbiological quality and safety of fresh-cut vegetables, it is necessary to adjust the concentration of sanitizer to a level that kills bacteria and does not produce sanitizer- injured cells when sanitizer is applied to the produce, and also to consider the storage temperature to inhibit the recovery of injured bacteria due to cold injury during the chilling storage period.

Ultraviolet (UV) -C is widely used to kill bacteria as it damages chromosomal DNA. We analyzed the denaturation of the protein function of Bacillus subtilis spores after UV-C irradiation. Almost all of the B. subtilis spores germinated in Luria-Bertani (LB) liquid medium, but the colony-forming unit (CFU) of the spores on LB agar plates decreased to approximately 1/10³ by 100 mJ/cm² of UV-C irradiation. Some of the spores germinated in LB liquid medium under phase-contrast microscopy, but almost no colonies formed on the LB agar plates after 1 J/cm² of UV-C irradiation. The fluorescence of the green fluorescent protein (GFP) -fused spore proteins, YeeK-GFP, YeeK is a coat protein, decreased following UV-C irradiation of over 1 J/cm², while that of SspA-GFP, SspA is a core protein, decreased following UV-C irradiation of over 2 J/ cm², respectively. These results revealed that UV-C affected on coat proteins more than core proteins. We conclude that 25 to 100 mJ/cm² of UV-C irradiation can cause DNA damage, and more than 1 J/cm² of UV-C irradiation can cause the denaturation of spore proteins involved in germination. Our study would contribute to improve the technology to detect the bacterial spores, especially after UV sterilization.