Biocontrol science最新文献

The conventional plate culture method is widely used as a method for detection of Legionella in environmental water samples, but to obtain results takes more than a week. Because it is much quicker, the gene detection method has become widespread as an alternative detection method. However, the results of gene detection and plate culture methods may differ even when the same sample is examined; the gene detection method shows a higher detection ratio than the plate culture method. The reason for this difference is that the plate culture method detects Legionella cells that have the ability to form colonies on an agar plate, whereas the gene detection method detects any Legionella genes present regardless of the state of the Legionella. In this paper, we consider the factors that cause differences between the results of the plate culture and gene detection methods, and how to interpret the results of each.

For the elucidation of the mechanism underlying the photocatalytic bactericidal activity of titanium dioxide (TiO₂), we focused on the peptidoglycan layer, a component of the bacterial cell wall. The effect of this layer on the photocatalytic bactericidal activity of TiO₂ was evaluated by determining the survival rates of Lactobacillus plantarum (intact cells) and its protoplast cells. Mesoplasma florum, which does not originally possess the peptidoglycan layer, was also used. Our results revealed that the survival rates of the intact cells were lower than those of the protoplast cells. In addition, there was no significance between the survival rates of M. florum cells and the protoplast cells of L. plantarum. It was suggested that the presence of the peptidoglycan layer increases the bactericidal effect by the photocatalysis.

This study examined the fungal flora contained in the dust of bedding used in 50 houses in Japan. The result showed that the mycoflora having the largest isolation rate was yeasts, which were isolated by 42 out of 50 houses (84%), and exceeded the isolation rate of Cladosporium spp. (80%) and Aspergillus spp. (66%). In addition, the isolation rate of Alternaria, which was an important fungus causing asthma, 66% was being considered as a high isolation rate, and this result was very interesting. The isolation rate of xerophilic fungi such as Aspergillus restrictus and Wallemia often found in house dust on the floor, was not very high. Forty-one strains of yeasts isolated from each dust sample were identified, and Naganishia diffluens species complex and Filobasidium magnum had a larger number of 13 strains, respectively. Since N. diffluens was the yeasts often isolated from human skin, it was thought to be an association between the fungal skin flora and fungal flora of bed dust. Meanwhile, there was no report of isolation of F. magnum from house dust previously. To the best of our knowledge, this is the first study showing its isolation from bedding with relatively high frequency.

Escherichia coli cells were suspended in phosphate-buffered saline solutions (pH 7.4) at physiological (0.9 %) and hyperosmotic (3.5, 5.0, and 10.0 %) concentrations of sodium chloride (NaCl) and stored at 5, 10, 15, 20, and 25 °C up to 48 d. During storage at 5 and 10 °C, viable cell counts decreased approximately from 9 log CFU/ml to 6-7 log CFU/ml, and NaCl showed slight protective effect on the decrease. When stored at 15, 20, and 25 °C, the counts decreased with increases in NaCl concentration and/or storage temperature. The cells in 10.0 % NaCl suspension became nondetectable after storage at 25 °C for 28 d. Under some storage conditions (NaCl ≤ 5 %, 20 and 25 °C), the counts approached constant values, indicating possible adaptation to NaCl. Injured cells were observed at 5.0 and 10.0 % NaCl. However, recovery was observed only at 5.0 % NaCl during storage at 20 °C. In addition, more cells were detected on nonselective medium when incubated at 37 °C than at 25 °C. Higher hyperosmotic NaCl solutions at higher storage temperatures reduced more viable cells of E. coli.

House dust mites, Dermatophagoides pteronyssinus are present in the indoor environments, such as pillows and carpets. In this study, we investigated the mite control effect of branched chain fatty acids (2-ethylhexanoic acid (iso-C8), 2-butyloctanoic acid (iso-C12), isopalmitic acid (iso-C16) and their mechanism of action. These fatty acids showed a higher acaricidal activity than the straight chain fatty acids. Among these, iso-C12 had the highest acaricidal activity (LC₅₀: 13mM) and more than 50% repellence rate at 0.20% (8.0mM) concentration. In the fumigant mortality bioassay, iso-C8 was 4 times more toxic than iso-C12 and isoC-16 in the gas phase. However, all branched chain fatty acids showed higher acaricidal activities on direct contact than fumigation. As the concentration of these fatty acids decreased, the number of deaths decreased and the number of escapes increased. There was no significant change in the mite epidermis due to contact with any of the fatty acids used. All branched chain fatty acids immobilized more than half of the mites within 90min of exposure. These results were consistent with the tendency of immobilizer type miticides targeting the respiratory system.

Rapid microbiological methods (RMMs) have been used as novel quality control technologies in industry. The ability of RMMs to detect stressed bacteria, in particular, is of continued interest due to the limitations of the conventional method in stressed bacteria detection. Accordingly, there is a need to better characterize an RMM's ability to detect stressed microorganisms. Previously we reported on the detection ability of an intrinsic fluorescence-based RMM using a 50% injured (determined based on colony-forming ability) bacterial cell group after heat treatment at 55°C for 8 min. In this study, we added further information about the physiological state of the heat treated Escherichia coli, besides proliferation ability, by investigating respiratory activity using CTC fluorescent staining and expression of DnaK, a heat shock protein. It was found that 89% of cells (control 96%) retained respiratory activity, but only 20% (control 41%) retained proliferation ability after heat treatment. The difference between the percentage of cells with respiratory activity versus that of cells still capable of proliferation further supports the existence of viable but non-culturable stressed cells in the test sample. Also, we suggest such analysis would be one approach to confirming the use of stressed as opposed to dead cells when evaluating an RMM's ability to detect stressed microorganisms.

Testing for Legionella spp. in public bath water samples is regulated in Japan. In this study, we used a total of 132 public bath water samples to compare the performance of Legiolert® and the conventional plate culture method for the enumeration of Legionella pneumophila. When Legiolert and plate culturing were performed at the same detection limit, L. pneumophila was detected in 26.5% of 132 samples by Legiolert, while 12.9% contained Legionella spp. (11.4% contained L. pneumophila) based on the plate culture method. Moreover, results of 83.3% of the total samples were consistent between the two methods, meaning that they were both positive or both negative. In this study, we demonstrated that Legiolert is a simpler and more effective method of monitoring for L. pneumophila in bath water samples.

Insufficient preservative efficacy leads to microbial contamination. Cosmetic-impregnated products composed of nonwoven fabrics, such as wipes and masks, can be contaminated with microbes owing to their special form. However, the reduction of preservative efficacy in cosmetic-impregnated products remains unverified. This study aimed to investigate whether preservative efficacy is reduced in nonwoven fabrics impregnated with a cosmetic liquid and the factors affecting this reduction. First, we evaluated the preservative efficacy of face wipes and confirmed that the preservative efficacy was reduced after impregnation of cosmetic liquids into nonwoven fabrics. We thus hypothesized that the adsorption of the antimicrobial components onto nonwoven fabrics decreases the preservative efficacy. Unexpectedly, the antimicrobial components were scarcely adsorbed onto the fabrics, while microbial growth activity was significantly increased on the fabrics, as determined through microbial calorimetry. Furthermore, the antibacterial effects were reduced in the nonwoven fabrics. These results indicate that the nonwoven fabrics enhanced microbial growth, thus decreasing the preservative efficacy. Our results provide novel insights into the microbial control of products composed of nonwoven fabrics.

Yamagawa Bay, located in Ibusuki, Kagoshima Prefecture, Japan, is a geographically enclosed coastal marine inlet, and its deteriorating seabed sediments are under an anoxic, reductive, sulfide-rich condition. In order to gain insight into diversity of anoxygenic photosynthetic bacteria (AnPBs) and their ecophysiological roles in the sediments, three approaches were adopted: isolation of AnPBs, PCR-DGGE of 16S rDNA, and PCR-DGGE of pufM. Among the bacterial isolates, relatives of Rhodobacter sphaeroides were most dominant, possibly contributing to transforming organic pollutants in the sediments. Abundance of Chlorobium phaeobacteroides BS1 was suggested by 16S rDNA PCR-DGGE. It could reflect intensive stratification and resultant formation of the anoxic, sulfide-rich layer in addition to extreme low-light adaptation of this strain. Diverse purple non-sulfur or sulfur bacteria as well as aerobic anoxygenic photoheterotrophs were also detected by pufM PCR-DGGE, which could be associated with organic or inorganic sulfur cycling. The outcome of the present study highlights ecophysiologically important roles of AnPBs in the organically polluted marine sediments.