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.
In order to evaluate injury of a stressed fungal spore population, a modification of formerly presented double subculture method, which consists of both the conventional plate count method and the growth delay analysis method, was proposed. In this method, an apparent logarithmic growth kinetics was assumed and the previous kinetic model was improved to be able to estimate injured subpopulations in two different modes containing early occurring growth-independent and late occurring growth-dependent injuries, called the λ and μ injuries, respectively. Based on the kinetic theory developed here, this novel method was applied to heat-treated conidia of Cladosporium cladosporioides and these two mode injuries were evaluated.
Halotolerant Brevibacterium sp. JCM 6894 grew at 37ºC in the presence of 2.3 M KCl, while the growth was repressed with the same concentration of NaCl. When resting cells, 107.4 ± 0.1 (CFU·mL-1), prepared from cells grown in the absence of salts at 30ºC, were exposed to 3.3 M NaCl for 36 h at 42ºC, reduction of the number of resting cells was maintained within a 1-log cycle in the presence of proline, betaine, or ectoine (50 mM). In the presence of 3.3 M KCl, the most functional osmoprotectant was sodium glutamate (50 mM), and the value was 107.2 ± 0.1 (CFU·mL-1) when exposed for 72 h at 42ºC. In the absence of osmoprotectants, the value was reduced to four orders of magnitude in each experimental condition. The number of resting cells, 106.8 ± 0.1 (CFU·mL-1), prepared from grown cells pre-adapted to 2.3 M KCl at 37ºC, was hardly reduced when exposed to 3.3 M KCl in the presence of sodium glutamate more than 50 mM for 72 h at 42ºC. Those results indicate that the isolate can sense the difference in hyper KCl stress as opposed to hyper NaCl stress, and different kinds of osmoadaptation systems can function to cope with each hyper salt stress.
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.
The Early Mortality Syndrome (EMS) caused by Vibrio parahaemolyticus has recently resulted in a serious loss in shrimp farms in the Mekong delta, Vietnam. Here, antibacterial activity of copper nanoparticles-chitosan composite (CuCS) against V. parahaemolyticus was investigated. Copper nanoparticles were synthesized using L-ascorbic acid as a green reducing agent and chitosan as a biopolymer matrix and stabilizing agent. The physical properties of CuCS were evaluated. Next, antibacterial activity of 2.5, 5.0, 10.0 ppm CuCS against V. parahaemolyticus inoculated in a sterilized shrimp-pond water was examined. CuCS at 2.5 ppm eliminated 91.47% and 95.26% of V. parahaemolyticus after 2 and 4 h of exposure, respectively. Complete elimination was attained following 2 h of 5.0 ppm CuCS exposure. A complete elimination of V. parahaemolyticus in a real EMS-infected shrimp-pond water was also described. This study is the first to report the antibacterial activity of CuCS against V. parahaemolyticus, an important pathogen in shrimp industry in the Mekong delta, Vietnam.
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.
Viridans group streptococci (VGS) are a common cause of infective endocarditis, and dental plaque is the major source of these bacteria. The present study examined the antibiotic resistance of 635 VGS isolates obtained from dental plaques. Isolates from supragingival plaques were identified using the rapid ID 32 Strep and mini API reader (bioMérieux, France), and minimal inhibitory concentrations (MICs) were determined by a broth microdilution method. High rates of resistance to ampicillin and tetracycline were detected among the isolates. The most resistant species were Streptococcus sanguinis and Streptococcus salivarius. Among the 635 isolates, 9.1% were resistant to erythromycin, and 20.6% to tetracycline. All isolates were sensitive to vancomycin. Resistance to amoxicillin was observed in 0.2% of all isolates. In this study, we showed the incidence of antimicrobial resistance and the susceptibility patterns among 635 VGS isolates from dental plaque.
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.