Development and evaluation of a loop-mediated isothermal amplification assay for rapid and sensitive detection of Vibrio parahaemolyticus.

Loop-mediated isothermal amplification (LAMP) assays targeting the rpoD and toxR genes were developed to detect Vibrio parahaemolyticus. All 78 tested V. parahaemolyticus strains yielded positive results within 40 min, while negative results were obtained for 69 strains of other organisms even at 60 min. For V. parahaemolyticus ATCC 17802 in pure culture, the detection limits of LAMP assays targeting rpoD and toxR were 3.7 and 450 CFU per test, respectively. Due to the higher sensitivity of rpoD-LAMP, it was further evaluated for the ability to detect V. parahaemolyticus in seafood samples. V. parahaemolyticus populations spiked in short-necked clams were enumerated by the most-probable-number (MPN) method combined with the rpoD-LAMP assay and the MPN method with a culture method using agar medium. The MPN-rpoD-LAMP method had better sensitivity and was more rapid than the conventional method. These results indicate that the MPN-LAMP assay targeting the rpoD gene is a specific, sensitive, and rapid method to enumerate V. parahaemolyticus organisms.

Development of interpretive criteria for tebipenem disk diffusion susceptibility testing with Staphylococcus spp. and Haemophilus influenzae.

Disk diffusion susceptibility interpretive criteria for tebipenem against Staphylococcus spp. and Haemophilus influenzae were developed using the Clinical and Laboratory Standards Institute (CLSI) guidelines. Tebipenem was tested by disk diffusion and broth microdilution methods against 119 clinical isolates of Staphylococcus spp. and 102 clinical isolates of H. influenzae. The zone diameters of 5-, 10-, and 30-µg disks were compared with broth microdilution minimum inhibitory concentration (MIC) results by scattergram and regression analysis. When the MIC breakpoint of 1 µg/ml was applied to the scattergrams, the 10-µg disk showed good correlation between the zone diameters and the MIC values. The corresponding disk diffusion zone diameter breakpoints with the 10-µg disk for Staphylococcus spp. were ≧22 mm (MIC ≦1 µg/ml) for susceptible, 20-21 mm (MIC = 2 µg/ml) for intermediate, and ≦19 mm (MIC ≧4 µg/ml) for resistant. We also proposed the breakpoint zone diameter of H. influenzae: ≧22 mm (MIC ≦1 µg/ml) for susceptible. These criteria demonstrated that the categorical agreements between disk diffusion and broth microdilution methods for Staphylococcus spp. and H. influenzae were 95.0% and 99.0%, respectively. The discrepancy rates of these criteria were acceptable to the CLSI guidelines.

Rapid, sensitive, and specific detection of the O4 group of Salmonella enterica by loop-mediated isothermal amplification.

The present study developed a loop-mediated isothermal amplification (LAMP) assay that amplifies the fragments of O4 Salmonella enterica-specific gene rfbJ and evaluates the potential use in detection of Salmonella enterica serovar Typhimurium (ST). The detection limit of the LAMP assay was 10(3) CFU/ml, which was lower than that of the PCR assay with the same target gene (10(5) CFU/ml), confirmed by electrophoresis. The increased turbidity of the final products of LAMP was also observed with more than 10(3) CFU/ml. Furthermore, the LAMP assay took only 60 min for a reaction, while the PCR assay needed 80-90 min for a reaction and approximately 30 min for the subsequent electrophoresis to confirm the specific band. The positive reaction was only observed for 55 strains of 11 serovars of O4 group Salmonella enterica. The LAMP assay developed in the present study is considered to be an effective method for specific detection of the O4 group Salmonella enterica serovars, including ST.

Rapid, sensitive and simple detection method for koi herpesvirus using loop-mediated isothermal amplification.

New methods were developed for the detection of koi herpesvirus (KHV, CyHV-3) by LAMP, which were compared with the PCR for specificity and sensitivity. We designed two primer sets targeting a specific sequence within the 9/5 PCR amplicon (9/5 LAMP) and the upper region of the SphI-5 PCR amplicon (SphI-5 LAMP), including a sequence highly conserved among the strains. The amplification was monitored in real-time based on the increase in turbidity, with magnesium pyrophosphate as the by-product. The reactions were carried out under isothermal conditions at 65 degrees C for 60 min. The detection limit of both LAMP was six copies, equal to the modified SphI-5 PCR. No cross-reactivity with other fish pathogenic viruses and bacteria was observed. SphI-5 LAMP was found to have a quicker response in terms of the reaction velocity than 9/5 LAMP. Therefore, we consider SphI-5 LAMP to be superior for routine use. Additionally, LAMP was found applicable to crude extract from gills and other organs. LAMP methods are superior in terms of sensitivity, specificity, rapidity and simplicity, and are potentially a valuable diagnostic tool for KHV infections.

Rapid and specific detection of the thermostable direct hemolysin gene in Vibrio parahaemolyticus by loop-mediated isothermal amplification.

Several investigators have reported that thermostable direct hemolysin (TDH) and TDH-related hemolysin are important virulence factors of Vibrio parahaemolyticus, but it has been difficult to detect these factors rapidly in seafood and other environmental samples. A novel nucleic acid amplification method, termed the loop-mediated isothermal amplification (LAMP), which amplifies DNA with high specificity and rapidity under isothermal conditions, was applied. In this study, we designed tdh gene-specific LAMP primers for detection of TDH-producing V. parahaemolyticus. The specificity of this assay was evaluated with 32 strains of TDH-producing V. parahaemolyticus, one strain of TDH-producing Grimontia hollisae, 10 strains of TDH-nonproducing V. parahaemolyticus, and 94 strains of TDH-nonproducing bacteria, and the sensitivity was high enough to detect one cell per test. Moreover, to investigate the detection of TDH-producing V. parahaemolyticus in oysters, the LAMP assay was performed with enrichment culture in alkaline peptone water of oyster samples inoculated with TDH-producing V. parahaemolyticus and TDH-nonproducing V. parahaemolyticus and V. alginolyticus after enrichment in alkaline peptone water. These results suggest that the LAMP assay targeting tdh gene has high sensitivity and specificity and is useful to detect TDH-producing V. parahaemolyticus in oyster after enrichment.

[Sensitive and rapid detection of Mycoplasma pneumoniae by loop-mediated isothermal amplification].

For establishment of a method for rapid diagnosis of Mycoplasma pneumoniae in clinical specimens, we designed and evaluated a loop-mediated isothermal amplification (LAMP) assay, using a set of primers targeting the SDC1 repetitive element of the M. pneumoniae genome. The method showed rapid and specific amplification for all the strains of M. pneumoniae tested (Type I and II), within 1 hour at 65 degrees C. No cross-reactivity with the most common causative organisms bacterial pneumonia was observed. The detection limit was shown as 6 copies, which was equal to or higher than that of the two nested PCRs used as references. Two hundred four clinical samples, comprising sputum samples, throat swabs, etc., were tested by both LAMP and PCR, and determination of the correlations revealed complete agreement individually (24 positives). The LAMP assay, a simple procedure in a closed system, allowed rapid amplification and accurate detection consistently; therefore we considered that it could become an caeasily available diagnostic method suitable for clinical situations requiring quick and appropriate decisions for treatments and care.

Loop-mediated isothermal amplification for the rapid, sensitive, and specific detection of the O9 group of Salmonella in chickens.

In the present study, the loop-mediated isothermal amplification (LAMP) assay was developed to amplify the fragments of the O9 Salmonella-specific insertion element and evaluated in the laboratory for its potential use in a field situation, such as poultry farms. Among the bacteria tested, a positive reaction was observed only for 128 strains of 6 serovars of the O9 group Salmonella, such as Enteritidis (SE) and Pullorum. The detection limit of the LAMP assay was 10(3)CFU/ml, which was more sensitive than that of the polymerase chain reaction (PCR) assay with the same target gene (10(6)CFU/ml). The final results were obtained within 30 min for the LAMP assay, while the PCR assay needed a total of 120 min. When the LAMP assay was applied to the enrichment broth mixed with cecal dropping samples either spiked with SE in vitro or excreted by SE-inoculated hens, the results were comparable to those of the conventional plating method including 2 separate enrichments. In conclusion, the LAMP assay developed in the present study is an effective method for the specific detection of the O9 group Salmonella serovars, including SE.

Sensitive and rapid detection of Vero toxin-producing Escherichia coli using loop-mediated isothermal amplification.

A loop-mediated isothermal amplification (LAMP) assay was developed to detect Vero toxin (VT)-producing Escherichia coli rapidly (within 60 min). The 24 strains of VT-producing E. coli were successfully amplified, but 6 strains of non-VT-producing E. coli and 46 bacterial species other than E. coli were not. The sensitivity of the LAMP assay was found to be >0.7 c.f.u. per test using serogroups O157, O26 and O111 of VT-producing E. coli; this sensitivity is greater than that obtained by PCR assay. Furthermore, the LAMP assay was examined for its ability to detect VT-producing E. coli in food because of the difficulty of detection in food samples. The recovery of VT-producing E. coli by LAMP assay from beef and radish sprouts inoculated with the pathogen was high, similar to that obtained using culture methods with direct plating and/or plating after immunomagnetic separation. Although PCR assay was unable to recover VT-producing E. coli from half of the radish samples, LAMP assay was successful in most samples. In addition, VT-producing E. coli was successfully detected in cultures of the beef samples by LAMP assay, but not by the culture method. The LAMP products in naturally contaminated beef samples were analysed to confirm the specific amplification of the VT-encoding gene, and were found to show a specific ladder band pattern on agarose gel after electrophoresis. Additionally the sequences of the LAMP products coincided well with the expected sequences of the VT-encoding gene. These results indicate that the proposed LAMP assay is a rapid, specific and sensitive method of detecting the VT-producing E. coli.

[Development and evaluation of novel loop-mediated isothermal amplification for rapid detection of bla(IMP-1) and bla(VIM-2) genes].

Loop-mediated isothermal amplification (LAMP) amplifies a target gene with high specificity and rapidity under isothermal conditions. LAMP assays were developed for the rapid detection of metallo-beta-lactamase (MBL) genes such as bla(IMP-1)) and bla(VIM-2). We initially designed specific primers to detect MBL genes for LAMP assays and evaluated the specificity and sensitivity of these assays. LAMP assays amplified MBL genes under a constant temperature of 63 degrees C within 1 hour, and were compared to PCR in MBL-producing strains. The results of MBL genes typing by LAMP assays agree completely with PCR results. The lower detection limits of bla(IMP-1)- and bla(VIM-2)-LAMP assays using real-time turbidimeters were 30cfu/test and 3cfu/test. After amplification, products were directly observed by the naked eye with a fluorescent detection reagent. In conclusion, LAMP assays are convenient, rapid, and fully feasible for detecting MBL genes in ordinary clinical microbiology laboratories without special apparatus.

Prevention of intestinal infection by glycomacropeptide.

The preventive effects of glycomacropeptide (GMP) against intestinal infection were investigated, and conjugates of GMP with xylooligosaccharide (XOS) and carboxymethyldextran (CMD) were prepared by the Maillard reaction to enhance the effect of GMP. The binding ability of GMP to intestinal pathogenic bacteria was evaluated by a binding assay with biotinylated bacteria. GMP showed the ability to bind to Salmonella enteritidis and enterohemorrhagic Escherichia coli O157:H7 (EHEC O157). This binding ability was decreased by a sialidase treatment and completely eliminated by periodate oxidation. These results indicate that such carbohydrate moieties as sialic acid in GMP are involved in binding to S. enteritidis and EHEC O157. The preventive effect of GMP on the adhesion of pathogenic bacteria to Caco-2 cells was also investigated. GMP showed an inhibitory effect on the adhesion of EHEC O157 in a dose-dependent manner, although it was not a potent inhibitor of the adhesion of Salmonella infection. However, in the case of Salmonella infection, GMP-XOS and GMP-CMD significantly suppressed IL-8 production which was the index of infection. Our results indicate GMP to be a promising agent for preventing intestinal infection.

Loop-mediated isothermal amplification for the rapid detection of Salmonella.

Loop-mediated isothermal amplification (LAMP) assay detected Salmonella within 60 min. The 220 strains of 39 serotypes of Salmonella subsp. enterica and 7 strains of Salmonella enterica subsp. arizonae were amplified, but not 62 strains of 23 bacterial species other than Salmonella. The sensitivity of the LAMP assay was found to be >2.2 cfu/test tube using nine serotypes. The specificity was similar to that of a PCR assay, but the sensitivity of LAMP was greater. Both fluorescence and turbidity were able to detect the products in the LAMP assay. S. enteritidis in a liquid egg sample artificially inoculated with the organism was detected by the LAMP assay at 2.8 cfu/test tube, although negative by PCR assay. These results indicate that the LAMP assay is a rapid, specific and sensitive detection method for Salmonella.

[Evaluation of Dipstick 'Eiken' Legionella for detection of Legionella pneumophila serogroup 1 urinary antigen using the immunochromatographical method].

Dipstick 'Eiken' Legionella is a reagent for detection of Legionella pneumophila serogroup 1 antigen in urine using the immunochromatographical method. The reagent was evaluated using the reference and clinical isolated strains and clinical specimens. BinaxNOW Legionella and Legionella antigen [Mitsubishi] were evaluated simultaneously. Using four of L. pneumophila serogroup 1 strains, the minimal detectable concentration of Dipstick 'Eiken' Legionella was 5.0 x 10(4) to 2.0 x 10(5) colony forming unit/ml, it was approximate four times high in comparison with other two kits. And no positive reaction was obtained from 45 of non-L. pneumophila serogroup 1 strains. When Dipstick 'Eiken' Legionella was compared with BinaxNOW Legionella among 50 urine samples obtained from patients with pneumonia and 50 urine from healthy adults, the sensitivity was 94.7%, the specificity was 100.0% and the agreement was 99.0%. Dipstick 'Eiken' Legionella is found to be useful diagnostic reagent for Legionella infection in clinical laboratories.

Comparative evaluation of standard dilution method and commercial kit for frozen plate antifungal susceptibility testing of yeasts using 200 clinical isolates.

A comparative evaluation of standard microdilution methods and a commercial kit for frozen plate antifungal susceptibility testing of yeasts was performed using amphotericin B, flucytosine, fluconazole, miconazole, and itraconazole on 200 yeast isolates. The isolates included 100 strains of Candida albicans, eight of C. tropicalis, twelve of C. parapsilosis, eight of C. glabrata, five of Cryptococcus neoformans, thirteen of Trichosporon asahii, and 54 other strains of seven other species of ascomycotic yeasts. Microdilution testing was performed according to the standard method for antifungal susceptibility testing published by the Japanese Society for Medical Mycology (JSMM), which are a modification of the method developed by the National Committee for Clinical Laboratory Standards (NCCLS) M27-P. The commercial kit was prepared according to the manufacturer's instructions. The degree of agreement within +/-1 dilution for 200 clinical isolates against five antifungal agents was excellent with values for amphotericin B, flucytosine, fluconazole, miconazole, and itraconazole of 100%, 99.0%, 97.5%, 97.0%, and 97.0%, respectively. Overall, the frozen plate antifungal susceptibility testing kit provided convenient and reproducible results comparable to those obtained with the JSMM standard method.

Evaluation of a novel automated chemiluminescent assay system for antimicrobial susceptibility testing.

The newly developed Rapid Lumi Eiken/IS60 (RL/IS60) system automatically determines MICs by detecting chemiluminescence produced in the reaction of a chemiluminescent probe and oxygen metabolites from living microorganisms. The present study evaluated this system for accuracy in antimicrobial susceptibility testing. Chemiluminescence intensities after 4 h of cultivation of clinically important strains were plotted against various concentrations of antimicrobial agents, which resulted in curves reflecting the levels of susceptibility. Sixty-percent inhibitory concentrations based on the susceptibility curves agreed with MICs determined by the reference microdilution method. When the MICs of antimicrobial agents for four quality control (QC) strains (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa) were determined by the RL/IS60 system, most (91.1%) of them were within the QC limits proposed by the National Committee for Clinical Laboratory Standards. The system was further assessed for a total of 162 clinical isolates, including E. coli, Citrobacter freundii, Enterobacter cloacae, Klebsiella pneumoniae, Serratia marcescens, Proteus mirabilis, Morganella morganii, P. aeruginosa, Haemophilus influenzae, S. aureus, coagulase-negative staphylococci, Enterococcus faecalis, Enterococcus faecium, and Streptococcus pneumoniae. Overall, there was 90.6% agreement between the RL/IS60 system and the reference microdilution method. Our results suggest that the RL/IS60 system provides rapid and reliable MICs of a variety of antimicrobial agents for clinical isolates as well as QC strains.

[Evaluation of the diagnostic reagents which detect group A Streptococcus with the immunochromatographical method].

Dipstick 'Eiken' Strep A was evaluated for this sensitivity and specificity. Dipstick 'Eiken' Strep A had a capacity to detect Group A Streptococcus in 1.5x10(5) cfu/swab. The sensitivity of Dipstick 'Eiken' Strep A was 4 times higher than the sensitivity of the latex agglutination test (Serodirect 'Eiken' Strep A) and was almost the same as the immunochromatography test (TESTPACK Plus STREP A, CLEARVIEW STREP A and ImmunoCard STAT! STREP A TEST). No cross reaction was observed among 27 strains of 25 species microorganisms with Dipstick 'Eiken' Strep A. Dipstick 'Eiken' Strep A was compared with TESTPACK Plus STREP A among throat swabs from 50 patients with pharyngitis. Dipstick 'Eiken' Strep A had a sensitivity of 92.9%, a specificity of 90.5% and an agreement of 91.8%. Dipstick 'Eiken' Strep A is found to be useful diagnostic assay in the clinical laboratories.

[Studies on efficient methods for detection of Legionella species from environmental water by use of its selective media].

To examine the optimal pH range for growth on media, growth of Legionella spp. on its selective media, BCYE alpha, WYO alpha and MWY agar media, in a pH range of 6.0-8.0 (at 0.5 intervals) was compared. The growth of two strains of L. pneumophila and one strain of L. micdadei on a WYO alpha agar supplemented with some selecting antimicrobial agents was markedly inhibited at all pH range except 6.0 and 7.0, suggesting a narrow optimal pH range for growth of these species compared to the BCYE alpha without selecting antimicrobioal agents. Vancomycin (VCM) added to the selective agar suppressed the growth of some Legionella spp. depending on the concentration. However, the extent of suppression was different among species and/or strains of Legionella spp. The selectivity for species other than Legionella spp. was also affected similarly by VCM concentration added to their media, suggesting that it is important to use proper amounts of the selecting antimicrobial agent depending on the species and/or strains of Legionella spp. or the other species in water samples. Amphothericin B (AMPH-B) added to a selective medium, MWY agar, in the concentration of 80 micrograms/ml hardly affected the growth of Legionella spp. examined, but effectively inhibited the growth of fungal strains identified as Aspergillus sp., Trichoderma sp., Scolecobasidium sp. and Mucor sp. which were isolated from cooling-tower water samples together with Legionella spp. Furthermore, the growth of a combination culture of one each of the 4 strains of isolated fungi and one each of the 3 strains of Legionella spp. was examined at various concentration of AMPH-B. Addition of AMPH-B to the selective medium at the concentration of 80 micrograms/ml suppressed the growth of spreading fungi, permitting the growth of Legionella spp. to allow efficient detection of the species.

[Effect of the pretreatment with organic acid buffer solutions on the recovery of Legionella species from environmental water samples].

Anti-microbial effect of the pretreatment with various organic acid buffer solutions against co-existing microorganisms which were isolated from cooling-tower water samples along with Legionella spp. was examined. Among several buffer solutions, a 0.1 M potassium citrate-citric acid buffer solution (hereafter, citrate buffer solution, pH 2.2) hardly affected the recovery of Legionella spp., but effectively inhibited the growth of co-existing microorganisms. To evaluate the buffer action of these buffer solutions, pHs of 9 cooling-tower water samples were evaluated after addition of an equal volume of each buffer solution. When a citrate buffer solution. pH 2.2 was combined to a 200-fold concentrated solution of each cooling-tower water sample, the pH of the combined solution became 2.5 to 2.7 and maintained a stably low pH value than that (pH 3.0 to 7.4) obtained after mixture of a 0.2 M HCl-KCl buffer solution (hereafter, HCl buffer solution, pH 2.2), suggesting strong buffer action of the citrate buffer solution, pH 2.2 in the combined solutions. Furthermore, when cooling-tower water samples were pretreated with a citrate buffer solution, pH 2.2, the recovery of Legionella spp. was successful in 7 out of 9 cooling-tower water samples, suggesting 3 times higher recovery rate than that obtained by addition of a HCl buffer solution, pH 2.2 (3 out of 9 cooling-tower water samples).