不同增菌基对食品沙门氏菌增菌检出效果比较

本试验以三种对A—E群沙门氏菌纯菌增菌和选择性增菌效果好的增菌基,对540份猪肉、250份白条鸡和200枚鸡蛋检样进行沙门氏菌培养,比较它们的增菌检出效果。结果表明:ISC对三种食品中沙门氏菌的平均检出率41.6％、菌株检出符合率94.1％、明显高于SC、SGB,说明ISC比SC和SBG适用性广、增菌性能好,在应用中可以取代SC和SBG。

Screening on Synergist of Bacillus thuringiensis Wettable Powder

[Objective] This study aimed to screen the best synergistic material for Bt wettable powder and evaluate their synergistic effect. [Method] The synergism of six different kinds of additives for Bacillus thuringiensis wettable powder （Bt WP） on the 2^nd instar larvae of Plutella xylostella was tested by method of leaf dipping in labora- tory. [Result] The mixtures of Bt with 0.1% ZnCl2, 0.5% ZnCl2, 1.0% ZnCl2, 1.0% MgCI2, 0.5% boric acid, 1.0% boric acid, 0.5% citric acid or 1.0% citric acid all ex- hibited synergistic effect, in which the synergistic effect of mixture containing 0.5% boric acid was the highest, with 17.2 synergistic ratio; followed by the mixture containing 1.0% ZnCl2, with 15.6 synergistic ratio. Moreover, addition of 0.5% boric acid could shorten the median lethal time of Bt wettable powder by about 10 h. After the mixtures of Bt with 0.5% boracic acid or 1.0% ZnCl2 was stored for 15 d at room temperature, toxicities of the two mixtures did not change significantly. [Conclusion] Boracic acid as the synergist of Bt wettable powder could not only increase insecti- cidal effect of Bt, but also accelerate its insecticidal rate. So, boracic acid could improve the disadvantages of Bt wettable powder such as poor insecticidal effect and slow insecticidal speed in a certain degree.

Detection of Listeria monocytogenes in Dairy Food by Loop-mediated Isothermal Amplification(LAMP)

[Objective] This study aimed to detect the reliability of LAMP method for detecting Listeria monocytogenes in dairy food. [Method] Based on the sequence of hlyA gene encoding listeriolysin O in Listeria monocytogenes, the LAMP method was established for detecting Listeria monocytogenes in dairy food. [Result] The es- tablished LAMP rapid detection method has .high specificity and sensitivity, which are equivalent to those of real-time fluorescent quantitative PCR. The detection re- sults of Listeria monocytogenes in dairy food by established LAMP method were completely consistent with those by bacterial isolation method. [Conclusion] The de- tection results of Listeria monocytogenes by LAMP method can be directly identified by naked eye, so the established LAMP method was suitable for the detection of Listeria monocytogenes in dairy food in emergency situations.

Antagonistic Activity, Antimicrobial Susceptibility and Potential Virulence Factors of Enterococcus faecalis

Enterococcus faecalis isolates （87） were phenotypically and genotypically identified and subsequently subjected to the antagonism test and antimicrobial susceptibility. The lipolitic, hemolytic and DNAse activities were identified along with the genes gelE, cylL, cylS, ccf, cpd and cob that, encode virulence determinants. Thirty seven percent of isolates inhibited Listeria monocytogenes （CERELA）, Listeria innocuous （CERELA）, Staphylococcus aureus （ATCC25932）, Lactococcus lactis （IL1403）, Micrococcus luteus （ATCC 10240） and Enterococcusfaecalis （ATCC29212）. All strains were sensitive to the ampicillin antibiotic, but 47% were resistant to at least one antimicrobial agent and 6% of isolates presented multidrug resistance. Ninety seven percent of isolates contained the gelE gene, but 77% of these isolates showed gelatinase activity. Presence of cylL and cylS genes was observed in 25% of the isolates, but only 5% presented hemolytic activity. None isolates showed lipase and DNAse activities. Eight percent of isolates contained the ccf gene and 2% showed the presence of the cpd and cob genes. The ability to inhibit pathogenic bacteria, low resistance to antibiotics and absence of virulence factors make some of Enterococcusfaecalis strains characterized in the present study promising for exploitation in other applications such as probiotics in aquaculture.

Effect of Riboflavin Operon Dosage on Riboflavin Productivity in Bacillus Subtilis

After deregulating the purine and riboflavin synthesis in the Gram-positive bacterium Bacillus subtilis,it is critical to amplify riboflavin operon with appropriate dosage in the host strain for remarkable increase of riboflavin production.Bacillus subtilis RH13, a riboflavin-producing strain, was selected as host strain in the construction of engineering strains by protoplast fusion. The integrative plasmid pRB63 and autonomous plasmid pRB49, pRB62 containing riboflavin operon of B.subtilis 24 were constructed and transformed into the host strain respectively. Increasing one operon copy in B.subtilis RH13 results in about 0.4 g/L improvement in riboflavin yield and the appropriate number of operon copies was about 7—8. Amplifying more riboflavin operons is of no use for further improvement of yield of riboflavin. Furthermore, excessive operon dosage results in metabolic unbalance and is fatal to the host cells producing riboflavin.

Identification and Diagnostics of Plant-Symbiotic and Phytopathogenic Bacteria

Rapid and reliable diagnostics and identification of pathogenic and symbiotic bacteria are at the top of the agenda. In the first case, they are important to control and prevent crop damages, and thus reduce economic losses. In the second, it＇s necessary to design and monitor quality of biofertilizer to raise its effectiveness and crop capacity. Development of accurately, rapidly, technically and commercially accessible methods remains a critical problem for the bacteria with comprehensive phylogenetic structure. In this work, we investigated pathogenic Xanthomonas and Ralstonia and symbiotic Sinorhizobium. The aim of this investigation was to examine the applicability of the novel methods for phylogenetic study, identification and diagnostics of closely related species of these genera. The conventional phenotypic and genotypic （16S rRNA, gyrB） methods were applied as referents. Novel polymerase chain reaction （PCR）-based approaches, single-adapter amplified fragment length polymorphism （saAFLP） and comparative analyses of hin-region and Xcc0006-0007 sequences, were first employed for the investigations. Phenotypic tests, 16S rRNA and gyrB analysis distinguished bacteria at the genus level, but failed to identify them to the species robustly. The new methods identified bacteria at the inter-species level more precisely. This identification agreed with the accepted genera＇s classifications. The only exceptions were X. fuscans ＆ X. cirri and X. perforance ＆ X. euvesicatoria which clustered together. The further outcome of this study was achieved hin-region-based genus-specific PCR primers for the express-diagnostics of the genera. Summary, these new methods can be applied for genome-based phylogeny investigations and as convenient and accurate tools for identification and routine laboratory diagnostics of these comprehensive genera.