Adhesion inhibitory effects of food additives, such as Polylysine (PL) and Whey protein (WP), as well as Sucrose fatty acid ester (SFE) with fatty acid of C8 to C18, Monoglycerin fatty acid ester (MFE) with fatty acid of C8 to C18, Gardenia yellow pigment (GY), Monascus pigment (MP), and Protamine (PT) that had been shown to inhibit adhesion of Salmonella Enteritidis onto microtiter plate, were determined on several bacteria. Among SFE tested, adhesion of S. Typhimurium onto microtiter plate was decreased to less than 50% of the control by SFE with fatty acid of C10, C12, C14, and C16 at 0.05% and that of C18 at 0.01%. MFE with fatty acid of C8, C10, C12, C16, C18 also inhibited the adhesion to less than 50% of the control. The adhesion of S. Typhimurium was also almost completely inhibited by PT and PL at 0.01%, 0.1% MP, 0.025% WP, and 1% GY. Adhesion of Pseudomonas aeruginosa was decreased to less than 50% of the control by SFE with C8 and C16 fatty acid at 0.05%, C12 and C14 at 0.01%, 0.1% PT, 0.01% PL, and 0.025% WP, but not by 0.05% MFE tested, 1% GY, and 1% MP. Adhesion of P. fluorescens was almost completely inhibited by SFE with fatty acid of C14, C16, and C18 at 0.05, 0.005, and 0.005%, respectively, and 1% GY, 1% MP, 0.1% PT, and 1% PL, but not by MFE and WP even at 0.05 and 0.25%, respectively. Adhesion of Listeria monocytogenes was decreased to less than 50% of the control by SFE with fatty acid of C10, C12, C16, and C18 at 0.05% and by MFE with fatty acid of C10, C14, C16, and C18 at 0.05, 0.05, 0.005, and 0.005, respectively. The adhesion decreased to less than 50% of the control by 0.1% MP, 1% PT, and 1% PL, but not by 1% GY and 0.25% WP. Adhesion of Staphylococcus aureus decreased to less than 50% of the control by SFE with fatty acid of C10, C12, C14, C16, and C18 at 0.05, 0.01, 0.005, 0.005, and 0.005%, respectively. The adhesion was inhibited by more than 50% by 0.05% MFE with C8 fatty acid and by 0.005% MFE with C10 to C18 fatty acid. GY, MP, PT, PL, and WP decreased the adhesion by more than 50% at 0.1, 0.01, 0.01, 0.01, and 0.025%, respectively. It seems to be important to select suitable substances for inhibition of adhesion of each of the bacterial species.
Petrifilm Enterobacteriaceae Count Plate (Petrifilm EB) was evaluated by comparing with ISO method in terms of enumeration of Enterobacteriaceae using domestic commercialized meat products, fish and seafood products, and prepared products. The number of food products was 30 for each category and the total number was 90. The incubation temperature of Petrifilm EB was 37°C and 35°C. There was a high correlation between Petrifilm EB incubated at 37°C and ISO method count results. Two sample t-test result shows it was not statistically significant at the significance level of 5% and Petrifilm EB was comparable to ISO method. There was also a high correlation between Petrifilm EB incubated at 35°C and ISO method count results. However, The Enterobacteriaceae count results of Petrifilm EB incubated at 35°C tended to be higher than of ISO method. Two sample t-test result shows it had significant difference at the significance level of 5% for meat products, and fish and seafood products. There was a high correlation between Petfrifilm EB 35°C and Petfrifilm EB 37°C incubation results. However, the Enterobacteriaceae count results of Petrifilm EB incubated at 35°C tended to be higher than of Petrifilm EB incubated at 37°C. Two sample t-test result shows it had significant difference at the significance level of 5% for each food products. These results indicate the suitability of Petrifilm EB incubated at 37°C as an alternative to ISO method. The benefit of Petrifilm EB is easy to use, faster time to result, no need to prepare the medium, and no need of confirmation test. The count results of Enterobacteriaceae would be changed depending on the condition of incubation. So it would be important that Petrifilm EB incubation condition should be identical to that of official reference method.
Four selective enrichment broths were compared to improve the Official Method in Japan for detection of Salmonella in feed ingredients and formula feed. The current Official Method specifies the use of both Hajna tetrathionate broth (HTT) and selenite cystine broth (SC) for selective enrichment following pre-enrichment. Because SC contains toxic sodium selenite, Rappaport-Vassiliadis enrichment broth (RV) and Rappaport-Vassiliadis soya peptone broth (RVS) were evaluated as alternatives. In a comparison study of spiked broths, 100 ml of RV and RVS were inoculated with 1 ml or 10 ml of pre-enrichment culture. When inoculated with culture that included Salmonella, there were no differences in Salmonella growth. When inoculated with Salmonella only, the Salmonella count in SC, RV and RVS reached ∼108 cfu/ml, but only ∼107 cfu/ml in HTT. When inoculated with cultures containing both Salmonella and a member of the coliform group, the Salmonella count remained about the same while the coliform group count reached ∼107-108 cfu/ml. The result showed that all four broths selectively increased Salmonella growth even in the presence of a coliform competitor. In a study on naturally contaminated feed, 13 out of 23 samples were Salmonella positive (56.5%) with all four broths. A delayed secondary enrichment on the 10 negative samples did not change those results. Comparison studies on routinely inspected feed showed that 6 of 288 samples were Salmonella positive (2.1%) using HTT, SC and RV and 12 of 404 samples were Salmonella positive (3.0%) using HTT, SC and RVS. Further comparison of those results against HTT, SC and RV or RVS showed no significant difference between the broths (p<0.05). In an inter-laboratory comparison, all six laboratories found consistent Salmonella-positive and -negative results for all four broths. These results demonstrate that RV and RVS are acceptable alternatives to SC as selective enrichment broths for detection of Salmonella in feed.
A study on evaluating Preston broth and Bolton broth for reliable detection of Campylobacter jejuni and C. coli from food samples was performed. Both broths were spiked with combination of C. jejuni and C. coli strains, and the growth of strains was determined by quantitative real-time PCR assay. The number of C. jejuni in Preston broth rose to 106-7 CFU/ml, while the number of C. coli ranged from less than 10 to 106 CFU/ml. The number of C. jejuni and C. coli spiked in Bolton broth increased to 106-7 CFU/ml. The result indicated that the Bolton broth excellent ability for growth of broth C. jejuni and C. coli. Trial for detection of C. jejuni and C. coli from retailed chicken meat was carried out with culture method using Preston and Bolton enrichment broths and a quantitative real-time PCR assay. The result of trial showed that the Bolton broth has higher performance for detecting C. coli than Preston broth has, and Preston broth is suitable to detect C. jejuni. These results suggested that use of both Preston and Bolton enrichment broths for detecting C. jejuni and C. coli is essential, and a quantitative real-time PCR assay is useful for rapid detection of Campylobacter.
Kamaboko (steamed surimi) is manufactured by gelling surimi, which is a refined fish protein product. Contamination by Leuconostoc sp. and Enterococcus sp. reduce the shelf-life of kamaboko products during preservation. Particularly, L. mesenteroides produces dextran, called “neto”, on kamaboko and lowers the quality of kamaboko products. Bacteriocins produced by lactic acid bacteria (LAB) were screened for potential use in the control of contamination by Leuconostoc sp. and Enterococcus sp., and the results showed that the bacteriocin produced by Carnobacterium maltalomaticum, which was a strain isolated from the intestine of a herring, had the ability to inhibit these bacteria. The screened bacteriocin was purified by several chromatography steps, and part of its structure was determined. The primary structure of this bacteriocin (called piscicolin KH1) was similar to that of piscicolin 126. Piscicolin KH1 had a strong ability to inhibit E. faecium and L. mesenteroides. Kamaboko samples containing piscicolin KH1 and/or nisin, which is a commonly used food preservative, were prepared, and growth of E. faecium and L. mesenteroides was monitored during preservation at 10°C. The results showed that bacterial growth was significantly inhibited on kamaboko containing piscicolin KH1. Piscicolin KH1 appeared to be more effective than nisin in inhibiting bacterial grown.