丹东口岸2003—2005年进口海产品中3种致病菌的检验

目的掌握丹东口岸进口海产品中单核细胞增生李斯特菌、沙门菌和副溶血性弧菌污染情况。方法对丹东口岸2003—2005年进口的海产品3种致病菌的检验结果进行了分析。结果1965批进口海产品中检出不合格产品44批（2．24％）。其中32批（1．63％）检出单核细胞增生李斯特菌、6批（0．31％）检出沙门菌和6批（0．31％）检出副溶血性弧菌。不合格产品主要为冻章鱼、冻海螺、冻紫石房蛤、活河螺、冻河螺肉等。结论从丹东口岸进口的海产品3种致病菌的污染比较严重，特别是被单核细胞增生李斯特菌的污染最严重，海产品中冻章鱼和冻海螺被这3种致病菌的污染比较普遍。     

Screening of lactic acid bacteria isolates from dairy and cereal products for exopolysaccharide production and genes involved

Scanning electron microscopy (SEM) studies revealed that exposure to 4lethal alkaline stress induced statistically significant (P < 0.05) changes in mean cell length, radius and volume in Listeria monocytogenes and a derived σ^B deficient mutant. Bacterial morphology was altered at pH values above 9.0, to include single filamentous or elongated chain forms. Such filamentation and chain formation was observed in the parent strain and in the σ^B deficient strain, and in buffered and non-buffered media. Giemsa staining revealed that the filaments were multi-nucleate, with nucleoids spaced along the length of the atypical cells. In buffered media, longer alkaline exposure was associated with increases in the frequency and length of filamentation. In non-buffered medium, longer exposure was associated with gradual decline in length and the frequency of observation of filaments. Transfer of alkaline treated cells to neutral conditions was associated with the formation of septa within filaments, cell division, and a rapid return to normal morphology, i.e. within 3 h. The observed effects, and their reversibility, may be important in increasing the alkaline tolerance of this pathogen during phagocytosis within the innate human immune system response, and in adaptation/survival in food environments treated with alkali detergents and/or sanitisers. Such atypical cells may be associated with increased survival of L. monocytogenes in adverse environments and may also contribute to qualitative and quantitative underestimation of this important pathogen in food processing environments, with potential implications in public health.     

Physical and antibacterial properties of edible films formulated with apple skin polyphenols

Fruit and vegetable skins have polyphenolic compounds, terpenes, and phenols with antimicrobial and antioxidant activity. These flavoring plant essential oil components are generally regarded as safe. Edible films made from fruits or vegetables containing apple skin polyphenols have the potential to be used commercially to protect food against contamination by pathogenic bacteria. The main objective of this study was to evaluate physical properties as well as antimicrobial activities against Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica of apple skin polyphenols at 0% to 10% (w/w) concentrations in apple puree film-forming solutions formulated into edible films. Commercial apple skin polyphenol powder had a water activity of 0.44 and high total soluble phenolic compounds and antioxidant capacity (995.3 mg chlorogenic acid/100 g and 14.4 mg Trolox/g, respectively). Antimicrobial activities of edible film containing apple skin polyphenols were determined by the overlay method. Apple edible film with apple skin polyphenols was highly effective against L. monocytogenes. The minimum concentration need to inactive L. monocytogenes was 1.5%. However, apple skin polyphenols did not show any antimicrobial effect against E. coli O157:H7 and S. enterica even at 10% level. The presence of apple skin polyphenols reduced water vapor permeability of films. Apple skin polyphenols increased elongation of films and darkened the color of films. The results of the present study show that apple skin polyphenols can be used to prepare apple-based antimicrobial edible films with good physical properties for food applications by direct contact.     

Mixed species biofilms of Listeria monocytogenes and Lactobacillus plantarum show enhanced resistance to benzalkonium chloride and peracetic acid

We investigated the formation of single and mixed species biofilms of Listeria monocytogenes strains EGD-e and LR-991, with Lactobacillus plantarum WCFS1 as secondary species, and their resistance to the disinfectants benzalkonium chloride and peracetic acid. Modulation of growth, biofilm formation, and biofilm composition was achieved by addition of manganese sulfate and/or glucose to the BHI medium. Composition analyses of the mixed species biofilms using plate counts and fluorescence microscopy with dual fluorophores showed that mixed species biofilms were formed in BHI (total count, 8-9 log₁₀ cfu/well) and that they contained 1-2 log₁₀ cfu/well more L. monocytogenes than L. plantarum cells. Addition of manganese sulfate resulted in equal numbers of both species (total count, 8 log₁₀ cfu/well) in the mixed species biofilm, while manganese sulfate in combination with glucose, resulted in 1-2 log₁₀ more L. plantarum than L. monocytogenes cells (total count, 9 log₁₀ cfu/well). Corresponding single species biofilms of L. monocytogenes and L. plantarum contained up to 9 log₁₀ cfu/well. Subsequent disinfection treatments showed mixed species biofilms to be more resistant to treatments with the selected disinfectants. In BHI with additional manganese sulfate, both L. monocytogenes strains and L. plantarum grown in the mixed species biofilm showed less than 2 log₁₀ cfu/well inactivation after exposure for 15 min to 100 μg/ml benzalkonium chloride, while single species biofilms of both L. monocytogenes strains showed 4.5 log₁₀ cfu/well inactivation and single species biofilms of L. plantarum showed 3.3 log₁₀ cfu/well inactivation. Our results indicate that L. monocytogenes and L. plantarum mixed species biofilms can be more resistant to disinfection treatments than single species biofilms.     

Biofilms of Listeria monocytogenes produced at 12 °C either in pure culture or in co-culture with Pseudomonas aeruginosa showed reduced susceptibility to sanitizers

The biofilm-forming ability of 21 Listeria monocytogenes isolates, previously pulsotyped and corresponding to 16 strains, from different origins was evaluated using the Calgary Biofilm Device, at 37 °C. Biofilms of 4 selected strains were also produced either on pure cultures or on co-cultures with Pseudomonas aeruginosa (PAO1), at 12 °C and at 37 °C. For these biofilms, the minimum biofilm eradication concentrations (MBECs) of 4 commercial dairy sanitizers (1 alkyl amine acetate based--T99, 2 chlorine based--T66 and DD, and 1 phosphoric acid based--BP) were determined. Listeria monocytogenes biofilms grown, either at 37 °C or 12 °C, were able to achieve similar cell densities by using different incubation periods (24 h and 7 d, respectively). In co-culture biofilms, P. aeruginosa was the dominant species, either at 37 °C or at 12 °C, representing 99% of a total biofilm population of 6 to 7 log CFU/peg. Co-culture biofilms were generally less susceptible than L. monocytogenes pure cultures. More interestingly, the biofilms produced at 12 °C were usually less susceptible to the sanitizers than when produced at 37 °C. Single or co-culture biofilms of L. monocytogenes and PAO1, particularly produced at 12 °C, retrieved MBEC values for agents T99 and BP that were, at times, above the maximum in-use recommended concentrations for these agents. The results presented here reinforce the importance of the temperature used for biofilm formation, when susceptibility to sanitizers is being assessed. PRACTICAL APPLICATION: Since most food plants have cold wet growth niches in production and storage areas, susceptibility testing should be performed on biofilms produced at refrigeration temperatures. Moreover, the efficiency of the sanitizers used in food industries should be performed on mixed culture biofilms, since in field conditions these will predominate. The results presented here highlight the importance of the temperature used for biofilm formation, when susceptibility to disinfectants is being assessed, as biofilms produced at lower temperature were less susceptible to sanitizers.     

Methods to determine the growth domain in a multidimensional environmental space

Data from a database on microbial responses to the food environment (ComBase, see www.combase.cc) were used to study the boundary of growth several pathogens (Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, Yersinia enterocolitica). Two methods were used to evaluate the growth/no growth interface. The first one is an application of the Minimum Convex Polyhedron (MCP) introduced by Baranyi et al. [Baranyi, J., Ross, T., McMeekin, T., Roberts, T.A., 1996. The effect of parameterisation on the performance of empirical models used in Predictive Microbiology. Food Microbiol. 13, 83–91.]. The second method applies logistic regression to define the boundary of growth. The combination of these two different techniques can be a useful tool to handle the problem of extrapolation of predictive models at the growth limits.     

李斯特单核增生菌在真空包装切片酱牛肉中的动态变化

将接种不同血清型（４ｂ，１／２ａ和１／２ｃ）李斯特单核增生菌混合物的切片酱牛肉真空包装，然后分别贮藏在４℃，７℃和１５℃，研究李斯特单核增生菌的生长情况。总的来讲，李斯特单核增生菌在所有的样品中生长情况相似。在整个实验期间，起始接菌量为５．４３ＬｏｇＣＦＵ／ｇ的样品上李斯特单核增生菌数量增加了１００倍，而接菌量为＜２．００ＬｏｇＣＦＵ／ｇ的样品上，李斯特单核增生菌数量则增加了１，０００，０００倍。这表明酱牛肉是李斯特单核增生菌生长的良好环境。所以在酱牛肉的生产过程中，一定要采取有效措施减少李斯特单核增生菌的污染。同时应研究安全、经济的手段以杀死污染在酱牛肉上的李斯特单核增生菌，保护消费者健康。     

一株食源性多重耐药单核细胞增生李斯特菌的耐药性研究

本研究对食品样本中分离的一株多重耐药单核细胞增生李斯特菌进行耐药机制的探讨,以期对食源性单核细胞增生李斯特菌多重耐药现象的控制提供理论依据。本文通过聚合酶链式反应筛选耐药决定因子,质粒消除及自然转化实验对耐药决定因子进行定位及传播能力的探讨,最后通过传代实验验证该菌株多重耐药性传播的稳定性。结果表明,对检测到的多重耐药菌株LM78(耐受氯霉素、红霉素、链霉素、四环素、复方新诺明)进行相关耐药基因检测,检测到cat、erm B、tet S 3个耐药基因。质粒消除后MIC值下降到敏感范围,且该质粒可通过自然转化在不同菌属间传递,说明这些耐药基因存在于质粒上。该质粒在无抗生素选择压力下连续传代,仍具有较高稳定性。食源性致病菌多重耐药性有可能通过不同细菌种属间转移,进而由食物链向人类传播,对人类健康造成潜在的威胁。     

Nisin treatments to control Listeria monocytogenes post-processing contamination on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages

Post-processing contamination and growth of Listeria monocytogenes in whey cheeses stored under refrigeration is an important safety concern. This study evaluated commercially available nisin (Nisaplin^®) as a biopreservative to control L. monocytogenes introduced post-processing on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages for up to 45 days. The whey used (pH 6.5–6.7) was from Feta cheese manufacture, and it was subjected either to natural acidification (pH 5.3, readjusted to 6.2 with 10% NaOH) prior to heating, or to direct acidification (pH 6.0–6.2) at 80°C with 10% citric acid. Nisin was added either to the whey (100 or 500 IU g⁻¹) prior to heating, or to the cheese (500 IU g⁻¹) prior to packaging, also inoculated with ca. 10⁴ cfu g⁻¹ of L. monocytogenes strain Scott A. In cheese samples without nisin, L. monocytogenes (PALCAM agar) exceeded 7 log cfu g⁻¹ after the first 10 days of storage, irrespective of the whey acidification method. All nisin treatments had an immediate lethal effect (0.7–2.2 log reduction) on L. monocytogenes populations at inoculation (day 0), which was more pronounced with 500 IU g⁻¹ added to the whey. This treatment also suppressed L. monocytogenes growth below the inoculation level for 30 and 45 days in naturally and directly acidified samples, respectively. All other treatments had weak antilisterial effects. Nisin reversed the natural spoilage flora of Anthotyros cheese from Gram-positive to Gram-negative, and this ecological alteration was far more pronounced in the most effective antilisterial treatments.