Frequency and antimicrobial resistance of enteric bacteria with spoilage potential isolated from table eggs

The prevalence of potential spoilage microorganisms on the shells and in the egg contents of table eggs sold in Trinidad was determined. Table eggs samples were obtained from 23 poultry layer farms, 14 shopping malls and 102 supermarkets across the country. Each farm was visited twice approximately one month apart and 25 pooled eggs constituted a composite sample. Shopping malls were each visited twice usually one month apart while supermarkets were each visited once over a 4-month period. For both mall and supermarkets, six pooled eggs constituted a composite sample. Swabs of egg shells and pooled yolk and albumen (egg content) were tested for selected bacteria using standard methods. The resistance of bacteria to seven antimicrobial agents was detected using the disc diffusion method. Of a total of 184 composite eggs (shells, yolk/albumen or both) sampled, 71 (38.6%) samples were positive for enteric microbes, other than E. coli, Salmonella, Campylobacter spp. and Listeria spp. Enterobacter spp. and Klebsiella spp. were isolated from 15 (8.2%) and 14 (7.6%), respectively, of pooled egg shells alone and from 6 (3.3%) and 3 (1.6%), respectively, of egg content samples alone. Prevalence of enteric bacteria in egg contents was generally higher than found on egg shells with faeces/blood or cracks compared with those without, but the differences were not significant (P > 0.05; X²). The microbial load of egg content was not significantly affected by type of housing of laying birds, source of feeds, use of medicated feeds and temperatures at which eggs were kept at sale outlets. Of a total of 131 bacterial isolates tested, 125 (95.4%) exhibited resistance to one or more antimicrobial agents and resistance was high to streptomycin (90.1%), tetracycline (51.9%) and kanamycin (30.5%). Failure to properly handle or heat table eggs sold in Trinidad poses a potential health hazard to consumers because of their poor microbial quality and high frequency of resistance to antimicrobial agent.     

Presence of multidrug-resistant enteric bacteria in dairy farm topsoil

In addition to human and veterinary medicine, antibiotics are extensively used in agricultural settings, such as for treatment of infections, growth enhancement, and prophylaxis in food animals, leading to selection of drug and multidrug-resistant bacteria. To help circumvent the problem of bacterial antibiotic resistance, it is first necessary to understand the scope of the problem. However, it is not fully understood how widespread antibiotic-resistant bacteria are in agricultural settings. The lack of such surveillance data is especially evident in dairy farm environments, such as soil. It is also unknown to what extent various physiological modulators, such as salicylate, a component of aspirin and known model modulator of multiple antibiotic resistance (mar) genes, influence bacterial multi-drug resistance. We isolated and identified enteric soil bacteria from local dairy farms within Roosevelt County, NM, determined the resistance profiles to antibiotics associated with mar, such as chloramphenicol, nalidixic acid, penicillin G, and tetracycline. We then purified and characterized plasmid DNA and detected mar phenotypic activity. The minimal inhibitory concentrations (MIC) of antibiotics for the isolates ranged from 6 to >50 microg/mL for chloramphenicol, 2 to 8 microg/mL for nalidixic acid, 25 to >300 microg/mL for penicillin G, and 1 to >80 microg/mL for tetracycline. On the other hand, many of the isolates had significantly enhanced MIC for the same antibiotics in the presence of 5 mM salicylate. Plasmid DNA extracted from 12 randomly chosen isolates ranged in size from 6 to 12.5 kb and, in several cases, conferred resistance to chloramphenicol and penicillin G. It is concluded that enteric bacteria from dairy farm topsoil are multidrug resistant and harbor antibiotic-resistance plasmids. A role for dairy topsoil in zoonoses is suggested, implicating this environment as a reservoir for development of bacterial resistance against clinically relevant antibiotics.     

A single method for recovery and concentration of enteric viruses and bacteria from fresh-cut vegetables

Fresh-cut vegetables are prone to be contaminated with foodborne pathogens during growth, harvest, transport and further processing and handling. As most of these products are generally eaten raw or mildly treated, there is an increase in the number of outbreaks caused by viruses and bacteria associated with fresh vegetables. Foodborne pathogens are usually present at very low levels and have to be concentrated (i.e. viruses) or enriched (i.e. bacteria) to enhance their detection. With this aim, a rapid concentration method has been developed for the simultaneous recovery of hepatitis A virus (HAV), norovirus (NV), murine norovirus (MNV) as a surrogate for NV, Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica. Initial experiments focused on evaluating the elution conditions suitable for virus release from vegetables. Finally, elution with buffered peptone water (BPW), using a Pulsifier, and concentration by polyethylene glycol (PEG) precipitation were the methods selected for the elution and concentration of both, enteric viruses and bacteria, from three different types of fresh-cut vegetables by quantitative PCR (qPCR) using specific primers. The average recoveries from inoculated parsley, spinach and salad, were ca. 9.2%, 43.5%, and 20.7% for NV, MNV, and HAV, respectively. Detection limits were 132 RT-PCR units (PCRU), 1.5 50% tissue culture infectious dose (TCID₅₀), and 6.6 TCID₅₀ for NV, MNV, and HAV, respectively. This protocol resulted in average recoveries of 57.4%, 64.5% and 64.6% in three vegetables for E. coli O157:H7, L. monocytogenes and Salmonella with corresponding detection limits of 10³, 10² and 10³ CFU/g, respectively.Based on these results, it can be concluded that the procedure herein is suitable to recover, detect and quantify enteric viruses and foodborne pathogenic bacteria within 5 h and can be applied for the simultaneous detection of both types of foodborne pathogens in fresh-cut vegetables.     

Antimicrobial resistance of gram-negative enteric bacteria from pigs in a nonantimicrobial-exposed herd before and after transportation.

Loading pigs onto trucks and transporting them for 30 min resulted in a significant increase in proportion of antimicrobial resistance of gram-negative enteric bacteria in fecal material. Similarly, the mean number of antimicrobial agents in the resistance patterns of these bacteria increased during loading and transportation. However, the increases were of a transient nature, as resistance values were similar to those of a nontransported control group 1 day after the pigs had been transported.     

乳酸菌固态发酵豆粕产酸性能分析

该研究以实验室保藏的优良乳酸菌为研究对象,探究6株乳酸菌液体和固态发酵豆粕产有机酸的变化。结果显示,6株乳酸菌MRS培养基液体发酵和固态发酵豆粕产酸效果均存在较大差异。菌株MRS培养基发酵结果表明,植物乳杆菌（Lactobacillus plantarum）BLCC2-0410、BLCC2-0069总酸含量分别为18.90 g/L、18.25 g/L,显著高于其余4株菌（P＜0.05）。固态发酵豆粕结果表明,使用植物乳杆菌BLCC2-0410发酵后豆粕pH值可下降到4.33,总酸含量最高为33.73 g/kg,乳酸含量为18.91 g/kg,酒石酸含量为10.43 g/kg,柠檬酸含量为3.79 g/kg,明显高于其他菌株,因此,确定发酵豆粕产酸的最适菌株为植物乳杆菌BLCC2-0410。     

Vibrio cholerae and enteric bacteria in oyster-producing areas of two urban estuaries in Australia

Three sampling sites in oyster-producing areas of 2 estuaries were monitored at intervals of about 2 weeks for 1 year. Oysters (Crassostrea commercialis), water and sediment were examined for Vibrio cholerae, Escherichia coli and Salmonella. V. cholerae was detected in 20, 30 and 11% of oyster, water and sediment samples respectively. The highest incidence was in the autumn (March-May), with few isolations from July to October. Most isolates were non-O1 serotypes. The presence of V. cholerae and the enteric bacteria appeared to be influenced by different, but perhaps overlapping, sets of factors in these high salinity waters. There was no relationship between rainfall or salinity and the detection of V. cholerae, whereas high counts of E. coli in oysters and the presence of Salmonella were correlated wtih rainfall and, to a lesser degree, reduced salinity. High counts of E. coli were correlated with V. cholerae isolations from water and with the presence of Salmonella. Oysters concentrated E. coli effectively. The counts of E. coli in oysters were 7.3 times higher than those in water. Examination of 8 batches of purified and unpurified oysters indicated that purification reduces the incidence of V. cholerae. However V. cholerae was detected in 3 of 25 market samples of oysters, demonstrating that it can be present in oysters throughout the distribution system. The highest V. cholerae count observed in oysters was 3/g.     

乳糖酸生产菌株的筛选与鉴定

乳糖酸具有良好的功能特性。经富集培养,从土壤样品中分离出了201株菌株,经x-gal平板培养基、伊红美蓝合成培养基和指示平板培养基筛选出29株疑似乳糖酸生产菌株。利用薄层色谱法定性鉴定出5株疑似乳糖酸生产菌株,最终用高效液相色谱法确定出一株优良的乳糖酸生产菌株Y20,其乳糖酸产量为127.65g/L,转化率为85.10%,经生理生化鉴定和16SrDNA分子鉴定,该菌为土生拉乌尔菌。      

乳酸菌生理功能的研究进展

本文综述了乳酸菌的生理功能的研究进展,并对乳酸菌的应用作了展望     

乳糖酸生产菌株的筛选与鉴定

乳糖酸具有良好的功能特性.经富集培养,从土壤样品中分离出了201株菌株,经x-gal平板培养基、伊红美蓝合成培养基和指示平板培养基筛选出29株疑似乳糖酸生产菌株.利用薄层色谱法定性鉴定出5株疑似乳糖酸生产菌株,最终用高效液相色谱法确定出一株优良的乳糖酸生产菌株Y20,其乳糖酸产量为127.65g/L,转化率为85.10％,经生理生化鉴定和16SrDNA分子鉴定,该菌为土生拉乌尔菌.     

Acid and bile tolerance of spore-forming lactic acid bacteria

Criteria for screening probiotics such as bile tolerance and resistance to acids were studied with 13 spore-forming lactic acid producing bacteria. Different strains of Sporolactobacillus, Bacillus laevolacticus, Bacillus racemilacticus and Bacillus coagulans grown in MRS broth were subjected to low pH conditions (2, 2.5 and 3) and increasing bile concentrations. Among these microorganisms, Bacillus laevolacticus DSM 6475 and all Sporolactobacillus strains tested except Sporolactobacillus racemicus IAM 12395, were resistant to pH 3. Only Bacillus racemilacticus and Bacillus coagulans strains were tolerant to bile concentrations over 0.3% (w/v).     

Acid phosphatase activity and color changes in consumer-style griddle-cooked ground beef patties

The U.S. Department of Agriculture and the Food and Drug Administration have issued temperature requirements to help consumers cook beef patty products that are free of pathogens. Verification of end-point temperature (EPT) is needed in cooked meat products due to concerns over outbreaks of Escherichia coli O157:H7. Acid phosphatase (ACP) activity was studied as a potential method for determination of EPT in ground beef patties cooked nonfrozen, patties frozen 7 days and thawed at room temperature 4 h in a refrigerator or by microwave, and patties made from ground beef frozen in store packages, then thawed in a refrigerator overnight. Pressed-out meat juices were analyzed from patties (n = 314) cooked to 57.2 degrees C (135 degrees F). 65.6 degrees C (150 degrees F), 71.1 degrees C (160 degrees F), and 79.4 degrees C (175 degrees F) target EPTs. Expressed meat juice and internal meat patty color decreased in redness as EPT increased. Freezing whole packs with slow refrigerator or room temperature thawing caused significantly greater loss of redness in expressed cooked meat juice than did other handling methods. Log10 ACP had a significant linear (R2 = 0.99) response to EPT. Results show that the 3- to 5-min ACP test could be used to verify EPT in griddle-cooked hamburger patties.     

Purification and properties of an acid phosphatase from Lactobacillus curvatus DPC2024

An acid phosphatase was purified to homogeneity from a cell-free extract of Lactobacillus curvatus DPC2024 by chromatography on diethylaminoethyl-Sephacel, Phenyl Sepharose, chelating Sepharose Fast Flow and MonoQ. The purified enzyme was a tetramer with a subunit molecular mass of 26 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis and gel filtration chromatography. Its optimum activity was at pH 4.5 and 70°C, with more than 65% of its activity retained after pre-heating for 30 min at 70°C. The enzyme was strongly inhibited by NaF (0.1 m ) and ZnCl₂ (1.0 m ); slightly inhibited by hexametaphosphate, tripolyphosphate or pyrophosphate at 1.0 m concentrations; but unaffected by 10 m ascorbic acid. The acid phosphatase hydrolysed a number of phosphate esters but not bis(p-nitrophenyl)phosphate nor uridine-5′-monophosphate. The N-terminal amino acid sequence of the first 20 residues of this enzyme showed 65% homology with an acid phosphatase from Lactobacillus plantarum DPC2739 and some homology with other phosphatases from mammals, yeasts and Escherichia coli.     

Acid phosphatase in the tubers of Dioscorea species and its purification from the white yam (D. rotundata poir)

Acid phosphatase activity was determined in 15 cultivars from four species of yam. A 12-fold purification of the enzyme from Dioscorea rotundata (cv. chikakwondo) gave a homogeneous preparation as demonstrated by polyacrylamide gel electrophoresis. This enzyme preparation has an apparent molecular weight of 115 000 ±2000 and an optimum activity at a pH of 5·20 and a temperature of 50°C. The K_m of the enzyme is 3·81 mM with disodium p-nitrophenylphosphate (p-NNP) as a substrate. The energy of activation, heat of activation, energy of inactivation and heat of inactivation are 7·0, 6·4, 4·41 and 4·34 kcal M^?1, respectively. Although it has very little activity with most organic phosphoric acid esters, it is significantly inhibited by Ca²⁺, Hg²⁺ and EDTA and activated by Mg²⁺. The enzyme has a half-life of 50,17 or 13 days, respectively, when stored at 6-8°C, 0°C or room temperature (29±2°C).     

应用高效液相色谱分析藏灵菇源乳酸菌发酵液中的四碳二羧酸

目的:分析藏灵菇源乳酸菌发酵液中的四碳二羧酸,研究发酵条件对合成四碳二羧酸的影响。方法:采用高效液相色谱分析藏灵菇源乳酸菌Tx、KS4、KL1菌株发酵液中的四碳二羧酸,通过四因素三水平[L9(34)]正交试验确定高产四碳二羧酸的发酵条件。结果:发酵液中草酰乙酸含量0.03318 g/L,延胡索酸含量0.05002 g/L,苹果酸含量0.000046 g/L;优化的发酵条件是:乳酸菌Tx、KS4与KL1菌种比例为3:3:3,接种量2%,发酵温度40℃,发酵时间24 h。在此条件下,合成四碳二羧酸含量是优化前的27.25倍,其中,草酰乙酸含量是优化前的41.21倍,延胡索酸含量是优化前的17.08倍,苹果酸含量是优化前的1 001.3倍。结论:在优化的发酵条件下,藏灵菇源乳酸菌混合发酵液中的四碳二羧酸含量明显提高。     

葡萄糖酸钠对仔猪肠道内乳酸菌增殖及培养条件的研究

该研究采用平板计数方法,研究了葡萄糖酸钠添加对仔猪肠道内乳酸菌增殖的影响情况,研究结果表明,添加一定量的葡萄糖酸钠于仔猪饲料能促进肠道内的乳酸菌的生长,使其增殖.从仔猪肠道内分离纯化出一种乳酸杆菌,并研究了葡萄糖酸钠对该菌的体外促进作用,研究结果显示,低浓度的葡萄糖酸钠能促进乳酸菌的生长,高浓度的葡萄糖酸钠能抑制乳酸菌的生长.     

硫酸水解法去除谷氨酸母液中的焦谷氨酸

焦谷氨酸没有鲜味,是谷氨酸产品中的无效成分,其安全性尚无定论.控制谷氨酸浓度为16 g/dL,焦谷氨酸的浓度为3.2 g/dL,实验研究了水解温度、硫酸加入量、水解时间等因素对降低谷氨酸母液中焦谷氨酸含量的影响.在保证谷氨酸回收率的基础上,确定出使焦谷氨酸含量达到1％及以下的最优水解组合:水解温度(95±5)℃、浓硫酸加入量(30％,V/V)、水解时间(2 h).在上述实验中,焦谷氨酸的初始含量均为20％.通过改变初始焦谷氨酸含量为20％～35％,最优水解组合下,水解后焦谷氨酸含量为0.96％～1.0％,仍可达到1％以下.     

Assessment of human enteric viruses in shellfish from the northern Adriatic sea

Incidence and circulation of different strains of hepatitis A and Norovirus in shellfish were studied on 235 samples (Tapes philippinarum, Mytilus galloprovincialis, Ostrea spp. and Chlamys spp.) obtained from different sites, representing the shellfish production areas of the northern Adriatic sea. Shellfish were harvested in the period of one year and, after depuration, were examined for bacterial (Escherichia coli and Salmonella) and viral (HAV and NoV) contamination. Viral contamination was present on average in 22% of samples: specifically, 6% of samples tested positive for HAV, 14% for NoV and 2% for both viruses. None of the samples revealed the presence of Salmonella, and in most of them (93%) the number of E. coli was below the European legislation limit of 230 MPN/100 g. T. philippinarum was the species most often contaminated, as well as being the only species in which the legal limit for E. coli was, in some cases, exceeded. Both HAV and NoV contamination were detected throughout the year; NoV detection was slightly more frequent during winter months, but positive samples were also present in summer. The sequencing of the PCR products showed the circulation of only one HAV genotype (IA) and four different NoV genotypes (Hawaii, Melksham, Lordsdale and GGIIb) with a prevalence of the GGIIb genotype in the second period of the monitoring.