Effect of gastro-intestinal conditions on the growth of Enterococcus mundtii ST4SA, and production of bacteriocin ST4SA recorded by real-time PCR

Enterococcus mundtii ST4SA, isolated from soybeans, produces a 3950 Da bacteriocin (bacST4SA) active against a variety of Gram-positive and Gram-negative bacteria, including human pathogens. In this study, the effect of gastro-intestinal conditions on the survival of strain ST4SA and production of bacST4SA was studied. Strain ST4SA was cultured in MRS broth at different pH and in MRS broth supplemented with bile, pancreatic enzymes, and contents of the stomach and small intestine of pigs, respectively. After 12 and 24 h at 37 degrees C, cells were harvested, RNA isolated and cDNA prepared. Expression of the genes encoding bacST4SA, RecA, GroES and 23 S rRNA was studied by real-time PCR (RT-PCR). No significant up- or down-regulation of the genes were recorded, except when cells were grown in MRS at pH 3.5. In this case only RecA and GroES were up-regulated. Growth of strain ST4SA and production of bacST4SA are not affected by conditions in the lower intestine and the strain could be used as a probiotic.     

自贡市肉及其制品中粪肠球菌耐药性毒力基因和多位点序列分析

目的了解四川省自贡市肉及其制品分离粪肠球菌的抗生素耐药性和携带毒力基因情况,以及多重耐药菌株的序列分型(ST)。方法 2013年4月17~21日对147份肉及其制品样品污染的粪肠球菌进行分离鉴定,使用全自动微生物鉴定仪对分离菌株的耐药性进行检验,应用聚合酶链式反应(PCR)方法检测分离到的粪肠球菌携带4种常见毒力基因的情况,并对多重耐药菌株进行多位点序列分型(MLST)研究。结果从147份肉及其制品样品中共分离到65株粪肠球菌,其中耐药菌株比例为58.5%(38/65);分离菌株对四环素的耐药率最高,为41.5%(27/65),对利福平、氯霉素和红霉素也均有较高的耐药率;分离菌株对高浓度链霉素和高浓度庆大霉素的耐药率分别达到了15.4%(10/65)和12.3%(8/65);未分离到对青霉素类(青霉素和氨苄西林)、糖肽类(万古霉素)和脂肽类(达托霉素)抗生素耐药的菌株。4种常见毒力基因(gel E、asa1、esp、cyl A)在65株分离株中均有携带,阳性率分别为56.9%(37/65)、21.5%(14/65)、9.2%(6/65)和7.7%(5/65)。14株多重耐药菌株共有9个MLST型别,包括4株ST16、2株ST81和2株ST480菌株,且相同ST型别的粪肠球菌有相似的耐药谱和毒力基因携带情况。结论四川省自贡市肉及其制品中相同ST型别的粪肠球菌有相似的耐药谱和毒力基因携带情况,应重视肉及其制品中耐药粪肠球菌对公众健康的潜在威胁。     

Screening for enterocins and detection of hemolysin and vancomycin resistance in enterococci of different origins

The inhibitory activity of 122 out of 426 Enterococcus strains of geographically widespread origin and from different sources (food and feed, animal isolates, clinical and nonclinical human isolates) was tested against a wide range of indicator bacteria. Seventy-two strains, mainly belonging to the species Enterococcus faecium and Enterococcus faecalis were bacteriocinogenic. A remarkable variation of inhibitory spectra occurred among the strains tested, including inhibition of, for instance, only closely related enterococci, other lactic acid bacteria (LAB), food spoilage and pathogenic bacteria. No correlation could be found between the origin of the strains and the type of inhibitory spectrum, although a clustering of human isolates from both fecal and clinical origin was observed in the group of strains inhibiting lactic acid bacteria, Listeria, and either Staphylococcus or Clostridium. No relationship could be established between the presence of enterocin structural genes and the origin of the strain either, and hence no correlation seemed to exist between the presence of known enterocin genes and the activity spectra of these enterococci. The structural gene of enterocin A was widely distributed among E. faecium strains, whereas that of enterocin B only occurred in the presence of enterocin A. The vancomycin resistance phenotype as well as the presence of vancomycin resistance genes was also investigated. The vanA gene only occurred among E. faecium strains. The incidence of beta-hemolysis was not restricted to E. faecalis strains, but among the E. faecium strains the structural genes of cytolysin were not detected. beta-Hemolysis occurred in strains both from food and nonfood origin. It has been concluded that bacteriocin-producing E. faecium strains lacking hemolytic activity and not carrying cytolysin nor vancomycin resistance genes may be useful as starter cultures, cocultures, or probiotics.     

Application of bacteriocinogenic Enterococcus mundtii CRL35 and Enterococcus faecium ST88Ch in the control of Listeria monocytogenes in fresh Minas cheese

Several strains of Enterococcus spp. are capable of producing bacteriocins with antimicrobial activity against important bacterial pathogens in dairy products. In this study, the bacteriocins produced by two Enterococcus strains (Enterococcus mundtii CRL35 and Enterococcus faecium ST88Ch), isolated from cheeses, were characterized and tested for their capability to control growth of Listeria monocytogenes 426 in experimentally contaminated fresh Minas cheese during refrigerated storage. Both strains were active against a variety of pathogenic and non-pathogenic microorganisms and bacteriocin absorption to various L. monocytogenes, Enterococcus faecalis ATCC 19443 and Lactobacillus sakei ATCC 15521 varied according to the strain and the testing conditions (pH, temperature, presence of salts and surfactants). Growth of L. monocytogenes 426 was inhibited in cheeses containing E. mundtii CRL35 up to 12 days at 8 °C, evidencing a bacteriostatic effect. E. faecium ST88Ch was less effective, as the bacteriostatic affect occurred only after 6 days at 8 °C. In cheeses containing nisin (12.5 mg/kg), less than one log reduction was observed. This research underlines the potential application of E. mundtii CRL35 in the control of L. monocytogenes in Minas cheese.     

Enterococcus faecium AS8及其胞外多糖对发酵乳流变学特性的影响

通过红外光谱、气相色谱-质谱联用和流变仪的检测,探究产自屎肠球菌（Enterococcus faecium）AS8的胞外多糖（exopolysaccharide,EPS）（AS8-EPS）的结构组成和流变性能。采用3 种发酵乳作为样品,分别为Streptococcus thermophilus＋Lactobacillus bulgaricus、EPS＋S. thermophilus＋L. bulgaricus和E. faecium AS8。结果表明,在贮藏期间,不同发酵乳样品具有不同的流变学性质。同时,补充添加EPS和原位EPS对发酵乳流变性能具有不同的影响。通过Sephadex G-100和Sephadex G-50的分离纯化,获得2 种多糖,分别为AS8-1-EPS和AS8-2-EPS。AS8-1-EPS主要单糖组成为甘露糖、葡萄糖和半乳糖（分别占59.1%、26.8%、7.9%）,还有含量很少的其他单糖;AS8-2-EPS主要单糖组成为甘露糖、葡萄糖、半乳糖和鼠李糖（分别占65.4%、21.3%、8.9%、4.4%）。红外光谱检测结果表明AS8-1-EPS和AS8-2-EPS均为杂多糖。     

Speciation and frequency of virulence genes of Enterococcus spp. isolated from rainwater tank samples in Southeast Queensland, Australia

In this study, 212 Enterococcus isolates from 23 rainwater tank samples in Southeast Queensland (SEQ), Australia were identified to the species level. The isolates were also tested for the presence of 6 virulence genes associated with Enterococcus related infections. Among the 23 rainwater tank samples, 20 (90%), 10 (44%), 7 (30%), 5 (22%), 4 (17%), 2 (9%), and 1 (4%) samples yielded E. faecalis, E. mundtii, E. casseliflavus, E. faecium, E. hirae, E. avium, and E. durans, respectively. Among the 6 virulence genes tested, gelE and efaA were most prevalent, detected in 19 (83%) and 18 (78%) of 23 rainwater tank samples, respectively. Virulence gene ace was also detected in 14 (61%) rainwater tank samples followed by AS, esp (E. faecalis variant), and cylA genes which were detected in 3 (13%), 2 (9%), and 1 (4%) samples, respectively. In all, 120 (57%) Enterococcus isolates from 20 rainwater tank samples harbored virulence genes. Among these tank water samples, Enterococcus spp. from 5 (25%) samples harbored a single virulence gene and 15 (75%) samples were harboring two or more virulence genes. The significance of these strains in terms of health implications remains to be assessed. The potential sources of these strains need to be identified for the improved management of captured rainwater quality. Finally, it is recommended that Enterococcus spp. should be used as an additional fecal indicator bacterium in conjunction with E. coli for the microbiological assessment of rainwater tanks.     

Enterococci from Appenzeller and Schabziger raw milk cheese: antibiotic resistance, virulence factors, and persistence of particular strains in the products

Enterococci are natural residents of human and animal intestinal tracts, and grow to high numbers in a variety of cheeses. The aim of this study was to determine the diversity of enterococci in two types of artisanal raw milk cheese (Schabziger and Appenzeller) and to investigate whether particular strains with triple resistance against chloramphenicol (Chl), tetracycline (Tet), and erythromycin (Ery) persist in the production system. Of 46 cheese samples, a total of 312 Enterococcus strains were isolated over a 5-month period on selective agar plates containing Chl, Tet, or, Ery. Enterococcus faecalis was the predominant species (80.7%), followed by Enterococcus faecium (5.1%), and Enterococcus durans (11.7%). According to the phenotypic resistance patterns, a selection of 150 strains was analyzed with PCR for the presence of genes encoding resistance to Ery (ereA, ereB, mphA, ermA, ermB, ermC, mrsA/mrsB, mefA/mefE), and Tet (tetM, tetL). Because virulence factors have been linked to the pathogenicity of enterococci, the strain selection was also tested for the presence of the following virulence factors: Agg, GelE, Cyl, Esp, EfaAfs, EfaAfm, Cpd, Cob, and Ccf. All tested strains contained at least two of the nine virulence genes taken into analysis. Pulsed-field gel electrophoresis patterns of the isolates showed a limited persistence of several strains over a period of 1 to 2 months in Schabziger, and more than 2 months in Appenzeller. Finally, the enterococcal flora in the two types of cheeses seems to be rather unrelated. Within 150 strains from 25 different cheese samples (11 Appenzeller and 14 Schabziger), 41 pulsed-field gel electrophoresis patterns could be identified, and only 1 of these was found in enterococci from both types of cheese.     

Altering the thermal resistance of foodborne bacterial pathogens with an eggshell membrane waste by-product

Eggshells from egg-breaking operations are a significant waste disposal problem. Thus, the development of value-added by-products from this waste would be welcomed by the industry. The ability of extracted eggshell membranes containing, several bacteriolytic enzymes (i.e., lysozyme and beta-N-acetylglucosaminidase) or other membrane components to alter the thermal resistance of gram-positive and gram-negative bacterial pathogens was evaluated. Mid-log phase cells of Salmonella Enteritidis (SE), Salmonella Typhimurium (ST), Escherichia coli O157:H7 (EC), Listeria monocytogenes Scott A (LM), and Staphylococcus aureus (SA) were suspended in 100 ml of 0.1% peptone water (pH 6.9, 10(7-8) CFU/ml) containing either 0 (control) or 10 g of an eggshell membrane extract and incubated at 37 degrees C for 45 min. Following exposure, membrane-free samples (1.5 ml) were heated in a 56 degrees C (LM, SA), 54 degrees C (SE, ST), or 52 degrees C (EC) water bath from 0 to 14 min in sealed glass reaction vials (12 by 32 mm), and the survivors were recovered on brain heart infusion agar. Population reductions ranging from 27.6% (SA) to 99.8% (LM) (ST, 43.8%; SE, 47.5%; EC, 71.8%) were observed for cells treated for 45 min with extracted membrane, as compared to controls. D-value reductions ranging from 0 (LM) to 87.2% (SE) (SA, 36.7%; EC, 83.3%; ST, 86.3%) were observed when membrane-treated cells were subsequently heat inactivated. The effects of exposure pH, time, temperature, and organic load on membrane activity were also evaluated with Salmonella Typhimurium. Exposure pH (5.0 versus 6.9), time (15 versus 45 min), and temperature (4 degrees C versus 37 degrees C) did not significantly reduce the impact of eggshell membranes on D-values. However, the presence of organic matter (0.1% peptone water versus skim milk) significantly reduced the thermal resistance-reducing capacity of the membranes. These preliminary findings provide information on the potential use of extracted eggshell membranes to alter bacterial heat resistance.     

全球副溶血弧菌环境菌株的基于碱基序列和肽链序列的多位点序列分型

为了了解来自全球的副溶血弧菌环境菌株的群组结构和克隆复合体构成,利用PubMLST公共数据的数据,筛选其中具有完整序列分型（sequence type,ST）及肽序列型（peptide sequence type,pST）的来自全球的副溶血弧菌环境菌株数据,进行亚群分析和克隆复合体分析,并分别构建了基于ST型和pST型的最小生成树。结果表明,从数据库中共筛选到具有ST型及pST型的来自全球的副溶血弧菌环境菌株数据886 条,共含有663 个ST型,以ST3型为最多,但也仅含27 条菌株信息。其中,有436 条菌株数据来自中国（包括大陆、香港和台湾）,覆盖了410 个ST型,每个ST型含1～4 条菌株数据,这436 条菌株数据又可分为128 个pST型,其中pST1型为最多,达116 条菌株数据。利用eBURST软件对数据进行分析,共发现了73 个组,483 个单体。STRUCTURE软件分析显示来自全球的副溶血弧菌环境菌株的适宜亚群数为4,各亚群内的样品平均距离为0.981 7。综上结果表明,来自全球的副溶血弧菌环境菌株具有高度多态性,可更细分为4 个亚群,MLST分型时以ST3型为多,AA-MLST分型时以pST1型为主。     

Short communication: First detection of Panton-Valentine leukocidin–positive methicillin-resistant Staphylococcus aureus ST30 in raw milk taken from dairy cows with mastitis in South Korea

We identified 199 Staphylococcus aureus isolates from quarter milk samples of 1,289 dairy cattle between 2014 and 2018. About 66% of the isolates were resistant to at least 1 antimicrobial agent; the highest rate of resistance was to penicillin, followed by resistance to ampicillin, erythromycin, and sulfadimethoxine. We obtained 30 methicillin-resistant S. aureus (MRSA) strains from 6 farms in 3 provinces. The MRSA strains exhibited a significantly higher resistance rate to most of the tested antimicrobials than the oxacillin-susceptible strains. The MRSA strains represented 5 genotypes: ST72-t324-SCCmec IV (n = 14), ST30-t1752-SCCmec IV (n = 8), ST188-t189-SCCmec NT (n = 6), ST188-t2284-SCCmec NT (n = 1), and NT-NT-SCCmec IV (n = 1). One of the ST188 MRSA strains represented a novel staphylococcal protein A (spa) type (t2284). In addition, 7 of the 8 ST30 MRSA strains were Panton-Valentine leukocidin (PVL)–positive and carried various staphylococcal enterotoxin encoding genes. This is the first report of PVL-positive ST30 MRSA-t1752-SCCmec IV from bovine mastitis in Korea. All of ST72-t324-SCCmec IV MRSA strains carried staphylococcal enterotoxin and leukotoxin encoding genes. They were also sensitive to most of the tested non-β-lactam antimicrobials. In contrast, ST188-t189 MRSA strains were resistant to multiple antimicrobials and predominantly carried the leukotoxin encoding gene. Taken together, these findings may indicate that dairy cows could be a major source for spreading MRSA strains, and contaminated milk could be a vehicle for transmission. Suitable hygienic measures should be established in dairy farms and processing plants to limit the likelihood of introducing MRSA into the food chain.     

Effect of Lactococcus garvieae, Lactococcus lactis and Enterococcus faecalis on the behaviour of Staphylococcus aureus in microfiltered milk

The effect of four strains of Lactococcus garvieae, three strains of Lactococcus lactis and one strain of Enterococcus faecalis on Staphylococcus aureus SA15 growth in microfiltered milk was evaluated. Lactococcus and Enterococcus strains were co-cultured with S. aureus in microfiltered milk and in medium buffered at pH 6.8. All Lactococcus and Enterococcus strains were able to inhibit S. aureus growth after 6h of incubation. Inhibition by L. lactis and E. faecalis strains could be partially attributed to the decrease in pH below 6.0 as it has been observed in medium buffered at pH 6.8. L. garvieae strains were the most effective to inhibit S. aureus growth without acidification. Inhibition of S. aureus could not be attributed neither to production of lactate, acetate or nor to antistaphylococcal substance. Amino acids competition was not involved in the inhibition by L. garvieae as addition of valine, isoleucine, threonine, methionine and phenylalanine did not suppress the inhibition of S. aureus.     

香蕉—菠萝复合果酒双酵母混合发酵工艺

采用2种果酒酵母菌株相混合对香蕉-菠萝复合汁液进行双酵母混合发酵实验,发现GJJM 1.69果酒酵母与GIM2.132白梨酒酵母相互混合与单一的GIM2.92葡萄酒酵母和其他组合的双酵母相比较,酿出的香蕉-菠萝复合果酒色香味较好,酒精生成量也较高。经正交试验得出GJJM 1.69与GIM2.132在香蕉-菠萝复合果酒中的双酵母发酵的最佳工艺条件为:接种量8×103个/mL、亚硫酸氢钠添加量0.008%、发酵初始糖度26%、发酵pH3.6。     

Ascorbate, green tea and grape seed extracts increase the shelf life of low sulphite beef patties

Green tea (GTE) and grape seed (GSE) extracts are proposed as preservatives for increasing the shelf life of low sulphite raw beef patties. The antioxidant and antimicrobial activities of both extracts were compared with ascorbate. Five groups were established for the patties: Control (with no additives), S (100 SO₂), SA (100 SO₂ + 400 sodium ascorbate), ST (100 SO₂ + 300 GTE) and SG (100 SO₂ + 300 GSE) (mg per kg of meat). Patties were stored at 4 °C in aerobic packaging for 0, 3, 6 or 9 days under retail display conditions. Meat spoilage (total viable and coliform counts, pH, lightness, chroma, hue angle, metmyoglobin and TBARS) was determined. The sensory contribution of the extracts to cooked patties was evaluated (colour, odour, flavour and texture). The results pointed to the possibility of using low SO₂-vegetable extract combinations to preserve raw meat products. ST, SG and SA delayed microbial spoilage, redness loss and lipid oxidation, thus increasing the shelf life of the raw sulphite beef patties by 3 days. ST, SG and SA also delayed the onset of rancid flavours in cooked patties. No anomalous sensory traits were caused by either extract. Ascorbate, GTE and GSE improved the preservative effects of SO₂ on beef patties, especially against meat oxidation. This suggested that the quantity of SO₂ added can be reduced to obtain healthier raw meat products.     

固态发酵淀粉渣生产蛋白饲料的研究

本文研究了用黑曲霉ＳＡ１１９和皮状丝孢酵母ＳＴ_（８５１）固态发酵淀粉渣生产饲料蛋白。ＳＡ１１９菌株在固态淀粉渣上可产生多种酶活性，并降解其中的纤维素物质，在２８±２℃的最适温度下，产生的木聚糖酶活性为２８５０．５４±３０４．２３ｕ／ｇ，半纤维素降解率为３３．９８±２．５１％。ＳＴ_（８５１）能与之很好的共生，两者混合培养使产品粗蛋白含量达到２１．４５％，氨基酸组成齐全，尤其是动物必需的第一限制性氨基酸─蛋氨酸含量在蛋白质中的比例，高出ＦＡＯ标准０．８倍。喂养试验证明，该产品可以代替部分鱼粉。毒理学试验证明该产品实属无毒，安全可靠。     

Vancomycin-resistant enterococci isolated from animals and food

One hundred and one chicken products, boiled ham and turkey cold meat were acquired from 18 different supermarkets in Spain during October 1997 to June 1998 and were analyzed for vancomycin-resistant enterococci (VRE). In the same way, 50 intestinal chicken samples from a slaughterhouse were also studied. VRE were detected in 25 of 92 samples of food of chicken origin (27.2%), but no VRE were found in cooked pork or turkey products. VRE were also detected in 8 of 50 intestinal chicken samples from the slaughterhouse (16%). VRE were identified as Enterococcus durans (n = 11), Enterococcus faecalis (n = 10), Enterococcus faecium (n = 10) and Enterococcus hirae (n = 2). All these strains were characterized as belonging to the vanA genotype by polymerase chain reaction. Ampicillin, quinupristin/dalfopristin and high level aminoglycoside resistance were frequently found among these strains. Heterogeneity was observed in susceptibility patterns among VRE strains, even in those of the same species. The high rate of colonization of chicken products by vanA containing enterococci detected 6 months to 1 year after the banning of avoparcin as a growth promoter, supports other studies suggesting that the food chain could be a source of VRE colonization in humans and thus a source of VRE infections.     

PubMLST数据库克罗诺杆菌中外分离株的分型比较

为了解中国与全球其他地区克罗诺杆菌（Cronobacter）分离株的差异,从PubMLST数据库下载具有完整序列型（ST）的菌株信息进行分离源、种、序列型及克隆复合体（CC）分析,并深入分析国内外食品及临床分离株。结果显示,具有完整ST型的中国克罗诺杆菌分离株（907株）最多,来源主要是婴儿配方奶粉、香料和即食食品。克罗诺杆菌中国分离株具有高度遗传多样性,我国的食品分离株（580株）中,CC4和CC7型菌株占比较高;但我国及其他东亚和南亚国家都没有临床株的信息。我国分离株明确致病型信息与欧美国家的差异较大,仅ST256（1株）、ST60（2株）、ST83（2株）与新生儿脑膜炎相关,欧美国家则主要包括ST4、ST1、ST12、ST7,说明我国的克罗诺杆菌与其他国家地域的菌株在系统进化和毒力可能具有差异,或与克罗诺杆菌的感染对象-人种的差异有关。     

Bile salt hydrolase activity of Enterococci isolated from food: screening and quantitative determination

One hundred seventeen enterococcal strains isolated from food (47 Enterococcus faecium, 48 Enterococcus faecalis, 16 Enterococcus durans, 2 Enterococcus gallinarum, 3 Enterococcus casseliflavus, and 1 Enterococcus malodoratus) were screened for bile salt hydrolase (BSH) activity on de Man, Rogosa, and Sharpe agar medium containing taurocholic acid and calcium chloride. The highest incidence of BSH-active strains was observed for E. faecalis (81%) followed by E. faecium (50%) and E. durans (44%). Isolates were grouped into four putative activity groups (no, low, medium, and high activity) based on the size of precipitation zones observed in the screening experiment. Our results showed that assumptions on BSH activity based on the size of bile precipitation zones in screening experiments did not correlate with actual activity as quantified by high-pressure liquid chromatography, but the screening assay is useful for assessing the presence or absence of BSH activity.     

Novel bacteriocinogenic Enterococcus hirae and Pediococcus pentosaceus strains with antilisterial activity isolated from Brazilian artisanal cheese

We isolated and characterized bacteriocin producers Enterococcus hirae ST57ACC and Pediococcus pentosaceus ST65ACC from raw milk artisanal cheeses. Their bacteriocins were tolerant to temperatures from 4°C to 100°C and under sterilization conditions (121°C for 15 min). Additionally, the tested bacteriocins remained active after being exposed to pH 2.0 to 10.0 for 2 h. The activity of the bacteriocins was affected by proteolytic enzymes but remained stable after treatment with EDTA, sodium dodecyl sulfate, NaCl, skim milk, and Tween 80. Cell-free supernatants were capable of inhibiting Listeria innocua and several strains of Listeria monocytogenes obtained from different sources and belonging to different serotypes. When L. monocytogenes 211 and L. monocytogenes 422 were treated with bacteriocins, growth was completely inhibited over 12 h. Cocultures of bacteriocinogenic strains and L. monocytogenes 422 in skim milk showed that E. hirae ST57ACC could control the growth of the pathogen in the matrix after 48 h. None of the selected isolates presented positive results on a screening panel for 25 bacteriocin-related genes, however, indicating that both strains might express novel bacteriocins.     

Assessment of safety of enterococci isolated throughout traditional Terrincho cheesemaking: virulence factors and antibiotic susceptibility

Enterococci account for an important fraction of the adventitious microflora of traditional cheeses manufactured in Mediterranean countries from small ruminants' raw milk and play an important role in the development of suitable organoleptic characteristics of the final product. It has been suggested that animals used for food or animals that supply edible products are a reservoir of antibiotic-resistant enterococci. The main purpose of this research effort was thus to identify, to the species level, a total of 73 enterococci with high tolerance to acidic pH and bile salts (as prevailing environmental conditions in the first portion of the gastrointestinal tract), which were previously isolated from the milk feedstock to the final product of Terrincho cheesemaking, and to determine their profiles of antibiotic susceptibility, coupled with the occurrence of specific virulence factors (especially in those that might eventually be claimed to exhibit suitable probiotic and technological performances). Isolates, identified by both API 20 STREP and PCR methods, were found to belong to the following Enterococcus species: E. casseliflavus, E. durans, E. faecalis, E. faecium, and E. gallinarum. Susceptibility of those isolates was observed to most antibiotics tested, whereas none harbored aminoglycoside resistance genes. PCR screenings for cytolysin genes (cylL(L), cylL(s), cylM, cylB, and cylA), surface adhesin genes (efaA(fs), efaA(fm), and esp), the aggregation protein gene (agg), and the extracellular metalloendopeptidase gene (gelE) were performed. All isolates proved negative for cylL(L), cylM, cylB, and agg genes. Both E. faecalis strains were positive for the cell wall-associated protein Esp and the cell wall adhesin efaA(fs), whereas the cell wall adhesin efaA(fm) was detected in 11 of the 12 E. faecium strains. Only one strain possessed the cylL(s) determinant, and another possessed the cylA gene. Incidence of virulence determinants was thus very low; hence, the enterococcal adventitious microflora tested is essentially safe.     

嗜酸乳杆菌GIM1.208产β-葡萄糖苷酶培养基及发酵条件优化

以嗜酸乳杆菌（Lactobacillus acidophilus）GIM1.208为研究对象,通过单因素、正交试验和响应面法优化其产β-葡萄糖苷酶的培养基及发酵条件。结果表明,嗜酸乳杆菌GIM1.208发酵产β-葡萄糖苷酶的最佳产酶条件为葡萄糖添加量3.0%,羧甲基纤维素钠添加量0.4%,初始pH值5.5,料液比1∶4（g∶mL）、发酵温度31 ℃,发酵时间24 h,接种量2.6%。在此优化条件下,β-葡萄糖苷酶活力为16.80 U/mL,是优化前的3.90倍。