Antibiotic resistance of lactic acid bacteria isolated from Chinese yogurts

The aim of this study was to evaluate the susceptibility of 43 strains of lactic acid bacteria, isolated from Chinese yogurts made in different geographical areas, to 11 antibiotics (ampicillin, penicillin G, roxithromycin, chloramphenicol, tetracycline, chlortetracycline, lincomycin, kanamycin, streptomycin, neomycin, and gentamycin). The 43 isolates (18 Lactobacillus bulgaricus and 25 Streptococcus thermophilus) were identified at species level and were typed by random amplified polymorphic DNA analysis. Thirty-five genotypically different strains were detected and their antimicrobial resistance to 11 antibiotics was determined using the agar dilution method. Widespread resistance to ampicillin, chloramphenicol, chlortetracycline, tetracyclines, lincomycin, streptomycin, neomycin, and gentamycin was found among the 35 strains tested. All of the Strep. thermophilus strains tested were susceptible to penicillin G and roxithromycin, whereas 23.5 and 64.7% of Lb. bulgaricus strains, respectively, were resistant. All of the Strep. thermophilus and Lb. bulgaricus strains were found to be resistant to kanamycin. The presence of the corresponding resistance genes in the resistant isolates was investigated through PCR, with the following genes detected: tet(M) in 1 Lb. bulgaricus and 2 Strep. thermophilus isolates, ant(6) in 2 Lb. bulgaricus and 2 Strep. thermophilus isolates, and aph(3')-IIIa in 5 Lb. bulgaricus and 2 Strep. thermophilus isolates. The main threat associated with these bacteria is that they may transfer resistance genes to pathogenic bacteria, which has been a major cause of concern to human and animal health. To our knowledge, the aph(3')-IIIa and ant(6) genes were found in Lb. bulgaricus and Strep. thermophilus for the first time. Further investigations are required to analyze whether the genes identified in Lb. bulgaricus and Strep. thermophilus isolates might be horizontally transferred to other species.     

Antibacterial activity and cholesterol assimilation of lactic acid bacteria isolated from traditional Iranian dairy products

In this study, lactic acid bacteria were isolated from ewe milk, traditional yoghurt and sour buttermilk samples collected from different areas of Azarbayjan-e-sharqi in Iran. All the isolates were screened for their ability to produce bacteriocin like inhibitory substances (BLIS) by studying their inhibitory action against pathogens like Listeria monocytogenes, Salmonella enteritidis and Staphylococcus aureus, after eliminating the effect of organic acids and hydrogen peroxide. According to results, four of the isolates identified as Lactobacillus brevis, Lactobacillus pentosus, Pedoicoccus acidilactici and Lactobacillus paracasei were unaffected by the action of pH neutralization and hydrogen peroxide and showed inhibitory action against the tested pathogens. The inhibitory activities demonstrated by these isolates were completely inhibited in the presence of proteolytic enzymes.     

Production of biogenic amines by lactic acid bacteria and bifidobacteria isolated from dairy products and beer

The aim was to monitor production of eight biogenic amines (BAs) (histamine, tyramine (TYR), tryptamine, putrescine, cadaverine (CAD), phenylethylamine, spermine and spermidine) by selected 81 lactic acid bacteria (LAB) strains: Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Tetragenococcus and Bifidobacterium. The tested LAB and bifidobacteria were isolated from dairy products and beer. The decarboxylase activity of the micro‐organisms was studied in growth medium after cultivation. The activity was monitored by HPLC after the pre‐column derivatisation with dansylchloride. Fifty LAB showed decarboxylase activity. Thirty‐one strains produced low concentrations of CAD (≤10 mg L^?1). Almost 70% of beer isolates generated higher amounts of TYR (≤3000 mg L^?1). Most of the tested LAB demonstrated decarboxylase activity. The above micro‐organisms can contribute to the increase of content of BAs in dairy products or beer and thereby threaten food safety and health of consumers. Production of BAs even by the representatives of some probiotic strains (Bifidobacterium and Lactobacillus rhamnosus) was detected in this research. This study has also proved that contaminating LAB can act as sources of higher amounts of CAD and TYR in beer.     

Selective enumeration of Lactobacillus acidophilus,Bifidobacterium spp., starter lactic acid bacteria and non-starter lactic acid bacteria from Cheddar cheese

Twelve media were evaluated for selective and/or differential enumeration of Lactobacillus. acidophilus, Bifidobacterium spp., starter lactic acid bacteria (SLAB) and non-starter lactic acid bacteria (NSLAB) from Cheddar cheese. All media showed variation in counts and selectivity. Some reported selective media failed to inhibit SLAB and NSLAB. The media that were selective and/or differential and also gave better recovery were Reinforced Clostridium Agar with bromocresol green and clindamycin (RCABC), which was selective for L. acidophilus spp. and Reinforced Clostridium Agar with aniline blue and dicloxacillin (RCAAD), which was differential for Bifidobacterium spp. and SLAB. Reinforced Clostridium Agar with bromocresol green and vancomycin (RCABV) was found suitable for NSLAB. Apart from pure cultures, these media were also tested with commercial Cheddar cheese containing L. acidophilus. Additionally, Cheddar cheese containing L. acidophilus and B. lactis was manufactured and the selected media were used to monitor the initial survival of probiotic bacteria, SLAB and NSLAB present.     

Thermophilic lactic acid bacteria phages isolated from Argentinian dairy industries

Sixty-one natural phages (59 of Streptococcus thermophilus and 2 of Lactobacillus delbrueckii subsp. bulgaricus) were isolated from Argentinian dairy plants from November 1994 to July 2000. Specifically, 17 yogurt samples (18% of all samples) and 26 cheese samples (79%) contained phages lytic to S. thermophilus strains. The number of viral particles found in samples ranged from 10(2) to 10(9) PFU/ml. The phages belonged to Bradley's group B or the Siphoviridae family (morphotype B1). They showed high burst size values and remarkably short latent periods. The results of this study show that phages were found more frequently in cheesemaking processes than in yogurt-making processes. The commercial streptococcus strains appeared to propagate more phages, whereas the natural strains propagated fewer phage strains. These results suggest that the naturally occurring cultures are inherently more phage resistant.     

乳酸菌及其发酵乳制品的发展趋势

综述了乳酸菌的生物学特性、功能及用于乳制品发酵生产的乳酸菌种类。概述了发酵乳制品的种类、生产流程、特点、功能及其发展趋势，以及乳酸菌发酵乳制品保健功能、风味物质及其生产技术的发展趋势。     

内蒙古传统发酵乳制品中乳酸菌的分离及其耐药性研究

以内蒙古通辽地区自制的奶豆腐和酸性奶油（乌日莫）为材料,采用稀释涂布法从中分离乳酸菌,通过分子生物学技术对其进行菌种鉴定,并对其耐药性进行研究。结果表明,共分离纯化得到80株乳酸菌,经鉴定,归属于13个种,分别为短乳杆菌（Lactobacillus brevis）、粪肠球菌（Enterococcus faecalis）、乳酸片球菌（Lactobacillus acidilacticii）、乳酸乳球菌（Lactococcus lactis）、瑞士乳杆菌（Lactobacillus helveticus）、屎肠球菌（Enterococcus faecium）、戊糖片球菌（Pediococcus pentosaceus）、副干酪乳杆菌（Lactobacillus paracasei）、食二酸乳杆菌（Lactobacillus digitalis）、奥塔基乳杆菌（Lactobacillus ottaki）、耐久肠球菌（Enterococcus durans）、植物乳杆菌（Lactobacillus plantarum）、开菲尔乳杆菌（Lactobacillus kefir）,表现出高的生物多样性。80株乳酸菌对萘啶酸的耐药率为100%;对链霉素、环丙沙星、万古霉素的耐药率较高,分别为95.00%、80.00%、72.50%;对利福平和四环素的耐药率中等,分别为51.25%,45.00%;对红霉素、氯霉素的耐药率较低,分别为26.25%、23.75%。此外,76株（95%）的乳酸菌还具有多重耐药性。     

Antibiotic resistance in non-enterococcal lactic acid bacteria and bifidobacteria

Over the last 50 years, human life expectancy and quality of life have increased dramatically due to improvements in nutrition and the use of antibiotics in the fight against infectious diseases. However, the heyday of antibiotic treatment is on the wane due to the appearance and spread of resistance among harmful microorganisms. At present, there is great concern that commensal bacterial populations from food and the gastrointestinal tract (GIT) of humans and animals, such as lactic acid bacteria (LAB) and bifidobacteria, could act as a reservoir for antibiotic resistance genes. Resistances could ultimately be transferred to human pathogenic and opportunistic bacteria hampering the treatment of infections. LAB species have traditionally been used as starter cultures in the production of fermented feed and foodstuffs. Further, LAB and bifidobacteria are normal inhabitants of the GIT where they are known to exert health-promoting effects, and selected strains are currently been used as probiotics. Antibiotic resistance genes carried by LAB and bifidobacteria can be transferred to human pathogenic bacteria either during food manufacture or during passage through the GIT. The aim of this review is to address well-stated and recent knowledge on antibiotic resistance in typical LAB and bifidobacteria species. Therefore, the commonest antibiotic resistance profiles, the distinction between intrinsic and atypical resistances, and some of the genetic determinants already discovered will all be discussed.     

新疆乳品中乳酸菌的多样性及耐药性分析

从新疆北部地区采集的样品中分离出103株乳酸菌并进行生理生化表型鉴定,对这些乳酸菌进行16S rRNA基因序列测序,构建系统发育树发现分离的乳酸菌主要为5个属分别为乳杆菌属、肠球菌属、乳球菌属、魏斯式菌属、明串珠菌属。采用纸片扩散法（K-B）研究不同属中不同乳酸菌对8种常见抗生素的耐药性分析。耐药性研究表明,分别有6株对链霉素、新霉素有耐药性,5株对红霉素有耐药性,7株对卡那霉素有耐药性,8株全部对萘啶酸具有耐药性,4株对万古霉素、四环素具有耐药性,2株对头孢唑肟存在耐药性。     

Selection of wild lactic acid bacteria isolated from traditional Egyptian dairy products according to production and technological criteria

A total of 755 wild lactic acid bacteria (LAB), belonging to Lactococcus, Lactobacillus, Enterococcus, Streptcoccus, Leuconostoc and Pediococcus isolated from Egyptian raw milk and its products were screened and selected according to their production and technological properties. Many strains showed high yield of biomass in fermentation and some strains were resistant to lyophilization conditions. Most strains showed a good separation after centrifugation, 2% of Lactococcus, 13% of Lactobacillus and 1% of Enterococcus were fast acidifying strains. Aminopeptidase and autolytic activity were generally higher for most lactobacilli compared to other strains. In milk cultures many strains were able to produce pleasant flavours. Antimicrobial activity was detected in 47% of Lactococcus, 21% of Lactobacillus and 41% of Enterococcus strains and some strains produced exopolysaccharides (slime and capsule). Several strains were able to maintain a high activity of two or three technological characteristics together. Detailed information about the characteristics of each strain is available in the culture collection of Faculty of Agriculture Alexandria University (FAAU). A wide variety of LAB from traditional Egyptian dairy products that showed potentially important properties are not only valuable for practical application but they may also provide an expanded gene pool for designing genetic modified strains with improved traits.     

Characterization of anti-listerial lactic acid bacteria isolated from Thai fermented fish products

Thai fermented fish products were screened for lactic acid bacteria capable of inhibitingListeriasp. (Listeria innocua). Of 4150 assumed lactic acid bacteria colonies from MRS agar plates that were screened by an agar-overlay method 58 (1.4%) were positive. Forty four of these strains were further characterized and 43 strains were inhibitory againstListeria monocytogenes. The strains were inhibitory to other Gram-positive (lactic acid) bacteria probably because of production of bacteriocins. All 44 strains inhibited bothVibrio choleraeandVibrio parahaemolyticusand 37 were inhibitory to a mesophilic fish spoilage bacterium (anAeromonassp.). Inhibition of Gram-negative bacteria was attributed to production of lactic acid. Most strains were identified asLactobacillusspp., and all grew well at ambient temperatures (25–37°C) and tolerated up to 6.5% NaCl. Glucose was fermented rapidly in laboratory media whereas pH decreased only very slowly in fish juice supplemented with 4% glucose and 3.5% NaCl or in a rice–fish mixture. Only four of 44 isolates could degrade and ferment complex carbohydrates such as rice, potatoes and maize starch. This indicates that other types of bacteria may be responsible for the rapid spontaneous fermentation of the products or that other yet-unknown factors ensure rapid fermentation. Overall anti-listerial lactic acid bacteria do occur in fermented fish products and the antibacterial activity against pathogenic bacteria indicates that they may be important in product safety.     

科尔沁地区传统发酵奶豆腐中乳酸菌的鉴定

从科尔沁地区采集到5份传统发酵制作的奶豆腐样中分离出12株供试菌株,将分离的菌株的16S rDNA进行PCR扩增、序列分析并构建系统发育树。结果表明,12株菌株都属于乳酸菌(Lactic Acid Bacteria),其中6株乳杆菌(Lactobacillus),分别是植物乳杆菌(Lactobacillus plantarum)4株、干酪乳杆菌(Lactobacillus casei)1株、戊糖乳杆菌(Lactobacillus pentosus)1株;6株乳球菌(Lactococcus)分别是乳糖片球菌(Pediococcus acidilactici)5株和戊糖片球菌(Pediococcus pentosaceus)1株。鉴定结果与生理生化实验结果一致,且以乳酸片球菌和植物乳杆菌为优势菌群。      

In vitro evaluation of probiotic lactic acid bacteria isolated from dairy and non-dairy environments

Four strains and 2 strains of lactic acid bacteria (LAB) were isolated from the commercial yogurt and kimchi products in Korea, respectively. Based on the 16S rRNA sequencing data, strain A from a drink-type yogurt manufactured by dairy company S, was a Gram-positive, rod-shaped Lactobacillus helveticus, and both strain B (company N) and D (company H) were identified as L. casei ssp. casei, and strain C (company L) as L. paracasei. None of yogurt strain B and D was recovered from the samples exposed to the simulated gastric juice, pH 2.0 for 1.5 hr. Of the 6 isolates tested, strain YS93 from kimchi was the most resistant to acidic condition using the simulated gastric juice, pH 2.0. Moreover, it was shown that 2 kimchi isolates and yogurt strain D produced antibacterial substances, probably bacteriocin-like peptide, which was inhibitory against Staphylococcus aureus as an indicator. In an adhesion assay using a Caco-2 cell, the adherence activity of kimchi strains YS29 and YS93 was significantly higher than those of 4 yogurt starter strains tested.     

新疆传统发酵乳品中乳酸菌与酵母菌生长的相互影响

对新疆传统发酵乳酪乳清中的优势菌株:马乳酒样乳杆菌、乳酸乳球菌、瑞士乳杆菌、植物乳杆菌、东方伊莎酵母菌在驼乳中的生长特性进行了研究。探讨了4株乳酸菌与东方伊莎酵母菌之间的相互作用。结果表明,在发酵过程中东方伊莎酵母菌显著促进马乳酒样乳杆菌和乳酸乳球菌的生长(p<0.05),对瑞士乳杆菌的生长促进作用不明显(p>0.05)。同时,4株乳酸菌抑制东方伊莎酵母菌的生长(p<0.05)。此外,乳酸菌与东方伊莎酵母菌共同接种发酵有利于保持发酵乳冷藏期间活菌数的稳定及缓解乳酸菌的过度产酸。综上所述:乳酸菌与酵母菌之间可能存在相互作用的关系。      

新疆传统发酵乳品中乳酸菌与酵母菌生长的相互影响

对新疆传统发酵乳酪乳清中的优势菌株:马乳酒样乳杆菌、乳酸乳球菌、瑞士乳杆菌、植物乳杆菌、东方伊莎酵母菌在驼乳中的生长特性进行了研究。探讨了4株乳酸菌与东方伊莎酵母菌之间的相互作用。结果表明,在发酵过程中东方伊莎酵母菌显著促进马乳酒样乳杆菌和乳酸乳球菌的生长(p0.05),对瑞士乳杆菌的生长促进作用不明显(p0.05)。同时,4株乳酸菌抑制东方伊莎酵母菌的生长(p0.05)。此外,乳酸菌与东方伊莎酵母菌共同接种发酵有利于保持发酵乳冷藏期间活菌数的稳定及缓解乳酸菌的过度产酸。综上所述:乳酸菌与酵母菌之间可能存在相互作用的关系。     

乳酸菌及其代谢产物在乳制品保鲜中的应用

乳酸菌及其某些代谢产物,以其天然、强抗菌性及安全可靠等优势,已逐步应用于食品保鲜中。对乳酸菌用于乳制品保鲜的类型、代谢产物抗菌机制以及应用进行了综述,为研究开发新型食品保鲜剂提供依据。     

传统乳制品中乳酸菌的筛选及发酵性能研究

为获得优良发酵性能的乳酸菌,采用传统培养方法从传统发酵乳样品中分离乳酸菌,并将分离菌株制备发酵乳。通过考察发酵乳的感官品质筛选优良菌株,采用形态学观察及16S rDNA序列分析对筛选菌株进行鉴定;并对其生长性能、产酸性能及其制备发酵乳贮藏期内品质变化进行测定。结果显示,共分离得到67株乳酸菌,筛选出5株性能较佳的菌株（编号为C-1、Q164、Q165、Q166和Q167）,均被鉴定为嗜热链球菌（Streptococcus thermophilus）。其中,菌株C-1生长性能和产酸性能最佳,该菌株制备的发酵乳奶香明显,口感细腻顺滑,感官评分最高（93.5分）,30 ℃贮藏21 d后,酸度为86.0 °T,活菌数为7.2×103 CFU/g。综上,嗜热链球菌C-1具备优良发酵性能菌株的应用潜力。     

Incidence and antibiotic susceptibility of bacteriocin‐producing lactic acid bacteria from dairy products

Screening for bacteriocin production by strains of lactic acid bacteria (LAB) from local dairy products in Iran resulted in the detection of 10 bacteriocin‐producing strains. Among 105 isolated, 10 bacteriocin producers were phenotypically and genotypically identified as Enterococcus spp. The antimicrobial compounds produced by these novel strains were inactivated by trypsin, proteinase k. These bacteriocins also were active in a wide range of pH and temperature values, and inhibited not only the closely related LAB, but also Listeria monocytogenes.     

Isolation of novel homopolysaccharide-producing lactic acid bacteria from Romanian raw milk and fermented dairy products

Traditionally fermented foods can be a rich source of diverse lactic acid bacteria (LAB) with interesting functional properties, such as exopolysaccharide (EPS) production. The objectives of this study were to map the mucoid and/or ropy LAB isolated from raw milk and traditionally fermented dairy products, collected in different regions of Romania, to study the species diversity within the samples and to further explore the EPS-producing capacity of the isolates. Seventy-three LAB strains were isolated and identified through (GTG)₅-PCR genomic fingerprinting and SDS-PAGE of whole-cell proteins. Lactococcus lactis was the most frequently encountered species, followed by Lactobacillus plantarum, Leuconostoc spp., and Enterococcus spp. Nine strains produced homopolysaccharides (HoPS, glucose monomers), namely L. lactis 1.8; Leuc. citreum 1.10, 1.11, 1.12, 2.8, and 4.11; Leuc. mesenteroides 21.2; Leuc. pseudomesenteroides 20.6; and Weisella confusa/cibaria 38.2, six of them in the concentrations above 10 g/L, both in milk and MRS medium supplemented with sucrose. In all EPS, the glucose constituents were connected by different α-linkages, among which α-1,6-linkages were the most prevalent.