Antibiotic resistance of potential probiotic bacteria of the genus <Emphasis Type="Italic">Lactobacillus</Emphasis> from human gastrointestinal microbiome

Thirteen Lactobacillus strains isolated from the gastrointestinal microbiome of people from the territory of the former Soviet Union have been studied for resistance to 15 antibiotics of different nature, namely, penicillins, aminoglycosides, macrolides, lincosamides, tetracyclines, chloramphenicol, and rifampicin. The strains included four strains of L. plantarum, four of L. helveticus, three of L. casei/paracasei, one of L. rhamnosus, and one of L. fermentum. All strains showed relative sensitivity to ampicillin, chloramphenicol, rifampicin, roxithromycin, erythromycin, and azithromycin, while none of them were sensitive to all tested antibiotics. L. plantarum strains had the broadest resistance spectra: one strain was resistant to tetracycline and three aminoglycosides and three strains were resistant to tetracycline and five aminoglycosides; one strain demonstrated high resistance to clindamycin and two strains to lincomycin. At the same time, two L. plantarum strains demonstrated resistance to benzylpenicillin coupled with sensitivity to ampicillin, another β-lactam antibiotic. Such resistance was clearly not related to the β-lactamase activity and could be explained by a specific mutation in one of the penicillin-binding proteins of the cell wall. Strains of L. helveticus, L. casei/paracasei, L. rhamnosus, and L. fermentum exhibited cross resistance to two to five different aminoglycosides. A PCR test of the resistance determinants for the widely clinically used antibiotics, tetracycline, chloramphenicol, and erythromycin revealed the presence of the tetM gene of conjugative transposon in L. casei/paracasei and two L. helveticus strains. Nucleotide sequence analysis of the amplified tetM fragments demonstrated their high homology with the tetM genes of Enterococcus faecalis and Streptococcus pneumoniae. The strains carrying tetM were tested for the genes of replication and conjugative transfer of plasmids in lactic acid bacteria. The results indicated that these strains contain genes identical or highly homologous to the rep and trsK genes of the plca36 plasmid and rep gene of the pLH1 and pLJ1 plasmids of lactic acid bacteria. The tetM gene is probably not expressed in strains sensitive to the corresponding antibiotic. However, the investigated lactobacilli cannot be directly used as probiotics, as they may serve as a source of genes for antibiotic resistance in the human microbiome.     

Functional properties of <Emphasis Type="Italic">Lactobacillus</Emphasis> strains isolated from dairy products

Twenty-four acid- and bile-tolerant lactobacilli isolates from dairy products were identified and further in vitro characterized for the presence of functional traits potentially useful for probiotic applications, which included desirable and undesirable traits, such as biofilm formation, ability to inhibit intestinal pathogens, antibiotic susceptibility, and enzyme activity. The majority of examined strains were susceptible to certain antimicrobial agents (streptomycin, gentamicin, clindamycin, erythromycin, tetracycline, quinupristin–dalfopristin), except for three strains of Lactobacillus rhamnosus with minimal inhibitory concentration levels for streptomycin higher than the microbiological breakpoints (≥32 μg/mL), which are considered as resistant. Undesirable traits such as α-chymotrypsin or N-acetyl-β-glucosaminidase activities were not detected, but low β-glucuronidase, and moderate and high β-glucosidase activities were recorded in nine strains, which were eliminated from further examination together with three isolates showing unsuitable antibiotic resistance. Of the remaining 12 isolates, 4 (Lactobacillus fermentum 202, Lactobacillus gallinarum 7001, L. rhamnosus 183, and Lactobacillus plantarum L2-1) manifested an outstanding potential to inhibit selected intestinal pathogens in an agar spot test, including Escherichia coli and Salmonella spp., and simultaneously demonstrated strong biofilm-forming capacity. In conclusion, the results of our in vitro experiments showed that the above four strains had a potential probiotic value and met the criteria to be identified as a possible probiotic microorganism, with the necessity of verification through well-designed in vivo experimental, clinical, and technological studies before the strains can be used as probiotics or as starter probiotic cultures.     

Selection of <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> TN627 as a new probiotic candidate based on <Emphasis Type="Italic">in vitro</Emphasis> functional properties

Nine lactobacilli previously selected for high antagonism against food borne bacterial pathogens were identified via 16S rRNA gene sequencing and screened for probiotic potential for use in poultry production. The lactobacilli were subjected to a subtractive in vitro analysis system using a certified probiotic as reference. This allowed for selection of a milk-derived Lactobacillus plantarum strain, termed TN627. This organic acid-producing bacterium was free of harmful enzymatic activity and sensitive to several antibiotics. It also showed good growth at pH 4 and in the presence of bile. L. plantarum TN627 also exhibited high efficacy of adhesion to chicken enterocytes, which correlated with detecting genes encoding the mucusbinding, adhesion-promoting proteins (Mub and MapA) and the adhesion-like factor EF-Tu, commonly involved in adherence of lactobacilli to mucosal surfaces. Taken together, our findings suggest that TN627 is a promising probiotic candidate with high potential for application as a supplement in the animal feed industry.     

Susceptibility of <Emphasis Type="Italic">Streptococcus thermophilus</Emphasis> to antibiotics

A total of 74 Streptococcus thermophilus isolates collected between 1948 and 2005 from different environments were investigated to assess erythromycin, clindamycin, streptomycin, gentamicin, tetracycline and ampicillin susceptibility by means of microdilution, Etest and disk diffusion methods. For this purpose a new S. thermophilus Susceptibility test Medium (SSM) was developed. This medium allowed a better identification of strains with atypical tetracycline resistance. The recipe is a mixed formulation of Iso-Sensitest medium (90% v/v) and M17 medium (10% v/v) supplemented with lactose (0.5% w/v). The overall agreement of the techniques was good with exception of tetracycline, for which Etest provided lower MICs than the microdilution method. Most strains were susceptible to all the antibiotics tested while a few erythromycin, tetracycline and streptomycin resistant strains were detected.     

Multidrug-Resistant Enterococci in Animal Meat and Faeces and Co-Transfer of Resistance from an <Emphasis Type="Italic">Enterococcus durans</Emphasis> to a Human <Emphasis Type="Italic">Enterococcus faecium</Emphasis>

Forty-eight isolates resistant to at least two antibiotics were selected from 53 antibiotic-resistant enterococci from chicken and pig meat and faeces and analysed for specific resistance determinants. Of the 48 multidrug-resistant (MDR) strains, 31 were resistant to two antibiotics (29 to erythromycin and tetracycline, 1 to erythromycin and vancomycin, 1 to vancomycin and tetracycline), 14 to three (erythromycin, tetracycline and vancomycin or ampicillin) and 3 to four (erythromycin, vancomycin, ampicillin and gentamicin). erm(B), tet(M), vanA and aac (6′)-Ie aph (2′′)-Ia were the antibiotic resistance genes most frequently detected. All 48 MDR enterococci were susceptible to linezolid and daptomycin. Enterococcus faecalis (16), Enterococcus faecium (8), Enterococcus mundtii (2) and Enterococcus gallinarum (1) were identified in meat, and E. faecium (13) and Enterococcus durans (13) in faeces. Clonal spread was not detected, suggesting a large role of gene transfer in the dissemination of antibiotic resistance. Conjugative transfer of resistance genes was more successful when donors were enterococcal strains isolated from faeces; co-transfer of vanA and erm(B) to a human E. faecium occurred from both E. faecium and E. durans pig faecal strains. These data show that multidrug resistance can be found in food and animal species other than E. faecium and E. faecalis, and that these species can efficiently transfer antibiotic resistance to human strains in inter-specific matings. In particular, the occurrence of MDR E. durans in the animal reservoir could have a role in the emergence of human enterococcal infections difficult to eradicate with antibiotics.     

Screening and molecular identification of lactic acid bacteria from <Emphasis Type="Italic">gari</Emphasis> and <Emphasis Type="Italic">fufu</Emphasis> and <Emphasis Type="Italic">gari</Emphasis> effluents

Bacterial strains were isolated from cassava-derived food products and, for the first time, from cassava by-products, with a focus on gari, a flour-like product, and the effluents from the production processes for gari and fufu (a dough also made from cassava flour). A total of 47 strains were isolated, all of which were tested to determine their resistance to acidic pH and to bile salt environments. Four of the 47 isolates tested positive in both environments, and these four isolates also showed antibacterial behaviour towards both Gram-positive and Gram-negative microbial pathogens (i.e. Methicillin-resistance Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Salmonella enteritidis, Escherichia coli, Escherichia coli (O157), Yersinia enterocolitica). In most cases, the antibacterial activity was related to bacteriocin production. Molecular identification analysis (16S rDNA and randomly amplified polymorphic DNA-PCR) revealed that the four isolates were different strains of the same species, Lactobacillus fermentum. These results demonstrate that bacteria isolated from cassava-derived food items and cassava by-products have interesting properties and could potentially be used as probiotics.     

Comparison of antibiotic resistance and copper tolerance of <Emphasis Type="Italic">Enterococcus</Emphasis> spp. and <Emphasis Type="Italic">Lactobacillus</Emphasis> spp. isolated from piglets before and after weaning

In China, antimicrobials and copper are used extensively as growth-promoting agents for piglets. This study aimed to characterize the role of in-feed copper in the emergence of copper-tolerant and antibiotic-resistant Enterococcus and Lactobacillus isolates in Chinese pig farms. Feces of the same eight piglets from four litters at 7 and 55 days old and their mothers were traced in order to isolate Enterococcus spp. and Lactobacillus spp.. The minimum inhibitory concentrations of 10 antimicrobials and copper sulfate were determined using an agar dilution method. The feed levels of Cu²⁺ for lactating sows, suckling piglets, and weaned piglets were 6, 177, and 18 mg/kg, respectively. All the 136 Enterococcus isolates were sensitive to vancomycin; and the resistance rates to penicillin, enrofloxacin, and high level streptomycin resistance increased significantly after weaning. For the 155 Lactobacillus isolates, the resistance rates to ampicillin, chloramphenicol, tetracycline, and enrofloxacin were significantly higher in weaned piglets. The ratios of copper tolerant Enterococcus and Lactobacillus isolates both increased significantly after weaning (P < 0.05). A phenotypic correlation was observed after classifying the isolates into two groups (CuSO₄ MIC₅₀ < 16 or ≧16 for enterococci; CuSO₄ MIC₅₀ < 12 or ≧12 for lactobacilli) and comparing the antimicrobial-resistant percentage of two groups. On species level, a significant increase of E. faecalis to enrofloxacin was observed in line with the increase of copper MIC (P < 0.05). The findings revealed the changes of the antibiotic resistance and copper tolerance level of enterococci and lactobacilli between suckling and weaned piglets and demonstrated that there might be a strong association between in-feed copper and increased antibiotic resistance in enterococci and lactobacilli in Chinese intensive swine farms.     

Characterization of antilisterial bacteriocins produced by <Emphasis Type="Italic">Enterococcus faecium</Emphasis> and <Emphasis Type="Italic">Enterococcus durans</Emphasis> isolates from Hispanic-style cheeses

Enterococci are often identified as constituents of the indigenous microflora from raw milk artisanal cheeses and are believed to contribute to the unique organoleptic qualities of these products. Many strains of enterococci are also known to produce antimicrobial peptides, enterocins, which may prevent the growth of certain food-born pathogens. In this study 33 enterococcal isolates from Hispanic-style cheeses were screened for the production of bacteriocins. Of the 33 isolates, 5 Enterococcus faecium and 1 Enterococcus durans isolates inhibited the growth of Listeria spp. The antilisterial activity was lost after treatment with pepsin, trypsin, pronase, proteinase K and α-chymotrypsin suggesting the active component was a protein or peptide. The active compounds were heat stable and had molecular weights between 4 and 8 kDa, which is characteristic of Class II enterocins. A PCR screen showed that four E. faecium isolates contained nucleic acid sequences for multiple enterocins. Isolate H41K contained entA and entP; and isolates H51Ca, H51Cb and H41B contained entA, entP and entL50AB, with H41B also containing entB. All PCR tests performed were negative for E. faecium isolate H41D, suggesting the production of a novel enterocin. The isolates were also screened for susceptibility to antibiotics, with only two showing low-level resistance to vancomycin (8 μg ml^−l). However, three isolates were highly resistant to both tetracycline and kanamycin, with two of the isolates also showing high resistance to erythromycin. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

<Emphasis Type="Italic">In Vitro</Emphasis> activity of telithromycin and quinupristin/dalfopristin against methicillin-resistant coagulase-negative staphylococci with defined resistance genotypes

We determined the activities of new antibiotics telithromycin (ketolide) and quinupristin/dalfopristin (streptogramins) against 88 macrolide and/or lincosamide resistant coagulase-negative staphylococci (CoNS) isolates with defined resistance gene status. Telithromycin susceptibility was determined only in erythromycin-sensitive isolates (15) indicating the same mechanisms of resistance. In contrast, all erythromycin-resistant isolates (73) were either constitutively resistant to telithromycin (13 isolates with constitutive erm genes) or demonstrated telithromycin D-shaped zone (60 isolates with inducible msr(A) and/or erm). However, the level of inducible resistance conferred by msr(A) (35 isolates) was borderline even after induction by erythromycin. No quinupristin/dalfopristin resistant isolate was observed if tested by disk-diffusion method (DDM) but 18 isolates were intermediate (MIC = 1-3 mg/L) and two isolates resistant (MIC = 8 mg/L) if tested by E-test. All these isolates were resistant to streptogramin A and harbored vga(A) gene (1 isolate) or vga(A)LC gene (19 isolates). MICs for quinupristin/dalfopristin were higher for isolates with combination of streptogramin A resistance and constitutive MLSB resistance (MIC = 3-8 mg/L in 4 isolates) than for streptogramin A-resistant isolates susceptible to streptogramin B (MIC = 0.5-2 mg/L in 16 isolates). In addition to S. haemolyticus, vga(A)LC was newly identified in S. epidermidis and S. warnerii indicating its widespread occurrence in CoNS. Misidentification of low-level resistant isolates by DDM may contribute to dissemination of streptogramin A resistance.     

The Potential of <Emphasis Type="Italic">Lactobacillus casei</Emphasis> and <Emphasis Type="Italic">Entercoccus faecium</Emphasis> Combination as a Preventive Probiotic Against <Emphasis Type="Italic">Entamoeba</Emphasis>

Travellers’ diarrhoea caused by enteric protozoa like Entamoeba histolytica is among the most common protozoan diseases in developing countries. In developing countries, amoebiasis is the second most prevalent protozoan disease. This protozoan parasite is often known to coexist as a part of the normal gut microbiota. It is estimated that around 50–60 % of population in developing countries might be harbouring Entamoeba in an asymptomatic manner. Due to physiological perturbation or upon immuno-compromise, it can become virulent and then cause diarrhoea, bloody stools and may invade other organs if left untreated. Nitroimidazole drugs, namely metronidazole and tinidazole, are widely used to treat protozoan infections. These drugs often show dose-dependent side effects. With emerging antibiotic resistance, novel therapeutics to prevent parasitic infections is required. This study aims to study effect of probiotics on prevention of Amoebiasis. In this study, we have investigated the effect of selected probiotics on the growth of Entamoeba. From the list of probiotics being currently used, five bacterial strains were selected for testing. These probiotic strains were co-cultured with Entamoeba, and their effect on Entamoeba proliferation was checked. Of the five probiotics chosen, individual treatments of Lactobacillus casei and Enterococcus faecium showed a significant reduction of up to 71 % in parasite survival only at higher CFUs. When the two probiotics were used in combination, the percentage of survival reduced gradually further to 80 % at a total CFU of 10⁹ cells/ml of bacteria. The study lays the foundation for providing cost-effective prophylactic treatment for amoebiasis without the overuse of antibiotics.     

Mercury Tolerance of Thermophilic <Emphasis Type="Italic">Bacillus</Emphasis> sp. and <Emphasis Type="Italic">Ureibacillus</Emphasis> sp

Although resistance of microorganisms to Hg(II) salts has been widely investigated and resistant strains have been reported from many eubacterial genera, there are few reports of mercuric ion resistance in extremophilic microorganisms. Moderately thermophilic mercury resistant bacteria were selected by growth at 62 °C on Luria agar containing HgCl₂. Sequence analysis of 16S rRNA genes of two isolates showed the closest matches to be with Bacillus pallidus and Ureibacillus thermosphaericus. Minimum inhibitory concentration (MIC) values for HgCl₂ were 80 μg/ml and 30 μg/ml for these isolates, respectively, compared to 10 μg/ml for B. pallidus H12 DSM3670, a mercury-sensitive control. The best-characterised mercury-resistant Bacillus strain, B. cereus RC607, had an MIC of 60 μg/ml. The new isolates had negligible mercuric reductase activity but removed Hg from the medium by the formation of a black precipitate, identified as HgS by X-ray powder diffraction analysis. No volatile H₂S was detected in the headspace of cultures in the absence or presence of Hg²⁺, and it is suggested that a new mechanism of Hg tolerance, based on the production of non-volatile thiol species, may have potential for decontamination of solutions containing Hg²⁺ without production of toxic volatile H₂S.     

Isolation of quinupristin/dalfopristin-resistant <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> from asymptomatic Korean women

Seven Streptococcus agalactiae isolates were obtained from the vagina of 80 asymptomatic women. Three of these isolates showed multi-drug resistant (MDR) phenotypes: two isolates were resistant to clarithromycin, clindamycin, erythromycin, and tetracycline; and one isolate was resistant to clarithromycin, clindamycin, erythromycin, tetracycline, and quinupristin/dalfopristin. There was no clonal relationship among the MDR isolates. This is the first report of quinupristin/dalfopristin-resistant S. agalactiae.     

Antimicrobial susceptibility of<Emphasis Type="Italic">Enterococcus</Emphasis> species isolated from slovak bryndza cheese

Three hundred and ten enterococcal isolates (178 Enterococcus faecium, 68 E. durans, 49 E. faecalis, 8 E. italicus, 3 E. gallinarum, 3 E. casseliflavus, and 1 E. hirae) from Slovak Bryndza cheese were evaluated for susceptibility to nine antimicrobial agents (vancomycin, teicoplanin, ampicillin, streptomycin, gentamicin, erythromycin, rifampicin, nitrofurantoin, and ciprofloxacin). All enterococcal isolates from Bryndza cheese were susceptible to ampicillin, streptomycin, gentamicin, vancomycin, and teicoplanin as determined by the disk diffusion method. Vancomycin resistance genes vanA and vanB were not detected. Resistance rates of enterococcal isolates to rifampicin, erythromycin, ciprofloxacin, and nitrofurantoin were 24, 26, 2, and 1 %, respectively. Thirty-six % of E. faecium isolates and 22 % of the E. faecalis isolates were resistant to erythromycin. Resistance to rifampicin was similar in E. faecium (31 %) and E. faecalis (29 %). Both E. faecium and E. faecalis strains showed the same resistance to ciprofloxacin (2 %). E. durans isolates showed low levels of resistance to rifampicin, erythromycin, ciprofloxacin, and nitrofurantoin (1-4 %). Forty-eight (30 %) of the E. faecium isolates, two (3 %) of the E. durans isolates, and six (12 %) of the E. faecalis isolates exhibited multidrug resistance. The highest frequency of resistant enterococci was observed in Bryndza produced in winter season.     

Influence of carbohydrates on cell properties of <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis>

Lactobacilli represent normal commensals of the human body, particularly in the gut and vagina where they protect these environments from incoming pathogens via a variety of mechanisms. The influence of the carbohydrate source present in reconstituted MRS growth medium on the different cell properties of two Lactobacillus rhamnosus strains were examined. Two human vaginal isolates, BGHV719 and exopolysaccharide producer strain BGHV954 were analyzed. The results demonstrated that unlike in reconstituted MRS with glucose as a carbon source, the presence of fructose, mannose, or rhamnose, significantly reduced cell surface hydrophobicity of both strains. In addition, differences in cell wall protein composition of L. rhamnosus BGHV719 and alterations in colony mucoidity of L. rhamnosus BGHV954 were also demonstrated. Light and SEM microscopy revealed differences on the cellular level when BGHV719 was cultivated in the presence of different sugars. The results of this study point out the importance of complex relationships between growth medium composition and the different aspects of bacterial behavior, and call for more detailed analyses of versatile bacterial responses to the changes in the environment, including vaginal ecosystem. This is especially important since lactobacilli are amongst the most widely used of probiotics.     

<Emphasis Type="Italic">A2144G</Emphasis> Is the Main Mutation in the <Emphasis Type="Italic">23S</Emphasis> rRNA Gene of <Emphasis Type="Italic">Helicobacter pylori</Emphasis> Associated with Clarithromycin Resistance

To detect point mutations A2115C, A2143G/C, and A2144G in the 23S rRNA gene of Helicobacter pylori associated with resistance of the microorganism to clarithromycin, a new powerful way of analysis was used. This method involved the reaction of minisequencing followed by MALDI-TOF mass spectrometry of reaction products. In ten analyzed clarithromycin-resistant clinical isolates of H. pylori obtained in Russia, the resistance was found to be mediated only by mutation A2144G in the 23S rRNA gene.     

Viability and Stress Response of Putative Probiotic <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> Strains in Honey Environment

Due to problem of preservation of dairy products which serve as a matrix for probiotics, it is challenging to use these probiotics as food supplements in many developing countries. To determine the suitability of the Lactobacillus strains for exploitation as probiotics in honey, we investigated the effect of their storage on the viability, functionality, and the mechanism associated with their protective effect. Three isolates obtained from our laboratory collection were identified through amplification of the 16S rRNA gene. The viability of the strains in honey at different storage conditions was studied. Three genes (hdc, gtf, and clpL) responsible for the resistance of bacteria in acidic environments were screened. SDS-PAGE analysis of total protein was performed to observe protein profile changes of the strains after exposure to honey. All the three isolates, namely, GGU, GLA51, and GLP56, were identified as Lactobacillus plantarum strains. After 28 days of storage in honey at 4 °C, viable cell concentrations of the three strains were higher than 2.04?×?10⁶ CFU/ml. During the same period at room temperature, only the Lactobacillus plantarum GLP56 strain remained viable with a cell concentration of 1.86?×?10⁴ CFU/ml. The clpL gene coding for ATPase was detected in all the three strains. The protein of molecular weight ~?50 kDa was absent in the protein profile of Lactobacillus plantarum GGU after 60 days of storage in honey at 4 °C. The Lactobacillus plantarum GLP56, Lactobacillus plantarum GLA51, and Lactobacillus plantarum GGU strains exposed to honey can withstand acidic environmental stress but their viability declines over time.     

Isolation,characterization, and evaluation of wild isolates of <Emphasis Type="Italic">Lactobacillus reuteri</Emphasis> from pig feces

Lactic acid bacteria (LAB) are a well-used probiotics for health improvements in both humans and animals. Despite of several benefits, non-host-specific LAB showed poor probiotics effects due to difficulty in colonization and competition with normal flora. Therefore, the feasibility of porcine LAB isolates was evaluated as a probiotics. Ten of 49 Lactobacillus spp. isolates harbored 2∼10 kb plasmid DNA. Seven strains were selected based on the safety test, such as hemolytic activity, ammonia, indole, and phenylalanine production. After safety test, five strains were selected again by several tests, such as epithelial adherence, antimicrobial activity, tolerance against acid, bile, heat, and cold-drying, and production of acid and hydrogen peroxide. Then, enzyme profiles (ZYM test) and antibiotics resistance were analyzed for further characterization. Five Lactobacillus reuteri isolates from pig feces were selected by safety and functional tests. The plasmid DNA which was able to develop vector system was detected in the isolates. Together with these approaches, pig-specific Lactobacillus spp. originated from pigs were selected. These strains may be useful tools to develop oral delivery system.     

Plasmids of<Emphasis Type="Italic">Staphylococcus cohnii</Emphasis> isolated from the intensive-care unit

Numerous isolates of both subspecies of Staphylococcus cohnii were found in the environment of the intensive-care unit of a pediatric hospital. These isolates carried in their cells many plasmids, up to fourteen, of a wide range of sizes (< 2 to > 56 kb). Striking was the occurrence of large plasmids not very common in staphylococci. These were present in > 80% of S. cohnii isolates. Fifty-two different plasmid profiles were found in 79 investigated isolates belonging to S. cohnii ssp. cohnii and S. cohnii ssp. urealyticus. Isolates similar in plasmid profiles were grouped in antibiotic-resistance clusters established for 9 antibiotics (gentamicin, ciprofloxacin, clindamycin, erythromycin, tetracycline, chloramphenicol, mupirocin, trimethoprim-sulfamethoxazole, vancomycin) using the method of unweighted pair group mathematical averages (UPGMA). Many isolates were multiresistant to antibiotics and produced bacteriocins.     

Probiotic properties of <Emphasis Type="Italic">Lactobacillus</Emphasis> and <Emphasis Type="Italic">Bifidobacterium</Emphasis> strains isolated from porcine gastrointestinal tract

One strain of Lactobacillus salivarius, two strains of Lactobacillus reuteri and Lactobacillus amylovorus, and two strains of Bifidobacterium thermacidophilum with antagonistic effect against Clostridium perfringens were isolated from porcine gastrointestinal tract. Isolates were assayed for their ability to survive in synthetic gastric juice at pH 2.5 and were examined for their ability to grow on agar plate containing porcine bile extract. There was a large variation in the survival of the isolates in gastric juice and growth in the medium containing 0.3% (w/v) bile. L. salivarius G11 and L. amylovorus S6 adhered to the HT-29 epithelial cell line. Cell-free supernatant of L. amylovorus S6 showed higher antagonistic activity as effective as the antibiotics such as neomycin, chlortetracycline, and oxytetracycline against bacterial pathogens including C. perfringens, Salmonella typhimurium, Staphylococcus aureus, Vibrio cholerae, Edwardsiella tarda, and Aeromonas salmonicida subsp. salmonicida.     

Susceptibility of some clinical isolates of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> to fractions from the aerial parts of <Emphasis Type="Italic">Leuzea carthamoides</Emphasis>

The antimicrobial activity of the dichloromethane extract from aerial parts of Leuzea carthamoides DC. was tested in vitro against 19 Staphylococcus aureus strains (ATCC 25923, CNCTC Mau 43/60, clinical isolates). The extract was fractionated by column chromatography on silica gel into six fractions (petroleum ether, toluene, dichloromethane, ethyl acetate, methanol and water). The minimum inhibitory concentrations (MICs) of the fractions ranged from 64 to 1024 μg/mL. An ethyl acetate fraction (EA 1) with the widest range of activity inhibited all of the strains with MIC in the range 128–512 μg/mL. This fraction exhibited potent activity against strains which showed associated resistance to oxacillin, ciprofloxacin and erythromycin.