Characterization of Lactobacillus sp. strain 100-37 from the murine gastrointestinal tract: ecology, plasmid content, and antagonistic activity toward Clostridium ramosum H1

Conjugal Transfer of Plasmid-Encoded Determinants for Bacteriocin Production and Immunity in Lactobacillus acidophilus 88

Lactobacillus acidophilus 88 produced a bacteriocin, designated lactacin F, that demonstrated inhibitory activity toward L. acidophilus 6032, L. lactis 970, L. helveticus 87, L. bulgaricus 1489, L. leichmanii 4797, L. fermentum 1750, and Streptococcus faecalis 19433. Production of lactacin F was pH dependent and could be maximized in MRS broth cultures maintained at pH 7.0. Lactacin F was heat stable and sensitive to ficin, proteinase K, trypsin, and Bacillus subtilis protease. L. acidophilus 88 harbored plasmids of 4 and 27 megadaltons. Variants of L. acidophilus 88 which were deficient in lactacin F production (Laf) and lactacin F immunity (Laf) retained the two resident plasmids. A Laf Laf derivative, L. acidophilus 89, was used as a recipient in agar surface mating experiments with L. acidophilus 88 (Laf Laf). Two types of Laf Laf transconjugants were recovered. One type (T-E) had acquired two plasmids of 68 (pPM68) and 52 (pPM52) megadaltons that were not detected in either the conjugal donor or the other type of Laf Laf transconjugants (T-89). Laf and Laf were unstable in the plasmid-bearing transconjugant. Plasmid analysis of Laf Laf variants revealed that pPM52 and pPM68 were cured with loss of Laf and Laf. Bacteriocin production and immunity phenotypes were genetically stable in Laf Laf transconjugants not harboring pPM52 and pPM68, suggesting chromosomal integration of the transferred determinants. The data demonstrated intragenic conjugation in L. acidophilus and provided direct evidence for involvement of transient plasmid determinants in Laf and Laf.

Effects of probiotics on radiation-induced intestinal injury in rats

OBJECTIVE

Radiotherapy is an important aspect of multimodal cancer therapy, but radiation-induced acute intestinal injury is a common and serious problem. Disruption of morphologic mucosal integrity and normal bacterial microflora after abdominal radiation leads to malabsorption and bacterial translocation.

METHODS

Lactobacillus bulgaricus strain isolated from yogurt was given as a probiotic to rats subjected to radiotherapy. On postradiation day 8 rats were killed. Mesenteric lymph nodes, liver, and spleen were excised for microbiologic examinations. Segments of jejunum, ileum, and colon were evaluated for the presence of inflammation, vascularity, and mucus cells.

RESULTS

The results of this study suggest that probiotics may have a protective effect on intestinal mucosa.

CONCLUSION

Probiotics added as substrates can be given by an oral or enteral route to patients who undergo radiotherapy to prevent radiation-induced enteritis and related malnutrition.

Bacteriocin-like activity production and resistance in selected enterococci and streptococci of animal origin

Antimicrobial proteins and peptides produced by bacteria, termed bacteriocins, are widely acknowledged to be important contributors to their producer organism survival. Enterocin A, enterocin B, enterocin P and enterolysin A belong to the best studied enterocins, i.e., bacteriocins produced by enterococci and streptococci. Twenty-one enterococcal and seven streptococcal isolates were analysed for bacteriocin-like activity production and resistance by overlay test. Up to 50% of tested strains showed antibacterial activity at least against one indicator strain. The occurrence of enterocin B structural gene in several isolates was confirmed by PCR method. The results of this study should broaden knowledge of bacteriocin-like activity production and resistance among gram-positive bacteria.

Specific probiotic characterization of Weissella hellenica DS-12 isolated from flounder intestine

A total of 199 microorganisms were isolated from the intestinal contents of flounder (Paralichthys olivaceus) in a fish farm in Seoul, Korea. Among these strains, DS-12 was selected as a candidate for flounder probiotics because of its excellent exhibition of antimicrobial activity against fish pathogens such as edwardsiella, pasteurella, aeromonas, and vibrio, and initiate growth in 10% NaCl, 10% bile, and in broth at pH 3 for 90 min. This strain was Gram-positive, and catalase-negative coccoid rods that produced gas from glucose and formed more than 90% of lactate as the D(-) isomer. This organism is positioned at a cluster in the genus Weissella on the phylogenetic tree based on 16S rRNA sequences, which were assigned to Weissella hellenica on the basis of DNA-DNA relatedness. However, the type strain of W. hellenica JCM 10103(T) had no antibacterial activity against the fish pathogenic bacteria and was found to be quite different from the DS-12 strain in some sugar fermentation patterns of alpha-methyl-D-glucoside, esculine, cellobiose, melibiose, D-raffinose, and D-turanose, being especially unable to grow at 15 and 35 degrees C in 7% NaCl and 10% bile. The results obtained in the present study demonstrated that the type strain of W. hellenica had no probiotic characteristics, but the strain DS-12 could be used as a specific probiotic for flounder.

Plasmids in Lactobacillus

This review describes Lactobacillus plasmids on distribution, structure, function, vector construction, vector stability, application, and prospective. About 38% of species of the genus Lactobacillus were found to contain plasmids with different sizes (from 1.2 to 150 kb) and varied numbers (1 or more). Some Lactobacillus plasmids with small sizes were highly similar to those of single strand plasmids from other Gram-positive bacteria. The extensive sequence homologies of plus origins, replication initiation proteins, minus origins, cointegration sites, and the presence of single strand intermediates supported the fact that these small Lactobacillus plasmids replicate with a rolling-circle replication mechanism. Some Lactobacillus plasmid replicons were of broad host range that could function in other Gram-positive bacteria, and even in Escherichia coli, while replicons of other Gram-positive bacteria also function in Lactobacillus. Although most Lactobacillus plasmids are cryptic, some plasmid-encoded functions have been discovered and applied to vector construction and Lactobacillus identification, detection, and modification.

Problems and priorities for controlling opportunistic pathogens with new antimicrobial strategies; an overview of current literature

An International Study Group on New Antimicrobial Strategies (ISGNAS) has been formed in response to the recognition that development of microbial resistance to antibiotics is becoming a serious, world-wide problem. The group met in 1993 for the first time to discuss the feasibility of developing rational alternatives to the use of antibiotics and prepared, as a result, a comprehensive overview of normal (physiological) mechanisms involved in the control of potentially pathogenic (oppotunistic) microorganisms. One objective of ISGNAS is to understand the conditions which allow opportunistic microbes present among the symbionts to cause an infection. There is a need for more coherent information concerning the habitat, growth requirements and host and pathogen properties which allow opportunistic pathogens to cause life-threatening infections. In particular, information is urgently being sought to understand the complexity of the interactions between the vast number of microbial species, and the interactions between the microbes and their host. Another goal is to inspire and enable basic and clinical research that will lead to the development of new therapies for regulating colonization, translocation and infection by opportunistic micro-organisms in patients during periods of decreased resistance. With a sufficient amount of knowledge of how healthy individuals keep opportunistic micro-organisms under control, it may become feasible for physicians to maintain host resistance and inter-microbial factors involved in the containment of opportunistic microbes. Therapies aimed at boostering natural resistance mechanisms will be of critical importance to individuals whose resistance has been compromised as a result of another clinical condition.

Is there a role for lactobacilli in prevention of urogenital and intestinal infections?

This review describes the importance of microbial adhesion in the ecology of the urogenital and intestinal tracts and the influence of host and microbial factors in bacterial interference. In a recent revival of interest in bacterial interference, lactobacillus administration has been studied as a means of treating and preventing disease. Although evidence is conflicting, Lactobacillus acidophilus appears to be involved in beneficial antagonistic and cooperative reactions that interfere with establishment of pathogens in the gastrointestinal tract. The mechanisms of action are believed to involve competitive exclusion and production of inhibitory substances, including bacteriocins. These characteristics, as well as demonstrated adherence abilities in vitro, led to selection of certain Lactobacillus strains for clinical studies of cystitis. Weekly intravaginal Lactobacillus therapy reduced the recurrence rate of uncomplicated lower urinary tract infections in women. Use of Lactobacillus strains resistant to Nonoxynol-9, a spermicide that kills members of the protective normal vaginal flora, may have potential for use in women with recurrent cystitis using this contraceptive agent. In veterinary studies, bacterial interference by administration of probiotics has also been beneficial in disease prevention in animals. Carefully selected bacterial mixtures integrate with the gastrointestinal flora of the animals and can confer disease resistance and improve physiological function. Additional human and animal trials are needed to determine the practical, long-term usefulness of bacterial interference as a protective mechanism against infectious diseases.

Preservation of intestinal integrity during radiotherapy using live Lactobacillus acidophilus cultures

Twenty-four female patients suffering from gynaecological malignancies and scheduled for internal and external irradiation of the pelvic area (pelvic dose 5000 cGy) were selected for a study on prevention of intestinal side-effects by live Lactobacillus acidophilus cultures. The patients were randomised into two groups. Both groups received dietary counselling recommending a low-fat and low-residue diet during radiotherapy. The control group received dietary counselling only. The test group received 150 ml of a fermented milk test product supplying them with at least 2 X 10(9) live Lactobacillus acidophilus bacteria daily and 6.5% lactulose as substrate for the bacteria. The results indicated that the test product appeared to prevent radiotherapy-associated diarrhoea. However, flatulence was increased probably due to lactulose ingestion in the test group.

Bacteriocins of lactic acid bacteria

Lactic acid bacteria produce a variety of antagonistic factors that include metabolic end products, antibiotic-like substances and bactericidal proteins, termed bacteriocins. The range of inhibitory activity by bacteriocins of lactic acid bacteria can be either narrow, inhibiting only those strains that are closely related to the producer organism, or wide, inhibiting a diverse group of Gram-positive microorganisms. The following review will discuss biochemical and genetic aspects of bacteriocins that have been identified and characterized from lactic acid bacteria.

Survival of lactic acid bacteria in the human stomach and adhesion to intestinal cells

The survival of four strains of lactic acid bacteria in human gastric juice, in vivo and in vitro, and in buffered saline, pH 1 to 5, has been investigated. The strains studied include two Lactobacillus acidophilus strains, Lactobacillus bulgaricus, and Streptococcus thermophilus. In addition, the adhesion of these strains to freshly collected human and pig small intestinal cells and to pig large intestinal cells has been studied and the effect of milk on both survival and adhesion tested. As a result of these investigations, an in vitro test system for screening potential cultures for use as human dietary adjuncts can be developed. The ability to survive in gastric juice and to adhere varied significantly for the strains tested; L. acidophilus ADH survived and adhered better than the others while S. thermophilus survived and adhered poorly. For all strains, both survival and adhesion was enhanced by milk. As all strains adhered to some extent to both human and pig intestinal cells, the adhesion mechanism is probably a nonspecific attachment as opposed to other reported specific Lactobacillus adhesion to gastric tissue. From the survival and adhesion data it seems feasible to obtain elevated levels of viable Lactobacillus sp. in human intestine by careful selection of the bacterial strains ingested. Furthermore, the in vitro methods used here should be valuable to screen potential strains. The data presented here can then be correlated with human in vivo studies monitoring the beneficial effect of ingestion of these Lactobacillus.

Cryptic plasmids in Lactobacillus strains isolated from the murine gastrointestinal tract

Ten of twenty Lactobacillus strains isolated from the gastrointestinal tracts of animals of several species contained plasmids of 80 to 90 megadaltons or less than 2.6 megadaltons in size, as analyzed by agarose gel electrophoresis. The large plasmids were found only in strains originally isolated from the keratinized epithelium of the murine stomach.

Purification and characterization of the Lactobacillus acidophilus bacteriocin lactacin B

Parameters for production and purification of a bacteriocin produced by Lactobacillus acidophilus N2 are described. Production of lactacin B was pH dependent, with maximum activity detected in broth cultures maintained at pH 6. Lactacin B was purified by ion-exchange chromatography, ultrafiltration, and successive gel filtrations in the presence of 8 M urea and then 0.1% sodium dodecyl sulfate. The molecular weight of lactacin B was ca. 6,000 to 6,500, and the purified compound showed maximum absorbance at 211 nm. The activity of purified lactacin B was bactericidal to sensitive cells and restricted to members of the family Lactobacilliaceae, L. leichmannii, L. bulgaricus, L. helveticus, and L. lactis. Characteristics identified for lactacin B indicated that it was a peptide and confirmed its identity as a bacteriocin.