Inhibition of Shigella sonnei by Lactobacillus casei and Lact. acidophilus.

The protective effect of feeding milk fermented with a mixture of Lactobacillus casei and Lact. acidophilus against Shigella sonnei was studied. There was a 100% survival rate in mice fed for 8 d with fermented milk and then dosed orally with Sh. sonnei. The survival rate in control mice was approximately 60% after 21 d. Colonization of the liver and spleen with Sh. sonnei was markedly inhibited by pretreatment with fermented milk. Differences in cell counts of 2-3 log units between treated and control mice were always obtained, shigellas were not detected in these organs by the 10th day in treated mice, while high levels were maintained in the controls. Higher levels of anti-shigella antibodies were found both in sera and in small intestinal fluid of mice treated with fermented milk, suggesting that the protective immunity could be mediated by the mucosal tissue. These results suggest that milk fermented with Lact. casei and Lact. acidophilus could be used as a prophylactic against gastrointestinal infections by shigellas.     

Manufacturing of fermented goat milk with a mixed starter culture of Bifidobacterium animalis and Lactobacillus acidophilus in a controlled bioreactor

AIMS: This work was undertaken to study the feasibility and the characteristics of a fermented product made of goat milk, using a mixed starter culture of Bifidobacterium animalis and Lactobacillus acidophilus under controlled conditions, and to determine their survival in the fermented milk during refrigerated storage. METHODS AND RESULTS: Goat milk was inoculated with Lact. acidophilus and Bif. animalis mixed starter, fermented in a glass bioreactor with controlled temperature (37 degrees C) and anaerobiosis, and monitored for growth and acidification. The fermented milk was then stored for 10 days under refrigeration, and monitored daily for starter microflora survival and pH changes. Lact. acidophilus viable counts reached a maximum of 7.1 x 10(8) colony-forming units (CFU) ml(-1), and Bif. animalis a maximum of 6.3 x 10(7) CFU ml(-1) by 20 h of fermentation. During refrigerated storage, both strains exhibited a good survival, with viable numbers remaining essentially constant throughout the experiment, whereas the pH of the fermented milk dropped slightly. CONCLUSIONS: Mixed cultures of Bif. animalis and Lact. acidophilus may be used to produce fermented goat milk with high counts of both probiotic strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Goat milk fermented with Bif. animalis and Lact. acidophilus can be manufactured as an alternative probiotic dairy product.     

In vitro studies on the growth of Shigella sonnei by Lactobacillus casei and Lact. acidophilus.

The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested. When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 +/- 2.5% at 6 h culture, 57.4 +/- 1.9% at 9 h and 91.2 +/- 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen : lactobacilli was 1:10(3). The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37 degrees C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei.     

In vitro studies on the inhibition of the growth of Shigella sonnei by Lactobacillus casei and Lact. acidophilus

The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested.
When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 ± 2.5% at 6 h culture, 57.4 ± 1.9% at 9 h and 91.2 ± 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen: lactobacilli was 1: 10³. The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37°C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei.     

Antagonistic effect of Lactobacillus acidophilus, Saccharomyces boulardii and Escherichia coli combinations against experimental infections with Shigella flexneri and Salmonella enteritidis subsp. typhimurium in gnotobiotic mice

Lactobacillus acidophilus, Saccharomyces boulardii and Escherichia coli are probiotic strains used individually to protect against enteropathogenic agents. In order to determine if a synergistic effect of the individual protective mechanisms ordinarily attributed to each of these biotherapeutic agents is possible, we orally administered Lact. acidophilus H2B20, S. boulardii and E. coli EMO (LSE) to germfree mice. Ten days after colonization of the digestive tract, groups of animals associated (experimental) or not (control) with LSE were challenged orally with streptomycin resistant (Sfr) or streptomycin sensitive (Sfs) Shigella flexneri strains or Salmonella enteritidis subsp. typhimurium. Bacterial counts in faeces from experimental mice showed that the Sfr strain was eliminated 11 d after challenge while Sfs and S. enteritidis subsp. typhimurium colonized the digestive tract and continued to be present at high population levels (108 CFU g-1 of faeces), which is similar to that observed in control animals. All possible di- and monoassociations of the three probiotics with gnotobiotic mice were also performed before experimental oral infection with Sfr. The data showed that antagonism was obtained only when E. coli EMO was present. Different sensitivity of Sh. flexneri Sfr and Sfs to E. coli EMO antagonism could be explained by the different generation times between Sfr and Sfs, as shown by colonization kinetic experiments in the digestive tract of gnotobiotic mice.     

Antagonistic Action of Lactobacilli and Bifidobacteria in Relation to Staphylococcus aureus and Their Influence on the Immune Response in Cases of Intravaginal Staphylococcosis in Mice

The antibacterial activity of Lactobacillus casei IMV B-7280, Lact. acidophilus IMV B-7279, Bifidobacterium longum VK1, and B. bifidum VK2 strains or their various compositions in relation to Staphylococcus aureus in vitro and on models of experimental intravaginal staphylococcosis of mice was determined. It was found that under the influence of these strains and their various compositions, the in vitro growth of Staph. aureus was inhibited, and the number of colonies of Staph. aureus plated from the vagina of infected mice was significantly reduced. The antibacterial activity of these strains separately and in compositions correlated with their ability to improve the performance of the immune response. These strains were the most effective in the following compositions: Lact. casei IMV B-7280-B. longum VK1-B. bifidum VK2. Strains of Lact. casei IMV B-7280, Lact. acidophilus IMV B-7279, B. bifidum VK2, and B. longum VK1 are prospective components of future probiotic drugs efficient in treating staphylococcosis and for immunity correction.     

Survivability of a probiotic Lactobacillus casei in the gastrointestinal tract of healthy human volunteers and its impact on the faecal microflora

AIM: The aim of this study was to measure the gastrointestinal survival of Lactobacillus casei and its impact on the gut microflora in healthy human volunteers. METHODS AND RESULTS: Twenty healthy volunteers took part in a double-blind placebo-controlled probiotic feeding study (10 fed probiotic, 10 fed placebo). The probiotic was delivered in two 65 ml aliquots of fermented milk drink (FMD) daily for 21 days at a dose of 8.6 +/- 0.1 Log(10)Lact. casei CFU ml(-1) FMD. Faecal samples were collected before, during and after FMD or placebo consumption, and important groups of faecal bacteria enumerated by fluorescent in situ hybridization (FISH) using oligonucleotide probes targeting the 16S rRNA. The fed Lact. casei was enumerated using selective nutrient agar and colony identity confirmed by pulsed field gel electrophoresis. Seven days after ingestion of FMD, the Lact. casei was recovered from faecal samples taken from the active treatment group at 7.1 +/- 0.4 Log(10) CFU g(-1) faeces (mean +/- SD, n = 9) and numbers were maintained at this level until day 21. Lact. casei persisted in six volunteers until day 28 at 5.0 +/- 0.9 Log(10) CFU g(-1) faeces (mean +/- SD, n = 6). Numbers of faecal lactobacilli increased significantly upon FMD ingestion. In addition, the numbers of bifidobacteria were higher on days 7 and 21 than on days 0 and 28 in both FMD fed and placebo fed groups. Consumption of Lact. casei had little discernible effect on other bacterial groups enumerated. CONCLUSIONS: Daily consumption of FMD enabled a probiotic Lact. casei strain to be maintained in the gastrointestinal tract of volunteers at a stable relatively high population level during the probiotic feeding period. SIGNIFICANCE AND IMPACT OF THE STUDY: The study has confirmed that this probiotic version of Lact. casei survives well within the human gastrointestinal tract.     

Effects of Lactobacillus casei on Pseudomonas aeruginosa infection in normal and dexamethasone-treated mice

A single intraperitoneal injection of Lactobacillus casei YIT 0003 into normal or dexamethasone-treated mice led to nonspecific resistance against intraperitoneal challenge with lethal doses of Pseudomonas aeruginosa PAO 3047. The enhanced resistance was retained for 14 days (P less than 0.05) after injection with living L. casei. In contrast, the statistically significant duration of the enhanced resistance in mice treated intraperitoneally with living L. acidophilus YIT 0075 was only 5 days. The in vivo killing activity of peritoneal exudate cells (PECs) against P. aeruginosa 5 and 7 days after intraperitoneal injection of living L. casei was significantly higher than in the case of PECs elicited by L. acidophilus. In the case of intravenous injection of heat-killed L. casei before intraperitoneal challenge with P. aeruginosa, there were no survivors in the late period after administration of L. casei. A high correlation existed between the patterns of in vivo killing of P. aeruginosa by PECs and survival rate of mice injected intravenously with heat-killed L. casei. The reduced in vivo killing activity of PECs from dexamethasone-treated mice against P. aeruginosa infection was also augmented by the intraperitoneal injection of heat-killed L. casei. These results indicate that L. casei possesses a resistance-enhancing capacity against P. aeruginosa infection in vivo. Differences in the duration of the enhanced resistance caused by L. casei and by L. acidophilus may be due to differences in chemical composition and/or physicochemical properties of the cell walls of the two kinds of bacteria.     

Differentiation of Lactobacillus isolates from infant faeces by SDS-PAGE and rRNA-targeted oligonucleotide probes

Isolates of lactobacilli from infant faeces phenotypically characterized as Lactobacillus paracasei subsp. paracasei (six strains), Lact. rhamnosus (six strains), Lact. gasseri (three strains), Lact. acidophilus (one strain) and Lact. fermentum/reuteri (three strains) according to recent classification systems were subjected to SDS-PAGE of whole cell proteins and rRNA-targeted oligonucleotide probe hybridization, in order to confirm the phenotypic characterization and elucidate the exact taxonomic position of the three strains that had properties between fermentum and reuteri. Results suggested a good agreement between the phenotypic characterization, SDS-PAGE and rRNA-targeted oligonucleotide probe hybridization for strains of all species except for the Lact. fermentum/reuteri strains. Results obtained by rRNA probes suggested a possible phylogenetic relatedness of the strains to Lact. reuteri. Isolates from infant faeces with interesting probiotic properties could be used as components of fermented milk products.     

Taxonomic characterization of Lactobacillus delbrueckii subsp. bulgaricus isolates from a Cameroonian zebu's fermented raw milk

Atypical thermophilic homofermentative lactobacilli were isolated as one of the major microflora from Pindidam, an indigenous Cameroonian zebu's fermented raw milk. On the basis of their physiological characteristics, obtained isolates constituted a homogeneous group belonging to the species Lactobacillus delbrueckii. Nevertheless, their carbohydrate fermentation pattern was unusual and their identification to one of two subspecies Lact. delbrueckii subsp. bulgaricus (Lact. d. bulgaricus ) or Lact. delbrueckii subsp. lactis (Lact. d. lactis ) was rendered difficult. DNA-DNA hybridization confirmed that they belonged to the species Lact. delbrueckii and the electrophoretic mobility of the D-(—)-lactate dehydrogenase (LDH) furthermore precisely assigned them to Lact. d. bulgaricus. Whole-cell protein profiles were only able to weakly discriminate between these wild isolates and type strains of the species Lact. delbrueckii. The isolates from Pindidam were well adapted to their specific environmental conditions and demonstrated both high growth rates and ability to support elevated acidic levels in fermented milk.     

Enhancement of host resistance against Listeria infection by Lactobacillus casei: efficacy of cell wall preparation of Lactobacillus casei

Cell wall, cytoplasm, polysaccharide, and peptidoglycan fractions prepared from Lactobacillus casei, L. plantarum, and L. acidophilus were examined for their efficacies to enhance resistance of host mice against Listeria monocytogenes infection. Intraperitoneal injections of those cellular fractions of L. casei led to elicitation of inflammatory cells in the peritoneal cavity and the efficacy was highest in the case of peptidoglycan. Macrophage ratio in the resultant peritoneal exudate cells was also highest in mice given peptidoglycan. Macrophages induced with cell wall fraction of L. casei showed the most potent phorbol myristate acetate (PMA)-triggered respiratory burst (chemiluminescence and O2- production determined on the basis of nitroblue tetrazolium reduction) followed by those elicited with peptidoglycan. All the macrophages induced with cell wall of L. casei (two strains) and L. acidophilus enhanced O2- production in response to PMA but L. plantarum did not enhance O2(-)-producing ability in such a manner. The L. casei-cell wall also enhanced in vitro listericidal activity of mouse peritoneal macrophages, but such an activity was not noted in the case of L. acidophilus-cell wall. When mice were intravenously given the cellular fractions 7 or 13 days before L. monocytogenes infection, cell wall fractions of L. casei caused the most potent protective activity. A weak protective activity was also found in peptidoglycan of L. casei. Therefore, the protective action of L. casei against L. monocytogenes infection in host mice may be attributed to cell wall compounds and partially to the peptidoglycan moiety.     

In vitro inhibition of Helicobacter pylori NCTC 11637 by organic acids and lactic acid bacteria

In this Study the effects of both pH and organic acids on Helicobacter pylori NCTC 11637 were tested. Lactobacillus acidophilus, Lact. casei, Lact. bulgaricus, Pediococcus pentosaceus and Bifidobacterium bifidus were assayed for their lactic acid production, pH and inhibition of H. pylori growth. A standard antimicrobial plate well diffusion assay was employed to examine inhibitory effects. Lactic, acetic and hydrochloric acids demonstrated inhibition of H. pylori growth in a concentration-dependent manner with the lactic acid demonstrating the greatest inhibition. This inhibition was due both to the pH of the solution and its concentration. Six strains of Lact. acidophilus and one strain of Lact. casei subsp. rhamnosus inhibited H. pylori growth where as Bifidobacterium bifidus, Ped. pentosaceus and Lact. bulgaricus did not. Concentrations of lactic acid produced by these strains ranged from 50 to 156 mmol 1⁻¹ and correlated with H. pylori inhibition. The role of probiotic organisms and their metabolic by-products in the eradication of H. pylori in vivo remains to be determined.     

Use of folic acid casei medium reveals trimethoprim susceptibility of Lactobacillus species

AIM: Lactobacilli have been reported to have intrinsic resistance to trimethoprim. The susceptibility of lactobacilli to trimethoprim on different media was investigated in order to search for a phenotypic test method that could indicate the presence of acquired resistance genes. METHODS AND RESULTS: Strains of Lactobacillus acidophilus, Lact. paracasei, Lact. rhamnosus and Lact. plantarum were susceptibility tested with E-tests on folic acid casei medium (FACM), MRS and defined medium 1. The effects of addition or removal of nucleosides and thymidine phosphorylase were investigated. E-tests on FACM yielded reproducible minimal inhibitory concentrations (MICs) for trimethoprim but addition of nucleosides was necessary for growth of Lact. acidophilus. MICs for the tested strains were 0.125-0.19, 0.25-3 and 0.064-0.19 microg ml(-1) for Lact. paracasei, Lact. rhamnosus and Lact. plantarum, respectively. With the addition of deoxyuridine and deoxyadenosine to FACM the MICs of Lact. acidophilus were 0.064-1 microg ml(-1). CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacilli do not have intrinsic resistance to trimethoprim. The results show that trimethoprim susceptibility testing of the tested Lactobacillus species is possible and indicate that transferable resistance genes are absent in all the tested strains.     

Comparative Evaluation of Oral Administration of Probiotic Lactobacilli-fermented Milks on Macrophage Function

Six strains of lactobacilli belonging to three species (Lactobacillus casei, Lactobacillus acidophilus and Lactobacillus helveticus) were evaluated for probiotic attributes viz. acid tolerance, bile tolerance and cell surface hydrophobicity. All the six strains exhibited probiotic attributes with considerable degree of variation. Three Lactobacillus strains selected on the basis of probiotic attributes were used for preparing three different fermented milks. In order to evaluate the effect of feeding these probiotic fermented milks on macrophage cell function, an in-vivo trial was conducted in mice for a period of 2, 5 and 8?days. The control group of mice was fed with skim milk. The phagocytic activity of macrophages increased significantly (P?<?0.05) on feeding fermented milk prepared using L. acidophilus, L. casei and L. helveticus as compared to milk group (control) on 2nd, 5th and 8th day of feeding, respectively. Likewise, the release of ??-glucuronidase and ??-galactosidase from peritoneal macrophages increased significantly (P?<?0.05) on 2nd, 5th and 8th day of feeding as compared to their respective control group (milk). The results thus depict that feeding of probiotic fermented milk enhances phagocytic activity of the macrophages.     

Protective effect of Lactobacillus sakei 2a against experimental challenge with Listeria monocytogenes in gnotobiotic mice

AIM: Lactobacillus sakei 2a isolated from sausage and presenting an in vitro antagonistic activity against Listeria monocytogenes Scott A was tested for a protective effect in mice experimentally challenged with the enterobacteria. METHODS AND RESULTS: In the experimental group, germ-free mice (n = 24) were inoculated intragastrically with 0.1 ml of a suspension containing 10(8) colony forming units (CFU) of Lact. sakei and 4 days later the animals were challenged intragastrically with 0.1 ml of a suspension containing 10(8) CFU of L. monocytogenes. Control group (n = 24) was only inoculated with the bacterial pathogen. Faecal counts showed that L. monocytogenes reached similar population levels (10(9) CFU g(-1) of contents) in both the groups. Animals in the control group showed lower (P = 0.0004) survival frequency (58.3%) when compared with the experimental one (100%). Anatomopathological examination confirmed the mortality data. CONCLUSIONS: Lactobacillus sakei 2a can survive in the mammal digestive tract where showed a protective effect against L. monocytogenes. This phenomenon was not due to an antagonistic activity. SIGNIFICANCE AND IMPACT OF THE STUDY: Use of Lact. sakei 2a as a meat starter could inhibit not only L. monocytogenes growth in the fermented product but also pathogen virulence in the gastrointestinal tract.     

In vitro growth control of selected pathogens by Lactobacillus acidophilus- and Lactobacillus casei-fermented milk

AIMS: Food-borne pathogen inhibition was tested in the presence of a mixture of Lactobacillus acidophilus and Lactobacillus casei during fermentation under controlled pH conditions. METHODS AND RESULTS: The growth of Escherichia coli O157:H7, Salmonella serotype Typhimurium, Staphylococcus aureus, Listeria innocua, Enterococcus faecium and Enterococcus faecalis was evaluated for 48 h at 37 degrees C. In the presence of the lactic acid bacteria (LAB), an increase of the generation time was observed for all the gram-positive bacteria evaluated. Staphylococcus aureus was the most sensitive strain showing an increase of the generation time by 210%. However, for all the gram-negative bacteria evaluated, no inhibition occurred after 8 h of fermentation. The soluble portion of Lact. acidophilus- and Lact. casei-fermented milk was recuperated and tested for its antimicrobial activity. Listeria innocua and Staph. aureus were the most sensitive to the presence of fermented milk supernatant showing an inhibition of 85.9% and 84.7%, respectively. This soluble fraction was neutralized to eliminate the antimicrobial effect of the organic acids produced; the most sensitive strains were L. innocua and E. coli O157:H7 showing an inhibition of 65.9% and 61.9%, respectively. Finally, the soluble fraction was neutralized and irradiated at 45 kGy using a (60)Co source to eliminate the possible antimicrobial effect of both organic acids and bacteriocin-like substances. Enterococcus faecalis, E. coli O157:H7 and Staph. aureus were the most affected bacteria by this fraction, showing 39.1, 32 and 31.2% inhibition, respectively. CONCLUSIONS: The results obtained in this study suggest the implication of both organic acids and bacteriocin-like inhibitory substances in the antimicrobial activity observed in the soluble fraction of the probiotic preparation. SIGNIFICANCE AND IMPACT OF THE STUDY: This study revealed the antimicrobial mechanisms of action of Lact. acidophilus- and Lact. casei-fermented milk used to prevent antibiotic-associated diarrhoea.     

Effect of curing conditions and Lactobacillus casei CRL705 on the hydrolysis of meat proteins

Aims:  The effect of the common curing conditions used during the manufacture of dry fermented sausage on the proteolytic activity of Lactobacillus casei CRL705 against meat proteins was investigated.
Methods and Results:  Hydrolysis of pork muscle sarcoplasmic and myofibrillar proteins was evaluated by SDS-PAGE and reverse phase-HPLC analysis. Ascorbic acid exerted a stimulatory effect on both sarcoplasmic and myofibrillar protein breakdown by Lact. casei CRL705 with the release of hydrophilic peptides and free amino acids, while NaCl and NaNO₂ mainly stimulated myofibrillar degradation.
Conclusions:  Even when processing temperature (25°C) did not positively affect bacterial protein hydrolysis, the presence of curing salts accounted for a remarkable increase in the non-volatile components that constitute taste-active compounds that strongly influence the final flavour of the product.
Significance and Impact of the Study:  To predict the suitability of Lact. casei CRL705 and its proteolytic enzymes as a starter culture for the dry processing of dry fermented sausages.     

Citrate method of extracting antigens from Shigella sonnei. I. Comparison with other methods

The comparative characteristic of extracts obtained from Sh. sonnei by the method of Raynaud and Digeon and neurotoxin obtained by sedimentation with trichloroacetic acid from chloroform autolysates by the method of Mesrobeanu et al. is presented. Both preparations were shown to be similar in their antigenic structure and immunogenicity for mice and guinea-pigs. Nevertheless the extracts obtained by the citrate method contained considerably less protein and endotoxin and had no enterotoxic activity. This allows to recommend the citrate method for extracting protective antigens from Sh. sonnei.     

Experimental study of the preventive properties of immune milk containing Shigella antibodies

The protective properties of the mammary gland secretions of cows immunized with Shigella sonnei into the udder were studied. As a model for this study the intranasal and intraperitoneal infection of white mice was used. Immune milk was found to have pronounced protective properties against S. sonnei. When introduced intraperitoneally, this milk protected the animals infected with S. sonnei from death. When introduced intranasally, it not only protected the animals from death, but perceptibly inhibited the development of the pathological process in the pulmonary tissue, preventing the multiplication of shigellae and accelerating the elimination of the infective agents from the lungs of the infected animals. As a rule, the degree of protective action was determined by the level of antibodies to shigellae in the substrate under test.     

Variable response to exogenous Lactobacillus acidophilus NCFM consumed in different delivery vehicles

AIMS: To study the effects of the delivery vehicle for Lactobacillus acidophilus on the human faecal microbiota. Our hypotheses were that (i) the delivery vehicle would influence faecal lactobacilli numbers and (ii) consumption of Lact. acidophilus would influence the populations of Bifidobacterium and hydrogen sulphide-producing bacteria. METHODS AND RESULTS: Ten subjects each received Lact. acidophilus with skim milk or water. Lactobacillus, Bifidobacterium and hydrogen sulphide-producing bacterial populations were analysed before, during and after each treatment. Regardless of the vehicle, faecal lactobacilli populations changed during treatment. Bifidobacteria and the hydrogen sulphide-producing bacteria underwent no statistically significant population changes. Intra- and intersubject variability was observed. CONCLUSIONS: The vehicle in which Lact. acidophilus was delivered did not influence faecal lactobacilli numbers. Consumption of Lact. acidophilus did not influence the populations of Bifidobacterium and hydrogen sulphide-producing bacteria. The lactobacilli populations of subjects were variable. The fed lactobacilli did not appear to colonize the gastrointestinal tract. SIGNIFICANCE AND IMPACT OF THE STUDY: We provide evidence that (i) there was no collective advantage to using skim milk as a delivery vehicle vs water; (ii) exogenous Lact. acidophilus did not affect endogenous bifidobacteria or hydrogen sulphide-producing bacteria; (iii) data should be carefully examined before pooling for analysis and (iv) continuous feeding was required to maintain an elevated lactobacilli population.