Use of a water-based probiotic to treat common gut pathogens.

This work reports the anti-pathogenic effect of a commercially available water-based probiotic suspension, Symprove™, against three commonly encountered infectious organisms; Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA) and Shigella sonnei. An isothermal calorimetric assay was used to the monitor growth of the species individually and in binary combinations, while colony plate counting was used to enumerate viable cell numbers. It was observed that all pathogenic species were faster growing than the probiotic bacteria in Symprove™ after inoculation into growth medium yet in all instances bacterial enumeration at the end of the experiments revealed a significant reduction in the pathogen population compared with the controls. A control population between 108 and 109 CFU/ml was obtained for E. coli and S. sonnei whilst approximately 106 CFU/ml was obtained for MRSA. Upon co-incubation for 48 h, no viable counts were obtained for E. coli; a 4-log reduction was obtained for S. sonnei whilst MRSA numbers were down to less than 10 cells/ml. The results show that Symprove™ has antipathogenic activity against E. coli, S. sonnei and MRSA.

The anti-apoptotic and anti-inflammatory effect of Lactobacillus acidophilus on Shigella sonnei and Vibrio cholerae interaction with intestinal epithelial cells: A comparison between invasive and non-invasive bacteria.

The aim of this study was to compare the effect of Lactobacillus acidophilus on the attachment, invasion, and interaction of Shigella sonnei and Vibrio cholerae with Caco-2 epithelial cells. Also, the anti-apoptotic and anti-inflammatory effect of L. acidophilus was investigated on S. sonnei and V. cholerae interaction with Caco-2 cells as the representatives of invasive and non-invasive intestinal bacteria. It was found that pretreatment with L. acidophilus significantly prevented from adherence and internalization of S. sonnei/V. cholerae and reduced the expression of tumour necrosis factor-α and interleukin-8 in host cells. No significant difference was observed in inhibitory effect of Lactobacilli in V. cholerae and S. sonnei attachment, emphasizing on the role of lactobacilli as a physical barrier in inhibiting direct contact with host cell by competitive exclusion, which may affect attachment and subsequent internalization of both invasive and non-invasive pathogenic bacteria in a same scale. The evaluation of early and late apoptosis in Caco-2 cells exposed to V. cholerae/S. sonnei and pretreated by L. acidophilus indicated no remarkable difference in L. acidophilus anti-apoptotic effect on Caco-2 cells against invasive and non-invasive bacterial infection. Moreover, L. acidophilus by itself showed no apoptotic effect on Caco-2 cells. Statistical analysis revealed that L. acidophilus in S. sonnei infected cells was able to reduce pro-inflammatory immune responses (TNF-α, IL-8 and IL-1ß) and NO and PGE2 secretion more strongly compared with V. cholerae infected cells. These data showed for the first time that the protective effect of Lactobacilli, as a probiotic bacterium, in interaction suppression was more in invasive bacteria including S. sonnei than in non-invasive V. cholerae.

Inhibition of Shigella sonnei and Shigella flexneri in Hummus Using Citric Acid and Garlic Extract.

Hummus (chickpea dip) is a ready-to-eat product that may pose a significant risk to human if pathogens are present. Several organisms including Shigella spp. have been isolated from hummus. However, studies on the survival and inhibition of Shigella spp. in food are scarce. This study investigated the growth pattern of Sh. sonnei and Sh. flexneri in hummus at different temperatures (4, 10, and 24 °C). Additionally, the inhibitory activity of different concentrations of citric acid (CA) (0.5%, 1.0%, and 2.0%) and garlic extract (GE) (1.0%, 2.0%, and 3.0%) against Sh. sonnei and Sh. flexneri inoculated into hummus and stored at 4 and 10 °C was investigated. Both Shigella spp. survived well at 4 °C, while both grew to >7.0 log10 after 4 d at 10 °C or 1 d at 24 °C. At 4 °C, CA at 0.5% and 1.0% resulted in a slight reduction in the count (approximately 1.0 log10 ); a complete elimination of Sh. sonnei was attained by using 2.0% CA. However, approximately 3.0 log10 reduction in Sh. sonnei was obtained at 10 °C. For Sh. flexneri, CA at 0.5% and 1.0% resulted in a bacteriostatic inhibition. GE at 1.0% and 2.0% resulted in approximately 1.0 to 2.0 log10 reduction in Sh. sonnei count at 4 °C, while at 3.0% GE, approximately 4.0 and 3.0 log10 reductions were obtained at 4 and 10 °C, respectively. In comparison, the 2.0% and 3.0% GE resulted in a bacteriostatic effect against Sh. flexneri at 4 and 10 °C.

Shigella sonnei Encodes a Functional T6SS Used for Interbacterial Competition and Niche Occupancy.

Shigella is a leading cause of dysentery worldwide, with the majority of infections caused by two subgroups, S. flexneri and S. sonnei. Although S. flexneri has been highly prevalent in low-income countries, global development has brought an increase in S. sonnei at the expense of S. flexneri. However, the mechanisms behind this shift are not understood. Here we report that S. sonnei, but not S. flexneri, encodes a type VI secretion system (T6SS) that provides a competitive advantage in the gut. S. sonnei competes against E. coli and S. flexneri in mixed cultures, but this advantage is reduced in T6SS mutant strains. In addition, S. sonnei can persist as well as outcompete E. coli and S. flexneri in mice in a T6SS-dependent manner. These findings suggest that S. sonnei has a competitive advantage over S. flexneri and potentially explain the increasing global prevalence of S. sonnei.

Antibacterial metabolites secreted under glucose-limited environment of the mimicked proximal colon model by lactobacilli abundant in infant feces.

The most abundance of anti-Salmonella lactic acid bacteria (LAB) was found in feces of naturally born, exclusively breastfed Thai infants. Six strains of Lactobacillus plantarum and one strain of Lactobacillus paracasei were selected and identified. In the co-cultivation assay, L. plantarum subsp. plantarum I62 showed the strongest and broadest antibacterial activity against Escherichia coli, Shigella sonnei, Salmonella Paratyphi A, and Salmonella Typhimurium SA 2093 under the mimicked proximal colon condition, in which glucose and other nutrients were limited. According to GC-MS analysis, the major antibacterial contribution of organic acids secreted by L. plantarum I62 grown in the presence of glucose was dramatically reduced from 95.8 to 41.9 % under glucose-limited niche. The production of low-pK a acids, such as lactic, 1,2-benzenedicarboxylic, and 3-phenyllactic acids, was remarkably dropped. Surprisingly, higher-pK a acids such as 5-chlorobenzimidazole-2-carboxylic, pyroglutamic, palmitic, and oleic acids were enhanced. Moreover, cyclic dipeptides, ketones, alkanes, alcohols, and miscellaneous compounds, which were pH-independent antibacterial metabolites, became dominant. The electron microscopy strongly supported the synergistic attacks of the multiple antibacterial components targeting outer and cytoplasmic membranes leading to severe leakage and cell disruption of Salmonella Typhimurium. This strain poses to be a potential probiotic candidate for effectively controlling and treating human foodborne bacterial infection.

Development of selective and differential medium for Shigella sonnei using three carbohydrates (lactose, sorbitol, and xylose) and X-Gal.

The aim of this study was to develop a new selective and differential medium for isolating Shigella sonnei (designated 3SD medium). The new medium was based on three carbohydrates (lactose, sorbitol, and xylose) and a chromogenic substrate (5-bromo-4-chloro-3-indolyl-ß-D-galactopyranoside, X-Gal). S. sonnei cannot ferment lactose, sorbitol, or xylose, but can ferment X-Gal, which generates turquoise-blue colonies with rough edges. Other bacteria (54 strains of foodborne pathogens and spoilage bacteria) produced visually distinct colonies on 3SD medium (colorless or pink-violet colonies), or their growth was inhibited on 3SD medium. The optimum concentration of 50 mg/L X-Gal was selected because it yielded the highest level of morphological discrimination between S. sonnei and other bacteria, and this concentration was cost-effective. Bile salt concentration optimization was performed using healthy, heat-injured, and acid-injured S. sonnei. The recovery rate differed significantly depending on the bile salt concentration; media containing >1.0 g/L bile salt showed significantly lower recovery of stress-injured cells than medium containing 0.5 g/L bile salt (P<0.05). Growth of all Gram-positive bacteria was inhibited on medium containing 0.5 g/L bile salt; therefore, this concentration was used as the optimal concentration. Previous media used to isolate Shigella spp. (MacConkey, xylose lysine desoxycholate, and Salmonella-Shigella agar) showed poor performance when used to support the growth of injured S. sonnei cells, whereas 3SD medium supported a high growth rate of injured and healthy cells (equivalent to that obtained with nutrient-rich tryptic soy agar). To validate the performance of 3SD medium with real specimens, S. sonnei and other bacteria were spiked into samples such as untreated water, carrot, salad, and oyster. 3SD medium showed superior specificity (100%) and sensitivity (100%) for S. sonnei, and yielded no false-positive or false-negative results. Thus, the novel 3SD medium described herein is a powerful tool for the rapid and efficient selective isolation of S. sonnei in research and clinical laboratories, and the food industry.

Antagonistic activity expressed by Shigella sonnei: identification of a putative new bacteriocin.

Bacteriocins are antibacterial, proteinaceous substances that mediate microbial dynamics. Bacteriocin production is a highly disseminated property among all major lineages of bacteria, including Shigella. In this paper, we addressed the purification and characterisation of a bacteriocin produced by a Shigella sonnei strain (SS9) isolated from a child with acute diarrhoea. The substance was purified through ammonium-sulphate precipitation and sequential steps of chromatography. The intracellular fraction obtained at 75% ammonium sulphate maintained activity following exposure to pH values from 1-11 and storage at -80ºC for more than two years and was inactivated by high temperatures and proteases. The molecular mass of the purified bacteriocin was determined by mass spectrometry to be 18.56 kDa. The N-terminal sequence of the bacteriocin did not match any other antibacterial proteins described. A putative new bacteriocin produced by S. sonnei has been detected. This bacteriocin may represent a newly described protein or a previously described protein with a newly detected function. Considering that SS9 expresses antagonism against other diarrhoeagenic bacteria, the bacteriocin may contribute to S. sonnei virulence and is potentially applicable to either preventing or controlling diarrhoeal disease.

Antagonistic activity expressed by Shigella sonnei: identification of a putative new bacteriocin

Bacteriocins are antibacterial, proteinaceous substances that mediate microbial dynamics. Bacteriocin production is a highly disseminated property among all major lineages of bacteria, including Shigella. In this paper, we addressed the purification and characterisation of a bacteriocin produced by a Shigella sonnei strain (SS9) isolated from a child with acute diarrhoea. The substance was purified through ammonium-sulphate precipitation and sequential steps of chromatography. The intracellular fraction obtained at 75% ammonium sulphate maintained activity following exposure to pH values from 1-11 and storage at -80ºC for more than two years and was inactivated by high temperatures and proteases. The molecular mass of the purified bacteriocin was determined by mass spectrometry to be 18.56 kDa. The N-terminal sequence of the bacteriocin did not match any other antibacterial proteins described. A putative new bacteriocin produced by S. sonnei has been detected. This bacteriocin may represent a newly described protein or a previously described protein with a newly detected function. Considering that SS9 expresses antagonism against other diarrhoeagenic bacteria, the bacteriocin may contribute to S. sonnei virulence and is potentially applicable to either preventing or controlling diarrhoeal disease.

Competitive inhibition of three novel bacteria isolated from faeces of breast milk-fed infants against selected enteropathogens.

Numerous in vitro and in vivo studies conducted using different probiotic micro-organisms have demonstrated their ability to interfere with the growth and virulence of a variety of enteropathogens. The reported beneficial effects of the use of probiotics to complement antibiotic therapy or prevent diarrhoea or gastrointestinal infection in infants have increased in recent years. In the present study, we demonstrated the capacity of supernatants obtained from three novel probiotics (Lactobacillus paracasei CNCM I-4034, Bifidobacterium breve CNCM I-4035 and Lactobacillus rhamnosus CNCM I-4036) isolated from the faeces of breastfed infants to inhibit the growth of enterotoxigenic and enteropathogenic (EPEC) bacteria, such as Escherichia coli, Salmonella and Shigella. To assess their potential antimicrobial activity, the 17 and 24 h cell-free supernatants broth concentrates (10×) having 1, 2 or 4 % of the three probiotics were incubated with EPEC bacteria strains. After 17 h of co-culture, the supernatants were able to inhibit the growth of E. coli, Salmonella and Shigella up to 40, 55 and 81 %, respectively. However, the inhibitory capacity of some supernatants was maintained or completely lost when the supernatants (pH 3·0) were neutralised (pH 6·5). Overall, these results demonstrated that L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036 produce compounds that exhibited strain-specific inhibition of enterobacteria and have the potential to be used as probiotics in functional foods.

Screening of probiotic lactobacilli for inhibition of Shigella sonnei and the macromolecules involved in inhibition.

A total of 91 lactobacilli were screened for antimicrobial activity against Shigella sonnei. Agar-well assay showed that 16 lactobacilli displayed strong antibacterial activity against S. sonnei. The nature of these antimicrobial agents were investigated and shown to be dependent on their production of organic acids. Adhesion tests showed that 6 lactobacilli demonstrated good adherence to HT-29 cells, of these Lactobacillus johnsonii F0421 were selected for acid and bile salt tolerance properties. We further research on L. johnsonii F0421 inhibition of S. sonnei adhesion to HT-29 cells. The result showed that L. johnsonii F0421 exhibited significant inhibitory activity and excluded, competed and displaced adhered S. sonnei by 48%, 38% and 33%, respectively. In order to elucidate the inhibitory functions of macromolecules involved in L. johnsonii F0421, the cells were treated with 5 M LiCl, 0.05 M sodium metaperiodate and heating and assayed for inhibition activity. The results suggested a role of S-layer proteins on L. johnsonii F0421 cells in inhibition of the adhesion process, but carbohydrates do not seem to be involved. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 40 kDa. In addition, 100 µg/well of S-layer proteins from L. johnsonii F0421 cells were effective in inhibiting adhesion of S. sonnei to HT-29 cells. These findings suggest that L. johnsonii F0421 possesses the capacity for inhibition of S. sonnei activity as well as probiotic properties, which could serve as a potential novel and effective probiotic strain for use in the food industry.

High-intensity 405 nm light inactivation of Listeria monocytogenes.

The antimicrobial properties of light is an area of increasing interest. This study investigates the sensitivity of the significant foodborne pathogen Listeria monocytogenes to selected wavelengths of visible light. Results demonstrate that exposure to wavelength region 400-450 nm, at sufficiently high dose levels (750 J cm(-2)), induced complete inactivation of a 5 log(10) population. Exposure to wavelengths longer than 450 nm did not cause significant inactivation. Analysis of 10 nm bandwidths between 400 and 450 nm confirmed 405(± 5) nm light to be most effective for the inactivation of L. monocytogenes, with a lesser bactericidal effect also evident at other wavelengths between 400 and 440 nm. Identification of the optimum bactericidal wavelength enabled the comparison of inactivation using 405(± 5) nm filtered light and a 405 nm light-emitting diode (LED) array (14 nm FWHM). Results demonstrate similar inactivation kinetics, indicating that the applied dose of 405 nm light is the important factor. Use of the 405 nm LED array for the inactivation of L. monocytogenes and other Listeria species resulted in similar kinetics, with up to 5 log(10) reductions with a dose of 185 J cm(-2). Comparative data for the 405 nm light inactivation of L. monocytogenes and other important foodborne pathogens, Escherichia coli, Salmonella enteritidis and Shigella sonnei, are also presented, with L. monocytogenes showing higher susceptibility to inactivation through 405 nm light exposure.

Bactericidal effects of 405 nm light exposure demonstrated by inactivation of Escherichia, Salmonella, Shigella, Listeria, and Mycobacterium species in liquid suspensions and on exposed surfaces.

The bactericidal effect of 405 nm light was investigated on taxonomically diverse bacterial pathogens from the genera Salmonella, Shigella, Escherichia, Listeria, and Mycobacterium. High-intensity 405 nm light, generated from an array of 405-nm light-emitting diodes (LEDs), was used to inactivate bacteria in liquid suspension and on exposed surfaces. L. monocytogenes was most readily inactivated in suspension, whereas S. enterica was most resistant. In surface exposure tests, L. monocytogenes was more susceptible than Gram-negative enteric bacteria to 405 nm light when exposed on an agar surface but interestingly less susceptible than S. enterica after drying onto PVC and acrylic surfaces. The study findings, that 405 nm light inactivates diverse types of bacteria in liquids and on surfaces, in addition to the safety advantages of this visible (non-UV wavelength) light, indicate the potential of this technology for a range of decontamination applications.

Lactobacillus fermentum isolated from human colonic mucosal biopsy inhibits the growth and adhesion of enteric and foodborne pathogens.

A number of Lactobacillus species are used as probiotic strains in order to benefit health. We have isolated L. fermentum from human colonic mucosal biopsy samples that possess antimicrobial activities against entroinvasive and foodborne pathogens such as Escherichia coli, Salmonella paratyphi A, Shigella sonnei, Staphylococcus aureus, Enterococcus faecalis, Proteus mirabilis, Pseudomonas aeruginosa, and Vibrio sp. In addition to lactic acid, L. fermentum secretes antimicrobial proteinacious compound(s) that was found to be active even at neutral pH (pH 7.0). The compound was sensitive to heat treatment and trypsin digestion. Lactobacillus fermentum inhibited the adhesion of enteropathogens to intestinal epithelial cells in vitro. Isolated cell surface associated proteins (SAPs) from L. fermentum were sufficient for the adhesion exclusions of enteropathogenic E. coli. Our results indicate that L. fermentum produces antimicrobial compounds and SAPs to inhibit the growth and adhesion of enteropathogens, respectively.

Acanthamoeba castellanii an environmental host for Shigella dysenteriae and Shigella sonnei.

The interaction between Shigella dysenteriae or Shigella sonnei and Acanthamoeba castellanii was studied by viable counts, gentamicin assay and electron microscopy. The result showed that Shigella dysenteriae or Shigella sonnei grew and survived in the presence of amoebae for more than 3 weeks. Gentamicin assay showed that the Shigella were viable inside the Acanthamoeba castellanii which was confirmed by electron microscopy that showed the Shigella localized in the cytoplasm of the Acanthamoeba castellanii. In conclusion, the relationship between Shigella dysenteriae and Shigella sonnei with Acanthamoeba castellanii is symbiotic, and accordingly free-living amoebae may serve as a transmission reservoir for Shigella in water.

Effects of a human milk-derived human milk fortifier on the antibacterial actions of human milk.

OBJECTIVES: To compare the effects of a human breastmilk-derived fortifier on the antibacterial activity of milk obtained from lactating mothers delivering prematurely with the effects of a powdered fortifier on the same milk. STUDY DESIGN: Human milk samples were obtained after the first week of postnatal life from 10 lactating mothers, who had delivered prematurely. A bovine milk-based powdered fortifier and a human breastmilk-based frozen fortifier were evaluated. All mothers were healthy and they were not on any medications, although they were taking prenatal vitamins during lactation. The effects of each fortifier on the antimicrobial activity of milk toward Enterobacter sakazaki (ES), Escherichia coli, Clostridium difficile (CD), and Shigella soneii (SS) were evaluated by both the filter paper method and the growth inhibition method. RESULTS: Human milk inhibited the growth of all of the test organisms. This antibacterial activity was almost totally inhibited by the addition of the bovine protein-based human milk fortifier, while it remained unaffected by the addition of the human breastmilk-based fortifier. CONCLUSIONS: Breastmilk from women who have delivered preterm has antibacterial activity that can be affected by the addition of bovine-based fortifier, but not by the addition of a human breastmilk-based fortifier.

Survival of Shigella sonnei on smooth tomato surfaces, in potato salad and in raw ground beef.

This study investigated the survival of a five-strain Shigella sonnei cocktail on smooth tomato surfaces, in potato salad and in raw ground beef. All inocula were resistant to the antibiotic rifampicin to allow simple detection of the target culture among the indigenous microflora of the food samples. Inoculated tomatoes were stored at 13 degrees C/85% relative humidity, the standard holding conditions for mature, green tomatoes. Inoculated potato salad and ground beef samples were stored at 2.5 degrees C and 8.0 degrees C to study the effects of varied refrigerated temperatures. Surviving populations were estimated using a three-tube most probable number (MPN) method. Tryptic soy broth tubes supplemented with 100 ppm rifampicin were inoculated with appropriate dilutions of the recovered inocula and scored for growth after overnight enrichment. S. sonnei populations declined rapidly to undetectable levels (2 days) when dried on smooth surfaces of tomatoes. S. sonnei populations did not decrease in potato salad and ground beef stored at 2.5 degrees C and 8.0 degrees C over the shelf-life of the products.

Elimination by ozone of Shigella sonnei in shredded lettuce and water.

Several outbreaks of shigellosis have been attributed to the consumption of contaminated fresh-cut vegetables. The minimal processing of these products make it difficult to ensure that fresh produce is safe for consumer. Chlorine-based agents have been often used to sanitize produce and reduce microbial populations in water applied during processing operations. However, the limited efficacy of chlorine-based agents and the production of chlorinated organic compounds with potential carcinogenic action have created the need to investigate the effectiveness of new decontamination techniques. In this study, the ability of ozone to inactivate S. sonnei inoculated on shredded lettuce and in water was evaluated. Furthermore, several disinfection kinetic models were considered to predict S. sonnei inactivation with ozone. Treatments with ozone (1.6 and 2.2 ppm) for 1 min decreased S. sonnei population in water by 3.7 and 5.6 log cfu mL(-1), respectively. Additionally, it was found that S. sonnei growth in nutrient broth was affected by ozone treatments. After 5.4 ppm ozone dose, lag-phases were longer for injured cells recovered at 10 degrees C than 37 degrees C. Furthermore, treated cells recovered in nutrient broth at 10 degrees C were unable to grow after 16.5 ppm ozone dose. Finally, after 5 min, S. sonnei counts were reduced by 0.9 and 1.4 log units in those shredded lettuce samples washed with 2 ppm of ozonated water with or without UV-C activation, respectively. In addition, S. sonnei counts were reduced by 1.8 log units in lettuce treated with 5 ppm for 5 min. Therefore, ozone can be an alternative treatment to chlorine for disinfection of wash water and for reduction of microbial population on fresh produce due to it decomposes to nontoxic products.

Acanthamoeba: could it be an environmental host of Shigella?

Shigellosis is a serious public health problem in Korea, because large outbreaks of Shigella sonnei infections were recorded in many parts of the country during the period 1998-2000. However, the epidemiological features of shigellosis are not well known. In this study, we devised conditions suitable for the growth and replication of Shigella in an amoebic intracellular environment, and investigate whether medium conditions affect the survival and replication of Shigella within Acanthamoeba. We evaluated the uptake rates of invasive and non invasive S. sonnei strains by three Acanthamoeba species, namely, A. castellanii Neff, A. astronyxis Ray & Hayes, and A. healyi OC-3A. When A. castellanii Neff was infected with S. sonnei 99OBS1 or 80DH248, shigellae was maintained for a longer time in cytoplasms than in other Acanthamoeba species. S. sonnei 99OBS1 strain (a virulent strain) was recovered in higher numbers than the non-virulent S. sonnei 80DH248 strain in all experiments. Moreover, S. sonnei was more easily engulfed by Acanthamoeba at 18 degrees C. The shigellae uptake rates of Neff strain, which was cultured in free-media (less nutrition), were higher (>10-fold) than those observed in original amoeba culture media (PYG medium) in all time points. S. sonnei 99OBS1 was localized, with an intact membrane, to the vacuoles of Acanthamoeba. We conclude that free-living amoebae more likely act as environmental hosts for shigellae, and thus, may have contributed to outbreaks of shigellosis in Korea.

Comparison of antagonistic ability against enteropathogens by G+ and G- anaerobic dominant components of human fecal microbiota.

To confirm if anaerobic G+-components are those responsible for the function of colonization resistance, obligate anaerobic G+- and G- -bacteria from normal dominant microbiota of human feces were isolated from three successive collections and then used in in vitro assays for antagonism against two enteropathogenic bacteria. The production of inhibitory diffusible compounds was determined on supplemented BHI agar and MRS agar media for G- - and G+-bacteria, respectively. Salmonella enterica subsp. enterica serovar Typhimurium and Shigella sonnei were used as indicators. G+-bacteria presented a higher overall antagonistic frequency against both pathogenic bacteria (57 and 64 % for S. enterica serovar Typhimurium and S. sonnei, respectively) when compared to G+-microorganisms but with a quite elevated variation between volunteers (0-100 %) and collection samples (40-72 and 40-80 % for S. enterica sv. Typhimurium and S. sonnei, respectively). On the other hand, only three among 143 G- -isolates tested showed antagonistic activity. The results showed that, at least in vitro, obligate anaerobic G+-components of the dominant human fecal microbiota present a higher potential for antagonism against the enteropathogenic models tested than do G- -bacteria.