Ecology and pathogenicity of gastrointestinal Streptococcus bovis

Persistence of antibiotic resistance: evaluation of a probiotic approach using antibiotic-sensitive Megasphaera elsdenii strains to prevent colonization of swine by antibiotic-resistant strains

Megasphaera elsdenii is a lactate-fermenting, obligately anaerobic bacterium commonly present in the gastrointestinal tracts of mammals, including humans. Swine M. elsdenii strains were previously shown to have high levels of tetracycline resistance (MIC=64 to >256 μg/ml) and to carry mosaic (recombinant) tetracycline resistance genes. Baby pigs inherit intestinal microbiota from the mother sow. In these investigations we addressed two questions. When do M. elsdenii strains from the sow colonize baby pigs? Can five antibiotic-sensitive M. elsdenii strains administered intragastrically to newborn pigs affect natural colonization of the piglets by antibiotic-resistant (AR) M. elsdenii strains from the mother? M. elsdenii natural colonization of newborn pigs was undetectable (<10(4) CFU/g [wet weight] of feces) prior to weaning (20 days after birth). After weaning, all pigs became colonized (4 × 10(5) to 2 × 10(8) CFU/g feces). In a separate study, 61% (76/125) of M. elsdenii isolates from a gravid sow never exposed to antibiotics were resistant to chlortetracycline, ampicillin, or tylosin. The inoculation of the sow's offspring with mixtures of M. elsdenii antibiotic-sensitive strains prevented colonization of the offspring by maternal AR strains until at least 11 days postweaning. At 25 and 53 days postweaning, however, AR strains predominated. Antibiotic susceptibility phenotypes and single nucleotide polymorphism (SNP)-based identities of M. elsdenii isolated from sow and offspring were unexpectedly diverse. These results suggest that dosing newborn piglets with M. elsdenii antibiotic-sensitive strains delays but does not prevent colonization by maternal resistant strains. M. elsdenii subspecies diversity offers an explanation for the persistence of resistant strains in the absence of antibiotic selection.

The association of Streptococcus bovis/gallolyticus with colorectal tumors: the nature and the underlying mechanisms of its etiological role

Streptococcus bovis (S. bovis) bacteria are associated with colorectal cancer and adenoma. S. bovis is currently named S. gallolyticus. 25 to 80% of patients with S. bovis/gallolyticus bacteremia have concomitant colorectal tumors. Colonic neoplasia may arise years after the presentation of bacteremia or infectious endocarditis of S. bovis/gallolyticus. The presence of S. bovis/gallolyticus bacteremia and/or endocarditis is also related to the presence of villous or tubular-villous adenomas in the large intestine. In addition, serological relationship of S. gallolyticus with colorectal tumors and direct colonization of S. gallolyticus in tissues of colorectal tumors were found. However, this association is still under controversy and has long been underestimated. Moreover, the etiological versus non-etiological nature of this associationis not settled yet. Therefore, by covering the most of up to date studies, this review attempts to clarify the nature and the core of S. bovis/gallolyicus association with colorectal tumors and analyze the possible underlying mechanisms.

Differentiation of species of the Streptococcus bovis/equinus-complex by MALDI-TOF Mass Spectrometry in comparison to sodA sequence analyses

The Streptococcus bovis/equinus complex is a heterogeneous group within the group D streptococci with important clinical relevance regarding infective endocarditis, sepsis and colon carcinoma. The taxonomic identification of species and sub-species of this complex, by the standard methods remains difficult. In the present study, we compared the cluster analysis of 88 strains of species of the S. bovis/equinus complex by sequence analysis of the manganese-dependent superoxide dismutase gene (sodA) and by Matrix Assisted Laser Desorption/Ionization-Time Of Flight Mass Spectrometry (MALDI-TOF MS). We observed a high congruence of strain grouping by MALDI-TOF MS in comparison with sodA sequence analyses, demonstrating the accuracy and reliability of MALDI-TOF MS in comparison to DNA sequence-based method. By generating mass spectra for each species and sub-species, we were able to discriminate all members of the S. bovis/equinus complex. Furthermore, we demonstrated reliable identifications to the species level by MALDI-TOF MS, independently of cultivation conditions.

Beneficial effects of lactic acid bacteria on human beings

Lactic acid bacteria are a diverse group of bacteria that produce lactic acid as their major fermented product. Most of them are normal flora of human being and animals and produce myriad beneficial effects for human beings include, alleviation of lactose intolerance, diarrhea, peptic ulcer, stimulation of immune system, antiallergic effects, antifungal actions, preservation of food, and prevention of colon cancer. This review highlights the potential species of Lactic acid bacteria responsible for producing these effects. It has been concluded that lactic acid bacteria are highly beneficial microorganisms for human beings and are present abundantly in dairy products so their use should be promoted for good human health.