Purification and characterization of two new antimicrobial molecules produced by an endophytic strain of Paenibacillus polymyxa.

An endophytic bacterium inhibiting pathogenic bacteria was isolated and the strain was genetically identified as Paenibacillus polymyxa. Biochemical characterization of fermentation broth indicated the presence of peptidic antimicrobial molecules. Liquid-liquid partition resulted in an organic fraction (OF) and an aqueous fraction (AF). OF presented a broad spectrum of activity against a panel of pathogenic bacteria and a fungus whereas the AF was active only against Gram-negative bacteria. AF was sequentially submitted to ion-exchange, desalting and reverse phase (RP) chromatography. A molecule with an RT of 2.45 min exhibited activity against all Gram-negative pathogenic strains tested beside P. mirabilis. The primary structure of the molecule, named AMP-Pp, was determined as Gly-Glu-Hyp-Gly-Ala by N-terminal sequencing. The molecular mass and amino acid sequence were confirmed by MS/MS. With a molecular mass of 463 Da, AMP-Pp is one of the smallest active natural peptides reported, yet. RP chromatography of OF resulted in four peaks. The first three peaks corresponded to known antimicrobials. MS analysis of peak 4 revealed the presence of an ion with m/z 3,376.4 Da, whose proposed molecular formula is C182H321N29O29. The compound, named polycerradin, showed a spectrum of activity against Gram-positive bacteria, Gram-negative bacteria (beside P. mirabilis) and a fungus.

paa, originally identified in attaching and effacing Escherichia coli, is also associated with enterotoxigenic E. coli.

Previous studies on virotypes and antimicrobial resistance in a collection of porcine enterotoxigenic Escherichia coli (ETEC) O149 strains from Quebec revealed an increase in the number of multiresistant strains (in particular to tetracycline) and the appearance of new virulence factors with time. Among these factors is paa (for porcine attaching- and effacing-associated), originally identified in a porcine enteropathogenic strain, but also present in enterohemorrhagic E. coli O157:H7. In the present study, the association of paa with other ETEC virulence genes, its conservation and expression were investigated in the O149 ETEC collection. All 37 paa-positive strains possessed estB, elt, astA and faeG, and more than half also carried the estA gene, defining two main virotypes, estA(+) and estA(-). Most strains were tetA- or tetB-positive, or both. paa is carried on high molecular weight plasmids. On tetA plasmids, paa is mostly found with enterotoxin gene estA and autotransporter gene sepA. Paa, a 30 kDa protein, is highly conserved and expressed in these strains. Moreover, paaETEC and porcine EPEC/EHEC contain IS signatures, suggesting that paa could be derived from a common ancestor. All these observations suggest a broader role than previously assessed in virulence for paa.

Enterotoxigenic Escherichia coli and probiotics in swine: what the bleep do we know?

The concept of certain microorganisms conferring direct benefits to the host relates to the term "probiotic". Probiotics are microorganisms, bacteria, or yeast that when administered orally in sufficient quantity can counteract the effect of pathogenic microorganisms. The gastrointestinal (GI) tract is the site where probiotics are believed to play the most important role. The proposed effects of probiotics include antagonism of pathogens, interference with adherence, competition for nutrients, enterotoxin inactivation, modulation of the immune response, and strengthening of the intestinal barrier. From birth to postweaning, piglets are very sensitive to gut colonisation by pathogens. Enterotoxigenic Escherichia coli represents one of the most common agents of swine diarrhoea. The enterotoxins produced by this E. coli virotype are responsible for the loss of electrolytes and water observed following infection. This review addresses more specifically the studies done during the last 10 years deciphering the molecular mechanisms at play between host cell and probiotic interactions in the swine GI tract.