Antagonistic activity of Lactobacillus plantarum C11: two new two-peptide bacteriocins, plantaricins EF and JK, and the induction factor plantaricin A

Six bacteriocinlike peptides (plantaricin A [PlnA], PlnE, PlnF, PlnJ, PlnK, and PlnN) produced by Lactobacillus plantarum C11 were detected by amino acid sequencing and mass spectrometry. Since purification to homogeneity was problematic, all six peptides were obtained by solid-phase peptide synthesis and were tested for bacteriocin activity. It was found that L. plantarum C11 produces two two-peptide bacteriocins (PlnEF and PlnJK); a strain-specific antagonistic activity was detected at nanomolar concentrations when PlnE and PlnF were combined and when PlnJ and PlnK were combined. Complementary peptides were at least 10(3) times more active when they were combined than when they were present individually, and optimal activity was obtained when the complementary peptides were present in approximately equal amounts. The interaction between complementary peptides was specific, since neither PlnE nor PlnF could complement PlnJ or PlnK, and none of these peptides could complement the peptides constituting the two-peptide bacteriocin lactococcin G. Interestingly, PlnA, which acts as an extracellular signal (pheromone) that triggers bacteriocin production, also possessed a strain-specific antagonistic activity. No bacteriocin activity could be detected for PlnN.     

Comparative cytologic study of nephron structure in higher vertebrates

A comparative study of the cytological characteristics of the epithelial lining of the nephron and collecting tubules was performed in 9 species of reptiles, 19 species of birds and 12 species of mammals. Representatives of each class of higher vertebrates were shown to have certain specific features of the epithelial lining of different parts of the nephron. Differentiation of various areas of the proximal part of the nephron proceded in phylogeny with different intensity and the maximum specialization was characteristic of the most proximal portion of this part of the nephron. In the cells of the proximal parts of nephrons of some reptiles there were phenomena of apocrine secretion. Evolution of the distal part of the nephron developed to form a loop and differentiation of the distal convoluted segment. The higher differentiation of the epithelial lining of the nephron distal part in birds and mammals, unlike in reptiles, seems to be associated with a more considerable functional specilization of this part. In the cytochemical characteristics of the epithelium of the uriniferous and collecting tubules of kidneys of higher vertebrate animals there are common regularities in the distribution of RNA, proteins and some enzymes. The polysaccharide content is maximum in the epithelial cells of kidneys of reptiles.     

Traveler's diarrhea

Travellers' diarrhea afflicts up to 50 percent of tourists in certain geographic regions. It is a syndrome caused by a variety of pathogens, the most common of which is enterotoxigenic E. coli. Other responsible pathogens include salmonellae, shigellae, Entamoeba histolytica, Yersinia enterocolitica, Giardia lamblia and virus-like agents, seldom vibrios. Symptoms persist for only a few days and are only serious in 1/5 of the cases.