Inactivation of DltA Modulates Virulence Factor Expression in Streptococcus pyogenes

D-alanylated lipoteichoic acid is a virtually ubiquitous component of gram-positive cell walls. Mutations in the dltABCD operon of numerous species exhibit pleiotropic effects, including reduced virulence, which has been attributed to increased binding of cationic antimicrobial peptides to the more negatively charged cell surface. In this study, we have further investigated the effects that mutating dltA has on virulence factor expression in Streptococcus pyogenes.Isogenic Delta dltA mutants had previously been created in two distinct M1T1 isolates of S. pyogenes. Immunoblots, flow cytometry, and immunofluorescence were used to quantitate M protein levels in these strains, as well as to assess their ability to bind complement. Bacteria were tested for their ability to interact with human PMN and to grow in whole human blood. Message levels for emm, sic, and various regulatory elements were assessed by quantitative RT-PCR. Cell walls of Delta dltA mutants contained much less M protein than cell walls of parent strains and this correlated with reduced levels of emm transcripts, increased deposition of complement, increased association of bacteria with polymorphonuclear leukocytes, and reduced bacterial growth in whole human blood. Transcription of at least one other gene of the mga regulon, sic, which encodes a protein that inactivates antimicrobial peptides, was also dramatically reduced in Delta dltA mutants. Concomitantly, ccpA and rofA were unaffected, while rgg and arcA were up-regulated.This study has identified a novel mechanism for the reduced virulence of dltA mutants of Streptococcus pyogenes in which gene regulatory networks somehow sense and respond to the loss of DltA and lack of D-alanine esterification of lipoteichoic acid. The mechanism remains to be determined, but the data indicate that the status of D-alanine-lipoteichoic acid can significantly influence the expression of at least some streptococcal virulence factors and provide further impetus to targeting the dlt operon of gram-positive pathogens in the search for novel antimicrobial compounds

Adaptive response of growing rat small intestine to acute Adriamycin injury.

The response of the intestinal mucosa to Adriamycin (ADR) was studied in the duodenum, jejunum, and ileum of 25-day-old rats. A single injection of ADR resulted in decreases in mucosal DNA per centimeter of length and in sucrase activity, which were proportional to the doses given (2, 5, and 8 mg/kg). ADR at 2 mg/kg had no significant effect on body weight, gut length, epithelial structure, or mucosal protein content per unit length. The morphological modifications occurred mostly in the proximal intestine and consisted of villous atrophy and degenerative changes of villus and crypt cells. A single dose of 5 mg ADR/kg acutely affected the gut. At 48 and 96 h the changes were characterized by marked decreases in mucosal weight, DNA per centimeter, sucrase activity, and villous shortening. At 144 h, the ADR-treated intestine entered a highly proliferative state and showed increased villous height, mucosal weight, and DNA per centimeter. Although villous hyperplasia was observed at 144 and 192 h, the mucosal weight and DNA concentrations did not exceed the corresponding levels in the control. During the period of active epithelial proliferation, sucrase activity remained depressed. We conclude that in the growing rat: (a) the acute intestinal injury of ADR is short-lived, dose dependent, and predominates in the proximal small intestine; (b) the enteric mucosa reacts to cytotoxic injury by excessive proliferation of immature enterocytes; and (c) the hyperplastic response to ADR is confined to the mucosal epithelium

Kyste du cholédoque: un cas avec dilatation des voies biliaires intrahépatiques et fibrose hépatique congénitale.

The authors report the case of a 2-year-old girl with hepatomegaly and failure to thrive in whom the diagnosis of congenital hepatic fibrosis was first considered on the basis of the histological examination of a percutaneous liver biopsy. Further radiographic and ultrasonic investigations of the biliary tree showed a choledocal cyst and dilatation of the intrahepatic ducts. Surgical operation consisted in complete removal of the cyst with hepaticojejunostomy. The congenital intrahepatic abnormalities associated with the choledochal cyst are commented