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

Primary sternal tuberculous ulcer with dissemination to the bone marrow: a clinical rarity

Primary tubercular osteomyelitis of the sternum with dissemination to bone marrow is a rarely described entity even in countries where tuberculosis is endemic. Delayed presentations can be in the form of sinus formation, spontaneous fracture of the sternum, extrasternal spread, and sepsis. Diagnosis can be made by CT of the chest wall and Ziehl–Neelsen staining of aspirate from the lesion or by tissue biopsy. We present a case of tuberculous osteomyelitis of the sternum with sinus formation along with widespread involvement of bone marrow, which was successfully treated with antituberculous therapy. Sternal osteomyelitis is difficult to diagnose on chest radiography and ultrasonography, but we were able to make the probable diagnosis of sternal tuberculous osteomyelitis. CT showed erosion of part of the sternal bone. Diagnosis was confirmed on histopathology and by bone marrow trephine biopsy. During the follow-up period of 3 months, the patient showed a satisfactory response to treatment