A Novel Competence Pathway in the Oral Pathogen Streptococcus sobrinus.

Streptococcus sobrinus is an etiologic cause of dental caries (tooth decay) in humans. Our knowledge of S. sobrinus is scant despite the organism's important role in oral health. It is widely believed that S. sobrinus lacks the natural competence pathways that are used by other streptococci to regulate growth, virulence, and quorum sensing. The lack of natural competence has also prevented genetic manipulation of S. sobrinus, limiting our knowledge of its pathogenicity. We discovered that most strains of S. sobrinus contain a new class of the ComRS competence system. Although S. sobrinus is typically placed among the mutans group streptococci, the S. sobrinus ComRS system is most similar to the competence pathways in the salivarius group. Unlike all other ComRS systems, the S. sobrinus pathway contains 2 copies of the transcriptional regulator ComR and has a peptide pheromone (XIP) that lacks any aromatic amino acids. Synthetic XIP enables transformation of S. sobrinus with plasmid or linear DNA, and we leverage this newfound genetic tractability to confirm that only 1 of the ComR homologs is required for induced competence while the other appears to suppress competence. Exogenous XIP increases the expression of bacteriocin gene clusters and produces an antimicrobial response that inhibits growth of S. mutans. We also identified 2 strains of S. sobrinus that appear to be "cheaters" by either not responding to or not producing XIP. We show how a recombination event in the nonresponsive strain could restore function of the ComRS pathway but delete the gene encoding XIP. Thus, the S. sobrinus ComRS pathway provides new tools for studying this pathogen and offers a lens into the evolution of ecological cheaters.

Acute disseminated aspergillosis during the neonatal period. Report of an instance in a 14-day-old infant.

We describe an infant who died with extensive lesions of disseminated aspergillosis on the 18th day of postnatal life. Aspergillus fumigatus was recovered from blood cultures. Initial clinical manifestations were suggestive of hepatitis, and steroids and antibiotics were used in the treatment. This therapy may have fostered the onset of an opportunistic mycosis. Advanced multisystemic aspergillotic lesions were seen at autopsy, especially prominent in lungs and gastrointestinal tract. The extent and magnitude of the lesions observed suggest inception of the disease very early in life, although no case of human aspergillosis has been known to be congenital. Neonatal aspergillosis is poorly characterized. Only four previously reported cases came to our notice in which the disease could be diagnosed in the first month of life. The ubiquitous nature of pathogenic Aspergillus, joined to aggresive treatments designed to achieve increased survivals in neonatology, could potentially result in greater numbers of cases of this and other uncommon mycoses.