Common nonsynonymous polymorphisms in the NOD2 gene are associated with resistance or susceptibility to tuberculosis disease in African Americans.

Pattern-recognition receptors (PRRs) play a key role in innate immunity against intracellular bacteria. NOD2 is one of the PRRs that contribute to the immune response to Mycobacterium tuberculosis infection. We sequenced coding regions of the NOD2 gene in 377 African Americans with tuberculosis (TB) disease and 187 ethnically matched control subjects. Three common nonsynonymous single-nucleotide polymorphisms--Pro268Ser, Arg702Trp, and Ala725Gly--demonstrated significant associations with TB disease. This finding may contribute to the future development of immunotherapy and immunoprophylaxis for TB disease.

Sequential outbreaks of infections by distinct Acinetobacter baumannii strains in a public teaching hospital in Houston, Texas.

Invasive disease due to Acinetobacter baumannii is an increasing problem in health care settings worldwide. Whether certain clones of A. baumannii are more likely to cause invasive disease in hospitalized patients is unknown. We studied all patients at a public teaching hospital in Houston, Texas, from whom the Acinetobacter calcoaceticus-Acinetobacter baumannii complex was isolated over a 14-month period in 2005 to 2006. One hundred seven unique patient isolates were identified, with 87 of the strains classified as being A. baumannii, the majority of which were multidrug resistant. The A. baumannii isolates were comprised of 18 unique pulsed-field types, with strains of clone A and clone B accounting for 66 of the 87 isolates. Epidemiologic analysis showed the predominance of the two A. baumannii clones at distinct time periods, with the remainder of the A. baumannii and non-A. baumannii strains being evenly distributed. Patients from whom clone A strains were isolated were more likely to be bacteremic than were patients with other A. baumannii isolates. Conversely, clone B strains were more likely to be isolated from patients with tertiary peritonitis. Patients from whom clone A was isolated had a significantly higher rate of mortality. Multilocus sequence typing demonstrated that clones A and B are related to each other and to A. baumannii strains previously isolated in Western Europe, sharing five of seven alleles. Taken together, we conclude that the outbreak of the A. calcoaceticus-A. baumannii complex in our institution was due to two distinct A. baumannii clones that were associated with significantly different patient outcomes.

Validation of the MycoAlign system for Mycobacterium spp. identification.

Validation of the MycoAlign assay, a newly developed Mycobacterium spp. identification system based on internal transcribed spacer-1 sequencing, was performed using 50 acid-fast bacilli (AFB)-positive clinical laboratory specimens. Forty-three (86%) diagnostic-level results were obtained, including 38 Mycobacterium spp. and 5 other AFB-positive genera. Three isolates (6%) had suboptimal identity scores with high probability (81-87% identity score). Four (8%) mixed-pattern results were obtained. Forty-five (90%) observations were concordant with the species identification by standard methods, including all controls.

Regulation of polysaccharide utilization contributes to the persistence of group a streptococcus in the oropharynx.

Group A Streptococcus (GAS) genes that encode proteins putatively involved in polysaccharide utilization show growth phase-dependent expression in human saliva. We sought to determine whether the putative polysaccharide transcriptional regulator MalR influences the expression of such genes and whether MalR helps GAS infect the oropharynx. Analysis of 32 strains of 17 distinct M protein serotypes revealed that MalR is highly conserved across GAS strains. malR transcripts were detectable in patients with GAS pharyngitis, and the levels increased significantly during growth in human saliva compared to the levels during growth in glucose-containing or nutrient-rich media. To determine if MalR influenced the expression of polysaccharide utilization genes, we compared the transcript levels of eight genes encoding putative polysaccharide utilization proteins in the parental serotype M1 strain MGAS5005 and its DeltamalR isogenic mutant derivative. The transcript levels of all eight genes were significantly increased in the DeltamalR strain compared to the parental strain, especially during growth in human saliva. Following experimental infection, the DeltamalR strain persistently colonized the oropharynx in significantly fewer mice than the parental strain colonized, and the numbers of DeltamalR strain CFU recovered were significantly lower than the numbers of the parental strain CFU recovered. These data led us to conclude that MalR influences the expression of genes putatively involved in polysaccharide utilization and that MalR contributes to the persistence of GAS in the oropharynx.

MalE of group A Streptococcus participates in the rapid transport of maltotriose and longer maltodextrins.

Study of the maltose/maltodextrin binding protein MalE in Escherichia coli has resulted in fundamental insights into the molecular mechanisms of microbial transport. Whether gram-positive bacteria employ a similar pathway for maltodextrin transport is unclear. The maltodextrin binding protein MalE has previously been shown to be key to the ability of group A Streptococcus (GAS) to colonize the oropharynx, the major site of GAS infection in humans. Here we used a multifaceted approach to elucidate the function and binding characteristics of GAS MalE. We found that GAS MalE is a central part of a highly efficient maltodextrin transport system capable of transporting linear maltodextrins that are up to at least seven glucose molecules long. Of the carbohydrates tested, GAS MalE had the highest affinity for maltotriose, a major breakdown product of starch in the human oropharynx. The thermodynamics and fluorescence changes induced by GAS MalE-maltodextrin binding were essentially opposite those reported for E. coli MalE. Moreover, unlike E. coli MalE, GAS MalE exhibited no specific binding of maltose or cyclic maltodextrins. Our data show that GAS developed a transport system optimized for linear maltodextrins longer than two glucose molecules that has several key differences from its well-studied E. coli counterpart.