Pneumococcal pneumonia: clinical features, diagnosis and management in HIV-infected and HIV noninfected patients:

Community-Acquired Pneumonia due to Streptococcus pneumoniae: When to Consider Coinfection with Active Pulmonary Tuberculosis

Community-acquired pneumonia (CAP) is an important cause of hospitalizations in adults. In the United States, Streptococcus pneumoniae is the most frequently identified bacterial pathogen responsible for CAP. Other etiologic pathogens of CAP vary based on the geographic region. Mycobacterium tuberculosis is an uncommon cause of CAP in the United States, while it is a principal cause in many African and Asian countries. Coinfection with Streptococcus pneumoniae and Mycobacterium tuberculosis is rare and has only been reported in the setting of underlying HIV infection in areas of high tuberculosis prevalence. Here, we report a case of CAP in the absence of HIV, where Streptococcus pneumoniae was identified on admission and delay in diagnosis of concomitant active pulmonary tuberculosis led to inappropriate isolation. In addition to a high index of suspicion, epidemiologic and radiographic findings can be helpful to recognize tuberculosis as a cause of CAP even when other pathogens have already been identified.

HIV-associated bacterial pneumonia

Community-acquired bacterial pneumonia (CAP) remains one of the most common opportunistic infections in patients who are infected with the human immunodeficiency virus (HIV). The risk of CAP increases as the CD4 cell count decreases. The common bacterial pathogens that cause CAP in HIV-infected persons are similar to those in HIV-uninfected individuals, with the pneumococcus being the most common pathogen. Prevention of CAP remains critical and necessitates a comprehensive approach addressing, among many other factors, cigarette smoking cessation strategies, antiretroviral therapy adherence, and immunization against those infections for which effective vaccinations are available.

Characterization of mutants deficient in the L,D-carboxypeptidase (DacB) and WalRK (VicRK) regulon, involved in peptidoglycan maturation of Streptococcus pneumoniae serotype 2 strain D39

Peptidoglycan (PG) hydrolases play critical roles in the remodeling of bacterial cell walls during division. PG hydrolases have been studied extensively in several bacillus species, such as Escherichia coli and Bacillus subtilis, but remain relatively uncharacterized in ovococcus species, such as Streptococcus pneumoniae (pneumococcus). In this work, we identified genes that encode proteins with putative PG hydrolytic domains in the genome of S. pneumoniae strain D39. Knockout mutations in these genes were constructed, and the resulting mutants were characterized in comparison with the parent strain for growth, cell morphology, PG peptide incorporation, and in some cases, PG peptide composition. In addition, we characterized deletion mutations in nonessential genes of unknown function in the WalRK(Spn) two-component system regulon, which also contains the essential pcsB cell division gene. Several mutants did not show overt phenotypes, which is perhaps indicative of redundancy. In contrast, two new mutants showed distinct defects in PG biosynthesis. One mutation was in a gene designated dacB (spd_0549), which we showed encodes an L,D-carboxypeptidase involved in PG maturation. Notably, dacB mutants, similar to dacA (D,D-carboxypeptidase) mutants, exhibited defects in cell shape and septation, consistent with the idea that the availability of PG peptide precursors is important for proper PG biosynthesis. Epistasis analysis indicated that DacA functions before DacB in D-Ala removal, and immunofluorescence microscopy showed that DacA and DacB are located over the entire surface of pneumococcal cells. The other mutation was in WalRK(Spn) regulon gene spd_0703, which encodes a putative membrane protein that may function as a type of conserved streptococcal shape, elongation, division, and sporulation (SEDS) protein.