The respiratory tract pathogen Streptococcus pneumoniae needs to adapt to the different levels of carbon dioxide (CO 2 ) it encounters during transmission, colonization, and infection. Since CO 2 is important for various cellular processes, factors that allow optimal CO 2 sequestering are likely to be important for pneumococcal growth and survival. In this study, we showed that the putative pneumococcal carbonic anhydrase (PCA) is essential for in vitro growth of S. pneumoniae under the CO 2 -poor conditions found in environmental ambient air. Enzymatic analysis showed that PCA catalyzes the reversible hydration of CO 2 to bicarbonate (HCO 3 ؊ ), an essential step to prevent the cellular release of CO 2 . The addition of unsaturated fatty acids (UFAs) reversed the CO 2 -dependent in vitro growth inhibition of S. pneumoniae strains lacking the pca gene (⌬pca), indicating that PCA-mediated CO 2 fixation is at least associated with HCO 3 ؊ -dependent de novo biosynthesis of UFAs. Besides being necessary for growth in environmental ambient conditions, PCA-mediated CO 2 fixation pathways appear to be required for intracellular survival in host cells. This effect was especially pronounced during invasion of human brain microvascular endothelial cells (HBMEC) and uptake by murine J774 macrophage cells but not during interaction of S. pneumoniae with Detroit 562 pharyngeal epithelial cells. Finally, the highly conserved pca gene was found to be invariably present in both CO 2 -independent and naturally circulating CO 2 -dependent strains, suggesting a conserved essential role for PCA and PCA-mediated CO 2 fixation pathways for pneumococcal growth and survival.The Gram-positive bacterium Streptococcus pneumoniae, or pneumococcus, is a human respiratory tract pathogen that contributes significantly to global mortality and morbidity. In addition, it is an important asymptomatic colonizer of the human nasopharynx, with carriage rates around 10% in adults and over 40% in children (6). Pneumococcal colonization and infection are closely linked, but knowledge of the factors that contribute to transmission, carriage, disease, and transition from carriage to disease is still limited. Research on components that physically contribute to host-pathogen interactions, such as capsular polysaccharides, adhesins, and toxins, has provided valuable insights into the process of pneumococcal pathogenesis (20). In contrast, the influence of environmental factors on pneumococcal growth and survival remains fairly unexplored.S. pneumoniae needs to adapt to various aerobic and anaerobic conditions, reflecting the different niches it occupies during transmission, colonization, and invasive disease. During niche transition, oxygen (O 2 ) levels change considerably. Levels of O 2 are 21% in ambient air, decrease to 10 to 15% in the alveoli of the lungs, and are about 5% in resting cells. In O 2 -rich conditions, S. pneumoniae expresses pyruvate oxidase (SpxB), which generates acetyl-phosphate as a source of ATP and hydrogen peroxide (H 2 O 2 ) fo...

Streptococcus pneumoniae and Staphylococcus aureus cause significant morbidity and mortality worldwide. We investigated both the colonization and co-colonization characteristics for these pathogens among 250 healthy children from 2 to 5 years of age in Merida, Venezuela, in 2007. The prevalence of S. pneumoniae colonization, S. aureus colonization, and S. pneumoniae–S. aureus co-colonization was 28%, 56%, and 16%, respectively. Pneumococcal serotypes 6B (14%), 19F (12%), 23F (12%), 15 (9%), 6A (8%), 11 (8%), 23A (6%), and 34 (6%) were the most prevalent. Non-respiratory atopy was a risk factor for S. aureus colonization (p = 0.017). Vaccine serotypes were negatively associated with preceding respiratory infection (p = 0.02) and with S. aureus colonization (p = 0.03). We observed a high prevalence of pneumococcal resistance against trimethoprim–sulfamethoxazole (40%), erythromycin (38%), and penicillin (14%). Semi-quantitative measurement of pneumococcal colonization density showed that children with young siblings and low socioeconomic status were more densely colonized (p = 0.02 and p = 0.02, respectively). In contrast, trimethoprim–sulfamethoxazole- and multidrug-resistant-pneumococci colonized children sparsely (p = 0.03 and p = 0.01, respectively). Our data form an important basis to monitor the future impact of pneumococcal vaccination on bacterial colonization, as well as to recommend a rationalized and restrictive antimicrobial use in our community.

SummaryThe respiratory tract pathogen Streptococcus pneumoniae encounters different levels of environmental CO2 during transmission, host colonization and disease. About 8% of all pneumococcal isolates are capnophiles that require CO2-enriched growth conditions. The underlying molecular mechanism for caphnophilic behaviour, as well as its biological function is unknown. Here, we found that capnophilic S. pneumoniae isolates from clonal complex (CC) 156 (i.e. Spain 9V -3 ancestry) and CC344 (i.e. Norway NT -42 ancestry) have a valine at position 179 in the MurF UDP-MurNAc-pentapeptide synthetase. At ≤ 30°C, the growth characteristics of capnophilic and noncapnophilic CC156 strains were equal, but at > 30°C growth and survival of MurF V179 strains was dependent on > 0.1% CO2-enriched conditions. Expression of MurF V179 in S. pneumoniae R6 and G54 rendered these, otherwise non-capnophilic strains, capnophilic. Timelapse microscopy revealed that a capnophilic CC156 strain undergoes rapid autolysis upon exposure to CO2-poor conditions at 37°C, and staining with fluorescently labelled vancomycin showed a defect in de novo cell wall synthesis. In summary, in capnophilic S. pneumoniae strains from CC156 and CC344 cell wall synthesis is placed under control of environmental CO2 levels and temperature. This mechanism might represent a novel strategy of the pneumococcus to rapidly adapt and colonize its host under changing environmental conditions.