In accordance with the World Health Organization, pneumonia still remains one of the main killers of children under the age of five, taking more than 1.1 million lives of boys and girls annually (WHO Pneumonia factsheet, 2013). Pneumonia is more prevalent in South Asia and sub-Saharan Africa. It is well known that pneumonia is a disease of respiratory system that affects the alveoli, which are the constituent part of the lungs. Normally alveoli fill with air during the breath of a healthy person, while the one with pneumonia has alveoli, which are filled with fluid and pus; hence the breathing process is painful and limits the oxygen consumption by organism. Pneumonia can be caused by several infectious agents, such as bacteria, fungi and viruses. The most common are Streptococcus pneumoniae, Haemophilus influenzae type b (Hib), Pneumocystis jiroveci. However, significant proportion of all pneumonia is caused by Streptococcus pneumoniae. In fact, the diseases caused by S. pneumoniae also include sinusitis, meningitis, otitis and some other problems, including septic arthritis, endocarditis and spontaneous bacterial peritonitis (WHO Pneumonia factsheet, 2013). The main aim of this paper is to familiarize the reader with Streptococcus pneumoniae and one particular disease that it causes - pneumonia.
Taxonomy, morphology, physiology, virulence factors of Streptococcus pneumoniae
Streptococcus pneumoniae is a bacterium, which has the following lineage: Firmicutes; Bacilli; Lactobacillales; Streptococcaceae; Streptococcus; Streptococcus pneumoniae (NCBI database taxonomy, 2001).
Streptococcus pneumoniae is a facultative anaerobe, which after performing a Gram-staining appears as blue-black cocci with the lancet shape, mostly in pairs and sometimes alone or in short chains. Its diameter varies between 0.5 to 1.25 mm and it also has a capsule. S. pneumoniae is capnophilic, preferring atmospheres of 5–10% carbon dioxide. Streptococcus pneumoniae can be distinguished from other streptococci, owing to the fact that it is catalase negative; can be inhibited by ethyl hydrocupreine; it is soluble in bile (due to activation of autolytic property, which consequently lead to cell lysis); it is α-haemolytic (it can be easily identified on agar plates, due to greenish discoloration of blood agar due to the production of pneumolysin) (Balakrishnan, 2006).
S. pneumoniae has some distinct virulence factors, which are proteins/enzymes that are expressed on the surface of gram-positive organisms. They are also the main contributors to the pathogenic character of the bacterium and its survival against the host defense mechanisms. According to Poll et al. (2009) virulence factors should be used in array, in order to be successful in coordinating ways for the tissue invasion. Some of the most important virulence properties are the adherence factors, genes responsible for invasion, some heavy-metal transporters, evasion the immune system of the host, production of...