STREPTOCOCCUS PNEUMONIA

BY:DR. Mohamed Taha Yassin Hassan

CLASSIFICATION OFStreptococcus

PneumoniaDomain: Bacteria Phylum: Firmicutes Class: Bacilli Order: Lactobacillales Family: Streptococcaceae Genus: Streptococcus Species: S. pneumoniae

*Streptococcus pneumoniae cells are Gram-positive*lancet-shaped cocci *Usually, they are seen as pairs of cocci (diplococci), but they may also occur singly and in short chains*They are nonspore forming bacteria*they are nonmotile*They are capsulated & the capsule encloses each pair.

General characteristics ofStreptococcus Pneumonia

STREPTOCOCCUS PNEUMONIA

*They grow only in enriched media.

*They are aerobes & facultative anaerobes.

*The optimum temperature being 37ºC & pH 7.8.

*Growth is improved by 5-10% CO2

Identification ofStreptococcus Pneumonia

Microscopy and Staining :

Perform Gram staining of the sample (sputum/CSF)

Gram staining shows Gram positive lanceolate shaped diplococci

Electron microscope image of Streptococcus Pneumonia

Colony morphology:Colonies on blood agar plate are small (0.5 mm), round, transluscent or mucoid with alpha-hemolysis (A green discolouration of the agar around the colonies) .

Alpha-hemolytic property differentiates S. pneumoniae  from many species

alpha-hemolytic colonies are further identified  by the following confirmatory tests

Biochemical identification*Optochin test (6 mm disc with 5µg).

*Inoculate blood agar plate with suspected alpha-hemolytic isolates.*Apply commercially available optochin discs on the

streaked blood agar plate*Incubate plates at 37°C with 5-10% CO2 for 18-24 hours.

*   Observe the zone of growth inhibition around the disc and interpret as:*A zone size > 14mm indicates susceptibility which is

diagnostic of Streptococcus pneumoniae.*alpha-haemolytic colonies with zone of inhibition between 9

and 13 mm should be tested for bile solubility.

Bile solubility test:*alpha-haemolytic colonies showing zone of inhibition around

optochin disc between  9 to 13 mm should be tested for bile solubility.*Prepare 1.0 ml of saline suspension of the organism from

blood agar plate. *Bile solubility test: Streptococcus pneumonie colonies are

lysed by bile*Inoculate 0.5 ml of the suspension into two tubes.*Add an equal amount (0.5 ml) of 2% sodium deoxycholate in

one tube marked as test and 0.5ml of saline into the second tube marked as control.*Shake gently and incubate the tubes at 37°C for 2 hours

Identification of Streptococcus Pneumonia

VIRULENCE FACTORS OF STREPTOCOCCUS

PNEUMONIA1-Capsule: is the major virulence factor of Streptococcus PneumoniaResistance to phagocytosis

2-Cell wall or(CWPS):Inflammatory Factors

Activation of the alternative complement pathway, resulting in anaphylatoxin production During complement activation, the anaphylatoxins C3a and C5a, which enhance vascular permeability, induce mast cell degranulation, and recruit and activate polymorphonuclear leukocytes (PMN) at the inflammation site

3-Pneumococcal Proteins:Include:A-Pneumolysin: stimulates the production of inflammatory cytokines like tumor necrosis factor alpha and interleukin-1b by human monocytes inhibits the beating of cilia on human respiratory epithelial cells disrupts the monolayers of cultured epithelial cells from the upper respiratory tract and from the alveoli decreases the bactericidal activity and migration of neutrophils inhibits lymphocyte proliferation and Ab synthesis

B- Pneumococcal surface protein A: .Pneumococcal surface protein A (PspA) is a surface protein with structural and antigenic variability between different pneumococcal strains.required for full virulence of pneumococciinhibition of complement activation PspA enhances pneumococcal virulenceC- Autolysin:Autolysin-negative mutants have been shown to be less virulent than wild-type pneumococciRelease of pneumolysin and cell wall productsautolysin triggered by human lysozyme, a defense factor released upon infection and inflammation.

Autolysin thus seems to take advantage of the (protective) function of lysozyme.

D- Complement factor H-binding component: Inhibition of complement activation

Inhibition of phagocytosisE-Peptide permeases:Enhancement of adhesionF-IgA1 protease:Counteracts mucosal defense mechanisms

4-Hydrogen peroxide:Lung injury

STREPTOCOCCUS PNEUMONIA

PATHOGENESISthe initiation of pneumonia requires escape from mucous defenses and bacterial migration into the alveolus.

Firm adherence of bacteria to the alveolar epithelium and subsequent replication and initiation of host damage

The pore-forming toxin pneumolysin and hydrogen peroxide released in copious amounts by the bacteria disrupt the alveolar epithelium and edema fluid accumulates in the alveolar space

Lipoteichoic acids, lipoproteins, and an array of proteins associated with the bacterial surface further amplify interactions with the host

*Streptococcus pneumoniae bacteria (“pneumococcus”).  These bacteria can cause diseases include:* pneumonia (infection of the lungs)* ear infections* sinus infections* meningitis (infection of the covering around the brain and spinal cord)* bacteremia (blood stream infection). Pneumococcus bacteria are spread through coughing, sneezing, and close contact with an infected person.*Symptoms of pneumococcal disease depend on the part of the body that is infected. They can include fever, cough, shortness of breath, chest pain, stiff neck, confusion and disorientation, sensitivity to light, joint pain, chills, ear pain, sleeplessness, and irritability.  In severe cases, pneumococcal disease can cause hearing loss, brain damage, and death.

TREATMENT:

*For penicillin sensitive strains Penicillin is drug of choice for serious cases & Amoxycillin for milder ones.

*For penicillin resistant strains a third generation cephalosporin is indicated.

*Vancomycin is to be reserved for life threatening illness with highly resistant strains.

REFRENCES:Albiger B, Dahlberg S, Sandgren A, Wartha F, Beiter K, Katsuragi H, Akira S, Normark S, Henriques-Normark B. 2007. Toll-like receptor 9 acts at an early stage in host defence against pneumococcal infection. Cell Microbiol 9: 633–644

Bagnoli F, Moschioni M, Donati C, Dimitrovska V, Ferlenghi I, Facciotti C, Muzzi A, Giusti F, Emolo C, Sinisi A, et al. 2008. A second pilus type in Streptococcus pneumoniae is prevalent in emerging serotypes and mediates adhesion to host cells. J Bacteriol 190: 5480–5492

Bergmann S, Rohde M, Chhatwal GS, Hammerschmidt S. 2001. α-Enolase of Streptococcus pneumoniae is a plasmin(ogen)-binding protein displayed on the bacterial cell surface. Mol Microbiol 40: 1273–1287