Sharq Elneil College School of Medical Laboratory Sciences Department of Microbiology Medical Bacteriology courseStreptococcus pneumoniae (Pneumococci) Dr.Mahadi Hassan Mahmoud email@example.com Bsc, Msc, MIBMS Microbiology
The natural habitat pneumococci is provided by the mucosa of the upper respiratory tract.About 40–70 % of healthy adults are carriers. Pneumococcal infections .Usually arise from this normal flora (endogenous infections).
Morphology Gram-positive, oval to lancet-shaped cocci (0.5 and 1.25micrometers in diameter)usually occur in pairs or shortchains surrounded by a thick capsule.
Culture &chaacteristics:on blood agar, Alpha -hemolytic colonies Mucoid (smooth, shiny) appearanceMutants without capsules producecolonies with a rough surface (“R” form-maintain integrity of nucleic acid target
streptococcus pneumoniae is a veryfragile bacterium contains within itself the enzymaticability to disrupt and to disintegrate thecells. autolysin.The physiological role of this autolysin isto cause the culture to undergo acharacteristic autolysis that kills the entireculture when grown to stationary phase.
Virtually all clinical isolates ofpneumococci harbor this autolysin andundergo lysis usually beginning between18-24 hours after initiation of growth underoptimal conditions. Autolysis is consistent with changes incolony morphology.Colonies initially appear with a plateau-type morphology, then start to collapse inthe centers when autolysis begins.
Streptococcus pneumoniae is afermentative aerotolerant anaerobeUnlike other streptococci, they donot display an M protein. they hydrolyze inulin, and theircell wall composition is characteristicboth in terms of their peptidoglycanand their teichoic acid.
Antigenic Structure Classified in 90 different serovarsbased on the fine chemical structure ofthe capsule polysaccharides acting asanti- gens. This capsule antigen can beidentified using specific antisera in areaction known as capsular swellingtest ( Quelling reaction
Antiphagocytic.Prevents the desposition ofcomplement and subsequentphagocytosis (opsonisation) in theabsence of type-specificantibodies.These serotypes are number andsubdivided on the basis ofmorphological similarity.
It was believed that most diseaseis caused by the 23 serotype, this isnot the case locally. It causes:otitis media, sinusitis, mastoiditisand pneumonia ,joint infections,endocarditis and meningitis.
Pathology: Capsule protects the pathogens fromphagocytosis and is the most importantdeterminant of pneumococcal viru-lence.Unencapsulated variants are notcapable of causing disease. Otherpotential virulence factors include : pneumolysin IgA protease..
Predisposing factors include : primary cardiopulmonary diseases,previous infections(e.g., influenza) extirpation of the spleen orcomplement system defects.
important pneumococcal infections: Lobar pneumonia consolidated mass, incontrast to the spongy texture of normal lungtissue.Bronchopneumonia. Acute exacerbation of chronicbronchitis Otitis mediaSinusitis
Meningitiscorneal ulcer. Severe pneumococcal infectionsfrequently involve sepsis
Laboratory diagnosisspecimens:Collection of SpacimenDirect ExamCultureIdentificaionSerologyMolecular characterization
Optochin sensitivityPneumococci are sensitive to optochin(ethylhydrocupreine hydrochloride). Method: Placing a disc (5 g) on a primarysputum culture and culturing the plate aerobically(not in CO2) can help to provide a rapid Result : The zone of inhibition should be atleast10 mm. Most viridans streptococci and otheralphahaemolytic streptococci are resistant tooptochin. If the zone of inhibition is less than 10mm (6 mm disc) the colonies should be tested forbile solubility
*Bile solubility test Method : a tube technique, the results of which are easy to read.Some workers, however, prefer to testsuspect alpha-haemolytic colonies directlyon a culture plate by touching a colony witha loopful of 2% sodium deoxycholateIncubation at 35–37 ºC for 30 minutes.Result: examining for lysis (disappearanceof the colony, indicating S. pneumoniae).
Agglutination Test Latex agglutination tests are widely used methods for identification and typing The speed of the observed agglutination reaction (positive reactionwithin 10 s) is a great advantage. The same is true for the ease of interpreting a reaction as positive compared to that in the normal capsular reaction test.
Treatments pencillinshigh-frequency occurrence of strainsresistant to penicillin CephalosporinsCephalexin ceftriaxoneMacrolides
Antibiotic Resistant extreme genetic flexibilityenabling S. pneumoniae toacquire antibiotic resistanceswitch the capsular serotype is aresult of the unique pneumococcalfeature: natural competence forgenetic transformation.
Natural competence is a transientphysiological state enabling thebacteria to acquire exogenous DNA. Competence is regulated byquorum sensing system and thusdepends on cell density and manyother factors
pathogen reservoir. Epidemiology and prophylaxis. Pneumococcal infections are endemic and occur in all seasons, more frequently in the elderly. Humans are the natural pathogen reservoir The vaccine product Pneumovax is available for immunization purposes.
jugate vaccine that is effective in children under two years purified capsule polysaccharides (PPV ) seven-valent conjugate vaccine a seven-valent con- effective in children of less than 2 year (PCV)
Streptococcus Viridansform part of the normal microbialflora of the upper respiratory tract(particularly oropharynx) andgastrointestinal tract.They may therefore be found withS. pneumoniae in sputum (ascommensals)
Morphology Gram-positive cocciusually occur in pairs or long chains
Culture:on blood agar, Alpha -hemolytic coloniesthe viridans group of streptococci can alsobe nonhaemolytic and occasionally beta-haemolytic.
A few species are pathogenic.S. mutans,S. sanguis,S. mitior)causing endocarditis, bacteraemia, anddental caries.
S. anginosus group(formerly S. milleri group) associated with deepabscesses in various sites in thebody (abdomen, chest, brain)often in association with otherbacteria.
Compare between Pnuemoccciand Viridans strepococci Optrichoin Bile Inulin solubility Ferment pneumoco Sensetive Posotive Ferment cci Viridans Resistant Negative Non ferment