3C-Streptococci.pdf

Streptococcus, & Enterococcus Medical Microbiology PTM 3520/4310 D. M. Mwenya 2024  Streptococcus Streptus (Greek): meaning easily bent or twisted, like a chain. Family: Streptococcaceae (contains the Streptococcus genus) Family: Enterococcceae (contains...

Streptococcus, & Enterococcus Medical Microbiology PTM 3520/4310 D. M. Mwenya 2024  Streptococcus Streptus (Greek): meaning easily bent or twisted, like a chain. Family: Streptococcaceae (contains the Streptococcus genus) Family: Enterococcceae (contains the Enterococcus genus).  Streptococcus & Enterococccus Streptococcus & Enterococccus are classified based on 1) serological (Lancefield) typing, 2) haemolysis on BA, & 3) biochemical tests. Streptococcus: Has over 100 species. Enterococccus: Has over 54 species.  Streptococcus & Enterococccus Description Gram +ve cocci, in pairs or chains (of 3-30 cells), 0.5 - 2µm in size. Facultative anaerobes, some are capnophilic (S. pneumoniae). Require enriched media (e.g. BA), except non fastidious Enterococcus; incubation t° at 35-37°C. May be haemolytic (α-, or β-haemolysis) or non- haemolytic (γ-haemolysis) colonies. Catalase negative, fermentative, non-spore forming, non-motile.  Streptococcus & Enterococccus Description Most common cause of human streptococcal infections are in three Lancefield groups: – Group A (S. pyogenes), group B (S. agalactiae), group C (contains varied streptococcal species). Rare causes of human streptococcal infections belong to Lancefield groups: – Group E, group F, group G, group L: Contain varied streptococcal species. Group D: Enterococcus genus (formerly Streptococcus).  β-haemolytic Streptococci-Lancefield Grps Lancefield Grp Colony size Species A largea S. pyogenes A small Anginosus grpb B large S. agalactiae C large S. dysgalactiae subsp. equisimilisc C small Anginosus grp F small Anginosus grp G large S. dysgalactiae subsp equisimilisc G small Anginosus grp Nongroupable small Anginosus grp aSmall = 2 years old and adults. 13-valent conjugated pneumococcal vaccine: – Currently recommended for infants younger than 2 years. – Administered in 4 doses (at 2, 4, 6, and 12 to 15 months).  Prevention Vaccines effectiveness: – Determined by prevalent serotypes responsible for invasive disease in the population. – Poor in pts with asplenia, sickle cell disease, hematologic malignancy, HIV, renal transplant; and the elderly.  β-Haemolytic streptococci Description Gram +ve cocci, in chains (3-30 cells), 1 – 2µm diameter. Facultative anaerobes, produce white, convex, ≤1 – 2 mm in diameter (see table below), β-haemolytic colonies on BA. Catalase negative, fermentative, bacitracin (0.04U) susceptibility test –ve, non-spore forming, non- motile. Pyrrolidonyl arylamidase (PYR) test –ve, Lancefield typing (variable groups),  Other β-Haemolytic streptococci Description Commonly associated with human disease: Grp C, F, and G. Important species: – Streptococcus dysgalactiae (grp C or G). – Anginosus group (grp A, C, F, G or lack group- specific Ag). – Species in this grp: see table below “β-haemolytic Streptococci-Lancefield Grps”.  β-haemolytic Streptococci-Lancefield Grps Lancefield Grp Colony size Species A largea S. pyogenes A small Anginosus grpb B large S. agalactiae C large S. dysgalactiae subsp. equisimilisc C small Anginosus grp F small Anginosus grp G large S. dysgalactiae subsp equisimilisc G small Anginosus grp Nongroupable small Anginosus grp aSmall = 12 hrs before delivery – increase risk of infection. ‘Early onset’ begin early in first 1 week days of life: presents Clinical with respiratory distress, fever, lethargy, hypotension; ‘Late characteristic onset’ – occur btn 7 days to 3 mth after birth. Group C & G Streptococci Can cause pharyngitis. S. Common cause of bacterial pneumonia especially in the under pneumoniae 5 yrs, the >50 yrs & people with impaired defense mechanism. Clinical Sudden onset; chill & high fever; Cough– pink to rusty sputum characteristic (blood); pleuritic chest pain. Other Meningitis, sinusitis, otitis media, endocarditis, arthritis, diseases peritonitis; cellulitis, puerperal sepsis. Viridans Transient bacteremia, subacute bacterial endocarditis, forms streptococci bacteria plagues on damaged heart valves. E. faecalis/ Cause 25% of UTI; endocarditis (often after instrumentation E. faecium of urinary tract); wound infection; abdominal abscess.