Microbiology & infectious diseases
Gram positive bacteria
Streptococcus-other
Author: Christopher S. Hale, M.D.
Last author update: 1 August 2013
Last staff update: 28 January 2023
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Streptococcus species[title]
Table of Contents
Definition / general | Terminology | Etiology | Laboratory | Treatment | Clinical images | Gross description | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Hale C. Streptococcus-other. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/microbiologystreptococci.html. Accessed December 22nd, 2024.
Definition / general
- Gram stain: positive
- Morphology: cocci in Chains
- Facultative anaerobe
- Non - pathogenic Streptococcal species are normal flora of mucosal surfaces
Terminology
- Greek "Strepto" (chain) + coccus, referring to chain - like morphology on Gram stain
- Grouped broadly according to hemolytic pattern on blood agar: alpha, beta
- Alpha (α) hemolytic: Strep. pneumoniae, viridans group Strep
- Beta (β) hemolytic: further divided serologically using Lancefield antigens into Groups A through V (some letters not used)
- Gamma (γ) hemolytic: formerly Group D Streptococci, re-classified as Enterococcus faecalis and Enterococcus faecium
- "Streptococcus viridans" (viridans = "green") not a species, but a group of non - S. pneumoniae alpha hemolytic species including S. mutans, S. mitis, S. anginosus and others (J Clin Microbiol 2010;48:3829)
- "Pyogenic Streptococci" refers not only to S. pyogenes, but all beta hemolytic streptococci and a few non - beta hemolytic streptococci (S. dysgalactiae)
- Lancefield Group A Streptococci (GAS) = S. pyogenes
- Lancefield Group B Streptococci (GBS) = S. agalactiae
- "pneumococcus" = Streptococcus pneumoniae
Etiology
- S. pyogenes (Group A Streptococci): pharyngitis, necrotizing fasciitis, cellulitis, erysipelas, scarlet fever, streptococal toxic shock syndrome; non - infectious immune sequelae includes post - infectious glomerulonephritis, acute rheumatic fever
- S. agalactiae (Group B streptococci): pneumonia, sepsis, meningitis in newborns
- S. pneumoniae: community - acquired pneumonia, meningitis, otitis media
- Viridans Group streptococci: endocarditis, bacteremia (particularly in setting of oral mucosal disruption)
Laboratory
- Culture conditions:
- Blood agar (non-contaminated sites), colistin nalidixic acid agar (contaminated sites)
- 35 - 37C
- Ambient air or 5% CO2, anaerobic conditions enhance growth (particularly Viridans group)
- Gram positive cocci in chains (S. pneumoniae classically diplococci)
- Catalase negative
- Alpha or beta hemolytic on blood agar, depending on species (gamma reclassified as Enterococcus)
- Bile solubility test (sodium deoxycholate) to distinguish alpha hemolytic species: Viridans group Strep. (bile insoluble) from S. pneumoniae (bile soluble)
- Latex agglutination card test for Lancefield serotyping of beta hemolytic strains
- S. pneumoniae: Quellung (Neufeld's quellung) reaction positive, optochin ("P" disc) sensitive
- S. pyogenes: positive PYR test (L-pyrrolidonyl-beta-naphthylamide), bacitracin sensitive, CAMP (Christie Atkins Munch-Petersen) test negative
- S. agalactiae: CAMP test positive, hippurate positive
- Biochemical identification especially useful for Viridans group
- Rapid antigen detection used clinically for Group A Strep; culture is gold standard
Treatment
- Penicillins, but resistance reported among beta hemolytic streptococci (Antimicrob Agents Chemother 2011;55:2983)
- Macrolide resistance increasing: mefA gene (drug efflux) or erm gene (methylation of macrolide binding site) (J Clin Microbiol 2004;42:5620)
- See Am Fam Physician 2013;88:338
Clinical images
Images hosted on other servers:
Various Strep group colonies
Gross description
- Gray - white glistening, alpha or beta hemolysis
- S. pneumoniae capsule gives colonies mucoid appearance, may have central depression
Molecular / cytogenetics description
- PCR screening for group B streptococci (GBS) in pregnant women (Mol Diagn Ther 2013;17:355)
- 16S rRNA useful to speciate alpha hemolytic strep (J Clin Microbiol 2012;50:4087)
Differential diagnosis
- Distinctive morphology on Gram stain when chains are seen, distinction more difficult among alpha strep species
- MALDI-TOF may discriminate often misdiagnosed alpha hemolytic streptococci (Infect Genet Evol 2011;11:1709)
- Other Gram positive cocci
Additional references
