Streptococcus Cheatsheet

Cheatsheet Content

### General Characteristics - **Gram Stain:** Gram-positive cocci (spherical bacteria) - **Arrangement:** Typically grow in chains or pairs (hence "strepto" from Greek for 'twisted chain') - **Metabolism:** Facultative anaerobes - **Catalase Test:** Negative (distinguishes from *Staphylococcus*) - **Hemolysis:** Classified by their hemolytic patterns on blood agar: - **Alpha-hemolytic ($\alpha$):** Partial hemolysis, produces a greenish discoloration (e.g., *S. pneumoniae*, *S. viridans* group) - **Beta-hemolytic ($\beta$):** Complete hemolysis, clear zone around colonies (e.g., *S. pyogenes*, *S. agalactiae*) - **Gamma-hemolytic ($\gamma$):** Non-hemolytic, no change (e.g., *Enterococcus* spp. - formerly Group D *Streptococcus*, some *S. bovis*) - **Lancefield Grouping:** Serological classification based on carbohydrate antigens in the cell wall (Groups A-H, K-V). Important for $\beta$-hemolytic strep. ### Important Species and Groups #### Group A Streptococcus (GAS) - *Streptococcus pyogenes* - **Pathogenicity:** Highly virulent - **Virulence Factors:** M protein (antiphagocytic), Streptolysin O/S (hemolysins), Hyaluronidase, Streptokinase, DNases, Exotoxins (superantigens) - **Diseases:** - **Suppurative (Pus-forming):** Pharyngitis ("strep throat"), Scarlet Fever (due to erythrogenic toxins), Impetigo, Cellulitis, Erysipelas, Necrotizing Fasciitis, Streptococcal Toxic Shock Syndrome - **Non-suppurative (Post-streptococcal):** Acute Rheumatic Fever (ARF), Acute Post-streptococcal Glomerulonephritis (APSGN) - **Diagnosis:** Rapid Strep Test (antigen detection), Throat culture, ASO titer (for ARF), Anti-DNase B (for APSGN) - **Treatment:** Penicillin is the drug of choice. #### Group B Streptococcus (GBS) - *Streptococcus agalactiae* - **Habitat:** Normal flora of gastrointestinal and genitourinary tracts in some individuals. - **Diseases:** - **Neonatal Infections:** Most common cause of sepsis and meningitis in newborns (early-onset within 7 days; late-onset 7 days to 3 months). Acquired during vaginal birth. - **Adult Infections:** UTIs, skin/soft tissue infections, pneumonia, sepsis in immunocompromised or elderly. - **Diagnosis:** Culture (vaginal/rectal swabs in pregnant women), PCR. - **Prevention:** Screening pregnant women at 35-37 weeks gestation; intrapartum antibiotic prophylaxis (IAP) for positive mothers. - **Treatment:** Penicillin or Ampicillin. #### *Streptococcus pneumoniae* (Pneumococcus) - **Arrangement:** Often seen as lancet-shaped diplococci. - **Virulence Factor:** Polysaccharide capsule (major virulence factor, prevents phagocytosis). - **Diseases:** - **CAP:** Community-Acquired Pneumonia (most common cause) - **OM:** Otitis Media (middle ear infection) - **Meningitis:** Bacterial meningitis in adults and children - **Sinusitis:** Infection of the sinuses - **Bacteremia/Sepsis** - **Diagnosis:** Gram stain and culture of sterile sites (blood, CSF), urine antigen test. - **Prevention:** Vaccines (Pneumococcal Conjugate Vaccine PCV13/PCV15/PCV20 for children, Pneumococcal Polysaccharide Vaccine PPSV23 for adults). - **Treatment:** Penicillin (resistance is a concern), Ceftriaxone, Macrolides, Fluoroquinolones. #### Viridans Group Streptococci - **Examples:** *S. mutans*, *S. sanguinis*, *S. mitis*, *S. oralis*. - **Habitat:** Normal flora of the oral cavity, GI tract, and genitourinary tract. - **Hemolysis:** Usually $\alpha$-hemolytic or $\gamma$-hemolytic. - **Diseases:** - **Endocarditis:** Subacute bacterial endocarditis (most common cause, especially in individuals with damaged heart valves or prosthetic valves). - **Dental Caries:** *S. mutans* is a primary cause. - **Sepsis:** In immunocompromised patients. - **Treatment:** Penicillin, Ceftriaxone, Vancomycin (for resistant strains or penicillin allergy). #### Group D Streptococcus (Enterococcus & Non-Enterococcus) - **Note:** *Enterococcus* species (e.g., *E. faecalis*, *E. faecium*) were formerly classified as Group D *Streptococcus* but are now a separate genus. They are still often discussed in relation to strep due to historical classification and shared habitat. - **Non-Enterococcal Group D:** *S. gallolyticus* (formerly *S. bovis*). - **Habitat:** Normal flora of the GI tract. - **Diseases:** - ***S. gallolyticus*:** Bacteremia, endocarditis (often associated with colon cancer). - ***Enterococcus*:** UTIs, endocarditis, wound infections, intra-abdominal infections, often nosocomial. Known for antibiotic resistance (VRE - Vancomycin-resistant Enterococci). - **Treatment:** - ***S. gallolyticus*:** Penicillin or Ampicillin. - ***Enterococcus*:** Ampicillin, Vancomycin, Linezolid, Daptomycin depending on resistance patterns. ### Common Treatments - **Penicillin:** First-line for most *Streptococcus* infections (e.g., GAS, GBS, Viridans group). - **Ampicillin:** Often used for GBS and Enterococci. - **Cephalosporins (e.g., Ceftriaxone):** Alternatives for penicillin allergy or for *S. pneumoniae* (especially in meningitis). - **Macrolides (e.g., Azithromycin, Clarithromycin):** For penicillin-allergic patients, but resistance is increasing. - **Vancomycin:** Used for severe infections, resistant strains (e.g., Penicillin-resistant *S. pneumoniae*, *Enterococcus*), or in cases of severe penicillin allergy. - **Linezolid/Daptomycin:** For multi-drug resistant strains, particularly VRE.