Gram Positive Bacteria


Gram Positive Bacteria section provides High Yield Information needed for USMLE, COMLEX, Medical School, Residency, and as a practicing Physician.



Cocci


Enterococcus

Enterococcus histological pneumonia 01
Photo Credit:Content Providers(s): CDC/Dr. Mike Miller, Public domain, via Wikimedia Commons
  • Features:
    • Gram-positive cocci
    • Normal flora of intestines
    • 2 Species: E faecalis – most common, E faecium- less common more serious infections
    • Grows in 6.5% NaCl
    • Bile resistant
  • Causes:
    • – UTI
    • – Endocarditis
    • – Biliary tree infection
  • Types:
    • E faecium
    • Most common species
    • Nosocomial infection that is resistant to almost every antibiotic
    • Causes: VRE vancomycin-resistant enterococcus
  • Treatment:
    • Linezolid: IV antibiotic
    • Tigecycline

Staph Aureus


Staph Epidermidis

  • Features:
    • Gram positive cocci in cluster
    • Normal flora in skin
    • Catalase positive
    • Coagulase negative
    • Urease positive
    • Novobiocin sensitive
    • Associated with prosthetic valve, prosthetic joint and catheter infections produces biofilm that adhere to prosthetic surfaces
    • **Most common cause of endocarditis affecting implanted/prosthetic valves
  • Treatment:
    • Vancomycin

Staph Saprophyticus

  • Features:
    • Gram positive cocci in cluster
    • Normal flora
    • Catalase positive
    • Coagulase negative
    • Novobiocin resistant
    • Commonly infects sexually active women
    • **Most common cause of UTI in sexually active women**
  • Treatment:
    • Vancomycin

Strep Pneumonia

  • Features:
    • Gram-positive diplococci lancet-shaped
    • Alpha hemolytic – partial hemolysis
    • Encapsulated: polysaccharide = major virulence factor
    • Protease cleaves IgA- allows colonization and invasion of the mucosa
    • Optochin sensitive
    • Bile soluble
  • Causes:
    • MOPS: meningitis, otitis media, pneumonia, sinusitis
    • Pneumonia- with rusty sputum
    • Higher risk patients
    • Post-splenectomy due to encapsulated bacteria
  • Treatment:
    • Erythromycin or Ceftriaxone
  • Vaccination:
    • Adult: 23 valent polysaccharide- IgM
    • Children: 7 valent polysaccharide conjugated- IgG

Strep Viridians

  • Features:
    • Gram positive diplococci
    • Alpha hemolytic
    • Optochin resistant
    • Bile resistant
  • Types:
    • Strep Mutans: causes: Mostly dental caries
    • Strep Sanguinus: infects blood : endocarditis in previously damaged heart valves. Adheres to fibrin platelet aggregates in damaged heart valves. synthesizes dextrans from glucose

Strep Pyogenes (Group A Strep)

Streptococcus pyogenes
Photo Credit:Content Providers(s):, Public domain, via Wikimedia Commons

Strep Agalactiae (Group B Strep)

  • Features:
    • Gram positive cocci in chains
    • Encapsulated with polysaccharide capsule
    • Beta hemolytic
    • Bacitracin resistant
    • Hydrolyzes Sodium Hippurate
    • Positive CAMP test – enhances hemolysis by staph aureus
  • Causes:
    • Very serious infections in newborns
      • Sepsis in newborn
      • Meningitis in newborn
      • Pneumonia in newborn
  • Treatment:
    • Treat mother with group B strep infection by 35 week AOG–> Intrapartum penicillin

Rods


Bacillus anthracis


Bacillus cereus


Clostridium botulinum


Clostridium difficile


Clostridium perfringens


Clostridium tetani


Corynebacterium diphtheriae

Corynebacterium diphtheriae Gram stain
Photo Credit:Content Providers(s):, Public domain, via Wikimedia Commons

Listeria monocytogenes

Listeria monocytogenes PHIL 2287 lores
Elizabeth White, Public domain, via Wikimedia Commons
  • Features:
    • Gram positive rod
    • Beta hemolytic
    • Motile
    • Facultative intracellular
    • Catalase positive
    • Survives in near freezing temperatures
  • Commonly seen in:
    • Unpasteurized milk
    • Packaged meat
    • Soft cheeses
    • Pregnant women – most susceptible to infection
      • Early pregnancy- early termination
      • Late pregnancy- disease in newborn
  • Causes:
    • Newborn meningitis
    • >60 years – meningitis
  • Treatment:
    • Adult meningitis: Vancomycin and Ceftriaxone
    • Elderly meningitis: Vancomycin, Ceftriaxone, and Ampicillin
    • Listeria: Ampicillin

Filamentous/Branching Rod


Actinomyces

  • Feature:
    • Gram positive filamentous rod/Branching rod
    • Obligate anaerobe
    • Normal flora of oral cavity
  • Classic presentation:
    • Dental procedure: Cervicofacial actinomycosis infection:
      • Infection associated with jaw trauma- infection spreads to head and neck- invades surrounding tissue
    • Actinomyces infection:
      • Slow course- non-tender lump on jaw then forms abscess. sinus tract appears and drains infection site through the skin
      • Yellow thick pus -yellow sulfur granules
  • Treatment:
    • Penicillin
    • If complicated: surgical drainage

Nocardia


Michaelphillipr, CC BY-SA 4.0, via Wikimedia Commons
  • Feature:
    • Nocardia asteroides
    • Gram positive filamentous/branching rod
    • Obligate aerobe
    • Found in soil primarily
    • Catalase positive
    • Urease positive
  • Seen commonly in immunocompromised patients:
    • Impaired cell mediated immunity
    • HIV
    • Transplant patients
    • Patients taking glucocorticoids
    • Men > women
  • Infection in 3 sites: Pulmonary, CNS, Cutaneous
    • Lung abscess. associated with cavitary lesions in lung – able to disseminate
    • Brain abscesses- high affinity to neural tissue
    • Open wound exposed to dirt–> pyogenic response
  • Treatment:
    • Sulfonamide

Gram Positive Bacterial Quiz 1

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