Gram-positive Bacteria & Diseases Flashcards
List major infections caused by Staphylococcus
S. aureus
- 1/3 healthy people carry
- skin infections, pneumonia, wound infections
S. epidermidis
- carried by everyone
- opportunistic, infecting prosthetic/foreign objects
S. saprophyticus
- normal gut and genital flora
- UTI in sexually active young females
List major infections caused by Streptococcus
Streptococcus pyogenes (Group A Strep)
- pharyngitis, scarlet fever, necrotizing fasciitis
Streptococcus agalactiae (Group B Strep)
- colonizes gut in 30% of people
- 10-30% of vaginas
- causes neonatal meningitis, septicemia (blood
infection)
Streptococcus pneumoniae
- otitis media, sinusitis, epiglottitis, pneumonia,
meningitis
Overgrowth of normal strep (viridians group)
- ex) streptococcus mutans = dental caries
Apply laboratory techniques to identify Staphylococcus species
-Gram +
-Agar plates (colony formation and hemolysis)
-medium sized colonies
-S. aureus –> dull gold, B-hemolysis
-S. epidermidis and S. saprophyticus –> white, y-
hemolysis
-salt tolernace (mannitol salt agar)
-all tolerate salt –> turn yellow on plate
-S. aureus ferments mannitol
-Produce catalase?
-all produce catalase –> drop of H2O2 creates a lot
of bubbles
-Produce coagulase? (in a test tube)
-S. aureus –> clots blood plasma; clotting at bottom of
tube
-Novobiocin sensitivity test
-only S. saprophyticus creates halo on plate
Apply laboratory techniques to identify Streptococcus species
-gram + diplococci or streptococci
-pin point sized colonies
-all streptococcal species
- catalase negative (does not bubble in presence of
H2O2)
-S. pyogenes
- sensitive to bacitracin
- B-hemolysis
-S. pneumoniae
- sensitive to optochin and bile
- a-hemolysis
-S. agalactiae
- B-hemolysis
What is B-hemolysis?
complete RBC lysis
What is Y-hemolysis?
non-hemolytic
What is a-hemolysis?
incomplete hemolysis; green halo from heme
Describe cellular and colony morphology of B. anthracis
(causes anthrax)
- described as medusa head
- gram-negative streptobacilli
- forms endospores
- confirmed with culture on blood agar
- antitoxin for systemic infection
Describe cellular and colony morphology of M. tuberculosis
- lipid rich cell wall
- hydrophobic
- hard to stain
- slow to grow
- once stained, can’t decolorize
- culture on Lowenstein-Jensen media
Describe the reservoir, transmission and major clinical features of anthrax
-cows, sheep, horse, and bioterrorist labs
-transmitted to human skin (cutaneous anthrax) or lungs (pulmonary anthrax)
-Cutaneous:
- eschar called malignant pustule (dry, dark scab or
skin falling away)
- black color starts in center
- hemoragic vesicles
- self-limiting
- some septicemia, generalized edema, death
-pulmonary:
- fever, cough, pulmonary edema, mediatinal
edema, die quickly once you become bacteremic
Explain the staining properties of M. tuberculosis in terms of cell wall structure
- hard to stain and decolorize
- Use Ziehl-Neelson or Auramine-rhodamine stain
- lipid rich cell wall makes it hardy, impenetrable, hydrophobic
Explain the major pathological mechanisms of M. tuberculosis as well as the immune defense
insidious onset (slow start)
-90% of primary tuberculosis is subclinical
chronic weight loss, low fever, night sweats
cough, hemoptysis, chest pain
Summarize major diagnostic approaches of M. tuberculosis infection
PPD test for cell-mediated immune response
X-ray
acid-fast stain
Lowenstein-Jensen culture
Describe cell morphology of Clostridium and their oxygen requirement
- Gram positive bacilli
- with terminal endospore
- anaerobic
List major Clostridium species and the diseases they cause
C. difficile: diarrhea secondary to antibiotic use
C. botulinum: botulism
C. tetani: tetanus
C. perfringens: diarrhea and gas gangrene
