Gram Positive Bacteria Flashcards
Streptococci in general
Gram positive cocci in chains (except S. pneumoniae is lancet-shaped diplococcus)
Catalase (-)
Lancefield groupings
S. pneumoniae, S pyogenes and S. agalactiae are encapsulated
Groups A, B and D exist
S. pyogenes
1 cause of bacterial pharyngitis
Group A streptococci
impetigo
–> rheumatic fever, rheumatic valvular disease and poststreptococcal glomerulonephritis.
Also causes necrotizing fasciitis, toxic shock syndrome (erythrogenic exotoxin, also causes scarlet fever rash)
Group B Strep
leading cause of neonatal septicemia, meningitis & peumonia
S. pneumoniae
1 cause of bacteial pneumonia in adults (virulence via capsule)
optochin sensitive
S. viridans
can cause dental caries, subacute endocarditis
Enterococci
Gram positive diplococci or short chains.
Catalase negative gamma hemolytic (i.e. non-hemolytic)
E. faecalis and E. faecium are part of normal intestinal flora
Cause urinary tract infections, bacteremia
VRE – vancomycin resistant enterococci
Rx – high-level of resistance to ampicillin
Resistance to vancomycin, aminoglycosides, and other antibiotics also occurs
Staphylococci
Gram positive cocci in clusters
Catalase (+) [H202→H20+02]
Staph aureus, epidermidis, saprophyticus
Dx: antibiotics, but lots of MRSA (beta lactamases) and some VRSA risistant to vancomycin (plasmid)
S. aureus:
coagulase positive (+)
pneumonia, meningitis, acute endocarditis, osteomyelitis, toxic shock syndrome, food poisoning,
Virulence factors:
clumpgin factor
polysaccharide capsule (resists phagocytosis)
Surface protein A
Exfoliative A&B toxins (scalded skin syndrome)
Superantigens (enterotoxins):
- Toxic shock syndrome (TST1) toxin
- Heat stable enterotoxin
S. epidermidis
coagulase negative (-)
Subacute endocarditis, infection of prosthesis via biofilms
Bacillus
gram-positive, boxcar-shaped rods
Spore-formers
Aerobe to facultative anaerobes
B. cereus
produces enterotoxins that cause food poisoning
Preformed enterotoxins lead to food poisoning with vomiting (heat stable toxin from contaminated rice) and diarrhea (heat labile toxin in meat or vegetables)
B. anthracis
Polyglutamyl (amino acid) capsule (survives phagocytosis)
Exotoxins
Cutaneous anthrax (95%);
Inhalation anthrax (woolsorters’ disease); spores inhaled, phagocytized (alveolar macrophages) and carried to regional lymph nodes, causes “cold” symptoms followed by hemorrhagic mediastinitis and necrosis in lymph nodes and lung (which leads to ARDS, hemoptysis and death)
Gastrointestinal anthrax; ingestion of contaminated meat
prevention: vaccine
Clostridia
Gram-positive rod
Spore-formers
Obligate anaerobes
C. tetani
a single exotoxin
Heroin users susceptible
(tetanospasmin/spasmogenic toxin/tetanus toxin fixes to gangliosides –> muscle spasms (lockjaw/trismus) and convulsions (tetanus)
Dx- anaerobic cultures
Prevention: tetanus toxoid vaccines (DPT, etc.) & tetanus toxoid (Td) booster
C. perfringens
Grows in anaerobic mixed wound infections leading to rapid myonecrosis via bacterial exotoxins
followed by gas gangrene
Dx- anaerobic cultures
C. botulinum
, produce one or more of 8 zinc protease botulinum exotoxin
block acetylcholine release
Type A is the most potent exotoxin known
from poorly canned foods, –> flaccid paralysis with diplopia, dysarthria, dysphonia (slurred), dysphagia, respiratory failure.
Infant botulism- bee honey
Wound botulism
difficult to culture even in strict anaerobic environment; PCR necessary
Rx- botulinum antitoxin
C. difficile
toxin A (enterotoxin) and toxin B (cytopathic agent)
pseudomembranous enterocolitis
dx- anaerobic cultures
Rx- oral vancomycin, metronidazole, bacterial recolonization
Think: ABCD: Toxins A & B for C. Diff.
Corynebacteria
gram-positive rod-like, sometimes club-shaped
Family mycobacteriaceae (MYCOLIC ACID in the cell wall)
C. diphtheriae
Toxigenic strains carry tox (diptheria toxin)
A (active) fragment is released into the host cell
–> inactivating elongation factor EF-2, effectively blocking protein synthesis
DX- a pseudomembranous material in the upper respiratory tract
Prevention: : DPT vaccine formalin inactivated toxin (i.e. toxoid) is required
Rx - Passive immunization with antitoxin
Listeria monocytogenes
Llisteria are gram-positive bacilli
Facultative intracellular parasite
Listeriolysin O allows it to survive and reproduce within macrophage phagolysosome
Capable of polymerizing host cell’s actin to produce motility and this allows spread from cell to cell without an extracellular stage
Listeriosis- food-borne disease (esp. important in pregnant women; crosses placenta –> infant death)
Listeria monocytogenes is ingested with contaminated food (hot dogs, various meats, milk, cheese and raw vegetables)
Gardnerella vaginalis
gram-variable coccobacilli (diptheroid)
cell wall is in reality GRAM POSITIVE
seen with bacterial vaginosis –> clue cells and fishy odor
dx- clue cells or culture
rx- metronidazole or clindamycin to kill anaerobic bacteria overgrowth
Gram positive anaerobic cocci
Anaerobic
Gram-positive cocci
Non-spore forming
Coccoid
Peptostreptococcus magnus
Oral infections: P. anaerobius
Skin and soft tissue infections and deep organ abscesses: P. magnus
dx: anaerobic culture and gram stain
