Gram Positive Bacteria

Question 1

Streptococci in general

Answer 1

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

Question 2

S. pyogenes

Answer 2

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)

Question 3

Group B Strep

Answer 3

leading cause of neonatal septicemia, meningitis & peumonia

Question 4

S. pneumoniae

Answer 4

1 cause of bacteial pneumonia in adults (virulence via capsule)

optochin sensitive

Question 5

S. viridans

Answer 5

can cause dental caries, subacute endocarditis

Question 6

Enterococci

Answer 6

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

Question 7

Staphylococci

Answer 7

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)

Question 8

S. aureus:

Answer 8

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

Question 9

S. epidermidis

Answer 9

coagulase negative (-)

Subacute endocarditis, infection of prosthesis via biofilms

Question 10

Bacillus

Answer 10

gram-positive, boxcar-shaped rods
Spore-formers
Aerobe to facultative anaerobes

Question 11

B. cereus

Answer 11

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)

Question 12

B. anthracis

Answer 12

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

Question 13

Clostridia

Answer 13

Gram-positive rod
Spore-formers
Obligate anaerobes

Question 14

C. tetani

Answer 14

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

Question 15

C. perfringens

Answer 15

Grows in anaerobic mixed wound infections leading to rapid myonecrosis via bacterial exotoxins
followed by gas gangrene

Dx- anaerobic cultures

Question 16

C. botulinum

Answer 16

, 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

Question 17

C. difficile

Answer 17

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.

Question 18

Corynebacteria

Answer 18

gram-positive rod-like, sometimes club-shaped

Family mycobacteriaceae (MYCOLIC ACID in the cell wall)

Question 19

C. diphtheriae

Answer 19

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

Question 20

Listeria monocytogenes

Answer 20

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)

Question 21

Gardnerella vaginalis

Answer 21

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

Question 22

Gram positive anaerobic cocci

Answer 22

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