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Clinical Micro > Gram Positive Bacteria > Flashcards

Gram Positive Bacteria Flashcards

1
Q

What are the 3 groups of streptococci based on lysis of red blood cells?

A

1) beta-hemolytoc- completely lyse red blood cells
2) alpha-hemolytic- partially lyse red blood cells
3) gamma-hemolytic- unable to hemolyze RBCs

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2
Q

In addition to RBC lysis, what other characteristic is commonly used to classify strep?

A

Lancefield antigens (on c carbohydrate on cell wall). Lacefield group A, B, and D contain pathogens

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3
Q

Basic description strep pyogenes

A

Group A (lancefield group A) beta hemolytic

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4
Q

What diseases does strep pyogenes cause by local invasion/ exotoxon release?

A

Streptococcal pharyngitis
Strep skin infections
Scarlet fever
Strep toxic shock syndrome

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5
Q

What antibiotic is used for group a beta hemolytic strep or strep pyogenes?

A

Penicillin G + clindamycin (clindamycin shuts down protein synthesis if pyrogenic toxin)

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6
Q

What is the species name for group B strep?

A

Streptococcus agalactiae

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7
Q

Who does group B strep primarily impact?

A

Babies

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8
Q

3 most common pathogens associated with meningitis in infants

A

E coli, listeria monocytogenes, and group B strep

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9
Q

Organisms that cause meningitis after 3 months of age

A

Neisseria meningitis, haemophilus influenzae

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10
Q

Symptoms group B strep pregnant women

A

Bacteremia, sepsis, stillbirth, spontaneous abortion

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11
Q

Strep commonly part of GI tract, esp gingival crevices and nasopharynx

A

Viridans group strep

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12
Q

3 infections viridans streptococci cause

A

1) dental infections
2) endocarditis
3) abcessses

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13
Q

Describe strep bovis

A

Group D strep, lives in GI, often affiliated with colon cancer

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14
Q

Describe enterococcus (faecalis and faecium)

A

Normal flora in intestines, common HAI- UTI, wound infection, native and prosthestic valve endocarditis, bacteremia via intravenous catheters, sepsis. Drug resistant (VRE)

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15
Q

What illnesses does strep pneumo cause?

A

Bacterial pneumonia
Meningitis in adults
Otitis media in children

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16
Q

What does strep pneumo look like?

A

No lancefield antigens, lancet shaped grams positive diplococci

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17
Q

Strep pneumo virulence factor

A

Capsule with 83 capsule serotypes

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18
Q

Which gram positive organism is catalase positive?

A

Staph

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19
Q

What are the 3 pathogenic staph species?

A

Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus

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20
Q

How do staph hemolyze RBCs on sheep agar?

A

Beta hemolytic- lyse red blood cells

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21
Q

Which staph is coagulase positive (causes blood to clot)?

A

Staph aureus

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22
Q

What proteins does staph aureus have that disable our immune defenses?

A
  1. Protein A (protects from opsonization)
  2. Coagulase
  3. Hemolysins
  4. Leukocidins(mrsa- panton valentine leukocidin)
  5. Penicillinase (beta lactamase)
  6. Novel penicillin binding protein (transpeptidase)
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23
Q

Toxins associated with staph aureus

A

All exotoxins
1. enterotoxins (food poisoning)
2. Toxic shock syndrome toxin- super antigen
3. Exfoliatin

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24
Q

Staph diseases caused by exotoxon release

A
  1. Gastroenteritis
  2. Toxic shock syndrome
  3. Scalded skin syndrome
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25
Q

Staph aureus diseases from direct organ invasion

A
  1. Pneumonia
  2. Meningitis
  3. Osteomyelitis
  4. Acute bacterial endocarditis
  5. Septic arthritis
  6. Skin infections
  7. Bacteremia/ sepsis
  8. UTI
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26
Q

Symptoms of toxic shock syndrome

A
  • high fever
  • diffuse erythematous rash
  • desquamation of palms and soles
  • vomiting and diarrhea
  • septic shock
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27
Q

Do antibiotics cure toxic shock syndrome?

A

No because it’s from toxin

28
Q

Dif between endocarditis from staph aureus and strep

A

Staph very fast and aggressive, strep slow onset

29
Q

Sites where people typically colonized with staph aureus

A

Nasopharynx and skin folds

30
Q

What type of antibiotics are community mrsa typically susceptible to?

A

Clindamycin and trimethoprim-sulfamethoxaxole

31
Q

First line defense antibiotic for HAI staph aureus? If mrsa?

A

Methecilin, nafacillin
Vancomycin

32
Q

describe staph epidermidis

A

Part of normal skin flora, coagulase negative

33
Q

What patients are at highest risk for staph epidermidis ?

A

Foley catheters and IV lines
Prosthetic devices

34
Q

How many blood cultures are needed for staph epidermidis? Why?

A

2, regular contaminant from skin

35
Q

How staph epidermidis causes bacteremia / infections from devices such as catheters

A

Forms biofilms, bacteria leeches out

36
Q

Second leading cause of UTI in sexually active women

A

Staph saprophyticus

37
Q

What is an aerobic gram positive spore forming rod?

A

Bacillus

38
Q

What is an anaerobic gram positive spore forming rod?

A

Clostridium

39
Q

What are the two pathogenic types of bacillus?

A

Bacillus anthracis and bacillus cereus

40
Q

What is the most common route of entry for anthrax?

A

Cutaneous, releases exotoxin which causes tissue necrosis

41
Q

Describe pulmonary anthrax

A

Concern for terrorism, taken into alveoli, gets into macrophages and lymphatic system

42
Q

What are the antibiotics used for bacillus anthracis?

A

Doxy and cipro

43
Q

Describe bacillus anthracis

A

Spore forming, gram positive rod, capsule made of protein which prevents phagocytosis, exotoxins

44
Q

Describe bacillus cereus

A

Gram positive, spore forming rods, aerobic, motile, non-encapsilated, resistant to penicillin and causes food poisoning.

45
Q

Describe clostridium botulinum

A

Gram positive, spore forming rod, anaerobic, spores enter food and neurotoxins block release of acetylcholine, causes flaccid muscle paralysis.

46
Q

Describe clostridium tetani

A

Gram positive, spore forming rod, anaerobic, transmitted by spores on object entering into puncture wound, releases exotoxin tetanospasmin, causes sustained contraction of muscles

47
Q

Describe clostridium perfringens

A

Gas gangrene, spores contaminate wounds, release exotoxins, anaerobic, gram positive spore forming rods

48
Q

What can Clostridioides difficile cause?

A

Pseudomembranous colitis

49
Q

What toxins does C. Diff release?

A

Toxin A- causes diarrhea, Toxin B- cytotoxic to colon cells

50
Q

More pathogenic strain C. Diff since 2002

A

NAP1/BI/027

51
Q

Dx for c. diff

A

Test for toxins, then PCR of stool, 3 or more liquid bowel movements in 24 hours

52
Q

Risk c diff

A

Antibiotics in past month

53
Q

Treatment c. Diff

A

Oral vacomycin, fidaxomicin

54
Q

What are the gram positive, non spore forming rods? What age group do they impact?

A

Corynebacterium diphtheriae and Listeria monocytogenes

Pediatric

55
Q

Describe clinical illness for corynebacterium diptheria

A

Forms grayish pseudomembrane in pharynx and releases exotoxin into bloodstream that damages heart and neural cells

56
Q

Agar for diptheria

A

Potassium telluride and loefflers coagulated blood serum

57
Q

Describe other non-diptheria corynebacterium, env and how they differ.

A

Normal inhabitants of water, soil, skin, mucous membranes. Common specimen contaminant.

Cause HAIs

Resistant to antibiotics, must be treated with IV vanco

58
Q

What are common corynebacterium HAIs organisms? Infections?

A

Corynebacterium jeikeium
Corynebacterium urealyticum, corynebacterium amycolatum
Corynebacterium striatum

Surgical wound infections
catheter/prosthetic valve infections
native/ prosthetic endocarditis

59
Q

Describe rhodococcus equi

A

Formerly corynbacterium (gram positive rod like, aerobic), but partially acid fast. Causes necrotizing pneumonia in immunocompromised and AIDS patients. Looks like TB or norcardia but lung imaging shows modules and cavities that form air fluid levels

60
Q

Basics of listeria monocytogenes

A

Gram positive rod, facultative anaerobe, non spore forming, motile, grows at low temps

61
Q

Virulence factor listeria

A

Listeriolysin O- avoids being killed by macrophages

62
Q

Risks for listeria

A
  1. Third trimester pregnancy- sepsis, bacteremia, neonatal death or premature birth with active infection
  2. Fetus and neonates- meningitis
  3. Elderly and immunocompromised - second leading cause of meningitis in people over 50 (behind pneumococcus)
63
Q

What is a facultative intracellular organism? Example?

A

Survives either outside or within cells
Listeria monocytogenes

64
Q

CSF bacterial meningitis

A

High neutrophils, high protein, low glucose

65
Q

What diseases can strep cause by delayed antibody mediated release?

A

Rheumatic fever
Glomerulonephritis

Clinical Micro (12 decks)

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