First Aid 2015 Micro G+ Organisms pp. 127-134

Question 0

How do you differentiate Viridans strep and S. pneumoniae?

Answer 0

Optochin
Viridans is resistant
S. pneumoniae is sensitive
(OVRPS “overpass”)

Question 1

How do you differentiate S. epidermidis and S. saprophyticus?

Answer 1

Novobicin
S. epidermidis is sensitive
S. saprophyticus is resistant
(NO StRESs)

Question 2

How do you differentiate group A strep (pyogenes) from group B strep (agalactiae)?

Answer 2

Bacitracin (BRASitracin)
Group B strep are resistant
Group A strep are sensitive
(B-BRAS)

Question 3

What defines alpha hemolytic bacteria? Which bacteria are alpha hemolytic?

Answer 3

They perform partial hemolysis causing a green ring around the colony on blood agar.

S. pneumoniae and Viridans strep (S. mutans)

Question 4

What defines beta hemolytic bacteria? Which bacteria are beta hemolytic?

Answer 4

They perform complete hemolysis causing a clear ring around the colony on blood agar.

S. aureus, S. pyogenes, S. agalactiae, L. monocytogenes

Question 5

Catalase +, Coagulase +, B-hemolytic

Answer 5

S. aureus

Question 6

Catalase +, Coagulase -, Novobiocin sensitive

Answer 6

S. epidermidis

Question 7

Catalase +, Coagulase -, Novobiocin resistant

Answer 7

S. saprophyticus

Question 8

Catalase -, a-hemolytic, Optochin sensitive

Answer 8

S. pneumoniae

Question 9

Catalase -, a-hemolytic, Optochin resistant

Answer 9

Viridans strep (S. mutans)

Question 10

Catalase -, B-hemolytic, Bacitracin sensitive

Answer 10

S. pyogenes

Question 11

Catalase -, B-hemolytic, Bacitracin resistant

Answer 11

S. agalactiae

Question 12

Catalase -, Growth in bile and NaCl

Answer 12

Group D Enterococcus - E. faecalis

Question 13

Catalase -, Growth in bile only

Answer 13

Group D NonEnterococcus - S. bovis

Question 14

S. aureus - microscopic appearance and normal site of colonization

Answer 14

Gram + cocci in clusters

Commonly colonizes nares

Question 15

S. aureus - virulence factor(s) and toxins/diseases

Answer 15

V: Protein A - binds FcIgG –> inhibit complement activation and phagocytosis
T: TSST-1 –> toxic shock syndrome - fever, rash, shock
T: Exfoliative Toxin –> scaled skin syndrome
T: Enterotoxin –> rapid onset food poisoning

Question 16

MRSA Significance and Mechanism of Resistance

Answer 16

Important cause of nosocomial and community acquired infections.

Resistant to nafcillin and methicillin because of altered penicillin binding protein.

Question 17

Toxic Shock Syndrome - Etiology, Mechanism, Symptoms

Answer 17

E: Prolonged use of tampons or nasal packing
M: TSST1 is a superantigen - binds constant region of MHC II and T cell receptor resulting in polyclonal T cell activation
Sxs: fever, vomiting, rash, desquamation, shock, end-organ failure

Question 18

Contrast S. pyogenes mediated TSS with S. aureus mediated

Answer 18

S. pyogenes mediated presents with a painful skin infection

Question 19

S. aureus food poisoning - Pathophysiology

Answer 19

Ingestion of preformed toxin –> short incubation (2-6 hrs) –> non-bloody diarrhea and emesis

Heat stable - not destroyed by cooking

Question 20

What does coagulase allow S. aureus to do?

Answer 20

It allows it to form a fibrin clot around itself, and better form an abscess.

Question 21

How does S. epidermidis cause infection?

Answer 21

Infects prosthetic devices (implants, heart valves) and IV catheters by producing adherent biofilms.

Question 22

Where is S. epidermidis normally found? What does it often contaminate?

Answer 22

Normal skin flora

Contaminates blood cultures

Question 23

What is the main infection caused by S. saprophyticus?

Answer 23

it is the second most common cause of uncomplicated UTI in young women.

Question 24

S. pneumo is the most common cause of:

Answer 24

Meningitis Otitis media (in children) Pneumonia Sinusitis

Question 25

What is the gross appearance of S. pneumo?

Answer 25

It is a lancet shaped diplococcus.

Question 26

What virulence factors does S. pneumo produce?

Answer 26

IgA protease (also encapsulated - not virulent without capsule)

Question 27

S. pneumo is associated with what color of sputum?

Answer 27

Rusty

Question 28

S. pneumo causes sepsis in what patient subset?

Answer 28

Patients with sickle cell disease

Question 29

Where are viridans strep normally found?

Answer 29

Oropharynx

Question 30

What species of viridans strep causes dental caries?

Answer 30

S. mutans

Question 31

What species of viridans strep causes endocarditis of previously damaged valves?

Answer 31

S. sanguinis

Question 32

How does S. sanguinis cause endocarditis?

Answer 32

It makes dextrans which bind to fibrin-platelet aggregates on damaged valves. (Sanguinis=blood)

Question 33

What pyogenic disease states are caused by S. pyogenes (group A strep)?

Answer 33

Pharyngitis - also tonsilitis Cellulitis Impetigo Erysipelas (more superficial than cellulitis)

Question 34

What toxigenic disease states are caused by S. pyogenes (group A strep)?

Answer 34

Scarlet fever Toxic shock like syndrome Necrotizing fasciitis

Question 35

What immunologic disease states are caused by S. pyogenes (group A strep)?

Answer 35

``` Rheumatic fever (mediated by M protein) Acute glomerulonephritis ```

Question 36

Which B hemolytic bacterium is pyrrolidonyl arylamidase (PYR) +?

Answer 36

S. pyogenes

Question 37

Titers of what antibody can be used to detect recent S. pyogenes infection?

Answer 37

ASO antibodies - anti-streptolysin O | could also check anti DNAse B antibody

Question 38

What are the criteria for acute rheumatic fever?

Answer 38

``` JONES Criteria Joints - polyarthritis O (heart shaped) - carditis Nodules - subcutaenous Erythema marginatum Sydenham chorea ```

Question 39

Is post strep glomerulonephritis more likely to occur after pharyngitis or impetigo?

Answer 39

Impetigo

Question 40

What bacteria causes scarlet fever and how does it present?

Answer 40

S. pyogenes Scarlet rash with sandpaper texture Strawberry tongue Circumoral pallor Subsequent desquamation

Question 41

Where is group B strep most commonly found?

Answer 41

In the vagina

Question 42

What population is most commonly affected by group B strep? What are the common conditions seen?

Answer 42

Babies Pneumonia, meningitis, and sepsis

Question 43

What bacterium produces CAMP factor? What does it do?

Answer 43

S. agalactiae (Group B strep) | It enlarges the area of hemolysis produced by S. aureus

Question 44

What bacterium has a positive Hippurate test?

Answer 44

S. agalactiae (Group B strep)

Question 45

Who should be screened/treated for group B strep?

Answer 45

Pregnant women should be screened at 35-37 weeks of gestation. If culture is positive, they should receive intrapartum penicillin prophylaxis.

Question 46

Where are Enterococci (group D strep) normally found?

Answer 46

Part of the normal colonic flora

Question 47

What disease states are caused by Enterococci (group D strep)?

Answer 47

UTI, biliary tract infections, and subacute endocarditis following GI/GU procedures

Question 48

Enterococci (group D strep) are resistant to what antibiotic?

Answer 48

Penicillin G

Question 49

Enterococci and Non-enterococci strep are both group D based on what system?

Answer 49

Lancefield grouping - based on C carbohydrate of cell wall

Question 50

Which group of enterococci are most commonly seen in nosocomial infections?

Answer 50

Vancomycin resistant enterococci

Question 51

Where are non-enterocci (Group D strep) normally found?

Answer 51

In the gut

Question 52

What species/subspecies of non-enteroccus (Group D strep) causes bacteremia and endocarditis in the setting of colon cancer?

Answer 52

S. gallolyticus (S. bovis biotype 1)

Question 53

How does C. diphtheriae cause diphtheria?

Answer 53

Exotoxin encoded by B-prophage inhibits protein synthesis by ADP-ribosylation of EF2 (elongation factor)

Question 54

How does diphtheria present?

Answer 54

Pseudomembranous pharyngitis (gray-white membrane) Lymphadenopathy Myocarditis Arrhythmias

Question 55

How do you identify C. diphtheriae in the lab?

Answer 55

G+ rods with blue/red metachromatic granules Forms black colonies on cystine-tellurite agar Can also do an Elek test for the toxin

Question 56

Characteristics of spores

Answer 56

Contain dipicolinic acid No metabolic activity Must be autoclaved to kill

Question 57

Which bacteria produce spores?

Answer 57

``` Bacillus anthracis Bacillus cereus Clostridium botulinum Clostridium difficile Clostridium perfringens Clostridium tetani Coxiella burnetii ```

Question 58

How does C. tetani cause tetanus?

Answer 58

Produces tetanospasmin which cleaves SNARE proteins and prevents exocytosis of GABA and glycine from the Renshaw cells of the spinal cord.

Question 59

What are the symptoms of tetanus?

Answer 59

Spastic paralysis, trismus (lockjaw), risus sardonicus (raised eyebrows and open grin)

Question 60

Treatment of tetanus

Answer 60

Antitoxin +/- vaccine booster and diazepam for muscle spasms Prevent with vaccine

Question 61

How does C. botulinum cause botulism?

Answer 61

Produces a preformed heat-labile toxin that cleaves SNARE proteins and inhibits ACh release

Question 62

How does botulism differ between adults and babies?

Answer 62

In babies, ingestion of spores (in honey) is enough to cause disease. In adults disease only occurs with ingestion of preformed toxin. Can also be found in bad bottles of food.

Question 63

How does C. perfringens cause disease?

Answer 63

It produces alpha toxin (lecithinase) that causes myonecrosis (gas gangrene) and hemolysis.

Question 64

How does C. difficile cause disease?

Answer 64

Produces two toxins. Toxin A (enterotoxin) binds to the gut brush border. Toxin B (cytotoxin) depolymerizes the actin cytoskeleton ---> pseudomembranous colitis --> diarrhea.

Question 65

Which two antibiotics classically lead to C. difficile infection?

Answer 65

Clindamycin and ampicillin

Question 66

What is the treatment for C. difficile? What about recurrent cases?

Answer 66

Metronidazole or oral vancomycin Recurrent cases may require a repeat treatment, fidaxomicin, or fecal transplant.

Question 67

What is special about Bacillus anthracis structure?

Answer 67

It is the only bacteria with a polypeptide capsule. The capsule contains D-glutamate.

Question 68

What are the symptoms of cutaneous anthrax?

Answer 68

Painless papule surrounded by vesicles --> painless ulcer with black eschar --> bacteremia/death (uncommon)

Question 69

What are the symptoms of pulmonary anthrax?

Answer 69

Flu-like symptoms with rapid progression to fever, pulmonary hemorrhage, mediastinitis, and shock. (Requires spore inhalation)

Question 70

How is Bacillus cereus commonly contracted?

Answer 70

Keeping rice warm causes spore germination. Spores survive the cooking and cause food poisoning. "Reheated rice syndrome"

Question 71

What are the two types of Bacillus cereus poisoning and what are the symptoms?

Answer 71

Emetic type: Seen with rice and pasta. N/V w/in 1-5 hours. Caused by cereulide, a preformed toxin. Diarrheal type: Watery non-bloody diarrhea and GI pain w/in 8-18 hours.

Question 72

What type of bacteria (metabolically) is Listeria? How is it usually acquired?

Answer 72

Facultative intracellular microbe Unpasturized dairy, deli meats, transplacental, vaginal birth

Question 73

How does Listeria move?

Answer 73

It forms "rocket tails" by rapid polymerization of actin that allow intracellular and cell-to-cell movement with a characteristic tumbling motility.

Question 74

What is special about the membrane/wall structure of Listeria?

Answer 74

It is the only G+ bacteria to produce endotoxin.

Question 75

What are the disease manifestations associated with Listeria infection during pregnancy?

Answer 75

Amnionitis, septicemia, and spontaneous abortion

Question 76

What are the disease manifestations associated with Listeria infection in an immunocompromised patient? How do you treat it?

Answer 76

Meningitis Treat with ampicillin

Question 77

What conditions does Listeria infection cause in newborns? How do you treat it?

Answer 77

Granulomatosis infantiseptica, neonatal meningitis Treat with ampicillin

Question 78

What are the symptoms of Listeria infection in a healthy adult?

Answer 78

Mild gastroenteritis (self limited)

Question 79

Both actinomyces and nocardia form branching filaments resembling fungi. Differentiate them based on: Metabolism Staining (most important) Normal location

Answer 79

Actinomyces is anaerobic Nocardia is aerobic Actinomyces is not acid fast Nocardia is acid fast Actinomyces is a normal part of oral flora Nocardia is found in the soil

Question 80

What are the manifestations of actinomyces infection? How do you treat it?

Answer 80

Causes oral/facial abscesses that drain through sinus tracts | Treat with penicillin Tx is a SNAP - Sulfonamide - Nocardia - Actinomyces - Penicillin

Question 81

What are the manifestations of nocardia infection? How do you treat it?

Answer 81

Pulmonary infections in immunocompromised Cutaneous infection after trauma in immunocompetent Treat with sulfonamides (Tx is a SNAP - Sulfonamide - Nocardia - Actinomyces - Penicillin)

Question 82

Describe the initial process of TB infection? What are the four possible outcomes?

Answer 82

Pulmonary infection forming Ghon complex of hilar lymphadenopathy and lower lobe infiltrates. Outcomes - Heal by fibrosis --> hypersensitized --> + PPD - Progressive lung disease --> Death (usu. w/HIV) - Bacteremia --> Miliary TB --> Death - Dissemination with dormancy --> reactivate as adult

Question 83

What is the pathologic manifestation of reactivated/reinfected TB in a previously sensitized person?

Answer 83

Caseating granuloma in upper lobe of lung

Question 84

Reactivated TB can disseminate to many organs. What is disease of the vertebral body called?

Answer 84

Pott disease

Question 85

When will a PPD be a true positive? What are causes of false positives? What test should be used to evaluate false positives?

Answer 85

True: current infection or past exposure False: BCG vaccination Evaluate FPs with IGRA assay

Question 86

When will a PPD be negative? When will it be a false negative?

Answer 86

Negative if no infection or past exposure False: - Anergy (steroids, immunocompromised, malnutrition) - Sarcoidosis

Question 87

What are the classic symptoms of TB?

Answer 87

Fever, night seats, weight loss, cough (may be productive), hemoptysis

Question 88

What two virulence factors does TB possess?

Answer 88

Cord factor: inhibits macro maturation and induces TNFa release Sulfatides on surface inhibit phagolysosome fusion

Question 89

Who is infected by M. avium-intracellulare? How do you prevent this?

Answer 89

HIV patients - disseminated non-TB disease Often resistant to multiple drugs so best strategy is to prevent it by giving prophylactic azithromycin when CD4+ count <50 cell/mm3.

Question 90

All mycobacteria stain with:

Answer 90

acid fast stain

Question 91

What are the manifestations of M. scrofulaceum infection?

Answer 91

Cervical lymphadenitis in children

Question 92

What are the manifestations of M. marinum infection?

Answer 92

Hand infection in aquarium handlers

Question 93

What disease is caused by M. leprae? What is its pathogenesis?

Answer 93

Leprosy or Hansen's Disease Infects skin and superficial nerves of hands and feet causing a "glove and stocking" loss of sensation

Question 94

Describe the disease manifestations and pathophysiology of lepromatous M. leprae infection.

Answer 94

Diffuse skin lesions with leonine facies Damage is caused by low cell mediated immunity with humoral Th2 response It is communicable.

Question 95

Describe the disease manifestations and pathophysiology of tuberculoid M. leprae infection.

Answer 95

Limited disease with a few hypoesthetic hairles skin plaques. Characterized by high cell mediated immunity with Th1 response.

Question 96

What is the treatment for tuberculoid M. leprae infection? What about lepromatous?

Answer 96

Dapsone and rifampin for tuberculoid | Add clofazimine for lepromatous