Clinical Bacteriology

Question 1

Gram +, bacilli, aerobic

Answer 1

Listeria, Bacillus, Corynebacterium

Question 2

Gram +, bacilli, anaerobic

Answer 2

Clostridium, Propionibacterium

Question 3

Gram +, cocci, anaerobic/facultative, catalase -, alpha hemolysis, optochin/bile resistant

Answer 3

Viridans streptococci (no capsule): S mutans, S mitis

Question 4

Gram +, cocci, anaerobic/facultative, catalase -, alpha hemolysis, optochin/bile sensitive

Answer 4

S. pneumoniae (encapsulated)

Question 5

Gram +, cocci, anaerobic/facultative, catalase -, beta hemolysis, bacitracin resistant

Answer 5

Group B strep: S agalactiae

Question 6

Gram +, cocci, anaerobic/facultative, catalase -, beta hemolysis, bacitracin sensitive

Answer 6

Group A strep: S pyogenes

Question 7

Gram +, cocci, anaerobic/facultative, catalase -, gamma hemolysis, no growth in 6.5% NaCl

Answer 7

Nonenterococcus, S bovis

Question 8

Gram +, cocci, anaerobic/facultative, catalase -, gamma hemolysis, growth in 6.5% NaCl

Answer 8

Group D (enterococcus): E faecium, E faecalis
Note: can also be alpha hemolytic

Question 9

Gram +, cocci, anaerobic/facultative, catalase +, coagulase -, novobiocin resistant

Answer 9

S saprophyticus

Question 10

Gram +, cocci, anaerobic/facultative, catalase +, coagulase -, novobiocin sensitive

Answer 10

S epidermidis

Question 11

Gram +, cocci, anaerobic/facultative, catalase +, coagulase +

Answer 11

S aureus

Question 12

Alpha-hemolysis

Answer 12

Gram + cocci

Partial reduction of hemoglobin causes greenish or brownish color without clearing around growth on blood agar

Question 13

Beta-hemolysis

Answer 13

Gram + cocci

Complete lysis of RBCs -> clear area surrounding colony on blood agar

Question 14

Staphylococcus aureus - virulence factor

Answer 14

Protein A: binds Fc-IgG, inhibiting complement activation and phagocytosis

Question 15

Staphylococcus aureus - colonization

Answer 15

Nares, axilla, and groin

Question 16

Staphylococcus aureus - infections

Answer 16

Inflammatory disease, toxin-mediated disease, MRSA

Question 17

Staphylococcus aureus - inflammatory disease

Answer 17

Skin infections, organ abscesses, pneumonia (only after influenza virus infection), endocarditis, septic arthritis, and osteomyelitis

Question 18

Staphylococcus aureus - organ abscess formation

Answer 18

“Bad staph” make coagulase and toxins

Forms fibrin clot around self -> abscess

Question 19

Staphylococcus aureus - toxin-mediated disease

Answer 19

Toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid onset food poisoning (enterotoxins)

Question 20

Staphylococcus aureus - MRSA infection

Answer 20

Methicillin-resistant Staphylococcus aureus
Important cause of serious nosocomial and community-acquired infections
Resistant to methicillin and nafcillin because of altered penicillin-binding protein

Question 21

Staphylococcal toxic shock syndrome - presentation

Answer 21

Fever, vomiting, rash, desquamation, shock, end-organ failure

Question 22

Staphylococcal toxic shock syndrome - labs

Answer 22

Increased AST, increased ALT, increased bilirubin

Question 23

Staphylococcal toxic shock syndrome - common association

Answer 23

Prolonged use of vaginal tampons or nasal packing

Question 24

TSST-1 - mechanism

Answer 24

Superantigen that binds to MHCII and T-cell receptor, resulting in polyclonal T-cell activation

Question 25

S aureus food poisoning - cause

Answer 25

Ingestion of preformed toxin -> short incubation period | Enterotoxin is heat stable -> not destroyed by cooking

Question 26

S aureus food poisoning - presentation

Answer 26

Quick onset (2-6 hours), non bloody diarrhea and emesis

Question 27

Staphylococcus epidermidis - colonization

Answer 27

Normal flora of skin | Contaminates blood cultures

Question 28

Staphylococcus epidermidis - infection sites

Answer 28

Prosthetic devices (eg, hip implant, heart valve) and IV catheters by producing adherent biofilms

Question 29

Staphylococcus saprophyticus - colonization

Answer 29

Normal flora of female genital tract and perineum

Question 30

Staphylococcus saprophyticus - infection

Answer 30

Second most common cause of uncomplicated UTI in young women (E coli most common)

Question 31

Streptococcus pneumoniae - shape

Answer 31

Lancet-shaped diplococci

Question 32

Streptococcus pneumoniae - virulence

Answer 32

Encapsulated (no virulence without the capsule) | IgA protease

Question 33

Streptococcus pneumoniae - common diseases

Answer 33

``` Most common cause of: Meningitis Otitis media (in children) Bacterial pneumonia Sinusitis ```

Question 34

Pneumococcus - associations

Answer 34

"Rusty" sputum | Sepsis in patients with sickle cell disease and asplenic patients

Question 35

Viridans group streptococci - colonization

Answer 35

Normal flora of the oropharynx

Question 36

Viridans group streptococci - infections

Answer 36

``` Dental caries (S mutans and S mitis) Subacute bacterial endocarditis at damaged heart valves (S sanguinis) ```

Question 37

S sanguinis - endocarditis mechanism

Answer 37

Makes dextran, which bind to fibrin-platelet aggregated on damaged heart valves

Question 38

Streptococcus pyogenes - pyogenic infections

Answer 38

Pharyngitis, cellulitis, impetigo ("honey-crusted" lesions), erysipelas

Question 39

Streptococcus pyogenes - toxigenic infections

Answer 39

Scarlet fever, toxic shock-like syndrome, necrotizing fasciitis

Question 40

Streptococcus pyogenes - immunologic infections

Answer 40

Rheumatic fever, post-streptococcal glomerulonephritis

Question 41

Streptococcus pyogenes - virulence

Answer 41

Hyaluronic acid capsule inhibits phagocytosis

Question 42

Streptococcus pyogenes - autoimmunity

Answer 42

Antibodies agains M protein enhance host defenses against S pyogenes but can give rise to rheumatic fever

Question 43

Streptococcus pyogenes - recent infection test

Answer 43

ASO titer or anti-DNase B antibodies indicate recent S pyogenes infection

Question 44

Streptococcus pyogenes - complications

Answer 44

Pharyngitis: rheumatic fever and glomerulonephritis Impetigo: glomerulonephritis

Question 45

Scarlet fever - presentation

Answer 45

Blanching, sandpaper-like body rash, strawberry tongue and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin +)