Bacteriology

Question 1

Enterobacteriaceae general characteristics

Answer 1

facultative anaerobes, grow on standard lab media incl. MacConkey agar, ferment glucose +/- lactose, oxidase negative, reduce nitrate to nitrite, catalase positive except Shigella dysenteriae, usually motile. Colonies are large, grey, and smooth.

Question 2

Lactose fermenters

Answer 2

Citrobacter, E. coli, Enterobacter, Klebsiella (CEEK)

Question 3

Non-motile:

Answer 3

Shigella, Klebsiella, Yersinia at 37°C (SKY)

Question 4

H2S producers

Answer 4

Salmonella, Proteus vulgaris, Proteus miribalis, Edwardsiella, Citrobacter

Question 5

Which two bacteria (one GP and one GN) produce DNAse?

Answer 5

S. auerus

serratia maracescens

Question 6

Which antibiotics are enterococci naturally resistant to

Answer 6

cephalosporins (altered PBP)
clindamycin
aminoglycosides (inability to penetrate cell wall)

Question 7

Enterococci have acquired resistance to which antibiotics?

Answer 7

penicillin (beta-lactamase, chromosomal)
vancomycin (multiple van genes)
high level resistance to aminoglycosides

Question 8

What are the 3 mechanisms of resistance for staph spp?

Answer 8

1. Beta-lactamase carried on plasmid resulting in penicillin resistance
2. Altered PBP2, chromosomal through mecA gene. Resistance to oxacillin, methicillin, nafcillin, 1-4 gen. cephalosporins
3. Alterations in cell wall by van A gene resulting in vancomycin resistance

Question 9

What is PBP2A test used for?

Answer 9

Identification of MRSA

Question 10

How do you distinguish S. saprophyticus from S. epidermidis?

Answer 10

Both are coag neg staph
S. saprophyticus is novobiocin R
S. epidermidis is novobiocin S

Question 11

What are the two major groups of beta-hemolytic strep and how do you distinguish them biochemically?

Answer 11

Strep pyogenes (group A): catalase (-), PYR (+), bacitracin S, Na hippurate (-), CAMP test (-)
Strep agalactiae (group B): catalase (-), Na hippurate (+), CAMP test (+), polysaccharide capsule

Question 12

What is the mechanism of antibiotic resistance in enterococcus?

Answer 12

Resistant to celphalosporins and penicillins; low-level resistance to aminoglycosides
Vancomycin resistance due to target site alterations encoded by van genes (E. faecium: vanA; E. faecalis: vanB)

Question 13

How can you biochemically distinguish bacillus antracis from bacillus cereus?

Answer 13

Both are catalaste (+)
B. anthracis: non-hemolytic, non-motile
B. cereus: beta-hemolytic, motile

Question 14

Bacillus cereus is resistant to which antibiotics?

Answer 14

penicillins, cephalosporins (broad spectrum beta-lactamase)

Question 15

How can you biochemically distinguish listeria from bacillus/

Answer 15

on gram stain, bacillus has spores
both are catalase (+)
listeria is CAMP test (+)

Question 16

Listeria is resistant to which antibiotic?

Answer 16

cephalosporins

Question 17

Which aerobic gram positive rods are MDR?

Answer 17

corynebacterium jeikeium

corynebacterium urealyticum

Question 18

How to distinguish Neisseria from moraxella on biochemically?

Answer 18

Both are gram neg diplococci and are oxidase (+)
Neisseria grows on selective media MTM, GC-lect and ferments glucose
Moraxella is a non-fermenter

Question 19

special growth characteristics Haemophilus spp?

Answer 19

chocolate agar only
H. influenza needs factor X (hemin) and V (NAD)
H. parainfluenza: factor V (NAD)
H. ducreyi: Factor X

Question 20

Anaerobic gram pos coccobacilli in chains SPS sens

Answer 20

peptostreptococcus

Question 21

What are the growth and biochemical characteristics of Bacteroides fragilis? what antibiotic is it resistant to?

Answer 21

gram-neg pleomorphic rods, safety pin shape
Grows on BBE (bacteroides bile esculin agar)
Col R Kan R Van R
Resistant to pencillin (beta-lactamase)

Question 22

What class of antibiotics is listeria monocytogenes resistant to?

Answer 22

cephalosporins

Question 23

What media is used to isolate nocardia

Answer 23

Buffered charcoal yeast extract (BCYE)

Question 24

What spp of nocardia is often causes disseminated & CNS infection and is MDR?

Answer 24

N. farcinica

Question 25

Which type of H. influenza is responsible for most disease and how can you detect?

Answer 25

type B | agglutination test

Question 26

What is the name of the toxin of Clostridium perfringens? And how can you detect?

Answer 26

alpha-toxin/lecithinase Egg yolk agar: ppt in presence of toxin Nagler test: no ppt in presence of antibodies to toxin

Question 27

What key biochemical test differentiates E. coli from klebsiella spp.?

Answer 27

Kleb is urease (+) E. coli and kleb oxytoca are indole (+) kleb pneumo is indole (-)

Question 28

Which gram neg rod is said to be swarming on agar with foul smell?

Answer 28

Proteus

Question 29

Which enterobacteriacea produce ESBL?

Answer 29

E. coli Klebsiella pneumoniae Proteus mirabilis

Question 30

Which enterobacteriacea have ampC mutations?

Answer 30

``` E. coli citrobacter enterobacter cloacae Providencia spp Morganella morganii serratia marcescens ```

Question 31

Which enterobacteriacea have KPC?

Answer 31

Klebsiella pneumonia Citrobacter serratia marcescens

Question 32

Resistance profile pseudomonas aeruginosa

Answer 32

``` ESBL carbapenemase ampC, inducible Efflux pumps Topoisomerase mutations ```

Question 33

Resistance profile acenitobacter

Answer 33

Beta-lactams aminoglycosides quinolones

Question 34

Resistance profile stenotrophomonas maltophila

Answer 34

intrinsically resistant to beta-lactams often resistant to quinolones Tx of choice=TMP/SMX

Question 35

Vibrio spp growth on TCBS

Answer 35

cholera: yellow parahemolyticus: green

Question 36

What gas do they AACEK group of bacteria require for growth?

Answer 36

CO2

Question 37

What does verigene detect?

Answer 37

nucleic acid microarray for gram (+) cocci from positive blood cx bottles

Question 38

Which enterobacteriacea are ureas pos

Answer 38

Proteus, Citrobacter, Klebsiella