Basics of Microbiology: bacterial ID

Question 1

Lancefield Grouping: A,B,C

Answer 1

Group A: Strep Pyogenes

Group B: Strep Agalactiae

Group D: Enterococcus

(Based on “C carbohydrates” in the cell wall that allow agglutination with particular antisera)

Question 2

+ Catalase Test=

Answer 2

Catalase positive = bubbling

Catalase negative = no bubbling

Differentiates Staph from Strep

Catalase enzyme produced by bacteria that use oxygen

Breaks down H2O2 into H2O and O2 (makes bubbles)

Hydrogen peroxide on slide → Add bacteria → Look for bubbles

Question 3

Chronic Granulomatous Disease catalase organism relevance:

Answer 3

CGD = Loss of function of NADPH oxidase • Phagocytes cannot generate H2O2 therefore,

Catalase (+) bacteria breakdown H2O2 • Host cells have no H2O2 to use → recurrent infections

Question 4

Coagulase Test

Differentiates

+=

Answer 4

Differentiates Staph Aureus from other Staph

Coagulase positive = clumping • Coagulase negative = no clumping

Question 5

Novobiocin Differentiates

resistant vs sensitive:

Answer 5

• Differentiates S. saprophyticus from S. epidermidis

Technique: • Plate bacteria on agar with Novobiocin “disk” & Measure clearance zone around disk

Resistant = Growth near edge of disk

Sensitive = Large zone of clearance around disk

Question 6

Bacitracin Differentiates

resistant vs sensitive:

Answer 6

• Differentiates Group A strep from Group B strep

Bacitracin: antibiotic that interferes with peptidoglycan synthesis

Resistant = Growth near edge of disk

Sensitive = Large zone of clearance around disk

Question 7

Optochin ethylhydrocupreine

differentiaties:

resistant vs sensitive:

Answer 7

• Differentiates S. pneumonia from S. viridans strep

Resistant = Growth near edge of disk

Sensitive = Large zone of clearance around disk

• S. pneumonia highly sensitive to Optochin!!!

Question 8

Bile Esculin Agar Selective for:

Answer 8

• Group D strep (Enterococci and S. bovis)

if color changes to brown/black, then you have group d strep

Question 9

NaCl Media differentiates:

Answer 9

Differentiates Enterococcus from non-enterococcus Group D bacteria (S. bovis)

Question 10

Mannitol Salt Agar differentiates:

Answer 10

Used to differentiate staph species

Mannitol fermenters make acid → Phenol red turns yellow

Staph aureus ferments mannitol, Most other staph do not

Growth on MSA with yellow color is Staph Aureus

Question 11

(-) bugs differentiated with Maltose:

Answer 11

Neisseria meningitidis can metabolize maltose

Neisseria gonorrhoeae cannot

Question 12

(-) Lactose Fermentation:

Selective media for _

Contains ___ as inhibitors of growth

Inhibit __

Lactose fermentation produces ___

Non-lactose fermenters are ___

Answer 12

Selective media for gram (-) bacteria

Contains bile salts as inhibitors of growth Gram (+) bacteria

( Inhibits fastidious gram (-): Neisseria, Pasteurella )

Lactose fermentation produces acid → turns agar pink •

Non-lactose fermenters are colorless

Question 13

Oxidase:

Answer 13

Test for presence of cytochrome oxidase

Bacterial colonies placed on paper discs with indicator present

If oxidase is present, color change occurs

Question 14

Campylobacter grows at ___

Vibrio grows on ___

Answer 14

Campylobacter grows at 42oC (Vibrio does not) • Vibrio grows on alkaline media (Campy does not)

Question 15

H2 S Production purpose:

Answer 15

Oxidase (-) organisms can be subdivided by H2S

Salmonella and proteus produce H2S

Shigella does NOT produce H2S

Triple Sugar Iron (TSI) test -Organisms that produce H2S will turn TSI media black