Wisconsin state health authorities alerted the CDC about an E. coli O157:H7 outbreak. Soon thereafter, officials from two other states reported that they also had cases of illness associated with this pathogen. Within days, the CDC determined that the E. coli strains from all three states were the same, and the likely source of the outbreak was a particular brand of pre-packaged fresh spinach. The CDC then issued a press release advising people not to eat bagged fresh spinach.
-You have identified the causative organism of the outbreak as E. coli. In an effort to characterize the strain of the organism involved, you do different tests. The results are as follows:
Gram stain-Gram-negative rods
Oxidase test-negative
Lactose fermentation-positive
Serological testing-O157:H7
Colony morphology-smooth
Creamy colonies
RFLPs-E. coli O157:H7
Antibiogram-resistant to ampicillin.
Which test(s) confirm the identity of the organism at the strain level?
A) Gram stain AND antibiogram
B) Serological testing AND colony morphology
C) RFLPs AND serological testing
D) Oxidase test AND RFLPs
E) Lactose fermentation AND oxidase test

Question

Wisconsin state health authorities alerted the CDC about an E. coli O157:H7 outbreak. Soon thereafter, officials from two other states reported that they also had cases of illness associated with this pathogen. Within days, the CDC determined that the E. coli strains from all three states were the same, and the likely source of the outbreak was a particular brand of pre-packaged fresh spinach. The CDC then issued a press release advising people not to eat bagged fresh spinach. 
-You have identified the causative organism of the outbreak as E. coli. In an effort to characterize the strain of the organism involved, you do different tests. The results are as follows:
Gram stain-Gram-negative rods
Oxidase test-negative
Lactose fermentation-positive
Serological testing-O157:H7
Colony morphology-smooth
Creamy colonies
RFLPs-E. coli O157:H7
Antibiogram-resistant to ampicillin.
Which test(s) confirm the identity of the organism at the strain level?
A) Gram stain AND antibiogram
B) Serological testing AND colony morphology
C) RFLPs AND serological testing
D) Oxidase test AND RFLPs
E) Lactose fermentation AND oxidase test

Quizplus · Accepted Answer

RFLPs and serological testing are the tests that confirm the identity of the organism at the strain level. RFLPs (Restriction Fragment Length Polymorphism) is a molecular technique that analyzes the DNA fragments produced by digesting a DNA sample with restriction enzymes. This technique separates the DNA fragments based on size and can be used to distinguish between different strains of the same species. Serological testing identifies the O and H antigens of the organism, which are specific to E. coli O157:H7. The other tests are useful in identifying the organism as E. coli and determining its characteristics but do not provide strain-level identification.

Wisconsin State Health Authorities Alerted the CDC About an E