Digital PSAT Reading and Writing Practice Question 140: Answer and Explanation

Question: 140

Lab technicians are able to pinpoint the best antibiotic by measuring the zone of inhibition on the microorganism growth plate. The zone with the largest diameter typically signifies that it will be the best at fighting the infection. Prescribing an antibiotic that tests positive for the inhibition of growth or completely stops the growth of the microorganism will hopefully help the patient heal faster and experience fewer side effects.

Figure 1 Zone of inhibition measurements to determine the effectiveness of certain antibiotics against the microorganisms E. coli and S. aureus.

Based on the information in the text and in Figure 1, which of these antibiotics would be most helpful in treating someone with an E. coli infection, assuming the patient was not allergic to any antibiotics and had no other illnesses besides the E. coli infection?

• A. Vancomycin
• B. Ciprofloxacin
• C. Amoxicillin
• D. Staphylococcus

Correct Answer: B

Explanation:

(B) The text states that the "zone with the largest diameter typically signifies that it will be the best at fighting infection." Under the E. coli column (2nd column), ciprofloxacin has the largest diameter at 17 mm. It would therefore be the most effective antibiotic in this particular instance, as in choice (B). Vancomycin would be the most effective medication against S. aureus, not against E. coli. Amoxicillin is the second most effective. Not only is there no data on Staphylococcus, but it also is actually a bacterial strain and not an antibiotic.