Question

A student streaks a plate using inoculum from a broth culture tube. The culture tube was labeled "Escherichia coli," indicating that the culture was composed of a single bacterial species. Which of the following best explains the unexpected plate result shown here after incubation?

a) The plate was exposed to airborne contaminants.
b) The loop wasn't flamed between quadrant streaks.
c) The plate was not rotated properly during the inoculation process.
d) The culture in the tube was contaminated.

Answer 1

Option (d), The unexpected result of seeing different colonies on an agar plate initially labeled as a pure Escherichia coli culture suggests that the culture in the tube was contaminated with other bacteria.

Step-by-step explanation:

The unexpected plate result after incubation might be best explained by option d) 'The culture in the tube was contaminated'. If the culture tube labeled "Escherichia coli" was composed of a single bacterial species, and unexpected colonies appear after incubation, it suggests that other bacterial species were present, indicating contamination.

While airborne contaminants or not flaming the loop between quadrant streaks could also lead to contamination, the most likely explanation given that the tube was initially a pure culture would be that the culture itself was contaminated before streaking the plate.