Question

2. For each of the following types of contamination suggest the most likely point in preparation (or later) at which the contaminant was introduced. Imagine you made the stuff, and it has contaminants. Where did you go wrong? a. Growth in all broth tubes. b. Growth in one broth tube. c. Growth only on the surface of a plate. d. Growth throughout the agar's thickness on a plate. e. All plates in a batch have the same type and density of contaminants. f. Only a few plates in a batch are contaminated, and each looks different.

Answer 1

a.Growth in all broth tubes – contamination of growth media (would not have sterilized properly)

b.Growth in one broth tube – one broth tube or inoculating loop would have contaminated (would not have sterilized)

c.Growth only on the surface of a plate – contamination at the inner surface of the cap of the plate

d.Growth throughout the agar’s thickness on a plate – Agar would have contaminated (or not properly sterilized by autoclaving before pouring)

d.All plates in a batch have the same type and density of contaminants – contamination in the agar media that has used for making plates.

e.Only a few plates in a batch are contaminated – It would have occurred when the contaminant particles entered on few plate surface while pouring the agar media or plate itself would have contaminated before pouring.