Question

The water used to prepare intravenous solutions in a hospital contained endotoxins. Infection control personnel performed plate counts to find the source of the bacteria. Their results:

All of the following conclusions about the bacteria can be drawn except which one?
a. They were present as a biofilm in the pipes.
b. They are gram-negative.
c. They come from fecal contamination.
d. They come from the city water supply.
e. none of the above

Accepted Answer

Step 1: Analyze the bacterial counts from the table. The municipal water pipes and boiler show zero bacteria per 100 ml, while the hot water line shows 300 bacteria per 100 ml. This suggests that the source of bacteria is not the municipal water or boiler but the hot water line. Step 2: Understand the nature of endotoxins. Endotoxins are components of the outer membrane of gram-negative bacteria, so the presence of endotoxins implies the bacteria are gram-negative. Step 3: Consider the possibility of biofilm formation. Since bacteria are detected only in the hot water line and not in the water supply or boiler, it is likely that bacteria are growing as a biofilm inside the hot water pipes, which can harbor bacteria even if the water itself is initially sterile. Step 4: Evaluate the source of bacteria. Since the municipal water pipes have zero bacteria, the bacteria in the hot water line do not come from the city water supply, ruling out option (d). Step 5: Assess fecal contamination. Endotoxins and gram-negative bacteria can be associated with fecal contamination, but since the municipal water is free of bacteria, fecal contamination is unlikely to be the source here.

Verified video answer for a similar problem:

Key Concepts

Endotoxins and Gram-negative Bacteria

Biofilms in Water Systems

Source Tracking of Bacterial Contamination