Final answer:
The provided information does not give an accurate determination of the proportion of rod-shaped bacterial cells in a single field.
Step-by-step explanation:
In a single field, approximately what proportion of the bacterial cells are rod-like (the microbiology term for rod-shaped cells is "bacilli")?
Based on the information provided, it is not possible to accurately determine the proportion of rod-shaped bacterial cells in a single field. The information given only states that most bacteria are harmless and lists examples of bacterial diseases. It does not provide specific data regarding the proportion of rod-shaped bacterial cells.