Which is a mode of bacterial transmission that involves physical contact?

The mode of bacterial transmission that involves physical contact is sharing utensils. This practice can facilitate the direct transfer of bacteria from one individual to another, as utensils can carry pathogens present on the surface of food or in the mouth of the person using them. When one person shares utensils, there's a potential for bacteria to spread easily, especially in settings where hygiene practices are lax.

In contrast, the other options involve different mechanisms of transmission. Ingestion of contaminated food typically refers to foodborne illness, where bacteria are ingested without requiring direct contact between individuals. Bacterial spores in the air indicates airborne transmission, where bacteria are carried through the air and inhaled, bypassing physical contact. Finally, vector-borne diseases involve transmission by insects or animals, which again does not necessitate physical contact between individuals.