Final answer:
The primary mode of transmission for Salmonella bacteria is through the fecal-oral route, specifically through contaminated water or undercooked meat, not airborne, vector-borne, or direct contact.
Step-by-step explanation:
The primary mode of transmission for Salmonella bacteria is not through airborne, vector-borne, or direct contact, but rather through the fecal-oral route, which is often associated with the consumption of contaminated water or undercooked meat. Salmonella can be transmitted through the ingestion of food that has been contaminated with the bacteria, particularly poultry and eggs, as these foods are a natural part of the microbiota of these animals. Preventative measures such as handwashing and cooking foods thoroughly are critical in reducing the risk of salmonellosis, which is the infection caused by Salmonella.