What microbial level is considered safe for oysters at the source?

The correct microbial level considered safe for oysters at the source is 230 Most Probable Number per 100 mL (MPNB). This level is based on the understanding that oysters can accumulate harmful bacteria from their environment, particularly Vibrio species, which are pathogenic. The regulatory agencies have established limits to ensure seafood safety.

The limit of 230 MPNB indicates a level at which the risk of illness is deemed manageable when proper handling and cooking methods are followed. Maintaining this threshold is crucial because oysters are frequently consumed raw or undercooked, which makes them more susceptible to transmit bacterial infections.

Other levels, such as 0 MPNB, would be ideal but are not realistic in natural environments where oysters grow, as some level of microbial presence is expected. The other options 50 MPNB and 100 MPNB suggest levels that are below what has been established as the safe upper limit for harvesting oysters, which may not reflect the actual conditions in the field while ensuring public health safety.