Hello from JustAnswer.
This is generally not a mode of transmission of syphilis. Syphilis is primarily transmitted by contact with a syphilis sore. Syphilis sores primarily occur on the genitalia, but a very small percentage of people can develop syphilis sores on the mouth. If there are no sores in the mouth, then there would not be any risk associated with contact with the mouth. If there is a sore on the mouth, then there is some risk of transmission by contact with the oral sore. Transmission of food from one person to another is not a recognized method of transmission of syphilis, but if there are any syphilis sores in the mouth, it makes sense to avoid transfers from the infected mouth.
Of course, since syphilis is treatable, the person is no longer contagious once the syphilis sores heal after antibiotic treatment.
So, this is not a recognized method of transmission of syphilis, but if there are sores in the mouth that have not yet healed from antibiotic treatment, it would be wise to avoid transfers of food from the infected mouth.
If I can provide any additional information, please let me know.
Please let me know if I can provide any further assistance.