These bacteria may be present on
your tongue,
in your mouth, Gums , nose, tonsils, esophagus or stomach. Tonsils are lymph nodes present in the mouth which when inflamed and calcified(tonsillitis with tinsiloliths) also releases foul smell.
Cleaning the tongue with tongue cleaner, using a mouth wash with mint etc may be tried. If the symptoms persist then get it evaluated from an ENT surgeon.