Bacterial persistence in vivo: resistance or tolerance to antibiotics

The in vivo persistence of bacteria in spite of "adequate" therapy may be due to a variety of causes or factors. The most "obvious" cause is the presence of drug resistant strains, missed in conventional testing because of heterogeneity of resistance, special test requirements or emergence during treatment. A second large group of causes is due to atypical forms, whereas a third cause is due to tolerance. A fourth group of causes may be termed invironmental factors, and this includes drug inactivation, bioconversion or antagonism, often a result of the infection itself.