Finally, it should not be forgotten that most of the spectacular therapeutic triumphs have been achieved in the treatment of bacterial disease. Those numerous infections caused by viruses, protozoa, helminths, and fungi are, with some notable exceptions, less amenable to chemotherapy. Indeed some non-bacterial infections are treatable only by toxic agents of restricted potency, and a few lie beyond the scope of systemic therapy altogether. Enzyme Bacterial enzymes which can breakdown antibiotic molecules rendering them inactive is a principal mechanism of resistance. This resistance can be overcome by providing an inhibitor to the degrading enzyme in combination with the antibiotic.
Some bacteria are always resistant to certain antibiotics.
Diagnosis of an infection There are many clinical and laboratory parameters which are frequently assumed to imply the presence of an infection but which may in fact have non-infective causes. It is important therefore to have criteria established for the diagnosis of an infection so as to give a more rational basis for antibiotic use. For example, once an accurate history and physical examination have been conducted, it is possible to arrive at a provisional diagnosis of infection and antibiotic therapy may need to be commenced if the situation is life-threatening. However, since the diagnosis is provisional, every attempt must be made to take appropriate samples for laboratory investigation prior to beginning antibiotic therapy in order to establish the diagnosis with greater certainty. From the discussion so far, it is clear that one of the reasons for a presumed failure of antibiotic therapy is in fact a wrong diagnosis.