Antibiotics ,the substances used to inhibit or destroy other micro-organims are either narrow-spectrum or broad-spectrum.Here the term ‘spectrum‘ refers to the full range of micro-organisms attacked by an antibiotic.For ex- Penicillin has a narrow spectrum used in case of pneumonia,bronchitis while chloramphenicol which is an borad-spectrum can be used in typhoid,dysentery,meningitis,pneumonia etc.