Ampicillin. Polarised light micrograph of crystals of the antibiotic drug ampicillin. This drug is a penicillin type of antibiotic, produced semi- synthetically, and used to treat infections by bacteria. Ampicillin is used commonly to treat cystitis, bronchitis, and ear infections. It is also a treatment for gonorrhoea, typhoid fever, and bacterial infections of the biliary (bile duct) system. Magnification: x25 at 35mm size.