Ans. is b, i.e. Culture on McCoy cellsRef: Harrion 18th/ed, p1426Patient is complaining of abdominal pain and vaginal discharge. On examination, cervicitis and mucopurulent discharge is seen -- which indicates she is having PID. The presence of pus cells in absence of organism indicates chlamydial infection (most common STD today). It is an intracellular organism that grows only on McCoy or HeLa cell cultures. It cannot be grown on other media and hence, often goes unnoticed, later leading to infertility.Culture in Me Coy cells is 100% specific for chlamydia but is inexpensive, technically difficult and takes 3-7 days to obtain the result.