Ampicillin
Ampicillin is an antibiotic belonging to the Penicillin family. It's used largely to treat uncomplicated but serious infections including meningitis and gonorrhea, among others.
Ampicillin works like most penicillins, by preventing bacteria from forming a cell wall, this means they can no longer survive and do not multiply any further, thus killing any infection.
[1] ampicillin, Omnipen, Polycillin, Principen. 2009. http://www.medicinenet.com/ampicillin/article.htm