<prompt> Undulant fever is caused bySalmonella typhiStaphylococcus aureusBrucella melitensisCoxiella burnetti  <response>: Acute brucellosis is mostly due to B.melitensis. It is usually known as undulent fever, but this is misleading as only some cases show the undulent pattern. It is associated with prolonged bacteremia and irregular fever. Ref: Textbook of microbiology; Ananthanarayan and panikers; 10th edition; Pg:347 