Chapter 46 - A Guinea Pig Model of Acute Otitis Media

Abstract

This chapter presents a guinea pig model of acute otitis media (OM), in which a direct injection of bacteria is made into the middle-ear cavity through the tympanic membrane. In this model, the animals are anesthetized with intraperitoneal ketamine and xylazine. Complete anesthesia occurs within 10–20 minutes and lasts for at least 30 minutes. The animals should have Lacri-Tube applied to their eyes to prevent corneal ulcerations. Once sedated, an operating microscope and a pediatric speculum are used to examine the external ear canal, which is then cleaned with alcohol and dried with cotton. A blunt-tipped needle is then passed through the tympanic membrane and into the middle-ear cavity, to inject the appropriate medium. The animals are observed for a brief period of time until they recover from anesthesia. They are then transported to specialized housing facilities, which include negative-pressure cubicles and isolation from other animals. The middle ears are intermittently assessed otoscopically before the animals are sacrificed as per the protocol. The guinea pig model has several advantages. The animals are relatively inexpensive to purchase and house. In addition, although the inoculation and subsequent treatment of the animals is technically more difficult compared to larger animals such as the chinchilla and monkey, this is a straightforward procedure that may consistently and competently be performed in experienced hands.