BACTERIA

The Kingdom Monera (Whittaker 1969) includes both the Archaebacteria and Eubacteria (“true bacteria”) (Keeton and Gould 1993b). Of these, only the Eubacteria are consid­ered of importance in the study of wildlife dis­eases, and the term “bacteria” generally will be used for this group.

Bacteria are ancient organisms (Keeton and Gould 1993a, 1993b), with evidence for their presence in the Precambrian Period. Collectively, they occur in a broader variety of habitats and lifestyles than do eukaryotic organisms (Keeton and Gould 1993a). Historically, there has been little consensus on eubacterial evolution. Bac­teria were among the first life forms, and one form recently was proposed as the last universal common ancestor (Ciccarelli et al. 2006). Clas­sification now is largely phylogenetically based, and molecular methods are used to establish these relationships (Grimont 1999). Currently, about 35 major groups are recognized among the bacteria, of which about 17 have species of specific interest to the study of wildlife diseases (App. 1: Table 7). However, these phylogenetic relationships can become complicated due to the common mobility of bacterial genes among unrelated groups (Narra and Ochman 2006, Bohannon 2008, Sheppard et al.

Bacterial Identification

Identification of bacteria is based on their meta­bolic activities, as determined by the enzymes they carry, as well as their cell wall characteristics and internal biochemistry. Typically, bacterial samples from a diseased host or other source are collected first; the suspect bacteria then are cultivated and isolated on bacteriological media (Miller and Holmes 1999, Reisner et al. 1999). The gram stain, based on differential presence of lipopolysaccharides in the cell wall, is probably the most important of many stains used in bacterial identification (Chapin and Murray 1999). In addition, bacterial identifica­tion typically involves establishing the presence of key enzymes such as those used to catabo- lize sugars such as glucose, lactose, or sucrose; there are a wide variety of manual and auto­mated systems for establishing profiles for key enzymes of bacteria (Miller and O’Hara 1999). Also, the presence of a bacterial agent may be determined by amplifying small remnants of its DNA through PCR until the DNA can be detected and identified (App. 2).

The species and serological group (sero­type) to which a bacterium belongs often can be determined from specific serological tests, including immunof luorescence, immuno­peroxidase, enzyme-linked immunosorbent assays (ELISA), histochemistry, and immu­nodiffusion tests (Gough 1997, Mahony and Chernesky 1999); some of the more commonly used ones are as described in Appendix 2. An increasing number of molecular techniques have emerged in recent years (Gough 1997), including the polymerase chain reaction (PCR), DNA sequencing, molecular hybridization, and restriction fragment length polymorphism; a few also are summarized in Appendix 2.

In addition to isolating and identifying bac­teria associated with a disease process, past bacterial infections also may be ascertained by sampling hosts for the presence of antibodies to specific bacterial agents by the use of a number of serological tests, as outlined in Appendix 2.