Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

The problem with gram-negative bacteria

Melissa Kaplan, 2000

Reptile bites are often more difficult to resolve than herp herp keepers and their physicans realize because of the presence of gram-negative as well as gram-positive bacteria in the reptile's mouth, which then gets transfered into the bite wound.

The distinctive feature of gram-negative bacteria is the presence of a double membrane surrounding each bacterial cell. Although all bacteria have an inner cell membrane, gram-negative bacteria have a unique outer membrane. This outer membrane excludes certain drugs and antibiotics from penetrating the cell, partially accounting for why gram-negative bacteria are generally more resistant to antibiotics than are gram-positive bacteria.

Some Examples Of Gram-Negative Bacilli
Bartonella, Brucella, Campylobacter, Enterobacter, Escherichia, Francisella, Hemophilus, Klebsiella, Morganella, Proteus, Providencia, Pseudomonas, Salmonella, Serratia, Shigella, Vibrio, and Yersinia.

The outer membrane of gram-negative bacteria is rich in a molecule called lipopolysaccharide. If gram-negative bacteria enter the bloodstream, lipopolysaccharide can trigger a cascade of events, including high fever and a drop in blood pressure. For this reason, lipopolysaccharide is often referred to as an endotoxin.

Gram-negative bacteria have a great facility for exchanging genetic material (DNA) among strains of the same species and even among different species.

This means that if a gram-negative bacterium either undergoes a genetic change (mutation) or acquires genetic material that confers resistance to an antibiotic, the bacterium may later share its DNA with another strain of bacteria and the second strain can become resistant as well.

Source: The Merck Manual: Home Edition. Section 17, Chapter 177: Bacillary Infections (online version).