18.01.1 Introduction to Bacteria

Bacteria are unicellular (one cell) micro-organisms that do not have a nucleus. The DNA information of bacteria is stored in a single chromosome. If the bacteria are spherical, they are called cocci, whereas if they are rod shaped, they are called bacilli. Each bacterium grows to a fixed size and then divides by binary fission to give two bacteria. Most bacteria are rendered harmless by the immune system, and this is one of the main functions of the immune system. The most common fatal bacterial infections are respiratory infections (e.g. pneumonia) and tuberculosis (TB).

Bacteria are separated into two groups by a stain developed by a person called Gram. These groups are Gram positive and Gram negative bacteria. Gram-positive microbials have a simple cell wall which is 50% peptidoglycan and 40-45% acidic polymer with a negative charge. Gram-negative microbials have a much more complex cell wall. Gram-positive microbials are much easier to treat than gram-negative microbials as they allow cell penetration by positively charged agents. Also, because of the petidoglycan structure of Gram-positive microbials, inhibitors of cell wall/peptidoglycan synthesis are more effective against Gram-positive than Gram-negative microbials.

Clinically significant Gram-positive bacteria include Staphylococci,which are associated with acne, and Streptococci, which can cause sore throat, middle ear infections, and bacterial pneumonia. Examples of pathogenic (disease-causing) Gram-negative bacteria include Neisseria meningitidis (meningitis), Neisseria gonorrhoea (gonorrhea), and Salmonella enteria (gastrointestinal upsets). Haemophilus influenzae, which causes bacterial meningitis and ear infections in children and pneumonia in adults, and is also Gram-negative.