Man and Microbes

Aims and Objectives

1. To know the different types of micro-organisms.
2. To understand their structural differences.
3. To understand that not all micro-organisms produce disease.

Introduction

Man is only one species in a world inhabited by many different flora and fauna. Like all other living organisms we inhabit an ecological niche in which we survive. Micro-organisms could be considered to be the greatest threat to our survival. In this course we will be looking at the balance which is maintained between those micro-organisms which cause infectious disease and ourselves. In this document we consider the important micro-organisms, the 'away team', and our host defences, 'the home team'.

THE AWAY TEAM

Micro-organisms are organisms which share the property of being sub-microscopic. They existed long before man and we have had to adapt to live in an environment where they are far more abundant. Many micro-organisms do not normally cause disease in man, existing in a state of either COMMENSALISM, where there is little or no benefit or harm to man, or in MUTUALISM, where there is some benefit gained by both partners. This non-harmful balance exists when the immune system works well, but these same organisms can cause infection when the latter fails. This changed property is shared by many other micro-organisms which can cause infectious disease in the immunocompetent individual, so-called PATHOGENS. These pathogens fall into five main groups:

• Viruses
• Bacteria
• Fungi
• Protozoa
• Helminths

In addition, by convention there are two further classes of small agents which are often included in the study of MICROBIOLOGY:

• Ticks and mites
• Mesozoa and leeches

As these latter organisms cause infestations rather than infectious disease they will not be further considered in this course.

Basic differences between different types of micro-organisms

The basic distinguishing features of the major classes of micro-organisms are in the following table.
Prokaryotic cells do not have a nucleus, have a cell wall, possess 70S ribosomes, no internal organelles, no cytoskeleton and have a non-"9+2" flagellar arrangement. Eukaryotic cells possess a nucleus, have 80S ribosomes, have internal organelles and a cytoskeleton, possess flagellae with a 9+2 arrangement if present, and may lack a cell wall.
Microbes and human disease
The normal result of an interaction between a micro-organism that is not a commensal and man is INFECTION. Infection is the invasion or colonisation of the body by pathogenic organisms. DISEASE results when this results in a change of the state of health. The manner by which the disease develops is called PATHOGENESIS.
source : http://microbiologybytes.com/iandi/1a.html