introduction

Introduction

Medical microbiology: the field of microbiology that deal with study of pathogenic microorganisms and their interactions with human as causative agents of infectious diseases, with the prevention, diagnosis and treatment of these diseases.
It covers the branches of bacteriology, virology, mycology, parasitology and immunology.
Microorganisms/microbes: are microscopic living organisms which are very diverse and invisible by naked eye. They can be found in nearly every environment. The life in our planet is impossible without microbes due to their important role in generation of energy.

Types of microbial pathogens :
The pathogenic organisms of infectious diseases can be classified into four major groups of organisms : viruses, bacteria , fungi and parasites. Differences between these groups are listed in table number (1).
Normal microbial flora: are permanent residents of certain body sites, especially skin, mouth, nose, colon and vagina, without causing any disease.
It includes various non-pathogenic bacteria and yeasts, while all viruses and most parasites are usually not considered as members of normal flora, although they present in asymptomatic individuals.
The members of normal flora vary in both number and kind from one site to another; although it is extensively populates many areas in the body, the internal organs are sterile.
Normal flora should be differentiated from carrier state and colonization: