Pathogenic Microbiology

Briefly, the goal of this book is to provide an introduction to common pathogenic organisms, the diseases they cause, and how they can be identified in clinical microbiology labs. As is common in most other texts, the pathogens surveyed will be discussed in groups according to common characteristics. This is intended for those curious to discover more about the microbes we live with. As such, the information is presented as simply as it can.

The first part of this book will focus on the basics of microbiology as they relate to identifying microbes. Next, common biochemical tests and media used in clinical micro labs will be presented. The remanding portion will be dedicated the classification of pathogen microbes and their diseases. Please contribute as much as possible seeing as this is still a work in progress. Thanks and have fun learning!

Before we can talk about pathogenic microbes, we must first have some background with basic microbiology! While we could talk about the history and the numerous scientists that helped advance the field, that is not the focus of this text.

To start off our journey with microbes, one first must realize that microbes are as different between each other as you and everyone else! They have different characteristics that can be used to distinguish between one another. Whether we are looking at an individual cell under a microscope or the colonies they form on media, there are numerous ways to classify the microbes around us. So we will cover some of the basics of cellular and colony morphology first!

The cellular morphology that are seen with all microbes fall within one of three basic shapes. They can be spherical or cocci, rods or bacilli, & spiral shaped or helicoidal as seen below! All bacteria have some deviation of these three basic shapes.

But that's not all! Some bacteria will actually form chains or clusters under a microscope, thus adding a further step in differentiating one species from another. For example, both genus Staphylcoccus andStreptococcus have microbes that are spherical in shape (as the name coccus implies). However, staph species form grape like clusters whereas strep species form chains of cocci.

As we start to cover the different genera of pathogenic organisms, you'll see the variety of shapes that can be encountered with microbes.

What is a colony? Good question! It is a cluster of identical cells that can be seen macroscopically as one mass. They result from an individual cell multiplying and dividing over and over again. In microbiology labs, bacteria are "inoculated", or placed, onto specialized nutrient surfaces called media to grow on. All of the individual cells have the potential to form an individual colony on a given media.

Depending on the species of microbe, these colonies can have all sorts of morphological characteristics that can all be used to tell them apart. These can include size, shape, elevation, color, and even smell (although this is "technically" not a morphological characteristic). Just compare the stark difference between colonies formed by S. aureus, E. coli, and Serratia Marcescens

Though the breath of diversity for colony morphology is large, it cannot be used alone for genus and species identification. Experienced clinical microbiologist could probably tell you both the genus and species of common microbes just by looking at it. However, they always confirm their results by running some sort of biochemical tests or kits.

Most pictures of microorganisms seen under a microscope has been stained in some way in order to view them. This is because the individual cells are colorless to begin with and may be impossible to see without it.

The basic principle for any stain involves the overall negative net charge surround the membrane of a bacteria. Taking advantage of this net negative charge, we can add dyes thaNow, the type of stain that one would perform on a slide of bacteria would depend on the purpose. If you just wanted to visual the cells, a simple stain would suffice. Besides showing the shape of the bacteria, this type of stain does not provide us with any additional information.

As such, a variety of different staining procedures have been developed to differentiate bacteria based on the characteristics of their cell wall. One of the most important stain used for classification of bacteria is called the Gram Stain. This stains separates bacteria as Gram + or Gram - based on the amount of peptidoglycan in their cell wall. Simply put, a Gram + bacteria has a thicker peptidoglycan layer. Gram - organisms have a thin peptidoglycan layer and also contains a lipopolysaccharide (LPS) layer. It should be noted, however, that some species can have Gram variable results.

[Note to self or others, need to place redirection links to other wikipages if possible for bolded terms. Most of the topics described so far are just very brief overviews intended for an introduction and further information could be found other pages. Still need to reedit Staining section, it is not finished]