BACTERIABACTERIAAn OverviewAn Overview

Staphlococcus aureus and human white

blood cells

Bacteria are

single-celled,

microscopic,

prokaryotic organisms

that we rely on and fight on a daily basis

“On any possible, reasonable or fair criterion, bacteria are—and always have been—the dominant forms of life on Earth.” – Stephen Jay Gould, 1996

Basic Characteristics:

Prokaryotic- no true nucleus, no membrane-bound organelles – different from eukaryotes (which make up all multi-cellular organisms and lots of single-celled organisms, too)

Single-celled organisms

Cell walls contain a peptidoglycan – aka murien – a polymer of sugars and acids found only in bacteria that forms a meshlike layer protecting the cell membrane

Tiny - measured in units called micrometers (μm - 1 micrometer = 0.0001 cm)

Lack a true nucleus; instead, have a region called the ‘nucleoid region‘where DNA congregates

DNA is free floating (no membrane surrounding DNA)

May have additional DNA which is not associated with this nucleoid region (called a plasmid)

Other Characteristics:

Rapid growth and cell division (binary fission) under favorable conditions

Mutants that arise from bacteria can become extremely resilient organisms because bacteria can:

Grow and reproduce cells quickly

Adapt quickly to changing environments

Plasmids impart additional resistant characteristics to bacteria via cell-to-cell transfer of this extra DNA material

Capable of colonizing in almost any environment

The overall form of a basic bacterial cell is that of a complex cell envelope that encloses cell cytoplasm. Cell appendages from the envelope protrude into the environment surrounding the cell.

Parts of a bacterial cell:

Pili: hair-like appendages used for pulling bacteria along surfaces or to exchange genetic information (plasmids) – sex pili

Fimbriae: filamentous protein outgrowths from cell envelope used to adhere to one another and to other cells

Capsule: Attachment to surfaces; protection against phagocytic engulfment, occasionally killing or digestion; reserve of nutrients or protection against desiccation

Cell wall: found on all bacteria – can be thick or thin – thick = Gram +ve, thin = Gram –ve due to response to Gram stain

Outer membrane and Plasma membrane : Permeability barrier; transport of nutrients and wastes; energy generation; location of numerous enzyme systems - outer membrane in Gram –ve species only

Cytoplasm: aqueous solution that bathes and surrounds everything inside the cell

Nucleoid region: DNA gathers here

Plasmids: DNA that can be copied and passed to other bacteria without going through reproduction

Ribosomes: Protein synthesis

Flagellum: long, whip-like appendage used for locomotion

Bacteria are one of the three domains – we further classify bacteria into phyla, class, order, family, genus, species as best we can, based on many different characteristics. We will cover the basic characteristics useful in classifying pathogenic bacteria.

Classifying Bacteria

Most microbiologists classify bacteria according to a phylogenetic classification system based on Bergey's Manual of Systematic Bacteriology (Bergey's Manual). The Bergey's Manual is a guide to distinguishing bacterial species based on phenotypic differences. For our purpose, and for simplicity's sake, we will use a more basic classification approach.

We can classify bacteria according to:

ShapeCell wall structure and the Gram StainCellular respiration

Public Health and Doctors also use Growth Media as an indicator

A couple of other criteria for classification:Forming endosporesMycolic acids

SHAPE

Cocci: spherical shape

Bacillus: rod shape

Spirochetes: spiral shape

3 general shapes:

GRAM STAINS

CAPSULES

USE OF OXYGEN (RESPIRATION)

PUTTING IT ALL TOGETHER - CLASSIFYING

Domain: BacteriaKingdom: BacteriaPhylum: ProteobacteriaClass: Gamma ProteobacteriaOrder: EnterobacterialesFamily: EnterobacteriaceaeGenus: EscherichiaSpecies: Escherichia coli (E. coli)

E. coli in intestine of a human

SEROTYPES

Try to match the following by using your new classification skills:

http://en.wikipedia.org/wiki/File:Conjugation.svg