Introduction to bacteria

Bacteria singular: bacterium / plural: bacteria1. Bacteria are classified into two kingdoms: Eubacteria (true bacteria) and Archaebacteria (Ancient Bacteria).2. BACTERIA are microscopic Prokaryotes. (“before nucleus”)3. Adapted to living in all environments (even some extreme) – they exist EVERYWHEREI. Bacterial Structure

1. Outside the plasma membrane of most cells is a rigid cell wall that keeps the cell from bursting or collapsing due to osmotic changes by peptidoglycan, a complex molecule containing a unique amino disaccharide and peptide fragments. a. The cell wall may be surrounded by an organized capsule called a glycocalyx and/or by a loose gelatinous sheath called a slime layer. b. In parasitic forms, these outer coverings protect the cell from host defenses.2. Some prokaryotes move by means of flagella, capable of 360o rotation which causes the cell to spin and move forward.3. Many prokaryotes adhere to surfaces by means of fimbriae, hairlike filaments extending from the surface. (gonorrhea, tooth decay)

4. Prokaryotic cells lack the membranous organelles of eukaryotic cells.

5. Various metabolic pathways are located on the plasma membrane.

6. A nucleoid is a dense area in prokaryotes where the chromosome is located; it is a single circular strand of DNA.

7. Plasmids are accessory rings of DNA found in some prokaryotes; they can be extracted and used as vectors to carry foreign DNA into bacteria during genetic engineering procedures.

8. Protein synthesis in prokaryotic cells is carried out by thousands of ribosomes, which are smaller than eukaryotic ribosomes.

Lecture 02 - Prokaryotic Cells

II. Reproduction in Prokaryotes

Binary fission is the splitting of a parent cell into two daughter cells; it is asexual reproduction in prokaryotes.In bacteria, genetic recombination can occur in three ways.Conjugation occurs when a bacterium passes DNA to a second bacterium through a tube (sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same or closely related species.Transformation involves bacteria taking up free pieces of DNA secreted by live bacteria or released by dead bacteria.In transduction, bacteriophages transfer portions of bacterial DNA from one cell to another.Plasmids can carry genes for resistance to antibiotics and transfer them between bacteria by any of these processes.Some bacteria form resistant endospores in response to unfavorable environmental conditions.III. Prokaryotic Nutrition

1. Bacteria differ in their need for, and tolerance of, oxygen (O2).a. Obligate anaerobes are unable to grow in the presence of O2; this includes anaerobic bacteria that cause botulism, gas gangrene, and tetanus.

b. Facultative anaerobes are able to grow in either the presence or absence of gaseous O2.

c. Aerobic organisms (including animals and most prokaryotes) require a constant supply of O2 to carry out cellular respiration.

2. Autotrophic Prokaryotes

a. Photoautotrophs are photosynthetic and use light energy to assemble the organic molecules they require.

b. Chemoautotrophs make organic molecules by using energy derived from the oxidation of inorganic compounds in the environment. (methanogens)

3. Heterotrophic Prokaryotes

a. Most free‑living bacteria are chemoheterotrophs that take in pre-formed organic nutrients.

b. As aerobic saprotrophs, there is probably no natural organic molecule that cannot be broken down by some prokaryotic species.

c. Detritivores (saprophytic bacteria) are critical in recycling materials in the ecosystem; they decompose dead organic matter and make it available to photosynthesizers.

* Prokaryotes produce chemicals including ethyl alcohol, acetic acid, butyl alcohol, and acetones.

* Prokaryotic action produces butter, cheese, sauerkraut, rubber, cotton, silk, coffee and cocoa.

Antibiotics are produced by some bacteria.

4. Some chemoheterotrophs are symbiotic, forming relationships with members of other species

Mutualistic nitrogen‑fixing Rhizobium bacteria live on roots of soybean, clover, and alfalfa where they reduce N2 to ammonia

Mutualistic bacteria that live in the intestines of humans benefit from undigested material and

IV. Bacterial Diseases in Humans

Microbes that cause disease are called pathogens.

Pathogens may be able to produce a toxin, and or adhere to surfaces and sometimes invade organs or cells.

-Toxins are small organic molecules, or small pieces of protein or parts of the bacterial cell wall, that are released when bacteria die.

-In almost all cases, the growth of the bacteria does not cause disease but instead the toxins they release cause the disease. Example: Clostridium tetani, the causative agent of tetanus.

capsules (slime layers) - help evade immune system and adhere to surfaces

V BACTERIA CLASSIFICATION

1. The Gram stain procedure (developed in the late 1880s by Hans Christian Gram) differentiates bacteria.

a. Gram‑positive bacteria stain purple, whereas Gram‑negative bacteria stain pink.

b. This difference is dependent on the thick or thin (respectively) peptidoglycan cell wall.

2. Bacteria have three basic shapes.

a. Coccus bacteria are spherical.

b. A bacillus is an elongated or rod‑shaped bacteria.

c. A spirillum is spiral‑shaped.

A. Bacillus

B. Streptococcus

C. Staphylococcus

D. Diplococcus

E. Spirllum

F. Vibrio

Gram Negative -- light red or pink color Gram Positive -- dark purple

Escherichia coli, Salmonella typhi, Staphylococcus epidermidis, Streptococcus pyogenes,

Vibrio cholerae and Bordetella pertussis and Clostridium tetani

Not all bacteria can be stained by Gram's method,

the best-known exception belong to the genus

Mycobacterium which have waxy cell walls.

How Gram Stains are Made

The Usual Suspects

Antibiotics and Antiseptics

Joseph Lister created the first antiseptic, an acid to spray on tables and instruments before surgery (1860)

The Discovery of Penicillin

1. Alexander Fleming noticed mold growing on petri dishes

2. Bacteria did not grow where the mold was growing

3. He isolated the chemical from the bold that was killing the bactera

4. Howard Flory built upon his work and stabilized the chemical

5. Both Fleming and Flory received a Nobel Prize in 1945

Table 1 Major Bacterial Pathogens

Table 1 is divided into organisms that are readily Gram-stained and those that are not. The readily stained organisms fall into four categories: gram-positive cocci, gram-negative cocci, gram-positive rods, and gram-negative rods. Because there are so many kinds of gram-negative rods, they have been divided into three groups:

Organisms associated with the enteric tract.

Organisms associated with the respiratory tract.

Organisms from animal sources (zoonotic bacteria).

For ease of understanding, the organisms associated with the enteric tract are further subdivided into three groups: (1) pathogens both inside and outside the enteric tract, (2) pathogens inside the enteric tract, and (3) pathogens outside the enteric tract.

As is true of any classification dealing with biologic entities, this one is not entirely precise. For example, Campylobacter causes enteric tract disease but frequently has an animal source. Nevertheless, despite some uncertainties, subdivision of the large number of gram-negative rods into these functional categories should be helpful to the reader.

The organisms that are not readily Gram-stained fall into six major categories: Mycobacterium species, which are acid-fast rods; Mycoplasma species, which have no cell wall and so do not stain with Gram stain; Treponema and Leptospira species, which are spirochetes too thin to be seen when stained with Gram stain; and Chlamydia and Rickettsia species, which stain well with Giemsa stain or other special stains but poorly with Gram stain. Chlamydia and Rickettsia species are obligate intracellular parasites, whereas members of the other four genera are not.

Table 2 presents the 10 most common "notifiable" bacterial diseases in the United States for 2007 as compiled by the Centers for Disease Control and Prevention. Note that only notifiable diseases are included and that certain common conditions such as streptococcal pharyngitis and impetigo are not included. Two sexually transmitted diseases, chlamydial infection and gonorrhea, are by far the most common diseases listed, followed by salmonellosis, syphilis, and Lyme disease in the top five.

Table 2 The 10 Most Common Notifiable Bacterial Diseases in the United States in 2007

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