MicrobiologyReview

Introduction to Microbiology

Microbiology: The study of microscopic life (>1mm)

Microbes (Micro-organisms): simple life form, usually single celled, that can not be seen with the naked eye.

The term microbiology includes the study of all microbes, including bacteria, fungi, algae, parasites, helminths & viruses

Cell Types/Structures

Important figure in Microbiology

Louis Pasteur (1822 – 1895) -Developed the germ theory of disease in 1798, Pasteurization technique

Anton van Leeuwenhoek – “father of microbiology” – first microbiologst – invented first microscope

Lynn Margulis – introduced and substantiated the theory of endosymbiotic evolution

Favorable environment for bacterial/microbial growth

Microbes need certain conditions to survive. These include: Food, moisture, favorable temperature, proper gaseous

atmosphere, appropriate pH and salt concentration

If these conditions are not favorable some bacteria will form spores to wait the return of favorable growth conditions.

Unlike other living beings some bacteria can live & grow without the presence of atmospheric O2

The conditions which can inhibit or limit bacterial growth

Lack of food Dryness—kills most bacteria but not spores Medium too high or too low in pH Antiseptics retard bacterial growth Disinfectants kill bacteria. Unfavorable temperature Cold/below freezing retards growth. Heat (boiling) kills most non-spore forming bacteria. Light direct rays of sun & UV light are harmful to bacteria.

Growth Requirements of Bacteria:

Bacteriologists grow bacteria by using nutrient agar, nutrient broth, gelatin, litmus milk & other media.

2. Food or energy sources a. Autotrophic —inorganic, nonpathogenic b. Heterotrophic —organic, pathogenic Parasites — utilize living organic matter Saprophytes — dead organic matter 3. Oxygen a. aerobic b. anaerobic c. micro-aerophilic

Growth & Reproduction

Under favorable conditions, bacteria reproduce by Binary fission —the cell divides in two halves after developing a transverse furrow in the cell wall around the bacteria.

In a period of 12 hours, one single bacteria may reproduce 16 million descendants to form bacterial colonies.

Bacterial reproduction

Exponential growth

Growth curve – figure 7.18 (page 210) As bacteria grow, they give off poisonous

wastes & enzymes –Toxins - which may cause disease or food spoilage

Overpopulation & accumulation of waste kill most bacteria

Irregular/complex habitats and biofilms give community stability and increase diversity

Study of special characteristics of the cell wall

Different stains give different colors to various types of cell walls.

Gram negative: cell wall is not as thick as in gram positive

bacteria it allows to secrete toxins Gram positive: cell wall is much thicker compared to the gram

negative bacteria it provides rigidity & strength to the organism

Spores

Toxins Endotoxins - remain within the cell produced by gram negative bacteria Signs/symptoms of endotoxins are produced

when the toxins enter the blood stream Exotoxins - toxins diffuse out of the cell wall produced by gram positive bacteria most potent toxins Responsible for tetanus, diphtheria, gas

gangrene

Relationship between living organisms

Independence Symbiosis Mutualism Commensalism Parasitism Antibiosis

Classification of bacteria on the basis of cell shape

i) Cocci =Spherical ii) Bacilli =Rod shaped iii) Spirilla=Spiral shaped , or curved Bacterial cells are often arranged into particular

patterns, because their cell walls remain attached to each other after cell division.

Locomotion Many bacteria have flagella Flagella propel the bacteria. Most spiral shaped bacteria are motile Sphere shaped cocci—non motile Many rod-shaped bacteria are motile, e.g. Typhoid

bacillus— has many flagella

Endospores Bacilli have ability to form spores. When spores develop

nothing can enter or leave the cell. This makes the bacteria very resistant to drying, temperature changes, & the action of stains & disinfectants. They become hard to kill—health hazard.

During spore stage bacterial cell is alive but inactive. Only bacilli (rod shaped) bacteria form spores. Spores present special problem in sterilization techniques. Killing of spores requires strict & longer sterilization

procedures For example, Bacillus anthracis, Clostridium species.

Bacteria

May be harmful or beneficial. Pathogenic—invade animal or plant tissue to

produce diseases. Non-pathogenic—perform useful functions decomposing refuse—improve fertility of soil curring of tobacco, tea & coffee making of yogurt, cheeses- acidophilus milk

Fungi

are very simple, eukaryotic, “plantlike” structures do not contain chlorophyll—can not carry

photosynthesis & produce their own food. They are saprophytes that obtain their nutrition from

dead and decaying organic material. Fungi are the scavengers of the microbes.

Fungi Yeasts-are the unicellular forms of fungi Molds are the multicellular, filamentous fungi—often found

on bread, cheese, and fruits Molds are of great importance- major source of antibiotics Both molds & yeasts have some harmful & some beneficial

members.

Yeasts are spherical or oval cells—microscopic Molds’ filaments are visible to naked eye. Rhizophus—black bread mold Penicillium—used to make penicillin

Helminths (Parasitic Worms)

Multicellular, usually macroscopic

Produce infestation in both humans and animals (fecal)

Can be prevented by cleanliness

Treated with antihelminthic drugs

Scolex (head) of a tape worm-Taenia saginata

Protozoa

microscopic, single celled animals - eukaryotes larger than fungi more complex & detailed internal structure many protozoa have cell organelles Responsible for diseases such as malaria, Chagas,

African sleeping sickness, Giardia

Giardia lamblia

is a parasite found in human intestine that causes dysentery.

most common intestinal parasite in USA causes traveler’s diarrhea. Due to cross contamination of drinking water &

sewage Diagnosed by cysts or trophozoite forms.

Viruses

smallest infections agents

intracellular parasites-can reproduce only in host cells can not carry on independent metabolism

viruses are not cellular – not autopoietic

consist only of a nucleic acid either DNA or RNA, surrounded by a protein coat.

Viruses continued the protein coat of the virus determines what type of

cells the virus can parasitize & acts to protect the nucleic acid inside

a virus that attacks the bacterial cells is known as a phage or bacteriophage.

a phage consists of a head made from a protein membrane with 20 facets (sides) surrounding either DNA or RNA

the tail combines a collar attached to a tail sheath.

HIV

HIV is carried in blood, semen, & body fluids.

usually fatal known to be dormant for years certain drug combinations slow the rate of

invasion of the White Blood cells by the virus.

cure is not yet on the horizon leading cause of death in young adults,

aged 25-44

Prions

Known as proteinaceous infectious particles non-immunogenic - they do not result in the

formation of antibodies – no evolved immune response

Prions contain nothing but proteins. No RNA or DNA

The known Prion diseases are all fatal and are referred to as spongiform encephalopathies—because they cause the brain to have holes like a sponge.

Mad cow disease is one example.

Prions

Classification of viruses

on the basis of: nucleic acid they contain the size, shape and structure of the virus the tissue the infect

Virus facts

generally more resistant to some disinfectants than most bacteria.

most are susceptible to heat, except hepatitis virus

not affected by antibiotics

DNA viruses

Poxivirus group (DNA) virus – pathogenic to skin small pox, cow pox

Herpes virus group (DNA) Latent infection may occur and lasts the life span of the host. Cold sores Shingles Chicken pox Adenovirus group (DNA) Conjunctivitis Papovirus group (DNA) Wart virus

Aids Virus (Retrovirus) Patients are prone to develop opportunistic

infections and diseases/disorders Incubation period (the period between becoming

infected and the actual development of the symptoms) from 6 months up to 10 years.

Sometimes a mild illness--flu like symptoms appears 7-14 days after infection

It is accepted that once infected with HIV, AIDS will develop at some time in the future in all cases.

At present there is no cure. Opportunistic infections associated with AIDS can be

treated.