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Microbiology. Review. 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.

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introduction to microbiology
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

important figure in microbiology
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
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
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
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
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.

exponential growth
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
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


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
Relationship between living organisms







classification of bacteria on the basis of cell shape
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.


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


Bacillihave ability to formspores. 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.


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


are very simple, eukaryotic, “plantlike” structures

do not contain chlorophyll—can not carry photosynthesis & produce their own food.

They are saprophytesthat obtain their nutrition from dead and decaying organic material.

Fungi are the scavengers of the microbes.


Yeasts-are the unicellular forms of fungi

Moldsare 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
Helminths (Parasitic Worms)

Multicellular, usually macroscopic

Produce infestation in both humans and animals (fecal)

Can be prevented by cleanliness

Treated with antihelminthic drugs


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
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.


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
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 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


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.

classification of viruses
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
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
DNA viruses

Poxivirusgroup (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


Chicken pox

Adenovirus group (DNA)


Papovirusgroup (DNA)

Wart virus

aids virus retrovirus
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.