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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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
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
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
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.
Cold/below freezing retards growth.
Heat (boiling) kills most non-spore forming bacteria.
Light direct rays of sun & UV light are harmful to 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
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.
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
Different stains give different colors to various types of cell walls.
cell wall is not as thick as in gram positive bacteria
it allows to secrete toxins
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
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
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
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.
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.
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.
on the basis of:
nucleic acid they contain
the size, shape and structure of the virus
the tissue the infect
generally more resistant to some disinfectants than most bacteria.
most are susceptible to heat, except hepatitis virus
not affected by antibiotics
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.
Adenovirus group (DNA)
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.