COMMON MICROORGANISMS OF MEDICAL IMPORTANCE

 common microorganisms of medical importance and the disease they cause

Definitions of Terms  

Prokaryote-microorganisms a with simple cell structure

Eukaryote- microorganisms a with complex  cell structure.

ACTIVITY:

Define the following terms:

• Prokaryote
• Eukaryote

 Explain prokaryote and eukaryote

PROKARYOTES

• microorganisms a with simple cell structure
• They include;bacteria,rickettsiae,Mycoplasma,chlamydiae
• Genetic material is not well organised
• Have single piece on DNA in cytoplasm
• Cell has simple enzyme system
• They lack mitochondria
• Multiply by binary fission

EUKARYOTE

• microorganisms a with complex  cell structure.

·         Includes protozoa and fungi

·         Genetic material is differentiated in to chromosomes(DNA and RNA)

·         Cells is able to make its own energy

·         Posses complex enzyme system, mitochondria and other organelles.

·         Multiply by mitosis

 common groups of micro organisms of medical importance and the diseases they cause             

·         Bacteria-causes bacteraemia and septicaemia

·         Mycoplasma-Eye infection

·         Ricketssiae-Typhus fever

·         Protozoa-parasitic infection

·         fungi -Dermatophytis

·         viruses-viral infection

 Explain the characteristics of each bacteria above

BACTERIA

• Are unicellular
• Measures 0.1-10um long
• Have both DNA and RNA
• Multiplyby binary fission
• Classified according to staining reactions,cultural characteristics,Biochemical reactions,serologically.
• Sensitive to antibiotics
• Can be seen in light microscope

·         Sensitive to some antibiotics 

RICKETSSIAE-

• They multiply replication in living cells only
• Has both DNA and RNA
• Can be seen in light microscope

·         Sensitive to some antibiotics 

CHLAMYDIA

• Gram –ve
• Measures 250-500 nm
• Replicate in living cells
• Has both DNA and RNA

MYCOPLASMA

• Lack rigid cell wall
• Measures 0.1-2.0um in diameter
• Can be grown in ordinary media
• The smallest and simplest organism

FUNGI

• Are non photosynthetic
• Cells are relatively rigid
• Can be saprophytic or parasitic
• Are eukaryotic cells
• Multiply by budding
• Are dimorphic

VIRUSES

• Have either DNA or RNA
• Multiply by replication
• Are intracellular
• Measures 20-300nm(0.02-0.3um)
• The infective subatance is known as virion
• Can be seen by electron microscope only
• Can grow only within living cell
• Have cell wall known as capsid

Explain the basic features of bacteria cell (drawing)

BACTERIA CELL STRUCTURE

Bacterial cell consists of the following parts

• NUCLEUS-A structure in  the cell which controls the activity and functions of the cell.It consists of DNA and RNA
• CYTOPLASM-A fluid substance in a bacterial cell.

It suspends the cell organelles.

• CYTOPLASMIC MEMBRANES-Encloses the cytoplam.Its involved in selective permeability and transprt of nutrients.The membrane is permeable ie allows materials to pass in and out of the cell.e.g nutrients.
• MESOSOMES-Are specialized invaginations on the cell memebrane involved in cell division.
• FLAGELLA-Are thread like structures protein in nature used by bacteria for locomation.
• PILLI(FIMBRIAE)-Are protein like structures finer in nature used by the bactreria for attachment to the host and in transfer of genetic materials from donor to recipient.Are shorter than flagella
• CAPSULE-A thick polysaccharide substance produced by the bacteria.It Surrounds the cell wall af a bacteria.It protects the bacteria from adverse conditions.it contributes to the invasiveness of a bacteria.
• CELL WALL-This is the structure that encloses the whole bacteria cell.It contains high concentrations of inorganic ions.The cell wall is strong to prevent fluid from being drawn into it.The cell wall gives the basis of classifying bacteria into Gram positive and Gram negative.

DRAWING

 List the morphology of bacteria

a)Cocci-diplococci-(occurs in pairs;e.g Neisseria gonorrhoeae, Neisseriae mennigitidis)

            -Staphylococci-(occurs in groups.e.g Staphylococci aureus)

            -Streptococci-(occurs in chains.Streptococcus pneumoniae)

            -Gaffkya-( occurs in 4 packets)

            -Sarcina-(occurs in 8 Packets)

b)Rods(Bacilli)-E.g Escherichia coli,bacillus anthracis

c)Comma shaped(vibrio’s)-are curved rods.E.g Vibrio cholera

d)Spirochaetes

e)Spirilla

           

 Describe the physiology of bacteria cell wall

The wall of bacterial has a strong wall composed of murein and mucopeptide(peptidoglycan).

Differences in bacterial cell wall  leads to differences in staining of bacteria.The cell wall is rigid, semi-permeable and maintains the shape of a bacteria.

Bacteria are classified into two major groups

GROUPS OF BACTERIA

• Gram positive
• Gram negative

GRAM POSITIVE BACTERIA

•      They retain the purple color of crystal violet stain after decolourization with acetone

.

GRAM POSITIVE  BACTERIA CELL WALL

•      The cell wall structure consists of

·         peptidoglycan layer(thick layer)

·         Techoic acid

·         Robitol phosphate

·         Glycerol phosphate

•      Peptidoglycan layer consists of

Ø  N-Acetyl glucosamine and N-Acetyl muramic Acid

Ø  Tetra peptide chains attached to N-Acetyl muramic acid

Ø  Peptide cross-bridge

Techoic acid contains major surface antigens of Gram positive species

GRAM NEGATIVE BACTEIA CELL WALL

•      They take up the red color of  the counter stain(neutral red/safranin) after decolourization with acetone

•      The wall consists of :-

Ø  Lipopolysaccharide layer

Ø  Outer membrane(thin layer)

Ø  Cytoplasmic membrane

 Importance of microorganisms 

·         Manufacture of  antibiotics e.g penicillin

·         Used as food eg. Mushrooms

·         Manufacture of biological weapon

·         Bio-degradation e.g plastic decomposition

:key points

Prokaryote-microorganisms a with simple cell structure

Eukaryote- microorganisms a with complex  cell structure.

BACTERIA

• Are unicellular
• Measures 0.1-10um long
• Have both DNA and RNA
• Multiplyby binary fission
• Classified according to staining reactions,cultural characteristics,Biochemical reactions,serologically.
• Sensitive to antibiotics
• Can be seen in light microscope

·         Sensitive to some antibiotics 

: List the morphology of bacteria

a)Cocci-diplococci-(occurs in pairs;e.g Neisseria gonorrhoeae, Neisseriae mennigitidis)

            -Staphylococci-(occurs in groups.e.g Staphylococci aureus)

            -Streptococci-(occurs in chains.Streptococcus pneumoniae)

            -Gaffkya-( occurs in 4 packets)

            -Sarcina-(occurs in 8 Packets)

b)Rods(Bacilli)-E.g Escherichia coli,bacillus anthracis

c)Comma shaped(vibrio’s)-are curved rods.E.g Vibrio cholera

d)Spirochaetes

e)Spirilla

Evaluation

1. Define
2. Prokaryote
3. Eukaryote
4. List 5 characteristics of bacteria
5. Mention 5 parts of a bacteria cell
6. Mention the morphology bacteria