monera kingdom

Dentistry college - first class
Medical biology- Lec.2
Lecturer – Dr. Hanan S.
5- Kingdom Monera
Members of the kingdom Monera are prokaryotic ,microscopic organisms that include bacteria and cyanobacteria ( blue – green algae or blue- green bacteria , it’s name came from the color of bacteria , they obtain their energy through photosynthesis ). Prokaryotes lack a nucleus , and they have no organelles except ribosomes. The genetic material exists as a single double-stranded DNA in a nuclear region, or nucleoid. Members of the kingdom multiply by an asexual process called binary fission . The name of bacteria was derived from the Greek "bakt rion" , meaning “small staff” , are large group of unicellular microorganism , microscopic in size typically a few micrometers varies between 0.5 – 5 ?m in length and 0.2 - 2 ?m in width, have many different shapes and widespread on earth .












Fig. typical prokaryotic cell structure

Morphology of bacteria
Morphology of bacterial cell are not always constant on contrary to higher organisms because it affected by many factors such as composition of media , temperature of incubation and pH values etc., so, the description of bacteria usually restricted to young actively growing cultures under the optimum conditions of growth but old cultures might show diverted characters of the organism.

Viewed under the light microscope , most bacteria appear in variations of four different shapes :

1- Spherical bacteria (cocci)
Cocci (coccus) are usually round but they may be oval elongated have several groups arranged according to the manner in which the resulting cells attaches together after division such as cluster for example Staphylococcus aureus.









2 - Rod shape (Bacilli)
The shape of cells like rod or bacilli on the base of cell arrangement for example streptobacilli like Bcillus anthrax






3- Spirilla
it’s a corkscrew shape with rigid cell wall and hair like projections called flagellum that help in movement of bacteria ex. Treponema pallidium.



4 - Filamentous bacteria
The body of this type consist of mycelium which resembles a mass of branched thin non – septate hyphae similar to that of fungi such as Actinomycetes .








Koch s postulates
Bacteria were first observed by Antoine Van Leeuwenhoek in 1676. using a single- lens microscope of his own design , he called them "animalcules". Louis Pasteur demonstrated in 1859 the fermentation process caused by growth of microorganism and this growth is not due to spontaneous generation . Robert Koch , was proved the germ theory by procedures used by Koch came to be known as Koch s postulates (Fig.) . They provided a set of principles whereby other microorganisms could be related to other diseases :
1- M.O must be present in every case of the disease but absent from healthy organisms.
2- The suspected M.O must be isolated and grown in a pure culture.
3- The same disease must result when the isolated M.O is inoculated into a healthy host.
4- The same M.O must be isolated again from the diseased host.





















Fig. The steps of Koch s postulates used to relate a specific microorganism to a specific disease. (a) Microorganisms are observed in a sick animal and (b) cultivated in the lab. (c) The organisms are injected into a healthy animal, and (d) the animal develops the disease then reisolated in the lab.




Mechanisms of bacterial pathogen
The steps when the pathogenic agents try to infect the host :
1-Adherence
2- Colonization
3- Evasion of host defenses
4- Causing disease
5- Exit from the host

Determinants of virulence
Pathogenic bacteria are able to produce disease because they possess certain structural biochemical or genetic traits that render them pathogenic or virulent such as :
1-flagella and pilli
2- capsule
3- enzymes such as hyaluronidase , streptokinase
4- toxin ( exotoxin & endotoxin)
5- lipopolysaccharid in outer membrane of G-ve bacteria .

Some of important definitions in medical microbiology
Pathogen : is a microorganism that is able to cause disease .
Pathogenicity : is the ability of M.O to produce disease in a host organism.
Virulence : refers to the degree of pathogenicity of the microbe.
Infection : The invasion of a host by M.O with subsequent establishment and multiplication of the agent ,an infection may or may not lead to cause disease .

Activities of bacteria
1- Bacteria play many beneficial roles in the environment , for example, some species of bacteria live on the roots of plants and “fix” nitrogen from the air into organic compounds that are then available to plants.
2- Other bacteria are responsible for the decomposing that occurs in foods , plants and the other dead bodies in the environment , these bacteria recycle the essential elements in the organic matter.
3- In the food industry, bacteria are used to prepare many products, such as cheeses, fermented dairy products , in other industries, bacteria are used to produce antibiotics, chemicals, dyes, numerous vitamins and enzymes, and a number of insecticides , also they are used in genetic engineering to synthesize certain pharmaceutical products that cannot be produced otherwise.
4- In the human intestine, bacteria synthesize several vitamins not widely obtained in food, especially vitamin K. Bacteria also often break down certain foods that otherwise escape digestion in the body.
5- Unfortunately, many bacteria are pathogenic; that is, they cause human disease such as tuberculosis, gonorrhea, syphilis, food poisoning, plague, tetanus, typhoid fever, and most pneumonias are due to bacteria. In many cases, the bacteria produce powerful toxins that interfere with normal body functions and bring about disease, the botulism (food poisoning) and tetanus toxins are examples.

**Atypical bacterial types
There are some small forms of bacteria that can be seen only with the electron microscope were Rickettsiae , Chlamydiae , Mycoplasma .
The Rickettsiae are intermediate forms between bacteria and viruses , they resemble some of bacteria in morphology but differing only in being of much smaller size but they are larger than viruses , rod – shaped forms have a diameter ranging from 0.2-0.5µ , others are spherical . Rickettsiae are similar to the bacteria in that they have a rigid cell wall and contain both genetic material DNA , RNA . Rickettsiae like viruses intracellular parasites in arthropods carry such as fleas ,mites and ticks . Rickettsiae causes typhus fever , the disease is transmitted by lice , fleas, ticks and mites , when an insect carrying the R. organism bite a man , it leaves some of the parasite cells in place of bite , scratching the affected part helps entrance of pathogen through a wound ,the pathogen will quickly find its way to the blood circulation .










Fig. Rickettsiae


Structure of bacterial cell
Bacterial cell have an essential structural components : cell wall, cytoplasm membrane , intra cytoplasm structure and cell surface appendages ( capsule , flagella , fimbriae , spore ) . The biochemical composition of these structures are macromolecules are arranged or sequenced in primary – structure of molecule in which the subunits are put together such as :

DNA , RNA -------- Nucléotides , Protein --------- amino acid
fatty acid -------- Phospholipids , sugars --------- Polysaccharide






A- Cell wall
The cell wall of a bacterium is an essential structure that protects the cell protoplast from osmotic lyses . The cell wall of bacteria consists of polymer of two sugar derivatives N- acetylglucosamine and N- acetylmuramic acid cross linked by short chains of amino acids (peptide), this molecule is a type of peptidoglycan called murein .







Functions of bacterial cell wall
1-It maintains the shape of bacterial cell.
2- It protects the bacterial cell from osmotic lyses .
3-It is responsible for endotoxic activity of G- ve bacteria and Gram
stain reaction.
4- It plays a role in cell division .


Example on cell wall deficient bacteria

a- Mycoplasma
This is naturally deficient in cell wall so , Mycoplasma is pleomorphic shape and not affected by penicillin treatment .

b- L- forms
Some of bacteria under certain condition are fail in synthesis of cell wall when the cells is subjected to penicillin drug or lysozymes.