Medical Microbiology

Transcription

1 Lecture 1 Dr. Ismail I. Daood Medical Microbiology A Glimpse of History : The concept that diseases are infectious and caused by unknown entities appeared in human history long before the discovery of the microbial world. Fracastora proposed "a germ theory of disease" in by Leeuwenhoek, people began to suspect that microorganisms might cause the disease. However, it was not easy to prove this. Because techniques were neither very sophisticated not well understood, scientists often produced conflicting results. Pasteure in 1794 protective vaccination (vacca = cow) work with cowpox by use living attenuated culture of pathogenic microbes against important infection like anthrax, M. tuberculosis (T.b), chicken cholera. Work Pasteur proof of the germ theory of disease. It was not until 1876 that Robert Koch offered convincing proof of germ theory of disease when he showed that Bacillus anthracis is the cause of anthrax, a serious and often fatal disease of human, sheep and other animals, with his microscope, he observed B. anthracis bacteria in the blood and spleen of dead sheep. He then inoculated mice with this infected sheep blood and was in addition he was able to grow the B. anthracis in pure culture and show that it caused anthrax when injected in to healthy mice. Microbiology and Medicine : Microbiology is the study of microorganisms, a large and divers group of microscopic that exist as single cell or cell clusters it also includes viruses which are microscopic but not - 1 -

2 cellular. Medical microbiology is the study of interactions between humans and the microorganisms which the coexist. Microbiology has also link with curative medicine, diagnosis, treatment of microbial diseases and concerned with a etiology (causation), pathogenesis (mechanism of attack on tissues). Laboratory diagnosis, treatment of infection in the individual and with epidemiology, control or prevention of infection in the community. It therefore, has also links with several other disciplines in to which the training of the doctor to form the medical curriculum e.g., pathology clinical medicine, surgery, pharmacology in therapeutics and preventive medicine. The changes that occur in the hosts tissues (patients) as the result of infection are often recognized by the pathologist or pathogenesis of particular pathogenic microorganisms this diagnostic by microbiologist in laboratory. e.g., Staphylococcus, Streptococcus, Pneumonia( Pneumococcal ), Tuberculosis. From up introduction microorganisms may be grouped according to: A. Nature interaction with humans : 1. Commercial organisms : The term "normal microbial flora " or non-pathogenic routinely colonize body surface without doing harm and are referred to as normal flora e.g., E. coli in intestinal tract, and Staphylococcus epidermidis on skin or on nose. 2. Pathogenic organisms : The pathogenesis of microorganisms infection includes initiation of the infectious process leading to development of sings and symptoms of disease characteristics of pathogens include transmissibility, adherence to host cell, invasion of cell and tissues, toxigenicity, and ability to evade the host s immune system and Damage the human (host) either by - 2 -

3 direct invasion and injury e.g., Shigella spp. Cause Shigellosis or by the production of harmful toxic products, e.g. Clostridium spp. Cause tetanus and Gasgangreen., Salmonella typhy Cause ( Salmonellosis ) 3. Opportunistic organisms : These usually found in the environment or as part of the normal flora, these are in normal individuals are harmless, but they may make or cause sever disease in immunocompromised patients or they pentrate a territory from which they are usually excluded as result. For example of trauma or surgery. e.g. Staph. epidermidis on skin, Neisseria spp. and Diphtheroids in nasopharrynx,salmonella and Shigella in gastrointestinal tract and rectum. 4. Zoonotic organisms : Some organisms are world wide distribution that infects a wide rang of animals and birds usually cause disease in human such as parasitizes,sporozoans and trematodes in vertebrates other than humans but may by acquired through contact with infected animals or animal products e.g., in malaria disease, by the bloodsucking bite of female Anopheles mosquitoes by Plasmodium malariae. in toxoplasmosis disease, by Toxoplasmosis gondii and in leishmaniasis infection by sand flies by Leishmania donavani. B. Pathogenic interaction with the humans : The pathogenic potential of many organisms is variable and influenced by both the properties of the microorganisms and the state of health of the human (host) depended on : 1. Host defenses and natural immunity : Before the a multi-component system of protective mechanisms that prevent entry of microorganisms in to normally sterile areas and limit the spread of those invaders that overcome the first line of defense. These - 3 -

4 mechanisms my by waked by a variety of insults including direct physical trauma, systemic disease, drugs, radiation, and toxins. If the human loses the ability to limit the injury and harm cause by microorganisms. 2. Microbial virulence : Microbial virulence is the ability of microorganism to cause disease. All the factors that contribute to microbial pathogenesis are known as virulence factors. Pathogenic bacteria may be have one or several virulence factors, but scientists can use virulence factors in application medicine as component vaccines based on the use of modified virulence factors that lack toxic effects but retain immunogenicity. Bacteriology : Classification of Microorganisms : Classification can be defined as arrangement of organisms into taxonomic groups on the basis of similarities or relationships. The majority of microorganisms may be classified in the following large biological groups as Prokaryotic and Eukaryotic which are different in characterize, size unicellular or multicellular etc..they group microbial world ed of : 1. Viruses 2. Mycoplasmas 3. Rikettsia 4. Bacteria 5. Mycoses (Fungi,Slime moulds ) 6. Parasites ( Protozoa ) 7. Algae Microbial world Prokaryotes Organisms (living) infectious agent (non-living) Bacteria Archaea viruses viroids prions Unicellular - 4 -

5 Eukaryotes Unicellular or protozoa Fungi Helminthes Multicellular unicellular multicellular Multicellular parasite Bacterial size : The used for the measurement of microorganisms micrometer ( m), nanometer (nm) and Angstrom (A o ).Size of bacteria 3000 x 500 nm, the viruses 500 x 250 nm For example: Bacteria E. coli size 3000 x 50 nm Staph. aureus size 1000 nm Spirochetes spp x m See the figure of the morphology and size of microorganisms

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7 Table : Distinguishing characteristic of Prokaryotic and Eukaryotic. Character Prokaryotic Eukaryotic 1. Size 1-10 m m 2. Nucleus - Nuclear membrane -Nucleolus Deoxyribonucleoprotein -Chromosome -Miotic division One More 3. Cell wall comp. Peptidoglycan Chitin, cellulose 4. Steroids 5. No. of ribosome Cytoplasm part - mitochondria - lysosyme - Golgi apparatus - Endoplasmic reticular 7. Chemical comp. - muramic acid - diamino pimelic acid May be present 8. Nitrogen fixation Possible Not possible 9. Respiration Anaerobic possible No The types of virulence factors : 1. Capsules : Capsules located externally to cell wall enable the bacterium to avoid of survive phagocytosis and adherence of bacteria to surface in - 7 -

8 their environment, including the cell of host. Bacteria capsulated are virulent and harm to the host, the composition of it often polysaccharide. such as Streptococcus pneumonia, Shigellae,Salmonella. 2. Adhesions : Many bacteria depend on the ability to adhere to mucosal cell as first step in the infectious process, is followed by development of micro colonies and stepsin pathogenesis of infection, to causing the disease, without adhesion factors many pharyngeal, intestinal and urinary tract would be washed away before they could cause disease, the types adhesion factors are surfaces structures e.g. Salmonella ```: a. Fimbriae. b. Pili. c. Lipopolysaccharide (LPS). d. M protein. 3. Invasion : For many disease-causing bacteria, invasion of the hosts epithelium is central to the infectious process, for many pathogenesis. Some bacteria (e.g. Salmonella species ) ability to invade the tissues host through the junctions between epithelial cells is integral to the disease process, e.g., in the case of Shigella a series of proteins known as invasion plasmid antigen (Ipa) and a protein called intracellular spread (Ics) expressed on the outer membrane play in the early stage of infection. 4. Exoenzymes : Many bacteria produce and secrete enzymes these enzyme play an important pathogenic role by variety of mechanisms. For example : a) Enzymes breakdown collagen and fibrin (i.e., collagenase, brinolysins) penetration of bacteria into tissues

9 b) Enzymes breakdown cellular material e.g., Proteases lecithinases in Clostridia c) Enzyme modify inactivate antibiotic. e.g., B. Lactamase in Moraxcella catarrhalis that are one of the primary mechanisms antibacterial resistance. 5. Toxins : Toxins produced by bacteria are generally classified into two groups. The primary features (characteristics ) of the two groups are listed in following Table : Exotoxins and Endotoxin. toxin can be classified into broad categories : a. Exotoxins : are proteins produced and released from the cell to cause toxicity. e.g., Clostridium tetani produce the tetanospasmin. Staphylococcus aureus produce coagulase. b. Endotoxin : are part of the bacterial cell wall. e.g. Gram (-ve) bacteria as Lipopolysacchride (LPS). e.g. types of E. coli, V. cholearae,shigella spp.. Table : Compares the main characteristic of Exotoxins and Endotoxins Exotoxins Endotoxins 1. Excreted by living cell in liquid media. Integral part of cell wall of gram ( -v ) bacteria released on death. 2. Produced by both gram ( ve ) Found only in gram( ve ) bacteria. and gram ( +ve ) bacteria. 3. Protein (polypeptides with a Lipopolysaccharid(toxicity) complexes molecular weight 10,000 lipid A portion 900, Unstable destroyed rapidly by Stable without loss of toxicity by heating at temperatures above heating at temperatures above 60 C. 60 C

10 5. Highly toxic, fatal to animals in microgram or less. Moderately toxic, fatal for animals in tens to hundreds micrograms. 6. Active bacteria Bacterial lysis 7. Usually do not produce fever in the host. Usually produce fever in the host by release of interleukin-1,or mediators. Morphological and Shapes of bacteria: The first step taken in the identification of an unknown bacterium is macroscopically examination, see the figure below: The morphological features of importance are the shape and size and grouping of the cell and their possession of any distinctive structures such as endospore, flagella (motility), capsules and intracellular granules. We can saw this by optical or light microscope and some others by elec. Microscope. After this diagnosis we demonstrated of certain structures use in grouped or taxonomic by shape of bacteria that they have specific shapes :

11 a. Spherical (round), cocous. e.g., Staphylococcus, Streptococcus b. Bacillus (cylindrical) as rod e.g., Clostridium, Salmonella c. Coccobacillus e.g., Pseudomonas. d. Vibrio e.g., Vibrio cholera, Spiral shape, Borrelia spp f. Spirochetes spp. e.g., Treponema, Leptospira g. Pleomorphic e.g. Moraxella spp. The basic bacterial Structure : 1. Cell wall : Cell wall thick nm, strong relatively rigid and maintain the characteristic shape of the bacteria in coccal, bacillary etc. It is determine gram-positive or gram-negative depend on the composition of it. Cell well contain peptidoglycan, lipid, structure of protein. 2. Cytoplasmic membrane :

12 Cytoplasmic membrane also terms as plasma membrane is the physical and metabolic barrier between the interior and exterior of the bacteria cell. This membrane is very important : a. Selective permeability. b. Bacterial electron transport system (a) energy system. c. Mesosomes. 3. Cytoplasmic components : a. DNA : the bacterial cell lacks nuclear membrane in cytoplasm as nucleotide it contain plasmids. b. Ribosome : are complex globular structures composed of several RNA molecules and proteins they have two sub-units terms 50 S and 30S it is important in synthesis of proteins. c. Strong granules : very important in metabolic activity. 4. External structures : a. Capsules : around many bacterial cell are composed of complex polysaccharides capsule also terms glycogalyx. b. Flagella : are present in many bacteria. It responsible for the motility it may be types in : 1. polar flagella : monotrichous, lophotrichous, amphitrichous 2.peritrichous c. Fimbriae use for adherence as protein fibers cover on the surface cell. d. Pili protein structure is important to transport genetic or sex (F) in conjugation and usually coded by plasmids

13 5. Endospore (Bacterial spores) : Some species of bacteria are capable of undergo and clostridia develop a highly resistant that can survive in a dormant state the along period that resistant to heat, radiation, crying and chemical. In sporulation each vegetative cell forms only one spore and in subsequent germination each spore gives a single vegetative cell. Spore may remain viable for many years. Cross-section of bacterial spore Types of spores : Spherical central, oval sub terminal,oval central,oval terminal, Oval sub terminal and spherical terminal

14 Glossary 1. Adhesion : A carbohydrate-specific binding protein used for adherence. 2. Antibiotic : A chemical substance produced certain mold and bacteria that inhibits the growth of or kills other microorganisms. 3. B. lactamase : An enzyme that cleaves the B. lactam ring of penicillin and related the antibiotic destroying their antibacterial activity. 4. Capsule: A gelatinous structure that surrounds some bacteria. 5. Chromosome : The array of genes responsible for the determination and transmission of hereditary characteristic. 6. Gram stain : A staining technique that divides bacteria into one of two groups. Gram (+ve) or Gram (-ve) on the basis of color. Among Eubacteria the staining reaction correlates well with the cell wall structure. 7. Pathogen : An organism that can cause disease. 8. Pathogenesis : The process by which disease develops. 9. pathogenic : Disease causing. 10. Virulence : The relative ability of a pathogen to overcome body defenses and cause disease. Also properties of microorganisms that assist pathogenicity