Microbiology Lecture 1 Introduction PDF

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (1) H A N INTRODUCTION A  -  The branch of sciences studying Microbes.  Living organisms that can be seen only by Microscopes.  Their sizes ar...

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (1) H A N INTRODUCTION A  -  The branch of sciences studying Microbes.  Living organisms that can be seen only by Microscopes.  Their sizes are usually measured in micrometers,  They are called microorganisms.  Medical Microbiology is dealing with microbes causing infections to man.  Microbial infection may or may not lead to human diseases.  Microbes may be:  Direct causes of diseases or  May play an indirect role to cause damage of the human tissues.  Types of microorganisms are bacteria, fungi, protozoa or viruses.  Making most of the microbial world.  The most common cause of human diseases.  Not living cells even, they are not cells.  Contain a single type on nucleic acid (DNA or RNA) surrounded by a protein coat. -  -  Bacteria belong to prokaryotic type of cells while human cells are eukaryotes.  The differences between Eukaryotic and Prokaryotic cells are important, Why??  To know how to design drugs that kill bacterial cells without causing damage to human cells (for Treatment of infections). -  Infection means that a microbe is getting in relation with a host.  Infection may or may not lead to human disease depending on many factors in both the microbe and the host.  -  Reservoir or source of infecting microbes to man may be:  Infection to human may come from: ① Human sources: ❖ Patients may be: 1. Typical cases. 2. Atypical cases. ❖ A person with no signs or symptoms of disease. ❖ They may be: 1. Incubatory carrier. 3. Contact carrier. 2. Convalescent carrier. ② Nonhuman sources:  Some human diseases are transmitted to man from other living creatures e.g.: ❖ Like rabies, plague or swine flu. ❖ Like avian flu. ❖ Like malaria.  Infection may be transmitted from: ① Contaminated instruments, ② Dust or from dried body secretions. -  Droplets during cough, sneezing or even talking.  Through stool or saliva.  Through contact (direct or indirect).  Through sexual contact and secretions.  Through needle sticks, blood transfusion, or blood-sucking insects.  Through bites, scratches, contact or sometimes their meat and milk.  Direct or indirect.  Of contaminated water or foods.  Either by contact (direct or indirect), insect bites, or in surgical wounds.  From diseased donner, needle sticks or contaminated surgical instruments.  Sexual relations  In utero, during delivery or lactation. -  -  Transmission of a microbe to a host does not mean progression to disease in all cases.  Very few infections will proceed to cause harmful effect in the new host (disease).  This is depending in factors in either the host or in the infecting agent (pathogen). ① Age:  Extremes of age (newborn or old age) are more liable to get diseases. ② Immune status:  Persons with good immunity are less susceptible to disease even after infection. ③ Underlying conditions:  Persons suffering from diabetes, malignancy or taking some drugs may develop diseases more frequent. ① Dose of infection:  Pathogens are causing disease only if they are transmitted in considerable number which is called infectious dose. ② Route of entry:  Some pathogens entering the body through respiratory or gastrointestinal tracts will not cause diseases but if transmitted through blood they will cause diseases. ③ Co-infection:  If two or more infecting agents are entering the body at the same time the possibility of disease production is increased. ④ Microbial virulence:  Virulent microbes are those causing disease even in immune persons. - ① Its ability to produce toxins   Toxigenic strains. ② Its ability to invade tissues ⇒  Invasiveness. ③ Its ability to escape immune response   E.g.: capsulated bacteria escaping phagocytosis.  Some bacteria have extra components, making them more pathogenic (virulence factors).  Virulence factors include:  Pili (fimbriae) to adhere to cells,  Some enzymes or proteins helping bacteria to defeat the immune reactions of the host.  - Clinical Case  Last year, Grandfather Ali suffered from fever, cough, pain in all muscles and joints and difficulty to take his breath. He was living with his 2 grandsons Mohamed and Hassan. They did not know that it was COVID-19, and they were not taking any safety precautions. After one week Hassan had similar symptoms and he was ill. Mohamed has no symptoms. Mohamed visited his friend Omar and stayed with him for one night. After about one week Omar became ill while Mohamed was still healthy. ① What is the causative microbe of COVID-19? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ② Who is the main source of infection in this family? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ③ What are methods of transmission of infection? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ④ Mohamed was not ill but he was a source of infection to Omar, is Mohamed a case or a carrier? What type of carriers is he? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ⑤ How to prevent spread of COVID -19 in our community? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..…………..  - Assignment What are the Differences between Human (eukaryotic) cells and bacterial (prokaryotic) cells and their importance in medicine? Summary ① Microbiology is dealing with study of microbes. ② Microbes are living organism with a very small size that can only be seen by microscopes. ③ Medical Microbiology is dealing with microbes causing disease or infection to man. ④ Microbes of medical importance may be: bacteria, fungi, viruses or protozoa. ⑤ Bacterial cell belongs to prokaryotic cells and are different from human cells (eukaryotic cells). ⑥ The source of microbial infection to man may be living or nonliving source. ⑦ Living sources of infection may be human or non-human (animals, birds or insects). ⑧ Human sources of infection may be a patient or a carrier. ⑨ Microbes exit from the source and are transmitted through different pathways depending on the site of infection. ⑩ Not all microbial infection to man are causing disease. ⑪ The fate of infection depends on Host and Microbial factors. ⑫ Host factors include age, immunity and underlying medical conditions. ⑬ Microbial factors include dose, route of infection, mixed infection and degree of pathogenicity (virulence).