Classification of pathogenic and �non pathogenic microorganisms-medical microbiology

Classification of pathogenic and �non pathogenic microorganisms-medical microbiology

1. Classification of pathogenic and non pathogenic microorganisms Saajida Sultaana Mahusook

2. Pathogenic and nonpathogenic bacteria are the two main types of bacteria other organisms are in contact with. The distinction between the two can be made based on the Koch’s Postulates. 

3. Non-Pathogenic Microorganisms: Non-Pathogenic  microorganisms are i ncapable of causing disease. i.e., harmless to  other organisms They mostly live in the environment as saprophytes. Some of them are autotrophs. Around 99% of bacteria are nonpathogenic. They are useful to man as they are involved in manufacturing   foods such as butter , cheese, alcohol , lactic acid, Probiotics and fermented products antibiotics gradual decomposition of organic matter (dead animals, plants and their wastes) on or in the soil . bio fertilizers etc. Some non-pathogenic bacteria live on the surface of animals as normal flora. They are commensals. But , these bacteria can become opportunistic pathogens when they invade the tissues. For example ,  E . coli  are non-pathogenic bacteria that live in the gastrointestinal tract and can trigger an immune response under certain circumstances.

4. It is estimated that the human body consists of approximately 10 13 cells and hosts 10 14 –10 15 individual micro-organisms. These micro-organisms can be divided into two groups: those that usually remain constant in their normal habitat (indigenous or resident flora ) and those that are accidentally acquired (transient flora) Body areas that usually harbor micro-organisms are skin, mouth, nasopharynx , oropharynx and tonsils, large intestine and lower ileum, external genitalia, anterior urethra, vagina, skin, and external ear. Some functions of normal flora Protects the body from pathogenic microorganisms Keeps us healthy Synthesize certain vitamins etc.

5. Pathogenic Microorganisms : Pathogenic microorganisms are those that can cause disease. Pathogenicity is the capacity of a microorganism to cause a disease. The diseases caused by pathogenic bacteria are generally called infections . P athogenic bacteria possess several genes that endow the capacity to cause diseases. The agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms).  Microorganism Disease Bacteria Mycobacterium tuberculosis Tuberculosis Bacillus anthracis Anthrax Fungi Candida albicans Candidiasis Tinea corporis Ringworm  Virus HIV (retro virus) AIDS Herpes virus Herpes

6. Isenberg and D’ Amato classified microorganisms in disease production as Murray et al. classified the pathogenicity of organisms as Categories in both classifications are not always equivalent . Opportunistic infections are defined as infection caused by non-pathogenic microorganisms which become pathogenic when the immune system is impaired by an unrelated disease . Example of an opportunistic microorganism is  Haemophilus ducreyi ,which infects its host through broken skin or epidermis.  commonly involved rarely involved occasionally involved High Potential Low

7. Pathogenicity : The ability of micro-organisms to induce disease, which may be assessed by disease-carriage ratios Virulence: The severity of the disease induced by micro-organisms. In epidemiological studies virulence may be assessed by mortality or morbidity rates and the degree of communicability Reservoir : The place where the organism maintains its presence, metabolizes, and replicates Source : The place from which the infectious agent passes to the host. In some cases the reservoir and the source are the same, but not always Infection : A microbiologically proven clinical diagnosis of inflammation Carriage: Permanent (minimally 1 week) presence of the same strain in any concentration in body sites normally not sterile (oropharynx, external nares, gut, vagina, skin) Abnormal carrier state: The abnormal carrier state exists when the isolated micro-organisms is not a constituent of normal flora (i.e., enterobacterial or pseudomonal strains) Colonization: The presence of micro-organisms in an internal organ that is normally sterile (e.g., lower airways, bladder). The diagnostic sample yields less than a predetermined level of cfu /ml of diagnostic sample.

8. Factors that Determine the Pathogenicity of Bacteria Host susceptibility Presence of mechanisms to fight with the infection by the host immune system Pathogenic mechanisms of bacteria Bacterial infectivity, host resistance, virulence genes, host- mediated pathogenesis (Gram-negative bacterial sepsis, tuberculosis , and tuberculoid leprosy) and intracellular growth Specific virulence factors Adherence and colonization factors, invasion factors, presence of a capsule and other surface components, endotoxins, exotoxins , and siderophores

9. R eference https ://pediaa.com/difference-between-pathogenic-and-nonpathogenic-bacteria / Classification of Micro-Organisms According to Their Pathogenicity M.A. DE LA CAL, E. CERDÀ, A. ABELLA, P. GARCIA-HIERRO https://www.ncbi.nlm.nih.gov/books/NBK8526/? report=classic https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/14%3A_Pathogenicity/14.2%3A_Overview_of_Microbe-Host_Interactions/14.2B%3A_Opportunistic_Microorganisms THANK YOU