Lect-7-Bacterial-Pathogenicity.pptx

BACTERIAL PATHOGENICIT Y Assistant Lecturer: Nagla Arab 2nd term INTRODUCTION  Microorganisms (viruses, bacteria, fungi and protozoans) are closely associated with human hosts.  All host-microbe associations are not pathogenic  Many factors can influence this association ...

BACTERIAL PATHOGENICIT Y Assistant Lecturer: Nagla Arab 2nd term INTRODUCTION  Microorganisms (viruses, bacteria, fungi and protozoans) are closely associated with human hosts.  All host-microbe associations are not pathogenic  Many factors can influence this association  Virulence  Site  Immune status of host  HOST – PARASITE RELATIONSHIP  One species living in or on the body of another  This association is called “Symbiotic association”  Can be harmless, or harmful  Usually on body surfaces – skin, mucosa  3 categories of associations 1. Commensalism 2. Mutualism 3. Parasitism  COMMENSALISM  Microorganism may use a body of a larger species for food and shelter  Normally does not cause harm to the host – normal flora / commensals  But can be harmful if environmental conditions change ( E. coli in urinary tract)  Opportunistic pathogens  Commensals can benefit the host  Intestinal organisms can prevent colonizing pathogens (Bacteroides spp)  Can produce metabolites which can be used by the host  MUTUALISM  Benefit both the host and the micro organism  Prevent colonization of pathogens on mucosal surfaces  Bacteria in ruminants (cattle, sheeps) intestines that digest cellulose Parasitism  Harmful to the host  Benefit only the micro organism  Rabies virus INTRODUCTION  Infection: growth and multiplication of a microbe in or on the body with or without the production of disease.  Pathogenicity: The capacity of a bacterium to initiate disease.  Pathogenesis refers both to the mechanism of infection and to the mechanism by which disease develops.  INTRODUCTION Infection occurs when imbalance between  The capacity of the microorganism to multiply, spread and cause disease and  The ability of the host to control and stop the infection  Innate and specific immune responses  General health of the host & age Early host response Delayed host – no infection response - disease  FREQUENCY OF CLINICALLY APPARENT DISEASE  In some infections all or majority infected will have clinical disease  Eg. Rabies, smallpox  But in other infections,  majority may have mild or asymptomatic infection and  Only a minority of infected will have clinical disease  Eg. Polio (~ 1% have clinical disease)  This is called “iceberg phenomenon”  Pathogenicity requires the attributes of,  Transmissibility (ability to move from one host or reservoir to another host)  Survival (in the new host)  Infectivity (ability to breech the new host defences)  Virulence (capacity of the pathogen to harm the host) TYPES OF BACTERIAL PATHOGENS  Primary pathogens: Capable of establishing infection and causing disease in previously healthy individuals with intact immunological defences.  Opportunistic pathogens: Rarely causes diseases in previously healthy individuals, but causes diseases with immunological defences.  Characteristics of pathogenic bacteria  Establishment of infection (source, route of entry, transmission)  Adherence to host cells  Invasion of host cells and tissue  Evasion of the host immune system  Toxigenicity  Source of infection  Patients (clinical disease or subclinical infections, infected carriers)  Normal commensal flora  Inanimate objects (a non-living thing)  Environmental (water, food, air etc.) ENTRY INTO THE HUMAN BODY The most frequent portals of entry- Mucus - Skin Routes: Ingestion, inhalation, ،‫ االستنشاق‬،‫االبتالع‬ trauma, needles, ،‫ اإلبر‬،‫الصدمات‬ catheters, arthropod ‫القسطرة‬، bite, sexual ،‫لدغة المفصليات‬ transmission ‫االنتقال الجنسي‬ TRANSMISSION OF INFECTION  Direct contact: from one person to another person  Indirect contact:  ingestion of contaminated food and water  air borne particles  via animals and insects PATHOLOGICAL MECHANISMS OF BACTERIAL INFECTIONS  Bacteria-mediated Pathogenesis  Host-mediated Pathogenesis  Bacterial virulence factors Bacteria-mediated Pathogenesis.Host-mediated Pathogenesis vs