Normal Flora & Bacterial Pathogenesis PDF

Normal flora & Bacterial Pathogenesis Dr. Mohamed Elmutasim Microbiology Department 2022  Normal flora (commensals) They are those microorganisms that are permanent residents of body that everyone has. Commensals are organisms that derive benefit from ano...

Normal flora & Bacterial Pathogenesis Dr. Mohamed Elmutasim Microbiology Department 2022  Normal flora (commensals) They are those microorganisms that are permanent residents of body that everyone has. Commensals are organisms that derive benefit from another host but do not damage that host. Normal flora (commensals) Normal flora organisms are: Bacteria or yeasts (No Viruses, protozoa & helminths) Inhabit body surfaces exposed to environment, such as : Skin- Oropharynx- Intestinal tract -Vagina. Differ in number & kind at various anatomic sites. Low-virulence organisms. In their usual anatomic site, they are nonpathogenic. If they leave their usual anatomic site, especially in immunocompromised individual disease. Colonization Some people can be colonized: - -transiently or for long periods - With certain organism (not members of normal flora). Colonization resistance: It occurs when members of normal flora occupy receptor sites on skin & mucosal surfaces preventing pathogens from binding to those receptors. Normal flora Normal flora (commensals)  Bacterial Pathogenesis Pathogen: are microbes capable of causing disease in immunocompetent people. Opportunistic Pathogen: It refers to microbes that are capable of causing disease only in immunocompromised people. Carriers (chronic carriers): Individuals in whom pathogenic organisms are present in significant numbers & are source of infection for others. Bacterial Pathogenesis Infection has two meanings: 1) Presence of microbes in body 2) Symptoms of disease. Presence of microbes in body does not always result in symptoms of disease Bacteria cause symptoms of disease by two main mechanisms: 1) Production of toxins (exotoxins & endotoxins) 2) Induction of inflammation. Bacterial Pathogenesis Virulence: It is measure of microbe's ability to cause disease. Asymptomatic or inapparent Infections: These infections occur when our host defenses have eliminated microorganism before it could multiply to sufficient numbers to cause symptoms of disease. Bacterial Pathogenesis Communicable Infection: Most bacterial infections are communicable, i.e., capable of spreading from person to person. Epidemiologic terms used to describe infections: Endemic :Infections that occur at persistent, usually low level in certain geographic area Epidemics: Infections occur at much higher rate than usual. Pandemics: Infection spread rapidly over large areas of globe Bacterial Pathogenesis Stages of Bacterial Pathogenesis: Transmission: from external source into portal of entry. Evasion: of primary host defenses (skin or stomach acid). Adherence: to mucous membranes, usually by bacterial pili. Colonization: by growth of bacteria at site of adherence. Disease symptoms: caused by toxin production or invasion accompanied by inflammation. Host responses:both nonspecific & specific (immunity). Progression: or resolution of disease. Determinants of Bacterial Pathogenesis: Transmission Determinants of Bacterial Pathogenesis: Transmission Determinants of Bacterial Pathogenesis: Transmission Vertical Transmission: It is transmission of Bacteria, viruses & other microbes from mother to offspring through: Placenta Birth canal during birth Breast milk. Horizontal Transmission: It is person-to-person transmission(from mother to offspring). Zoonoses: Human diseases for which animals are reservoir Determinants of Bacterial Pathogenesis: Transmission The main "portals of entry" into body : Respiratory tract Gastrointestinal tract Skin Genital tract. Determinants of Bacterial Pathogenesis: Toxin Production Determinants of Bacterial Pathogenesis: Toxin Production Exotoxins: Many exotoxins have A–B subunit structure: - A (active) subunit possesses toxic activity - B (binding) subunit is responsible for binding exotoxin to specific receptors on membrane of human cell. Typical Stages of Infectious Disease Incubation period: time between moment person is exposed to microbe (or toxin) & appearance of symptoms. Prodrome period: time during which nonspecific symptoms occur. Specific-illness period: time during which characteristic features of disease occur. Recovery period: time during which symptoms resolve & health is restored. Typical Stages of Infectious Disease After recovery period, some people become: -chronic carriers of organism. -latent infections develop: Some people have subclinical infections during which they remain asymptomatic. Thank You