Batterjee Medical College

Dr. Manal El Said Department Head of Microbiology Normal flora

Batterjee Medical College Normal flora 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)

Batterjee Medical College Normal flora 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.

Batterjee Medical College Normal flora Some people can be colonized: - transiently or for long periods - With certain organism (not members of normal flora). Colonization It occurs when members of normal flora occupy receptor sites on skin & mucosal surfaces preventing pathogens from binding to those receptors. Colonization resistance

Batterjee Medical College Normal flora

Batterjee Medical College Important Members of the Normal Flora

Batterjee Medical College Bacterial Pathogenesis

Batterjee Medical College Pathogen are microbes capable of causing disease in immunocompetent people. Bacterial Pathogenesis Pathogen It refers to microbes that are capable of causing disease only in immunocompromised people. Opportunistic Pathogen Individuals in whom pathogenic organisms are present in significant numbers & are source of infection for others. Carriers (chronic carriers)

Batterjee Medical College It is measure of microbe's ability to cause disease Bacterial Pathogenesis Virulence These infections occur when our host defenses have eliminated microorganism before it could multiply to sufficient numbers to cause symptoms of disease. Asymptomatic or inapparent Infections

Batterjee Medical College 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 Infection

Batterjee Medical College Most bacterial infections are communicable, i.e., capable of spreading from person to person Bacterial Pathogenesis Communicable Infection 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 Epidemiologic terms used to describe infections

Batterjee Medical College Bacterial Pathogenesis Stages of Bacterial Pathogenesis 1.Transmission from external source into portal of entry. 2.Evasion of primary host defenses (skin or stomach acid). 3.Adherence to mucous membranes, usually by bacterial pili. 4.Colonization by growth of bacteria at site of adherence. 5.Disease symptoms caused by toxin production or invasion accompanied by inflammation. 6.Host responses, both nonspecific & specific (immunity) 7.Progression or resolution of disease.

Batterjee Medical College Mode of Transmission Comment I. Human to human A. Direct contact Intimate contact, e.g. Sexual Passage through birth canal B. No direct contact Fecal–oral, e.g., excreted in human feces, then ingested in food or water C. Transplacental Bacteria cross the placenta and infect the fetus D. Blood-borneTransfused blood or intravenous drug use can transmit bacteria and viruses Determinants of Bacterial Pathogenesis: Transmission

Batterjee Medical College Mode of Transmission Comment II. Nonhuman to human A. Soil source wound in skin B. Water source water aerosol are inhaled into lungs C. Animal source 1. Directly cat scratch 2. Via insect vector tick bite 3. Via animal excreta cattle feces are ingested in undercooked hamburger D. Fomite source towel, are transferred onto the skin Determinants of Bacterial Pathogenesis: Transmission

Batterjee Medical College It is transmission of Bacteria, viruses & other microbes from mother to offspring through: - Placenta - Birth canal during birth - Breast milk. Vertical Transmission Horizontal Transmission It is person-to-person transmission (not from mother to offspring). Determinants of Bacterial Pathogenesis: Transmission Human diseases for which animals are reservoir Zoonoses

Batterjee Medical College The main "portals of entry" into body : Respiratory tract Gastrointestinal tract Skin Genital tract. Determinants of Bacterial Pathogenesis: Transmission

Batterjee Medical College PropertyExotoxinEndotoxin SourceCertain species of gram-positive and gram-negative bacteria Cell wall of gram-negative bacteria Secreted from cellYesNo ChemistryPolypeptideLipopolysaccharide Location of genesPlasmid or bacteriophageBacterial chromosome ToxicityHigh (fatal dose on order of 1 g)Low (fatal dose on order of hundreds of micrograms) Clinical effectsVarious effectsFever, shock Mode of actionVarious modesIncludes TNF and interleukin-1 AntigenicityInduces high-titer antibodies called antitoxins Poorly antigenic VaccinesToxoids used as vaccinesNo toxoids formed and no vaccine Heat stabilityDestroyed rapidly at 60°C (except staphylococcal enterotoxin) Stable at 100°C for 1 hour Typical diseasesTetanus, botulism, diphtheriaMeningococcemia, sepsis by gram-negative rods Determinants of Bacterial Pathogenesis: Toxin Production

Batterjee Medical College 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. Determinants of Bacterial Pathogenesis: Toxin Production

Batterjee Medical College 1.Incubation period: time between moment person is exposed to microbe (or toxin) & appearance of symptoms. 2.Prodrome period: time during which nonspecific symptoms occur. 3.Specific-illness period: time during which characteristic features of disease occur. 4.Recovery period: time during which symptoms resolve & health is restored. Typical Stages of Infectious Disease

Batterjee Medical College 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.