Exam 3 Ch. 10 Pathology, Normal Flora, Nosocomial Infections

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pathology

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study of disease including causes of disease (etiology) and manner in which disease develops (pathogenesis) and effects of disease on body

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infection

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invasion of body by pathogenic microorganisms (infection CAN LEAD TO disease); infection can exist without resulting in symptoms of a disease

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disease

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result of infection, causing change from health to an abnormal state in which a part or the whole body isn't properly functioning (destruction of cells)

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normal flora

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large number of microorganisms that are inhabitants of the human body (NOT HARMFUL)

-mostly bacteria but does have some fungi and protozoa

-mostly lives on inner surfaces of body (including mucous membranes lining nose, mouth, upper respiratory tract and genitourinary tract

-NOT IN ORGANS; ONLY IN LININGS (healthy human is free of microorganisms of internal organs and tissues)

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Does fetus of a health animal have microorganisms?

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NO

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Normal flora can be categorized by

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their presence (resident or transient) and function (commensal, mutualist or opportunistic pathogens)

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residents

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harmless, don't cause disease and are permanent occupants

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transients

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not considered part of normal flora; may establish themselves briefly but are utlimately excluded by competition or the host's defense mechanism

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commensals

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-include most of normal flora microbes

-benefit from host but doesn't affect host

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mutualists

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-host and microorganism both benefit from eachother

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opportunistic pathogens

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-cause infection, if tissue injury occurs ata specific body site or if resistance of body to infection is decreased

-may occur if organism is moved from one specific site of body to another

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origin of normal flora

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1. 100% health fetus should be free of mircoorganisms

2. First comes in contact with microorganisms while passing through mom's birth canal (surface contact and later by swallowing or inhaling)

3. other microorganisms join later from different sources in surrounding environment

4. As infant is exposed to full range of microorganisms in immediate environment, microbes that best compete with others in particular sites, become dominant and form a stable normal flora for that individual

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Effects of Normal Flora on human host (environments used to test the effects)

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1. germfree: life in absence of microorganisms; sterile environment (high vitamin B, K)

2. Gnotobiotic: life in normal environment with at least 1 or more known microorganisms (low vitamin B, K)

-germfree animals have underdeveloped immune system (unusual susceptibility to infection if exposed to microorganisms)

-germfree animals vulnerable/susceptible to pathogenic and nonpathogenic bacteria

-germfree animals need higher levels of B vitamins in their diet; need vitamin K entirely from diet (Gnotobiotic/normal animals can supply their own vitamin K)

-normal cflora contributes greatly to satisfy vitamin requirements of the host

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Adherence to host cell

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-normal flora attach to surface of host's epithelial cells (interaction between microbial cell surface and chemical receptor on body cell)

-allows bacteria to multiply while avoiding removal by flusing effects (shedding of skin) of surface fluids

-this attachment may often by specific to 1 particular body site

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desquamation

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-detach from host's epithelial cells as host's cells detach from body surfaces and get replaced by new cells (CAUSES elimination of microorganisms that are not part of normal flora, transients) which may be weakly attached to epithelial cells

-normal flora microorganisms are able to reattach firmly to fresh epithelial layer and persist at their specific body sites

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production of antimicroial substances

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-some normal flora microorganisms can produce metabolic products that can inhibit other microorganisms

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What could happen if normal flora is introduced to other locations of the body?

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can cause disease especially if there are predisposing factors

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blood, other body fluids and tissues

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-normal human doesn't have microorganisms here (unless microbes cross protective epithelial barriers as a result of trauma)

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transent bacteremia

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-can be present if microbes from the bloodstream are filtered out in the pulmonary capillaries or removed by immune cells

-causes infection of damaged or abnormal heart valves

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subacute bacterial endocarditis

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inflammation of membrane lining the heart and valves

-can be caused by transient bacteremia

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skin

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epidermis and dermis form an effective barrier to shield against most other microorganisms

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What prevents microorganisms from growing on skin?

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1. lack of moisture: inhibits microbial growth; cause many bacteria to become dormant which can lead to their death (moist areas have more normal flora organisms)

2. lower pH: skin pH of 3-5 due to acid production (by-products) of some normal flora on skin

3. inhibitory substances: bactericidal or bacteriostatic compounds present on the skin (ie: sweat glands secrete lysozyme which destroys peptidoglycan of bacterial cell walls)

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eyes (conjunctiva)

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-conjunctiva: delicate membrane that lines eyelids and covers eyeballs

-continuation of skin at margin of eyelids and is a mucous membrane that is contiually washed by flow of tears which removes microorganisms

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respiratory tract (which areas most difficult for bacteria to colonize)

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-mouth, tonsils, naspharynx, throat, trachea, tracheal branches, lungs

1. upper respiratory tract: portion above larynx; mucous membrane of upper respiratory tract is moister than skin but can be problematic for microorganisms trying to colonize

2. lower respiratory tract: mucous membrane of trachea and bronchi; lacks normal flora because of efficient removal of miroorganisms by an upward flow of mucus

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mouth

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-ideal environment for bacterial growth because it is moist and contains nutrients

-continued flow of saliva causes microoganisms in mouth to be flused

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Normal flora of mouth

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1. until eruption of 1st teeth: only aerobes and facultative anaerobes

2. after eruptiono f 1st teeth: gram (-) anaerobes like Streptococcus mutans adheres to teeth and cause tooth decay or dental caries (major cause of dental caries and plaque)

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GI tract

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-contains highest concentration of normal flora (esophagus, stomach, small and large intestine)

-WITHIN GI TRACT, stomach has lowest amount of bacteria because bactericidal effects of acidic digestive enzymes)

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GU tract

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-kidneys, uretus, urinary bladder and urethra

1. upper portion of urethra: not open to outside (contained) free of bacteria

2. lower portion of urethra: contain bacteria because it is open to outside environment

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nosocomial infections

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hospital-acquired infections

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importance of nosocomial infections

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-all accredited hospitals required to have infection-control plan and program

-plus surveillance: systematic observation and recording of the transmissible disease cases

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epidemiology of nosocomial infections

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-study of factors that influence the occurrence and distribution of hospital acquired infections and transmissible diseases

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What are the factors in the epidemiology of nosocomial infections?

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1. source of microorganism

2. Route of transmission

3. host susceptibility

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endogenous infection

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reservoir of infection of a living organism that harbors pathogens

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fomite

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reservoir of infection of an inanimate object that is contaminated with the infectious microorganisms (exogenous infection)

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exogenous infection

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caused by microbes from an external source (ie environment or fomites)

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endogenous infection

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caused by microorganisms that are a part of a person's own normal flora (ie health care personnel member's hands, patient's salva)

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infectious cycle

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transmission of infectious microorganism from 1 host to another and the subsequent infection of a new host (during this cycle, pathogens may exit their reservoir in many ways like sneeze, cough, talking or fluids)

-can contaminate other people or objects

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Who has the lowest immunity levels?

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infants and elderly more susceptible to infections

-also patient with clinical conditions and medical procedures (normal flora might transfer from their usual habitats to other locations of body and become opportunistic pathogens)

-E.coli inhabitant of intestinal tract but can cause serious infection if moves to urinary tract

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cycle of infection

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-must be completed for infection to occur

-pathogen must exit reservoir, have mode of transmission and have a portal of entry to susceptible host

-interruption at any stage in cycle can prevent infection

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purpose of infection control

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to break the cycle (should occur at transmission step because hosts and infectious agents are more difficult to control)

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hand washing

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most important procedure to reduce spread of pathogens between patients

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isolation of patient

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separate patients to prevent spreading pathogens to others

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asepsis

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exclusion of pathogenic microorganisms to avoid infection

1. medical asepsis: practices used to keep environment free from infectious microorganisms as much as possible

2. surgical asepsis: procedures that prevent microorganisms from entering surgical wounds and tissues during operation (ie sterilize instruments)

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hospital disinfection and sterilization

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has 3 categories of equipments used based on risk of infection

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critical items

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invasive items introduced into blood stream or other normally sterile areas of body

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semi-critical

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non-invasive instruments come in contact with but don't penetrate body surface

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noncritical items

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touched by intact skin only like beds