SJSU MICR20 CHAPTER 13

human body & microorganisms

- human body in a state of dynamic equilibrium

- interaction b/w human body & microorganisms involve development of biofilms

- colonization of body involves constant "give & take)

most significant interactions of microbes

- provide protective & stabilization effect on body surfaces

- involved in maturation of host defenses & development of immune system

- invade & grow in sterile tissues, causing disease

normal resident microbiota

- microbes that engage in mutual or commensal associations w/ humans

- aka indigenous, microflora, normal flora, & commensals

infection

condition in which pathogenic microbes penetrate host defenses, enter tissues, & multiply

pathogen

microbe acting as infectious agent

infectious disease

infection that causes damage or disruption to tissues

microbe-free

- internal organs, tissues, fluids

- most areas of body in contact w/ outside environment harbor resident microbes

transients

- microbes that occupy the body for only short periods

- cling to surface, but doesn't grow there

- influenced by hygiene

residents

- microbes that become established

- stable, predictable

- less influenced by hygiene

- primarily bacteria & yeasts

sites that harbor normal resident microbes

- skin

- upper respiratory tract

- GI tract

- outer opening of urethra

- external genitalia

- vagina

- external ear & canal

- external eye

microbial antagonism

- microbiota benefits host by preventing overgrowth of harmful microbes

endogenous infections

- occur when normal flora is introduced to a site that was previously sterile

- infection caused by an infectious agent that is present or in host prior to start of infections

microbiota

- generally stable, but fluctuates w/ general health, age, diet, hygiene, hormones, & drug therapy

microbe-free sites

- heart & circulatory system\

- liver

- kidney & bladder

- lungs

- brain & spinal cord

- muscles

- bones

- ovaries/testes

- glands (pancreas, salivary)

- sinuses

- middle & inner ear

- internal ear

microbe-free fluids

- blood

- urine in kidney, ureters, bladder

- cerebrospinal fluid

- saliva prior to entering oral cavity

- semen prior to entering urethra

skin

- largest & most accessible organ

- 2 cutaneous pop.: transients & residents

microbiota of gastrointestinal tract

- long hollow tube; exposed to environment

- bounded by mucous membranes

- variations in flora distribution due to shifting conditions (pH, oxygen tension, anatomy)

- oral cav., LI, & rectum harbor appreciable flora

microbiota of mouth

- most diverse & unique flora of body

- numerous adaptive niches in microhabitats

- cheek epithelium, gingiva, tongue, floor of mouth, & tooth enamel

- teeth eruption establish anaerobic habitat in gingival crevice favoring colonization by anaerobic bac.

most common residents of mouth

- aerobic Streptococcus species

- S. sanguis, S. salivararius, S. mitis

bacterial count of saliva

5 x 10^9 cells/mL

microbiota of large intestine

- complex & profound interactions w/host

- 10^8 to 10^11 microbes/gm of feces (more or equal to 30% fecal vol.)

- intestines favor anaerobic bac.

bacteria in large intestine

- Bacteroids

- Bifidobacterium

- Fusobacterium

- Clostridium

microbiota useful byproducts to host

- fermentation of waste material in feces generates vitamins & acids

- B12, K, pyridoxine, riboflavin & thiamine

- acetic, butyric, & propionic

- bacterial digestive enzymes that convert disaccharides to monosaccharides or promote steroid metabolism

- intestinal bac. contribute to intestinal odor

inhabitants of respiratory tract

- first organisms to colonize: oral streptococci

- Staphylococcus aureus: nasal entrance, nasal vestibule, anterior nasopharynx

- Neisseria species; mucous membranes of nasopharynx

- Assorted streptococci & Haemophilus: tonsils & lower pharynx

- no flora in bronchi & lungs

microbiota of genitourinary tract

- internal reproductive organs kept sterile through physical barriers (cervical plug)

- kidney, ureter, bladder, & upper urethra kept sterile by urine flow & bladder emptying

sites of genitourinary tract that harbor microflora

- female: vagina & outer opening of urethra

- male: anterior urethra

changes in physiology influence composition of normal flora

- estrogen

- glycogen

- pH

maintenance of normal microbiota

- normal flora is essential to health of humans

- flora create environment that prevent infections & enhance host defenses

- antibiotics, dietary changes, & disease may alter flora

- probiotics

probiotics

introduce known microbes back into body

development of infection

1. finding portal of entry

2. attaching firmly

3. surviving host defenses

4. cause damage & disease

5. exiting host

portal of entries

- skin

- GI tract

- respiratory tract

- urogenital tract

- endogenous biota

how pathogens attach

- fimbriae

- capsules

- surface proteins

- viral spikes

- hooks

how pathogens survive host defenses

- avoid phagocytosis

- avoid death inside phagocyte

- evade actions of immune system

phagocyte

- type of immune cell

- play role in body's defense against pathogens

- macrophage

- neutrophils

- dendritic cells

- eosinophils

phagocytosis

- cellular process in which phagocytes engulf & digest large particles

- large particles: pathogens, dead cells, & debris

causes of damage & disease

- direct damage: toxin, enzymes, & lysis

- indirect damage: host response is inappropriate & excessive

portals of exit

- respiratory tract, salivary glands

- skin cells

- fecal matter

- urogenital tract

- blood

factors that weaken host defense & increase susceptibility to infection

- old age & extreme youth

- genetic defects in immunity & acquired defects in immunity

- surgery & organ transplants

- organic disease: cancer, liver malfunction, & diabetes

- chemotherapy/immunosuppressive drugs

- physical & mental stress

- other infections

true pathogens

- capable of causing disease in healthy persons w/normal immune disease

- influenza virus, plague bacillus, malarial protozoan

opportunistic pathogens

- cause disease when host's defenses are compromised or when they grow in part of the body that is not natural to them

- Pseudomonas sp. & Candida albicans

virulence factor

- characteristic or structure that contributes to ability of a microbe to cause disease

- severity of disease depends on virulence of pathogen

portal of entry definition

characteristic route a microbe follows to enter tissue of body

exogenous agents

originate from source outside the body

endogenous agents

already exist on or in body (normal flora)

portal of entry: skin

nicks, abrasions, punctures, incisions

portal of entry: GI tract

food, drink, & other ingested materials

portal of entry: respiratory tract

oral & nasal cavities

portal of entry: urogenital tract

sexual, displaced organisms

portal of entry: transplacental

pathogens transferred from mother to fetus through placenta

infectious dose (ID)

- minimum number of microbes required for infection to proceed

- microbes w/small IDs have greater virulence

- lack of ID will not result in infection

estimated infectious doses of selected pathogens

adhesion

- microbes gain stable foothold at portal of entry

- dependent on binding b/w specific molecules on host & pathogens

toxin

specific chemical products of microbes, plants, & some animals that has poisonous effects on other organ

toxinoses

adverse effects of toxins

toxemias

- when toxin is spread by blood from site of infections

- tetanus, diphtheria

intoxications

caused by ingestion of toxins (botulism)

types of bacterial toxins

- endotoxin

- exotoxin

endotoxin

- not secreted, but released after host cell is damaged

- composed of part of outer membrane of gram-negative cell walls

exotoxin

- secreted by a living bacterial cell into infected tissue

- strong specificity for a target cell, disrupting membrane

- hemolysins

- A-B toxins (A-active, B-binding)

hemolysins

disrupt membrane of red blood cells, killing them

differential characteristics of bacterial exotoxins and endotoxins

toxoid

inactivated toxin used in vaccines

antitoxin

antibody that reacts specifically w/toxin

four distinct stages of clinical infectious

1. incubation period

2. prodromal stage

3. period of invasion

4. convalescent period

incubation period

- time from initial contact w/infectious agent to appearance of first symptoms

- agent is multiplying but damage is insufficient to cause symptoms

- several hours to several years

prodromal stage

- vague feelings of discomfort

- nonspecific complaints

period of invasion

- multiplies at high levels

- becomes well-established

- more specific signs to symptoms

patterns of infection

- localized infection

- systemic infection

- focal infection

- mixed infection

localized infection

- microbes enter body & remains confined to a specific tissue

systemic infection

infection spreads to several sites & tissue fluids usually in bloodstream

focal infection

when infectious agent breaks loose from a local infection & is carried to other tissues

mixed infection

- several microbes grow simultaneously at infection site

- polymicrobial

primary infection

initial infection

secondary infection

subsequent infection by a different microbe

acute infection

comes on rapidly & sever, but short-lived effects

chronic infections

progress & persist over long period of time

sign

objective evidence of disease as noted by an observer

symptom

subjective evidence of disease as sensed by patient

common signs and symptoms of infectious disease

- fever: chills

- septicemia: pain, irritation

- microbes in tissue fluids that should be sterile: nausea

- abnormal chest sounds: malaise, fatigue

- skin eruptions: chest tightness

- leukocytosis: itching

- leukopenia: headache

- swollen lymph nodes: weakness

- abscesses: abdominal cramps

- increased heart rate (tachycardia): anorexia

- antibodies in serum: sore throat

earliest symptoms of disease as a result of activation of body defenses

- fever, pain, soreness, swelling

signs of inflammation (lesions)

- edema

- granulomas & abscesses

- lymphadenitis

edema

accumulation of fluid

granulomas & abscesses

walled-off collections of inflammatory cells & microbes

lymphadenitis

swollen lymph nodes

changes in number of circulating white blood cells

- leukocytosis

- leukopenia

- septicemia, bacteremia, viremia

leukocytosis

increase in WBCs

leukopenia

decrease in WBCs

septicemia

microorganisms multiplying in blood & present in large numbers

bacteremia

small numbers of bacteria present in blood not necessarily multiplying

viremia

small number of viruses present in blood, not necessarily multiplying

asymptomatic (subclinical) infections

- although infected, host doesn't show any signs of disease

- rather common for an infection to produce no noticeable or typical symptoms

- inapparent infection, patients experience no symptoms, so doesn't seek medical attention

portals of exit definition

- pathogens depart by a specific avenue

- greatly influences the dissemination/spreading of infections

persistence of microbes & pathogenic conditions

- apparent recovery of host does not always mean microbe has been removed

- latency

- chronic carrier

- sequelae

latency

- after initial symptoms in certain chronic diseases, microbe can periodically become active & produce a recurrent disease

- person may or may not shed it during latent stage

chronic carrier

- person w/a latent infection who sheds the infectious agent fora long period

sequelae

long-term or permanent damage to tissues or organs

epidemiology

- study of frequency & distribution of disease & other health-related factors in defined human pop.

- involves many disciplines - not only microbiology, but anatomy, physiology, immunology, medicine psychology, sociology, ecology, & statistics

- considers many disease other than infectious ones, including heart disease, cancer, drug addiction, & mental illness

reservoir

- primary habitat of pathogen in natural world

- human or animal carrier, soil, water, plants

source

individual or object from which an infection is actually acquired

carrier

- individual who inconspicuously shelters a pathogen & spread it to others

- asymptomatic carrier

- passive carrier