Chapter 13: Microbe, Human interactions

Infection

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

Infectious disease

an infection that causes damage or disruption to tissues and organs

Transients

microbes that occupy the body for only short periods

microbe free areas of body

Internal organs, tissues, and fluids

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

Initial Colonization of Fetus and Newborn

Nature of the microbiota initially colonizing large intestine is influenced by whether the baby receives breast milk or formula

-Breaking of fetal membrane exposes the infant to microbes

Colonizers of the Human Skin

Two cutaneous populations

1.Transients: cling to the surface but do not grow there; influenced by hygiene

2.Residents: stable, predictable, less influenced by hygiene, primarily bacteria and yeasts

Microbial Residents of GI Tract

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

-Oral cavity, large intestine, and rectum harbor permanent microbes

-GI tract is a long hollow tube, bounded by mucous membranes; tube is exposed to the environment

Microbiota of the Mouth

Most diverse and unique flora of the body

-Numerous adaptive niches in microhabitats: cheek epithelium, gingiva, tongue, floor of the mouth, and tooth enamel

-most common residents are aerobic Streptococcus species

Microbiota of Large Intestine

-Has complex and profound interactions with host microbes per gram of feces (≥30% fecal volume)

-contribute to intestinal odor

-Intestinal environment favors anaerobic bacteria

-ex: Bacteroides, Bifidobacterium, Fusobacterium, Clostridium

byproducts of microbiota of large intestine

1.Fermentation of waste materials in the feces generates vitamins (B12, K, pyridoxine, riboflavin, and thiamine) and acids (acetic, butyric, and propionic)

2.Bacterial digestive enzymes that convert disaccharides to monosaccharides or promote steroid metabolism

microbiota of respiratory tract

Oral streptococci, first organisms to colonize

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

Mucous membranes of nasopharynx: Neisseria species

-Tonsils and lower pharynx: Assorted streptococci and Haemophilus

-No flora in bronchi and lungs

Microbiota of the Genitourinary Tract

Sites that harbor microflora: Females: Vagina and outer opening of urethra; Males: Anterior urethra

-Internal reproductive organs kept sterile through physical barriers (i.e. cervical plug)

-Kidney, ureter, bladder, and upper urethra kept sterile by urine flow

-Changes in physiology influence composition of normal flora, Vagina (estrogen, glycogen, pH)

altering microbiota

Antibiotics, dietary changes, and disease

True pathogens

capable of causing disease in healthy persons with normal immune defenses

-Influenza virus, plague bacillus, malarial protozoan

Opportunistic pathogens

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

-ex: Pseudomonas sp. and Candida albicans

Virulence factor

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

-can be a singular feature or multiple features

Portals of entry

Characteristic route a microbe follows to enter the tissues of the body

Exogenous agents

originate from source outside the body

Endogenous agents

already exist on or in the body (normal flora)

portals of entry

1. Skin -nicks, abrasions, punctures, incisions

2. Gastrointestinal tract - food, drink, and other ingested materials

3.Respiratory tract - oral and nasal cavities

4.Urogenital tract - sexual, displaced organisms

5.Transplacental

TORCH infections

Toxoplasmosis

Other (syphilis, varicella-zoster virus, parvovirus B19, HIV)

Rubella

Cytomegalovirus

Herpes

-Pathogens That Infect during Pregnancy

Infectious Dose (ID)

Minimum number of microbes required for infection to proceed

-Microbes with small IDs have greater virulence

-Number of microbes below ID will not result in infection

Adhesion

microbes gain a stable foothold at the portal of entry

-dependent on binding between specific molecules on host and pathogen

-mechanisms: Fimbriae, Pili, Flagella, Capsules, Suckers, Hooks, Barbs

Antiphagocytic factors

virulence factors that help pathogens to avoid phagocytes

-some secrete a slime or capsule to make it difficult for phagocytes to engulf them

-some adapted to survive inside phagocytes

-some produce leukocidins to impair and sometimes lyses leukocytes (white blood cells)

exoenzyme

a factor in invasiveness of pathogens; disrupt the structure of tissues

mucinase

digests the protective coating on mucous membranes

-a factor in amoebic dysentery

-promotes spread of microbes

keratinase

digests keratin (component of skin, hair, nails)

-secreted by fungi that cause ringworm

collagenase

breaks down collagen which forms connective tissue

-invasive factor of Clostridum species and some parasitic worms

hyaluronidase

digests polysaccharides that hold cells together

-important virulence factor in staph, clostridia, streptococci, pneumococci

Toxin

specific chemical product of microbes, plants, and some animals that has poisonous effects on other organisms

Toxinoses

Disease whose adverse effects are primarily due to the production and release of toxins

Toxemias

when the toxin is spread by the blood from the site of infection -ex: tetanus, diphtheria

Intoxications

caused by ingestion of toxins

- ex: botulism

Endotoxin

not secreted, but released after the host cell is damaged

-composed of a phospholipid-polysaccharide complex that is an integral part of gram-negative bacterial cell walls

-can cause severe shock and fever

Exotoxin

secreted by a living bacterial cell into the infected tissue and acts upon a specific cellular target

-disrupts cell membrane

-sub group: Hemolysins

Hemolysins

toxins that lyse red blood cells

-ex: A-B toxins

Four stages of clinical infections

1. incubation period

2. prodromal stage

3. period of invasion

4. convalescent period

Incubation period

time from initial contact with the infectious agent to the 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 and symptoms

Convalescent period

as person begins to respond to the infection, symptoms decline

-immune response begins to clear infectious agent

Localized infection

microbes enter the body and remains confined to a specific tissue

-ex: boils, fungal skin infection, warts

Systemic infection

infection spreads to several sites and tissue fluids usually in the bloodstream

-ex: viral, bacterial and fungal diseases (measles, AIDS, anthrax, rabies)

Focal infection

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

-ex: tuberculosis, toxemia

Mixed infection

several microbes grow simultaneously atthe infection site (polymicrobial)

-result of biofilm formation at site of infection

Acute infection

comes on rapidly, severe but short-lived effects

Chronic infections

progress and persist over long period of time

Sign

objective evidence of disease as noted by an observer

-more precise and measured

-ex: fever, swollen lymphnodes, antibodies in serum

Symptom

subjective evidence of disease as sensed by the patient

-ex: chills, pain, nausea, itching, headache

signs of inflammation

-Edema: accumulation of fluid

-Granulomas and abscesses: walled-off collections of inflammatory cells and microbes

-Lymphadenitis: swollen lymph nodes

-rednesss, pain, swelling

signs of infection in the blood

Changes in the number of circulating white blood cells

Leukocytosis

increase in white blood cells

Leukopenia

decrease in white blood cells

Septicemia

microorganisms are multiplying in the blood and present in large numbers

Portals of Exit

greatly influences the dissemination of infection•

-Respiratory and salivary portals, mucus, sputum, nasal drainage, saliva

-Epithelial cells: skin and scalp

-Fecal exit, Urogenital tract; Removal of blood or bleeding

Latency

-peroid of inactiveness

-after the initial symptoms in certain chronic diseases, the microbe can periodically become active and produce a recurrent disease; person may or may not shed it during the latent stage

Sequelae

long-term or permanent damage to tissues or organs

Epidemiology

study of the frequency and distribution of disease and other health-related factors in defined human populations

Incubation carriers

spread the infectious agent during the incubation period

-ex: HIV

Convalescent carriers

recuperating patients without symptoms; they continue to shed viable microbes and convey the infection to others

-ex: norovirus

Chronic carrier

individual who shelters the infectious agent for a long period

-ex: herpes, hepatitis

Vector

animal that transmits an infectious agent from one host to another

-fleas, mosquitoes, flies, and ticks

-mammals, birds, lower vertebrates

Mechanical vector

not necessary to the life cycle of an infectious agent and merely transports it without being infected

Biological vectors

actively participate in a pathogen's life cycle

Zoonosis

Infection indigenous to animals naturally transmissible to humans

-Impossible to eradicate the disease without eradicating the animal reservoir

Communicable disease

when an infected host can transmit the infectious agent to another host and establish infection in that host

-highly communicable disease is contagious

-ex: influenza, measles

Non-communicable infectious disease

does not arise through transmission from host to host

-Occurs primarily when a compromised person is invaded by their own microbiota

-Contact with organism in natural, non-living reservoir

-ex: some fungal diseases

Surveillance

Epidemiologists collecting, analyzing, and reporting data on rates of occurrence, mortality, morbidity and transmission of infections

Prevalence

total number of existing cases with respect to the entire population usually represented by a percentage of the population

Incidence

measures the number of new cases over a certain time period, as compared with the general healthy population

-morbidity rate/case rate (# of people affected)

Endemic Occurrence

disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale

-ex: lyme disease cases

Sporadic Occurrence

when occasional cases are reported at irregular intervals

Epidemic Occurrence

when prevalence of a disease is increasing beyond what is expected

Outbreak

small scale epidemic in a more limited area

Propagated epidemic

shows sustained increase overtime, indicating that it is being communicated from person to person

Common-source epidemic

all cases from exposure to the same source

Nosocomial infections

diseases that are acquired during a hospital stay

-From surgical procedures, equipment, personnel, and exposure to drug-resistant microorganisms

-most common involve surgical incisions and the respiratory tract, GI tract, skin, urinary tract, and blood

-ex: Gram-negative intestinal flora, Gram-positive bacteria, yeasts, hep B, influenza