MIcro exam 3

Normal flora/microbiota

• microorganisms that live on the human body and do not normally cause disease, native types of bacteria, fungi, and viruses that normally reside on the body

• microbes that engage in mutual or commensal associations with individuals

Commensal symbiotic relationship

where both benefit 

• ex. the normal microbiota strains of Escherichia coli in the human intestine that don’t produce virulence factors such as toxins that cause bloody, mucoidy diarrhea, these normal strains of E. coli help us digest our food and produce vitamin K

Commensal relationship

where one organism benefits while the other is unaffected

What makes normal microbiota “normal”

• is the immune system’s ability to keep it in check

• some of the normal microbiota are opportunistic and can cause infections if circumstances change such as if the host becomes immunocompromised due to age, medical condition, certain infections, certain treatments

Microbial antagonism

the effect “good” microbes have on intruder microbes

• the microbiota that exists in well established biofilm are unlikely to be displaced by incoming microbes

• normal microbiota compete with potential pathogens for nutrients, space

• normal microbiota can create conditions and sometimes secrete substances that make it more difficult for potential pathogens to thrive

Normal flora will have beneficial effects only if

host in good health, functioning immune system, flora stay in their natural habitats

• Aids pts - often contract pneumonia from Streptococcus pneumoniae, usually a normal flora of the nasopharynx

• E. Coli - entering from the large intestine into bladder causing urinary tract infection

Sites that harbor normal microbiota

• Skin and its mucus membranes

• Upper respiratory tract - oral cavity, pharynx, nasal mucosa 

• GI tract - rectum, anus, mouth, colon

• Outer opening of urethra, vagina, external genitalia

• External ear and canal

• Eyelids and lash follicles

Sites that don't harbor normal microbiota

• All internal tissues and organs/bones/muscles

• Fluids within an organ/tissue

Flora of the skin

• Staphylococcus

• yeast 

Flora of the oral cavity

• Fusobacterium

• lactobacillus 

Flora of the large intestine

• Candida

• clostridium 

Flora on the genital tract

• Ditheroids

• escherichia  

Flora on the urinary tract

• Corynebacterium

• streptococcus 

Factors that predispose person to infection

• Old age and extreme youth (infancy, prematurity)

• Genetic defects in immunity and acquired defects in immunity, Surgery, organ transplants

• Organic disease: cancer, liver malfunction, diabetes

• Chemotherapy/immunosuppressive drugs

• Physical and mental stress, Other infections

The course of an infection

1. Find a portal of entry

2. Attach to host structures through adhesion

3. Survive the hosts defenses

4. Cause damage and disease to the host - direct/indirect

5. Portal of exit

Portal of entry

• skin – nicks, abrasions, punctures, incisions

• Gastrointestinal tract – food, drink, and other ingested materials

• Respiratory tract – oral and nasal cavities

• Urogenital tract – sexual contact, displaced organisms, Transplacental

Attach to host structures through adhesion

process by which pathogens must gain a more stable foothold at the portal of entry in order to cause disease

• Bacteria, Fungi & Protozoa use fimbriae, flagella, adhesive slime and capsules

• Viruses use specialized receptors

• Parasitic worms use suckers, hooks and barbs

Survive the hosts defenses

Initial response of host defenses comes from phagocytes (Immune cells that can engulf pathogens and destroy them)

• Avoid phagocytosis or being engulfed by the host’s immune cells

• Species of Staphylococcus and Streptococcus produce leukocidins (toxins that kill white blood cells)

• Slime layer or capsule makes phagocytosis difficult 

Cause damage and disease to the host

• Indirect damage

  • The immune system’s response might cause damage

  • May be inappropriate or excessive

• Direct damage

  • Virulence factors such as toxins and enzymes

  • Lysis

Portal of exit

released or shed from body through secretion, excretion, discharge, sloughed tissue

• respiratory tract/salivary glands - mucus, sputum, nasal drainage, coughing, sneezing, talking, laughing  

• skin cells - shedding, skin lesions 

• fecal matter, urogenital tract, blood

Stages of clinical infections

1. incubation period

2. prodromal stage

3. period of invasion

4. convalescent period

Incubation period

initial contact with infectious agent at portal of entry, agent is multiplying but no damage to elicit symptoms

lasts several hours to years 

Prodromal stage

vague feelings of discomfort (malaise, head/muscle aches, fatigue)

lasts 1-2 days 

Period of invasion

highly multiplies, greatest toxicity, well established, prominent signs and symptoms

last varies 

Convalescent period

patient begins to respond to infection, symptoms decline, recovering 

Pathogen

parasitic microbes that cause infection and disease

Pathogenicity

capacity of an organism to cause infection and disease

True pathogens

capability of causing disease in healthy persons with normal immune defenses

• Influenza virus, plague bacillus, malarial protozoan

Opportunistic pathogens

causes disease when host defenses are compromised or when they grow in part of body that is not natural to them

Virulence

capacity of a pathogen to invade and harm host cells (degree of pathogenicity)

Virulence factors

characteristic or structure that contributes to ability of microbe to cause disease/product of microbe such as an enzyme or toxin that increases the microbes pathogenicity

local infection

microbes enter body and remain confined to specific tissue

systemic infection

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

focal infection

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

mixed infection

several microbes grow simultaneously at infection site (polymicrobial infection)

primary infection

initial infection

secondary infection

another infection by a different microbe

signs

subjective evidence of disease as sensed by the patient

Symptoms

objective evidence of disease as noted by an observer

syndrome

specific group of symptoms or signs which accompany a particular disease

Leukocytosis

high leukocytes/WBCs

Leukopenia

low level leukocytes/WBCs

Septicemia

• general state of having microbes multiply in blood and are present in large numbers

Bacteremia

small numbers of bacteria in the blood, not necessarily multiplying in the blood

Viremia

small numbers of virus in the blood, not necessarily multiplying in the blood

latency

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

chronic carrier

person with latent infection who sheds infectious agent

Sequelae

long-term or permanent damage to tissues or organs

Reservoir

primary habitat of pathogen in the natural world

• Human or animal carrier, soil, water, plants

• Some sources are reservoirs (i.e. syphilis) and some are not (hepatitis A: reservoir human carrier, source-contaminated food)

Infection source

individual or object from which infection is actually acquired

Vector

A live animal (other than human) that transmits an infectious agent from one host to another

arthropods

• Majority of vectors (fleas, mosquitoes, flies, and ticks)

• and some larger animals can also spread infection (mammals, birds, lower vertebrates)

Biological vectors

actively participate in pathogen’s life cycle, serving as a site in which it can multiply or complete its development 

Mechanical vector

not necessary to life cycle of infectious agent and merely transports it without being infected, transferred to humans indirectly by food or direct contact like eye infections, mainly by houseflies 

zoonosis

An infection indigenous to animals but naturally transmissible to humans

• humans don’t usually pass zoonoses to others

• at least 150 zoonoses exist worldwide; make up 70% of all new emerging diseases worldwide

• impossible to eradicate disease without eradicating animal reservoir

Nonliving reservoirs

Soil, water and air 

Incubation carriers

spread infectious agent during incubation period before symptoms appear 

Convalescent carriers

• individuals who are recuperating and recovering from the illness but continue to shed the pathogen despite no longer showing symptoms

Passive carrier

•  contaminated healthcare provider picks up pathogens and transfers them to other patients

Communicable disease

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

iIf agent is highly communicable, especially direct contact - contagious 

Non-communicable

infectious disease does not arise through transmission from host to host

• occurs primarily when a compromised person is invaded by his or her own normal microflora or with accidental contact with a facultative parasite that exists in a nonliving reservoir like soil 

Direct Transmission

physical contact or fine aerosol droplets transmit the pathogen

Indirect Transmission

pathogen passes from infected host to intermediate conveyor and then to another host, (when inanimate objects are contaminated)

• Vehicle - inanimate material, food, water, biological products

• fomites - any inanimate object that harbors and transmits pathogens except food, water, bio. product

Airborne transmitters

• droplet nuclei (dried residue of mucus and saliva)

• aerosols (suspensions of fine dust or moisture particles in air that contain a live pathogen)

Nosocomial Infection

HAIs

• from surgical procedures, equipment, personnel, exposure to drug-resistant microorganisms

• 2 to 4 million cases/year in U.S. with 90,000 deaths 

• most commonly involve urinary tract, respiratory tract, and surgical incisions

• Most common organisms involved: Gram-negative intestinal flora (E.coli, pseudo, staph)

Epidemiology

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

Surveillance

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

CDC

in Atlanta, GA, principal government agency responsible for keeping track of infectious diseases nationwide, home to the NNDSS

• The Morbidity and Mortality Weekly Report: a weekly notice of diseases

Mortality rate: total number of deaths in a population due to a certain disease

Morbidity rate: number of people afflicted with a certain disease

Prevalence:

 total cumulative number of cases of a disease in a certain area and time period

Incidence

number of new cases of a disease occurring during a time period

Endemic

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

Sporadic -

when occasional cases are reported at irregular intervals

Epidemic -

when prevalence of disease is increasing beyond what is expected

Pandemic

epidemic across continents

Infectious Dose (ID)

minimum number of a particular pathogen required to establish infection

• Low ID = only a few organisms needed to make you sick, have greater virulence

• High ID = many organisms needed to cause infection

• Very high ID = rapid onset 

virulence factors

Antiphagocytic factors

Extracellular enzymes: exoenzymes

Bacterial toxins: exo/endotoxins

Antiphagocytic factors

ways used by pathogens to avoid phagocytes

• Species of Staphylococcus and Streptococcus produce leukocidins (toxins that kill white blood cells)

• Slime layer or capsule makes phagocytosis difficult 

Extracellular enzymes

exoenzymes that break down and inflict damages on tissues

Can dissolve extracellular barriers and penetrate through or between cells

Extracellular enzymes - Mucinase

• dissolves mucous membranes

Extracellular enzymes - Keratinase

• dissolves main component of skin/hair (ringworm)

Extracellular enzymes - Collagenase

• dissolves collagen, the principle fiber of connective tissue (Clostridium, certain worms)

Extracellular enzymes - Hyaluronidase

• dissolves hyaluronic acid, the “cement” that holds animal cells together (various bacterial sp.

Extracellular enzymes - Bacterial kinases

• breaks down fibrin clots

Toxin

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

Toxigenicity

tendency for a pathogen to produce toxins

Toxinosis

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

Toxemia

toxin is spread by blood from the infection site 

Exotoxins

• secreted by a bacterial cell into infected tissues, have highly specific targets and physiologic effects 

• Hemolysins (lyse blood cells, used by Streptococcus pyogenes & Staphylococcus aureus)

• A-B toxins (two-part toxin: A-active, B-binding, ex. tetanus toxin & botulism toxin)

Endotoxins

• released only after cell is damaged/lysed, have general physiologic effects, high levels lead to shock 

  • lipopolysaccharide (LPS), part of outer membrane of gram-negative cell walls  

endotoxin or exotoxin? toxic in high quantities 

endotoxin

endotoxin or exotoxin? generalized physiological effects, systemic but less specific 

endotoxin

endotoxin or exotoxin? substance called lipopolysaccharide which is part of the outer membrane of gram negative cell envelopes; when gram neg bacteria cause infections some of the bacteria eventually lyse and release these LPS molecules on the infection site/ into circulation

endotoxin

endotoxin or exotoxin? heat denaturation stable 

endotoxin

endotoxin or exotoxin? cannot be converted to toxiod

endotoxin

endotoxin or exotoxin? has immune response

endotoxin

endotoxin or exotoxin? has fever stimulation

endotoxin

endotoxin or exotoxin? released from cell wall during lysis 

endotoxin

endotoxin or exotoxin? source is all gram neg bacteria 

endotoxin

endotoxin or exotoxin? meningitis, endotoxic shock, salmonellosis 

endotoxin

endotoxin or exotoxin? strong specificity for a target cell and very powerful deadly effects

exotoxin