MICR:3164 Microbe-Human Interactions

MecA

• another route of beta-lactam resistance

• antibacterial resistance gene

• penicillin attacks peptidoglycan by binding to its target, PBP

• mecA allows bacteria to make another version of target protein called PBP2a

what are microbe-host interaction?

• contact between microbes and hosts

• can be beneficial, neutral, or pathogenic

humans are constantly in contact with microbes, but why aren’t we constantly sick?

• host defenses (immune system)

• resident biota / normal flora

resident biota / normal flora

microbes colonized in/on a host that don’t normally cause disease

colonization

the act of microbes taking up long-term residence in a human host

infection

entry and multiplication of microbes in host tissues

disease

any deviation, including when a microbial infection damages or disrupts host tissues and organs

how do normal flora prevent intruder infection?

• normal flora are colonized and unlikely to be displaced due to limited attachment sites

• normal flora create a hostile environment for other organisms

• normal flora keep each other in check, so that no singular species takes over and causes disease

normal flora preventing intruder infection is an example of what?

microbial antagonism

how do we acquire normal flora?

• microbes present in utero

• acquired during birth

• breastfeeding/formula

• shared from caregivers and family

• environment

pathogenicity

an organism’s potential to cause disease

true pathogens

capable of causing disease in healthy people with normal immune defenses

opportunistic pathogens

cause disease when the host’s defenses are compromised

most infections are likely?

polymicrobialp

polymicrobial

multiple microbes contribute to the disease

ex. influenza and pneumonia

• infection by influenza virus → lungs damaged

• bacteria can easily colonize in wake of influenza

virulence

• describes the severity of disease caused by a microbe

  • ability to establish itself in host

  • ability to cause damage

virulence factor

a characteristic or structure of a microbe that contributes to virulence

steps of establishing infection

1. portals of entry

2. attachment and interaction with microbiome

3. surviving host defenses

4. causing disease

5. vacating host

portal of entry

• route by which a microbe enters a host

• typically a cutaneous (skin) or membranous route

• microbes adapt to use a certain portal of entry otherwise, entry won’t cause infection

infectious dose (ID)

the minimum number of microbes required to establish infection

adhesion

microbes need to gain a stable foothold on host tissues

how do microbes attach and interact?

• adhesion

• microbe may have specific requirements for attachments (eg receptors)

• microbes may have special structures for attachment

why is firm attachment a requirement for microbes?

because many methods of detaching microbes from host tissues exist

how do microbes survive host defenses?

• host immune system recognized “foreign” microbes

• attacks with phagocytes, other immune cells, antibodies, etc.

• microbes have ways to attack back (capsules, toxins, etc.)

how do microbes damage the host?

• directly thru enzymes or toxins

• indirectly by inducing host defenses and producing an excessive response

• epigenetic changes made to host cells

extracellular enzymes

• exoenzymes

• ex. mucinase (degrades mucous)

• ex. coagulase (clots blood)

toxins

specific chemical products of microbes that are poisonous to other organismst

2 types of toxins

exotoxins and endotoxins

exotoxins

proteins with specificity for a target cell and powerful effects

ex. hemolysins lyse RBC

endotoxins

one molecule, LPS, causes a variety of effects on tissues and organs

ex. fever, inflammation, hemorrhage

many aspects of disease are caused by the host trying to what?

trying to rid itself of a pathogen (eg fever, inflammation)

are all responses directly due to something microbe does?

no, not all responses are directly due to something microbe does, but instead the responses it elicits

epigenetics

alterations to DNA that impact how or if a gene is expressed, but the DNA sequence doesn’t change

how do microbes cause epigenetic changes in host cells?

they secrete molecules that interact with DNA to shut off host genes

on the scale of likeliness to cause disease, most microbes fall somewhere in the middle. so what tips the scale?

• microbe

  • virulence factors

  • infectious dose

  • correct portal of entry

• host

  • genetic variability of host defense

  • previous exposure

  • general health

how do disease manifest in the body?

there are many different ways like localized infection, systemic, focal, primary, etc.

sign

any objective evidence of disease as noted by an observer

observed externally

symptom

subjective evidence of disease as sensed by the patient

observed internally

syndrome

when a disease can be identified or defined by certain signs and symptoms

what does inflammatory responses include?

cells and chemicals that respond nonspecifically to disruptions in the tissues

symptoms of inflammation

• fever

• pain

• soreness

• swelling

signs of inflammation

• edema

• granulomas and abscesses

• lymphadenitis

edema

accumulation of fluid in tissue

granulomas and abscesses

walled-off collections of inflammatory cells and microbes in the tissues

lymphadenitis

swollen lymph nodes

signs of infection in the blood

• changes in the number of white blood cells

• presence of a microbe or its products in the blood

changes in the number of circulating WBC

• leukocytosis

• leukopenia

leukocytosis

increase in white blood cell countsle

leukopenia

decrease in white blood cell counts

presence of a microbe or its products in the blood

• septicemia

• bacteremia / viremia

septicemia

microbes are multiplying in the blood

bacteremia / viremia

these microbes are present in blood

infections that commonly cause no symptoms are called?

asymptomatic or subclinical infections

portals of exit

microbes are released from the host through secretion, excretion, discharge, or sloughed tissue

the more microbes released, the more likely…

infection is to spread

does recovery mean microbe is gone?

not always

latency

infectious agent retreats into a dormant state and may recur

sequelae

consequences in the form of long-term or permanent damage to tissues or organs

4 distinct phases of infection course

• incubation

• prodrome

• acute

• convalescence

incubation phase

• from initial contact to first symptoms

• pathogen is multiplying

• established timeline for most infections

• usually 2-30 days

prodrome phase

• earliest notable symptoms

• vague discomfort, but may have specific symptoms

• short period (1-2 days)

acute phase

• microbe is multiplying quickly

• greatest virulence

• well established infection

• fever, cough, rash, etc.

• length is variable

convalescence period

• recovery period

• symptoms decline as body responds to infection

• microbes are still present

continuation phase

• only present in some infections

• organism is present or symptoms continue

reservoir

primary habitat in the natural world where a potential pathogen makes its home

ex. living reservoir: humans, arthropods, animals / non-living: soil, water, air

carrier

an individual who inconspicuously shelters a pathogen and spreads it to others

types of carriers

• asymptomatic

• incubating

• convalescent

• chronic

• passive

asymptomatic carrier

infected but no symptomsi

incubating carrier

spread infection during infection period

convalescent carrier

spread infection during convalescent period

chronic carrier

shelter an infectious agent for a long period because of latency or persistent infections

passive carrier

healthcare workers who handle heavily contaminated patient materials and pass infectious agents to other patients

zoonosis

an infectious agent usually present in animals spreads to humans

ex. rabies, influenza

can human transmit zoonosis to other humans?

usually dead-end hosts as human-human transmission does not occur

what percentage do zoonoses make up in new emerging diseases?

70% of all new emerging diseases

is eradicating of zoonosis diseases with reservoirs easy or hard?

difficult

communicable

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

contagious

when a disease is highly communicable

noncommunicable

infection and disease is not acquired through transmission of an infectious agent host-to-host

ex. infections acquired thru soil

horizontal vs vertical transmission

horizontal is to each other while vertical is to offspring

types of horizontal transmission

• direct contact

• indirect contact

• vector-borne

• foodborne

  • waterborne

direct contact transmision

coming into contact with saliva, mucous, blood, or feces containing germs

indirect contact transmission

coming into contact with areas that have been contaminated with germs

vector-borne transmission

being bitten by a tick or a mosquito carrying a disease-causing agent

foodborne transmission

eating food contaminated with germs

waterborne transmission

drinking or coming into contact with contaminated water

fomite

inanimate object that harbors and transmits pathogens like doorknobs, phones, faucet handles

vehicle

a natural, nonliving material that can transmit infectious agents like aerosols/droplets

aerosols/droplets

suspensions of dust or moisture in air

transmission aids

• fomite

• vehicle

healthcare-associated infections (HAIs)

• nosocomial

• infectious disease that are acquired or developed during a hospital or healthcare facility stay

• patients are often immunocompromised and bring in infectious agents like pneumonia, GI illness, UTIs, bloodstream infections, and surgical site infections

etiologic agent

the precise, causative agent of disease

koch’s postulates

isolate hypothesized agent, inoculate naive population, and see the same disease

epidemiology

study of the frequency and distribution of disease and other health factors

goal of epidemiology

help public health departments develop prevention and treatment programs

reportable diseases

disease that must be reported to authorities by law like anthrax, cancer, foodborne diseases, petussis, tetanus, measles, HIV, lyme disease

prevalence

• total number of existing cases in a given population

• prevALence = ALl cases / population @ risk

incidence

• number of new cases over a certain time period

• iNcidence = New cases / population @ risk

mortality rate

the total number of deaths in a population due to a certain disease

morbidity rate

the number of people afflicted with an infectious disease