Host Microbe Interactions Kathy Huschle Northland Community and Technical College

Host Microbe InteractionsHost Microbe Interactions

Kathy HuschleKathy Huschle

Northland Community and Technical CollegeNorthland Community and Technical College


daily we daily we – ingest thousands of microorganisms on the food we ingest thousands of microorganisms on the food we

eateat– inhale hundreds of thousands of microorganisms in inhale hundreds of thousands of microorganisms in

the air we breaththe air we breath– have microorganisms stick to us wherever we gohave microorganisms stick to us wherever we go

most of these invaders have no ill effect on us as we most of these invaders have no ill effect on us as we slough, cough, gag, urinate and defecate them awayslough, cough, gag, urinate and defecate them away

we are also protected by the “friendly” resident we are also protected by the “friendly” resident microorganisms found throughout our bodymicroorganisms found throughout our body


microorganisms very easily colonize the warm, moist, microorganisms very easily colonize the warm, moist, nutrient rich environment we call the human bodynutrient rich environment we call the human body– usually they live as normal florausually they live as normal flora– in some cases, they are able to overcome the bodies in some cases, they are able to overcome the bodies

defenses, and cause diseasedefenses, and cause disease– organisms that can cause any noticeable damage, organisms that can cause any noticeable damage,

invade tissue, or produce toxins are called pathogensinvade tissue, or produce toxins are called pathogens

please review the terms used for the study of infectious please review the terms used for the study of infectious disease found in Table 19.1 on page 460 in your text disease found in Table 19.1 on page 460 in your text

Anatomical BarriersAnatomical Barriers

in addition to providing barriers to in addition to providing barriers to the microbial world, skin and the microbial world, skin and mucous membranes also create mucous membranes also create an environment for interacting an environment for interacting microorganisms and the human microorganisms and the human bodybodythese interactions are referred to these interactions are referred to as symbiosis, which means living as symbiosis, which means living togethertogether– the players in symbiosis are the players in symbiosis are

referred to as symbiontsreferred to as symbionts

Anatomical BarriersAnatomical Barriers

symbiotic relationships between microorganisms and a symbiotic relationships between microorganisms and a host includehost include– mutualismmutualism– commensalismcommensalism– parasitismparasitism

MutualismMutualism

in this type of relationship, both partners benefitin this type of relationship, both partners benefit– E. coliE. coli synthesizes vitamin K in the intestine synthesizes vitamin K in the intestine– in exchange the large intestine provides nutrients in exchange the large intestine provides nutrients

necessary for survival of the microorganismsnecessary for survival of the microorganisms

E. coliE. coli

CommensalismCommensalism

one organism is benefited and the other is unaffected by one organism is benefited and the other is unaffected by this type of relationshipthis type of relationship– many of the microorganisms that make up our normal many of the microorganisms that make up our normal

flora inhabit places like the eyes, ears, and external flora inhabit places like the eyes, ears, and external genitaliagenitalia

these bacteria live on secretions and sloughed off these bacteria live on secretions and sloughed off cellscells

they bring no benefit to the host and yet the they bring no benefit to the host and yet the microorganisms benefit greatly from the microorganisms benefit greatly from the environment they inhabitenvironment they inhabit

ParasitismParasitism

one organism benefits at the expense of the otherone organism benefits at the expense of the other– all pathogens are parasitesall pathogens are parasites

parasitic microorganisms

Normal FloraNormal Flora

microorganisms that colonize a host without causing microorganisms that colonize a host without causing diseasedisease

two types of normal flora existtwo types of normal flora exist– resident flora are microorganisms that inhabit sites on resident flora are microorganisms that inhabit sites on

the body for extended periodsthe body for extended periods– transient flora are microorganisms that are temporarytransient flora are microorganisms that are temporary


the presence of normal florathe presence of normal flora– cover potential adherence sites for invading cover potential adherence sites for invading

microorganismsmicroorganisms– consume the available nutrientsconsume the available nutrients– produce compounds toxic to other microorganismsproduce compounds toxic to other microorganisms

bacteria found on skin


when the balance between normal flora and when the balance between normal flora and pathogens is upset, disease can resultpathogens is upset, disease can result– the normal bacterial microorganisms of the adult the normal bacterial microorganisms of the adult

human vagina maintain the pH at about 3.4 – 4.5human vagina maintain the pH at about 3.4 – 4.5– the presence of this normal flora inhibits the the presence of this normal flora inhibits the

overgrowth of overgrowth of Candida albicansCandida albicans, yeast, yeast


– if the presence of the normal flora is eliminated by if the presence of the normal flora is eliminated by antibiotics, or excessive douching, the pH of the antibiotics, or excessive douching, the pH of the vagina becomes nearly neutral, creating an vagina becomes nearly neutral, creating an environment very conducive to the growth of environment very conducive to the growth of C. C. albicansalbicans

C. albicans

Principles of Infectious DiseasePrinciples of Infectious Disease

a parasitic relationship between a microorganism and a a parasitic relationship between a microorganism and a host is called an infectionhost is called an infection– infections can be subclinical or inapparent: meaning infections can be subclinical or inapparent: meaning

no symptoms or the symptoms are so mild as to be no symptoms or the symptoms are so mild as to be noticednoticed

infection that causes impairment of body function is infection that causes impairment of body function is called diseasecalled disease


pathogenicitypathogenicity is the ability of a microorganism to cause is the ability of a microorganism to cause disease by overcoming the host defensesdisease by overcoming the host defenses– this can be accomplished withthis can be accomplished with

a a primary pathogenprimary pathogen: microorganism capable of : microorganism capable of causing disease in a healthy hostcausing disease in a healthy host

opportunistic pathogenopportunistic pathogen: is only capable of : is only capable of causing disease when the immune system is causing disease when the immune system is overcome, or the organism is introduced to an overcome, or the organism is introduced to an unusual locationunusual location

– opportunistic organisms can be part of the opportunistic organisms can be part of the normal flora or found in the environmentnormal flora or found in the environment


the more virulent a pathogen is the more disease the more virulent a pathogen is the more disease promoting attributes it possessespromoting attributes it possesses– virulence factors are substances or features of a virulence factors are substances or features of a

microorganism that help it infect and cause diseasemicroorganism that help it infect and cause disease– they may includethey may include

ability to adhereability to adhere

ability to overcome host defenseability to overcome host defense

ability to evade host defenseability to evade host defense

Terminology of Infectious DiseasesTerminology of Infectious Diseases

communicablecommunicable– disease that spreads from one host to another, either disease that spreads from one host to another, either

through direct or indirect contactthrough direct or indirect contact

infectious doseinfectious dose– # of microbes needed to establish infection# of microbes needed to establish infection

some microorganisms are less contagious than some microorganisms are less contagious than others and as a result require a larger number of others and as a result require a larger number of pathogens present to establish diseasepathogens present to establish disease


signsign– objective changes that are observable and objective changes that are observable and

measurablemeasurable– examples of signs include swelling, fever, paralysis examples of signs include swelling, fever, paralysis

symptomssymptoms– subjective effects experienced by patientsubjective effects experienced by patient– examples of symptoms include pain or nauseaexamples of symptoms include pain or nausea


disease stagesdisease stages– incubationincubation

the time between the initial infection and the first the time between the initial infection and the first appearance of any signs or symptomsappearance of any signs or symptomsthis time can vary depending on the pathogen and this time can vary depending on the pathogen and the condition of the hostthe condition of the host

– illnessillnesssigns and symptoms of the disease are experiencedsigns and symptoms of the disease are experiencedif the disease is not successfully overcome or if the disease is not successfully overcome or treated, the patient dies during this periodtreated, the patient dies during this period

– convalescenceconvalescenceperson regains strength and the body returns to its person regains strength and the body returns to its pre-diseased statepre-diseased state

Terminology of Infectious DiseasesTerminology of Infectious Diseasestypes of infectious diseasestypes of infectious diseases– acute diseaseacute disease

rapid onset, short durationrapid onset, short durationinfluenza is an acute diseaseinfluenza is an acute disease

– chronic diseasechronic diseasedevelop slowly, last longerdevelop slowly, last longerthe body’s reaction may be less severethe body’s reaction may be less severehepatitis B is a chronic disusehepatitis B is a chronic disuse

– latent diseaselatent diseasecausative agent is never completely eliminatedcausative agent is never completely eliminatedremains inactive, but can become reactivated and remains inactive, but can become reactivated and symptomatic if immune response is diminishedsymptomatic if immune response is diminishedshingles is a latent diseaseshingles is a latent disease


localized infectionslocalized infections– invading microorganisms are limited to a small areainvading microorganisms are limited to a small area– boils and abscesses are local infectionsboils and abscesses are local infections

systemic infectionssystemic infections– infectious agent spread throughout body by blood or infectious agent spread throughout body by blood or

lymphlymph– measles is a systemic infectionmeasles is a systemic infection

Establishing the Cause of Infectious Establishing the Cause of Infectious DiseaseDisease

Koch’s PostulatesKoch’s Postulates– criteria for establishing the fact that specific microbes criteria for establishing the fact that specific microbes

cause specific diseasescause specific diseases– determined by Robert Koch in 1877 while looking for determined by Robert Koch in 1877 while looking for

the causative agent for anthraxthe causative agent for anthrax


Koch’s PostulatesKoch’s Postulates– in order to determine that a microbe causes a in order to determine that a microbe causes a

particular disease, the following postulates must be particular disease, the following postulates must be met:met:

1.1. The microorganism must be present in every case of The microorganism must be present in every case of the disease.the disease.

2.2. The organism must be grown in a pure culture from The organism must be grown in a pure culture from diseased hosts.diseased hosts.

3.3. The same disease must be produced when a pure The same disease must be produced when a pure culture of the organism is introduced into a susceptible culture of the organism is introduced into a susceptible host.host.

4.4. The organism must be recovered from the The organism must be recovered from the experimentally infected hosts.experimentally infected hosts.


exceptions to Koch’s Postulates includeexceptions to Koch’s Postulates include– some organisms cannot be cultured in a labsome organisms cannot be cultured in a lab– some pathogens can cause several disease conditions some pathogens can cause several disease conditions

such as such as S. pyogensS. pyogens which can cause sore throat, which can cause sore throat, scarlet fever, skin infections and other diseasesscarlet fever, skin infections and other diseases

– there may be ethical reasons that does not allow there may be ethical reasons that does not allow testingtesting

Mechanisms of PathogenesisMechanisms of Pathogenesis

pathogenesis is the manner in which a disease developspathogenesis is the manner in which a disease develops– patterns that disease-causing microorganisms may patterns that disease-causing microorganisms may

follow includefollow include

production of ingested toxinsproduction of ingested toxins– foodborne intoxicationfoodborne intoxication– the causative agent must produce toxinsthe causative agent must produce toxins– few organisms are capable of causing disease few organisms are capable of causing disease

this way, the few that can include this way, the few that can include Clostridium Clostridium botulinumbotulinum or or Staphylococcus aureusStaphylococcus aureus


colonization of host surface, then toxin productioncolonization of host surface, then toxin production– invading pathogen is able to grow to high invading pathogen is able to grow to high

numbers on host surfaces such as the numbers on host surfaces such as the respiratory and intestinal tractrespiratory and intestinal tract

– they then produce a toxin that is damaging to they then produce a toxin that is damaging to the cellsthe cells

– organisms that use this mechanism include organisms that use this mechanism include VibrioVibrio choleraecholerae, which causes cholera or , which causes cholera or Corynebacterium diphtheriaeCorynebacterium diphtheriae, which causes , which causes diphtheriadiphtheria


invasion of host tissueinvasion of host tissue– breaching body’s barriers then multiplies in the breaching body’s barriers then multiplies in the

body’s tissuesbody’s tissues– these organisms have mechanisms that allow these organisms have mechanisms that allow

them to avoid macrophage destructionthem to avoid macrophage destruction– some are also capable of avoiding detection by some are also capable of avoiding detection by

antibodiesantibodies– organisms that use this mechanism include organisms that use this mechanism include

Mycobacterium tuberculosisMycobacterium tuberculosis, causative agent , causative agent for tuberculosis, and for tuberculosis, and Yersinia pestisYersinia pestis, causative , causative agent for plaqueagent for plaque


invasion of tissue, then toxin productioninvasion of tissue, then toxin production– breach the body’s barriers, then make toxinsbreach the body’s barriers, then make toxins– in addition to invasion, these organisms also in addition to invasion, these organisms also

make toxinsmake toxins– organisms that use this mechanism include organisms that use this mechanism include

ShigellaShigella dysenteriaedysenteriae and and Streptococcus Streptococcus pyogenespyogenes


in order to cause disease microorganisms need to be in order to cause disease microorganisms need to be able toable to– adhere and colonize host tissueadhere and colonize host tissue– avoid the innate defensesavoid the innate defenses– avoid the adapted defensesavoid the adapted defenses– cause damage related to the diseasecause damage related to the disease

AdherenceAdherence

to establish disease the causative agent needs toto establish disease the causative agent needs to– adhereadhere

difficult to overcome our first-line defenses so difficult to overcome our first-line defenses so adherence is imperative adherence is imperative

many bacteria have adhesions, generally found on many bacteria have adhesions, generally found on the pilithe pili

ColonizationColonization

causative agent needs tocausative agent needs to– multiply in order to colonizemultiply in order to colonize

to multiply, they must compete successfully with to multiply, they must compete successfully with the normal flora for space and nutrientsthe normal flora for space and nutrients

– toxins that may be produced by the normal flora toxins that may be produced by the normal flora must be overcomemust be overcome

Avoiding Innate SystemAvoiding Innate Systemwhile some bacteria are able to cause disease while while some bacteria are able to cause disease while remaining on the surface of the skin or mucosa, remaining on the surface of the skin or mucosa, many need to penetrate that barriermany need to penetrate that barrier

once this is done, those pathogens have it on easy once this is done, those pathogens have it on easy street, exclusive rights to rich nutrition and street, exclusive rights to rich nutrition and multiplying without any competitionmultiplying without any competition

penetrating the skin is extremely difficultpenetrating the skin is extremely difficult– bacteria take advantage of trauma to provide a bacteria take advantage of trauma to provide a

break in the skinbreak in the skin– West Nile Virus is transmitted to the host through West Nile Virus is transmitted to the host through

a mosquito bite, a penetration of the skina mosquito bite, a penetration of the skin

Avoiding Innate SystemAvoiding Innate System

mucous membranes penetration is the most common mucous membranes penetration is the most common entry for most microorganismsentry for most microorganisms– one method that is used is referred to as rufflingone method that is used is referred to as ruffling

once the microorganism attaches to the once the microorganism attaches to the membrane, it can direct the that cell to engulf the membrane, it can direct the that cell to engulf the bacterium:bacterium: this is referred to as rufflingthis is referred to as ruffling

ruffling on the surface of mucous membrane

Avoiding Innate and Adaptive SystemAvoiding Innate and Adaptive System

several mechanisms can be used by microorganisms to several mechanisms can be used by microorganisms to avoid the potentially lethal effects of our immune systemavoid the potentially lethal effects of our immune system– hide inside a host cellhide inside a host cell

phagocytes, complement and antibodies can’t find phagocytes, complement and antibodies can’t find them: remember self and non-self!them: remember self and non-self!

– interfere with the activation of complement (which interfere with the activation of complement (which attracts phagocytes)attracts phagocytes)


avoid destruction by phagocytes by simply preventing avoid destruction by phagocytes by simply preventing encounters with phagocytesencounters with phagocytes– C5a peptides are an enzyme that is made by some C5a peptides are an enzyme that is made by some

bacteriabacteria– C5a peptide C5a peptide destroys the complement componentdestroys the complement component

if the complement is not activated, neither are the if the complement is not activated, neither are the phagocytesphagocytes

– some bacteria produce membrane-damaging toxins some bacteria produce membrane-damaging toxins that that kill phagocyteskill phagocytes


avoid recognition and attachment to phagocytes byavoid recognition and attachment to phagocytes by– producing capsules to prevent phagocytosisproducing capsules to prevent phagocytosis

Streprococcus pneumoniaeStreprococcus pneumoniae procduces capsules procduces capsules

survive in the phagocytesurvive in the phagocyte– they don’t worry about being engulfed, simply enjoy they don’t worry about being engulfed, simply enjoy

the “free ride”the “free ride”some microorganisms can escape from the some microorganisms can escape from the phagosome before being fused with the enzyme phagosome before being fused with the enzyme lysosomelysosome


survive in the phagocytesurvive in the phagocyte– some microorganisms can block the fusion of the some microorganisms can block the fusion of the

phagosome and lysosomephagosome and lysosome– a few organisms can actually survive the lysosome a few organisms can actually survive the lysosome

environmentenvironment

Avoiding the Adaptive SystemAvoiding the Adaptive Systemavoiding antibodies which integral to the adaptive avoiding antibodies which integral to the adaptive system; this can be accomplished several ways includingsystem; this can be accomplished several ways including– IgA proteaseIgA protease

cleaves IgA class of antibodies found in mucus cleaves IgA class of antibodies found in mucus and other secretionsand other secretions

– antigenic variationantigenic variation

alter structure of antigensalter structure of antigens

stay ahead of antibody production and destruction stay ahead of antibody production and destruction by altering the structure the antibodies are by altering the structure the antibodies are searching forsearching for

– mimic host moleculesmimic host molecules

some microorganisms have the ability to cover some microorganisms have the ability to cover themselves with molecules similar to “self”themselves with molecules similar to “self”

Host DamageHost Damage

in order for disease to happen damage of some sort in order for disease to happen damage of some sort must happen to the hostmust happen to the host– in most cases damage to the host facilitates dispersal in most cases damage to the host facilitates dispersal

of the pathogenof the pathogen

damage to the host can occur eitherdamage to the host can occur either– directlydirectly– indirectlyindirectly

Direct Host DamageDirect Host Damage

toxins produced by the invading pathogen cause direct toxins produced by the invading pathogen cause direct damage to the host which results in diseasedamage to the host which results in disease

toxins capable of causing damage includetoxins capable of causing damage include– exotoxinsexotoxins

a protein toxin released from a living cella protein toxin released from a living cell

mostly found in Gram + cellsmostly found in Gram + cells

Bacillus anthraxis produces an exotoxin

ExotoxoinsExotoxoins

exotoxins are secreted by the bacteria or released exotoxins are secreted by the bacteria or released following lysisfollowing lysis

exotoxins are soluble in body fluids which makes them exotoxins are soluble in body fluids which makes them easily diffused into blood and then are rapidly easily diffused into blood and then are rapidly transported throughout the bodytransported throughout the body

exotoxins work by destroying particular parts of the host exotoxins work by destroying particular parts of the host cells or by inhibiting certain metabolic functionscells or by inhibiting certain metabolic functions

ExotoxinsExotoxinsexotoxins are highly specificexotoxins are highly specific

exotoxins are among the most lethal substances known exotoxins are among the most lethal substances known to manto man– 1 gram of the exotoxin produced from 1 gram of the exotoxin produced from Clostridium Clostridium

botulinumbotulinum is capable of killing the entire population of is capable of killing the entire population of the United States, close to 300 million peoplethe United States, close to 300 million people

the danger with exotoxins the danger with exotoxins is notis not the ingestion of the the ingestion of the bacterium, but the ingestion of the toxinbacterium, but the ingestion of the toxin

Clostricium botulinum

ExotoxinsExotoxins

most exotoxins are grouped according to the tissues most exotoxins are grouped according to the tissues they adversely impactthey adversely impact– neurotoxins damage the nervous systemneurotoxins damage the nervous system– entereotoxins upset the intestinal systementereotoxins upset the intestinal system– cytotoxins afflict their damage on many different types cytotoxins afflict their damage on many different types

of cells by disrupting cellular function of by lysing the of cells by disrupting cellular function of by lysing the cellcell

please look at the list of exotoxins in Table 19.2 on page please look at the list of exotoxins in Table 19.2 on page 47e in your textbook47e in your textbook

EndotoxinsEndotoxins

endotoxins are lioopolysaccharides (LPS) found in endotoxins are lioopolysaccharides (LPS) found in the lipid portion of the outer wall of Gram – bacteriathe lipid portion of the outer wall of Gram – bacteria– endotoxins are released when Gram – bacteria die endotoxins are released when Gram – bacteria die

and the cell wall undergoes lysisand the cell wall undergoes lysis

antibiotics that are used to treat Gram – antibiotics that are used to treat Gram – diseases can lyse the bacterial cells, releasing diseases can lyse the bacterial cells, releasing the endotoxinthe endotoxin

– this can lead to an immediate worsening of this can lead to an immediate worsening of the symptomsthe symptoms

– these symptoms usually improve as the these symptoms usually improve as the endotoxins break downendotoxins break down

EndotoxinsEndotoxins

endotoxins can also activate blood-clotting proteins, endotoxins can also activate blood-clotting proteins, causing the formation of small blood clotscausing the formation of small blood clots– blood clots obstruct capillaries, resulting in decreased blood clots obstruct capillaries, resulting in decreased

blood supply, which can lead to tissue deathblood supply, which can lead to tissue death

this is referred to as disseminated intravascular this is referred to as disseminated intravascular coagultaioncoagultaion

endotoxins also cause fever (pyrogenic response) and endotoxins also cause fever (pyrogenic response) and rapid blood pressure decreaserapid blood pressure decrease

Immune Response DamageImmune Response Damage

inflammatory response can destroy tissue inflammatory response can destroy tissue – antibody-antigen complexes formed during the antibody-antigen complexes formed during the

immune response settle in kidneys and jointsimmune response settle in kidneys and joints

activates complement, which produces damaging activates complement, which produces damaging inflammationinflammation

Viral Pathogenesis MechanismsViral Pathogenesis Mechanisms

viral pathogenesis is very dependent onviral pathogenesis is very dependent on– gaining access to the hostgaining access to the host– evading the host’s defensesevading the host’s defenses– causing damage to or death of the host cell while causing damage to or death of the host cell while

continuing to reproduce themselvescontinuing to reproduce themselves

viral access to the host was discussed in the virus viral access to the host was discussed in the virus lecture; remember viral attraction is specific to the hostlecture; remember viral attraction is specific to the host– viruses bind more successfully to organisms found in viruses bind more successfully to organisms found in

mucous membranesmucous membranes

Viral Evasion of HostViral Evasion of Host

interferons play a role in limiting the ability of viruses interferons play a role in limiting the ability of viruses moving from neighbor cell to neighbor cellmoving from neighbor cell to neighbor cell– once infected cells are capable of producing a protein once infected cells are capable of producing a protein

that can regulate and limit viral replicationthat can regulate and limit viral replication

some viruses are able to encode proteins to shut some viruses are able to encode proteins to shut down this cellular protective devicedown this cellular protective device

Viral Evasion of HostViral Evasion of Host

though limited in the ability to control viruses, those few though limited in the ability to control viruses, those few antibodies that are used can be circumvented by viruses antibodies that are used can be circumvented by viruses that have developed methods to transfer directly from that have developed methods to transfer directly from one cell to its immediate neighborone cell to its immediate neighbor– since antibodies control viruses by neutralizing since antibodies control viruses by neutralizing

extracellular viral particles, the above renders this extracellular viral particles, the above renders this uselessuseless

Virus and Host DamageVirus and Host Damage

some viruses take-over and destroy the cellsome viruses take-over and destroy the cell

virus causes inflammatory response – more damage – virus causes inflammatory response – more damage – more activation of inflammatory responsemore activation of inflammatory response– often times, in particular with the case of the common often times, in particular with the case of the common

cold, the inflammatory response initiated by the virus cold, the inflammatory response initiated by the virus causes much less effect than the domino effect of the causes much less effect than the domino effect of the inflammatory response that followsinflammatory response that follows

Mechanisms of Eukaryotic Mechanisms of Eukaryotic PathogenesisPathogenesis

these mechanisms are not clearly understood, though these mechanisms are not clearly understood, though the mechanisms include colonization of the host, evasion the mechanisms include colonization of the host, evasion of the host defenses and damage to the hostof the host defenses and damage to the host

fungifungi– these organisms are generally opportunistic, taking these organisms are generally opportunistic, taking

advantage of a weakening or change in our immune advantage of a weakening or change in our immune systemsystem

excessive growth of excessive growth of Candida albicansCandida albicans is often a is often a result in immunocompormised hostsresult in immunocompormised hosts

– C. albicansC. albicans is the causative agent of thrush, a is the causative agent of thrush, a common occurrence in AIDS patientscommon occurrence in AIDS patients

Mechanisms of Eukaryotic Mechanisms of Eukaryotic PathogenesisPathogenesis

eukaroytic parasiteseukaroytic parasites– are generally found in the intestinal tract or have are generally found in the intestinal tract or have

gained access through an insect bitegained access through an insect bite– attach with specific receptorsattach with specific receptors– are capable of hiding within the host cell are capable of hiding within the host cell – the damage they can inflict variesthe damage they can inflict varies

some cause malnutrition by competing for some cause malnutrition by competing for nutrientsnutrients

some can cause direct damage by the enzymes some can cause direct damage by the enzymes they producethey produce

Documents

Host Microbe Interactions Kathy Huschle Northland Community and Technical College