Upload
mubosscz
View
475
Download
2
Tags:
Embed Size (px)
Citation preview
Institute for Microbiology, Medical Faculty of Masaryk University Institute for Microbiology, Medical Faculty of Masaryk University and St. Anna Faculty Hospital in Brno and St. Anna Faculty Hospital in Brno
Miroslav Votava, Vladana WoznicováMiroslav Votava, Vladana Woznicová
PATHOGENICITY AND PATHOGENICITY AND VIRULENCEVIRULENCE
Lecture for 2nd-year studentsLecture for 2nd-year studentsMarch 3March 300, 200, 20099
Pathogenicity Pathogenicity
= = AAbility of a microbe bility of a microbe to be to be harmfulharmful to health and to health and to cause diseaseto cause disease
IInfectiousness nfectiousness = ability to cause infection= ability to cause infection
Infection Infection – broader term than disease– broader term than disease
In the diseaseIn the disease,, symptoms of disease symptoms of disease are presentare present (the infection is (the infection is manifest manifest one)one)
But the infection may proceed without symptoms But the infection may proceed without symptoms ((inapparent inapparent infection)infection)
Apart from infectionsApart from infections,, microbes can cause food microbes can cause food poisoningpoisoning,, as wellas well
Ecological remarkEcological remarkEcology Ecology = science on mutual relations among organisms = science on mutual relations among organisms
and relations between organisms and their environmentand relations between organisms and their environmentSymbiosis Symbiosis = close association of two di= close association of two differentfferent organisms organisms
Three forms of symbiosisThree forms of symbiosis::
Mutualism Mutualism – – bothboth partners partners benefitbenefit from the association from the association and are unable to survive without itand are unable to survive without it
Commensalism Commensalism – the association – the association is is beneficial for one beneficial for one partner and indifferent to the otherpartner and indifferent to the other
Parasitism Parasitism – the association – the association benefits one partner and benefits one partner and harms the otherharms the other (the host) (the host) → → consequence = consequence = pathogenicitypathogenicity
InfectionInfection
Definition of infection is not an easy oneDefinition of infection is not an easy one
Infection Infection = situation when the = situation when the etiological agent etiological agent of infection of infection invades invades an organism and an organism and multiplies multiplies in it; or it settles on bodily surfaces in it; or it settles on bodily surfaces and acts adversely thereand acts adversely there
Colonization Colonization = settlement of bodily surface by = settlement of bodily surface by a a nonpathogenicnonpathogenic microbe (or by a pathogen microbe (or by a pathogen that does not cause pathological symptoms that does not cause pathological symptoms there)there)
History of infectious diseasesHistory of infectious diseases
Physiological thesis of Hippocrates:Physiological thesis of Hippocrates:(Infectious) disease = consequence of certain (Infectious) disease = consequence of certain
inadequacy of organisminadequacy of organism
Microbial antithesis of Pasteur and Koch:Microbial antithesis of Pasteur and Koch:The cause of the infectious disease is a microbeThe cause of the infectious disease is a microbe
Ecological synthesis:Ecological synthesis:= synthesis of physiological thesis and microbial = synthesis of physiological thesis and microbial
antithesis – for the antithesis – for the occurenceoccurence of the of the infectious infectious diseasedisease the microbe, host and environment the microbe, host and environment are are responsibleresponsible
Koch´s postulatesKoch´s postulates
A particularA particular microbe is the etiological agent, if microbe is the etiological agent, if
1.1. it is present it is present in every casein every case of the disease and its of the disease and its localization in the body corresponds to localization in the body corresponds to the the damages observed;damages observed;
2.2. it is it is isolated from the hostisolated from the host and kept in pure and kept in pure culture for several generations; culture for several generations;
3.3. by means of the microbe grown in this way it is by means of the microbe grown in this way it is possible to imitate the possible to imitate the disease on another hostdisease on another host;;
4.4. it is it is again isolatedagain isolated from the experimentally from the experimentally infected host.infected host.
Relationship between the Relationship between the microbe and the hostmicrobe and the host
Dynamic Dynamic and influenced by the and influenced by the environmentenvironment microbemicrobe host host
environmentenvironmentIllness is not a rule – peaceful coexistence is Illness is not a rule – peaceful coexistence is
usually better for the parasiteusually better for the parasiteIn spite of that the host tries In spite of that the host tries to get ridto get rid of the of the
parasiteparasite – to destroy, remove – to destroy, remove or at least or at least to localize itto localize it
PathogenicityPathogenicity
PathogenicityPathogenicity depends ondepends on bothboth microbial and microbial and host host speciesspecies
ParticularParticular microbial species is microbial species is pathogenicpathogenic for for
a specific host species only, for another a specific host species only, for another species it may be species it may be non-pathogenicnon-pathogenic
This host species is This host species is susceptible susceptible to the to the relevant microbial species, to relevant microbial species, to aa different different microbial species it can be microbial species it can be resistantresistant
Primary and opportune pathogensPrimary and opportune pathogens
Primary (obligate) pathogens →Primary (obligate) pathogens → disease also in disease also in otherwise healthy individuals: chiefly agents of otherwise healthy individuals: chiefly agents of classical infectionsclassical infections (diphtheria, typhoid fever, (diphtheria, typhoid fever, plague, gonorrhea, tetanus, influenza, morbilli plague, gonorrhea, tetanus, influenza, morbilli etc.)etc.)
Opportunistic (facultative) pathogens →Opportunistic (facultative) pathogens → disease disease under certain conditions or at a certain under certain conditions or at a certain disposition only: usually members of disposition only: usually members of normal normal floraflora
• when they reach another site in the body when they reach another site in the body • or when the immunity of the individual is loweredor when the immunity of the individual is lowered
Natural and experimental Natural and experimental pathogenicitypathogenicity
Microbes naturally pathogenic Microbes naturally pathogenic forfor man man && animals:animals:Staph. aureus, Francisella tularensis, Clostridium Staph. aureus, Francisella tularensis, Clostridium
botulinum, botulinum, rabies v., tick-borne encephalitis v.rabies v., tick-borne encephalitis v.
Microbes pathogenic for animals experimentally:Microbes pathogenic for animals experimentally:Bacillus anthracis, Streptococcus pneumoniae, Clostridium Bacillus anthracis, Streptococcus pneumoniae, Clostridium
tetani –tetani – mouse mouse Mycobact. tuberculosis, Mycobact. tuberculosis, rickettsiaerickettsiae – – guinea pigguinea pig Treponema pallidum, Treponema pallidum, herpes simplex v. – rabbit herpes simplex v. – rabbit
MiMiccrobes pathogenic for man only: robes pathogenic for man only: Neisseria gonorrhoeae, Haemophilus ducreyiNeisseria gonorrhoeae, Haemophilus ducreyi
MiMiccrobes non-pathogenic for man:robes non-pathogenic for man:Majority of soil and water microorganismsMajority of soil and water microorganisms
Opportunistic pathogens – IOpportunistic pathogens – I
TypicalTypical opportunistic pathogen: opportunistic pathogen:
Escherichia coliEscherichia coli
A part of normal colonic flora (but 1 % only)A part of normal colonic flora (but 1 % only)
Outside the large intestine = pathogenOutside the large intestine = pathogen• cystitis, pyelonephritis, urosepsiscystitis, pyelonephritis, urosepsis• cholecystitis, peritonitischolecystitis, peritonitis• wound infectionswound infections
At lowered immunity (newborns): At lowered immunity (newborns): • meningitismeningitis • diarrhea (EPEC – serotypes O55, O111)diarrhea (EPEC – serotypes O55, O111)
S. aureus bacteria escaping destruction by human white blood cells
http://www3.niaid.nih.gov
http://www.podiatrytoday.com
Opportunistic pathogens – IIOpportunistic pathogens – II
AnotherAnother opportunistic pathogen: opportunistic pathogen:Staphylococcus epidermidisStaphylococcus epidermidis
Part of normal skin and mucosal floraPart of normal skin and mucosal floraOutside the skin and mucosae = pathogenOutside the skin and mucosae = pathogen• wound infections (also surgical: sternum, eye)wound infections (also surgical: sternum, eye)• CystitisCystitis
At lowered immunity:At lowered immunity:• above all blood stream infections in individuals above all blood stream infections in individuals
with i.v. catheters, infections of implants and with i.v. catheters, infections of implants and other devicesother devices
• sepsis in newborns and neutropenic individuals sepsis in newborns and neutropenic individuals
Virulence Virulence
VirulenceVirulence = = degreedegree (measure) (measure) of pathogenicityof pathogenicity
VirulenceVirulence = property of certain = property of certain strainstrain – a pathogenic – a pathogenic species can incorporate species can incorporate highly virulent strains highly virulent strains as well as almost as well as almost avirulent avirulent onesones
Indicator of strain virulence:Indicator of strain virulence: ability to kill ability to kill
LDLD5050 = 50% lethal dose (the amount of microbe that = 50% lethal dose (the amount of microbe that
is able to kill exactly ½ of experimental animals)is able to kill exactly ½ of experimental animals)
Increasing virulence: Increasing virulence: repeated passages of the repeated passages of the strain (be cautious with the strains from strain (be cautious with the strains from dissection material)dissection material)
Attenuation Attenuation = artificial = artificial weakening of virulenceweakening of virulence
AttenuationAttenuation
BCG-vaccine BCG-vaccine (bacille Calmette-Guérin) (bacille Calmette-Guérin) against TBCagainst TBC
Original strain: Original strain: Mycobacterium bovisMycobacterium bovis – – is less is less pathogenic for man than pathogenic for man than Mycob. tuberculosisMycob. tuberculosis
The selected The selected strain was tormented 12 years on strain was tormented 12 years on potato with bilepotato with bile until it lost most of its virulence until it lost most of its virulence (it is almost avirulent)(it is almost avirulent)
InIn a normal newborn a normal newborn BCGBCG causes causes only a local only a local processprocess in the site of injection or in a regional in the site of injection or in a regional lymph nodelymph node
Very rarely in an Very rarely in an immunodeficient newbornimmunodeficient newborn it can it can cause the cause the generalized infectiongeneralized infection
MICROBEMICROBE
obligatelyobligately opportunistically opportunisticallySpecies:Species: pathogenic pathogenic non-pathogenicpathogenic pathogenic non-pathogenic
Strain:Strain: virulent avirulentvirulent avirulent
Individual:Individual: sensitive nonspecifically unresponsive sensitive nonspecifically unresponsive or specifically immuneor specifically immune
Species:Species: susceptible susceptible resistantresistant
HOSTHOST
Recommended reading materialRecommended reading material
Paul de Kruif: Microbe HuntersPaul de Kruif: Microbe Hunters
Paul de Kruif: Men against DeathPaul de Kruif: Men against Death
Axel Munthe: The Story of San MicheleAxel Munthe: The Story of San Michele
Sinclair Lewis: ArrowsmithSinclair Lewis: Arrowsmith
André Maurois: La vie de Sir Alexander André Maurois: La vie de Sir Alexander FlemingFleming
Hans Zinsser: Rats, Lice, and HistoryHans Zinsser: Rats, Lice, and History
Thank you for your attentionThank you for your attention