BMED2404!!–!Semester'1"Understand)the)principles)of)the)current)problems)and)emerging)threats)that)are)posed)by)microorganisms.)It)is))not)necessary)to)remember)the)statistics)of)infectious)diseases)that)are)presented,)but)you)should)define)and))understand)the)terms)used)))

Mortality) Cause)of)death"mostly"due"to"infectious"killers"(e.g."pneumonia,"TB,"malaria,"HIV)"

Morbidity) • Impact"of"illness"="condition)of)being)diseased"

• So"sick"→"cannot"contribute"to"the"community"(measured"as"disability"adjusted"life"

years"–"DALYs)"

Virulence) Degree)or)intensity)of)pathogenicity"�"Increased)virulence)=)more)likely)to)harm"

Normal)Human)Microbiota)

• Residents"associated"with"healthy"individuals""

• Aid)resistance)to)infection"by"competing"with"pathogenic"invaders"for"nutrients"and"

attachment"sites"

• Stimulate)immune)response)+)aid)digestion"

• Note:"Some"normal"flora"become"pathogenic"if"they"move"to"a"new"location"(e.g.)Staphylcoccus)aureus)becomes)pathogenic)if)it)invades)deep)skin)tissue)"

Emerging)infections) New,)reDemerging)or)drug)resistant)infections)whose)incidence)in)humans)has)increased))within)the)past)2)decades)or)whose)incidence)threatens)to)increase)in)the)near)future)

Influenced"by:"

• Human"demographics"and"behaviour"""

• Technology"and"industry"""

• Economic"development"and"land"use"""

• International"travel"and"commerce""�"known"infections"spreading"to"new"areas"

• Microbial"adaptation"and"change"�"causing"new"infection"types"

• Old"infections"reemerging"as"a"result"of"antimicrobial"resistance"in"known"agents"

or"breakdowns"in"public"health"measures"""

Methods)of)eradicating)disease:)

• Active)immunization"�"establish"longOlasting"immunity"against"pathogens""

• Sex)education"(prevent"spread"of"STIs)"

• Free)medical)treatments"in"low"socioOeconomic"areas"

• Defending)national)borders"to"protect"against"microbial"invaders"

!

!! )

Be)familiar)with)the)characteristics)of)parasitism)))

Pathogens:"

• Organisms"that"invade)the)body/host"and"thrive"by"causing"tissue"damage"or"infectious)diseases"

• Transmission"via"air,"water"or"contact"etc.""

• Medical)microbiology)is)the)study)of)the)medically)important)microorganisms)that)cause)infection)and)disease)in)humans)))

)

Understand)the)dynamics)of)the)host/parasite)battle)in)which)each)tries)to)get)the)upper)hand)))

)HOST/PARASITE)BATTLE"is"a"CONTINUING)BATTLE"where"the"winner)dominates)the)relationship"

!Understand)what)factors,)both)in)the)host)and)in)the)microbe,)govern)where)a)host/microbe)relationship)will)fit))on)the)symbiosis)spectrum)))

SYMBIOSIS'SPECTRUM'='DYNAMIC'whereby"the"BALANCE)DEPENDS)ON"BOTH"the"microbe"AND"host"

!Both)microbe)

and)host)benefit!One)benefits"while"other"remains"unaffected! Microbe)benefits)

while)host)is)harmed)

!Factors)affecting)symbiosis:)

1. Number)of)organisms) Increased"numbers"" Shifts"to"parasitism"(increased"disease)"

2. Virulence)of)organisms) Increased"virulence"(intensity)" Shifts"to"parasitism"(more"likely"to"harm)"

3. Host’s)defence)or)resistance) Decreased"resistance"" Shifts"to"parasitism"

" Healthy"host" High"resistance"(little"effect)"

*All"about"a"dynamic"relationship"between"the"host"and"microbe"–"winner"dominates"relationship"

"

NOTE:)

• SARS"epidemic"due"to"virus"acquiring"new"virulence"factors"to"produce"atypical)pneumonia"

• Bacteria,"Virus,"Fungi"and"Protists"(e.g."trypanosomes)"can"all"act"as"pathogens"

"

! )

L2:)Epidemiology)&)Transmission)of)Disease))!Koch’s)Postulates:"The"same"pathogen"from"the"pure"culture"must:")

1."present)in)every)case)of"the"disease""

2."be"isolated)from)the)diseased)host)and"grown"in"pure"culture""

3."cause)the)disease)when"inoculated"into"a"healthy,"susceptible"laboratory"animal""

4."again"be"isolated)from)the)inoculated)animal)and"must"be"shown"to"be"the"

original"organism""

*NOTE:"Koch’s"postulates"do"not"consider"viruses,"which"cannot"be"cultured"

!Be)familiar)with)the)terms)used)in)the)science)of)epidemiology)))

!!

Epidemiology! the"study"of"the"distribution"and"determinants"of"healthOrelated"states"or"events"

(including""disease),"and"the"application"of"this"study"to"the"control"of"diseases"and"

other"health"problems!Sporadic)disease! Unpredictable"with"no"pattern"of"occurrence"(random)!Outbreak! sudden,"unexpected"increase"in"incidence;"usually"isolated"to"a"single"part"of"a"society!Endemic)disease! Disease"constantly)present"in"a"population"usu."at"low"frequency"(cyclic"+"no"outbreaks)"

Epidemic)disease) Disease"suddenly"increases)in)population""

Pandemic)disease) Disease"increases)WITHIN)large)widespread)populations"usu."worldwide""

)

! )

Understand)with)how)epidemiologists)recognise)epidemics)))

"!2"types"of"epidemics""

1. Common)source)epidemic) • rapid"increase"and"decrease"in"incidence""

2. Propagated)epidemic) • increases"over"longer"period"of"time;"

• "usually"transmitted"between"people;""

• dependent)on)susceptibility"of"individual"

"

Herd"Immunity"O"Thresholds""

"

Those"who"are"vaccinated"or"survived"the"disease"protect"

those"who"are"susceptible"�"thus"reducing"spread"

"

As"the"number"of"susceptible"people"reduce,"the"

spread"also"decreases"as"less"people"to"infect"

Be)familiar)with)the)properties)of)influenza)virus)and)its)disease)))

!HA)trimer! Allows"virus"to"bind"to"host!NA)tetramer! Allows"virus"to"punch"holes"in"the"cell"wall"so"virus"DNA"

can"get"in!Drift! Small)alteration"to"a"single"protein"�"not"effectively"

recognised"by"the"immune"system!Shift) Major)alteration"�"completely"no"longer"recognised"by"

the"immune"system"

Influenza"pandemics"resulting"from"antigenic"shifts"

H1N1)) different"H"and"N"strains"due"to"mutations"in"HA"and"NA"

! !

Danger?)CoOinfection"with"animal"and"

human"strains"can"produce"different"virus"

strains"due"to"genetic"recombination)Spread?)Easy"transmission"via"aerosolised"

particles)Who)at)risk?"Children,"elderly,"those"who"have"never"been"infected"before"

Understand)the)relationship)between)epidemiology)and)the)infectious)disease)cycle)AND)how"the"links"in"the"infectious"disease"cycle"interrelate))

Infectious)disease)cycle:)

!*Virulence)=)intensity)of)pathogenicity)

!Understand)the)interrelationship)between)virulence)and)transmission)in)the)host)pathogen)interaction.)))TRANSMISSION)METHODS:)

) Method) Disease)example)

AirDborne) aerosols:"coughing,"talking,"sneezing:") ‘flu,"chicken"pox,"mumps,"measles"etc)

) dust:"hospitals"="nosocomial"infection) )

Contact) Direct"usu."skin"to"skin) utensils,"STI’s)

Vehicle) contaminated"food"/"water) cholera,"food"poisoning)

Vectors) Mosquitoes,"rats" malaria,"trypanosomiasis"

"

MAJOR)RELATIONSHIP)between)virulence)and)transmission:)

• Highly"virulent"pathogens"will"cause"host"to"be"bedridden."This"means"there"is"reduced"contact"and"hence,"

less"transmission"of"the"pathogen."Similarly,"pathogens"that"are"dependent"vector"transmission"(e.g."African"

sleeping"sickness)"may"also"experienced"reduce"spread"if"vector"absent"(since"virulence"is"independent"to"

transmission)"

• Conversely,"the"common"cold"is"low"in"virulence"but"can"be"easily"transmissible"as"host"remains"active"and"

can"continue"to"make"contact."

"

Know)how)these)links)can)be)broken)in)order)to)control)epidemics))

Source)of)pathogen)) Transmission)–)most)effective) Host)susceptibility))

• Eliminate"contaminated"food"or"

water""

• Quarantine"carriers"and"diseased"

individuals""(e.g."smallpox)"

• Destroy"animal"carriers"""

• Identify"reservoir"(e.g."bats"in"

SARS"outbreak)"

• Change"behaviour""�"sex"ed"""

• Destroy"insect"vectors"–"mosquitos"

and"malaria"

• Control"animal"vectors"–"cattle,"TB"

• Improve"nutrition"

• "Vaccinate"""

• Problem"with"lack"of"

immunoincompetence"

" )

L3:)Pathogenicity and virulence factors )Know)the)microbial)strategies)and/or)products)that)allow)microbes)to)accomplish)each)of)the)following)steps:)colonisation,"invasion,"evasion,"and"damage"their"host))Virulence)factors)function)to:)

1. Aid"colonisation""

2. Invasion"="Allow"penetration"of"host"tissue"

3. Evade"immune"host"response""

4. Cause"direct"damage"(e.g."toxicity)"

5. "

Virulence"Factor" Explanation"

Colonisation" Specific"Attachment""

• Afrimbrial)Adhesins/Ligands) bind"to"receptors"on"the"cell"

• Adhesive)Pili)and)Fimbriae) short"stumpy"brush"border"used"for"adhesion"+"very"

tight"bonding"

• Viral)protein)spikes) binds"to"receptors"on"the"cell""(e.g."influenza)"

"

NonO"Specific"Attachment""

• Glycocalyx"–"sugar"contributes"to"stickiness"that"assist"in"adhesion""

"

Invasion"

(Host)Cell)Penetration)&)Growth))

)

Uptake"of"bacteria"via:"

• Invasins) some"bacteria"produce"surface"proteins"that"promote"its"

ingestion"by"cells"undergoing"mitosis"

• Endocytosis) non"phagocytic"cells"(e.g."influenza"virus)"

"

"

"

"

• Exocytosis) actin"tail"propulsion"

• Phagocytosis) microorganism"engulfed"

• Membrane)fusion) membranes"fuses"(e.g."measles"virus)"

"

"

"

""

Enzymes"

)(survival,)penetration,)damage)to)host))

Enzymes"crucial"for"microbial"survival"and"dissemination:"

• Coagulase) Coagulates"blood"

• Kinases) Digests"fibrin"clots"

• Hyaluronidase) Hydrolyses"hyaluronic"acid"

• Collagenase) Hydrolyzes"collagen"

• IgA"proteases) Destroys"IgA"antibodies"="survival"

• " ""

Evasion"of"

immune"

response"

)

1. Alter)surface)proteins"(antigenic"change"or"mimicry)"to"evade"immune"response"""

2. Large)thick)slime/glycocalyx)capsules"hide"antigenic"sites"and"create"protective"barrier"to"evade"detection"

3. Produce"antibody)proteases:"destroy"immunoglobulins""

4. Intracellular)survival"within"phagocyte"

5. Either:"

o destroy"phagocyte"or""

o inhibit"phagocytosis"by"resisting:"

- "lysosomal"enzymes"

- chemotaxis"and""

- phagosome/lysosome"fusion"

Damaging"the"

host"

• Microbial)toxins)–)endotoxins)and)exotoxins)))

• Pathogenicity)islands)� )contribute)to)pathogenicity)

o MECHANISM"OF"Pathogenicity"islands"include:"

o Large"segments"of"DNA"that"contain"insertionOlike"sequences"="mobile,"encode"major"

virulence""factors"and"associated"with"tRNA"encoding"genes"""

o Pathogens"may"have">1"Pathogenicity"Islands"""

o Maybe"plasmids"""

o CellOcell"acquired"by"horizontal"gene"transfer"""

• EXAMPLES:"

o "alter"actin"microfilaments"to"mediate"adherence""

o modulate"host"activities"

"

! )

Compare)and)contrast)the)actions)and)effects)of)exoD)vs)endotoxins)produced)by)bacteria)on)the)human)body)

) Exotoxins) Endotoxins!Source) Gram"+ve" Gram"–ve"

Metabolic)Product) By"products"of"growing"cell"" Present"in"LPS"of"outer"membrane"

Chemistry) Protein) Lipid)

Fever) No" Yes)

Neutralised)by)antitoxin) Yes) No"(as"lipid"based)"

)

" "

"

Know)and)understand)how)some)of)these)toxins)exert)their)effects)on)host)cells))

Bacterial"Exotoxins"(their"target"and"effect)"

Membrane)disrupting)exotoxins)

(Clostridium)perfringens)aOtoxin"�"causes"gas"

gangrene)"

"

"

"

• Channel/pore"forming"toxin"causes"

change"osmolarity"�"cell"lysis"

• Phospholipase"chops"off"phosphate"

heads""

• Destroys"the"integrity"of"the"

membrane"

ADB)exotoxins)))

(e.g.)cholera'exotoxin)produced)by)vibrio)cholera)�)causes)massive)fluid)efflux)=)diarrhea))

)

)

)

)

)

)

'

• A)=)active"protein"""

• B)=)binding"protein"""

Mechanism"of"action)

• B"binds"and"releases)A)into)the)cell"or)

• A"and"B"ingested"via"endocytosis)

• A"binds"to"regulator"protein"and"

changes"response")

)

Superantigens) • able"to"create)massive)immune)response"""

• Class"of"antigens"which"cause"nonO

specific"activation"of"TOcells"resulting"

in:"

"polyclonal"T"cell"activation"and"

"massive"cytokine"release"""

"

Rare)strains)of)Staphylococcus)aureus)produce)TSSFtoxin)(toxic)shock)syndrome)))

"

Bacterial"Endotoxins"(their"target"and"effect)"

"

" "

Key"feature"of"GramDpositive)bacteria:"• Thick)peptidoglycan"layer,"LTA,)TA)� )less"

endotoxic"than"LPS"

Key"feature"of"GramDnegative)bacteria:"• LPS)layer)� )lipid"based"toxin"that"causes"fever,"septic"shock"

+"greater"inflammatory"response"

)Inflammatory"Action"of"Endotoxins""

!! )

Be#able#to#describe#examples#of#infection#caused#by:## Staphylococcus#aureus#(pyogenic*skin*infection)# Chlamydia#trachomatis#(intracellular*dependent)# Mycobacterium#tuberculosis#(chronic*inflammatory*respiratory*infection)#

Characteristics# • Gram#+ve#• Clustered*Cocci**

• <0.45μm!

• Small*genome*(has*RNA*+*DNA)*BUT#has*prokaryotic*ribosomes!

• Gram#–ve!

• Obligate*intracellular*parasite*(needs*host)!

• Cell*wall*=*No*peptidoglycan*and*muramic*acid!

• Aerobe!

• Fastidious!

• Slow*growing!

• Gram#+ve#

• HIGH#INCIDENCE#(1/3#infected#worldwide)#due*to:*o HIV*epidemic**(AIDS*infection*with*atypical*strains)*o Antibiotic*resistance#*

Transmission# Direct*contact*or*inoculation* Intimate*direct*contact*+*STI* Aerosol*

Symptoms# • Red*pimply,**• Pus*and*red*boils*

• Scalded*skin*

*

MALES# FEMALES#

• Pain*urinating*

• Inflammation**

• Discharge***

• Slight*discharge*–*80%*asymptomatic***

• Inflammation*of*cervix***

• Burning*urinating****

• Bad*chronic*cough**�*Coughing*up*blood/sputum*

• Chest*pain***

• No*appetite*�*massive*weight*loss***

• Chills**• Fever*

Pathogenesis# *

Cell#wall#component# Effect#

Capsule# Provides*adhesion*and*hides*antigenic*sites*

Protein#A# AntiPphagocytic*(stop*ingestion*by*macrophage)*

Peptidoglycan# AntiPphagocytic*+*stimulates*endotoxic*shock*

Technoic#acid# Allows*invasion*and*mucosal*attachment*

*

**

• Unique#metabolism*–*synthesise*own*proteins,*nucleic*acids*and*lipids*BUT#needs#host#to#obtain#ATP*

• BINDS#TO#MUCOSA#→#Causes*scarring*that*blocks*fallopian#tubes,*urethra#or#vas#deferens**

• Can*reach*ovary*

*• Infection*spreads*W*salpingitis*PID*

• RESULT:*→*infertility**

• Waxy#(mycolic!acid)#lipids#→#resistant#to#disinfectants*(acid*fast*stain)*

• NO#TOXIN#PRODUCED#1. Enters*URT*in*small*aerosol*droplets**

2. Bypasses*ciliated*mucosa**3. Ingested*by*macrophages**and*replicates*intracellularly*4. Kills*phagocytes*to*stimulate*the*immune*response*to*recruit*more*

phagocytes*and*immune*cells*=*TUBERCLE#FORMATION*(casseous*necrosis*traps*TB*by*surrounding*it*with*macrophages*and*T*cells*to*seal*offWcalcify)*→*possible*dissemination**

• Preferential*uptake*by*complement*and*mannose*receptor*–*inhibits*uptake*by*Fc*receptor***

• Inhibits*phagosome/lysosome*fusion*****

• Th1*cells*secrete*IFNW γ*+***Macrophage*secrete*TNF*[OPTIMUM#activation#OF#MACROPHAGES#→#release#ROS,#enzymes#to#kill]**

o Consistent*activation*leads*to*granuloma***

Enzymes:!# *

βPlactamase## inactivates*Penicillin*

Catalase## Breaks*down*reactive*oxidative*species*(H2O2)*in*phagocytosis**

Coagulase##Host*fibrinogen*→*fibrin*→*coating*on*Staph.*→*cells*clumping*(antiWphagocytic)*

*

Toxin# *

Enterotoxins## GIT,*cause*food*poisoning**

Cytotoxic#haemolysins##

• α:!erythrocytes,!skin!!

• β:!erythrocytes,!sphingomyelin!!

• δ!&!γ:!erythrocytes**

Leukocidins##

• Kill*PMNs*• Inhibit*phagocytosis*by*

granulocytes*→*cell*death*and*pus*formation*(necrotic*PMNs)*

• Release*of*granule*contents*from*lysed*PMNs*�*tissue*necrosis*and*inflammation*

Exfoliative#toxins#A#&#B## Surface*layers*of*skin;*shedding**

Toxic#shock#syndrome## Systemic*effects*→*fever*+*shock**

*

*

!Infective!elementary!bodies!(black!full!arrows)!and!large!reproducing!reticulate!bodies!(white!arrows)!

*

*2*types*of*TB*infections***

Latent*(Controlled)*

• Activated*macrophages*kill*TB***

• Tubercles*calcify*=*granuloma*→Bacteria*survive*inside*walled*off*lesions*in*lungs*and*other*sites*

• No*symptoms*and*not*contagious***

• Can*be*reactivated*though**(≈*20*years*later)*

Diseased/Active#(Uncontrolled)*

• Insufficient#immune#response###

• Centre*of*tubercles*liquefy##*

• Bacteria*coughed*up*in*sputum**

• Dissemination*to*organs*via*blood**

• 50%*mortality*rate***

• Identify#in#sputum#sample**o Stain:*Acid*fast*rod*in*smear**

o Culture*in*Lowenstein*Jensen*medium*[SLOW]*�*dry*waxy*appearance*to*confirm*

o Molecular*techniques*=*PCR*(QUICK)**

• Chest#xPray**(Faster)*

• Tuberculin#(Mantoux)#test#

o Inoculate*tuberculoW*protein*PPD*into*intradermal*skin*�*stimulate*cellWmediated*hypersensitivity*

o Detects*latent/active*TB*or*successful*BCG*vaccination*

o –ve!result!=!no!skin!reaction!post!2!days!�!i.e.!never!infected!(false!+ve!with!TB!meningitis)!

Control# • Personal*hygiene*• Prevent*direct*contact*with*infected*

• Abstinence***• Wearing*protection***

• Communication***

• Limit*transmission*(i.e.*prevent*close#contact)*• Improve*living*conditions***

• BCG#(Bacille#CalmettePGuérin)#vaccines*–*initiates*cell*mediated*response*to*induce*memory*T*cell*protection*

Treatment# Antibiotics*(not*resistance)* Susceptible*to*many*Antibiotics* • >2*drugs*given*together*to*minimize*antibiotic*resistance*–*Isoniazid,!rifampicin,!pyrazinamide!ethambutol*BUT#poor#compliance#by#users*

Describe%the%type%of%vaccines%currently%in%use%%%!

Vaccine%Type% Killed%Inactivated%Vaccines& Live%Attenuated%Vaccines&

Method%of%action& • Micro-organisms&killed&by&physical&or&chemical&inactivation&(formaldehyde)&

• Eliminate&infectivity&without&affecting&antigenicity&

• Micro-organisms&lose&pathogenicity&BUT&still&capable&of&transient&growth&in&host&

• Extensive&culture&in&“abnormal”&media&�&causes&random&or&specific&mutations&to&accumulate&

Example% Salk%Polio%vaccine%(Inactivated&poliomyelitis(IPV))&�&poliovirus&type&1,&type&2&and&type&3;&monkey&kidney&cells&

Obtained&via&inactivation&with&formaldehyde&

Sabin%polio%vaccine:&passage&of&virus&through&monkey&kidney&cells&(e.g.&57&independent&mutations&in&Sabin&1&strain)&&

Disease%treated% Cholera,&HepA. Measles,&mumps,&rubella,&BCG.

Advantages& • Safe%from%reversion&to&virulence&

• Acceptable&for&immuno-compromised&individuals&&

• Stable&for&transport&and&storage&

• Authentic%immune%response%elicited%

• Long-term&protective&immunity&(replicate)&• ONLY&single-dose&(no&adjuvants)&

• Transfer&non-immune&contacts&&

Disadvantages& • Less%effective%than%live%vaccines&(which&provide&cell-mediated&I.R)&

• Multiple%doses&required&&

• Needs&adjuvants&to&enhance&responses&

• Possible%reversion&back&into&virulent&form&(e.g.&1&in&4&mill&for&Sabin)&

• Complications&similar&to&natural&disease&&

• Growth&media/culture&cells&produce&adverse&reactions&

• Limited&shelf&life;&refrigeration&in&tropics&

%

&&

!CASE&STUDY:&Attenuated%vs%Inactivated%vaccines:&Polio:&major&killer&in&1950s&

1954% Salk%vaccine&(inactivated&poliovirus)&

Injected&(SAFE)& • High&levels&circulating&IgG,&little&mucosal&immunity&

• BUT:&did&not&stop&virus&spread&in&GI&

1961% Sabin&vaccine&(attenuated&poliovirus)&

Oral& • Stimulates&high&level&IgA&

• Control&virus&GI&by&limiting&spread&

! !