2LEARNING OBJECTIVES Identify the principal portals of entry and exit. Using examples, explain how microbes adhere to host cells.Explain how capsules and cell wall components contribute to pathogenicity.Compare the effects of coagulases, kinases, hyaluronidase, and collagenase.Describe the function of siderophores.Provide an example of direct damage, and compare this to toxin production.Contrast the nature and effects of exotoxins and endotoxins.Outline the mechanisms of action of A-B toxins, membrane-disrupting toxins, and superantigensClassify diphtheria toxin, erythrogenic toxin, botulinum toxin, tetanus toxin, Vibrio enterotoxin, and staphylococcal enterotoxin
3Vocabulary Attachment is step 1: Bacteria use ___________ ___________ Pathogenicity: Ability of a pathogen to cause disease by overcoming the host defensesVirulence: Degree of pathogenicity.Attachment is step 1:Bacteria use ______________________Viruses use ___________
4(Preferred) Portals of Entry Mucous membranesConjunctivaRespiratory tract: Droplet inhalation of moisture and dust particles. Most common portal of entry.GI tract: food, water, contaminated fingersGenitourinary tractSkinImpenetrable for most microorganisms; can enter through hair follicles and sweat ducts.Parenteral RouteTrauma (S. aureus, C. tetani)Arthropods (Y. pestis)Injections
5Numbers of Invading Microbes ID50: Infectious dose for 50% of the test populationLD50: Lethal dose (of a toxin) for 50% of the test populationBacillus anthracisPortal of EntryID50Skin10–50 endosporesInhalation10,000–20,000 endosporesIngestion250,000–1,000,000 endosporesClinical and Epidemiologic Principles of Anthrax at
6AdherenceAdhesins: surface projections on pathogen, mostly made of glycoproteins or lipoproteins. Adhere to complementary receptors on the host cells. Adhesins can be part of:Glycocalyx: e.g.Streptococcus mutansFimbriae (also pili and flagella): e.g.E. coliHost cell receptors are most commonly sugars (e.g. mannose for E. coliBiofilms provide attachment and resistance to antimicrobial agents.
7Overcoming Host Defenses Capsules: inhibition or prevention of _____________Cell Wall Proteins: e.g. M protein of S. pyogenesAntigenic Variation: Avoidance of IS, e.g. Trypanosoma NeisseriaPenetration into the Host Cell Cytoskeleton: Salmonella and E. coli produce invasins, proteins that cause the actin of the host cell’s cytoskeleton to form a basket that carries the bacteria into the cell.ANIMATION Virulence Factors: Hiding from Host Defenses
8Penetration into the Host Cell Cytoskeleton InvasinsSalmonella alters host actin to enter a host cellUse actin to move from one cell to the nextListeriaFig 15.2
9EnzymesCoagulase: Blood clot formation. Protection from phagocytosis (virulent S. aureus)Kinase: blood clot dissolve (e.g.: streptokinase)Hyaluronidase: (Spreading factor) Digestion of “intercellular cement” tissue penetrationCollagenase: Collagen hydrolysisIgA protease: IgA destruction
12Toxins Exotoxins: proteins (Gram- and + bacteria can produce) Endotoxins: Gram- bacteria only. LPS, Lipid A part released upon cell death. Symptoms due to vigorous inflammation. Massive release endotoxic shockFoundation Fig 15.4ANIMATION Virulence Factors: Exotoxins
13Vocabulary related to Toxin Production Toxin: Substances that contribute to pathogenicity.Toxigenicity: Ability to produce a toxin.Toxemia:Toxoid:Antitoxin:Antitoxin: Antibodies against a specific toxin.
14By-products of growing cell Exotoxins SummarySource:Gram + and Gram -Relation to microbe:By-products of growing cellChemistry:ProteinFever?NoNeutralized by antitoxin?YesLD50:SmallCirculate to site of activity. Affect body before immune response possible.Exotoxins with special action sites: Neuro-, and enterotoxins
15Toxin Examples Portal of Entry ID50 Botulinum (in mice) 0.03 ng/kg Shiga toxin250 ng/kgStaphylococcal enterotoxin1350 ng/kgWhich is the least potent toxin?BotulinumShigaStaph
16Type of Exotoxins: A-B Exotoxins Fig 15.5Fig 15.5
17Membrane-Disrupting Toxins Lyse host’s cells byMaking protein channels into the plasma membrane, e.g. S. aureusDisrupting phospholipid bilayer, e.g. C. perfringensExamples:Leukocidin: PMN and M destructionHemolysin (e.g.: Streptolysin) : RBCs lysis get at?
18Superantigens Special type of Exotoxin Nonspecifically stimulate T-cells.Cause intense immune response due to release of cytokines from host cells.Fever, nausea, vomiting, diarrhea, shock, and death.
20EndotoxinsBacterial cell death, antibiotics, and antibodies may cause the release of endotoxins.Endotoxins cause fever (by inducing the release of interleukin-1) and shock (because of a TNF-induced decrease in blood pressure).TNF release also allows bacteria to cross BBB.The LAL assay (Limulus amoebocyte lysate) is used to detect endotoxins in drugs and on medical devices.Fig 15.6
21Endotoxin Summary Source: Gram – Relation to microbe: Present in LPS of outer membraneChemistry:Lipid A component of LPSFever?YesNeutralized by antitoxin?NoLD50:Relatively large
22Inflammation Following Eye Surgery Patient did not have an infectionThe LAL assay of solution used in eye surgeryWhat was the cause of the eye inflammation?What was the source?Clinical Focus, p. 440
23Pathogenic Properties of Viruses Evasion of IS byGrowing inside cellsRabies virus spikes mimic AchHIV hides attachment site CD4 long and slenderVisible effects of viral infection = Cytopathic Effectscytocidal (cell death)noncytocidal effects (damage but not death).
24Pathogenic Properties of Fungi Fungal waste products may cause symptomsChronic infections provoke allergic responsesProteasesCandida, TrichophytonCapsule prevents phagocytosisCryptococcusFungal ToxinsErgot toxinClaviceps purpureaAflatoxinAspergillus flavusThis month's fungus is a plant parasite, commonly found on grains of rye (as shown here) or sometimes on other grasses such as quackgrass. The fungus infects the flowers when they're young and cause the growths you see. It induces the cells to divide (hyperplasia) and to enlarge (hypertrophy), creating the relatively large brown sclerotia to the left. These sclerotia are hard resting structures that allow the fungus to survive adverse conditions, such as winter and desiccation. In the life cycle of this organism, the sclerotia fall to the ground and overwinter, germinating in the spring to produce a stroma that contains perithecia, which produces spores to. Someday I'll have a good picture of this to put online-- the stroma are fragile and don't photograph well so far.It's really not a devastating parasite to the plant. You might think its main detriment is that is replaces one of the grains of the plant, thus reducing yield. However it also draws nutrients away from the other uninfected grains so that they become stunted, thus reducing yield quite a bit more. But its worst problem is when the sclerotia inadvertently get mixed in with the grains and are incorporated into foods, thus causing a devastating and sometimes deadly syndrome called ergotism in humans and other animals.Ergotism is caused by the chemicals in the fungus called ergot (pronounced AIR-got). Consumption of foods contaminated with ergot and ergot derivatives may cause vomiting, diarrhea, hallucinations, and may lead to gangrene in serious cases. Historically the fungus has been implicated in epidemics causing thousands of fatalities, but due to increased knowledge of this fungus and a more varied modern diet such epidemics no longer occur in humans. However, chronic exposure through consumption of contaminated foods can lead to health complications.However as recently as 1951, in Pont-St. Esprit, a small town in France, there was an outbreak of the disease. First a bit of background-- in Europe it is the custom to buy fresh bread nearly every day. Much more civilized than our American custom of buying bread with preservatives in it that allow it to last several weeks. In this small town there was only one bakery and everyone bought bread from it. Strange things started happening. People developed a burning sensation in their limbs, began to hallucinate that they could fly, did strange things to their dogs with forks and in general acted weirdly. This outbreak is chronicled in a marvelous (but out of print) book called "The day of St Anthony's Fire" by John Grant Fuller. St. Anthony is the patron saint of lost causes (incidentally I went to St. Anthony's church until I was about 18). When all of the other saints have failed, St. Anthony is the one you are supposed to pray to. And St. Anthony's fire was rampant in the town that day. Similar outbreaks probably occurred throughout the world wherever the conditions were right for the growth of Claviceps purpurea. The chemical responsible for the hallucinations is actually LSD! lysergic acid. There was even an outbreak of egotism on the television show "Quincy" starring Jack Klugman, who played a coroner. He was aboard a cruise ship and people were acting very strangely. Quincy finally traced the behavior to contamination of the flour tortillas that had been served aboard ship. I haven't seen this episode for 15 years, but I still remember it because I figured it out before Quincy did!
25Pathogenic Properties of Protozoa & Helminths Presence of protozoaProtozoan waste products may cause symptomsAvoid host defenses byGrowing in phagocytesAntigenic variationPresence of helminths interferes with host functionHelminths metabolic waste can cause symptomsWuchereria bancrofti
26Portals of Exit Respiratory tract: Coughing and sneezing Gastrointestinal tract: Feces and salivaGenitourinary tract: Urine and vaginal secretionsSkinBlood: Biting arthropods and needles or syringes
27Microbial Mechanisms of Pathogenicity - Overview Foundation Fig 15.9The End