bacterial+pathogenesis

7/29/2019 Bacterial+Pathogenesis

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Bacterial Pathogenesis

Kunle Kassim, PhD, MPH

Professor, MicrobiologyAugust, 2010


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URGENT!!!!

It is important for you to review the lecture

powerpoint on Host/Bacteria Interactions

from first yearbefore coming to class forthis lecture.


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Objectives

Review the diversity and significance of bacterial flora in the maintenance ofimmunity

Review the various types of flora distruption and health consequences to the host.

Review determinants of pathogenicity

Discuss the roles of endotoxin and exotoxins in specific instances of bacterial

pathogenesis Illustrate invasiveness and dissemination of bacterial pathogenesis with Salmonella

and Shigella pathogenesis.

Discuss the different ways that bacterial pathogens exert damage and injury to thehost, using cystic fibrosis, lyme disease and bacterial urethritis as illustrations

Present the different types of host defenses, including the constitutive elements ofinnate and adaptive immunity, humoral and cellular immunity, inflammatory and

acute phase responses. Describe the emerging patterns and serious significance of nosocomial infections

Discuss the nature, usefulness and schedule of bacterial vaccines, particularly inpreventing childhood infectious diseases.


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Normal Bacterial Flora

Bacterial Virulence Factors

Mechanisms of Pathogenicity

Host Defense Mechanisms

Selected Bacterial Diseases

(Review lecture materials on Bacteria/Host

Intreactions)


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Distruption of Normal Flora

Trauma

- appendix rupture, dental extraction, auto

accidents, gun violence Flora displacement/contamination

- UTI, bacterial vaginosis

Excessive antibiotic use- vaginal candidaisis, pseudomembranous

colitis by Clostridium difficile


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Distruption of Normal Flora

UTI

Tumors

Bladder incontinence Ureteric reflux

Poor hygiene

E. coli infections


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Determinants of Pathogenicity

Ports of entry

Modes of transmission

Bacterial adherence

Invasiveness/Dissemination

Pathological damage

Endotoxin / Exotoxins

Fever / Disease onset

Host defenses

Evasion of host defenses

Siderophore production Plasmids

Bacterial vaccines

(Review last years lecture materials on Bacteria/Host Interactions)


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Toxins Endotoxin (Lipid A component ofLPS)

-Unlike exotoxins, lipid A is not antigenic and cannot beconverted to a toxoid; responsible for gram negativesepticemia, with a fatality rate of 25-50 percent in USA

Exotoxins

-most are polypeptides, are antigenic and can be convertedto toxoids


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Endotoxin and Septicemia

Fever

Activation of coagulation process

Depression of RES

Vascular collapse


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Lipid A, Coagulation and RES

Lipid A activates clotting mechanism, withformation of fibrin

Fibrin may clog small blood vessels,causing intravascular coagulation, followedby shock

Lipid A may inhibit macrophages fromdegrading fibrin polymers trapped in bloodvessels


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Lipid A and Vascular Collapse

Lipid A activates macrophages to release

TNF-, which causes increased vascular

permeability and dilatation

This causes low blood pressure

(hypotension), impairs blood flow to vital

organs (kidneys, liver, lung, brain),followed by shock, multiple organ failure

and death


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Neisseria species

Are all gram negative cocci

Oxidase, catalase positive

Multiply intracellularly

Neisseria meningitidis

Neisseria gonorrhea Neisseria sicca


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Neisseria meningitidis

Gram negative diplococci

Infection from aerosol transmission in close contacts

Polysacharide capsule is antiphagocytic

LPS, capsule and sIgA protease are major virulence factors

Meningitis, fever, pneumonia, meningococcemia withhemorrhagic lesions are major clinical manifestations

Prevented by immunization with polysacharide-protein

conjugate vaccine


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Meningococcemia


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Death from Neisseria septicemia and

meningitis


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Neisseria urethritis

Gonorrhea with

purulent discharge

Disseminatedinfections via blood

to skin, joints

Ophthalmianeonatorium

(acquired eye

infection)


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Complications of Gonococcal

Infection Skin lesion

Septic arthritis

Ophthalmia

neonatorium


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Neisseria gonococcus / Chlamydia

Urethritis Differentiation


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Bacterial Classification and Pathogenesis


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Meningitis

(Strep pneumo, H. influenzae, N. meningitidis)


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Exotoxins

Enzymatic lysis

alpha toxinClostridium perfringes

Pore formation

alpha toxinStaph aureus

Protein synthesis inhibition

diphtheria & shigella toxins

Nerve-muscle transmission-inhibition

tetanus toxin-spastic paralysis

botulinum toxin-flaccid paralysis


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Modes of Action of Selected Exotoxins


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Cholera

(Vibrio cholerae)


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Clostridium and Bacillus

Identification of species based on spore location

and oxygen metabolism:

- C. tetanus- C. botulinum

- C. perfringes

- C. difficile- B. anthracis

- B. cereus


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Spore Location for Species ID


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Tetanus

(Clostridium tetani and skeletal muscle flexion)


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Bacillus anthracis

(potential bioterrorism agent, 2001)


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Gram Stain ofB. anthracis in Lung

Exudate of an Anthrax Patient


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Bacterial Classification and Pathogenesis


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Staphylococcus and Streptococcus

Tetrad cocci of

Staph aureus

(MRSA)

String-like cocci of Streppneomoniae/ Strep

viridans Enterococcus faecalis

MDR-Strep/Entero


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Staphylococcus aureus

Diseases

Toxin-mediated food poisoning, toxic shock syndrome;cutaneous impetigo, folliculitis, wound infections,

pneumonia, osteomyelitis, septic arthritisVirulence Factors

Capsule, protein A, cytotoxins/hemolysins, enterotoxins,exfoliative toxin; coagulase/catalase/beta-lactamaseenzymes

Methycillin-resistant Staph aureus (MRSA)

(antibiotic resistant strain, serious problem in hospitals, inthe US military, among athletes)


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Scalded skin syndrome due to

Staphylococcus aureus exotoxin


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Gram Stain ofStrep viridans in

exudate of cardiac valves


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Bacterial endocarditis

from a dental extraction


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E. coli Pathogenesis

Diseases

Gastroenteritis, bacteremia, UTI, cystitis,

pyelonephritis, neonatal meningitis,intraabdominal infections

Virulence Factors

Capsule, LPS, shiga toxins, hemolysins,siderophores (enterobactin, aerobactin),

R-plasmid


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Invasiveness / Dissemination

Exotoxins and Extracellular enzymes

Extracellular enzymes

Hyaluronidase dissolves connective tissue Collagenase hydrolyses muscle connective tissue

Streptokinase lyses blood clots

Phospholipases damage cell membranes

Lecithinase damages cell membranes

Staphylokinase (fibrinolysin) dissolves fibrin clots

_ Hemolysins lyse erythrocytes and white blood cells


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Shigella/Salmonella Invasive &

Dissemination Mechanisms Shigella

Invades M cells w 4 invasionproteins (IpaA,B,C,D)

Replicates in host cellcytoplasm

Induces apoptosis ofphagocytes

Produces cytotoxin (60sribosome protein inhibitor)

Invades deeper tissues, but notblood circulation

Causes diarrhea, dysentery

Low infective dose (100 cells)

Salmonella

Invades w invasion proteins

Replicates in acidic host cellvacuole

Replicates and transported bymacrophages in bloodcirculation

Invades other systemic organs,but not deeper GI tissues

Causes diarrhea, enteric fever High infective dose (>I million

cells)


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Salmonella/Shigella Invasive &

Mechanisms


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Cystic Fibrosis

Genetically inherited disorder occurring in 1 of

2500 live Caucasian births

Caused by pancreatic insufficiency, abnormalsweat electrolyte concentrations, viscid bronchial

secretions

Bronchial secretions lead to stasis in lungs and

disposition to infections ( Staph aureus, H.influenzae, Pseudomonas aeruginosamost

virulent and antibiotic resistant) and pneumonia


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Cystic Fibrosis


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Lyme Disease


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Lyme Disease

Caused by Borrelia burgdorferi

Transmitted by hard ticks (Ixodes species)

Human infections most prevalent in summer months in

Europe and USA Accompanied by fever, headache, myalgia,lymphadenopathy, skin lesions (erythema chronicummigrans)

Neurological complications (meningitis, encephalitis,

peripheral neuropathy) Cardiological (heart block, myopericarditis)

Arthralgia, arthritis (immune complex mediated)

Treatable with penicillin or tetracycline at early stage


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Lyme Disease

(rash of erythema chronicum/

inflammation)


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Lyme Disease


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Host Defenses

Barriers to Infection

Innate and adaptive immunity

Humoral and cellular immunity Phagocytosis

Complement activation

Inflammation Acute phase response

Hypersensitivity Reactions


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Barriers to Infection


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Innate and Adaptive Immunity


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Antibody Responses to Infections


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Various Roles of Macrophages


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Macrophage and Neutrophil


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Host immune responses to bacterial

infections


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Cytokine and Antibody Networks in

Bacterial Infections


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Inflammation

Consequence of a microbial infection

Recruitment of inflammatory cells (neutrophils,macrophages, basophils, eosinophils) andendogenous mediators (complement,

prostaglandin E2) to sites of infection

Production of inflammatory cytokines ( IL-1,

IL-6, TNF-) to induce acute-phase response May be accompanied by antigen neutralization

and cytotoxicity


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Stages of Inflammation

Tissue Damage

Vasodilation Exudation

Endothelial adherence

Diapedes (phagocytemigration)

Tissue repair


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Inflammation from Lyme Disease

(rash of erythema chronicum)


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Induction of acute phase proteins in

response to an infection


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Acute Phase Response

Also a response to infection as with inflammation

Triggered by IL-1, IL-6, TNF-, inflammation,prostaglandin E2, interferon

Induce production of acute phase proteins(C-reactive protein, complement components,coagulation proteins)

Reinforce innate defenses (complement activation,

phagocytosis) against infection, but excessiveproduction during sepsis by LPS can lead to shock

What are other acute phase responses???


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Hypersensitivity Reactions to

Bacterial Infections


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Antigenic Variation

Periodic changes ofsurface antigens by theorganism allows it to

bypass and not beaffected by the hostimmune responses.This occurs in HIV

infection, Lymedisease andtrypanosomiasis.


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Stages of a Disease


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Hospital-acquired (Nosocomial)

Infections


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Pennsylvania 2004 Nosocomial

Infections


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Sites of Antibiotic Activities


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Immunization

Passive maternal antibodies thr placenta

and mothers milk

Active -- natural exposure to microbes

- exposure to vaccines

Live vaccineattenuated Mycobacteriumbovis

Inactivated toxoidtetanus vaccine

Inactivated killedtyphoid vaccine

Subunit capsular polysacharides (poor immunogens)

-Hemophilus influenzae b, Neisseria meningitidis, Streptococcuspneumoniae Salmonella typhi

Conjugate vaccinespolysacharide units conjugated to proteinmolecules


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Childhood Immunization Schedule


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Case Studies


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CASE 1: URINARY TRACT INFECTION

Mr. Hamilton, a 69-year old man, underwent a transurethral

prostatectomy for cancer of the prostate. Because of concern about

postoperative bleeding during urination, the surgeons placed a

Foley catheter into his bladder. Three days later, Mr. Hamilton

developed a urinary tract infection with low-grade fever, some

pain, and pyuria. Laboratory cultures yielded 3 x 105 colonies ofEscherichia coli per ml of urine. The organisms were resistant to

all tested antibiotics except for aminoglycosides. Within 2 days,

Mr. Hamilton developed bacteremia with hypotension and shock.

His doctor eventually controlled his bacteremia with gentamycintherapy.


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Questions (#1)

I. What was the source of Mr. Hamilton'sinfection?

2. What bacterial component induced his fever,

hypotension and shock and how?

3. List three characteristics of aminoglycosidesand their modes of action.

4. What other organism could have been isolatedfrom his infection site? Give reasons for yourchoice of organism.

CASE 2: NOSOCOMIAL WOUND INFECTION


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CASE 2: NOSOCOMIAL WOUND INFECTION

Ms. Wilson, an 85-year-old woman with rheumatic heart disease, underwent a mitral

valve replacement along with surgery for a coronary artery bypass graft. Her

postoperative course was complicated by bleeding in the mediastinum, which

required more surgery .She did well after these operations and was discharged after

12 days. Three weeks later, Ms. Wilson, noticed some purulent drainage along the

wound site on her chest. She continued to have pain but did not tell her family,

assuming that the pain was related to her healing process. When she returned to see

the surgeon I month later, she reported her pain and low-grade fever. The surgeonnoted that there was considerable drainage at the wound site. Probing the wound, he

noticed a lot of pus. Ms. Wilson was hospitalized again for radical debridement

(cleaning) of her chest wound. Cultures of the pus yielded Staphylococcus

epidermidis. She was treated intravenously with vancomycin for 6 weeks and her

wound was debrided, with the wires in her sternum removed. At the end of thisperiod, she required a plastic surgical procedure and a muscle flap to close the

wound. After 2 more months of hospitalization, she was discharged and continued

her convalescence at home.


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Questions (#2)

I. Describe the bacterial pathogenesis of rheumatic heartdisease., including the organisms that may be associatedwith its causation.

2. What was the source of her postoperative wound

infection? 3 .What is the mode of action of vancomycin and why was

it the drug of choice for Mrs. Wilson's

wound infection?

4. In the absence of vancomycin, what other antibiotic(s)would you choose to clinically manage the woundinfection? Describe its mode of action.


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Case # 4

Simo da Silva, 36-year-old male resident of New Jersey, developed joint and muscle pains

and an expanding erythematous skin lesion on his left leg shortly after his summer vacation.

A week later, he started experiencing severe headache, neck stiffness and photophobia. He

also noticed multiple secondary annular skin lesions three weeks later. Blood analysis

reveled a high titer of IgM antibodies against a Gram negative spirochete, but the IgG

response was negative. Ten months after the resolution of the initial symptoms, Mr .da Silvahad severe neuritic pain on the skin of his abdomen within the distribution of the T8 through

T 11 dermatomes. This symptom was followed by intermittent joint pains, which occurred

in one joint at a time for several days, followed by longer pain- free periods. During the

second year of illness, the patient had a sudden onset of severe swelling of one knee and

then the other. Synovial fluid analysis revealed numerous white cells, and his antibody

response was high for IgG and low for IgM. His immunogenic profile showed that he had

Ill-A-DR4 and Ill-A-DR+ specificities. The swelling of the knees remained for about one

year, but then subsided.


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Questions (#4)

I. How did Mr. da Silva acquire the spirochete infection and what isyour identification of the organism?

2. What antibiotics would you use to treat his initial and late diseases?Is this a case of acute or chronic infection or disease?

3. What bacterial and immune factors are responsible for hisintermittent joint pains and knee swelling?

4. Explain the initial high IgM and no IgG titers in the early stage ofthe disease and the low IgM and high IgG titers in Mr .da Silva latedisease stage.

5. What type of white cells ( T cells, B cells, neutrophils, basophils,macrophages ) were found in the synovial fluid?

6. What does his immunologic profile ofHLA-DRA4 and HLA-DR2specificities mean?


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Case #5

Three young males were brought to HowardUniversity Hospital Emergency Clinic over thecourse of two days. They were diagnosed with

bacterial meningitis, but their cerebrospinal fluid(csf) cultures yielded three different organisms.They were all lethargic with fevers of 101 to

104o F, white blood cell (wbc) counts of over15,000 cells/l, mostly neutrophils. One of the

bacterial isolates was identified as Streptococcuspneumoniae, the second asHemophilus influenzaetybe b and the third asNeisseria meninigitidis.


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Questions (#5)

What bacterial culture chracteristics and laboratory methods wereused to separately identify the three organisms?

What is the pathogenic bacterial structure that is common to the threeorganisms and how is its composition different for each organism?

Describe the pathway(s) that were taken by the organisms to get intothe patients csf.

What are the epidemiological characteristics of the meningitis causedby each organism?

What antibiotics of choice would you use to treat the patients? Givereasons for your choice.

What are the modes of action for your choice of antibiotics? What types of resistance mechanism may be used by each of theorganisms to inhibit the activity of your selected antibiotics?


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Home-Work Exercise

List organisms that may be associated with the following conditions

1. Bacteremia

2. Endocarditis

3. Meningitis

4. Pharyngitis 5. Pneumonia

6. Conjunctivitis

7. lntra-abdominal abscess

8. Gastroenteritis

9. Urinary Tract infections 10. lmpetigo

11. Cellulitis

12. Sepsis


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Reading References

Chapters 9-13, 18 , 47 in Medical Microbiology,

6th edition by Patrick Murray et al, Mosby, Inc.,

2009

Chapters 8 -10 in Medical Microbiology, 3rd

edition by Cedric Mims, et al, Mosby, Inc., 2004.

Chapters 6, 7, 8 and 9 in Mechanisms of Microbial

Diseases, 3rd edition by Moselio Schaechter, etal, William & Wilkins, 1998.

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