Bacterial Pathogenesis
Kunle Kassim, PhD, MPH
Professor, Microbiology
August, 2010
URGENT!!!!
It is important for you to review the lecture
powerpoint on Host/Bacteria Interactions
from first yearbefore coming to class for
this lecture.
Objectives
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Review the diversity and significance of bacterial flora in the maintenance of
immunity
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 the
host, using cystic fibrosis, lyme disease and bacterial urethritis as illustrations
Present the different types of host defenses, including the constitutive elements of
innate 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 in
preventing childhood infectious diseases.
Normal Bacterial Flora
Bacterial Virulence Factors
Mechanisms of Pathogenicity
Host Defense Mechanisms
Selected Bacterial Diseases
(Review lecture materials on Bacteria/Host
Intreactions)
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
Distruption of Normal Flora
• UTI
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Tumors
Bladder incontinence
Ureteric reflux
Poor hygiene
– E. coli infections
Determinants of Pathogenicity
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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 year’s lecture materials on Bacteria/Host Interactions)
Toxins
• Endotoxin (Lipid A component of
LPS)
-Unlike exotoxins, lipid A is not antigenic and cannot be
converted to a toxoid; responsible for gram negative
septicemia, with a fatality rate of 25-50 percent in USA
• Exotoxins
-most are polypeptides, are antigenic and can be converted
to toxoids
Endotoxin and Septicemia
• Fever
• Activation of coagulation process
• Depression of RES
• Vascular collapse
Lipid A, Coagulation and RES
• Lipid A activates clotting mechanism, with
formation of fibrin
• Fibrin may clog small blood vessels,
causing intravascular coagulation, followed
by shock
• Lipid A may inhibit macrophages from
degrading fibrin polymers trapped in blood
vessels
Lipid A and Vascular Collapse
• Lipid A activates macrophages to release
TNF-α, 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
Neisseria species
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Are all gram negative cocci
Oxidase, catalase positive
Multiply intracellularly
Neisseria meningitidis
Neisseria gonorrhea
Neisseria sicca
Neisseria meningitidis
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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 with
hemorrhagic lesions are major clinical manifestations
• Prevented by immunization with polysacharide-protein
conjugate vaccine
Meningococcemia
Death from Neisseria septicemia and
meningitis
Neisseria urethritis
• Gonorrhea with
purulent discharge
• Disseminated
infections via blood
to skin, joints
• Ophthalmia
neonatorium
(acquired eye
infection)
Complications of Gonococcal
Infection
• Skin lesion
• Septic arthritis
• Ophthalmia
neonatorium
Neisseria gonococcus / Chlamydia
Urethritis Differentiation
Bacterial Classification and Pathogenesis
Meningitis
(Strep pneumo, H. influenzae, N. meningitidis)
Exotoxins
• Enzymatic lysis
alpha toxin—Clostridium perfringes
• Pore formation
alpha toxin—Staph aureus
• Protein synthesis inhibition
diphtheria & shigella toxins
• Nerve-muscle transmission-inhibition
tetanus toxin-spastic paralysis
botulinum toxin-flaccid paralysis
Modes of Action of Selected Exotoxins
Cholera
(Vibrio cholerae)
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
Spore Location for Species ID
Tetanus
(Clostridium tetani and skeletal muscle flexion)
Bacillus anthracis
(potential bioterrorism agent, 2001)
Gram Stain of B. anthracis in Lung
Exudate of an Anthrax Patient
Bacterial Classification and Pathogenesis
Staphylococcus and Streptococcus
• Tetrad cocci of
Staph aureus
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• String-like cocci of Strep
pneomoniae/ Strep
viridans
• Enterococcus faecalis
• MDR-Strep/Entero
Staphylococcus aureus
Diseases
• Toxin-mediated food poisoning, toxic shock syndrome;
cutaneous impetigo, folliculitis, wound infections,
pneumonia, osteomyelitis, septic arthritis
Virulence Factors
• Capsule, protein A, cytotoxins/hemolysins, enterotoxins,
exfoliative toxin; coagulase/catalase/beta-lactamase
enzymes
• Methycillin-resistant Staph aureus (MRSA)
(antibiotic resistant strain, serious problem in hospitals, in
the US military, among athletes)
Scalded skin syndrome due to
Staphylococcus aureus exotoxin
Gram Stain of Strep viridans in
exudate of cardiac valves
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
Invasiveness / Dissemination
• Exotoxins and Extracellular enzymes
Extracellular enzymes
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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
Shigella/Salmonella Invasive &
Dissemination Mechanisms
• Shigella
• Invades M cells w 4 invasion
proteins (IpaA,B,C,D)
• Replicates in host cell
cytoplasm
• Induces apoptosis of
phagocytes
• Produces cytotoxin (60s
ribosome protein inhibitor)
• Invades deeper tissues, but not
blood circulation
• Causes diarrhea, dysentery
• Low infective dose (100 cells)
• Salmonella
• Invades w invasion proteins
• Replicates in acidic host cell
vacuole
• Replicates and transported by
macrophages in blood
circulation
• Invades other systemic organs,
but not deeper GI tissues
• Causes diarrhea, enteric fever
• High infective dose (>I million
cells)
Salmonella/Shigella Invasive &
Mechanisms
Cystic Fibrosis
• Genetically inherited disorder occurring in 1 of
2500 live Caucasian births
• Caused by pancreatic insufficiency, abnormal
sweat electrolyte concentrations, viscid bronchial
secretions
• Bronchial secretions lead to stasis in lungs and
disposition to infections ( Staph aureus, H.
influenzae, Pseudomonas aeruginosa –most
virulent and antibiotic resistant) and pneumonia
Cystic Fibrosis
Lyme Disease
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 chronicum
migrans)
• Neurological complications (meningitis, encephalitis,
peripheral neuropathy)
• Cardiological (heart block, myopericarditis)
• Arthralgia, arthritis (immune complex mediated)
• Treatable with penicillin or tetracycline at early stage
Lyme Disease
(rash of erythema chronicum/
inflammation)
Lyme Disease
Host Defenses
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Barriers to Infection
Innate and adaptive immunity
Humoral and cellular immunity
Phagocytosis
Complement activation
Inflammation
Acute phase response
Hypersensitivity Reactions
Barriers to Infection
Innate and Adaptive Immunity
Antibody Responses to Infections
Various Roles of Macrophages
Macrophage and Neutrophil
Host immune responses to bacterial
infections
Cytokine and Antibody Networks in
Bacterial Infections
Inflammation
• Consequence of a microbial infection
• Recruitment of inflammatory cells (neutrophils,
macrophages, basophils, eosinophils) and
endogenous mediators (complement,
prostaglandin E2) to sites of infection
• Production of inflammatory cytokines ( IL-1,
IL-6, TNF-α) to induce acute-phase response
• May be accompanied by antigen neutralization
and cytotoxicity
Stages of Inflammation
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Tissue Damage
Vasodilation
Exudation
Endothelial adherence
Diapedes (phagocyte
migration)
• Tissue repair
Inflammation from Lyme Disease
(rash of erythema chronicum)
Induction of acute phase proteins in
response to an infection
Acute Phase Response
• Also a response to infection as with inflammation
• Triggered by IL-1, IL-6, TNF-α, 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 excessive
production during sepsis by LPS can lead to shock
• What are other acute phase responses???
Hypersensitivity Reactions to
Bacterial Infections
Antigenic Variation
• Periodic changes of
surface antigens by the
organism allows it to
bypass and not be
affected by the host
immune responses.
This occurs in HIV
infection, Lyme
disease and
trypanosomiasis.
Stages of a Disease
Hospital-acquired (Nosocomial)
Infections
Pennsylvania 2004 Nosocomial
Infections
Sites of Antibiotic Activities
Immunization
• Passive – maternal antibodies thr’ placenta
and mother’s milk
• Active -- natural exposure to microbes
- exposure to vaccines
• Live vaccine – attenuated Mycobacterium
bovis
• Inactivated toxoid – tetanus vaccine
• Inactivated killed – typhoid vaccine
• Subunit capsular polysacharides (poor immunogens)
-Hemophilus influenzae b, Neisseria meningitidis, Streptococcus
pneumoniae Salmonella typhi
• Conjugate vaccines – polysacharide units conjugated to protein
molecules
Childhood Immunization Schedule
Case Studies
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 of
Escherichia 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 gentamycin
therapy.
Questions (#1)
• I. What was the source of Mr. Hamilton's
infection?
• 2. What bacterial component induced his fever,
hypotension and shock and how?
• 3. List three characteristics of aminoglycosides
and their modes of action.
• 4. What other organism could have been isolated
from his infection site? Give reasons for your
choice of organism.
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 surgeon
noted 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 this
period, 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.
Questions (#2)
 I. Describe the bacterial pathogenesis of rheumatic heart
disease., including the organisms that may be associated
with 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 wound
infection? Describe its mode of action.
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 Silva
had 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.
Questions (#4)
• I. How did Mr. da Silva acquire the spirochete infection and what is
your 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 his
intermittent joint pains and knee swelling?
• 4. Explain the initial high IgM and no IgG titers in the early stage of
the disease and the low IgM and high IgG titers in Mr .da Silva late
disease 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-DR2
specificities mean?
Case #5
Three young males were brought to Howard
University Hospital Emergency Clinic over the
course 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 over
15,000 cells/μl, mostly neutrophils. One of the
bacterial isolates was identified as Streptococcus
pneumoniae, the second as Hemophilus influenzae
tybe b and the third as Neisseria meninigitidis.
Questions (#5)
• What bacterial culture chracteristics and laboratory methods were
used to separately identify the three organisms?
• What is the pathogenic bacterial structure that is common to the three
organisms and how is its composition different for each organism?
• Describe the pathway(s) that were taken by the organisms to get into
the patients’ csf.
• What are the epidemiological characteristics of the meningitis caused
by each organism?
• What antibiotics of choice would you use to treat the patients? Give
reasons 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 the
organisms to inhibit the activity of your selected antibiotics?
Home-Work Exercise
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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
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, et
al, William & Wilkins, 1998.