Microbe-Human Interactions: Infection and Disease
I.
Human Host
A. Contact, Infection, Disease-A Continuum
1. Contamination
2. Infection
3. Disease
B. Normal Microbiota
1. Transient microbiota
a. In body only hours to months
b. In same regions as resident flora
c. Cannot persist in body
2. Resident microbiota
a. Colonize body normally without causing disease
b. Commensals; prevent overgrowth of pathogens
c. Bacteria, fungi, protozoa, viruses, arthropods
d. Some areas are microbe-free
e. Found in areas that communicate with outside environment
3. Acquisition of Normal Microbiota
a. Womb is axenic
b. Microbiota begin to develop during birthing
c. Most established during first months of life
4. Flora of the Human Skin
a. Reside on dead cell layers, follicles, glands of epidermis
b. More prolific in moist areas
c. Bacteria
1) Staphylococcus
2) Corynebacterium
3) Proprionibacterium
4) Mycobacterium
5) Yeasts in moist skin folds
5. Flora of the Gastrointestinal Tract
a. Flora of Mouth
1) Cheek epithelium, gingival, tongue, floor of mouth,
tooth enamel
2) Streptococcus sanguis, S. salivarius, S. mitisepithelial surfaces
3) S. mutans, S. sanguis-dental caries
4) Anaerobes ingingival crevices
5) Saliva has high bacterial count
b. Flora of Large Intestine
1) 10-30% of feces
2) Most are strict anaerobes-Bacteroides,
Bifidobacterium, Fusobacterium, Clostridium
3) Coliforms-Escherichia coli, Enterobacter,
Citrobacter present in small numbers
II.
4) Generate vitamins
5) Skatole
6) Lactose intolerance
6. Flora of Respiratory Tract
a. Fist are mostly oral streptococci
b. Staphylococcus aureus-nasal entrance, nasal
vestibule,anterior nasopharynx
c. Neisseria species in nasopharynx
d. Assorted streptococci and Haemophilus on tonsil, lower
pharynx
7. Flora of Genitourinary Tract
a. In vagina and outer opening of urethra in female
b. Anterior urethra in males
c. Urethra-nonhelolytic streptococci, staphylococci,
corynebacteria, occasionally coliforms
d. Vagina-Before puberty and post-menopausal-diphtheroids,
staphylococci, streptococci, some coliforms
e. Vagina- at puberty, acid producing lactobacilli
The Progress of an Infection
A. Introduction
1. True pathogens
2. Opportunistic pathogens
B. Portal of Entry: Gateway to Infection
1. Skin
a. Cuts, abrasions
b. Staphylococcus aureus, Streptococcus pyogenes
c. Dermatophytes, agents of gangrene, tetanus, herpes
simplex type 1
d. Some helminthes burrow
e. Bites of arthropods, other animals
f. Contaminated needles
g. Conjunctiva-Haemophilus aegyptius, Chlamydia
trachomatis, Neisseria gonorrhoeae
2. Mucous membranes
a. Line body cavities open to environment
b. Moist, warm
c. Respiratory tract –most commonly used site
3. Gastrointestinal Tract as Portal
a. Pathogens in food, drink, other ingested substances
b. Survive digestive enzymes and pH changes
c. G- bacci-Salmonella, Shigella, Vibrio, Escherichia coli
d. Viruses-poliovirus, hepatitis A, echovirus, rotavirus
e. Protozoans-Entaemoba histolytica, Giardia lamblia
4. Respiratory Portal of Entry
a. Oral and nasal cavities
b. Bacteria of streptococcal sore throat, meningitis, diphtheria,
whooping cough
c. Viruses of influenza, measles, mumps, rubella, chickenpox
d. Pneumonia-Bacteria (Streptococcus pneumoniae,
Klebsiella, Mycoplasmas), fungi (Cryptococcus,
Pneumocystis)
e. Other lung diseases-Mycobacterium tuberculosis, fungus
Histoplasma
5. Urogenital Portals of Entry
a. Sexually transmitted diseases
b. Some microbes penetrate unbroken surfaces; others need
cut or abrasion
c. Genital warts, syphilis, gonorrhea, chlamydia, herpes, HIV,
Trichomonas (protozoan), Candida albicans , hepatitis B
6. Pathogens that infect during Pregnancy and Birth
a. Placenta usually an effective barrier to pathogens
b. Syphilis spirochete
c. Herpes simplex
d. STORCH-syphilis, toxoplasmosis, other diseases, rubella,
cytomegalovirus, herples simples virus
C. Size of the Inoculum
1. Infectious dose
2. Varies greatly
D. Mechanisms of Invasion and Establishment of the Pathogen
1. Adhesion
a. Specialized structures-fimbrae, flagella, capsules, cilia,
suckers, hooks, barbs
b. Attachment proteins- surface lipoproteins or glycoproteins
c. Interaction of ligand with host
2. Virulence Factors of Infectious Disease
a. Pathogenicity
b. Virulence
c. Exoenzymes (Extracellular enzymes)
1) Secreted by pathogen
2) Disolve structural chemicals in body
3) Mucinase, keratinase, collagenase, hyaluronidase
d. Toxigenicity (toxins)
1) Chemicals produced by pathogen
2) Exotoxins
3) Endotoxins
e. Antiphagocytic factors
1) Bacterial capsule
2) Chemicals
3. Stages of Infectious Disease
a. Incubation- no signs or symptoms
b. Prodromal- vague, general symptoms
III.
c. Illness- most severe signs and symptoms
d. Decline- declining signs and symptoms
e. Convalescence – no signs and symptoms
4. Patterns of Infection
a. Localized infection
b. Systemic infection
c. Focal infection
d. Mixed infection
e. Secondary infection
f. Sign
g. Symptom
h. Inflammation
i. Leukocytosis
j. Leukopenia
k. Septicemia
l. Bacteremia or viremia
m. Asymptomatic, subclinical or inapparent
E. Portal of Exit: Vacating the Host
1. Respiratory, saliva
2. Skin scales
3. Fecal exit
4. Urogenital tract
5. Removal of blood
F. Persistence of Microbes and Pathologic Conditions
1. Latency
2. Sequelae
Epidemiology: The Study of Disease in Populations
A. Early Epidemiology
1. John Snow, English physician
2. 1854-cholera outbreak in London
3. Caused by fecal contamination of water at Broad St. pump
B. Epidemiology
1. Definition
2. Surveillance
3. Reportable, notifiable diseases
4. Centers for Disease Control and Prevention (CDC)-Atlanta,GA.
5. Prevalence
6. Incidence
7. Mortality rate
8. Morbidity rate
9. Patterns of disease occurrence
a. Endemic
b. Sporadic
c. Epidemic
d. Pandemic
C. Reservoirs of Infection
1. Definition
2. Types
a. Animal reservoir- zoonoses; direct contact, eating animals,
bloodsucking arthropods
b. Human carrier
1) Asymptomatic-incubation, convalescent, chronic
2) Passive-contaminated but not infected
c. Nonliving reservoir-soil, natural bodies of water
D. Patterns of transmission
1. Direct contact
a. Droplets
b. Kissing, sex, nursing, placental transfer, bites of vectors
2. Indirect contact
a. Vehicle- fomites, food
b. Airborne- droplet nuclei and aerosols
E. Nosocomial Infections: the Hospital as a Source of Disease
1. Acquired during hospital stay
2. Urinary tract, respiratory tract, surgical incisions
3. G- intestinal flora, (E. coli, Klebsiella, Pseudomonas)
4. G+ staphylococci, streptococci and yeasts
5. Types
a. Exogenous
b. Endogenous
c. Iatrogenic
6. Control
a. Universal precautions
b. Hand washing
F. Koch’s Postulates