Microbiology Chapter 15 & 16

The body maintains ______with microorganisms

dynamic equilibrium

Normal microbiota (flora)

microbes that inhabit the body without causing disease

Resident microbiota

long-term, stable inhabitants (part of normal flora)

Transient microbiota

temporary visitors (part of normal flora)

Functions of normal microbiota

compete with pathogens (microbial antagonism), produce beneficial compounds (e.g., vitamin K), and prevent colonization by harmful species

__________ __________ occur when normal flora enter sterile areas (e.g., E.coli in the bladder)

endogenous infections

pathology

study of diseasee

Etiology

study of the cause of disease

pathogen

microorganism capable of causing disease

pathogenesis

mechanism of disease development

infection

successful colonization of host

disease

abnormal state impairing function

sign

objective, measurable evidence (fever, rash)

symptom

subjective experience (pain, fatigue)

syndrome

set of signs/symptoms characteristic of a disease

infectious diseases

caused by pathogens (e.g., malaria)

noninfectious diseases

genetic or environmental (e.g., sickle cell disease)

communicable diseases

spread between hosts

contagious diseases

easily spread (e.g., influenza) (in communicable category)

noncommunicable diseases

not spread person-to-person (e.g., tetanus)

iatrogenic diseases

from medical procedures

zoonotic diseases

transmitted from animals to humans

Periods of disease

incubation, prodromal, illness, decline, convalescence

Incubation period

no symptoms, pathogen multiplying

Prodromal period

mild, early symptoms

Illness period

peak of symptoms; immune response strongest

Decline period

symptoms subside

Convalescence period

recovery; pathogen cleared or latent

Acute duration

rapid onset, short duration (e.g., flu)

Chronic duration

slow progression, long-lasting (e.g., tuberculosis)

Latent duration

inactive phase, later reactivation (e.g., herpes simplex)

Koch’s Postulates

used to determine causative agents of disease

steps for Koch’s Postulates

pathogen present in every case, isolate and grow in pure culture, cause disease in a healthy host, re-isolate pathogen from newly infected host

Limitations of Koch’s Postulates

some microbes can’t be cultured or cause different symptoms in different hosts

Step 1 of Koch’s Postulates

pathogen present in every case

Step 2 of Koch’s Postulates

isolate and grow in pure culture

Step 3 of Koch’s Postulates

cause disease in a healthy host

Step 4 of Koch’s Postulatees

re-isolate pathogen from newly infected host

Pathogenicity

ability to cause disease

Virulence

degree of pathogenicity

Virulence factors

traits aiding colonization, immune evasion, and tissue damage

Factors in virulence factors

adhesion factors, invasion factors, toxins, antiphagocytic factors

Infection dose (ID)

number of microbes needed to cause infection in 50% of hosts

Lethal dose (LD)

amount of toxin lethal to 50% of hosts

Smalled ID/LD

higher virulence

Primary (true) pathogens

cause disease in healthy hosts (e.g., Mycobacterium tuberculosis)

Opportunistic pathogens

cause disease when defenses are compromised (e.g., Candida albicans)

Virulence factors

adhestion, invasion, antiphagocytic factors, toxins

Adhesion

pathogens use adhesins, pili, fimbriae, and biofilms to attach to host cells

Adhesion example

Streptococcus mutans adheres to enamel via glycocalyx

Invasion

pathogens enter tissues via enzymes, collagenase and hyaluronidase break down connective tissues

Invasion example

Clostridium perfringens produces collagenase to spread through tissue

Antiphagocytic factors

capsules/slime layers prevent recognition and engulfment, chemicals that kill or inhibit phagocytes

Antiphagocytic factors example

Streptococcus pyogenes M protein

Toxins categories

exotoxins and endotoxins

Exotoxins

secreted proteins, highly specific, A-B toxins: A = active; B = binding subunit

Exotoxins example

C. botulinum, C. tetani

Endotoxins

lipid A of gram-negative LPS; released when cells lyse —> fever, shock, inflammation

Stages of pathogenesis

exposure (contact), adhesion (colonization), invasion, infection, portals of exit

Exposure (contact) stage - via portals of entry (skin, mucosa, placenta)

Exogenous: external source, Endogenous: internal flora, TORCH infections: toxoplasmosis, other (syphilis, etc.), Rubella, Cytomegalovirus, Herpes

Adhesion (colonization) stage

binding to receptors or forming biofilms

Invasion stage

penetration and spread to deeper tissues

Infection stage

multiplication and establishment in host

Portals of exit

respiratory droplets, feces, urine, blood, etc.

Epidemiology

study of disease distributiion and determinants in populations

Etiology

cause of disease

Predisposing factor

condition increasing susceptibility (age, lifestyle, genetics)

Morbidity

incidence of illnessMo

rtality

number of deaths

Incidence

new cases within time period

Prevalence

total number of existing cases

Centers for Disease Control and Prevention (CDC)

collects, analyzes, and disseminates disease data, publishes Morbidity and Mortality Weekly Report (MMWR), and collaborates with WHO on global health surveillance

Patterns of disease occurrence

endemic, sporadic, epidemic, pandemic

Endemic

constantly present in a population (e.g., common cold)

Sporadic

occurs irregularly (e.g., rabies)E

Epidemic

sudden increase in cases (e.g., influenze outbreak)

Pandemic

global epidemic (e.g., COVID-19)

Reservoir

natural habitat of pathogen (human, animal, soil, water)

Source

direct origin of infection

Carrier

individual harboring and transmitting infection

Carrier types

asymptomatic, active, passive

Asymptomatic carrier

no symptoms (e.g., Typhoid Mary)

Active carrier

currently ill

Passive carrier

transfers via contaminated materials

Methods of disease transmission

contact, vehicle, vector

Types of contact transmission

direct, indirect, and droplet

Direct contact transmission

person-to-person contact, Vertical: mother → fetus, Horizontal:between individuals

Indirect contact transmission

via fomites (doorknobs, utensils)

Droplet contact transmission

<1 m distance via sneezing/coughing

Types of vehicle transmission

airborne, waterborne, foodborne

Airborne vehicle transmission

>1 m via aerosol (e.g., TB)

Waterborne vehicle transmission

contaminated water (e.g., cholera)

Foodborne vehicle transmission

improperly prepared or stored food

Types of vector transmission 

mechanical and biological

Mechanical vectors transmission

carry pathogens externally (e.g., flies)

Biological vectors transmission

part of pathogen’s life cycle (e.g., mosquitoes → malaria)

Healthcare-Associated Infections (HAIs)

also called nosocomial infections

Common causes of HAIs

Staphylococcus aureus, E. coli, Pseudomonas

Transmission of HAIs promoted by

invasive procedures, catheters, antibiotic misuse, immunocompromised patients

Prevention of HAIs

hand hygiene, sterilization, isolation, antibiotic stewardship