Intro to Bacteriology: Flora and Pathogenesis Flashcards
Initial Colonization of Host
Wjere do microbes come from in the womb?
- Uterus is usually sterile
- Fetal membranes break, and fetus is exposed to vaginal flora during birth
- 8-10 hours after deliver, newborn is colonized by many microbes
Indigenous Flora Characteristics
Two types of flora
Microbes commonly found on or in the body of a healthy person
Resident flora: colonize the site for months/years
Transient flora: temporary colonizers, which are eliminated
Human Microbiota
3 times more bacterial cells than human cells
Microbiota includes viruses, fungi, archaea, single-celled eukaryotes.
Gut Microbiome and Health and Disease
Host-microbial interactions maintain health, if disrupted > illness
Gut microbiome changes induced by diet, antibiotics, immune, genetics
Dysbiosis: influence bioavailabilty/efficacy of therapeutic drugs
What Influences Microbiota Type and Number on the Body
6 things
- Oxygen availability
- Receptor sites for attachment
- pH
- Nutrient availability
- Influence of other microbes at thte site
- Immunological response of host to the microbe
Role of Normal Flora
3 things
- Immune stimulation
- Keep out invaders
- Human nutrition/metabolism (gut flora)
How Gut Flora Benefit Human Hosts
5 ways
- Synthesize essential metabolites
- Break down plant fibers
- Inactivate toxic substances in food or made by pathogens
- Prevent pathogens from benefiting from the resources of the human gut
- Interact with epithelium to trigger development of secondary lymphoid tissue
Koch’s Postulates
Diseased organism can be cultured, and that culture can be inoculated into a healthy organism, and that organism will get the disease
Course of Infectious Disease
5 steps
Incubation: time from eposure to onset of symptoms, dependent on infection
Prodromal: incubation period and before the characteristic symptoms of infection, can transmit to other people, mild and nonspecific response
Illness: displaying symptoms of infection, dependent of type, dose, and host immune response
Decline: immune system successfully defends, symptoms improve, secondary infections may occur
Convalescence: symptoms resolve, normal functions or damage
True Pathogen
Primary pathogen
Causes disease in a healthy person
Opportunistic Pathogen
Typically part of normal flora
Causes disease when:
- Immune system weakened
- New microbe introduced and disrupts flora
- Breakdown of defense barriers (catheters)
Timing of Infections
3 timings
Acute infections: develop quickly
Subacute: more suddenly than chronic but less than acute
Chronic: insidious onset, maybe even years, lasts a long time
Latent: silent or dormant stage, go from symptomatic to asymptomatic back to symptomatic
How Infectious Diseases Take Place
Four steps
Encounter/acquisition: agent meets and colonizes host surface
Attachment: agent multiplies and breaches defenses
Dissemination: agent penetrates deeper and comes in contact with immune response
Outcome: agent or host wins during infection, or coexist
Outcome depends on host health or pathogenicity of agent
Types of Acquisition
2 types
Endogenous: caused by agents in or on the body
Exogenous: agents in the environment
Contact Transmission
Direct skin to skin, mucous membrane to mucous membrane, fecal-oral, transfusion
Airborne Transmission
What is it also affected by?
Carried on air currents in droplet nuclei, can tavel longer distances
Affected by
- microbial load in particles
- stability of microbe in the aerosol
- infectious dose
Droplet Transmission
Larger particles, usually stay within 3 feet of inected person
Vector Transmission
Arthropod, blood meal, biting
Vehicular Transmission
Food, water, fomites
Infectiousness
Depends on?
Depends on infectious agent, individual characteristics, duration of infectiousness, virulence of microbe, infectious dose
Virulence Factor: Exo/Endotoxins
Exotoxins: gram positive microbes, secreted by living cell
- subunit for binding and subunit with toxicity
- toxins kill host cell or destroy intracellular activity
Endotoxins: gram negative, lipopolysaccharides, released upon cell lysis/death
- disrupts clotting, causes fever and activates immune system
- hypotension, shock, death
Host Factors of Infection
Age: change in immune status, flora
Sex: anatomic structures
Stress: excess cortisone, suppresses inflammatory process
Diet: obese or lacking vitamins/proteins more susceptible
Disease or trauma: other diseases, smoking, burns
Therapy for other diseases: change immune status
Infection Outcome
Dependent on? Possible outcomes?
Dependent on: host health, diagnosis and treatment, virulence of pathogen
Outcomes:
- restore complete health
- restore health, residual effects
- survive, severely compromised
- death
Healthcare Associated Infection Types
Pneumonia - ventilators
Bloodstream - central lines
Surgical site infections
UTI - catheters
Causes of Healthcare Associated Infections
Staphylococcus aureus: surgical wounds, respir. tract, bloodstream
Enterococci: surgical wound, urinary tract, bloodstream
Enterobacterales (E. coli, K. pneumoniae): urinary tract, surgical wound, bloodstream
Non fermenting GNR: urinary tract, surgical wound, respir. tract
Clostridiodes difficile
Many are antibiotic resistant strains
Infection Control: Types of Precautions
Airborne or contact precautions
Droplet or standard precautions
Enhanced contact isolation
