Lectures 1-3
Microbiology Medical Microbiology with Goin at University of Pittsburgh - Pittsburgh
About this deck
By: Joshua Weis
Created: 2011-02-24
Size: 25 flashcards
Views: 4
Created: 2011-02-24
Size: 25 flashcards
Views: 4
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Koch's Postualtes
The organism:
-is always found in the diseased, but not healthy animals
-can be isolated and grown in pure culture
-in pure culture causes the same disease when reinoculated into susceptible animals
-can be reisolated from those diseased animals
Limitations of Koch's postulates
Some organisms can’t be cultured away from animals
There are no animal models for some human infections
Some infections are caused by many different pathogens
Some healthy people can be colonized by pathogens
Virulence
# number of organisms needed to cause infection
Using animal models, can determine LD50, or ED50
Virulence factors = toxins, adhesins, capsules
Molecular Koch's Postulates
The property encoded by the virulence gene should be associated with virulent strains
Inactivation of the virulence gene should lead to a loss of virulence
Addition of the wild-type virulence gene to the mutant should restore virulence
Carriers
Colonization of the body by a pathogen does NOT always lead to disease, e.g., the carrier state
Carriers can be an important reservoir for future infections of the carrier or others
Infectious Cycle
Entry Adherence/Colonization Invasion Evasion of host defenses Damage Dissemination
Staphylococci Morphology
G+ clusters
Strep pyogenes Morphology
G+ chains
Pneumonococci Morphology
G+ diplococci
Neisseriae Morphology
G- diplococci
O - Antigen
On G- bacteria (part of LPS)
Provides resistance to lysis by complement
Provides bile-resistance (LOS lacks O antigen)
Used for epidemiologic serotyping: –O Antigen –H Antigen (flagella) –K Antigen (capsule)
Porins
Outer membrane provides permeability barrier that can protect the G-negative cell.
To accomplish movement of molecules accross the outer membrane, the G- cell uses porins
Alterations or loss of porins = mechanisms of antibiotic resistance
Mycobacterium spp.
Acid-fast positive
“Waxy” cell envelope
Envelope is antiphagocytic and helps disease transmission
Rickettsiae
Obligate intracellular pathogens, probably because they require some energy from host cells
Vector-borne
Morphology like Gram-negatives
Chlamydiae and Chlamydophila
Obligate intracellular pathogens because they are energy thieves
Complex life cycle (EBs and RBs)
Small, with two membranes like Gram-negatives (but no peptidoglycan)
Mycoplasma spp.
Distinguishing features include:
-lack of a cell wall
-presence of sterols in their plasma membranes
Absence of cell wall important for therapy
Important Factors for Bacterial Growth
Temperature
pH
Oxygen (Redox) conditions
Nutrients (e.g., iron)
Osmolarity
Importance of Iron for Bacterial Growth
Host restriction of iron by iron-binding proteins is an important defense mechanism
However, pathogens overcome this by:
-Producing their own iron-binding molecules (siderophores)
-Binding host transferrin or lactoferrin to steal iron
Oxygen Requirements for Bacterial Growth
•Aerobes: require O2
–Special case: microaerophiles
•Facultative Anaerobes: respiration in the presence of O2 but fermentation if O2 isn’t available
Aerotolerants: grow by fermentation regardless of whether O2 is present or not
Anaerobes: killed by O2
Anaerobes Molecular Environment
-Often lack catalase and superoxide dismutase
-Often have sensitive enzymes that must be in a reduced environment to function properly
Growth of Anaerobes in Human Tissue
The redox potential of healthy tissue is too high for anaerobes to grow.
Medical conditions can lower tissue redox potential:
-Circulatory problems
-Tight orthopedic casts
-The co-presence of facultative anaerobes, which can consume O2
Characteristics of Nonclostridial Anaerobic Infections
-Abscess formation (anywhere in body)
-Often polymicrobic
-Often involve highly antibiotic-resistant isolates
-Can involve a mix of nonclostridial anaerobes and facultative anaerobes
-Often difficult to treat
Characteristics of Nonclostridial Anaerobic Infections -II
-low virulence, yet can cause fatal infections.
-often slow-growing, fastidious, and produce gases-Exotoxins generally not so important for pathogenesis
Bacterial Endospores
-Most resistant life forms
-Only medically-important sporeformers are Clostridium spp. (anaerobic) and Bacillus spp. (aerobic or facultative anaerobes)
-Sporulation is not a reproductive strategy but it is a great survival strategy
Bacterial Endospores II
Resistant to:
-Heat, Radiation, Chemicals, Drying
Resistant due to low water content and presence of DNA stabilizing proteins
Can remain viable for long periods because they are metabolically inert
Sterilization is aimed at killing bacterial endospores
About this deck
By: Joshua Weis
Created: 2011-02-24
Size: 25 flashcards
Views: 4
Created: 2011-02-24
Size: 25 flashcards
Views: 4
About StudyBlue
STUDYBLUE makes things that make you better at school.
Things like online flashcards with photos and audio.
Things like personalized quizzes and friendly reminders about when (and what) to study next.
Think of it as a digital backpack™: access to all of your study materials online and on your phone.
STUDYBLUE exists to make studying efficient and effective for every student, for free. Join us.
“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy
Kathy