Clinical Bacteriology I & II Flashcards
What is a biofilm?
A bacterial community
What is a consortium?
Another term for a community of bacteria
What are the two phyla of bacteria which are predominant in the GI tract?
1) firmicutes
2) bacteroidetes
What are some characteristics of bacteria present in biofilms?
1) grow slower
2) more abx resistant
3) might use different metabolic pathways
4) more diverse
What surface on the human body demonstrates biofilms most readily?
teeth!
What are the five steps in the biofilm lifecycle?
1) adhesion
2) colonization
3) accumulation
4) climax community
5) dispersal
What determines whether a biofilm will grow in a certain environment?
whether the surface is shedding or non-shedding
On what clinical surfaces would you find biofilms?
1) orthopedics
2) catheters
3) hospital equipment
What two micriobiological diagnostic tools can physicians use?
1) staining and cultured growth
2) abx sensitivity tests
What is a substratum?
surface for bacterial colonization
What is a pioneer?
the first bacterial colonizers
What are two non-culturable bacteria?
1) treponema
2) mycobacterium leprae
What are the factors that we need to grow bacteria from a clinical specimen?
1) temperature
2) ph
3) gaseous requirements
4) minerals, trace elements, and vitamins
5) nitrogen and carbon sources
6) energy generation
What are five categories of bacteria by gaseous requirements?
1) obligate aerobes
2) microaerophiles
3) capnophiles
4) facultative anaerobes
5) obligate anaerobes
What is unique about obligate aerobes?
They NEED oxygen in order to survive
What is unique about microaerophiles?
They are inhibited by oxygen content, but will not be killed by increased oxygen
What is unique about capnophiles?
They grow best in hypercapnic conditions
What is unique about facultative anaerobes?
they can grow in all oxygen environments
What is unique about obligate anaerobes?
They cannot grow in any oxygen environment and exposure to oxygen kills the cells
What is dysbiosis?
Microbial imbalance in the “normal” microbiota of the body
Which group of bacteria is the most medically important?
facultative anaerobes
For what purpose is liquid media used to select bacteria?
It is used to culture bacteria that are from usually sterile sites and which there will generally be a monoculture.
For what purpose is solid media used to select bacteria?
It is used for all other populations of bacteria and dilution and separation of the bacteria of interest can be more easily obtained
Outline the blood culture technique.
Take a small amount of blood and inject it into multiple “blood bottles” over time intervals. You take it at different times and different places to minimize risk of contamination
What are the four phases of the bacterial growth curve?
1) lag
2) log
3) stationary
4) death
What is the lag phase?
Time where growth is minimal as the bacteria adapt to the host.
What is the log phase?
Time where bacteria grow the fastest. This is where signs and symptoms appear and you get tissue destruction
What is the stationary phase?
The growth of bacteria is offset by the their death facilitated by phagocytosis with antibodies
What is the death phase?
This is where bacteria are cleared from the system
At what point will a spore-forming bacteria sporulate?
At the inflection point between the log phase and the stationary phase
In which phase is a bacteria most susceptible to antibiotics?
The log phase because the bacteria are the most metabolically active
What are the five techniques in which to identify bacteria in the “clin lab”?
1) direct microscopic identification
2) antigen detection/serology
3) cell component detection - chemical/biochemical analysis
4) molecular diagnosis
5) culture
What are the two main microscopic morphologies?
1) cocci
2) rods (bacilli)
What is the Gram’s stain?
The Gram’s stain will test for the presence of a particular cell wall and separate bacteria into gram-positive and gram-negative
What are the steps of the Gram’s stain procedure?
1) dye with crystal violet
2) dye with iodide
3) decolorize with ethanol
4) counterstain with safranin
What are the six bacteria which can cause bacterial meningitis?
1) strep pneumoniae
2) strep agalactiae
3) listeria monocytogenes
4) neisseriea meningitidis
5) escherichia coli
6) haemophilus influenza
What is a primary cause of neonatal sepsis?
strep agalactiae
Which bacteria can cross the placental barrier?
listeria monocytogenes
What does the acid-fast stain stain for?
Mycobacterium
How do you know you have an acceptable sputum culture?
Presence of PMNs
What are the three groups of solid media?
1) general purpose
2) differential or partially selective
3) selective
What is chocolate agar?
Agar plated with RBCs that have become lysed
What is chocolate agar used for?
Fastidious bacteria such as H. influenzae which need particular conditions
What is sheep’s blood agar?
An agar-based plate with 5% sheep’s blood whose RBCs are plated intact
What is unique about blood agar plates?
Because the RBCs are intact, it can show specific strains of bacteria which are hemolytic
What is beta hemolysis?
This is complete hemolysis which goes through the full width of the plate
What is alpha hemolysis?
This is the discoloration of RBCs but incomplete lysis usually due to production of hydrogen peroxide
Why are differential plates also called partially selective plates?
Because they select for some strains by suppressing the growth of particular strains. And they dye others to separate strains by some type of quality (“differential”)
What is MacConkey Agar?
This inhibits the growth of Gram positive bacteria, while selecting for growth of lactose fermenters which will dye the media
What pathogens does MacConkey Agar select for?
Enteric pathogens
What is a selective media?
That which combines a solid media with both antifungals and certain antibiotics
What is a type of selective media?
Thayer-Martin agar
What does Thayer-Martin agar select for?
It is particular good at selecting for neisseria strains, as they are sometimes found in populations which have yeast or other mixed populations which might make them otherwise hard to isolate
What defines a bacterial colony?
it is a clonal population that has grown out of one bacteria
What are three ways to identify different colony morphologies?
1) form
2) elevation
3) margin
What do most antibiotics targets?
cell wall assembly
What functions have the cell wall replaced in the prokaryotic cell?
organelles
What is the major constituent of the cell wall?
peptidoglycan
What does the cell membrane of a prokaryote lack which cell membranes of eukaryotes have?
cholesterol
What is the only organelle that prokaryotes do have?
ribosome
Which two species of bacteria have no cell wall?
mycoplasma and ureaplasma
What do the plasma membranes of mycoplasma and ureaplasma have to make up for having no cell wall?
sterols
What are the different strategies which bacteria use to counteract their hosts?
1) adherence
2) anti-complementary
3) anti-phagocytic
4) mechanisms to subvert humoral immunity
5) mechanisms to subvert cellular immunity
6) production of exo- and endotoxins
Pili, fimbriae, and the bacterial capsule are all pathogenic strategies of?
adherence
The capsule of a protein serves which purposes for host-pathogen interaction?
1) adherence
2) anti-complement
3) anti-phagocytic
What are proteases particularly useful for in defense of a bacterium?
- degradation of complement proteins
- degradation of immunoglobulins
What are specific mechanisms which bacteria use to subvert humoral immunity?
Fc receptors, Ig proteases, endotoxins, LPS/LTA, cell wall
To what two antigens do we develop vaccines?
1) capsule
2) endotoxins
Where is the capsule located?
most externally located
What are two other names for the capsule?
1) slime
2) glycocalyx
What is a capsule typically made of?
polysaccharides
What is the exception to polysaccharide capsules?
Bacillus, which uses a proteinaceous capsule
What is capsule termed in gram negative bacteria?
K antigen
How is a capsule antigenically diverse?
It might have a lot of different types of antigenic capsules expressing different antigens or combinations of such
What are examples of virulence factors?
1) flagella
2) capsule
3) toxins
4) adhesive proteins
What are flagella termed in gram negative bacteria?
H antigen
How are flagella driven?
proton-motive force
What is a flagellum composed of?
helically arranged flagellin
What was the original distinction between those bacteria which had fimbriae and those which had pili?
Gram positive bacteria had fimbriae. Gram negative bacteria had pili.
What is it termed when a structure can be “turned” on and off?
phase variation
Flagella, fimbriae, and pili are all examples of what, in terms of immunity?
MAMPs
How do pili exert tropism for a particular tissue?
act as lectins in that they bind only to specified sugar moieties
What is the structure of the bacterial cell wall?
NAM and NAG disaccharide backbone with tetrapeptide cross-linkages
What are Gram-negative bacteria lacking in their peptidoglycan?
cross linkages between tetrapeptides
From which sugar does the tetrapeptide come off of in peptidoglycan?
N-acetylmuramic acid
What amino acid does the tetrapeptide begin and end with?
alanine
What is the third amino acid in the tetrapeptide sequence?
always a di-amino acid
What is the name of the antigen that is recognized by PRRs in peptidoglycan?
muramyl dipeptide
What do mycobacteria add to their cell wall?
layers of mycolic acid
What is the difference between lipoteichoic and teichoic acid?
Teichoic acid is covalently linked to cell wall.
To what is lipoteichoic acid tethered?
Plasma membrane due to a lipid chain
What are the purposes of LTA/TA?
capturing cations and maybe adhesion
Why is LTA/TA like the LPS in Gram - bacteria?
it is highly pro-inflammatory
What immune responses does LPS elicit?
-polyclonal B cell activation
How does LPS elicit an immune response?
acts as a potent MAMP and is recognized by CD14 and TL4
What is LPS composed of?
1) lipid A
2) core polysaccharide
3) O polysaccharide
What is O polysaccharide also called?
somatic antigen
What function does the outer membrane of Gram-negative bacteria function as?
1) effective barrier
2) molecular sieve
3) attachment site for adhesion
4) pathogenic determinants
What is the layer which contains peptidoglycan called in Gram negative bacteria?
periplasmic space
What are the outer membrane components of E.coli?
LPS and porins
What is the periplasmic space used as?
1) area of import/export
2) area for hydrolytic enzymes
What is most extrachromosomal DNA in a bacterium?
plasmids
What do plasmid genes confer?
selective advantage
What type of proteins are used in the transeptal processes in binary fission?
cytoskeletal proteins
What can be in inclusion granules?
polyphosphate, glycogen/starch, and lipid
What are the only medically relevant bacteria which produce spores?
Gram-positive rods (Clostridium and Bacillus)
What is the difference between Clostridium and Bacillus?
Clostridium is gram-negative whereas Bacillus is gram-positive
At what point do these species usually produce spores?
In late log phase. usually when there is a limitation of the amino acid alanine
