2 Flashcards
catalyst
substance that helps speed up a chemical reaction and are not used up or changed during a reaction
anabolism
refers to endergonic pathways involved in biosynthesis, converting simpler molecules into complex molecules fueled by the use of cellular energy
catabolism
refers to exergonic pathways that break down complex molecules into simpler ones
enzyme function
serve as catalysts that lower the activation energy of a reaction
enzyme made of
proteins (amino acids)
active site
where substrates bond to the enzyme
induced fit
enzyme changes its structure slightly to find the best fit between the substrate and active site
slight temp increase affect on enzyme
generally increases reaction rate/enzymes catalyzed
affect on enzymes of increasing temp outside normal range
affects chemical bonds within the active site making them less suitable to bind substrates
high temp affect on enzymes
cause enzymes to denature, losing 3D structure and function. breaks bonds that fold the protein
denaturation
implies loss of secondary, tertiary, or quaternary structure and function without loss of primary structure
pH affect on enzymes
extreme pH values can cause enzymes to denature. active site amino acids have their own acidic/basic properties and are sensitive to changes in pH
substrate concentration affect on enzyme activity
activity is increased at higher concentrations or substrate until it reaches a saturation point at which the enzyme can bind no additional substrate
cofactor and coenzyme function
enzymes do not work optimally, or at all, unless bound to coenzymes or cofactors that alter the enzyme’s active site to bind substrates
cofactors
inorganic ions that help stabilize enzymatic conformation and function
coenzymes
organic helper molecules, usually vitamins, that are required for enzymatic action and are reusable
apoenzyme
enzyme lacking necessary cofactor/enzyme that is inactive
holoenzyme
enzyme with necessary cofactor/enzyme and is active
competitive inhibitor
structurally similar enough to substrate that it can compete for the enzyme’s active site by blocking the substrate from binding
competitive inhibitor concentration
in order to be effective, inhibitor concentration needs to be approx. equal to substrate concentration
noncompetitive (allosteric) inhibitor
binds to enzyme at site other than active site and blocks substrate binding by altering enzyme’s active site
allosteric site
any site on the enzyme other than the active site
noncompetitive inhibitor concentration
one noncompetitive inhibitor is needed per enzyme. equal to the amount of enzymes
allosteric activators
bind to allosteric site, cause change to active site that increases substrate affinity
negative feedback inhibition
use of pathway product to regulate its own production, product acts as an allosteric inhibitor for the enzyme that produces it
exoenzyme
extra cellular enzymes that are produced by microbes
exoenzyme function
to acquire nutrients, break down bigger molecules for transport into the cell, or evade death in order to reproduce
classes of exoenzymes
glycohydrolases, nucleases, phospholipases, proteases, amylase, catalase, lipase, beta galactosidase
glycohydrolase function
degrade hyaluronic acid that cement cells together to promote spreading through tissues
nuclease function
degrade DNA released by dying cells that can trap the bacteria, thus promoting spread
phospholipase function
degrade phospholipid bilayer of host cells, causing lysis, and degrade membrane of phagosomes to enable escape into cytoplasm
protease function
degrade collagen in connective tissue to promote spread
amylase function
degrades carbohydrates
catalase function
protects oxygen respiring organisms from toxic hydrogen peroxide by breaking it down into water and oxygen
lipase function
degrades lipids
beta galactosidase function
breaks down lactose into its monosaccharides, glucose and galactose
lactose monomers
glucose and galactose
sucrose monomers
glucose and fructose
toxins
biological poisons that assist a pathogen’s ability to invade and cause damage to tissues
endotoxin example
lipid A part of lipopolysaccharide
exotoxin example
botulinum toxin (cause botulism)
endotoxin source
gram negative bacteria
endotoxin compostition
lipid A component of lipopolysaccharide
endotoxin’s effect on host
general systemic symptoms of inflammation and fever
endotoxin’s heat stability
heat stable
endotoxin’s LD50
high
exotoxin source
primarily gram positive, some gram negative
exotoxin composition
protein
exotoxin’s effect on host
specific damage to cells dependent upon receptor-mediated targeting of cells and specific mechanisms of action
exotoxin’s heat stability
most are heat liable, some are heat stable
exotoxin’s LD50
low
structural genes
encode for products that serve as cellular structures or enzymes
regulatory genes
encode products that regulate gene expression
gene regulation involves three factors:
complex web of interactions among signals from the cell’s environment, signaling molecules within the cell, and the cell’s DNA
operon
a genome block in prokaryotes in which structural proteins with related functions are encoded together
promoter
controls the transcription of a single operon. a sequence of DNA to which proteins bind to initiate transcription
regulatory region
includes promoter and region surrounding promoter (operator), to which transcription factors can bind
transcription factors function
influence the binding of RNA polymerase to the promoter
types of transcription factors (regulatory molecules)
repressors, activator, reducer
operator
where transcription factors bind
operator location
between RNA polymerase binding site of promoter and transcriptional start site of first structural gene
repressor
transcription factor that suppresses transcription of a gene in response to an external stimulus by binding to the operator
activator
transcription factor that increase the transcription of a gene in response to an external stimulus by facilitating RNA polymerase binding to the promoter
inducer
transcription factor that either activates or represses transcription by interacting with a repressor or activator
constitutively expressed operons
transcribed and translated continuously (unregulated) to provide the cell with constant intermediate levels of the protein products
gene regulation
process used to control the timing, location, and amount genes are expressed
gene expression
process by which genes are transcribed and translated, made by the cell into proteins. synthesis of a specific protein with a sequence of amino acids that is encoded in the gene.
repressible operons contain genes that
encode for enzymes required for a biosynthetic pathway
repressible operon is expressed when
the product of the pathway is required by the cell
repressible operon is repressed when
product of pathway is not needed by the cell
inducible operons contain genes that
encode for enzymes in a pathway involved in metabolism of a specific substrate
inducible operons are expressed when
the substrate is present in the cell
inducible operons are repressed when
substrate is not found in cell
repressible operons are regulated by
the absence or presence of the product of the pathway
inducible operons are regulated by
the absence or presence of the substrate
trp operon: when trp is not present in the cell…
repressor itself does not bind to the operator, the operon is active and tryptophan is synthesized
trp operon: when trp is in the cell…
2 trp molecules bind to the repressor which changes its shape, allowing it to bind to the trp operator, blocking RNA polymerase from transcribing the structural genes, stopping expression of the operon
lac operon: when lactose is absent in the cell…
lac repressor is bound to operator, physically preventing RNA polymerase from transcribing structural genes
lac operon: when lactose is present in the cell…
allolactose serves as inducer molecule, binding to repressor, changing its shape so that it is no longer able to bind to the operator
First step in expressing lac operon
enzyme IIA becomes phosphorylated when glucose levels drop
Second step in expressing lac operon
phosphorylated enzyme IIA activates adenylyl cyclase, an enzyme that converts some of the remaining ATP to cyclic AMP (cAMP), and cAMP levels start to rise in the cell
cAMP
a cyclic derivative of AMP and important signaling molecule involved in energy metabolism in E. coli
third step in expressing lac operon
accumulating cAMP binds to catabolite activator protein (CAP) aka cAMP receptor protein (CRP) on promoter region of lac operon which increases the binding ability of RNA polymerase to the promoter region to initiate transcription of the structural genes
glucose: +, CAP binds: -, lactose: -, repressor: +
transcription:
no
glucose: +, CAP binds: -, lactose: +, repressor: -
transcription:
some
glucose: -, CAP binds: +, lactose: -, repressor: +
transcription:
no
glucose: -, CAP binds: +, lactose: +, repressor: -
transcription:
yes
regulon
a group of operons controlled simultaneously
global response in prokaryotes
there are several higher levels of gene regulation that have the ability to control transcriptions of many related operons simultaneously
alarmones
small intracellular nucleotide derivatives that are produced during impending stress
alarmones function
change which genes are expressed and stimulate the expression of specific stress response genes
o factor function
subunit of bacterial RNA polymerase confers specificity as to which promoters should be transcribed
altering o factor
cell senses specific environmental conditions, may respond by changing which o factor it expresses, degrading old one and producing new one to transcribe the operons whose products will be useful under the new environmental condition
example of alternate o factor
bacteria in the genera Bacillus and Clostridium, a group of o factors control the expression of many genes that are need for sporulation in response to sporulation-stimulating signals
attenuation
controls completion of transcription and translation. secondary stem-loop structure formed within 5’ end of mRNA being transcribed determine if transcription to complete the synthesis of this mRNA will occur and if this mRNA will be used for translation
attenuation example
controls expression of trp operon in E.coli. when terminator stem-loop forms, transcription terminates. when antiterminator stem-loop forms, it prevents the formation of the terminator stem-loop, so RNA polymerase can transcribe the structural genes
riboswitch: what is it?
a small region of noncoding RNA found within the 5’ end of some prokaryotic RNA molecules
riboswitch function
may bind to small intracellular molecule to stabilize certain secondary structures of the mRNA molecule. This determines which stem-loop forms, thus influencing the completion of mRNA synthesis and protein synthesis
enhancers
regions of DNA where proteins can bind through DNA looping facilitated between the enhancer and promoter. eukaryotic transcription influencer
epigenetic regulation
in eukaryotes, DNA molecules or associated histones can be chemically modified in such a way to influence transcription
methylation of cytosine nucleotides (epigenetic regulation)
influences use of that DNA for transcription, with DNA methylation commonly correlating to lowered levels of gene expression
acetylation and deacetylation (epigenetic regulation)
chemically modify histones, influencing the packaging state of DNA and thus affecting the availability of loosely wound DNA for transcription
epigenetic change heritability
chemical modifications can sometimes be maintained through multiple rounds of cell division, making at least some of the epigenetic changes heritable
extracellular matrix (biofilm)
where clusters of microbes are imbedded: interspersed w/ open water channels, consists of extracellular polymeric structures secreted by the organisms, makes up 50-90% of biofilm’s mass
extracellular polymeric structure (EPS) composition
hydrated gel composed of mainly polysaccharides, contains other macromolecules like proteins, nucleic acids, and lipids
extracellular polymeric structure function
key role in maintaining integrity and function of biofilm. channels allow movement of nutrients, wastes, gases. keeps cell hydrated, prevents desiccation. shelters organisms in the biofilm from predation by other microbes or cells
planktonic cells
free-floating microbial cells that live in an aquatic environment
sessile
what planktonic cells are called when they are attached to a substrate (surface)
First stage in biofilm formation
attachment of planktonic cells to a surface coated w/ a conditioning film of organic material (happens in seconds). this is reversible
second stage in biofilm formation
first colonizers become irreversibly attached (happens in seconds)
third stage in biofilm formation
growth and cellular division occur (happens in hours, days)
fourth stage in biofilm formation
production of EPS and formation of water channels (happens in hours, days)
fifth stage in biofilm formation
attachment of secondary secondary colonizers and dispersion of microbes to new sites (days, months)
dispersal
last stage (fifth) of biofilm life cycle, cells on exterior of biofilm revert to a planktonic lifestyle, sloughing off the mature biofilm to colonize new sites
structures required for establishment of mature biofilm
appendages such as fimbriae, pili, and flagella
metabolic collaborations in biofilms
when the waste product of one organism becomes the nutrient of another
metabolic collaboration example
aerobic microbes consume oxygen, creating anaerobic regions that promote the growth of anaerobes
quorum sensing
the mechanism by which cells in a biofilm coordinate their activities in response to environmental stimuli
quorum sensing function
can occur between different species of microbes and enables microbes to detect their cell density through the release of small molecules called autoinducers
quorum
when cell population reaches a critical threshold
autoinducer function
when quorum is reached, they initiate a cascade of reactions that activate genes associated w/ cellular functions that are only beneficial when a population reaches a critical density
gram negative signaling molecules
communicate using N-acylated homoserine lactones
gram positive signaling molecules
communicate using small peptides
first step in quorum sensing
consists of the binding of the autoinducer to its specific receptor only when a threshold concentration of signaling molecules is reached
second step in quorum sensing
a cascade of signaling events lead to changes in gene expression
third step in quorum sensing
activation of biological responses linked to quorum sensing, notably an increase in the production of signaling molecules themselves, hence the term autoinducer
reasons why biofilms exhibit a higher resistance to antibiotics
cells deep within biofilms are metabolically inactive, EPS may slow diffusion of antibiotics, phenotypic changes like increased production of efflux pumps, biofilms provide ideal environment for exchange of extrachromosomal DNA
saliva function
constantly bathes teeth and gums w/ buffers and aids in maintaining a neutral pH and washes away food particles that may get stuck in the teeth
saliva composition
contains buffers that neutralize acids produced during fermentation of sugars in the mouth
dental caries
cavities, are microbial lesions that cause damage to the teeth
plaque
a biofilm of microbes in the mouth that are attracted to the carbohydrates in the mouth
Streptococcus mutans
carcinogenic species in plaque, cause of dental caries, breaks down sucrose into its monomers
glucose, metabolized by S. mutans, is made into
dextran or glucan, which are part of the extracellular matrix of a biofilm
fructose, metabolized by S. mutans, is made into
fermented, producing organic acids such as lactic acid
lactic acid effect on teeth
dissolve minerals of tooth, including the enamel
tartar (dental calculus)
when plaque biofilm becomes thick and calcifies
fluoride function
protects tooth from acidity, is bacteriostatic, slowing enamel degradation
antiseptic mouthwash function
contain phenolics that are stable and persist on surfaces, denature proteins, and disrupt membranes
periodontal disease
result of infections that lead to inflammation and tissue damage in structures surrounding the teeth
gingivitis
inflammation of the gums that can lead to irritation and bleeding
gingivitis cause
when plaque accumulates on teeth, bacteria get trapped underneath and colonize, their products cause inflammation and gum damage
bacterial products that cause periodontal disease
lipopolysaccharide, proteases, lipoteichoic acids, and others
bacteria that cause periodontal disease
Porphyromonas, Streptococcus, and Actinomyces
periodontitis
chronic gingivitis, the gums recede and expose parts of tooth below the crown, bacteria can grow and cause cavities
severe periodontitis
erosion of cementum from collagenase produced by bacteria, leads to movement of teeth or loss of teeth caused by degradation of the ligament
cementum
part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament, which hold the teeth in place
trench mouth cause
when certain bacteria such as Prevotella intermedia, Fusobacterium spp., and Treponema vicentii are involved and periodontal disease progresses
trench mouth symptoms
severe periodontitis characterized by erosion of the gums, ulcers, substantial pain when chewing, and halitosis
characteristics of S. mutans that cause dental caries
the fermentation of fructose producing lactic acid and the that it can make a biofilm with the production of surface adhesion P1, which binds to salivary agglutinin on the surface of the tooth
DNA function
genetic material responsible for inheritance and directs and regulates the construction of proteins necessary for cell growth and reproduction
genome
contains full complement of DNA within a cell
transcription
gene composed of DNA is read to produce an RNA molecule called mRNA
translation
process where mRNA provides information for the ribosome to catalyze protein synthesis
transcription and translation are referred to as
gene expression
central dogma
states that DNA organized into genes specifies the sequences of mRNA which, in turn, specifies the amino acid sequence of the proteins
genotype
the full collection of genes a cell contains
phenotype
set of cell’s observable characteristics that result from the genes the cell is expressing at a given time under a certain environmental condition
organization of genetic material
vast majority of organism’s genome is organized into the cell’s chromosome(s)
diploid
contains two copies of each chromosome
chromosome
discrete DNA structure within cells that control cellular activity, contains several thousand genes
haploid
contains one copy of each chromosome
gene
segments of DNA molecules that contain the instructional code necessary for synthesizing various proteins, enzymes, or stable RNA molecules
supercoiling
refers to the process by which DNA is twisted to fit inside the cell
overwound DNA
more than one turn per 10 base pairs
underwound DNA
less than one turn of the helix per 10 base pairs
topoisomerases
enzymes that help maintain the structure of supercoiled chromosomes, preventing the overwinding of DNA during DNA replication
histones
DNA binding proteins that perform various levels of DNA wrapping and attachment to scaffolding proteins
chromatin
combination of DNA with attached proteins
epigenetics
influence of environmental factors on DNA packing
DNA gyrase
type of topoisomerase, found in bacteria and some archaea, that helps prevent the overwinding of DNA
organization of prokaryotic chromosomes
organized in several supercoiled domains
noncoding DNA
regions of DNA that do not encode proteins or stable RNA products
noncoding DNA location
commonly found in areas prior to the start of coding sequences of genes, as well as intergenic regions
intergenic regions
DNA sequences located between genes
noncoding DNA function
contribute to the regulation of transcription and translation through production of small noncoding RNA molecules, DNA packaging, and chromosomal stability
extrachromosomal DNA
cell’s additional molecules of DNA outside the chromosome that are apart of its genome
eukaryotic extrachromosomal DNA
mitochondria and chloroplasts
prokaryotic extrachromosomal DNA
plasmids
vertical gene transfer
transmission of genetic information from generation to generation
genetic diversity in meiosis
independent assortment and crossing over
genetic diversity in asexual organisms
mutations and horizontal gene transfer
horizontal gene transfer
introduction of genetic material from on organism to another organism within the same generation
HGT mechanisms
transformation, transduction, conjugation
transformation
competent prokaryotes take up naked DNA from its environment that comes from lysed cells and recombine it in their chromosome or it remains in cytoplasm as plasmid
naturally competent cell
cell naturally actively binds to environmental DNA, transport it across their cell envelops into their cytoplasm, making it single stranded
artificial competence
cell reaches competence by artificial mean, use of chemicals to weaken membrane and increases permeability to make taking up extracellular DNA easier
transduction
bacteriophages move short pieces of DNA from one bacterium to another
generalized transduction
any piece of chromosomal DNA may be transferred to a new host cell by accidental packing of chromosomal DNA into a phage head during phage assembly
specialized transduction
results from imprecise excision of a lysogenic prophage from the bacterial chromosome such that it carries with it a piece of the bacterial chromosome from either side of the phage’s integration site to a new host cell
bacteria that gain pathogenic gene from transduction
Corynebacterium diphtheriae and Clostridium botulinum
conjugation
DNA is directly transferred from one prokaryote to another by mean of a conjugation pilus, which brings the organisms in contact with each other
F plasmid
fertility factor. genes encoding the ability to conjugate, to form an F pilus, and those involved in rolling circle replication of the plasmid
F pilus
the conjugation pilus
F+ cells
donor cells, contain F plasmid and are able to form an F pilus
F- cells
recipient cells, do not contain an F plasmid and cannot form an F pilus
first step in conjugation of the F plasmid
pilus of donor cell attaches to the recipient cell. pilus contracts, drawing cells together to make contact with one another
second step in conjugation of the F plasmid
one strand of F plasmid DNA transfers from donor cell to recipient cell
third step in conjugation of the F plasmid
donor synthesizes complementary strand to restore plasmid. recipient cell synthesizes complementary strand to become F+ cell with pilus
Hfr cell
when plasmid DNA integrates into bacterial chromosome through recombination
Hfr stands for
high frequency of recombination
F’ plasmid
F plasmid is imprecisely excised from chromosome and carries with it some chromosomal DNA adjacent to the integration site
Hfr conjugation
Hfr cell may treat the entire chromosome as one large plasmid and attempt to transfer whole chromosome to recipient cell. it is unusual for whole chromosome to be transferred because it takes a long time, it is only partially transfer. the recipient cell will only become a F+ cell if the whole chromosome is transferred.
R plasmid
contain genes encoding proteins that make a bacterial cell resistant to particular antibiotics. can be transferred to different species and commonly contain genes conferring resistance to multiple antibiotics
R plasmid functions
contain genes encoding for antibiotic resistance and contain genes that control conjugation and transfer of the plasmid
transposons
molecules of DNA that include special inverted repeat sequences at their ends and a gene encoding for the enzyme transposase
transposition
process by which transposons independently excise their entire sequence, and may carry additional genes, from one location of a DNA molecule and integrate into the DNA elsewhere
nonreplicative transposons
transposons that move in a “cut and paste” fashion,
replicative transposons
transposons that move in a “copy and paste” fashion, retaining their location in the DNA while making a copy to be inserted elsewhere
transposon range
within a DNA molecule, from one DNA molecule to another, from chromosome to plasmid, from one cell to another
bacteriophage
non-living infectious agents (viruses) that infect bacteria
bacteriophage host range determined by
host range is bacteria and is determined by surface receptors on the target’s exterior
bacteriophage composition
use DNA or RNA as genome enclosed in a capsid made of protein
productive phage
a phage that goes through a lytic cycle in which it is producing more bacteriophages
virulent phages
typically lead to death of the cell through cell lysis
latent phage
phage that is in a lysogenic cycle where it is not actively producing more bacteriophages
temperature phage
can become part of the host chromosome and are replicated with the cell genome until such a time as they are induced to make progeny viruses
progeny viruses
newly assembled virses
lytic cycle
virulent phage takes over the cell, produces new phages, and destroys the cell
first stage in lytic cycle
attachment: phage interacts with specific bacterial surface receptors, attaching to the cell
Second stage in lytic cycle
penetration: tail sheath contract and act like a hypodermic needle to inject viral genome through cell wall and membrane, enzymes degrade periplasmic peptidoglycan layer of cell wall
third stage in lytic cycle
transcription: early viral genes are transcribed, synthesizing endonucleases to degrade bacterial chromosome
fourth stage in lytic cycle
Replication of viral DNA and viral proteins (biosynthesis): phage hijacks host cell to replicate, transcribe, and translate necessary components for assembly of new viruses
fifth stage in lytic cycle
Assembly (maturation): new virions are created by assembling parts made in previous stage, bacterial cell wall is disrupted by phage proteins holin or lysozyme
six stage in lytic cycle
release (lysis): viruses burst out of cell in a process called lysis, destroying the cell. viruses are freed into environment to infect new cells
burst size
number of bacteriophages that are present in the bacterial cell when it bursts and releases the bacteriophages
lysogenic cycle
temperate phage genome integrates into bacterial chromosome instead of killing the cell
prophage
the integrated phage genome
lysogen
a bacterial host with a prophage
lysogeny
process by which a bacterium is infected with a temperate phage
lysogenic conversion
when the presence of a phage alters the phenotype of the host
first stage in lysogenic cycle
attachment: phage interacts with specific bacterial surface receptors, attaching to the cell
second stage in lysogenic cycle
penetration: tail sheath contract and act like a hypodermic needle to inject viral genome through cell wall and membrane, enzymes degrade periplasmic peptidoglycan layer of cell wall
third stage in lysogenic cycle
integration: phage genome integrates into bacterial chromosome and becomes part of the host
fourth stage in lysogenic cycle
binary fission: bacterium replicates its chromosome, replicates phage’s DNA and passes it to daughter cells during reproduction
factor that causes latent phage to enter productive cycle
some sort of environmental pressure influencing the phage to excise out of the host’s DNA
induction
excision of viral genome from host chromosome and proceeds through a lytic cycle
intracellular targeting toxins
A-B exotoxins
A-B toxins acquired by
Bacteriophage: lysogenic conversion
A-B toxins components
A is for active enzyme B is for binding receptor
B component function
responsible for cellular specificity of the toxin and mediates the initial attachment of the toxin to specific cell surface receptors
A component function
after being brought into cell by endocytosis, A component enters the cell’s cytoplasm and interferes with the specific internal cellular function that it targets
examples of A-B toxin
diphtheria, cholera, botulinum, and tetanus toxins that are all acquired through lysogenic conversion by a bacteriophage
direct cell count
refers to counting the cells in a liquid culture or colonies on a plate. direct way of estimating how many organisms are present in a sample
direct microscopic cell count
involves transferring a known volume of culture on a calibrated slide and counting the cells under a light microscope
Petroff-Hausser chamber
calibrated slide used for direct microscopic cell count
does counting chamber work on dilute or concentrated cultures?
more concentrated cultures, there might not be enough cells to count in dilute cultures
does counting chamber count distinguish between live and dead cells?
it does not give an accurate number of live cells in a culture unless stained with fluorescence
electronic counting device
counts changes in electrical resistance in a saline solution (number of cells) does not count live cells
viable plate count
a count of viable or live cells and expressed as colony-forming units per milliliter
Colony-forming units range for plate count
microbiologists typically count plates with 30-300 colonies
plaque forming units
if bacteriophage are counted, the bacteriophage plaques formed on the lawn of appropriate bacteria
serial dilution
dilutes sample to obtain plates with 30-300 CFU and the process involves several dilutions in multiples of 10
pour plate method
bacterial sample mixed w/ warm agar, sample poured onto sterile plate, sample swirled to mix and allowed to solidify, plate incubated until bacterial colonies grow
spread plate method
sample (0.1mL) poured onto solid medium, sample spread evenly over surface, plate incubated until bacterial colonies grow on the surface of the medium
membrane filtration technique
concentrates a dilute sample by running it through a membrane that traps the microorganisms to be transferred and grown on plate
most probable number (MPN) method function
a statistical procedure for estimating the number of viable microorganisms in a sample. tests dilute samples
MPN procedure
tested by inoculating 5 tubes w/ 10mL of sample, 5 tubes w/ 1mL of sample, and 5 tubes w/ 0.1mL of sample
indirect detection of cell density function
most commonly used to estimate and compare cell densities in a culture
methods of indirect cell count
measurement of turbidity, measure of dry weight, measure cell activity by following production of metabolic products or disappearance of reactants
pure colony
results when a single bacterial cell not touching any other cells multiplies
techniques used to separate pure culture
pour plate, streak plate, spread plate
pour plate technique
adding loop of broth culture to a tube of melted agar and then the liquid agar is poured onto sterile dish. cells are suspended in media and spread out as agar is poured to grow individual colonies
streak plate technique
involves transferring loop of broth culture to surface of a solid agar medium in dish. single loop of full agar is then diluted over surface of plate
point mutation
change one base in an amino acid sequence for another. includes nonsense, silence, and substitution (missense) mutations
nonsense mutation
point mutation that results in a stop codon in the wrong place
silent mutation
point mutation that causes no change to the amino acid
substitution (missense) mutation
point mutation that one amino acid is exchanged for another
frameshift mutation
deletes or inserts a base, causing changes to multiple codons and amino acids
homologous recombination
a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA
Neisseria gonorrhoeae reservoir
humans
Neisseria gonorrhoeae pathogenesis
pili and outer membrane proteins allow bacterium to attach to a variety of cell receptors, pili help prevent phagocytosis by neutrophils and increases adherence to phagocyte
Neisseria gonorrhoeae target
epithelial cell receptors: urethra, cervix, pharynx, etc.
N. gonorrhoeae action
produces IgA protease which destroys IgA antibodies on mucosal cells which normally blocks cell receptor sites from the bacterium
N. gonorrhoeae enters epithelial cell by
endocytosis
N. gonorrhoeae killed by
macrophages but persists in neutrophils
N. gonorrhoeae causes
microabscesses and epithelial cell death
N. gonorrhoeae evades antibodies by
regularly shedding its pili and produces new pili w/ different protein composition so no antibody is effective
Modes of resistance for N. gonorrhoeae
plasmid resident resistance (enzymatic modification of drug), chromosome resident resistance (modification of microbial target)
Plasmid resident resistance (N. gonorrhoeae)
produces penicillinase, genes from R plasmid, that chemically alters penicillin, making it ineffective.
PPNG stands for
penicillinase producing Neisseria gonorrhoeae
Chromosome resident resistance (N. gonorrhoeae)
produce altered forms of penicillin binding protein 2 (PBP2) that have decreased affinity for penicillin which prevents penicillin from binding to peptidoglycan synthesis enzymes
CMRNG stands for
chromosome mediated resistant Neisseria gonorrhoeae
Corynebacterium diphtheriae mode of transmission
highly contagious: droplets inhaled or contact w/ contaminated particles
C. diphtheriae reservoir
humans
C. diphtheriae causes symptoms in
upper respiratory tract, infects nasal tissues, larynx, and skin (ulcers)
C. diphtheriae gets pathogenicity from
corynephage, bacteriophage which causes lysogenic conversion
C. diphtheriae pathogen
A-B toxin
Symptoms if C. diphtheriae
sore throat, fever, pseudomembrane
lipase positive test
clear zone around bacterial growth on tributyrin
catalase positive test
bubbling on bacterial growth on nutrient agar when hydrogen peroxide is added
amylase positive test
clear zone around bacterial growth on starch agar
beta galactosidase positive test
bright yellow solution with ONPG discs
