Bacterial Structure and Function Flashcards
external structures on bacteria
capsules, flagella, and pili
capsules
layers of organic polymers attached to the exterior of bacteria that for hydrophilic gels surrounding the cells of some bacteria
usually polysaccharides except in Bacillus anthracis, which ahs a poly-D-glutamic acid capsule
capsules prevent dessiccation in the environment
crucial role in the virulence of certain pathogens
prevents phagocytosis by preventing complement activation on the cell surface
human pathogens in which a capsule is considered to be an important virulence determinant
- Streptococcus pneumoniae*
- Neisseria meningitidis*
- Haemophilus influenzae*
- Klebsiella pneumoniae*
- Streptococcus agalactiae*
some E. Coli
K antigen
capsules of certain bacteria used for serological typing
what two types of disease do encapsulated bacteria primarily cause?
meningitis and bacteremia in individuals without functional spleens
flagella
long, helical filaments
hollow and rigid
composed of a single protein, flagellin
flagellin passes through the hollow filament and self-assembles at the tipck
flexible hook connects the flagellum to a basal body in the bacterial envelope
basal body is the motor
responsible for bacterial motility
H antigens
flagella that can be used to serologically distinguish and classify certain bacteria
flagella and movement
rotate up to 40-60 revolutions/second
energy is from the flow of protins into the cell
as fast as 100 cell lengths/second
chemotaxis
the ability to move toward attractants and away form repellents
toll-like receptor-5 (TLR-5)
recognize the presence of flagella through binding
leads to an inflammatory response
pili (fimbriae)
long, thin filamentous structures distributed over the surface of some bacteria
made up of pilin and sometimes minor proteins
mediate adherence, bind receptors that consists of sugar residues on glycolipids or glycoproteins int he host cell membrane
twitching motility
biofilm formation
phase variation
the ability to turn production of particular surface proteins, such as flagellin or pili, on and off
leads to antigenic variation because the changing of these surface proteins deceives the host immune system
bacterial cytoplasm
site of synthetic reactions, many ribosomes
mostly proteins and RNA
bacterial ribosomes
70S ribonucleoproteins tructures composed of 50S and 30S subunits
the 50S subunit has 2 RNA molecules and 34 proteins
the 30S subunit had one RNA molecule and 21 proteins
bacterial chromosome
a single circular molecule, known as the nucleoid
E. Coli chromosome is 1 mm long with 4.6 megabases
chromosome is very tightly packed within the bacterium
contains circular molecules called palsmids, which often contain drug resistant genes
chromosome replicate by DNA polymerase, starting at the oriC
daughter chromosomes are initially linked but are separated by DNA gyrase
transcription and translation
genes on the chromosome are transcribed by RNA polymerase
genes can be organized into operons
first amino acid is a formyl-methionine
multiple ribosomes may translate a single mRNA simultaneously
translation and transcription are linked
identification of nonculturable bacteria
16S rRNA PCR amplification
broad-range PCR primers
sequencing the amplified region
infer the phylogeny of the unknown organism
ex. bacillary angiomatosis (Bartonella henselae)
ex. Whipple’s disease (Tropheryma whippelii)
WQhipple’s DIsease
fever
malabsorption
weight loss
arthralgias
rarely heart or CNS involvement
can’t culture bacteria that causes this disease
bacterial spores
highly resistant, metabolically inactive dormant forms of bacteria
developed within the vegetative cells
promote survival under environmentally unfavorable conditions
resistant to heat, UV irradiation, drying, and chemical agents
favorable conditions -> spores germinate and form vegetative cells
only some gram-positive bacilli (Clostridium and Bacillus)
endospore
some Gram-positive bacilli are able to form these tructures that deveop within vegetative (dividing) cells
O-antigens
O-side chains
bacterial metabolism
10 to 100 times faster than the cells in our bodies
must obtain nutrients from the environment such as iron
developed ways of stealing it from human hosts
siderophores
low molecular weight molecules secreted by bacterial cells that removes iron from host molecules and allow bacterial cells to take it up
other bacteria produce surface receptors to which lactoferrin and transferrin can bind, donating its iron
fermentation
organic compounds serve as electron donor sand acceptors
energy is generated by substrate-level phosphorylation
ineffiicent generation of energy
does not require oxygen
respiration
the electron acceptor is O2 for aerobic respiration or nitrate (or some othe rinorganic compound) for anaerobic respiration
electrons are transported through carriers
produces relatively large amounts of energy
respiration - ETC
sequence of carrier molecules that are capable of oxidation and reduction
electrons pass through the chain
energy is released
drives chemiosmosis
pushed to final electron acceptor
results in the majority of ATP production
oxidase test
measures the ability of bacteria to oxidize and therefore change the color of N,N-dimethyl-p-phenylenediamine
bacteria that contain cytochrome c are “oxidase positive”
chemiosmosis
electron transport
protons pumped from the cytosol to the external side of the cytoplasmic membrane
protonmotive force generates energy gradient to make ATP from ADP
powers flagellar rotation and uptake of some small molecules into the cell
metabolism as an identification tool
oxidase test
identification based on the sugars and other molecules they can use as a fuel source
bacterial utilization of oxygen
different bacteria may use oxygen as part of energy generation and respiration
some are unable to use oxygen and are killed by its deleterious effects
two toxic products are hydrogen peroxide and superoxid anion
superoxide dismutase
degrades superoxide
2O2- + 2H+ -> H2O2 + O2
catalase
degrades hydrogen peroxide into water and oxygen
H2O2 + H2O2 -> 2H2O + O2
aerobe (strict aerobe)
grows with oxygen
does not grow without oxygen
contains superoxide dismutase and catalase
cannot ferment
anaerobe (strict anaerobe)
doies not grow with oxygen
grows without oxygen
does not contain superoxide dismutase and catalase
killed by oxygen, ferments in the absence of oxygen
facultative
grows with oxygen
grows without oxygen
contains superoxide dismutase and catalase
respires with oxygen
ferments in the absence of oxygen
indifferent (aerotolerant anaerobe)
grows with oxygen
grows without oxygen
contains superoxide dismutase and catalase
ferments in the presence or absence of oxygen
microaerophilic bacteria
bacteria that gorw best in an environment with less oxygen than is normally found in air
identifying bacterial pathogens in the clinical microbiology laboratory
direct stain of clinical speciments
growth of bacteria from clinical specimens
antibody tests
PCR
bacterial growth
bacteria divide by binary fission
offspring identical to parent
may divide every 20 minutes
media used in the clinical microbiology laboratory
enrichment media
selective media
differential media
enrichment media
contains ingredients that encourage the growth of certain organisms
selective media
contains one or more components that inhibit the growth of certain groups of organisms
differential media
allows colonies of certain organisms to be distinguished from those of other organisms
ex. sheep blood in a medium -> hemolytic vs. nonhemolytic colonies
sheep blood cell agar
commonly used agar
complex media
supports the groth of many organisms
MacConkey agar
selective agar for enteric Gram-negative rods
differnetial media: lactose fermentation
obligate intracellular bacteria
bacteria that cna grow only inside eukaryotic cells
Rickettsia and Chlamydia - two important groups
these bacteria must grown on monolayers of itssu culture cells rather than agar plates
bacterial growth phases
lag phase
exponential (or log) phase
stationary phase
lag phase
bacteria adapt to new environment
only a very small increase in bacterial numbers is noted during this time
exponential (or log) phase
bacteria are rapidly dividing, and bacterial numbers increase in an exponential pattern
stationary phase
exhaustion of nutrients and accumulation of waste -> bacterial numbers plateau or decrease
numbers of viable bacteria decreases
minimum inhibitory concentration (MIC)
least amount of antibiotic that prevents growth of the organism under standardized conditions
minimum bactericidal concentration (MBC)
the least amount of antibiotic required to kill a predetermined portion of an inoculum (usually 99.9%) in a given time
dilution tests
tests where bacteria are grown in liquid media containing serial dilutions of an antibiotic
diffusion tests
pacteria are plated onto solid agar, and disks impregnated with antibiotics are placed on the agar
the antibiotics diffuse out from a disk or strip, preventing growth of the bacteria in the region surrounding the disk if the bacteria are susceptible
zones of inhibition of growth are measured
biofilms
organized three-dimensional communities of microorganisms and extracellular material that grow on solid surfaces
often form at solid-liquid or solid-air interfaces
especially problematic when they form on prosthetic material within the human body
resistant to the action of antibiotics (even though planktonic bacteria may be sensitive)
antibiotic susceptibility
bactericidal activity - the ability to kill bacteria
bacteriostatic activity - the ability to prevent bacterial growth and division
transformation
DNA released by some cells is taken up by others
only certain bacteria are naturally competent
others are artificially competent (E. coli)
artificial competence is of importance in research laboratories - cloning
naturally competent bacteria
- Streptococcus pnumoniae*
- Bacillus* spp.
- Haemophilus influenzae*
- Neisseria* spp.
transduction
bacteriophages act as vectors to introduce DNA from donor bacteria into recipient bacteria by infection
generalized transduction
bacteriophages produce capsids that are capable of packaging any fragment of DNA
if the host cell DNA fragments are present, they will be packaged and injected into neighboring cells upon infection
specialized transduction
when phages that normally package only integrated phage DNA imprecisely excise this DNA from the host chromosome, causing some host DNA to be packaged along with the phage DNA
allows transfer of host DNA but only that DNA which is adjacent to phage DNA
conjugation
bacterial “sex”
cell-to-cell contact between two cells leading to the unidirectional transfer of genetic material from a donor to a recipient cell
mediated by “conjugative plasmids” and “integrative and conjugative elements (ICEs)”
F plasmid
encodes conjugation machinery including sex pilus - cell to cell contact
a copy of this plasmid is passed through the pilus to the recipient cell
in rare cases, the F plasmid integrates into the chromosome of the donor cell
conjugation events lead to transfer of part of the F plasmid DNA as well as the part of the donor cell chromosome
types of bacterial genetic elements
transposable elements
plasmids
bacteriophages
integrons
transposable elements
DNA fragments that mediate their own movement from one location on a chromosome or plasmid to another
important in transfer of antibiotic resistance and creating mutations
two types exist - insertion sequences and transposons
insertion sequences
the smallest transposable elements - 1kb
inverted repeated base sequences at ends, genes encoding transposases
transposase recognizes the inverted repeats and catalyzes the cutting and resealing of DNA
allows movement of IS elements form one location to another
transposons
larger transposable elements that carry extraneous genes in addition to the transposition genes
may encode antibiotic resistance or virulence determinants
some transposons consist of extraneous genes flanked by IS eelements
other complex transposons contain inverted repeats of about 30-40 bps at each end, bu tnot IS elements
plasmids
small, extrachromosomal circular double-stranded DNA molecules that can replicate themselves
may carry and allow dissemination of antibiotic resistance genes and genes that encode virulence determinants
two types - conjugative plasmids and nonconjugative plasmids
conjugative plasmids
generally larger plasmids than are capable of transferring to other cells such as F plasmid, R plasmid (or R factor)
R plasmid - plasmid that acarries genes encoding antibiotic resistance, often carry multiple antibiotic resistance genes
nonconjugative plasmids
unable to mediate their own transfer between bacterial cells
bacteriophages
also called “phages” - viruses that infect bacteria
individual particles consist of a protein capsid enclosing genomic nucleic DNA or RNA
infect bacteria by binding to specific receptors on the bacterium’s surface
inject DNA or RNA into the bacterium
two types of bacteriophages
virulent and temperate phages
phage conversion - the host bacterium acquires new properties, some of which mat may be important in virulence
temperate phage
phages that cause either a lytic infection or a lysogenic infection, where a quiescent form in which the bacterium continues to grow and divide but passes the phage into its progeny
prophages reside inside the cells and can be activated through stress
some temperate phages have acquired genes that are unrelated to phage processes but change the characteristics of the bacteriuum
virulent phage
these phage cause the human bacterium to lyse (“lytic infection”) as a consequence of the synthesis of many new virions within the infected cell
integron
genetic entities that capture exogenous gene cassettes and ensure their expression
not mobile but often linked to mobile genetic elements
composed of three core components: a promoter, a primary recombination stie located downstream of the promoter, a gene encoding an integrase
integrase inserts “gene cassettes” into the integron
most gene cassettes are a single gene encoding for antibiotic resistance
end-to-end gene cassettes are exposed from the integron promoter
targets for antibiotic therapy
cell wall/membrane integrity
protein synthesis
RNA synthesis
DNA replication
metabolism
themes of pathogenesis
entry
persistence
wreaking havoc
