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Flashcards in Bacterial Structure and Function Deck (77):

external structures on bacteria

capsules, flagella, and pili



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



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




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



weight loss


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)




some Gram-positive bacilli are able to form these tructures that deveop within vegetative (dividing) cells



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



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



organic compounds serve as electron donor sand acceptors

energy is generated by substrate-level phosphorylation

ineffiicent generation of energy

does not require oxygen



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"



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



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



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



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



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



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.



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



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





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



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



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



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



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



themes of pathogenesis



wreaking havoc