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Compare and contrast mutation and horizontal gene transfer as methods of enabling bacteria to respond to selective pressures and adapt to new environments.
- mutation is usually harmful to the organism and very rare
- hgf - can help bacteria develop resistance
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Define horizontal gene transfer and state the most common form of horizontal gene transfer in bacteria.
- transfer of genetic material between relatives
- most common = conjugation
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Briefly describe the mechanisms for transformation in bacteria.
- DNA fragments released from dead bacterium and they bind to DNA binding proteins on surface of competent living bacterium
- either both strands of DNA penetrate the recipient or nuclease degrades one strand and the other strand enters the bacterium
- DNA fragment from the donor is exchanged for a piece of the recipients DNA by RecA proteins
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Describe generalized transduction
- when the phage capsid accidentally assembles around a small fragment of bacterial DNA
- when this bacteriophage infects another bacterium, it exchanges the bacterial donor DNA for recipient DNA by homologous recombination
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Describe specialized transduction
when an error in spontaneous induction during the lysogenic life cycle causes a DNA fragment from one bacterium to be transferred to another by temperate bacteriophage
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Describe the transfer of conjugative plasmids
- they encode genes that enable mating pairs to form
- also enable mobilizable plasmids & non-conjugative plasmids to be transferred to the recipient
- posess promiscous transfer systems that allow transfer of DNA to unrelated species
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Describe the transfer of Conjugative transposons and mobilizable plasmids in Gram-negative bacteria
- conjugation/sex pilus on donor binds to recipient
- pilus retracts, pulling the two together
- mating pair is formed by membrane proteins
- nuclease breaks one strand of plasmid DNA at oriT site
- nicked strand enters recipient bacterium
- other strand remains behind in donor bacterium
- both donor/recipient strands make a complementary copy of themselves
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Describe the following mechanism of horizontal gene transfer in bacteria: F+ conjugation
- F+ conjugation results in the transfer of an F+ plasmid possessing tra genes coding only for a conjugation pilus and mating pair formation from a donor bacterium to a recipient bacterium
- One strand of the F+ plasmid is broken with a nuclease at the origin of transfer (oriT) sequence that determines where on the plasmid DNA transfer is initiated
- This serves as the replication start site where DNA replication enzymes will nick the DNA to initiate DNA replication and transfer
- The nicked strand enters the recipient bacterium while the other plasmid strand remains in the donor
- Each strand then makes a complementary copy
- The recipient then becomes an F+ male and can make a sex pilus.
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Describe the following mechanism of horizontal gene transfer: Hfr conjugation
- F+ plasmid with tra genes inserts into nucleoid to form Hfr bacterium in donor chromosome
- nuclease breaks one strand of donor chromosome, part of which enters the bacterium (not the whole thing)
- both donor/recipient make complementary strands
- transfer of chromosomal DNA to recipient but NOT the ability to form conjugation pilus
- recipient DNA undergoes homologous recombination
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Define pathogenicity
the ability of a microbe to cause disease and inflict damage upon its host
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Define virulence
the degree of pathogenicity within a group of microbes
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**Define and briefly describe the overall process of quorum sensing in bacteria and how it may enable bacteria to behave as a multicellular population.
- bacterial genes code for production of autoinducers
- autoinducers bind to signaling receptors (either on bacterial surface or in cytoplasm)
- when autoinducers reach critical level, they activate quorum sensing genes
- this enables bacteria to act as a multicellular population and formation of biofilm is initated
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State at least two possible advantages of individual bacterial behavior.
- allow bacteria to gain a better foothold in their environment
- capable of motility, which allows them to remain in an environment via taxis
- can move through the mucous layer and attach to epithelial cells
- can resist flushing by making pili, adhesins, capsule
- forming a capsule allows them to resist phagocytosis
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State at least two possible advantages of multicellular bacterial behavior.
- better enable the bacterial pop. to persist in the body
- individual bacteria within a group can benefit from the activity of the entire group
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State what is meant by intraspecies, interspecies, and interkingdom communication.
- intraspecies - within species
- interspecies - with other genus/species
- interkingdom - bacteria communicating w/animal or plant host
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State the function of bacterial secretions systems (injectosomes) such as the type 3 and type 6 secretion systems in bacterial pathogenicity.
- enable bacteria to alter the host cell's machinery to its own benefit
- T6SS can also kill other bacteria
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Describe 6 different ways antibiotics or disinfectants may affect bacterial structures or macromolecules and state how each ultimately causes harm to the cell.
- inhibit synthesis of peptidoglycan -> causes osmotic lysis
- inhibit synthesis of acid-fast cell wall -> causes osmotic lysis
- alter membrane -> causes leakage of molecules and enzymes needed for metabolism
- alter bacterial ribosomes -> interferes with translation
- inhibit nucleic acid replication -> interferes with transcription
- disinfectants can damage membrane and cause it to leak OR denature enzymes -> blocks metabolism
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Function of macrolides (erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.), oxazolidinones (linezolid), and streptogramins
- bind to 50S subunit
- inhibit elongation by preventing pepteidyltransferase from forming peptide bonds betw amino acids
- prevent transfer of tRNA from A-site to P-site
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Function of penicillins, monobactams, carbapenems, cephalosporins, and vancomycin
- bind to transpeptidase enzymes
- prevent them from reforming peptide cross links
- peptidoglycan cell wall cannot be finished and osmotic lysis occurs
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Function of fluoroquinolones (norfloxacin, lomefloxacin, fleroxacin, ciprofloxacin, enoxacin, trovafloxacin, etc.), sulfonamides and trimethoprim, and metronidazole
- inhibit topoisomerases
- this interferes with transcription
- proteins cannot be made so metabolism cannot occur
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Function of aminoglycosides (streptomycin, neomycin, netilmicin, tobramycin, gentamicin, amikacin, etc.) and tetracyclines (tetracycline, doxycycline, demeclocycline, minocycline, etc.)
- bind to 30S subunit
- prevent elongation of polypeptide chain
- also causes misreading of codons
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Name 2 bacteria that have low-permeability membrane barriers and are thereby intrinsically resistant to many antibiotics.
- Mycobacterium tuberculosis
- Enterococcus
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**Briefly describe 4 different mechanisms as a result of genetic changes in a bacterium that may enable that bacterium to resist an antibiotic.
- produce enzymes that inactivate the antibiotic
- altering target site receptor to reduce/block binding of antibiotic
- altering membrane/transport proteins to prevent entry of antibiotics
- use of efflux pump to transport bacterium out
- modulate gene expression to produce more of the enzyme that is being altered by the antibiotic
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Describe R (Resistance) plasmids and state their significance to medical microbiology.
- have genes coding for multiple antibiotic resistance
- also have transfer genes coding for sex pilus
- they can accumulate transposons to increase bacterial resistance
- important in medicine bc pathogens can have R-plasmids and be resistant to antibiotics
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State what the following stands for: MRSA
methicillin-resistant staphylococcus aureus
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State what the following stands for: VRE
vancomycin-resistant enterococcus
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State what the following stands for: ESBLs
extended spectrum beta-lactamases
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State what the following stands for: XDR TB.
extensively drug-resistant tuberculosis
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Define antibiotic tolerance/dormant persisters
- the tolerant bacterium is not killed but simple stops growing when antibiotic is present
- once the antibiotic is no longer present in the host, it can recover and start growing again
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Define selective toxicity
the chemical being used should inhibit or kill the intended pathogen without seriously harming the host
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Define broad spectrum antibiotic
one that is generally effective against a variety of Gram-positive and Gram-negative bacteria
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Define narrow spectrum antibiotic
generally works against just Gram-positives, Gram-negatives, or only a few bacteria
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Define antibiotic
a metabolic product produced by one microorganism that inhibits or kills other microorganisms
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Define chemotherapeutic synthetic drug
- antimicrobial drugs synthesized by chemical procedures in the laboratory
- Synthetic chemicals that can be used therapeutically
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Define cidal
this agent kills microorganisms
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Define static
this agent inhibits the growth of microorganisms
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Define sterilization
the process of destroying all living organisms and viruses
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Define disinfection
the elimination of microorganisms, but not necessarily endospores, from inanimate objects or surfaces
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Define disinfectant
an agent used to disinfect inanimate objects but generally too toxic to use on human tissues
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Define antiseptic
an agent that kills or inhibits growth of microbes but is safe to use on human tissue
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Define physical agent
include such methods of control as high or low temperature, desiccation, osmotic pressure, radiation, and filtration
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