Microbiology Exam 3!

microbiome

community of microbes growing and living together in a specific habitat

symbiosis: microbial relationships

interaction between two organisms, may be any type of relationship pos or neg

microbial and host interaction

a host is an organism that has a close relationship with a microbe, may be mutualistic, parasitic, etc.

stomach environment

low pH, oxygen present

small intestine environment

anaerobic, not many bacteria

large intestine

anaerobic, lots of bacteria

characteristics of the gut microbiome

oxygen poor and high stomach pH

vaginal microbiome

lots of glucose, low pH

skin microbiome characteristics

some skin may be moist (feet, groin, knee pit), sebaceous (oil/sebum) on face, scalp, back can be metabolized by bacteria, skin may be dry and that’s where the highest diversity is

oral microbiome

moist environment, teeth are a good surface for biofilms to form

characteristics of bacterial DNA

a singular circular chromosome, contains one origin of replication, DNA gyrase is unique to prokaryotes and is used to separate the two circular DNA strands after replication

DNA gyrase

an enzyme unique to bacteria that separates the two circular strands of DNA during replication

bacterial transcription

the process of transcribing DNA into RNA using the enzyme RNA polymerase, RNA polymerase binds to a promoter which is the gene sequence that promotes gene expression, sigma factors are unique to bacteria and they help RNA polymerase bind to the promoter

sigma factors

proteins that bind to the promoter to help RNA polymerase, there are specific sigma factors for each gene

bacterial translation

process of translating RNA into proteins through the use of ribosomes, this process happens at the SAME TIME as transcription in bacteria because there is no physical barrier between DNA and ribosomes

operon

operons area gene structure that helps bacteria regulate the expression of their genes

trp operon

a repressible operon, meaning, that this operon promotes the expression of the genes used to make tryptophan, an amino acid, in the absence of tryptophan, the repressor is not bound and RNA polymerase is able to bind and transcribe, but as tryptophan levels rise, trp binds to the repressor causing a change in conformation and the repressor binds to the operator, preventing RNA polymerase from transcribing

lac operon

an inducible operon, the repressor is bound to the operator in the absence of lactose preventing the transcription of the genes that code for proteins that break down lactose, however, when lactose is present, lactose binds to the repressor causing a conformation change and RNA polymerase transcribes the genes needed to break down lactose for energy. However, when glucose is also present, the rate of transcription is slow because the body would rather use glucose. High glucose, high ATP means low cAMP. Therefore, cAMP does not bind to CAP and the rate of transcription stays the same. Although, when glucose is not present, ATP is low, and cAMP is high. Therefore, cAMP binds to CAP, and they bind to the promoter and increase the rate of transcription.

horizontal gene transfer

the transmission of genetic material from one bacteria to another, creates genetic variation at a faster rate than natural selection

mechanisms of HGT

transformation, conjucation, transduction

transformation

genetic information is taken in from the environment

conjucation

two bacteria form a sex pilus between them and transfer genes from one bacterium to another

transduction

genetic information comes from a virus

where do antibiotics come from

most antibiotics come from compounds made by fungi or bacteria

narrow spectrum

antibiotic kills a specific bacteria type

broad spectrum

antibiotic kills acid fast, gram neg and pos

selective toxicity

good antibiotics target structures that are only present in antibiotic cells, and not host cels

sensitive bacteria

bacteria are killed by an antibiotic

resistant bacteria

bacteria can survive and grow in the presence of an antibiotic

beta-lactams (bacteriacidal)

a class of antibiotics that target the cell wall by inactivating the enzyme transpeptidase. Transpeptidase is responsible for maintaining and creating the cross linkages of the amino acid chains attached to the polysaccarides. The links are created at D-ala-D-ala, and beta-lactams resemble this amino acid sequence so they can bind to transpeptidase. If the cross linkages are not made the integrity of the cell wall is weakened and the cell lyses

penicillin (bactericidal)

class: beta lactam, target: cell wall, mechanism of action: inactivates transpeptidase, type of bacteria killed: gram positive

ampicilin (bactericidal)

class: beta lactam, target: cell wall, mechanism of action: inactivate transpeptidase, type of bacteria killed: mostly gram positive

cephalosporin (bactericidal)

class: beta lactam, target: cell wall, mechanism of action: inactivate transpeptidase, type of bacteria killed: gram pos and gram neg (more broad spectrum)

carbapenams (bactericidal)

class: beta lactam, target: cell wall, mechanism of action: inactivates transpeptidase, type of bacteria killed: broad spectrum

monobactums (bactericidal)

class: beta-lactam, target: cell wall, mechanism of action: inactivation of transpeptidase, type of bacteria killed: gram negative

glycopeptides(bactericidal)

a class of antibiotics that targets the cell wall, the mechanism of action is that the antibiotic binds to the D-ala-D-ala sequence on the peptide chains to prevent the binding of transpeptidase. The cross linkages are not made and the cell wall weakens causing cell lysis

beta-lactam resistance

bacteria can produce beta lactamase which is an enzyme that breaks down beta lactams (antibiotic hydrolysis)

vancomyocin resistance

bacteria can change the amino sequence from D-ala-D-ala to D-ala-D-lactate, so that the glycopeptides cannot bind (target modification)

vancomyocin (bactericidal)

class: glycopeptides, target: cell wall, mechanism of action: binds to D-ala-D-ala to prevent transpeptidase from working, type of bacteria killed: gram positive

bacitracin (bactericidal)

class: bacitracin, target: cell wall, mechanism of action: inhibits cell wall precursor molecules, type of bacteria killed: gram positve

isoniazid (bactericidal)

class: isoniazid, target: cell wall, mechanism of action: inhibits production of mycolic acid, type of bacteria killed: acid fast bacteria

polymixins (bactericidal)

a class of antibiotics that target the plasma membrane, their mechanims of action is that they bind to LPS embedded in the membrane, disrupting the structure, as the tails of the polymixins become embedded, and the cell lyses. This antibiotic can only kill gram negative bacteria because only gram negative have LPS in their outer membrane

resistance to polymixins

alteration of LPS molecules so that polymixins cannot bind (target modification)

aminoglycosides (bactericidal)

target: ribosome, mechanism of action: these antibiotics bind to the decoding site of the ribosome and cause codon/anti codon mismatches, the incorrect tRNA is inserted, which causes the incorrect protein to be made, incorrect proteins are inserted into the cell membrane and causes lysis, type of bacteria killed: broad spectrum

tetracyclines (bacteriostatic)

target: ribosome, mechanism of action: prevents tRNA from binding to the A site on the ribosome, which prevents protein synthesis, prolonged exposure to tetracyclines cause bacterial death, type of bacteria killed: broad spectrum

macrolides (bacteriostatic)

target: large subunit of ribosome, mechanism of action: blocks peptide chain elongation (block addition of amino acids) so proteins cannot be made, type of bacteria killed: broad spectrum

lincosamides (bacteriostatic)

target: large subunit of ribosome, mechanism of action: blocks peptide chain elongation so proteins cannot be made, type of bacteria killed: gram positive

chloramphenicol (bacteriostatic)

target: large subunit of ribosome, mechanism of action: blocks peptide chain elongation so proteins cannot be made, type of bacteria killed: broad spectrum

oxazolidinones (bacteriostatic)

target: ribosome, mechanism of action: blocks large ribosomal subunit from binding to the small subunit which prevents protein synthesis, type of bacteria killed: broad spectrum

quinolones (bacteriostatic)

target: DNA replication/synthesis, mechanism of action: interferes with the enzyme DNA gyrase, which is responsible for separating the two DNA strands after replication, by causing double strand breaks. DNA gyrase cuts the strands, but does not bind them back together, so the DNA strands become non functional. type of bacteria killed: broad spectrum

rifampin (bactericidal or bacteristatic)

target: RNA synthesis, mechanism of action: blocks RNA polymerase by binding to the enlongation site on RNA polymerase, causing no production of RNA molecules, therefore, important proteins necessary for cell function are not made. type of bacteria killed: gram positive

antibiotic hydrolysis

a resistant bacterium may produce an enzyme that breaks down the bonds in an antibiotic, ex. beta lactamase

antibiotic modification

resistant bacteria may enzymatically add a functional group to an antibiotic so that it doesn’t function

membrane modification

resistant bacteria may prevent the antibiotic from entering the cytoplasm by preventing the antibiotic from crossing the cell membrane or by pumping the antibiotic out of the cell

target modification

resistant bacteria may change the target of the antibiotic so that the antibiotic cannot bind

how does antibiotic resistance spread

mutations randomly appear, bacteria with mutations that make them resistant survive and reproduce, bacteria use HGT to transfer mutations to other bacteria

what increases antibiotic resistance?

overuse of antibiotics in agriculture, misuse and overuse of antibiotics in medicine

components of a virus

sheath and caspid (proteins), and genetic material

stages of viral infection

1\. attachment to specific receptor on cell surface, 2. penetration, genetic material is inserted into host cell, 3. biosynthesis, the replication of virus genetic material and production of viral proteins, 4. assembly/maturation, viral particles are assembled

lytic life cycle

1\. attachment to specific receptor on cell surface, 2. penetration, genetic material is inserted into host cell, 3. biosynthesis, the replication of virus genetic material and production of viral proteins, 4. assembly/maturation, viral particles are assembled, 5. release of viral particles (lysis)

lysogenic life cycle

the stages are the same as a lytic cycle, however, there is a pause between cell entry and biosynthesis. The viral DNA hides in the host genome and waits for an environmental trigger to begin biosynthesis

bacteriophage

a virus that infects bacterial cells