Unit IV Flashcards
What is the bacterial equivalent of tubulin?
FtsZ
What is the bacterial equivalent of actin?
MreB
What is the bacterial equivalent of intermediate filament?
CresS
What is glycocalyx used for?
formation of microbial biofilms
What molecules attaches the outer membrane of gram negative bacteria to peptidoglycan?
Lipoproteins
What is another word for lipopolysaccharides?
Endotoxin
What are the three components of LPS?
Lipid A (the toxic component) core polysaccharide O antigen that functions as a somatic antigen
What is the classification of enteric bacteria based on their flagella?
H antigens
What is a bacteriophage?
virus that infects bacteria
What are heterotrophic bacteria?
Require organic carbon for survival
What are autotrophic bacteria?
bacteria that obtain their carbon exclusively from CO2
What are obligate intracellular bacteria? t
Bacteria that can grow within eukaryotic cells but
cannot be cultivated on artificial media.
How do heterotrophic bacteria obtain both energy and
reducing power?
fermentation or respiration
β-lactams
inhibit the final transpeptidation reaction in cross-linking of peptidoglycan.
ex: penicillin, cepalosporins
What is the role of vancomycin?
inhibits utilization of lipid-linked intermediate at an
intermediate step in peptidoglycan synsthesis, e.g., elongation of the peptidoglycan chain.
cycloserine
inhibits alanine racemase, preventing formation of
muramyl pentapeptide, an early intermediate in peptidoglycan synthesis.
Polymyxins
cationic surfactants that disrupt bacterial outer and cytoplasmic membranes. They are less active on mammalian cell membranes.
Aminoglycosides
bind to specific target proteins in the 30S ribosomal subunit and inhibit protein synthesis.
Tetracyclines
reversibly bind to the 30S ribosomal subunit and inhibit
binding of aminoacyl tRNA.
chloramphenicol
binds reversibly to the 50S ribosomal subunit and inhibits peptidyl transferase and peptide bond formation.
Macrolides
bind to the 23S ribosomal RNA of the 50S subunit and inhibit peptidyl transferase.
Quinolones
inhibit DNA gyrase and topoisomerase and interfere with DNA replication
Rifampicin
inhibits RNA polymerase and interferes with the
initiation of transcription.
Sulfonamides
structural analogs of p-aminobenzoic acid (PABA), which is a component of folic acid. Sulfonamides inhibit the formation of folic acid by competing
with PABA, and this in turn prevents nucleic acid synthesis.
**humans don’t make folic acid, we get it from bacteria in our gut
Trimethoprim
interferes with folate metabolism by inhibiting
the enzyme dihydrofolate reductase. Since both bacterial and host cells both possess this enzyme, the basis of selective toxicity lies in the 50,000-fold greater sensitivity of the bacterial enzyme to this drug.
Isoniazid
inhibits lipid synthesis (probably mycolic acid synthesis) in
susceptible Mycobacteria.
Metronidazole
appears to specifically interfere with anaerobic metabolism.
virulence genes are often expressed under what conditions?
low iron conditions that are encountered IN the host
How does Salmonella typhimurium generate genetic diversity?
It has an invertible segment of DNA which includes the promoter region of H2. When reversed the H2 promoter is expressed and H2 is made. H1 is blocked .
How does Neisseria gonorrhoeae generate genetic diversity?
Recombinational exchange between the expressed and a nonexpressed copy of the pilin genes results in a new pilin gene at the expression site and production of a new antigenically distinct pili on the cell surface.
**Phase Variation
What are examples of mutations that are of medical importance?
i) increased resistance to antimicrobials in Pseudomonas and Mycobacterium tuberculosis
ii) Streptococcus pyogenes strains with an increased
likelihood of causing invasive disease due to a single amino acid change in pyogenic exotoxin B.
What is fermentation?
the catabolic process in which organic compounds serve as both electron donor and electron acceptor
What is respiration?
need a terminal electron acceptor typically O2
What are the two forms of energy currency for bacteria?
- ATP - biosynthetic interconversions
2. Proton Motor Force - flagellar rotation, membrane transport
How do you convert ATP into PMF?
ATPase
What is the active component in transformation?
naked DNA, probably DNA from lysing cells
explain transformation
crude extracts, and ultimately pure DNA, taken from virulent, encapsulated strains of the pneumococcus (S forms) could convert avirulent, nonencapsulated strains (R form) to the virulent phenotype.
How are some bacteria induced to become “competent” to transformation?
calcium chloride and low temperatures
What is transduction?
gene transfer mediated by a bacteriophage
what is a lysogenic response?
the host cell remains viable and the infecting phage DNA is maintained by the host cell in a noninfectious state called a “prophage”
What is a prophage?
phage DNA which is linearly inserted into the host cell genome where it becomes passively replicated as part of the bacterial chromosome.
How is the lysogenic stage maintained?
by repressor proteins that blocks expression of the
phage genes necessary for viral DNA replication and lytic development.
What is bacteriophage conversion (lysogenic conversion)?
the genes controlling the new phenotypic trait are found only as a component of the phage genome; that is, the converting genes are not found alone as normal constituents of the bacterial genome.
What is generalized transduction?
caused by error in DNA packaging where that phage mistakenly packages bacterial DNA instead of viral DNA. It can still attach to other bacterial cells and inject this DNA to cause recombination with homologous segments
What is bacterial conjugation mediated by?
bacterial plasmids
What often encode antibiotic resistance and virulence factors?
plasmids
What type of plasmids are self transmissible?
conjugative plasmids
The mechanism of antibiotic resistance transfer is particularly prevalent among which type of bacteria?
gram positive bacteria
The F plasmid contains genetic information encoding what traits?
i. Autonomous replication of the plasmid DNA
ii. Synthesis of sex pili (F pili) which are essential for mediating pair formation between donor and recipient cells
iii. Conjugative transfer of F DNA to recipient (F- ) cells
iv. Ability to integrate into the bacterial chromosome
What is bacterial conjugation?
a form of genetic transfer that is dependent upon physical
contact between the donor and recipient cells, and is usually mediated by certain types of bacterial plasmids
What are spores?
specialized cells that are produced by certain bacteria, such as Clostridium sp. and Bacillus sp.,
when the nutritional supply of carbon, nitrogen or phosphorus is limited
Define peritrichous?
Bacterial that have flagellar all around them
What are the three most common organisms responsible for infective bacterial endocarditis?
Staphylococcus aureus
Streptococci of the viridans group
coagulase negative Staphylococci **staphylcocci epidermidis
What bacteria is catalase positive?
staphylcocci
Which bacteria is catalase negative?
streptococci
Which bacteria is coagulase positive?
staphylcoccus aureus
What is an alternative name for staphylcocci epidermidis?
staph species, NOT aureus (SSNA)
coagulase negative staphylcoccus (CNS)
What bacteria is the causative agent of common
“strep throat”?
streptococcus pyogenes
How does streptococcus pyogenes avoid phagocytosis?
They are surrounded with M protein
Describe the distinct features of group a streptococcal lesions
The typical lesion is that of a SPREADING infection of the cutaneous and subcutaneous tissues (cellulitis). [Contrast with typical S. aureus infections-which are more prone to produce focal abscesses, which may be accompanied by a surrounding cellulitis]
What are Post-streptococcal diseases?
Glomerulonephritis- Streptococcal antigen-antibody complexes are deposited in the kidney and accumulate at the basement membrane.
Rheumatic fever- antibodies recognizing and binding to
specific host antigens of the myocardium and heart valves.. This leads to progressive antibody-mediated damage to these tissues.
What are the “big three pathogens” for antibiotic use?
MRSA, pseudomonas, and anaerobes
Which enzyme cross links peptidoglycan?
Penicillin Binding Proteins
What reactions are driven by penicillin binding proteins?
transpeptidase and transglycosylase
How do beta lactam antibiotics work?
they irreversibly bind and inactivate the transpeptidase reaction of penicillin binding proteins therefore, INHIBITS cross linking and synthesis of peptidoglycans
How do bacteria become resistant to beta lactam?
They produce beta lactamase which destroys the beta lactam - MODIFYING THE DRUG
Produce altered penicillin binding proteins so that the beta lactam no longer can bind - MODIFYING THE TARGET
PREVENTING DRUG TARGET INTERACTION - modifying porin channel and drug efflux mechanisms so beta lactam cannot reach its target
Where can beta lactamase be found?
in gram positive and gram negative bacteria
Is beta lactamase more commonly found in gram positive or gram negative bacteria?
Gram negative
How are beta lactamases encoded?
chromosomal or transferable genes
Narrow-spectrum β-lactamases are resistant to what type of antibiotics?
penicillins-type antibiotics (penicillin, amoxicillin, ampicillin and possibly piperacilllin)
Narrow-spectrum β-lactamases bacteria are sensitive to what drugs?
cephalosporins or carbapenems
extended spectrum beta-lactamases are notable for their resistance to what drugs?
cephalosporins
**can still be treated with beta lactamase inhibitors
Where are extended spectrum beta-lactamases found?
plasmids
What type of bacteria are beta lactamases?
gram negative
What are notable features of ampC-encoded β-lactamase?
it is chromosomally located
can hydrolyze penicillins, 1st 2nd and 3rd generation cephalosporins
NOT inhibited by beta-lactamase inhibitors
Which bacterias have ampC-encoded β-lactamase?
gram negative bacteria: enterobacter and pseudomonas
What are lipopolysaccarides an example of?
Pathogen associated molecular pattern (PAMP)
How are lipopolysaccarides recognized?
via the innate immune system -CD14 and TLR4
What are hemolysins?
erythrocyte membrane damaging toxins that kill target cells
cytolysins?
general terms for membrane damaging toxins that kill target cells.
Form pores that cause the lysis of cells
What are the most potent T cell activators?
superantigens
How does pseudomonas aeruginosa inhibit protein synthesis?
exotoxin A inactivates elongation factor 2 (EF-2) which is required for peptide chain elongation.
What are examples of ribosyltransferases?
Diphtheria toxin and pseudomonas aeruginosa exotoxin A both inactivate EF-2
How do shiga toxins of shigella and e.coli work?
they are RNA N-glycosidases that remove an adenine residue, inactivating the ribosomes