Bacterial Growth and Physiology

Question 1

Iron Acquisition

Answer 1

• Iron (Fe3+) extremely insoluble in oxidizing environment -FeOH)3
• Bound to proteins (transferrin, hemoglobin, lactoferrin) in humans
• Many bacteria secrete siderophores to scavenge iron. Siderophores have a very high affinity for iron.
• Some bacteria acquire iron directly from cellular proteins.
• Virulence trait

Question 2

Obligate aerobes

Answer 2

Require O2 to grow (20%)

Question 3

Obligate anaerobes

Answer 3

Sensitive to O2

Question 4

Facultative anaerobes

Answer 4

Use O2 if available

Question 5

Aerotolerant anaerobes

Answer 5

Do not use O2, not killed by it

Question 6

Microaerophiles

Answer 6

Require low O2 (5-10%)

Question 7

Why is O2 toxic?

Answer 7

• Oxygen can react with electrons to produce ROS (hydrogen peroxide -H2O2 or superoxide ion -O2-)
• ROS are toxic b/c they react with DNA or lipids and they covalently attach/modify
• Bacteria have enzymes to get rid of ROS
• Catalase: H2O2→H2O
• Superoxide Dismutase: O2-→ H2O
• Obligate anaerobes do not have these enzymes

Question 8

Respiration

Answer 8

More efficient, TCA cycle to produce ATP, NADH, and FADH2 in presence of O2

Question 9

Fermentation

Answer 9

Glycolysis, pyruvate → ATP in absence of O2, recycling of NADH → NAD+

Question 10

Pentose Phosphate

Answer 10

Produces reducing power (NADPH), hexose monophosphate shunt

Question 11

Biochemical mechanisms of resistance

Answer 11

• Enzymatic inactivation or modification of antibiotic
• Modification of target site
• Altered permeability: change in porin, efflux pump

Question 12

Genetic Mechanisms of Resistance

Answer 12

• Chromosomal mutation
• Genetic exchange: acquisition of a resistance gene (usually on a plasmid)

Question 13

Peptidoglycan biosynthesis

Answer 13

• Carried out by penicillin binding proteins
• Transglycosylation: attach subunits to glycan chain
• Transpeptidation: crosslink peptides

Question 14

Beta-Lactams

Answer 14

Beta-Lactams (Penicillin) block Transpeptidation

Question 15

Peptidoglycan Synthesis Inhibitors

Answer 15

• Beta-lactams
• 4-member beta-lactam ring
• Penicillin, Cephalosporin, Carbapenem, Monobactam
• Beta-lactam ring is a structural analog of D-ala D-ala

Question 16

By adding penicillin to cell

Answer 16

Block PCP and bacteria can no longer make peptidoglycan

Question 17

Beta-lactamase

Answer 17

Destroys antibiotic by cleaving 4-member ring

Question 18

Carbapenems can pretty much

Answer 18

Degrade all beta-lactams

Extra carbon makes them very resistant to penicillinases

Question 19

Vancomycin

Answer 19

• Works only on Gram (+) bacteria due to large size (cannot get across outer membrane of Gram (-)
• Binds to precursor of cell wall synthesis
• Binds to D-ala-D-ala

Question 20

Vancomycin Resistance

Answer 20

Terminal D -ala replaced with -lactate (genes for this on a transposon)

Question 21

Two main cell wall synthesis inhibitors

Answer 21

Beta-Lactamases

Vancomycin

Question 22

DNA Synthesis (Chromosome Replication)

Answer 22

• DNA polymerase replicates DNA
• Topoisomerase II (gyrase) needed to remove supercoils ahead of replication fork
• Topoisomerase IV needed for chromosome resolution
• Topoisomerases are targets of quinolones
• Quinolones covalents attach to topoisomerase and block its activity

Question 23

Transcription and Translation

Answer 23

• Rifampin used in mycobacterium tuberculosis. Very hydrophobic and does not work on gram (-). Blocks RNA polymerase binding to promoter. Blocks transcription.
• Protein synthesis inhibitors: Tetracyclines, aminoglycosides, macrolides, chloramphenicol, lincosamides, oxazolidinones. Block steps in protein synthesis. Bacteriostatic (except aminoglycosides).
• Aminoglycosides make ribosome make mistakes. Put a lot of long aa’s into protein so bacteriocidal (protein aggregates disrupt cell membrane)

Question 24

Resistance to Tetracycline

Answer 24

Gene encoding efflux pump

Question 25

Resistance to aminoglycosides

Answer 25

Genes encode modifying enzymes

Add phosphoryl or methyl group

Question 26

Chloramphenicol resistance

Answer 26

Gene encodes modifying enzymes

Add acetyl group

Question 27

Erythromycin Resistance

Answer 27

Gene that modifies ribosomal RNA

Add methyl group

Question 28

Folates: Co-factors in one-carbon transfer reactions for nucleotide and amino acid biosynthesis

Answer 28

• Tetrahydrofolic acid is produced through a 2-step synthesis
• THF is necessary to make thymidine, purines and methionine (necessary to make DNA, RNA, Protein)
• Sulfanomide blocks first step to produce Dihydrofolic acid. This step does not occur in humans (we get dihydrofolate from our diet)
• Dihydrofolate reductase 9second step) is sensitive to Trimethropin. Eukaryotic dihydrofolate reductase is sensitive to methotrexate (different).

Question 29

Colistin (type of polymixin)

Answer 29

• Not used b/c of toxicity except as last resort for Gram (-)
• Binds to LPS (lipopolysaccharides) and disrupts membrane.
• Resistance caused by Mcr-1 gene on plasmid which encodes enzyme that modifies LPS and reduces Colistin binding

Question 30

Resistance to germicidal chemicals

Answer 30

Bacterial spores > Mycobacteria> Small viruses (nonlipid) >Lipid-containing viruses>Bacteria > Fungi

Question 31

Antiseptic

Answer 31

Chemical agent used on tissue to reduce # of microbes

Question 32

Aseptic

Answer 32

Absence of pathogenic microbes

Question 33

Septic

Answer 33

Pathogenic microbes in living tissues

Question 34

Disinfectant

Answer 34

Used to kill microorganisms, usually a liquid chemical agent, does not meet criteria for sterilization

Question 35

Sterilization

Answer 35

Complete killing by physical or chemical agents