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MSK Personal > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Prokaryote Characteristics

A

Lack Nuclei

No membrane bound organelles

No endocytosis

Different composition of ribosomes and lipids

Usually haploid

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2
Q

Three general categories of challenges to microbes

A

Nutrition (intermittent availability of food)

Occupancy (need to live in specific habitats)

Resistance (to damaging agents)

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3
Q

Plaque is an example of a mechanism for defeating what challenge?

A

Occupancy

Plaques are polysaccharide compounds that help bacteria to adhere to the teeth when they get access to their nutritional needs

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4
Q

What is a consequnce of the small size of bacteria?

A

Very high metabolic rates

High surface area to volume ratio means that diffusion can occur rapidly in comparison to eukaryotic cells giving bacteria a distinct advantage in the speed of their metabolism

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5
Q

What obligate structures do bacteria have? What other structures are possessed by some bacteria?

A

All have a cytoplasmic membrane

Most also have a cell wall, outer membrane, flagella, pili, and/or a capsule

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6
Q

How do gram positive bacteria protect their cytoplasm?

A

They have a thick cell wall composed of murein which is also called peptidoglycan

Determines the shape of the bacteria

rods (bacilli), spheres (cocci), helices (spirilla)

Lysozyme can remove murein causing bacteria to burst

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7
Q

How do gram negative bacteria protect their cytoplasm?

A

They have an outer membrane outside the murein cell wall

Bilayered structure whose outer leaflet contains LPS

LPS is composed of Lipid A, Core (Ketodeoxyoctanoic Acid and heptose), and O antigen (exclude hydrophobic compounds)

Outer membrane has special channels that permit movement of hydrophilic compounds (Porins)

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8
Q

What hydrophilic compounds are too large for Porins

A

Vitamin B12, sugars larger than trisaccharides, and Iron in the form of chelates

Each have their own dedicated mechanism for transport across the outher membrane

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9
Q

What is the general mechanism of action of penicillins, cephalosporins, and B-lactams

A

Penicillins, Cephlosporins, and B-lactams all interfere with the formation of the murein cell wall.

Enzymes that block the action of these antibiotics are present within the periplasmic space of gram-negative bacteria

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10
Q

What is the general mechanism of action of Vancomycin

A

Inhibits the linking of sugars to the growing murein chain

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11
Q

What is the general mechanism of action of bacitracin?

A

Inhibits the regeneration of the lipid carrier responsible for bringing the monomers that compose murein from the cytoplasm to the membrane

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12
Q

Why is it not advisaable to give an antibiotic that inhibits cell growth while also giving penicillin?

A

Bacterial death caused by penicillin is relatied to the continued growth of the cell without the proper continued formation of murein leading to cell lysis

If there is no cell growth then lysis will not occur

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13
Q

Why are mycoplasmas unaffected by penicillin

A

Mycoplasmas have no murein cell wall and therefore will not lyse when murein is not properly synthesized.

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14
Q

What are siderophores?

A

Unique chelating compounds that are secreted by bacteria which allow them to preferentially take up the iron that is necessary for them to grow

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15
Q

Describe the action of DNA gyrase and Topoisomerase 1

A

DNA gyrase introduces supercoils into the circular bacterial DNA

Topoisomerase 1 release supercoils by making single stranded nicks

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16
Q

What is the general mechanisms for flouroquinolones?

A

They interfere with DNA gyrase or topoisomerase 1 and introduce double stranded DNA breaks that are lethal to the bacteria

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17
Q

How do strict aerobes create energy? Strict anaerobes?

A

Strict aerobes must use respiration with the final electron acceptor being oxygen

Strict anaerobes must use fermentation where the final electron acceptor is an organic molecule

Strict anerobes cannot live in oxygenated environments and visa versa

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18
Q

How do Sulfa drugs cause an effect?

A

Sulfa drugs interfere with the ability of the bacteria to create folic acid.

Bacteria that synthesize folic acid can not take it up from their environment

The cells of the body are dependent upon already synthesized folic and acid and are unaffected

It is a competitive inhibitor

19
Q

Resistance to penicillins, cephalosporins, and carbapanems

A

Plasmid Borne

Modification of the Drug

Hydrolosis of the B-lactam ring by B-lactamase

20
Q

Resistance to Methicillin

A

Not plasmid borne

Target modification

Acquisition of a resistant penicillin binding protein

21
Q

Tetracyclines

A

Plasmid borne

Efflux pump transports the drug out of the cell

22
Q

Resistance to aminoglycosides

A

Plasmid borne

Modification of the drug results in reduced affinity for the ribosome and reduced transport into the cell

23
Q

Resistance to sulfonamides

A

Plasmid borne

Target modification

Sulfanilimide resistant dihydropteroate synthase

24
Q

Resistance to trimethoprim

A

Plasmid borne

Target modification of dihydrofolate reductase

25
Q

Erythromycin resistance

A

Plasmid borne

Methylation of 23S ribosomal subunit RNA

26
Q

Chloramphenicol resistance

A

Plasmid borne

Modification of the drug by acetylation of the hydroxyl groups prevents its uptake into the cell

27
Q

Oxazolidinones resisistance

A

Not plasmid borne

mutaton of 23s ribosomal subunit

28
Q

Quinolones resistance

A

Not plasmid borne

Mutations in the gene encoding DNA gyrase and topoisomerase IV

29
Q

Vancomycin resistance

A

Change in binding site is convered in a plasmid borne manner

Restricted access to drug target is not plasmid borne

30
Q

Daptomycin resistance

A

Restricted access to drug target is not plasmid borne

31
Q

Exotoxins

A

Proteins usually secreted by bacteria into surrounding medium

Occasionally bound in cytoplasm and released by lysis of the cell

Often bind to surface receptor and are endocytosed where they are activated by acidity of the mature endosome

Usually have an A:B conformation

32
Q

What are the two most common forms of major pathogens?

A

Gram-negative rods and gram-positive cocci

33
Q

What are the two most medically relevent gram-positive cocci?

A

Staphylococcus and Streptococcus

34
Q

What are the two subdivisions of Streptococci?

A

Alpha hemolytic which cause blood agar to turn green

Beta hemolytic which can be seen by a clear ring around colonies on blood agar

Beta hemolytic are the most common for infectious pathogens

35
Q

What is meant by Streptococci are Oxygen-Tolerant Anaerobes?

A

Normally streptococci only carry out fermentation. However, most can tolerate oxygen environments and therefore are not obligate anaerobes

36
Q

What is group A strep?

A

The A subdivision of beta-hemolytic gram positive streptococci

It is more specifically referred to as S. Pyogenes

They are the infectious agent of Strep Throat, Soft tissue strep, and other serious infections

37
Q

What is the one important pathogen of Strep that is Alpha hemolytic?

A

S. Pneuminae

Causes pneumonia

38
Q

What are the two main agents of Staph infections?

A

S. Aureus and S. Saprophyticus

Other opportunistic infections of normal microbiota like S. Epidermidis can occur

39
Q

What are the visual differences under the microscope between Staph and Strep?

A

Strep appears like a string of pearls

Staph appears like clusters of grapes or arrays of buckshot

Staph also has larger colonies when plated on agar.

40
Q

What enzyme is only produced by S. Aureus and what does it do?

A

Coagulase

Clots the plasma

41
Q

What are the two important forms of Gram Negative Cocci?

A

Gonococcus (Neisseria gonorrhoeae)

Meningococcus (Neisseria meningidae)

Cause gonorrhea and meningitis respectively

42
Q

What are the characteristics of gram-positive rods?

A

Abundant in the environment

Rarely cause disease in developed world

Can be Aerobic (Bacillus) or Strict Anaerobes (Clostridium)

Symptoms of disease are caused by powerful exotoxins

43
Q
A

MSK Personal (12 decks)

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