Question

Introduction to Microbiology [Tutorial]

Answer 1

\({\bf{Microscopy:}}\)
- resolving power: minimum distance at which two points are distinguishable
- bright field microscopy: microscopy technique based on contrast between observable and the medium, may require staining
- phase contrast microscopy: microscopy technique based on differences in the refractive index, allows live bacteria to be observed
- electron microscopy: microscopy technique that uses electrons, requires staining
- confocal scanning laser microscopy: microscopy technique capable of producing a 3D image

avg prokaryotic microbe ~ 1 micron
avg eukaryotic micobe ~ 1 mm

\({\bf{Gram-Staining:}}\)
Basic Procedure:
1. stain w/ crystal violet (+ charge, reacts w/ - charge on membranes) + iodine
2. wash away CV w/ alcohol
3. safranin (gram neg --> red stain)

other chemicals may be used if the microbe has a protective layer/wax or lacks a cell wall

\({\bf{Basic~Bacterial~Structures:}}\)
- capsule (matrix around bacteria): adherence, inhibits drying out and phagocytosis, defense against certain pathogens
- pilli: protein extensions, functions in adherence, movement, conjugation (covered later)
- flagella: rotation, movement

Answer 2

\({\bf{Membrane~Structure:}}\)
polysaccharide chain w/ peptide cross linkages
NAG and NAM (NAM found exclusively in bacteria)
[long names: N-acetylglucosamine, N-acetylmuramic acid]

Gram-Neg:
outer leaflet: LPS, lipid A
inner leaflet: phospholipid (phosphatidylethanolamine)
lipid A = toxin, increases depending on acyl side chain # and phosphate group #
thin peptidoglycan
porins

Gram-Pos:
techoic acid (anchored to peptidoglycan)
lipitechoic acid (anchored to lipid)
thick peptidoglycan layer, synthesis is susceptible to penicillin

Answer 3

\({\bf{Basics~of~Bacterial~Growth:}}\)
- autotroph: obtains carbon from CO2
- heterotroph: obtains carbon from other organisms
- medium: substance used to grow bacteria

Subtypes of growth media:
- defined: chemical composition known exactly
- complex: not known exactly, often a mixture of organic material from various organisms
- general: used to grow a wide variety of organisms
- differentiation: bacteria grown will look different depending on their physical properties
- selective: only allows certain microbes to grow
- enrichment: contains substances that promote growth of certain microbes

Growth vs. temperature, in order from lowest T preferred to highest T:
- psycrophile
- mesophile (this is where humans are classified)
- thermophile
- hypothermophile

if T is too low --> membrane gelling, metabolism too slow
if T too high --> protein denaturing

\({\bf{Measuring~Growth:}}\)
- turbidity (based on optical density), can not tell live cells/dead cells apart
- viable cell count: (based on serial dilutions, counting bacteria, then reverse-engineering how many were originally present), is not monoclonal
- counting chamber method: (based on dividing the viewing window into a grid and counting) does not work well with fast bacteria and cannot tell live cells/dead cells apart
- dry weight: (based on mass) only measures yield not cell #

Answer 4

\({\bf{Basics~of~Metabolism:}}\)
- NADH: reducing agent in electron transfer reactions
- high NADH presence indicates high ATP production
- NADH involved in the reduction of pyruvate (also lactate dehydrogenase LDL)
- NAD+ produced in fermentation
- hydrolysis of ATP or equivalents provide energy for cell functions
- pyruvate --> acetyl CoA --> TCA cycle
- ion transport: requires membrane protein + proton motive force
- ATP binding casette: membrane transport system (periplasmic proteins + transporter)
- PTS system: uses phosphoenelpyruvate to power transport of sugars

Answer 5

Anyway that's the end, I hope this is a useful resource. I am not an expert by any means but I will attempt to answer questions to the best of my ability.