microlab bacterial quantification

in ideal conditions bacterial populations can expand at what rate

exponential

bacterial growth has an optimal generation time of

20 minutes

exponential progression can be expressed as

2^n

n in exponential means

number of generations

what is colony forming unit (CFU)

measurement used to estimate the number of viable bacteria or fungal cells in a sample

a cell is only considered viable if

able to multiply via binary fission under the controlled conditions

colony forming units can be calculated by

spreading a specific volume of the microbial culture onto an agar plate

after incubation of agar plate the number of colonies is proportional to

the number of viable conditions in the tube

cfu/mL

colonies/volume spread cfu per milliliters is equal to colonies divided by volume millimeters

when bacteria colonies can not be counted directly what needs to be performed

serial dilutions

serial dilutions function

decrease the number of cells that you use for spreading

in order to calculate the cfu/mL of a diluted sample what needs to be multiplied

number of colonies with the dilution factor

the number of bacteria in a sample can also be quantified with other techniques such as

examination with a microscope

other techniques for examination require

significant growth and also don’t exclude dead or non-viable cells

when are serial dilutions useful

when we want to obtain a very diluted solution from very concentrated stock solutions

aliquot

smaller portion taken from a large quantity

sterile techniques are used to ensure

a “clean” lab environment

in sterile labs doors and windows are kept closed to prevent

air currents and surface microorganisms becoming airborne

what must be sterilized before and after use with Bunsen burner

wire loop and glass spreader

lids from bottles and tubes are held when removed not placed where

on bench (during material transfer from one bottle or tube to another)

neck of bottle or tube must be immediately heated using bunsen burner so air flow is ___

outward

all work must be performed near

Bunsen burner flame

media and equipment are sterilized to prevent

growth of unwanted microorganisms

what is antibiotic resistance

general process in which bacteria (usually infectious) becomes insensitive to a specific drug or class of drugs

when does antibiotic resistance usually appear

when a microbe is exposed to sub-lethal concentrations of a specific antibiotic

how can a microbe develop resistance mechanisms across several generations

selective pressure

resistance mechanism categories

modification of the primary target of antibiotic

inactivation of the antibiotic compound itself

preventing the antibiotic from reaching target

using alternative metabolic pathways

example of modification of the primary target if the antibiotic

transpeptidase of ampicillin resistance

example of inactivation of the antibiotic compound itself

production of B-lactamase enzymes to degrade penicillin G inside the cell.

example of preventing the antibiotic from reaching its target

ciprofloxacinby reducing the permability of the membrane or using efflux pump to keep drugs outside cell wall

a drug-resistant bacterial strain can transfer

the resistance gene to other strains of the same species - or to individuals of a different species altogether - that have never been exposed to the drug in the first place. This way, antibiotic resistance can spread widely and compromise whole antibiotic therapies.

accumulation of antibiotic resistance genes leads to creation of

superbugs

describe superbugs

bacterial strains that are immune to all but the most drastic treatments

what are current strageties to overcome antibiotic resistance

discover new antibiotics with novel modes of actions or use different antibiotics in cocktails

describe antibiotics in “cocktails”

presuming the bacteria might survive facing one, but not two or three antibiotics simultaneously

common method for transformed cells

based on antibiotic resistance genes that are a part of the vector construct

what is e.coli

rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms.

harmless strains of e.coli can benefit host by

producing vitamin K2 and prevent colonization of the intestine with pathogenic bacteria

why is e. coli one of the best studied model organisms

can be grown and cultured easily and inexpensively in a lab setting

e. coli has served as the host organism for the majority of work with

recombinant dna

e. coli’s generation time is only under favorable conditions

20 mins