Micro Lab Exam 2

Closed System

No nutrients added later and no wastes removed

Lag, Exponential, Stationary, and Death

List the 4 growth phases in microbial growth curve

Lag phase

adjustment period where there is initially no cell division

Exponential (log) phase

time of max growth that is limited almost exclusively by the organism's reproductive potential

Stationary phase

Period where the growth rate declines to where the death rate is more or less equal to the reproductive rate

Death phase

The nutrients are depleted or the medium becomes toxic to the organism which causes a decline in the population

Continuous culture

an open system in chemostat, maintains a continuously growing microbial culture at exponential phase, supplies fresh nutrients continually, removes waste and products continually and is used in industries to extract useful primary metabolites, including amino acids, organic acids, etc.

Bioluminescence

Emission of light by living organisms, often gram neg rods, only occurs in presence of O2 and when population density has reached a certain threshold, requires enzyme lucifase and FMNH2

Quorum Sensing

The ability of bacteria to regulate gene expression based on density of cells

Fluorescence

To emit light of a different color than the light that is being received

Differentiate based on fermentation or oxidation of sugars; uses bromothymol blue to indicate pH change, uses mineral oil, green/blue shows no oxidation, while yellow shows oxidation, used to separate Enterobacteriaceae from Pseudomonas and Alcaligenes

Oxidation-Fermentation Test

Differentiate based on fermentation of specific carbohydrates to separate members of Enterobacteriaceae from other gram neg rods; phenol red is indicator, has tube to catch gas bubbles, acid produced turns yellow, gas produced gets bubble, turns pink is alkaline due to peptone degradation

Phenol Red Broth (Carbohydrate fermentation test)

Amylase is used to hydrolyze polysaccharides, done on petri dish, uses iodine, clearing around bacteria indicates amylase is present

Starch Hydrolysis (Amylase Test)

Casein is milk protein and a source of amino acids for organisms that can hydrolyze it, casease hydrolyzes casein, clearing around growth indicates casease is present

Casein Hydrolysis

Gelatin is protein derived from connective tissue in animals, gelatinase serves as collagenase and allows organism to be more invasive if infecting an animal; done in slant, if liquified, gelatinase is present, if still solid, gelatinase is negative

Gelatin Hydrolysis

Urea is product of decarboxylation of amino acids, hydrolyzed to ammonia and CO2 by urease; done in test tubes, read at 24 hours, uses phenol red as indicator, will turn pink if urease is positive, yellow or brown if negative for urease

Urea Hydrolysis (Urease Test)

include Indole, Methyl Red, Voges Proskauer, Citrate, and differentiate members of Enterobacteriaceae and distinguish them from other Gram neg rods

IMViC tests

Differentiation of enterobacteriaceae, salmonella, and shigella; uses Kovac's reagent with indole to form red color, sulfur reduction has occurred if solution turns black, red layer in alcohol top layer if organism produces tryptophanase and hydrolyzes tryptophan into indole and pyruvate; murky growth radiating out from stab means motility

Indole Test using SIM medium

Tests for mixed acid fermentation, uses methyl red dye to test pH which is red at 4.4 but yellow above 6.2 on pH scale; red color is positive for mixed acid fermentation

Methyl Red test

Tests for conversion of glucose products to acetoin and 2,3-butenadiol; reagents react with acetoin to form diacetyl, which reacts with guanidiine nuclei from peptone to produce red color, which is the positive result color, can take 1 hour

Voges-Proskauer test

Citrate is component of Krebs cycle, sodium citrate only carbon source, ammonium phosphate only nitrogen source, only cells that have citrate-permease will grow, uses bromothymol blue which turns from green to blue as pH goes up, blue color is a positive result for citrate, green is negative

Citrate Slant

Tests for Nitrate reductase which reduces nitrate (NO3) to nitrite (NO2), use durham tubes to collect any gases made, any gas initially made means nitrate reduction has occurred; then add reagents, if it turns red, positive for nitrate reduction; if not add zinc to remaining tubes, here red color means negative result for nitrate reduction

Nitrate Reduction Test

Detects the presence of catalase which protects cells from hydrogen peroxide; differentiates Staph and Micrococcus from Strepto, entero, and lactococcus; if bubbles are present, it is positive for catalase

Catalase test

Tests for presence of cytochrome C oxidase, uses oxidase reagent, dark blue/purple within 20 seconds indicates that cytochrome C oxidase is present, no color change means no cytochrome C oxidase

Oxidase test

Found in S. aureus that makes it resistant to antimicrobials and body's immune response, most staph species don't produce coagulase, makes fibrin barriers around bacterial cells which prevents phagocytosis; tube test detects presence of either bound or free coagulase, if medium is solid within 24 hours, it is positive for coagulase; slide test only detects bound coagulase, if there is clumping, cells are positive for coagulase

Coagulase Test

Tests for Staphylococcus aureus, uses coagulase test, if positive for coagulase it is S. aureus, if negative for coagulase, it is S. epidermis

Rapid Staph test

Take throat swab, if two reddish-purple colored lines, it is positive for strep, if only one colored line, then it is negative for strep

Rapid Strep test

Sterilization

any process that kills or destroys all forms of life, including bacterial endospores, usually achieved by physical methods

Disinfection

any process that reduces a microbial population on an inanimate surface to an acceptable level, achieved using a disinfectant, usually a chemical

Antisepsis

any process that reduced a microbial population on living tissue to an acceptable level, achieved using an antiseptic, usually a chemical

-cidal

suffix used to identify agents that kill or destroy microorganisms

-static

suffix used to identify agents that do not kill, but only inhibit the growth of microorganisms

Dry Heat

kills organisms by oxidizing proteins and lipids, need high temps and long heating times such as 160 C for 2 hours, used for glassware and metal objects

Moist Heat

also called autoclaving, denatures proteins and membrane lipids, uses steam under pressure, uses 121 C at 15 psi for 15 min

Non-ionizing radiation

UV light, is used for disinfection or sterilization, induces formation of thymine dimers, effective between 290-220 nm and is optimal at 260 nm

Ionizing radtions

using x-rays or gamma-rays and is used for sterilization, induces double stranded breaks in DNA that cannot be repaired, effectiveness is proportional to amount of DNA, good penetrating power and can be used to sterilize prepackaged items

Filtration

uses filters (0.45 or 0.22 um pore size) to physically remove microorganisms from a liquid solution

Chemotherapeutic agent

A chemical that interferes directly with the proliferation of microorganisms at concentrations tolerated by the host

Antibiotic

A type of chemotherapeutic agent that may be naturally occurring or chemically synthesized. Naturally occurring antibiotics are primarily produced by sporulating organisms at the time of sporulation. However, once identified the antibiotics may be chemically modified to alter their effectiveness.

Antimycotics

kill or inhibit the growth of fungi

Antivirals

inhibit the replication of viruses within the host cells

0.5 McFarland standard, agar plate swabbed 3 different directions, place disks evenly across the surface

Kirby Bauer Method

Bacitracin interferes with synthesis of peptidoglycan which inhibits bacterial cell wall synthesis, any zone of inhibition 10 mm or greater is interpreted as being bacitracin susceptible, used to differentiate B-hemolytic, group A streptococcus pyogenes from other B-hemolytic streptococci

Bacitracin Susceptibility test

Novobiocin interferes with ATPase activity, should produce zone of inhibition 16 mm or greater, used to differentiate coagulase negative staphylococci, most often used to identify staph saprophyticus, a common cause of UTIs in women

Novobiocin Susceptibility test

interferes with ATPase activity and ATP production, 14 mm zone of inhibition, differentiates strep pneumoniae from other a-hemolytic sprep, as s. pneumoniae is the only strep susceptible to optochin

Optochin Susceptibility test