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80 Cards in this Set

  • Front
  • Back
Osmotic pressure
the force developed when two solutions of different concentrations are separated by a membrane that is permeable only to the solvent.
Solvent
the liquid, usually water, that dissolves a substance (the solute).
Solute
The substance that is being dissolved by the liquid, or solvent.
Water activity (aw)
quantitative expression of water availability. Pure water has an aw of 1.00, whereas cereals and other dried foods have aw values of .60 or lower.
Hypotonic solution
low solute, high water content. If a bacterium is placed in this solution, water will enter the cell and cause it to burst unless something is done to prevent the influx. Most bacteria have rigid cell walls that maintain the shape and integrity of the cell; thus, hypotonic solutions are not harmful to these bacteria.
Hypertonic solution

Plasmolysis
high solute, lower water content. When bacteria are placed in this solution, water leaves, and the plasma membrane shrinks away from the wall, a process known as plasmolysis. This dehydrates the cell, and it ceases to grow.
Halophiles
bacteria that prefer or require high (hypertonic) salt concentrations. (optimum salt concentration is 6.5%)
Extreme halophiles
bacteria that prefer or require very salty environments
Moderate halophiles
bacteria that live in the sea.
Haloduric
can tolerate high salt concentrations.
Isotonic solution
The concentration of solutes is the same outside and inside the bacterium. The bacterium is in osmotic equilibrium with its environment and does not change volume.
Microbicidal
To kill bacteria.
Microbiostatic
To Inhibit bacterial growth.
Disinfectants
agents, usually chemicals, used to carry out disinfection (the killing of vegetative forms of pathogenic microorganisms or viruses) and are normally used only on inaminate objects. It is not a means of sterilization.
Antibiotics
Destroy microoorganisms within the body.
Antiseptics
Destroy microorganisms on living tissue/skin. (i.e. 70% ethanol, 3% Hydrogen Pyroxide, 1% Iodine in 70% Ethanol.
Phenol Coefficient
is calculated by dividing the highest dilution of the antimicrobrial of interest, which kills all organisms after incubation for 10 minutes but not after 5 minutes, by the highest dilution of phenol that has the same characteristics. Chemicals that have a PC greater than 1 are more effective than phenol, and those that have a PC less than 1 are less effective than phenol.
Kirby-Bauer Method
The sensitive disk method that is used to determine antibiotic susceptibility. In this method, antibiotics are impregnated onto paper disks and then placed on a seeded Mueller-Hinton agar plate using a mechanical dispenser. The plate is then incubated for 16-18 hours, and the diameter of the zone of inhibition around the disk is measured to te nearest millimeter.
Zone of Inhibition
The diameter that is produced will indicate the susceptibility of resistance of a bacterium to the antibiotic. Zones of smaller diameter or no zone at all show that the bacterium is resistant to the antibiotic. A Zone fo a certain size indicates susceptibility. The biggest difference in # is used to determine which antibiotic is most effective.
Antibiograms
Antibiotic susceptibility patterns. Can be determined by comparing the zone diameter obtained with the zone diameter size for susceptibility.
Factors involved in sensitivity disk testing that must be controlled:
Size of the inoculum, distribution of the inoculum, incubation period, depth of the agar, diffusion rate of the antibiotic, concentration of antibiotic in the disk, and growth rate of the bacterium.
Mueller-Hinton Agar
Contains beef infusion, peptones, and starch, and is used for antimicrobrial susceptibility testing. The plate is large which prevents the diameters of the zones of inhibition from overlapping.
Pour plate Technique
Will yield isolated colonies. The original sample is diluted several times to reduce the microbial population sufficiently to obtain separate colonies upon plating. The small volumes of several diluted samples are added to sterile petri plates and mixed with liquid troy soy agar that has been cooled to about 48-50C. After the agar has hardened, each cell is fixed in placed and will form an individual colony if the sample is dilute enough.
CFU
Colony Forming Units. # of bacteria that can form a colony.
Dilution Factor
# colonies/ bacteria counted: #colonies (1/dilution raised to a negative #) = # x 10 raised to positive number.
4 phases of growth of a bacterial population.
Can be determined by measuring the turbidity of the population in a broth culture. 1) lag- cells are getting ready to divide. 2) Logarithmic - cells doubling, generation time, exponential growth. 3) Stationary- growth slows down and stops. 4) Death or decline- bacteria decline because due to death.
Turbidity
not a direct measure of bacterial numbers, but an indirect measure of biomass, which can be correlated with cell density during the log growth phase. Since about 10^7 bacterial cells per mL must be present to detect turbidity with the unaided eye, a spectrophotometer can be used to achieve increased sensitivity and obtain quantitative data.
Bacterial Growth Curve
increase and decrease in cell numbers versus time. Requries that aliquots of a shake-flask culture be measured for population size at intervals over an extended time.
Generation Time
the time required for a bacterial population to double. The graphical determination is made for extrapolation from the log phase. i.e. Select two points on the Absorbance scale that represent a doubling of turbidity. Using a ruler, extrapolate by drawing a line between each absorbance on the ordinate, and the plotted log or exponential phase of the growth curve. From these two points, draw perpendicular lines to the time intervals on the abscissa. From these data, the generation time can be calculated as:GT= t(A of 0.4) - t(A of 0.2). GT= 90 minutes - 60 minutes= 30 minutes. OR GT = (0.301t) / (log10 Nt - log10No). No= bacterial populaiton at point B or any other point at the beginning of the log phase. Nt= bacterial population at point b or any other point at or near the end of the log phase. t= time in minutes between b and B
Growth Rate Constant
provides Microbiologists with a valuable tool for comparison between differential microbrial species when standard growth and environmental conditions are maintained. Can be determined from the data: strainght line is obtained, the slope of which can be used to determine the value of g or k. The dimensions of k are reciprocal hours or per hour. The growth rate constant will be the same during exponential growth regardless of the component measured.
Mean generation Time
(Doubling time) can be calculated once the growth rate constant is known using: g = 1/k.
Mean Growth Rate Constant
The rate of increase of cells in proportional to the number of cells present at any particular time. k = n/t n = # generations per unit time. k = mean growth rate constant. OR k = (logNt - logNo) / 0.301t
Normal Microbiota
The microorganisms of the human body that are usually harmless, although some are potential pathogens or opportunists. These latter microorganisms may cause disease under certain circumstances.
Throat Culture
Blood Agar. Mostly Gram + cocci. S. viridans. S. aureus, S. pyogenes.
Skin Culture
Nutrient Agar- then palced on TSA plate and Gram stained. Gram + cocci and rods. S. epidermidis, Corynebacterium spp. (diphtheroids), Bacillus spp., S. viridans.
Anal Culture
EMB plate. Only Gram - Bacillus. E. coli, Enterobacter aerogenes. Do TSI slant alter then LIA, SIM deep, and MRVP.
Nasal Culture
PRMS. Gram + cocci. S. aureus.
Tongue
Sabouraud Dextrose Agar. Sacromycetes albicans.
Gum/ Teeth
Mitis Salivanus Agar. Streptococcus mutants.
Staphylococcus genus
consists of gram + cocci, 0.5 to 1.5 micrometers in diameter, usually in irregular clusters, within which pairs and tetrads are commonly seen. They are nonmotile and nonsporing. Members are facultatively anaerobic. Colonies are round, convex, mucoid, and adherent to the agar. They are chemoorganotrophic, requiring nutritionally rich media. They have respiratory and fermentative metabolism, producing acid but no gas from carbohydrates. They are able to grow on nutrient agar with 5% NaCl and are usually positive for catalase. Oxidase negative members contain cytochromes and are VP positive. Most species reduce nitrate to nitrite. Optimum growth is at 37C. Staphylococci are commensals on the skin and in the human mouth and upper respiratory tract. They can be human pathogens.
S. aureus
Most important clinical member of Staphylococcus genus. It may be isolated from the skin or mucous membranes of the body. It can cause various infections throughout the body. In addition, some are resistant to penicillin. This resistance comes about when the bacteria produce penicillinase (B- lactamase), which hydrolyzes the B-lactam ring of penicillin. Coagulase +. Catalase +. Ferments glucose (+). Mannitol Agar (+). Nitrate Reduction (+). Hemolysis (B). Mannitol Salt and DNase test agar is selective for Staph (yellow for mannitol) from nonpathogenic micrococcus spp. (no color change on mannitol)
S. epidermidis
usually a nonpathogenic member of Staphylococcus genus; however, it can be an opportunistic member. It is part of the nortmal microbiota of the skin. Coagulase -. Blood agar (-/weak). Nitrate +.
S. saprophyticus
can be isolated and may be responsible for urinary tract infections-especially in females.
Blood Agar plates.
A hemolysis
B hemolysis
G hemolysis
One of the most popular ways to isolate and identify S. aureus and other gram + cocci of medical importance. Enriched medium and differential medium. Exotoxins, hemolysins causes lysis of RBCs. The degree of hemolysis = identification of G+ cocci. A hemolysis- lysis the RBCs. a zone of greenish coloration with an indistinct margin forms around colonies growing on blood agar. The color results from patrial decomposition of hemoglobin. (formation of methhemoglobin- iron is oxidized). B hemolysis- completely lyse and digest RBCs and hemoglobin. sharply defined zone of clear hemolysis with no greenish tinge surrounding the colony. G hemolysis- No change in medium.. No hemolysis.
Streptococci
gram + cocci arranged in chains. Classified according to their hemolytic activity, immunologic properties (the serological classification of Lancefield), and resistance to chemical and physical factors.
Streptolysins
produced by S. pyogenes. Cause the lysis of RBCs in vitro, producing B-hemolysis (a clear zone of hemolysis with no color change) on blood agar. Two types of beta-lysins are produced: streptolysin O and streptolysin S. The former is oxygen-labile, while the latter is oxygen-stable. Streptolysin O is demonstrated only in deep colonies on the blood agar madium. S. pyogenes produce both types on lysins.
Group A Streptococci- S. pyogenes
classified based on a chemical substance known as C carbohydrate (an antigenic, group-specific hapten) found in the cell wall. Members are most responsible for human infections, such as tonsilitis, septic sore throat, scarlet fever, otitis media, rheumatic fever, meningitis, etc. S. pyogenes produces many enzymes and toxins such as streptokinase, leukocidins, streptodornase, hyaluronidase, hemolysins (Streptolysin O and S), nucleases, and erythrogenic toxin. B-hemolysis, Bacitracin sensitive (can't grow), CAMP -, Bile Esculin -, and resistant to SXT sensitivity.
S. pyogenes- medium of choice; optimal temperature; locations found
Medium of choice is blood agar. The colonies are opaque, domed, about 0.5mm in diameter, and surrounded by a zone of B-hemolysis. The optimal temp for growth is 35C. It may be found in the throat and nasopharyngeal areas of humans.
Group B streptococci
can be distinguished from other B-hemolytic streptococci by their production of a substance called the CAMP factor. CAMP= names of investigators (Christie, Atkins, and Munch-Peterson_ who first described the factor. This factor is a peptide that acts together with the B-hemolysin produced by some strains of S. aureus, enhancing the effect of the latter on a sheep blood agar plate. B-hemolysis, bacitracin resistant, CAMP +, Bile Esculin -, SXT (R).
Group C
viridans, S. salvarius. produce eithre A-hemolysis (as evidenced by greenish to gray pigmentation produced around the colony growth on blood agar) or no hemolysis. Viridans streptococci do not produce C carbohydrate and are usually nonpathogenic opportunists. Bacitracin (R), CAMP -, Bile Esculin -, SXT sensitive.
Group D streptococci (S. bovis) and enterococci
can be differentiated from other streptococci by using bile esculin agar slants. Group D streptococci grow readily on the bile esculin agar and hydrolyze the esculin, imparting a dark brown color to the medium. This reaction denotes their bile tolerance to hydrolyze esculin, and constitutes a positive reaction. G+ bacteria (other than Group D strept and entero) are inhibited by bile salts.
Yeasts
unicellular fungi that are spherical, ellipsoidal, or oval in shape, and usually (with the exception of the dimorphic yeasts such as Candida) do not form hyphae (fungal filaments). They are about 5-10 times larger than bacteria. Commonly reproduce asexually by budding, a process in which a new cell (called daughter cell) is formed by the parent cell from a protuberance called a bud. When reproduce sexually, they produce several types of sexual spore(ie. ascospores). The type os spore produced is very useful in classifying yeasts. Metabolic activities are also used to identify and classify yeasts. ie. Saccharomyces cerevisiae will ferment glucose but not sucrose.
Sabouraud Dextrose Agar
commonly used to isolate yeasts. It is a selective medium containing glucose and peptone, and has a low pH, which inhibits the growth of most other microoorganisms. Basic medium for culture of many molds- high sugar concentration and low pH (5.6) of this medium make it unsuitable for the growth of most bacteria, thus guarding against contamination. Most fungi grow well at pH 5.6
S. cerevisiae
used in making bread and in various alcoholic fermentations.
C. albicans
a yeast that is most commonly found in the mouth. In healthy individuals, it does not produce disease. However, if the normal microbiota of the mouth is upset, or the individual is compromised, the disease candidiasis may result.
Molds
multicellular, filamentous fungi. Grow at comparatively slow rates, often requiring several days to weeks to form macroscopically visible colonies. Usually, the growth will spread over the entire culture plate. They produce spores on brighly colored aerial hyphae. Most grow best at room temperature (25C) rather than at 35C.
Molds- Thallus, mycelium, hypha, vegetative hyphae, reproductive hyphae, spores or conidia, rhizoidal hyphae, septum, septate hyphae, coencytic hyphae.
The macroscopic aggregation (colony) of mold cells. It is composed of a mass of strands called a mycelium; each strand is a hypha. Vegetative hyphae grow on surface of culture media. They form aerial hyphae, called reproductive hyphae, that bear asexual reproductive spores or conidia. The hyphae that grow below the surface of culture media are called rhizoidal hyphae. The hyphal strand of some molds may be separated by a crosswall called a septum. Hyphae that contain septa are called septate hyphae, Molds with hyphae that lack septa are called coenocytic hyphae. Molds are classified by their sexual stages of reproduction and by appearance of the colony, organization of the hyphae, and structure and organization of the spores.
Ascomycetes
septate hyphae, conidia, exposed condispores- Penicillin
Phycomycetes
nonseptate hyphae, enclosed sporangium- Rhizopus(sporangia and zygotes)
Coagulases
enzymes that clot blood plasma by a mechanism that is similar to normal clotting. Good indicator of the pathogenic potential of S. aureus.
Coagulase positive
coagulase-producing staphylococci form a fibrin clot around themselves and avoid attack by the host's defenses. They will cause the plasma to clot by using coagulase to initiate the clotting cascade. Citrate and EDTA are usually added to act as anticoagulants and prevent false-positive results.
Coagulase negative
considered negative if they are unclotted after 4 hours. S. epidermidis.
DNase
Most pathogenic strains of staphylococci produce this nuclease enzyme. It degrades host DNA and increases the pathogenecity of staphylococci that posses it. To demonstrate the presence of DNase, agar containing dissolved DNA is spot-inoculated with staphylocci, A zone of clearing occurs because the large DNA molecule has been degraded by the enzyme, and the end products (nucleotides) dissolve in the added acid (HCl). Intact DNA does not dissolve in weak acid but rather it is precipitated by it; thus, the medium around the colonies that do not produce DNase becomes opaque. (pos=DNase degradation- S. aureus, neg=no degradation- S. epidermidis)
API 20E System
A standardized, miniature version of conventional biochemical procedures used in the identification of Enterobacteriaceae and other gram - bacteria. A total of 127 tax can be identified with this system. It is a ready-to0use, microtube system that performs 22 standard biochemical tests on pure bacterial culture from appropriate, primary isolation media. Consists of a strip containing 20 chambers, each consisting of a microtube and a depression called a cupule. The tubes contains dehydrated substrates. The substrates are rehydrated by adding a bacterial saline suspension. To create anaerobic conditions, sterile mineral oil is added to several of the microtubes. The strip is incubated for 18-24 hours at 35-37C so that the bacteria can act on the substrates. The strip is read by noting the color changes after various indicator systems have been affected by the metabolites and added reagents. The identification of the unknown bacterium is achieved by determining a seven-digit profile index number and consulting the API 20E profile recognition system or the API 20E profile index booklet. Charts can also be used to determine the unknown bacterium.
Enterotube II system
faster, easy, and cost efficient in the identification of gram -, glucose fermentating, oxidase-negative Enterobacteriaceae. Consists of a single tube with 12 compartments, each containing a different agar-solidified culture medium. Compartments that require aerobic conditions have small openings that allow air in; those requiring anaerobic conditions have a layer or paraffin waxon the top of the media. There is a self-enclosed inoculating needle. This needle can touch an isolated bacterial colony and then in one movement can be drawn through the 12 compartments, inoculating the test media. 15 standardized tests are performed. After 18-24 hours of incubation, the color changes that occur in each of the compartments are recorded and intepreted according to the manufacturer's instructions. This is done by determining a five-digit code from the results and consulting a coding manual, or by comparing the results obtained with those outlined in a differential chart provided by the manufacturer. This quick multitest system also has a computer-assisted program called ENCISE (Enterobacteriaceae Numerical Coding and Idenitfication System for Enterotube).
Cardinal Temperatures:
Minimum, maximum, and optimum
Minimum growth temperature
The lowest temperature at which growth can occur
Maximum growth temperature
The highest temperature at which growth can occur
Optimum growth temperature
The temperature at which the rate of cellular reproduction is most rapid. The optimum temperature for growth of a given microorganism is correlated with the temperature of the normal habitat of the microorganism.
Psychrophiles
Microorganisms that grow well at 0C and have an optimum growth temperature of 15C and lower
Psychrotrophs
Falcultative psychrotrophs that can grow at 0 to 7C
Mesophiles
Microorganisms that have a growth optima from 25-45C. Most microorganisms fall into this category.
Thermophiles
Microorganisms that have a growth optima of 55C and higher.
Hyperthermophiles
Microorganisms that have a growth optima of 90C and higher.
Thermoduric
Bacteria that survive bioling though they are unable to grow. Many of the spore formers (Bacallus subtilis) can withstand boiling for 15 minutes because of their heat-resistant endospores.
pH
dramatically affects prokaryotic growth because it affects the activity of the enzymes. Each microbrial species posses a definite pH growth range and distinct pH growth optimum.
Acidophiles
Microorganisms with a growth optimum between pH0.0 and 5.5. Most molds and yeast (4-6). Also algae.
Neutrophiles
Microorganisms with a growth optimum between pH 5.5 and 8.0. Majority of bacteria and protozoa.
Alkalophiles
Microorganisms with a growth optimum between pH 8.5 and 11.5
Buffers
produce a pH equilibrium by preventing bacteria from producing metabolic acids that may lower the pH and inhibit their growth. buffers neutralize these acids.