Practical Flashcards
(100 cards)
1
Q
normal microbiota
A
- regularly found in specific areas of the body
- specificity depends on environmental factors such as pH, oxygen concentration, amount of moisture present, and types of secretions associated with each anatomical site
2
Q
skin native microbiota
A
- staphylococci (S. epidermidis)
- streptococci (a-hemolysis, nonhemolytic, and enterococci)
- ditheroid bacilli
- yeasts
- fungi
3
Q
eye conjunctiva normal microbiota
A
- staphylococci
- streptococci
- diptheroids
- neisseriae
4
Q
upper respiratory tract native microbiota
A
- staphylococci
- streptococci
- enterococci
- diptheroids
- spirochetes
- members of genera Branhamella, Neisseria, and Haemophilus
5
Q
Mouth and teeth normal microbiota
A
- anaerobic spirochetes and vibrios
- fusiform bacteria
- staphylococci
- aerobic levan-producing and dextran-producing streptococci responsible for dental caries
6
Q
intestinal tract normal microbiota
A
- upper intestine: lactobacilli and enterococci
- lower intestine and colon: 96-99% anaerobes(Bacteroides, Lactobacillus, Clostridium, and Streptococcus); and 1-4% is aerobes (coliforms, enterococci, and small amount of Proteus, Pseudomonas, and Candida species)
7
Q
Genitourinary tract normal microbiota
A
- staphylococci
- streptococci
- lactobacilli
- Gram-negative enteric bacilli
- clostridia
- spirochetes
- yeasts
- protozoa (trichomonas species)
8
Q
chocolate agar plate
A
- inoculated to detect Neisseria species by means of the oxidase test
- used principally in the cultivation of members of the genera Neisseria and Haemophilus which are fastidious microorganisms and require a growth medium low in oxygen and rich in CO2
- members of this genus are recognized when the colonies develop coloration that is pink to dark purple upon addition of p-aminodimethylaniline oxalate following incubation
9
Q
Mueller-Hinton Tellurite agar
A
- inoculated to demonstrate the presence of diptheroids which appear as black, pinpoint colonies on this medium
- coloration is due to the diffusion of the tellurite ions into the bacterial cells and their subsequent reduction to tellurium metal which precipitates inside the cells
10
Q
Saburaud agar plate
A
- inoculated to detect yeasts and molds
- yeast cells develop pigmented or nonpigmented colonies that are elevated, moist, and glistening
- mold colonies will appear as fuzzy, powdery growths arising from a mycelial mat in the agar medium
11
Q
lactophenol cotton-blue
A
- stains molds and yeasts
- stain consists of phenol which kills any live organisms, lactic acid which preserves the structure of fungi, and cotton blue which stains chitin (an essential component of fungal cell walls)
12
Q
Common causes of UTI
A
- primarily caused by E. coli, and secondarily by Staphylococcus saprophyticus
- other bacteria: Klebsiella, Proteus, Pseudomonas, and Enterococcus
13
Q
Quantitative limit that indicates a UTI
A
- isolated pure colonies of 10^4 to 10^5 CFU/mL or greater are considered significant and indicative of a UTI
- plates that have a significant count with a variety of 3 or more different microorganisms are usually indicative of a contaminated, improperly collected sample (esp. if there are gram + organisms present)
14
Q
CHROMagar
A
- non-selective medium that contains chromogenic (capable of being converted into a pigment or dye) substrates that produce different colored compounds when they are degraded by specific microbial enzymes
- used to cultivate and differentiate organisms that are routinely isolated from UTIs based on the colors produced by the degradation of the specific chromogenic substances
- can be used quantitatively(determine number of infective organisms in a urine sample) and qualitatively (identify the species of microorganisms implicated in a UTI
15
Q
Mannitol Salt Agar
A
- selective for salt-tolerant organisms like staphylococci
- differential for the ability to ferment mannitol
- following incubation, mannitol-fermenting organisms have a yellow halo surrounding growth, nonfermenting strains do not
16
Q
Staphylococci
A
- gram positive cocci
- include pathogenic and generally non-pathogenic strains
- mesophilic
- non-spore forming
- often found on the skin and mucous membranes
17
Q
S. aureus
A
- can cause many types of infections
- abcesses, biols, sepsis, pneumonia, enteritis, toxic shock, necrotizing fasciitis
18
Q
S. saprophyticus
A
- generally avirulent
- may cause UTI
19
Q
S. epidermidis
A
- generally avirulent
- may cause skin lesions and endocarditis
20
Q
Group A strep
A
- S. pyogenes
- beta hemolytic
- pathogenic
- cause strep throat, impetigo, necrotizing, fasciitis, etc
21
Q
Group B strep
A
- A. agalactiae
- beta hemolytic
- pathogenic, especially in neonates
22
Q
Group C strep
A
- S. equi
- beta hemolytic
- can cause some infections
23
Q
Group D strep
A
- Enterococcus
- alpha or gamma hemolytic
- gut commensals that can cause UTIs and endocarditis
24
Q
coagulase test
A
- production of coagulase is indicative of an S. aureus strain
- converts fibrinogen to fibrin in host tissue–> fibrin meshwork that is formed by this conversion surrounds the bacterial cells or infected tissues, protecting the organism from nonspecific host resistance mechanisms like phagocytosis
- coagulase test tube is periodically examined for fibrin formation/coagulation
- clot formation within 4 hours= POSITIVE result(indicative of S. aureus)
- absence of coagulation after 24 hours of incubation is a negative result (avirulent strain)
25
DNase test
- generally, coagulase positive staphylococci also produce the hydrolytic enzyme DNase--> this test reconfirms the identity of S. aureus
- organism is grown on agar containing DNA
- DNase activity is determined by the addition of 0.1% toluidine blue to the surface of the agar
- ANase-positive cultures capable of DNA hydrolysis will show a rose pink halo around the area of growth
- absence of halo= NEGATIVE result (no DNase production)
26
Novobiocin sensitivity
- this test is used to distinguish S. epidermidis from S. saprophyticus
- inoculate Mueller-Hinton agar plate with the test organism and application of a 30 microgram novobiocin antibiotic disk to the surface of the agar
- following incubation, the sensitivity of an organism to the antibiotic is determined by the Kirby-Bauer method
- S aureus, S epidermidis are susceptible to novobiocin
- S saprophyticus is resistant
27
Bacitracin test
- filter-paper disc impregnated with 0.04 unit of bacitracin is applied to the surface of a blood agar plate streaked with the organism to be identified
- following incubation, the appearance of a zone of growth inhibition surrounding the disc is indicative of Group A strep (Group A is susceptible to Bacitracin)
- absence of this zone suggests a non-Group A organism
28
CAMP test
- identifies Group B streptococci
- Group B Strep produce a peptide, the CAMP substance(a bacterial toxin) that acts in concert with the beta-hemolysis produced by some strains of Staph aureus, causing inc hemolytic effect
- resultant effect appears as an arrow shaped zone of hemolysis adjacent to the central streak of S. aureus growth
- non group-B streptococci do not produce this reaction
29
ELISA
- enzyme-linked immunosorbant assay
- rely on antibodies to detect the presence of antigens in liquid samples
- ELISA can detect minute amounts of disease agents in samples such as body fluids
- home pregnancy tests, ovulation tests, disease detection in people, animals, and plants, detecting illegal drug use, testing indoor air quality, determining if food is labelled properly
30
antigen for ELISA
- chicken gamma globulin
- serves as a generic representation of any hypothetican antigen, protein, or otherwise
31
primary antibody
- the antibody used to recognize and bind to antigens like disease agents
- polyclonal rabbit antibody raised against chicken gamma globulin
32
secondary antibodies
- recognize and bind to primary antibodies
- made in animals of a different species than that used to make the primary antibody--> provokes an immune response
- goat immunized with rabbit IgG to make the secondary antibodies
- frequently labeled to make them visible (Horseradish peroxidase produces blue color)
33
what sources might contaminate food/water
- soil water
- food utensils
- enteric microorganisms of hummans and animals (find their way into the soil and water from which they contaminate plants and are carried by wind currents onto utensils or prepared and exposed food items)
- food handlers (microorganisms on hands and clothing are easily transmitted)
- animal hides and feeds (microorganisms may migrate into the musculature of the animals and remain viable following its slaughter)
34
What roles do BHI and EMB play in this experiment
- EMB allows forthe indication of coliform bacteria and other enteric organisms in food--> indicates fecal contamination
- BHI indicates presence of fastidious bacteria; often suggests presence of pathogens
35
Bacillary dysentery, typhoid fever, cholera, paratyphoid fever
- responsible for intestinal infections
- associated with contaminated water by feces
- human sewage is one of the principal causes of fecal contamination of waters (also cattle/domestic animals, wild animals)
36
indicator organisms
- easily detected
- commonly associated with a wide variety of fecal sources
- standard indicator organism= E. coli (because E coli are found in high numbers in most fecal samples, persist in the environment longer than most pathogens, relatively easy to cultivate, numerous methods for identification)
37
coliforms
- indicators of fecal contamination
- gram negative
- non-spore forming baccilli that ferment lactose with the production of acid and gas that is detectable after 24 hour incubation period
38
Presumptive test
- detects coliform bacteria
- water is added to lactose broth with inverted glass vial
- these bacteria can ise lactose as a carbon source
- lactose fermentation broth also contains a surface-tension depressant= bile salts= suppresses growth of organisms other than coliform bacteria
- development of gas in any of the tubes is "presumptive" evidence of the presence of coliform bacteria in the sample
39
most probable number test
- part of presumptive test that enables the microbiologist to get an idea of the number of coliform organisms
-estimated by determining the number of tubes in each group that show gas following the incubation period
40
Lauryl Tryptose broth
- lauryl tryptose broth used with lactose is used for the culture of water samples to perform a presumptive test for the presence of coliform bacterial contamination
- lauryl sulfate is a detergent that selects for members of the coliform group (Enterobacteruaceae)
41
Brilliant Green Lactose Broth
- selective medium containing lactose and inhibitory bile salts in the medium
- test tube contains Durham tube to collect gas produced by lactose fermentation
- positive test= displays turbidity and gas production
42
confirmed test
- performed using BGLB
- positive test= turbidity and gas production
- another test is necessary to determine if pathogenic E coli is present--> completed test
43
completed test
- the selective and differential media like EMB or endo agar be streaked from a positive lactose broth tube obtained from the presumptive test
- EMB contains methylene blue which inhibits gram positive organisms; in acidic environment, EMB produces green sheen that is characteristic of E coli (major indicator of fecal contamination)
- Endo agar has fuchsin dye in colorless state; production of acid produced by coliform bacteria= fuchsin forms a dark pink complex that turns the E coli colonies and surrounding medium pink
44
Bactericidal
kills the microbes
45
bacteriostatic
inhibits the reproductive capacities of the cells and maintains the microbial population at a constant size
46
methods for control of microbial growth
- cell wall injury
- cell membrane damage
- alteration of the colloidal state of cytoplasm
- inactivation of enzyme
- interference with the structure and function of the DNA molecule
47
cell wall injury
- lysis of the cell wall= protoplast is susceptible to osmotic damage, and a hypotonic environment may cause lysis of the vulnerable protoplast
- or some agents inhibit cell wall synthesis which is essential during microbial cell production--> failure to synthesize a missing segment of the cell wall results in an unprotected protoplast
48
cell membrane damage
- can be the result of lysis of the membrane which will cause immediate cell death
- selective nature of the membrane may be affected without causing its complete disruption--> may be loss of essential cellular molecules or interference with the uptake of nutrients
- in both cases, metabolic processes will be disrupted
49
alteration of the colloidal state of cytoplasm
- certain agents cause denaturing of cytoplasmic proteins --> produces irreversible cell damage
- uncoiling of these macromolecules leads to coagulation of the proteins, which in their clumped state are biologically inactive
50
inactivation of enzymes
- results from the activity of certain physical and chemical agents
- cell cannot perform essential life functions
- inactivation of enzymes by these agents occurs through the mechanisms of competitive or noncompetitive inhibition
51
interference with the structure and function of the DNA molecule
- DNA is the control center of the cell and may also represent a cellular target area for destruction or inhibition
- come agents have an affinity for DNA and cause breakage or distortion of the molecule, thereby interfering with its replication and role in protein synthesis
52
antiseptics
chemical substances used on living tissue that kill or inhibit the growth of vegetative microbial forms
53
disinfectants
chemical substances that kill or inhibit the growth of vegetative microbial forms on nonliving materials
54
chemotherapeutic agents
chemical substances that destroy or inhibit the growth of microorganisms in living tissues
55
factors influencing the efficiency of disinfectants and antiseptics
- concentration
- length of exposure
- type of microbial population to be destroyed
- environmental conditions (temperature, pH, type of material on which the microorganisms exist)
56
concentration
- the concentration of a chemical substance markedly influences its effect on microorganisms, with higher concentrations producing more rapid death
- toxicity of the chemical to the tissues being treated and the damaging effect on nonliving materials must also be considered
57
length of exposure
- all microbes are not destroyed within the same exposure time
- sensitive forms are destroyed more rapidly than resistant ones
- longer the exposure to the agent, the greater its antimicrobial activity
- toxicity and environmental conditions must be considered in assessing the length of time necessary for disinfection or asepsis
58
type of microbial population to be destroyed
- microorganisms vary in their susceptibility to destruction by chemicals
- bacterial spores are the most resistant forms
- capsulated bacteria are more resistant than non-capsulated
- acid-fast are more resistant than non-acid fast
- older, metabolically less active are more resistant than younger cells
- type of organism present will change the choice of agent
59
temperature
- cells are killed as the result of a chemical reaction between the agent and cellular component
- as increasing temperatures inc the rate of chemical reactions, application of heat during disinfections markedly increases the rate at which the microbial population is destroyed
60
pH
- may not only affect the microorganism, but also the compound
- extremes in pH are harmful to many microorganisms and may enhance the antimicrobial action of a chemical
- deviation from a neutral pH may cause ionization of the disinfectant--> depending on agent, can inc or dec the chemical's microbicidal action
61
type of material on which the microorganisms exist
- the destructive power of the compound on cells is due to its combination with organic cellular molecules
- if the material is primarily organic (blood, pus, tissue fluids), the agent will combine with these extracellular organic molecules, and its antimicrobial activity will be reduced
62
broad spectrum antibiotics
effective against both gram positive and gram negative bacteria
- beta lactams
- glycopoptide
- intracellular
63
beta lactams
- inhibit peptidoglycan synthesis
- broad spectrum
64
glycopeptide
- inhibit peptidoglycan chain elongation
- broad spectrum
65
intracellular
- inhibit peptidoglycan subunit synthesis
- broad spectrum
66
narrow spectrum antibiotics
effective against only a subset of bacteria
- usually either grap positive OR gram negative
- colistin (polymyxin)
67
Colistin (Polymyxin)
- inserts into outer membrane of gram negative bacteria
- narrow spectrum
68
antibiotics
synthesized and secreted by some bacteria, actinomycetes, and fungi that destroy or inhibit the growth of other microorganisms
- some antibiotics are lab synthesized or modified, however, their origins are living cells
69
synthetic drugs
are synthesized in the lab
70
competitive inhibition
- substrate molecule is prevented from binding to the active site of an enzyme by a molecule that is structurally similar to the substrate
- ex: Sulfadiazine produces a static effect on a wide range of microorganisms--> active component of the drug acts as anti-metabolite that competes with the essential metabolite, during the synthesis of folic acid in the microbial cell
71
antimetabolite
- chemical that competes with, replaces, or inhibits a specific metabolite of a cell, interfering with the cell's normal metabolic functioning
- mimics metabolite but disrupts metabolism
72
essential metabolite
- normal substance involved in metabolism
- substrate, intermediate, product in a metabolic pathway
- what the enzyme naturally acts on or produces
- natural substrate outcompeted by inhibitor/antimetabolite
73
Kirby-Bauer Antibiotic Sensitivity test
- standardized filter paper disc-agar diffusion procedure
- determines drug susceptibility of microorganisms
- allows determination of the efficacy of a drug by measuring the diameter of the zone of inhibition that results from the diffusion of the agent into the medium surrounding the disc
- filter discs are impregnated with specific concentrations of antibiotics and placed on the surface of an agar plate seeded with test organism
- medium of choice= Mueller-Hinton agar
- plates are heavily inoculated with a standardized inoculum with a cotton swab to ensure the confluent growth of the organism
- discs aseptically applied to the surface of the agar plate at well-spaced intervals, once applied, each disc is gently touched with a sterile applicator stick to ensure firm contact with the agar surface
74
zone of inhibition
- zone of clearing
- results from diffusion of the agent into the medium surrounding the disc
75
how to handle resistant colonies when taking measurements of zone of inhibition
-- check for resistant colonies within the zone of inhibition
- when present, the distance of resistant colonies should be measured rater than measuring the more sensitive outer ring of growth
76
minimum possible zone of inhibition
- filter disc is 6 mm in diameter and measurements of 6 mm are considered to have no zone of inhibition
77
autoclaving
- free flowing steam under pressure
- double-walled metal vessel that allows steam to be pressurized in the outer jacket
- saturated steam is released into inner chamber where there is no air
- steam in the inner chamber can reach temperatures in excess of 100 degrees C
- pressure of 15 pounds/inch squared achieves a temperature of 121 degrees C and sterilizes in 20 minutes
78
tyndallization
free flowing steam at 100 degrees C
- intermittent/fractional sterilization
- exposure of material to free-flowing steam at 100 degrees C for 15 minutes on 3 consecutive days with intermittent incubation at 37 degrees C
- steaming kills all vegetative cells
- any spores that may be present germinate during the period of incubation and are destroyed during subsequent exposure to a temperature of 100 degrees C
- repeating this procedure for 3 days ensures germination of all spores and their destruction in the vegetative form
- used for sterilization of materials that are composed of thermolabile chemicals and that might be subject to decomposition at higher temps
79
pasteurization
- use of lower temperatures
- exposed thermolabile products like milk, wine, and beer for a given period of time to a temp that is high enough to destroy pathogens and some spoilage-causing microorganisms that may be present, without necessarily destroying all vegetative cells
- high temp, short time (flash) procedure: requires temp of 71 degrees C for 15 seconds
- low temperature, long-time method: 63 degrees C for 30 minutes
80
exposure to boiling water for 30 minutes
- disinfection only
- all vegetative cells will be killed but not necessarily the more heat-resistant species
81
heat resistance of bacterial vegetative cells and spores
- bacterial spores: require temps above 100 degrees C for destruction
- bacterial vegetative cells: killed at temps of 60 degrees C to 70 degrees C in 10 minutes
82
Relative heat resistance of fungal cells and spores
- fungi can be killed at 50 to 60 degrees C
- spores: require 70 to 80 degrees C for 10 minutes for destruction
83
gamma radiation
originates from unstable atomic nuclei
- ionizing form of radiation
84
X- radiation
- originating from outside of the atomic nucleus
- ionizing form of radiation
85
Gamma radiation and X-radiation
- transfer their energy through quanta (photons) to the matter through which they pass, causing excitation and the loss of electrons from molecules in their paths
- nonspecific= any molecule in the path of radiation will undergo ionization
- water can produce free radicals, which can combine and form hydrogen peroxide which is highly toxic to cells lacking catalase/peroxidases
- can be used for sterilization, particularly of thermolabile materials
86
ultraviolet light
- lower energy content than ionizing radiations
- can produce a lethal effect in cells exposed to the low penetrating wavelengths in the range 210 nm to 300 nm
- nucleic acids absorb UV light--> DNA damage
- pyrimidines especially absorb UV light--> thymine dimerization
- low penetrability= cannot be used as a means of sterilization, practical only for surface or air disinfection
87
thymine dimerization
- covalent bonding of 2 adjacent thymine molecules on one nucleic acid strand in the DNA
- dimer formation distorts configuration of the DNA molecule--> interferes with DNA replication and transcription during protein synthesis
88
transient microbes
- not normally found on the skin
89
native microbiota
indegenous to the skin
90
chromosomal DNA
where a mutation of chromosomal DNA occurs
- can be spontaneous or induced and is usually specific to one type of antibiotics
91
Extrachromosomal DNA
- where bacteria acquire resistant(R) plasmids that carry resistant genes by conjugation or transduction
- resistance can be to one or more types of antibiotics
- plasmid DNA usually contains genes for one or more traits that may be beneficial to bacterial survival
- in nature, bacteria can transfer plasmids back and forth allowing them to share these beneficial genes--> allows bacteria to adapt to new environments
92
mechanisms of antibiotic resistance
- blocking entry
- enzymes
- alteration of targets
- alteration of membrane permeability
- alteration of metabolic pathways
93
blocking entry and resistance
- alteration of porins present in the outer membrane of gram-negative bacteria that prevent the passage of the antibiotic through the outer membrane
- applies only to gram negative bacteria (gram positive lack outer membrane)
94
enzymes and resistance
- enzymes that destroy/inactivate antimicrobial agents
- Beta-lactamase
95
alteration of targets and resistance
- alteration of antibiotic targets like ribosomes, where the targeted portion is altered and the formerly inhibited reaction occurs
96
alteration of membrane permeability and resistance
- change the nature of proteins in the membrane like efflux pumps so the antibiotic is pumped out of the cell at a higher rate
97
alteration of metabolic pathways and resistance
- bacteria are able to by-pass the reaction inhibited by the antimicrobial
98
genetic transformation
- change caused by genes
- involves insertion of a gene or set of genes into an organism in order to change the organism's trait
99
selection
- selective agent= antibiotic
- selection for cells that have been transformed with pGreen DNA is accomplished by growth on plates containing the antibiotic
- transformed cells harboring the pGreen plasmid will grow on antibiotic plates containing ampicillin whereas those cells that did not acquire the plasmid will be killed by the antibiotic
- transformed cells will appear white on plates, upon UV exposure, the bacteria will glow green (production of GFP)
100
heat shock
- increases bacterial uptake of foreign DNA
- increases permeability of the cell membrane to DNA
