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MicroLab 3
Microbiology lab test 3, enumeration, heat killing, and antibiotics
| Term | Definition |
|---|---|
| Enumeration | determine number of cells, usually to find out cell concentrations |
| Direct methods of enumeration | counting chambers (hemocytometer), flow cytometry, weighing the mass |
| Indirect methods of cell enumeration | viable cell count using serial dilution |
| CFU range (for counting on a spread plate) | 30-300 |
| CFU (stands for?) | Colony forming unit |
| Serial dilution | series of individual measured transfers, starting with the undiluted sample then moving from one tube to the next reducing the cell density by a known factor |
| OCD / Original cell density (formula) | CFU / (dilution * volume plated) |
| dilution (formula) | (volume taken) / (volume taken +volume of diluent) |
| Dilution Factor | inverse of the dilution (just flip the number over) |
| If the D.F. is 1/3 then the dilution is | 3 |
| If the D.F 1/12 then the dilution is | 12 |
| Five factors that may affect the bacteria kill rate | 1.Endospores,2.Types of lipids, 3.cell concentration, 4.concentration of chemical, 5.presence of other substances |
| Name 2 bacteria types known to form endospores/capsules | Bacilus and Clostridium |
| Why would the concentration of cells affect the bacteria kill rate? | It is harder to kill every bacteria if are more cells present |
| Name a type of lipid that affects the kill rate of a bacteria | mycolic acid in Mycobacterium |
| What are the 3 levels of control? | Decontamination, Disinfection, Sterilization |
| Decontamination | physical reduction of microorganism load |
| Is it safe to NOT wear personal protective equipment when decontamination has been used | Yes |
| Disinfection | Removes 99.9 percent of microorganism |
| Sterilization | complete removal, including endospores |
| Endospores | Dormant form of bacteria covered with keratin; formed in response to damage by temperature, chemicals, or limited nutrients |
| Heat Kill | disrupts cell membrane and denatures proteins |
| Examples of dry heat (heat killing) | over, Bunsen burner, incinerator |
| Examples of moist heat | Autoclave, Boiling water |
| Autoclave parameters | Steam at 121 Celsius, 15 psi (pressure) for 15 min (which is equal to 160 C of hot air for two hours) |
| Does boiling water at 15 min at 100 Celsius kill vegetative cells and endospores? | Vegetative cells = yes Endospores = no |
| Pasteurization | heating at a low temperature, only achieves disinfection, usually used for food (which cannot withstand very high temps) |
| UV light (definition and types) | A type of electromagnetic energy. (UV-A, UV-B, UV-C) |
| Wavelengths of the 3 types of bacteria | UV-A : 315-400 nanometers UV-B: 280-315 nm UV-C: 100-280 nm |
| What type of UV-light is the most harmful to bacteria? | UV-C at 254 nm |
| How does UV-C light cause damage? | IT damages the DNA by causing pyrimidine dimers |
| What process can sometimes repair bacteria from UV-light damage if the damage is small? | Photolyase or dark repair |
| Oligodynamic action | action by heavy metals to kill bacteria (toxic) |
| Metals that have olgiodyanmic action | zinc, silver, copper |
| What change in the materials used for doors caused the spread of infection? | Door knobs that used to be made of brass (zinc and copper alloy) are now made of stainless steel or aluminium. Stainless steel and aluminum do not have oligodynamic action |
| Brass door knobs disinfect themselves every _____? | 8 hours |
| This is put into the eyes of babies in order to prevent infection | Silver nitrate |
| Antimicrobial agents testing process | 1. Beads are coated with bacteria 2. Beads are exposed to germicide 3. Beads are transfer to growth medium 4. No growth = effective germicide |
| What percentage of the time do germicides need to be effective in order to be approved of by the FDA or FDA? | 95% |
| Bactericidal vs. Bacteriostatic | Bactericidal: kills Bacteriostatic: inhibits growth |
| Alcohol (mechanism) | 1. damages plasma membrane 2. denatures protein |
| Alcohol (effectiveness) | -more effective against Gram negative -70% alcohol is more affect because water aids in killing and 100% alcohol is very volatile |
| Hydrogen peroxide (H2O2) (mechanism) | produces superoxide radical(O2-) and hydroxyl (OH-)oxidizing agent |
| Hydrogen peroxide (effectiveness) | -final products are water and oxygen (rapidly degrades into this products especially if exposed to light; reason it is in brown bottles instead of clear) |
| Triclosan (mechanism) | inhibits fatty acid synthesis |
| Triclosan (effectiveness) | -chlorinated aromatic compound with phenol and ether group -ingredient in hand soap -was used in control of MRSA |
| Chlorine/ Bleach (mechanism) | causes formation of irreversible aggregates, forms hypochlorous acid, full mechanism unknown |
| Zone of inibition | area in which bacteria is unable to grow |
| Antiseptic (applied to?) | antimicrobial; applied to living tissue |
| Antibiotic (applied to ?) | antmicrobial; taken into the lymphatic system to destroy bacteria |
| Disinfectant (applied to ?) | antimicrobial; applied to non-living objects |
| Susceptibility (to antibiotics) | the antibiotic is successful; bactericidal or bacteriostatic effect |
| Resistance (to antibiotics) | the antibiotic is unsuccessful; still able to live and grow |
| Chloramphenicol (cell target) | prevent peptide bond formation during translation |
| Chloramphenicol (resistance) | 1. poor uptake of drug 2. inactivation of drug |
| Ciprofloxacin (cell target) | interferes with DNA replication |
| Ciprofloxacin (resistance) | 1. altered cell target 2. poor uptake of drug |
| Penicillin and Ampicillin (cell target) | inhibits cross-linking of peptidoglycan in cell wall (causes cell lysis) |
| Penicillin and Ampicillin (resistance) | 1. altered target (mutation) 2.poor uptake of drug 3.production of beta-lactamase |
| Amicoglycosides: neomycin, streptomycin, kanamycin (cell target) | interferes with protein synthesis by binding to rRNA |
| Amicoglycosides: neomycin, streptomycin, kanamycin (resistance) | altered target |
| Why do penicillin and aminoglycoside work together well? | Remember that pencillin works by inhibiting petidoglycan in the cell wall. Destruction of the cell wall allows aminoglycoside to better penetrate the cell. |
| What is Kibry-Bauer used for? | Tests the susceptibility of a bacteria to specific antibody. Can test different concentrations of the antibiotic. |
| How does Kirby-Bauer test disk test concentration? | The concentration of the antibiotic decreases as you move away from the disk. Therefore, there will be a certain distance (and corresponding concentration) at which the antiobiotic is no longer effective. |
| Larger zone of inhibition means? | more susceptible (because even at lower concentrations far away from the disk the bacteria still dies |
| Smaller zone of inhibition means? | more resistant (because even at higher concentrations close to the disk the bacteria still lives |
Created by:
Carleybundt
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