micro exam 3 chapter 13

Sepsis

Bacterial contamination

Asepsis

Absence of significant contamination

Sterilization

Destruction of ALL living cells, spore, and/or viruses

Commerical sterilization

Kills all spores without altering the quality of the food

• not fr sterilization

Disinfection

Removal of disease causing microoganisms from inanimate surfaces

Antisepsis

Removal of disease causing microorganisms from living tissues, such as skin or mucous membrane

Degerming

Mechanical removal of microbes from a limited area

Sanitization

Reducing microbe numbers to “safe” levels

Biocide

Lethal effects

• Bactericidal agents kill bacteria

• Fungicides kill fungi

• etc.

Bacteriostasis

Slow/stop metabolism or reproduction, but not lethal

• Bacteriostatic agents inhibit bacterial growth

• Fungistatic agents inhibit fungal growth

• etc.

TDP (thermal death point)

Lowest temperature at which cells in a liquid culture are killed in 10 minutes

TDT (thermal death time)

Minimal time for all bacteria in a liquid culture to be killed at a particular temperature

DRT or D-value (decimal reduction time)

Time it takes to reduce a microbial population by 90% (kill 90% of cells)

Autoclave Sterilization v.s. Pasteurization

Autoclave

• High temperature AND high pressure

Pasteurization

• Moderately high temperature and NO pressure to kill bacteria that causes spoilage

Describe uses of filtration

Filter through a pore size of 0.2 μm to remove:

• bacteria

• bacterial endospores

• yeasts

• mold spores

• algae

• protozoa

CANNOT FILTER VIRUS

• virus require pore size of 20 nm or 0.001 μm

Conditions for irradiation can be used to sterilize

Irradiation uses high energy electromagnetic radiation to sterilize

Non-ionizing radiation

• UV light

  • does not penetrate liquid or solids well —> useful for surface sterilization

Ionizing radiation (damages cellular structure —> effective for sterilization)

• Gamma rays (Cobalt-60)

  • Used to sterilize plastic petri plates in plastic wrapping paper

• Electron beams

  • Used for sterilization

• X-rays

Factors that can affect the efficacy of a disinfectant

• Presence of organic matter

  • blood or feces can neutralize

• Types of microbes present

  • Endospore forming organisms (Clostridium botulinum high resistant)

  • Gram - is resistant due to outer membrane

  • Non-enveloped viruses more resistant

• Corrosiveness

• Stability, odor, surface tension

Explain CDC levels of how disinfectants are compared

High

• kills bacterial cells, mycobacteria, spores, fungi, and enveloped/non-enveloped viruses 

• ex: Ethylene oxide, glutaraldehyde, and formaldehyde

Intermediate

• kills everything like high except for spores

• ex: Phenolics and Halogens

Low

• kills bacterial cells, fungi, and some viruses

• can’t kill mycobacteria or spores

• ex: alcohol, quaternary ammonium compounds

Gas sterilization

Used for disposable plasticware as they can’t be heat sterilized or chemically disinfected

• petri dishes, syringes, sutures, etc.

Sterilized by gamma irradiation or antimicrobial gases (ethylene oxide)

How do microbes build resistance to disinfectants?

When a target experiences low concentration of disinfectant, it doesn’t immediately die, but it develops mutation to resist

Efflux pumps: bacteria literally pushing it out of cell

Biofilms: make it hard for disinfectant to penetrate

Explain selective toxicity and its importance for clinically useful antibiotics

Antibiotic are harmful to specific bacteria without harming the eukaryotic organisms

Minimum Inhibitory Concentration (MIC)

Minimum antibiotic concentration to inhibit bacterial growth

Drug concentration —> MIC during treatment

Minimum Bacterial Concentration (MBC)

Minimum antibiotic concentration to kill all bacteria

Requires plating to determine if any cells survive

Synergistic

Drug have greater effectiveness when used together

Antagonistic

Drug interferes with each other and decrease effectiveness

Disk diffusion assay

clear zone around disk shows effectiveness of an antibiotic

Chemotherapeutic index

Therapeutic dose: minimum dose per kg of body weight that stops growth

Toxic dose: maximum dose tolderated by the patient

Chemotherapeutic index: toxic/therapeutic

• Higher the chemotherapeutic index, the safe the drug

What are DNA replication inhibitors?

Quinolones

Inhibit DNA synthesis by blocking action of DNA gyrase, preventing the bacteria from regulating supercoiling

What targets cell membrane integrity?

Polymyxin

Disrupts inner and outer membrane because (+) charge is interacting with negatively charged membrane

• Only for Gram(-) bacteria because they have inner and outer membrane

Chloramphenicol (Protein synthesis inhibitor)

• binds to 50s ribosome subunit

• prevents peptide bond formation

Macrolides (Protein synthesis inhibitor)

• binds to 50s ribosome subunit

• block peptide bond elongation

• prevent peptidyltransferase activity and translocation

Tetracyclines (Protein synthesis inhibitor)

• binds to 30s ribosome subunit

• block peptide bond elongation

• prevent aminoacyl-tRNA entry into the A site

What affect intermediary metabolism?

Sulfonamides

• Block acid formation

• Doesn’t harm humans because we get it from diet

Cell wall antibiotics to stop cell wall crosslinking

Penicillin

Vancomycin

Cephalosporins

They lead to cell lysis

Beta-lactam antibiotics

Enzymes that produce cross-links to in cell walls are collectively called penicillin-binding proteins

Penicillin, Vancomycin, Cephalosporins bind to them to prevent peptidoglycan (cell wall) synthesis

Explain antibiotic resistance in beta lactams

Beta-lactamase cuts the beta-lactam ring in antibiotics, making them ineffective

__ is the process by which a chemical kills disease-producing microbes on inanimate surfaces

B) Disinfection

The effectiveness of a chemical agent is determined by the ___

B) decimal reduction time

Agent A acting on Staphylococcus aureus has a D-value of 5 minutes. If the population of microbes start at a cell density of 5 × 10^8 CFYs/ml, how many viable cells will remain after 15 minutes?

D) 5 × 10^5 CFUs/ml

Pasteurization conditions are designed to kill which of the following microbes from millk?

A) Coxiella burnetii

You are developing a liquid food supplement for populations of developing nations after natural disasters. It must have a long shelf life without refrigeration. Which microbial control technique would best accomplish your goal?

C) Gamma irradiation

In a use-dilution test against Staphylococcus aureus, agent A at 0.01 M killed all the bacteria with 10 minutes of exposure, while agent B did the same at 0.005 M, Which one would make the better anticeptic?

D) More data are needed

A chemical agent that can kill mycobacteria and spores but not prions is considered a ___

C) high level disinfectant

Which of the following agents is effective for sterilizing plasticware and petri plates?

B) Ethylene oxide gas

A series of culture tubes containing dilutions of an antibiotic are inoculated with a bacterial pathogen. Tube 1 has the highest concentration of the drug and tube 6 has the lowest. Growth occurs in tubes 5 and 6; no growth is seen in tubes 1-4. What can we conclude from this serial dilution?

A) The drug concentration in tube 4 is the MIC

These photographs who the effectiveness of two antibiotics on a bacterial pathogen isolated from spinal fluid. Which of the following could explain why a clinician might choose to treat the patient with drug A?

A) Drug B might not penetrate into the brain

B) Drug B might be known to have a toxic effect on the patient (patient allergy)

C) The level of drug A might be higher and maintained longer than that of drug B

D) All of the above

D) All of the above

Which of the following antibiotic classes and host targets are matched correctly?

A) Penicillin / membrane synthesis

B) Aminoglycoside / 30s ribosome

C) Quinolone / folic acid synthesis

D) Macrolide / 30s ribosome

B) Aminoglycoside / 30s ribosome

A bacterial pathogen that produces the enzyme beta-lactamase will be resistant to which of the following antibiotics?

D) Penicillin

Which of the following antibiotics is primarily bacteriostatic?

A) Chloramphenicol

B) Gentamicin

C) Oxacillin

D) Centriaxone

A) Chloramphenicol

__ is a single bacterial system that can provide resistance to multiple classes of antibiotics simultaneously

A) A multidrug efflux pump

B) A beta-lactamase

C) An enzyme that modifies antibiotic structure

D) An enzyme that blocks a drug’s access to its target

A) A multidrug efflux pump

Clavulanic acid ___

B) acts as a decoy for beta-lactamase

What is the primary driving force in bacteria for developing antibiotic resistance?

A) Growth inhibition

B) Membrane permeability to the antibiotic

C) Virulence potential of the pathogen

D) Concentration of the antibiotic

A) Growth inhibition

Which of the following classes of antivirals is used to treat influenza?

C) Neuraminidase inhibitors

Which of the following best explains selective toxicity of antiviral nucleoside analogs?

A) Viral polymerase are less selective than host polymerases

B) Viral polymerases catalyze different reactions than host polymerases

C) The antiviral nucleoside analogs function normally with host polymerase

D) There is a host enzyme that converts the analog incorporated in DNA to the proper nucleotide

A) Viral polymerase are less selective than host polymerases

A male patient complains of an itchy irritation in his genital region. Your diagnosis is a superficial fungal infection. Which of the following drugs is the usual treatment for this disease?

A) Itraconazole

B) Miconazole

C) Griseofulvin

D) Amphotericin B

B) Miconazole

A female patient enters the hospital in severe respiratory distress. The lab report indicates that she has a lung infection caused by the fungus Histoplasma. Which of the following drugs would be most appropriate to give the patient?

A) Amoxicillin

B) Nystatin

C) Acyclovir

D) Amphotericin B

D) Amphotericin B

What drugs to treat malaria?

A) Azithromycin

B) Metronidazole

C) Artemisinin

D) Chloroquine

C) Artemisinin