Microbial Growth & Control: In Vitro & In Vivo, Superbugs and Drug Resistance

Flashcards covering sterilization, disinfection, aseptic techniques, filtration, chemical methods, susceptibility testing, antimicrobial resistance, superbugs, and empiric therapy concepts drawn from the lecture notes.

What is sterilization?

Destruction or elimination of all microbes, except prions.

What is disinfection?

Elimination of most pathogens (except bacterial spores) from nonliving objects; some endospores may be killed with prolonged aldehyde exposure.

Differentiate antiseptics, disinfectants, and sanitizers.

Antiseptics: chemicals used on living tissues to reduce infection risk. Disinfectants: chemicals used on inanimate objects to kill pathogens. Sanitizers: reduce microbial populations to levels considered safe by public health standards.

What is aseptic technique?

Techniques used to keep the work area and instruments clean and sterile to minimize cross-contamination.

What is sterile technique?

Practices that exclude all microorganisms from a defined area.

Name two physical methods of sterilization.

Dry heat and moist heat (steam under pressure/autoclaving).

What are common chemical methods of sterilization? Give examples.

Ethylene oxide gas and formaldehyde are examples (also include agents like hydrogen peroxide, glutaraldehyde, peracetic acid).

What are the standard autoclave conditions for sterilizing media?

121°C at 15 psi for 15–30 minutes.

Define tyndallization.

Moist heat applied intermittently: 100°C for 30 minutes on 3 consecutive days.

Define inspissation.

Moist heat at 75–80°C for 2 hours on 3 consecutive days, used for egg-based/high-protein media.

Differentiate depth filters and membrane filters.

Depth filters use fibrous/granular media (e.g., Berkfeld, asbestos, Chamberlain) to trap organisms; membrane filters use defined pore sizes (cellulose acetate, polycarbonate) for sterilization.

What is cold sterilization / ionizing radiation?

Use of gamma radiation to sterilize heat-sensitive items (e.g., disposable syringes, gloves, catheters).

Name chemical methods of sterilization and give an example for each.

Ethylene oxide (gas sterilant); Formaldehyde (and hydrogen peroxide in some contexts); Glutaraldehyde; Peracetic acid.

What is 2% glutaraldehyde used for and its sporicidal activity?

Sporicidal; kills spores in 3–10 hours; used for sterilizing medical equipment.

What is peracetic acid used for?

Effective in the presence of organic material; used as a sterilant/disinfectant.

What is pasteurization and its limitation?

Heating to destroy pathogens in foods like milk; not a sterilization method because endospores may survive.

What is non-ionizing radiation used for in disinfection?

UV light from mercury-arc lamps used to disinfect surfaces.

What are disinfectants?

Chemical agents used to inhibit the growth of pathogens on inanimate objects.

What are antiseptics?

Solutions used to disinfect living tissues (skin, mucous membranes).

What are the characteristics of an ideal chemical antimicrobial agent?

Kills a wide variety of microbes, acts quickly, not affected by organic matter, non-toxic to humans, non-damaging to materials, no residual film, easy to apply, inexpensive, stable, and odorless.

What should an ideal chemical antimicrobial agent avoid leaving on treated surfaces?

Residual antimicrobial film.

What types of agents are typically used as disinfectants and what do they target?

Disinfectants like soaps, detergents, alcohols, phenolics, halogens, hydrogen peroxide, formaldehyde, and ethylene oxide; they often target and disrupt cell membranes or enzymes.

What is disk diffusion and MIC used for?

Antimicrobial susceptibility testing methods: disk diffusion uses antibiotic discs to create zones of inhibition; MIC is the lowest concentration that prevents visible growth.

What is a superbug?

An organism resistant to one or more antimicrobial agents.

Name some especially troublesome “superbugs.”

MRSA, MRSE, VRE, P. aeruginosa, C. difficile, Acinetobacter baumannii, Klebsiella pneumoniae, MDR-TB (multidrug-resistant tuberculosis), among others.

List major mechanisms by which bacteria become resistant to drugs.

Enzymatic destruction/inactivation of the drug; blocking entry (permeability barriers); alteration of the drug’s target; active efflux pumps; and alterations in metabolic pathways.

What is beta-lactamase and why is it important?

An enzyme that hydrolyzes the beta-lactam ring, rendering beta-lactam antibiotics ineffective (a common resistance mechanism).

How can Gram-negative bacteria reduce antibiotic entry?

By modifying porins to restrict antibiotic entry (and other permeability changes).

What is the role of efflux pumps in resistance?

Pumps that actively expel antibiotics from the cell, reducing intracellular concentrations.

What is horizontal gene transfer and its relevance to resistance?

Conjugation, transduction, or transformation spread resistance genes between bacteria, accelerating resistance. Aufgelassen outside of chromosomal mutations.

What is MRSA and what does it signify?

Methicillin-resistant Staphylococcus aureus; a well-known resistant pathogen requiring alternative therapies.

What is VISA/VRSA?

VISA = vancomycin-intermediate S. aureus; VRSA = vancomycin-resistant S. aureus; indicates reduced or no susceptibility to vancomycin.

What is MDR-TB and what is XDR-TB?

MDR-TB is multidrug-resistant tuberculosis (resistant to at least isoniazid and rifampin). XDR-TB is extensively drug-resistant TB (resistant to second-line drugs as well).