Microbiology Lecture Exam 3

Decontamination

remove or reduce microbial populations to render an object safe for handling

Sterilization

eliminates all bacteria, viruses, and endospores

Disinfection

reduces microbial numbers

When is sterilization used?

used for drugs, objects used for invasive medical procedures, media, and glassware used for culturing microbes in the lab

When is disinfection used?

used for cosmetics, foods, surfaces, and medical equipment that does not contact internal body tissues 

At what refrigeration temperature can we slow the growth of microbes?

Yes (4°C)

At what freezer temperature can we slow the growth of microbes?

Yes, (0°C)

What is refrigeration used for?

• Is used to preserve specimen isolates and increase the shelf life of media and other reagents 

• Also preserves clinical samples (e.g., blood, tissue biospies, swabs containing suspected pathogens) until they are delivered to the lab for analysis

• -Cultures and other medical specimens can be stored for long periods at ultra-low temperatures

Define thermal death time and thermal death point.

• Thermal death time: shorest period of time that a given temperature must be held to kill all microbes in a sample 

• Thermal Death point: the minimum temperature needed to kill all microbes in a sample within 10 minutes

Provide examples of heat-related control methods.

• Autoclaving

• Boiling 

• Pasteurization 

• Dry Heat

What is an autoclave and what is it used for?

• Machine that applies steam heat along with pressure to sterilize 

• Used to sterilize media and assorted medical or lab equipment

What are the standard autoclave settings for time, pressure and temperature?

• 20 minutes 

• 15psi 

• 121°C

 What are the disadvantages of using an autoclave?

Only materials that withstand moisture, high heat and pressure can be treated; Plastics easily melt and bottles collapse; Certain media and drugs cannot be autoclaved without affecting their chemical integrity

What organisms are destroyed by boiling water for 5 minutes? Which are not destroyed?

• Eliminates most pathogenic bacteria, protozoans and viruses 

• Some endospores can withstand hours of boiling 

• “Boil water advisory” occurs when drinking water is contaminated

Is boiling a decontamination, sterilization or disinfection strategy?

Decontamination

What is pasteurization and what is it used for?

• Application of moderate heat, below the liquid’s boiling point, eliminates pathogens and reduces harmless microbes that cause spoilage 

• Used in dairy industry (milk, coffee, creamer)

• Also used for juices, liquid eggs, soy milk, wine, and beer 

• Two different methods, HTST and UHT, are commonly used to kill pathogens associated with milk spoilage

What pathogens found in milk are affected by pasteurization?

• Listeria 

• Salmonella 

• E. coli O157:H7 

• Coxiella burnetii

 Why is milk refrigerated after pasteurization?

To prevent the growth of milk-spoiling microbes that remain

What is dry heat?

• Incineration or hot-air ovens can be used for sterilization or disinfection 

• Sterilizing a loop, often referred to as “flaming a loop” is a common component of aseptic in the microbiology laboratory and is used to incinerate any microorganisms on the loop 

• A bactericineratory may be used to reduce aerosolization of microbes and remove the presence of an open flame in the laboratory.

List examples of dry heat sterilization

• Heating an inoculating to red hot 

• Incinerating waste 

• Placing an object at 170°C for about 2 hours in a dry-heat oven

What is high pressure processing used for?

• Can be used to kill microbes in food 

• Hyperbaric oxygen therapy to increase oxygen saturating is used to treat certain infections

What is desiccation? Can it be accelerated? If so, how?

• Used to preserve foods

• Accelerated through the addition of salt or sugar 

• Decreases water activity in foods

Define lyophilization.

• Combines cold exposure and desiccation for long-term storage foods and lab materials

• Microbes remain and can be rehydrated

Define radiation.

Radiation or high-energy waves serve as a disinfection or sterilization tool

Ionizing radiation

Gamma rays and X-rays are types of ionizing radiation

High-energy waves generate ions that kill microbes and inactivate viruses by damaging their nucleic acids

Useful in food and pharmaceutical industries because this type of radiation can pass through packaging

Also sterilize medical supplies that cannot be autoclaved

Approved for eliminating microbes on dried spices, meats, and vegetables

Foods are exposed to gamma radiation by passing on a conveyor belt through a radiation chamber

Gamma-irradiated foods must be clearly labeled and display the irradiation symbol, known as the “radura”

Non-ionizing radiation

• UV rays 

• Change the bond structure of DNA, leading to mutations and cell death 

• Disinfect surfaces in operating rooms and biosafety cabinet surfaces in labs 

• UV radiation causes the formation of thymine dimers in DNA, leading to lethal mutations in the exposed microbes 

• Germicidal lamps that emit UV light are commonly used in the laboratory to sterilize equipment

What is a HEPA filter? Where is it used? What does it remove from the air? What doesn’t it  remove from the air?

• High-efficiency particulate air filters are used in clinics, hospitals, labs, and homes to remove bacteria, environmental allergens, fungi, and even larger viruses from the air 

• Remove 99.97% of airborne substances that are 0.3um or larger

What are LifeStraws? Do the “straws” sterilize water? Explain your answer.

• Can be used to remove pathogens from drinking water and are used by people in remote areas or communities that lack municipal water treatment 

• Do not sterilize water since viruses are not fully removed

List the two intermediate-level disinfectant alcohols commonly used in healthcare. How do  they work? What are they used for?

• Ethanol and isopropanol are two intermediate-level disinfectants commonly used in healthcare 

• They denature proteins and attack lipid membrane 

• Used to disinfect small equipment (thermometers, scissors, stethoscope) 

• Alcohol wipes are used to clean small surfaces (stoppers, outside of equipment ventilators) and as skin antiseptics

What are the disadvantages of using alcohol?

• Can react with plastic tubing and rubber components 

• Flammable 

• Evaporate readily

What aldehydes are used in healthcare? How do they work? What are they used for?

• Formaldehyde and glutaraldehyde are higher or intermediate level of disinfectants based on their concentrations 

• Both work by reacting with proteins and nucleic acids

• Used to sterilize surgical instruments, endospores, dialyzers, anesthesia, and respiratory equipment

What are the disadvantages of aldehydes?

• Toxicity 

• Formaldehyde generates fumes and is suspected to be a carcinogen 

• Glutaraldehyde irritates the skin and mucous membrane 

• Both leave residues on equipment-rinsing required

What is the newest aldehyde called? List its characteristics.

Ortho-phthalaldehyde: newer chemical; higher-level disinfectant; safer, less irritating and stable at several pH levels

What are phenols and phenol derivatives used for? What products contain them?

• Used for personal hygiene and clinical use 

• Found in mouthwashes, soaps, and Lysol

This phenol is found in antibacterial soaps, plastics and textiles.

Triclosan

How do phenols work? What are they used for? What are the disadvantages of phenols?

• Intermediate-level germicides 

• Destroy bacteria cell walls and interact with proteins 

• Used for surface disinfection (bed rails, tables, floors) and to disinfect semi-critical and noncritical equipment 

• Disadvantages: 

  • Easily absorbed by porous surfaces 

  • Irritating to the skin 

  • All residue must be rinsed off before reusable equipment can be used for another patient

Provide examples of halogens

• Chlorine 

• Iodine

How do halogens work? Can they be inactivated?

• Oxidize cell components 

• Can be inactivated by blood, soil, or feces

What is the most widely used halogen disinfectant? What is it used for?

• Chlorine bleach 

  • The concentration of bleach determines its level of disinfection 

  • Chlorine can be used on medical equipment and floors 

  • Added to drinking water to remove potential pathogens 

  • Cheap, act fast, and don't leave residue

Discuss the use of iodine as a chemical method to control microbial growth

• Tinctures are used as antiseptics to decontaminate skin 

• Iodophors are used as an antiseptic and disinfectant against bacteria, mycobacteria, and viruses (not endospores); must be diluted to be used as an antiseptic and higher concentrations as a disinfectant; non-staining and non-irritating 

• Povidone-iodine is used as an antiseptic or disinfectant for medical equipment (thermometers, endoscopes)

Provide examples of heavy metals

• Mercury

• Silver

• Copper

• Zinc

What are heavy metals used for?

Long been used for disinfection and preservation

What are the disadvantages of heavy metals?

• Some have toxicity (mercury)

• Environmental risks (mercury)

What are the two common types of peroxygens? What molecules do they attack? What are  they used as?

• Strong oxidizing properties that attack proteins, nucleic acids, and other biomolecules 

• Hydrogen peroxide and peracetic acid are two common types 

• Used as antiseptics and disinfectants

At high concentration, peroxygens are considered _______________ disinfectants

high-level

Hydrogen peroxide can be used to disinfect _________________.

Soft contact lenses, ventilators, fabrics, and endospores

Peracetic acid is effective in the presence of _____________________.

Blood, pus or feces; automated washing and sterilizing machine in USA that uses peracetic acid

Dialysis centers use newer disinfectants with _________________________ together for  hemodialyzers

Hydrogen peroxide and peracetic acid

Is ethylene oxide a liquid, gas or solid?

Gas

Ethylene oxide is a good _______________ method. It damages what?

• Sterilization method 

• Damages proteins and nucleic acids

Ethylene oxide can be used on ______ and __________.

Implant devices (pacemakers) and tissue (heart valves before transplantation)

What are the disadvantages of using ethylene oxide?

• Highly toxic 

• Flammable 

• Costly 

• Time-consuming to use

What are detergents? What do they damage? What do work mostly as?

• Amphipathic molecules (remove water-soluble and water-insoluble substances) 

• Damage the liquid envelope of certain viruses and the lipid membrane of certain bacterial cells 

• Work mostly as cleaning agents that reduce microbial counts by washing them away

What are the classes of detergents used for controlling microbial growth?

• Anionic detergents: hand soaps, shampoos, laundry detergents, household cleaning agents

• Cationic detergents: quaternary ammonium compounds (QACs) 

  • Bacterial activity: Sporostatic (inhibits spore germination)

  • Used as antiseptics on unbroken skin and disinfectants on non-critical equipment and surfaces

What structure is disrupted by bisbiguanides?

Cell membranes cause contents to gel

Provide two examples of bisbiguanides. What are they used for?

Chlorhexidine and alexidine are used for surgical scrubs, for handwashing (clinical settings), and in prescription oral rinses

 List the characteristics of pressurized carbon dioxide

In the form of a supercritical fluid, easily permeates packaged materials and cells -> forms carbonic acid and lowers the pH

At low temperatures, pressurized carbon dioxide can be used to _________ medical devices,  implants and transplanted tissues

Sterilization

Which acids are chemical preservatives? What are they added to? What molecule do they  target?

• Sorbic acid, Benzoic acid, Propionic acid 

• Added to the variety of foods 

• Inhibit enzymes or reduce intracellular pH

 What are the naturally produced preservatives mentioned in the lecture notes?

Nisin and Natamycin

Which natural preservative is used against Gram-positive bacteria? Fungi?

• Nisin: is effective against gram-positive 

• Natamycin: is effective against fungi

What factors need to be considered when selecting an appropriate germicide?

• Item uses 

• Germicide reactivity 

• Germicide concentration and treatment times 

• Types of infectious agents being controlled 

• Presence of organic and inorganic matter on treated item 

• Impact of germicide residues on equipment use 

• Germicide toxicity

Define bacteriostatic drugs.

Drugs that cause a reversinle inhibition of growth with bacterial growth restarting after the elimination of the drug

Define bactericidal drugs

Drugs that kill their targert bacteria

• Narrow-spectrum antimicrobial drug 

Targets only specific subsets of bacterial pathogens (Gram-positive only; gram-negative only)

Broad-spectrum antimicrobial drug

• Targets a wide variety of bacterial pathogens (gram-positive and gram negative)

• Frequently used as empire therapy to cover a wide range of pathogens while waiting for lab identification of the infecting pathogen

What is a superinfection? When can it develop? Provide two specific examples of  superinfections.

• Associated with using broad-spectrum antimicrobials 

• Develops when the antibacterial intended for the preexisting infection kills the protective microbiota (normal flora) allowing another pathogen resistant to the antibacterial drug to proliferate and causes a secondary infection 

• Examples 

  • Yeast infections (Candidiasis)

  • Pseudomembranous colitis (Clostridium difficile)-can be fatal

What is selective toxicity?

Antimicrobial drug selectively kills or inhibits the growth of microbial targets while causing minimal or no harm to the host

List the modes of action of antibacterial drugs.

• Inhibits cell wall biosynthesis 

• Inhibit protein biosynthesis 

• Disrupt membranes 

• Inhibit nucleic acid synthesis 

• Antimetabolites 

• Mycobacterial adenosine triphosphate (ATP) synthase inhibitor

List the drug classes and their targets that inhibit cell wall biosynthesis

Target	Drug Class
Penicillin-binding proteins	B-lactams: penicillins, cephalosporins, monobactams, carbapenems
Peptidoglycan subunits	Glycopeptides
Peptidoglycan subunit transport	Bacitracin

List the drug classes and their targets that inhibit protein synthesis.

Target	Drug Class
30S ribosomal subunit	Aminoglycosides, Tetracyclines
50S ribsomal subunit	Macroslides, Lincosamides, Chloramphenicol, Oxazolidinones

List the drug class and its target that disrupt membranes.

Target	Drug Class
Lipopolysaccharide, inner and outer membranes	Polymyxin B, Colistin, Dapromycin

List the drug classes and their targets that inhibit nucleic acid synthesis

Target	Drug Class
RNA	Rifamycin
DNA	Fluoroquinolones

List the drug classes and their targets that act as antimetabolites.

Target	Drug class
Folic acid synthesis enzyme	Sulfonamides, Trimethoprim
Mycolic acid synthesis enzyme	Isonicotinic acid hydrazide

1. List the drug class and its target that inhibits mycobacterial adenosine triphosphate synthase.

Target	Drug Class
Mycobacterial ATP Synthase	Diarylquinoline

Is antimicrobial resistance on the rise? If so, what is it the result of?

On the rise and the result of selection of drug-resistant stains in clinical environments, overuse and misuseof antibacterial drugs, the use of subterapeutic doses of antibacterial drugs and poor patient compliance with antibacterial drug therapies

Where are drug resistance genes found?

They are carried on plasmids often in transposons

What is the microbiome?

• Scientists have coined the term microbiome to refer to all prokaroytic and eukaryotic microorganisms and their genetic material that are associated with a certain organism or environment

• Within the human microbiome, there are resistant and transient microbiota

Define resident microbiota and transient microbiota.

• Resident microbiota: consist of microbes that constantly live in or on our bodies 

• Transcient microbiota: microbes that are only temporarily found in the human body; may include pathogenic microorganism

What two factors can alter both resident and transient microbiota?

Both hygiene and diet can alter both resident and transient microbiota

Define symbiotic relationship

• Any interaction between different species that are associated with each other within a community is called symbiosis 

• Such interactions fall among a continuum between opposition and cooperation

Interactions in a symbiotic relationship may be ______________________________.

Beneficial or harmful, or have no effect on one or both species involved

Define virulence factors.

Contributes to to an organisms ability to cause disease

List the virulence factors mentioned in the lecture notes and describe how each allows  microbes to cause disease

• Exoenzymes and Toxins: allow pathogens to invade host tissue and damage 

• Endotoxin: lipid A component of LPS and Gram-negative envelope

• Exotoxins: proteins secreted mainly by Gram-positive bacteria; also secreted by phagocytosis by WBCs

• Adhesins: initiating infections by viruses 

• Antigentic drift and Antigentic Shift: used by Influenza viruses to avoid being recognized by immune system 

• Lipopolysaccharide: is composed of lipid A, a core glycolipid, and an O-specific polysaccharide side chain 

• Lipid A is the toxic component that promotes inflammation and fever

Mutualism

 both populations benefit

Commensalism

one population is benefited, and the other is population is unaffected

Neutralism

both populations are unaffected by one another

Parasitism

one population benefits and the other population is harmed

Amensalism:

one population is harmed, and the other is unaffected

List and describe the stages of infectious disease

• Incubation period: initial entry of pathogen into host; time the pathogen begins multiplying in the host 

• Prodromal period: pathogen continues to multiply and the host begins to experience general signs and symptoms of illness 

• Period of illness: the signs and symptoms of the disease are most obvious and severe 

• Period of decline: the number of pathogen particles begins to decrease and the signs and symptoms of illness begin to decline 

• Convalescent phase: the patient generally returns to normal function; some diseases inflict permanent damage that the body connot fully repair

Define nosocomial infections

Diseases acrequired in hospital settings are known as nosocomial diseases

What factors contribute to the prevalence and severity of nosocomial diseases.

• First, sick patients bring numerous pathogens into hospitals, and some of these pathogens can be transmitted easily via improperly sterilized medical equipment, bed sheets, call buttons, door handles, or by clinicians, nurses, or therapists who do not wash their hands before touching a patient 

• Second, many hospital patients have weakened immune systems, making them more susceptible to infections 

• Third, the prevalence of antibiotics in hospital settings can select for drug-resistant bacteria that can cause very serious infections that are difficult to treat

Define standard precautions. What practices are included?

• Minimum infection prevention practices that apply to all patient care 

  • Hand hygiene

  • PPE (gloves, masks, eyewear)

  • Respiratory hygiene/cough etiquette 

  • Sharpes safety

  • Safe injections practices

  • Sterile instruments and devices

  • Clean and disinfect environmental surfaces

What are the three types of transmission-based precautions? Define each.

• Contact precautions: for patients known or suspected infections that represent an increased for contact transmission 

• Droplet precautions: for patients known or suspected to be infected with pathogens transmitted by respiratory droplets that are generated by a patient who is coughing, sneezing or talking 

• Airborne precautions: for patients known or suspected to be infected with pathogens transmitted by airborne route (TB, measles, chickenpox, disseminated herpes zoster)

Where can we find microorganisms?

• In our everyday common experiences, microbes are virtually ubiquitous 

• They are in the air we breathe, the foods we eat, and the water we drink 

• Microorganisms contaminate the surfaces of objects that we use (like this sheet of paper) as well as the skin of our fingers 

• In practical terms, the only places where microorganisms are not found are places where we intentionally exclude them. For example, microorganisms are usually not found in our blood or cerebrospinal fluids 

• We invest a lot of energy into immune defenses that keep these fluids sterile (free of microbial contamination) and we get very sick when our immune defenses fail 

• In silicon wafer manufacturing plants, millions of dollars are spent on “clean rooms” designed to eliminate contamination

What is a primary pathogen?

Cause disease in a host regardless of the host’s resident microbiota or immune system

What is an opportunistic pathogen?

• Only causes disease in situations that compromise the host’s defenses 

  • Susceptinle individuals include very young, elderly, pregnant women, chemotherapy patients, people with immunodeficiencies-AIDS, people recovering from surgery and those with a breach of protective barriers-severe wound or burn

Define the following: signs, symptoms, noninfectious diseases, acute disease, chronic  disease, and latent diseases.

• Signs: objective and measures 

• Symptoms: subjective and are reported by the patient

• Noninfectious diseases: due to genetics and environment 

• Infectious diseases: due to pathogens 

• Acute diseases: short duration 

• Chronic diseases: lasts for months or years 

• Latent diseases: last for years; lack of replication during extended dormant periods

Discuss communicable diseases (include how they are caused, transmitted, examples).

• They are infectious diseases 

• These are illnesses caused by infectious agents such as bacteria, viruses, fungi, or parasites. They can be transmitted from person to person, through contact with contaminated surfaces or objects, or via vectors like mosquitoes or ticks 

• Communicable diseases are usually contagious and can spread directly or indirectly from an infected person, animal, or environmental source to a susceptible host 

• Ex: influenza, tuberculosis, HIV/AIDS, malaria, COVID-19

Discuss noncommunicable diseases (include how they are caused, lifestyle factors,  examples).

• These are chronic diseases

• These are diseases that are not caused by infectious agents and are generally of long duration 

• They often develop over time and are influenced by a combination of generic, environmental, behavioral, and metabolic factors

• Are often associated with lifestyle factors such as unhealthy diet, physical inactivity, tobacco use, and excessive alcohol assumption. Genetic predisposition can also contribute to their development 

• Ex. Cardiovascular diseases, diabetes, chronic respiratory disease, certain types of cancer