exam 3

kirby-bauer disc diffusion test

• used to determine susceptibility of bacteria to antibiotics

  • bacteria spread on plate, antibiotic discs placed on top

  • drugs diffuse

• zone of inhibition compared to charts to determine if susceptible, intermediate, or resistant

  • drug characteristics must be taken into account (ie molecular weight)

minimum inhibitory concentration

• aka MIC

• the lowest concentration that prevents growth in vitro

• serial dilutions of chemical in growth medium used, culture added, incubated, examined

• inhibition ≠ sucessful treatment

  • differs btwn ppl

minimum bacteria concentration

• aka MBC

• lowest concentration of chemical that kills 99.9% of cells in vitro

  • determined from plate count from tubes w/ no growth in MIC

• precise but labor intensive

Etest

• can be used to determine the MIC of an antibiotic

  • alternative!

• unfluent bacterial lawn inoculated, plastic strips w/ antibacterial gradient are placed

  • as growth happens, diffusion of med does

• rate of drug diffusion = concentration

• elipitical zone of inhibition

resistance to antimicrobial medications

• upped use, misuse → resistance

  • ex: 3% of S. aureus resistant to penicillin G, not 90%

• alarming!

  • cost, complication, treatment impact

• requires understanding of mechanism & spread of resistance

mechanisms of acquired resistance

• drug-inactivating enzymes

• alteration in target molecule

  • drug unable to bind

• lowered reuptake of a drug

  • drug unable to enter cell

• higher drug elimination

  • efflux pumps

aquisition of resistance

• spontaneous mutation

• drugs w/ multiple targets better!

• gene transfer

• conjugative transfer of R plasmids

spontaneous mutation

• less likely w/ several diff targets/binding sites

• combination therapy

combination therapy

• multiple antibiotics used

• unlikely cells will simultaneously develop resistance

drugs w/ multiple targets

• better!

• combos can be used

• resistance arises to 1 drug, second kills bacteria

gene transfer

• genes encoding resistance spread

  • strains, species, genra

conjugative transfer of R plasmids

• common!

• R plasmids often carry resistance genes

halting the spread of antibiotic resistance

• physician responsibility (better diagnosis, appropriate treatment)

• pt responsibility (following instructions)

• educating the public (antibiotics ≠ viruses)

• global impact (antibiotic availability, use in livestock, etc)

physical methods to controlling microbial growth

• heat

• filtration

• irradication

• washing

chemical methods to controlling microbial growth

• antimicrobial chemicals

biosafetly lvls

• established by CDC & NIH

• determined by

  • agent’s infectability

  • ease of transmission

  • potential disease security

  • type of work being done

• lvls 1-4

BSL 1

• lowest risk of infection

• fewest precautions required

• don’t cause infection in healthy ppl

  • e. coli, b. subtilis

BSL 2

• moderate risk to humans

• include microbes commonly found in area

• precautions: PPE, safety cabinets

BSL 3

• potential to be lethal via inhalation

• indigenous/exotoxic

  • mycobacterium tuberculosis, bacillus anthrasis, west nile virus

• precautions: respiratpr, safety cabinet

BSL 4

• most dangerous, often fatal

• transmitted by inhalation

• agents have no treatment/vaccination

• highest lvl of precautions

factors that influence lvl of control

• what is an item going ot be used for?

• identifiy the situation

  • daily life

  • hospitals

  • microbio labs

  • industry (food, water, etc)

fomite

• inanimate object used by ppl that can transmit microbes

• indirect transmission

  • doorknobs, towels, syringes

highly resistant microbes

• bacterial endospores (resistant to head, drying, chemicals)

  • clostridium botulinum

• protozoa cysts & oocysts (in feces, diarrheal disease)

• mycobacterium species (cell wall structure = resistance_

• pseudomonas species (can grow w/ many disinfectants)

• naked virus (no envelope, resistant to chemicals)

critical items

• used in body, penetrate body tissues

• sterile!

  • surgical instruments, catheters, IVs

semicritical items

• contacts mucous membrane, nonintact skin

• doesn’t penetrate tissues

  • gastrointestinal endoscopes, respiratory therapies

noncritical items

• contacts unbroken skin, must be clean

  • bed liners, furnitures, stethoscopes, BP cuffs

d value

• time required to kill 90% of population under specific conditions

methods of control

• sterilization

• disinfection

• pasteurization

• decontamination

• sanitation

• degerming

• antiseptics

• preservaion

sterilization

• eliminates all forms of life

  • prions not included

  • surgeries/needles

    • autoclave (heat), radiation, chemicals

• labs, manufacturing, food industry

sterilants

• chemicals that achieve sterilization

  • good for heat sensitive instruments

disinfection

• inactivates most microbes on fomite surface using antimicrobial chemicals/heat

  • bench, bathroom, clinical surfaces

• not sterilzation

  • bleach

pasteruization

• reduces # of spoilage organisms & pathogens, maintains food quality

  • not sterile, still spoils

• louie pasteur in 1860s

• in food typically

  • milk & juice @ 72C

• 2 types

high temp short time pasteurization

• aka HTST

• 72C for 15sec

• lowers bacterial #s while preserving milk quality

ultra high temp pasteruization

• aka UHT

• 138C for 2+ sec

• can be stored for a long time in sealed containers

  • no refrigeration needed!

decontamination

• reduces pathogens to a lvl considered “safe”

sanitation

• lowers microbial population to lvl acceptable for public health

  • dishwashing, cleaning public utensils

degerming

• signifigantly reduce microbial #s

  • handwashing

antiseptics

• antimicrobial chemicals safe for use on skin surfaces

  • hydrogen peroxide, isopropyl alcohol

• cleaning injuries

preservation

• slows/inhibits growth of microbes in food/other stuff

aseptic technique

• prevents contamination of sterile surfaces

• maintain sterility → prevent pt contamination

• not followed? sepsis

• sterile fields

sepsis

• systemic inflammatory response to infection

• high fever, upped HR & RR, shock, death

sterile field

• area designated free of all vegetative microbes, endospores, viruses

  • for medical prodecutes

medical procedues

• use sterilized materials & strict procedures for washing & application of sterilants

autoclave

• charles chamberland in 1879

• sterilization @ 121C & PSI 15 for 15 min

  • effective against endospores (check for them!)

• big in labs

commercial sterilization

• uses heat at a temp low enough to preserve food quality, but high enough to destory common pathogens

  • c. botulinum

    • pressure canning reccomended

using heat for sterilizing

• moist heat

• dry heat

moist heat methods

• fast, reliable, inexpensive, denatures proteins

• boiling

• pasteruization

• pressurized steam (autoclave)

boiling

• for 5 min

• destorys most microorganisms/viruses

  • not endospores

dry heat methods

• incineration

• dry heat ovens

refrigeration

• temps btwn 0-7C

• inhibits microbial metabolism, slows microorganism growth, preserves refrigerated products like food/medical supplies

freezing

• below -2C

• stops microbial growth, kills suseptible orgnaism

• cultures, medical speciments

• ultra low → -70C

• liquid nitrogen

radiation

• ionizing (3 sources)

  • gamma radaition

  • x-rays

  • electron

• damages DNA & maybe plasma membrane

• sterilizes heat sensitive material

  • medical equipment, surgical supplies, meds

• some endospores resistant

UV radiation

• thymine dimers

• germicidal lamps

filtration

• air!

  • HEPA filters

  • membrane filtration

  • liquid filtration

HEPA filters

• remove nearly all air microbes

• 0.3 micometer filters

membrane filtration

• variety of sizes

  • larger: larger units. like a machine

  • smaller: syringe filters

liquid filtration

• for heat sensitive fluids

• traps microbes on filter

germicidal chemicals

• sterilants

• high lvl, intermediate lvl, low lvl disinfectants

high lvl disinfectants

• treat semicritical insturments

  • ex: endoscopes

intermediate lvl disinfectants

• treat non-critical instuements

  • ex: stethoscopes

low lvl disinfectants

• disinfect fomites, floor, walls

selecting the right gemicidal chemical

• toxicity

• presence of organic matter

• compatability w/ material tested

• residue

• cost & availability

• ease of use

• storage/stability

• envrionmental risk

alcohols

• kill bacteria, fungi (not endospores/non-enveloped)

• denatures proteins, disrupts membranes

• commonly used on skin

  • swabbing before needles

  • hand sanitizers

• Sars CoV-2 good for!

hand sanitizer

• rub hands until dry (20sec)

• should be btwn 60-90% alcohol

aldehydes

• inactivate enzymes & nucleic acids

• strong, broad spectrum

  • kills bacteria/fungi, viruses, endospores

    • sterilization at a low temp!

• 2% alkaline gluteraldehyde

• good for heat sentivie things

• irritates skin

formaldehyde

• preserves biological specimins

  • crosslinks proteins

ethylene oxide

• gaseous sterilizing agent

  • fabric, pillows, pacemakers, petri dishes

• penetrate! can sterilize items in plastic bags (catherers, disposables)

• special chamber!

• “cold sterilization” - good for heat sensitive

bisbiguanides

• surgery antiseptics - hand scrib

• chlorhexide

• broad-spectrum activity against yeasts, gram + bacteria, gram - bacteria, enveloped viruses

  • pseudomonas, mycobacterium, spores, nonenveloped exception

chlorhexide

• common ingedient

  • skin creams

  • disinfectants

  • mouthwashes/oral rinses

    • also for catheters or surgical mesh

halogens

• chlorine, sodium hypochloride, chloramine, iodine, chloride dioxide

• drinking water - 0.5ppm chlorine

• irritates skin, eyes. nose

• some protozoa resistant

chlorine

• swimming pools, liquid waste, surfaces, drinking water

sodium hypochloride

• bleach

• kills bacteria & viruses

• less reliable when organic material present

chloramine

• disinfects drinking water

  • military tablets

chlorine dioxide

• gaseous agent

• fumigation & sterilization of enclosed areas

• water disinfection

iodine

• oxidizes cellular components, destabilized macromolecules

• betadine

betadine

• medial personnel hand scrub prior to surgery

heavy metals

• bind to protiens, inhibit enzymatic activity

• small concentrations accumulate in cells → proteins denature

• not selective toxic

• mercury, silver, copper, nickel, zinc

mercury

• not used in US due to toxicity concerns

silver

• used as antiseptic

• silvadune cream, silver nitrate drops

• some cathethers & bandages contain silver

silvadune cream

• topical for burn wounds

silver nitrate drops

• used for newborn eye infections

  • opthamalia neonatorum

• replaced by antibiotic creams

copper, nickel, zinc

• copper → algacide

• zinc chloride → mouthwashes

• zinc oxide → topical antiseptic cream

  • calamine lotion, diaper ointments

phenolics

• 1800s → chemicals used for disinfection

• 1860s → joseph lister used carbolic acid as a disinfectant for surgical wounds

  • pHisoHex

  • tricolsan

• in mouthwashes & throat lozenges

  • less toxic than phenol - disrupt membrane, denature protiens

• listerine, lysol

pHisoHex

• handwashing in hospitals

• effective for staph & strep that cause skin infections

tricolsan

• in many antimicrobials until 2016 - FDA banned

• banned from over-the-counter antiseptic wash products (hand soaps, foams, fels, bars, body washes)

• ppl asked to provide data that these were safe & prevented infection

  • no! same chances

epidemiology

• the study of factors influencing the frequency & distribution of diseases

  • causes of disease in populations

epidemiologists

• collect, compile abt sources of disease & risk factors

  • design strategies to prevent/predict spread of disease

  • expertise in many disciplines → ecology, microbio, sociology, stats, psych

  • many daily habits based on epidemiologists

communicable diseases

• contagious

• from 1 host → another

  • ex: measles, colds, influenza

• can be direct/indirect

non-comminicable diseases

• don’t spread from host to host

• microorganisms often arise from individual’s normal microbiota/envrionment

  • leigonella pneumophilia in water systems

rates of disease in a pop

• epidemiologists more concened w/ rate than absolute # of cases

  • usually per 100k

attack rate

• % of ppl who become ill in a pop. after exposure to infectious agents

  • reflects infectious dose, immune status of pop.

incidence

• # of new cases/time/pop

  • measure of risk of an individual contracting a disease

prevalence

• total # of cases at any time or for a specific period in a given pop.

  • reflects overall impact of disease on society

  • includes old & new cases, as well as duration of disease

morbidity

• incidence of disease in a pop

  • contagious diseases often have higher morbidity rate, infected individual may transmit to several others

    • ex: flu

mortality

• overall death rate in pop.

case-fatality rate

• % of pop. that dies from a specific disease

  • ebola virus disease (EVB) feared bc of very high case-fatality rate

endemic disease

• constantly present in pop.

  • ex: common cold in US

sporadic

• few cases from time to time

epidemic

• unusually high # of cases

  • can be from indroduced or endemic disease

outbreak

• group of cases @ specific time & pop.