Kirby-Bauer Method

In one study, __% of nurses gloves get contaminated with MRSA

42

How does antibiotic resistance develop?

Destruction or inactivation of the drug; prevention of penetration; drug site is altered; rapid ejection;

Enterococcus species resistant to vancomycin is known as ____.

VRE

___ is the leading cause of healthcare associated bacteremia, as well as surgical wound infections and urinary tract infections.

VRE

E. coli and S. aureus were chosen to represent Gram (-) and Gram (+) bacteria respectively. For a given antibiotic, is there a difference in susceptibility between the - and + bacteria? If so, what differences do you see?

Yes. Antibiotics that affect the pg of the cell wall are more effective against gram + cells because of their greater abundance of pg.

Could an organism that is susceptible to an antimicrobial agent in lab testing fail to respond to it when that drug is used to treat the patient?

Yes. The human body is a complex environment. Many factors can affect the effectiveness of the antimicrobial: pH, organics, failure to reach target.

Antibiotics are classified based on the range of different microbial types they affect. If they affect both gram - and gram + bacteria, they are called _____ _____ antibiotics.

broad spectrum

The zone of inhibition is the measurement of the _____ of ____ ____ of the zone circle in millimeters.

diameter; no growth;

The depth is important because of its effect upon _____.

diffusion

Factors to consider when interpreting antibiotic sensitivity of a pathogen: -The rate of _____ of antibiotic through the agar medium-controlled by using MH plates of the correct depth. -Degree of _____ of the bacteria to the antibiotic drug- each strain is different; must do the test to know for sure. -Number of organisms on the plate- controlled by using the _____ __. -Rate of ____ of the organism- controlled by putting plates in incubator at body temp. -_____ of the antibiotic- controlled by using disks with standard concentrations only.

diffusion; susceptibility; mcfarland std; growth; concentration;

If there is no zone or a very small zone of inhibition around the disk, the organism is considered to be ____ to the drug.

resistant

Paul Ehrlich finally came up with _____ (salvation from syphillis); this compound contained arsenic and phenol.

salvarsan

_____ (S) = antibiotic is useful against the bacteria. _____ (I) = antibiotic may be useful against the bacteria. _____ (R) = antibiotic is not useful against the bacteria.

susceptible; intermediate; resistant

The antimicrobial susceptibility testing of an isolated pathogen indicates: whether a pathogen is _____ or ____ to the antimicrobial agent.

susceptible; resistant

VRE can be transmitted by: - ___ contact with stool, urine or blood containing VRE. - _____ by contaminated hands of healthcare providers or contact with contaminated environmental surfaces such as bedrails, wheelchairs, thermometers, doorknobs, bed linens and patient gowns.

direct; indirectly

____ ____ is the single most important procedure in preventing the spread of MRSA and VRE.

hand hygiene

Who is an increased risk of contracting VRE?

weakened immune systems; previously taken vancomycin; long term antibiotics, indwelling devices.

In the test, antimicrobic impregnated paper disks are placed on a plate that has been inoculated to form a bacterial lawn. The plates are incubated to allow growth of the bacteria and time for the agent to diffuse into the agar. As the drug moves through the agar, it establishes a concentration gradient. If the organism is susceptible to it, a clear ___ __ ______ will appear around the disk where growth has been inhibited.

zone of inhibition

Interpreting Kirby-Bauer Results: -____ of ____ is compared to a standardized chart. After incubation plates are examined for clear rings (no growth) around the antimicrobial disks.

zone of inhibition

Use filter paper discs impregnated with an antibiotic on a Mueller Hinton agar plate that has been covered with organisms. View this diffusion method after 12-24 hours of growth and look for the zone of inhibition.

Kirby-Bauer

___ is the most common superbug worldwide

MRSA

____ is commonly a cause of surgical wound infections, urinary tract infections, blood stream infections and pneumonia.

MRSA

Staph aureus strains, especially those resistant to the drug _____, referred to as MRSA. Another even more dangerous resistance is coming: VRSA. ______ is the drug of last resort.

Methicillin; Vancomycin

VRE is ___ usually spread by casual contact such as hugging or touching or through the air.

NOT

During the early part of the 20th century, ________ speculated that some "magic bullet" would find and destroy pathogens in the body without harming the person. This idea provided the basis for _____.

Paul Ehrlich; chemotherapy

What microbes were used for this experiment?

Staph aureus and E. coli

How does the antibiotic get from the disk into the agar?

The antibiotic diffuses out of the disk and into the agar. This diffusion can be affected by temperature and depth of agar in the plate.

In clinical applications of the Kirby-Bauer test, diluted cultures (for the McFarland standard comparison) must be used within 30 minutes. Why is this important?

The cells divide as time passes. What was equivalent to a .5 McFarland standard may be considered more dense after 30 min.

After incubation, does the antibiotic extend into the agar beyond the zone of inhibition? How does your answer relate to the concept of MIC?

The edge of the zone of inhibition is not the limit of antibiotic diffusion. Diffusion occurs beyond the zone, but the concentration of the antibiotic is too low to be lethal. The edge of the zone represents the minimum inhibitory concentration (MIC) of the antibiotic.

In the past decade, the number of MRSA infected patients has ___.

tripled

The mechanism of inhibition of the growth of colonies on solid medium is called ____.

antibiosis

A term for an antimicrobial compound produced by living organisms that inhibits another microorganism.

antibiotic

The zone may be produced as a result of killing the bacteria, in which case it is said to be ______.

bactericidal

In other cases, the drug may only stop bacterial growth without killing them, in which case it is said to be _______.

bacteriostatic

The bark of the ____ tree was used in South America to cure malaria.

cinchona

Mix the E. coli culture and the ____ ____ until they reach their max turbidity.

mcfarland standard

You must measure the diameter of the zone of inhibition in ____.

millimeters

The size of this zone of inhibition depends on the sensitivity of the bacteria to the specific antimicrobial agent and the point at which the chemical's ____ ____ _____ is reached.

minimum inhibitory concentration (MIC)

Peruvian Indians called it "quina quina"; from this the name _____ evolved

quinine

Why are pure cultures used for antimicrobial susceptibility testing?

To specifically determine which microbe is susceptible to which antimicrobial.

Suppose you do this test on a hypothetical Staph species with the antibiotics penicillin and tetracycline. You record zone diameters of 20mm for the tetracycline disc and 25mm for the penicillin disc. Which antibiotic would be most effective against this organism? What does this tell you about comparing zone diameter to each other and the importance of the interpretive chart?

According to the chart, a zone of 25mm for Staph around a penicillin disk indicates resistance to the antibiotic. A 20mm zone around a tetracycline disk for same species indicates susceptibility. Therefore, even though the zone is smaller, tetracycline would be the more effective antibiotic against this organism.

Natural antimicrobial agents produced by microorganisms.

Antibiotics

Some antibiotics come from bacteria of the genus ____ and others from molds, mostly from the genera _____ and _____.

Bacillus, Penicillium, Cephalosporium

___ are becoming a serious problem. Gram neg rods resistant to carbapenem antibiotics, which have been used as drugs of last resort. Have a very high mortality rate.

CRE

____-producing bacteria are gram neg rods resistant to all penicillins, cephalosporins and monobactams.

ESBL

Why is a pure culture used?

If have a mixed culture, the results may be confusing and the test results will not be valid.

Determining the susceptibility of pathogens using the filter paper disk agar diffusion method.

Kirby bauer method

The Mueller-Hinton II plates are supposed to be used within a specific time after their prep and should be free of visible moisture. What negative effect (s) might moisture have on the test?

The older the plates, the drier they become. This could affect the ability of the antibiotic to diffuse through the agar. Moisture might help spread the antibiotic further than diffusion alone.

All aspects of the Kirby-Bauer test are standardized to assure reliability of comparison with the published standards. What might the consequence be of pouring the plates 2mm deep instead of 4mm?

This would affect the distance the antibiotic diffuses from the disk. The thicker the agar, the more downward diffusion there is and the less antibiotic available to diffuse outward. Thus, the zone would be smaller.

What is the value of the McFarland No. 0.5 turbidity standard?

To assure that you have enough microbes in broth and to standardize the numbers of microbes being spread on the plate.

Targets for antibiotics: 1. inhibition of ___ ____ synthesis. interferes with amino acid cross linking of PG. 2. Inhibition of ____ synthesis. 3.inhibition of enzymatic activity 4. injury to plasma membrane 5. inhibition of nucleic acid synthesis.

cell wall; protein

During world war ii, this park was not available, so chemists went to work and synthesized _____ and ____.

chloroquine; primaquine;

In hospitals, the most important reservoirs of MRSA are ____ ____- those with the bacteria in or on the body but not causing disease.

colonized patients

Also called the disk diffusion test, is a valuable standard tool for measuring the effectiveness of antimicrobics against pathogenic microorganisms.

kirby bauer

____ _____ agar, which has a pH between 7.2 and 7.4, is poured to a depth of 4mm in either 150mm or 100mm Petri dishes.

mueller hinton

Kirby Bauer Method: 1.____ method-must be performed as directed. 2. A ____ ____ agar plate is inoculated so that a lawn of the bacteria to be tested is placed on the plate. 3. A 0.5 _____ ____ is used to dilute the broth culture so that the number of bacteria placed on the plate is standardized.

standardized; mueller hinton; mcfarland standard;

Two important bacteria have become resistant to multiple antimicrobial agents.

staph aureus; enterococcus

More than half of the antibiotics we use come from a species of _____ filamentous bacteria found in soil.

streptomyces

Hospital personnel can also act as reservoirs of infection and most often act as a link for ____.

transmission

Bacterial resistance to antibodies has developed to the use of antimicrobials (not antibiotics) like ____ in soaps and other products.

triclosan

Commonly acquired MRSA is more ____ than MRSA found in hospitals, combining resistance with virulence.

virulent

Clear area around the antibiotic disc where microbes didnt grow.

zone of inhibtion