Micro Lab 16

resistance

Community-acquired MRSA is not as / is more virulent than MRSA found in hospitals, combining _______ with virulence.

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

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

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.

Describe the Kirby-Bauer method of antimicrobial agent susceptibility testing.

Clear area around the antibiotic disc where microbes didn't grow.

Describe the zone of inhibition:

Kirby-Bauer Method

Determining the susceptibility of pathogens using the filter paper disk agar diffusion method of the National Committee for Clinical Laboratory Standards (NCCLS).

chloroquine and primaquine

During World War II, this bark was not available, so chemists went to work and synthesized

chemotherapy

During the early part of the 20th century, Paul Ehrlich (a chemist in Germany) speculated that some "magic bullet" would find and destroy pathogens in the body without harming the person. This idea provided the basis for

1. Inhibition of cell wall synthesis: interferes with amino acid cross-linking of peptidoglycan 2. Inhibition of protein synthesis: can prevent ribosome from binding to the mRNA, can prevent peptides from being added, etc. 3. Inhibition of enzymatic activity 4. Injury to plasma membrane 5. Inhibition of nucleic acid synthesis, either RNA or DNA

"Targets" for Antibiotics:

1. Destruction or inactivation of the drug - microbes can make enzymes to target the drug. 2. Prevention of penetration of the drug to the target site in the microbe 3. Drug site is altered so binding cannot occur 4. Rapid ejection of the drug out of the cell before it can be effective

HOW Does Antibiotic Resistance Develop?

Salvarsan

He finally came up with _______ (salvation from syphilis); this compound contained arsenic and phenol.

strict adherence to barrier precautions proper hand hygiene isolation of infected patients

Healthcare workers can slow transmission of diseases by:

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

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

Alexander Fleming

In 1928, _________ discovered a substance produced by the mold (fungus) Penicillium notatum. The antibiotic penicillin resulted from this discovery.

IS

MRSA is / is not easily spread between patients.

surgical wound infections, urinary tract infections, blood stream infections and pneumonia.

MRSA is commonly a cause of

Methicillin-resistant Staphylococcus aureus

MRSA stands for

direct contact with stool, urine or blood containing VRE indirectly by contaminated hands of healthcare providers or contact with contaminated environmental surfaces such as bedrails, wheelchairs, thermometers, doorknobs, bed linens and patient gowns.

VRE can be transmitted by:

IS NOT

VRE is / is not usually spread by casual contact such as hugging or touching or through the air.

Vancomycin-resistant Enterococcus

VRE stands for

millimeters

You must measure the diameter of the zone of inhibition in

Resistant (R)

antibiotic is not useful against the bacteria

Susceptible (S)

antibiotic is useful against the bacteria

Intermediate (I)

antibiotic may be useful against the bacteria

Carbapenem-Resistant Enterobacteriaceae (CRE)

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

Enterococcus species

resistant to vancomycin, known as vancomycin-resistant enterococcus, or VRE.

Extended-Spectrum β-Lactamase (ESBL)

producing bacteria are Gram negative rods resistant to all penicillins, cephalosporins and monobactams

The edge of the zone 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.

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

broad-spectrum antibiotics

Antibiotics are classified based on the range of different microbial types they affect. If they affect both Gram (+) and Gram (-) bacteria, they are called ______ ________

1.Do not use antibiotics unless they are absolutely required. 2. Use the optimum strength of antibiotic 3. Administer 2 or more drugs simultaneously to reduce the chances of resistance 4. Boost the body's immune system: eat properly, exercise, get enough sleep

BEST WAYS TO OVERCOME RESISTANCE:

1. Overuse of antibiotics (MDs prescribe when patients don't really need them) 2. Misuse of antibiotics (wrong ones used) 3. Patients do not complete the dose regimen (do not take as directed) 4. Antibiotics in animal feeds to fatten them for market faster 5. Resistant strains are common among people who work in hospitals where drugs are constantly used. 6. Use of antimicrobials (NOT antibiotics) like triclosan in soaps and other products

Bacterial Resistance to Antibiotics has developed due to:

Yes. Antibiotics that affect the peptidoglycan of the cell wall (e.g. penicillin) are more effective against Gram (+) cells because of their greater abundance of peptidoglycan.

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 Gram (+) and Gram (-) bacteria? If so, what differences do you see?

resistant

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

The cells divide as time passes. What was equivalent to a 0.5 McFarland standard may be considerably more dense after 30 minutes.

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?

colonized

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

spider

In many cases, MRSA has mistakenly been diagnosed as _____ bites that won't heal.

42%

In one study, _____ of nurses' gloves became contaminated with MRSA when the nurses touched items in the room of MRSA patients but did not actually touch the patient.

tripled

In the past decade, the number of MRSA-infected patients has:

Penicillium and Cephalosporium

More than half of the antibiotics we use come from a species of Streptomyces, filamentous bacteria found in the soil. Some antibiotics come from bacteria of the genus Bacillus (bacitracin) and others from molds, mostly from the genera _________ and __________

CAN

Studies have shown that healthcare professionals can / cannot lower infection rates.

According to the chart in Table 7-2, a zone of 25 mm for Staphylococcus around a penicillin disk indicates resistance to the antibiotic. A 20 mm zone around a tetracycline disk for the same species indicates susceptibility. Therefore, even though the zone of inhibition is smaller, tetracycline would be the more effective antibiotic against this organism.

Suppose you do this test on a hypothetical Staphylococcus species with the antibiotics penicillin (P-10) and tetracycline (TE-30). You record zone diameters of 20 mm for the tetracycline disc and 25 mm 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?

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.

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

whether a pathogen is susceptible or resistant to the antimicrobial agent.

The antimicrobial susceptibility testing of an isolated pathogen indicates:

cinchona

The bark of the ______ tree was used in South America to cure malaria. Peruvian Indians called it "quina-quina" (bark of bark); from this the name "quinine" evolved.

antibiosis

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

skin to skin contact cuts or abrasions patient - care items furniture

What are the usual routes of transmission of MRSA?

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

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

Staphylococcus aureus and Escherichia coli

What microbes were used for this experiment.

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 might the consequence be of pouring the plates 2 mm deep instead of 4 mm?

patients with weakened immune systems patients previously treated with vancomycin and other antibiotics. Long-term antibiotic therapy patients Patients with indwelling devices

Who is at increased risk of contracting VRE?

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

Why is a pure culture used?

VRE

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

hand hygiene

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

Hospital

______ personnel can also act as reservoirs of infection and most often act as a link for transmission.

Superbugs

_______ cause infections so virulent that they can and have turned deadly in a matter of days.

Clostridium difficile

___________ is an emerging concern.

antibiotic

a term for an antimicrobial compound produced by living organisms (fungi, bacteria) that inhibits another microorganism.

Mueller-Hinton (MH)

agar plate is inoculated so that a lawn of the bacteria to be tested is placed on the plate.

Rate of growth of the organism

controlled by putting plates in incubator at body temperature

Concentration of the antibiotic

controlled by using disks with standard concentrations only

Number of organisms

controlled by using the McFarland std

Staphylococcus aureus strains

especially those resistant to the drug methicillin, referred to as methicillin-resistant Staphylococcus aureus, or MRSA. Another even more dangerous resistance is coming: VRSA - vancomycin-resistant Staphylococcus aureus. Vancomycin is the drug "of last resort."

ZONE OF INHIBITION

is compared to a standardized chart. After incubation plates are examined for clear rings (no growth) around the antimicrobial disks.

McFarland standard

is used to dilute the broth culture so that the number of bacteria placed on the plate is standardized.

rate of diffusion

of antibiotic through the agar medium—controlled by using MH plates of the correct depth

Degree of susceptibility

of the bacteria to the antibiotic drug—each strain is different; must do the test to know for sure

MRSA

the most common superbug worldwide