Question

describe 10 importance of antimicrobial susceptibility testing in the context of quality assurance.

Answer 1

Answer:

10 importance of antimicrobial susceptibility testing in the context of quality assurance:-

1. Most of the clinically important bacteria causing infections in humans are capable of exhibiting resistance to antimicrobial agents commonly used for the treatment. Therefore, upon isolation of the organism in the clinical microbiology laboratory, characterization frequently also employs tests to detect its antimicrobial susceptibility. Thus, the report produced by clinical microbiology laboratory for the physician, also includes organism’s susceptibility profile to different antimicrobials along with its identification.

Antimicrobial susceptibility testing (AST) is performed on bacteria that are isolated from clinical specimens to determine if the bacterial etiology of concern can be killed or inhibited by antimicrobial drugs that are potential choices for therapy, at the concentrations of the drugs that are attainable at the site of infection using the dosing regimen indicated in the drug product’s labeling. The results of AST are generally reported with interpretive categories. The category “susceptible” indicates that the bacteria are inhibited by the usually achievable concentrations of antimicrobial agent when the dosage recommended to treat the site of infection is used.

2. The majority of infectious diseases are bacterial in origin. With the discovery of laboratory methods to grow these microorganisms using appropriate growth medium known as “culture,” determining the sensitivity and resistance of specific pathogens to a wide range of antimicrobial agents becomes necessary so that healthcare providers can immediately institute proper treatment regimens to their patients.

Antimicrobial susceptibility testing (AST) is a laboratory procedure performed by medical technologists (clinical laboratory scientists) to identify which antimicrobial regimen is specifically effective for individual patients. On a larger scale, it aids in the evaluation of treatment services provided by hospitals, clinics and national programs for control and prevention of infectious diseases. Recently, researchers have to implement continuous surveillance activities for resistance patterns due to the mutations in bacterial DNA.

3. Specimen requirements for routine susceptibility testing using the disk diffusion method and MIC method are similar to the guidelines for collecting samples for bacterial culture since a certain number of well-isolated colonies (usually 3 to 5) grown from a culture is necessary to prepare a suspension of inoculum. Usual specimens sent for culture and sensitivity tests are blood, urine, cerebrospinal fluid, sputum, wound, stool, and other body fluids and discharge.

Special susceptibility tests via commercial systems may not always require bacterial colonies from culture because they can detect resistance to certain antimicrobial drugs by employing molecular techniques for detecting resistant genes. An example would be the Xpert MTB/Rif assay which determines sensitivity or resistance to rifampicin directly from sputum specimens.

4. Susceptibility testing for antimicrobials is necessary for patients who raise suspicion of infection with specific pathogens based on disease manifestation and clinical correlation. Antibacterial agents are then used to detect sensitivity or resistance from bacteria. Although the purpose of this review is primarily towards the susceptibility testing for bacterial pathogens, it is important to note that antifungal susceptibility tests also exist for addressing fungal infection (e.g., Candida, Aspergillus spp.). Furthermore, antiviral susceptibility tests are also available (e.g., influenza) via molecular technologies including sequencing analysis such as Sanger and pyrosequencing methods.

5. A unique impact of AST to patient management is the identification of the specific diagnosis, and additionally, targeting the particular etiologic agent causing the disease. No two patients can be managed similarly, especially if they have the same signs and symptoms (disease manifestation) but with different treatment regimens because the same causative organism can have different resistance patterns. For example, two patients may present with an ordinary strain of Staphylococcus aureus vs. methicillin-resistant Staphylococcus aureus (MRSA); and another example would be patients with drug-susceptible (DS-TB) and drug-resistant tuberculosis (DR-TB).

6. For disk diffusion, measuring the zone of inhibition is done by using a dedicated caliper. Correctly measure the diameter by the edges of the inhibition zone. For MIC panels, reading each set of wells for an antibiotic drug is done. MIC determination is by either a clear or slight whiteness on the well. Reporting the results of the inhibition zones and MIC breakpoints is made using either the terms “susceptible” or “resistant” based on the set cut-off range for zone diameter in the nearest whole millimeter and microgram per milliliter, respectively. The Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) developed expert-approved guidelines on breakpoints for reporting results of these methods (e.g., CLSI M100-ED29:2019 Performance Standards for Antimicrobial Susceptibility Testing, EUCAST Clinical breakpoints for bacteria).

7. Several factors affect the result of the susceptibility testing which covers the whole sampling, testing and reporting procedures. Any deviation from the standard AST procedure can significantly impact succeeding areas of laboratory workflow which in turn could later affect patient diagnosis, treatment, and management. Support systems of the laboratory workflow require strict monitoring, and laboratory personnel should be well trained and competent enough to perform the procedure.

For instance, "poor specimen quality" can be a first sign leading to an erroneous result. A perfectly carried out inoculation to MHA plate using “mixed colonies” will turn out unsatisfactory results. Poor standardization of bacterial suspension and a "longer depth of agar" could yield misleading endpoints. Supportive supervision for laboratory staff is necessary, to prevent wasting time and resources.

Purchasing poor quality MIC panels can lead to "dehydrated wells" or "mixed wells." Doing the procedure without personal protective equipment (PPE) can increase the incidence of laboratory-acquired infections. Inadequacy and lack of supplies needed to perform AST will extend turn-around time and therefore, decrease laboratory productivity and delay patient therapy. Providing AST on drugs which do not align with the hospital’s formulary makes laboratory service available yet ineffective.

8. Inconsistencies in the AST results must be investigated and acted upon immediately. No results should be released when quality control measures are not satisfactory. Releasing inaccurate drug susceptibility or resistance results can inflict more harm to the patients, leading to severe clinical conditions and poor prognosis. A worse consequence in delivering false AST results can result in wrong treatment management plans which might cause further mutations to these infectious organisms, exposing the patients and the community to a higher risk.

9. Patients should be adequately informed about the AST and its indications, patient requirements, and its clinical use for patient management. Healthcare providers such as physicians, laboratory personnel, nurses and pharmacologists are encouraged to disseminate correct information about the test. However, interpretation of the AST results must take place between the patient and the physician to facilitate good compliance with the prescribed medications and to prevent self-medication. With the rise of antimicrobial resistance, the importance of AST requires emphasis to medical, laboratory and nursing staff, as well as patients and their family members, and the whole community leading to a unified approach.

10. Once antimicrobial susceptibility results become available, treatment regimens for each patient can be developed by healthcare providers. Prescribed medications of appropriate antibiotics need individualization for each patient diagnosed with an infectious disease. Moreover, resistance from primary drugs will require a higher level of antimicrobial stewardship, including prudent use of second-line drugs.