Purpose The purpose of the Kirby-Bauer disk diffusion susceptibility test is to determine the sensitivity or resistance of pathogenic aerobic and facultative anaerobic bacteria to various antimicrobial compounds in order to assist a physician in selecting treatment options for his or her patients.
What is the Kirby Bauer disk diffusion test protocol?
Kirby-Bauer Disk Diffusion Susceptibility Test Protocol Protocol (PDF) The Kirby-Bauer disk diffusion susceptibility test determines the sensitivity or resistance of pathogenic bacteria to various antimicrobial compounds in order to assist physicians in selecting treatment options their patients.
What is Kirby Bauer test?
Kirby Bauer tests also known as the Disc diffusion test is used for antibiotic susceptibility testing. Lacks of standardization creates a problem in the 1960s and later Kirby and Bauer reviewed the description. In 1961, WHO standardized the procedure.
What is disc diffusion test?
As the Broth dilution method are time-consuming, many laboratories in the United States adopted disc diffusion tests in the early 1950s. Kirby Bauer tests also known as the Disc diffusion test is used for antibiotic susceptibility testing.
What is confluent growth of Kirby-Bauer technique?
Confluent growth of Kirby-Bauer technique The inoculum can be placed on the plate by flooding with a bacterial suspension and drying before the discs are applied.
What is the purpose of the susceptibility test?
Susceptibility tests determine a microbe's vulnerability to antimicrobial drugs by exposing a standardized concentration of organism to specific concentrations of antimicrobial drugs. Susceptibility testing can be done for bacteria, fungi, and viruses.
What is the purpose of a Kirby-Bauer test and what is a zone of inhibition?
A Zone of Inhibition Test, also called a Kirby-Bauer Test, is a qualitative method used clinically to measure antibiotic resistance and industrially to test the ability of solids and textiles to inhibit microbial growth.
What is the importance of doing antimicrobial susceptibility testing by disc diffusion?
The selection of appropriate and accurate antimicrobial susceptibility tests is important for the prescription of optimal antibiotics, the management of H. pylori treatment, the determination of patient-specific treatment, and epidemiological resistance surveillance[2].
What are the advantages of Kirby-Bauer method?
Advantages. This test is used in determining the antibiotics of choice to treat an infection. It can be useful in monitoring antimicrobials and for the selection of proper antibacterial agents. It doesn't require special equipment to perform and can be interpreted by all medical personnel.
What is the purpose of the Kirby-Bauer method quizlet?
to determine the sensitivity of bacteria to select antiseptics and disinfectants.
What does the Kirby-Bauer disk diffusion test assess quizlet?
Also called the disk diffusion test, is a valuable standard tool for measuring the effectiveness of antimicrobics against pathogenic microorganisms. In the test, antimicrobic impregnated paper disks are placed on a plate that has been inoculated to form a bacterial lawn.
What does the Kirby-Bauer test assess?
The Kirby-Bauer disk diffusion susceptibility test determines the sensitivity or resistance of pathogenic bacteria to various antimicrobial compounds in order to assist physicians in selecting treatment options their patients.
What is the principle of antimicrobial susceptibility testing?
Principle : A standardized inoculum of bacteria (usually 0.5Mcf) is dabbed onto the surface of a dish of Mueller-Hinton (MH) agar . Filter paper discs impregnated with antimicrobial agents are placed on the agar. After overnight incubation, the diameter of the zone of inhibition is measured around each disc.
What is the purpose of antimicrobial sensitivity test?
An antibiotic sensitivity test can help find out which antibiotic will be most effective in treating your infection. The test can also be helpful in finding a treatment for antibiotic-resistant infections.
What is disc diffusion test used for?
In diagnostic laboratories, the disk diffusion test is used to determine the susceptibility of clinical isolates of bacteria to different antibiotics. An effective antibiotic will produce a large zone of inhibition (disk C), while an ineffective antibiotic may not affect bacterial growth at all (disk A).
What is the advantage of disc diffusion method?
Disk diffusion has many advantages, as it is cheap, flexible and allows visibility of growth, correct inoculum, mixed cultures and other abnormalities. Another benefit is the possibility of executing direct susceptibility testing (DST).
What is the principle involved in disk-diffusion technique?
This method is based on the principle that antibiotic-impregnated disk, placed on agar previously inoculated with the test bacterium, pick-up moisture and the antibiotic diffuse radially outward through the agar medium producing an antibiotic concentration gradient.
What is the purpose of the disc diffusion method?
In diagnostic laboratories, the disk diffusion test is used to determine the susceptibility of clinical isolates of bacteria to different antibiotics. An effective antibiotic will produce a large zone of inhibition (disk C), while an ineffective antibiotic may not affect bacterial growth at all (disk A).
Why would it be important for the Kirby Bauer disc diffusion test to use a standard concentration number of cells in the sample of each of the bacterial strains being tested?
Why would it be important for the Kirby-Bauer disc diffusion test to use a standard concentration of the bacterial strain being tested? Higher or lower concentrations can affect the size of the zone of inhibition.
What is disc diffusion method for antimicrobial activity?
The method consists of placing paper disks saturated with antimicrobial agents on a lawn of bacteria seeded on the surface of an agar medium, incubating the plate overnight, and measuring the presence or absence of a zone of inhibition around the disks (Figure 1).
Which of the following is an important advantage of the broth dilution method over the disk diffusion method of susceptibility testing?
The broth dilution method is considered to be superior to the disk diffusion method because it provides the MIC in addition to an interpretation of S, I, or R. 5 Comparing the MIC to the achievable antibiotic plasma concentration allows consideration of the relative susceptibility of the bacteria to each antibiotic.
Why is the MIC used in the Kirby-Bauer test?
The MIC is currently the standard test run for antibiotic sensitivity testing because it produces more pertinent information on minimal dosages. The Mueller-Hinton medium being used for the Kirby-Bauer test is very high in protein.
When was the Kirby-Bauer test developed?
The Kirby-Bauer test for antibiotic susceptibility (also called the disc diffusion test) is a standard that has been used for years. First developed in the 1950s, it was refined and by W. Kirby and A. Bauer, then standardized by the World Health Organization in 1961. It has been superseded in clinical labs by automated tests.
How to incubate agar in sterile inoculating loop?
Lightly touch each disc with your sterile inoculating loop to make sure that it is in good contact with the agar surface. Incubate upside down and incubate at 37 o C.
How long to dry plate before placing antibiotic disks on agar?
Allow the surface to dry for about 5 minutes before placing antibiotic disks on the agar.
How to measure antibiotic sensitivity?
Figure 9. 1: Kirby-Bauer Test to Measure Antibiotic Sensitivity. In Kirby-Bau er testing, bacteria are placed on a plate of solid growth medium and wafers of antibiotics (white disks, shown) are added to the plate. After allowing the bacteria to grow overnight, areas of clear media surrounding the disks indicate that the antibiotic inhibits bacterial growth. The concentration of antibiotic that diffuses into the media decreases with increasing distance from the source. Therefore, the more sensitive the bacteria are to a given antibiotic, the larger the clear bacteria-free zone that forms around the disk containing that antibiotic. (Public domain; via Wikipedia).
What happens to the concentration of antibiotics that diffuses into the media?
The concentration of antibiotic that diffuses into the media decreases with increasing distance from the source. Therefore, the more sensitive the bacteria are to a given antibiotic, the larger the clear bacteria-free zone that forms around the disk containing that antibiotic. (Public domain; via Wikipedia).
What measurement is used to measure disc diameter?
Use millimeter measurements. The disc diameter will actually be part of that number.
What is disk diffusion susceptibility test?
Disk-diffusion susceptibility testing is most frequently used to measure the antimicrobial resistance of isolates of N. gonorrhoeaefor patient management whereas determination of the minimal inhibitory concentration (MIC) is more appropriate for surveillance programs. The methodology varies in different parts of the world and can be performed on both blood-containing media (Fig 2.45and 2.46). or on GC agar base supplemented with IsoVitaleX or an equivalent and to the use of either high- or low-dose discs.13
What makes disc diffusion tests difficult to interpret?
Variation in inoculum density makes the result of disc diffusion tests difficult to interpret. The size of zone decreases with increasingly heavy inocula.
What is the primary method of MIC testing?
In most clinical laboratories, the disk dif fusion(DD) test, E-test strips, broth microdilution method (BMD) and the Vitek 2 system remain the routine susceptibility methods, among which the BMD is suggested as the primary method for polymyxins minimum inhibitory concentration (MIC) testing. But the truth is that conventional methods have many drawbacks (Humphries, 2015). As aless toxin prodrug commonly used for therapy, the CMS yields erroneously high MICs in vitro so that it not be used for susceptibility testing (Landman et al., 2008). The poor and slow diffusion of polymyxins lead the results of DD test nonreliable, yielding small zones of inhibition (Lo-Ten-Foe et al., 2007). False susceptibility (32%) occurred with E-test, which MICs were significantly lower than those obtained by BMD for resistant isolates (Hindler and Humphries, 2013). Their amphiphilic nature make them adhere to the polystyrene surface of BMD microdilution plates, and lower concentrations of polymyxins showed higher absorption proportionally (Karvanen et al., 2013). Although the adsorption of colistin to polystyrene can be mitigated by the addition of a surfactant such as polysorbate 80 (P-80, namely toween-80), the use of P-80 is still questionable (Humphries, 2015). All above methods are laborious, manual preparation or expensive. The automatic systems allow rapid identification and antimicrobial susceptibility testing and perform reliable results (Lo-Ten-Foe et al., 2007; Poirel et al., 2017). However, the Vitek 2 system displayed low sensitivity in the detection of polymyxins resistant Enterobacteriaceaeand care should be taken in the interpretation of the known heteroresistance subpopulations (Tan and Ng, 2007; Lo-Ten-Foe et al., 2007). It is time to ask for a suitable and standard method to detect resistant subpopulations. Additionally, polymyxins resistance would disappear after long-term storage at − 70°C (Hindler and Humphries, 2013), which calls for an easy, inexpensive and sensitive techniques to screen polymyxins resistance from fresh cultures or even clinical samples directly in routine laboratories. Colistin and polymyxin B breakpoints were interpreted according to the documents given by Clinical and Laboratory and Standards Institute (CLSI) or European Committee on Antimicrobial Susceptibility Testing (EUCAST) in the past. Nowadays, the CLSI/EUCAST Joint Working Group recommended an update clinical breakpoints of Acinetobacterspp. and Pseudomonas aeruginosa, as shown in Table 2(2016). However, there were insufficient data to establish clinical breakpoints for Enterobacteriaceae, so the epidemiological cutoff values (ECVs) of Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Raoultella ornithinolyticawere set, as shown in Table 3. Among Enterobacteriaceae, the MIC of other genera and species distributions may be different. Meanwhile, neither PK-PD nor clinical data have been evaluated for polymyxins with any Enterobacteriaceae. So, the ECV interpretations are applied only for laboratorians, clinicians, and public health professionals to identify isolates that have colistin MICs above the wild-type (those with acquired and/or mutational resistance mechanisms to colistin, such as mcr-1). Recently, the Rapid Polymyxin NP test based on the detection of bacterial growth in the presence of a defined polymyxin concentration has been demonstrated with high specificity (99.3%) and sensitivity (95.4%) (Nordmann et al., 2016a). A Selective medium named “SuperPolymyxin”, which contains a colistin concentration (3.5 μg/mL), can detect any type of polymyxin resistant Gram-negative organism and prevent swarming of Proteusspp. The sensitivity and specificity of this medium can reach 100% (Nordmann et al., 2016b). In molecular level, a SYBR green-based real-time PCR assay that considered as a simple, specific, sensitive, and rapid method for detection of mcr-1-positive isolates was recently published (Bontron et al., 2016).
What is disk diffusion?
The disk diffusion method is among the most flexible susceptibility testing methods in terms of antimicrobial agents that can be tested. The method consists of placing paper disks saturated with antimicrobial agents on a lawn of bacteria seeded on the surface of an agar medium, incubating the plate overnight, and measuring the presence or absence of a zone of inhibition around the disks (Figure 1 ). Studies conducted at the University of Washington in the mid-1960s resulted in the technique often referred to as the ‘Kirby–Bauer method,’ which was published by Bauer and colleagues in 1966. This method standardized the variables of disk size, inoculum size, temperature, and time of incubation. Results are reported qualitatively as susceptible, intermediate, or resistant. The disk diffusion method described by Bauer and colleagues has been continually expanded and improved by the Clinical and Laboratory Standards Institute (CLSI) in the United States. Several other international societies (e.g., the European Union Committee for Antimicrobial Susceptibility Testing (EUCAST), and the British Society for Antimicrobial Chemotherapy) use similar techniques. Alternative disk-based methods, including the Roscoe NeoSensitabs and the Australian CDM method, are also used in some countries. Instruments that measure the zones of inhibition using cameras can speed the process of reading disk diffusion plates. These instruments can also transform the zone diameter readings into approximate MIC values.
What is the disk diffusion microbioassay?
A disk diffusion microbioassay with Bacillus subtilis (ATCC 6633) was used to evaluate the bactericidal effectiveness and the pharmacodynamic profile of moxifloxacin in cerebrospinal fluid (CSF) and to compare the bactericidal activity with that of ceftriaxone and meropenem therapy [172].
What are the methods of susceptibility testing?
The main methods for susceptibility testing are broth dilution, agar dilution, and disk diffusion. In addition, several systems for automated AST are available. It is important to note that each method may have limitations for certain organism–drug combinations and that there may be minor differences between the results generated by the automated systems. For example, certain organism–drug combinations cannot be reliably tested on automated systems. Laboratories should ensure that they have implemented the recommended changes to their software if using automated instruments.
Why is microscan used?
MicroScan uses substrates that release fluorophores after interaction with bacterial enzymes, a process resulting in increased fluorescence. A major disadvantage is that some bacteria fail to release fluorophores after growth.92To solve this problem, MicroScan has incorporated rapid, turbidimetric readers in the panels. Depending on the organism, results are available between 4.5 and 18 hours of incubation.