Table 1.

Advantages and disadvantages of the common methods of antimicrobial susceptibility testing.

Method	Advantage	Disadvantage	Comments
Broth dilution	Well-standardised	Time-consuming	Quantitative **
	Harmonised	Individual mistakes
	Commercially available tests are easy to perform
Agar Dilution	Well-standardised	Time-consuming	Quantitative
	Suitable for testing a large number of isolates	Limited concentration of antimicrobial agents	Possible automation in part
Disk diffusion	Simple to perform	Time-consuming	Qualitative *
	Low cost	No MIC value
	Simple and fast interpretation	The inability for some antibiotics to be tested
	The high number of test antibiotics per test
	High flexibility in antibiotic selection
	Detection of resistance patterns
	Mass use and the possibility of automatisation
	A number of a different use (AST, identification, screening, etc.)
	Detection of heteroresistant population or contamination
Gradient test	Convenient and flexible	Relatively expensive	Quantitative
	Simple to perform	Relatively long incubation
	Does not require expertise
	Detection of resistance patterns
Automated systems	Simple to perform	Relatively expensive	Semi-quantitative ***
Chromogenic media	Mass use and the possibility of automatisation	Not completely susceptible and specific	Qualitative with no interpretation criteria (S, I, R)
	Simple to perform	Time-consuming
	Simple and fast interpretation	Limited spectra or single antibiotic
		Relatively expensive
		Screening only or required confirmatory identification
		No MIC value
MALDI-TOF MS	Rapid turnaround time	High cost of the MALDI-TOF MS
	Simple to perform	Need further optimisation for each species and antibiotic combination
	Low sample volume requirements	No MIC value
	Low per-sample costs
Genetic methods	Rapid	Limited spectra	Qualitative
	Highly accurate	Limited throughput	Semi-quantitative
	Sensitive	High cost
	Reproducible
	Increased ability to detect slow-growing or non-cultivable organisms
Genomic methods	Highly accurate	High cost	Qualitative
	Sensitive	Time-consuming
	Increased ability to detect slow-growing or non-cultivable organisms	Challenging interpretation of results

* Qualitative; results are expressed as susceptible (S), susceptible, increased exposure (I), or resistant (R) based on established criteria from EUCAST. ** Quantitative; results are expressed as minimal inhibitory concentration (MIC) for each drug. Susceptibility reports should include interpretation of MIC, such as S, I, or R. *** Semi-quantitative; results are expressed as MIC using three to four antimicrobial dilutions for each drug. Precise MIC values cannot be established if the MIC falls below or above the three to four dilutions used in the test panel. Susceptibility reports include interpretation of breakpoint MIC as S, I, or R. MALDI-TOF MS—matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.