Table 1.

Characteristics of genotypic and phenotypic antimicrobial resistance.

Characteristic	Genetic AMR	Phenotypic AMR
Resistance directly attributable to a genetic change (de novo mutation or acquisition of new genes)	Yes	No
Resistance manifest in progeny of the resistant bacterial cells	Yes	No or limited
MIC, relative to sensitive strain	Increased	Unchanged
MBC, relative to sensitive strain	Increased	Increased under some circumstances
Clinical outcome	Primary treatment failure	Primary treatment failure
		Relapse
		Emergence of genetic AMR
Clinical strategy	Switch antibiotics	Combine antibiotics
		Include antibiotics that kill bacteria expressing phenotypic AMR to conventional antibiotics
		Increase treatment time

MIC, minimum inhibitory concentration, the lowest concentration of the antibiotic required to prevent growth of the bacteria over a defined period of time; MBC, minimum bactericidal concentration, the lowest concentration of the antibiotic that kills a given proportion of the population (typically 99%) in a given period of time; AMR, antimicrobial resistance.