The antimicrobial spectrum of an
antibiotic means the range of
microorganisms it can kill or inhibit. Antibiotics can be divided into
broad-spectrum antibiotics, extended-spectrum antibiotics and
narrow-spectrum antibiotics based on their spectrum of activity. Detailedly, broad-spectrum antibiotics can kill or inhibit a wide range of microorganisms; extended-spectrum antibiotic can kill or inhibit
Gram positive bacteria and some
Gram negative bacteria; narrow-spectrum antibiotic can only kill or inhibit limited species of bacteria.[1][2][3]
Currently no antibiotic's spectrum can completely cover all types of microorganisms.[4]
Determination
The antimicrobial spectrum of an antibiotic can be determined by testing its antimicrobial activity against a wide range of microbes in vitro. Nonetheless, the range of microorganisms which an antibiotic can kill or inhibit in vivo may not always be the same as the antimicrobial spectrum based on data collected in vitro.[2][5]
Significance
Narrow-spectrum antibiotics have low propensity to induce
bacterial resistance and are less likely to disrupt the
microbiome (normal
microflora).[3] On the other hand, indiscriminate use of
broad-spectrum antibiotics may not only induce the development of bacterial resistance and promote the emergency of
multidrug-resistant organisms, but also cause off-target effects due to
dysbiosis.[3][6] They may also have side effects, such as diarrhea or rash.[7] Generally, a broad antibiotic has more clinical indications, and therefore are more widely used.[2][8] The Healthcare Infection Control Practices Advisory Committee (HICPAC) recommends the use of narrow-spectrum antibiotics whenever possible.[9]