Amikacin microbiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Microbiology
Gram-negative
- Pseudomonas species
- Escherichia coli
- Proteus species (indole-positive and indole-negative)
- Providencia species
- Klebsiella species
- Enterobacter species
- Serratia species
- Acinetobacter species
- Citrobacter freundii
When strains of the above organisms are found to be resistant to other aminoglycosides, including gentamicin, tobramycin and kanamycin, many are susceptible to amikacin in vitro.
Gram-positive
- Penicillinase and non-penicillinase-producing Staphylococcus species, including methicillin-resistant strains.
However, aminoglycosides in general have a low order of activity against other Gram-positive organisms, viz., Streptococcus pyogenes, enterococci and Streptococcus pneumoniae (formerly Diplococcus pneumoniae).
Amikacin resists degradation by most aminoglycoside inactivating enzymes known to affect gentamicin, tobramycin, and kanamycin.
In vitro studies have shown that amikacin sulfate combined with a beta-lactam antibiotic acts synergistically against many clinically significant Gram-negative organisms.
Disc Susceptibility Test
Quantitative methods that require measurement of zone diameters give the most precise estimates of antibiotic susceptibility. One such procedure[1] has been recommended for use with discs to test susceptibility to amikacin. Interpretation involves correlation of the diameters obtained in the disc test with MIC values for amikacin. When the causative organism is tested by the Kirby-Bauer method of disc susceptibility, a 30 mcg amikacin disc should give a zone of 17 mm or greater to indicate susceptibility. Zone sizes of 14 mm or less indicate resistance. Zone sizes of 15 to 16 mm indicate intermediate susceptibility. With this procedure, a report from the laboratory of "susceptible" indicates that the infecting organism is likely to respond to therapy. A report of "resistant" indicates that the infecting organism is not likely to respond to therapy. A report of "intermediate susceptibility" suggests that the organism would be susceptible if the infection is confined to tissues and fluids (e.g., urine) in which high antibiotic levels are attained.[2]
References
Adapted from the FDA Package Insert.