RELATIONSHIP BETWEEN THE ANTIMICROBIAL SUSCEPTIBILITIES OF KLEBSIELLA SPECIES AND THEIR PRODUCTIONS OF INDOLE AND PIGMENT

Abstract

Minimum inhibitory concentrations (MICs) of eight antibiotics for 448 Klebsiella isolates were examined to study the relationship between the antimicrobial susceptibilities of Klebsiella species and their productions of indole and pigment. There were no major differences in the susceptibility patterns of the indole-negative strains and the indole-positive, pigment non-producing strains. Pigment non-producing strains were almost similar to the pigment producing strains in susceptibilities to cefoxitin, ceftizoxime, kanamycin, gentamicin, and tetracycline but differed in showing greater susceptibilities to ampicillin, cephalothin, and cefazolin. At an inoculum of 10⁶ colony-forming units, 228 strains (97.0%) were inhibited by cefazolin at a concentration of 12.5μg/ml, as compared with 84 strains (94.4%) of indole-positive, pigment non-producing strains and 104 strains (83.9%) of pigment producing strains. The concentration of cefazolin required to inhibit the growth of 90% of total number (MIC₉₀) of the pigment producing strains were 100μg/ml, whereas the MIC₉₀ of cefazolin against the indole-negative strains and the indole-positive, pigment non-producing strains were 3.13, and 6.25μg/ml, respectively.
Of the 32 cefazolin-resistant Klebsiella strains, 14 were isolated from urine and 11 from feces. There were no evidence of epidemics of infection due to the cefazolin-resistant strains during the investigation period.