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 Original Articles |
| Effect of Coexistence of Antimicrobial-susceptible Gram-negative Bacilli on the Resistant Gram-negative Bacilli in the Absence of Antimicrobial Agents |
| Dong Eun Yong/Eung Chil Choi/Kyung Won Lee/Jong Hwa Yum/Yun Sop Chong |
| Department of Clinical Pathology and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Korea. |
Vol.34 Num.1 (p9~17)
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Background: Carrying antimicrobial resistance genes is a burden to bacteria. Therefore, in the absence of antimicrobial selective pressure, susceptible bacteria are expected to replace resistant ones. The cost was reported to decrease with
time, but the effect of different species of susceptible bacteria on extended-specturm β-lactamase (ESBL)-. AMPC β-lactamase-, and VIM-2 metallo-β-lactamase-producing gram-negative bacilli are not known. The aim of this study was to determine the effect in vitro.
Methods: Antimicrobial-susceptible and -resistant strains of Escherichia coli, enterobacter aerogenes, Klebsiella pneumoniae, and Acinetobacter baumannii were subcultured daily in glucose limited minimal salt medium at 30℃ and 37℃, and
the numbers of cells (CFU/㎖) were determined by culturing on Mueller-Hinton agar and MacConkey agar plates.
Results: Continued incubation without subculture of both individual and mixed cultures at 37℃ showed higher counts of a ESBL-producing K. pneumoniae than a susceptible E. coli. Daily subcultures of two strains in a tube showed the counts
were:ESBL-producing K. pneumoniae >susceptible E. coli; susceptible E. aerogenes >ESBL-producing K. pneumoniae; susceptible E. aerogenes >VIM-2-β-lactamase-producing Acinetobacter baumannii. The counts were similar for susceptible K. pneumoniae and AmpC β-lactamase-hyperproducing E. aerogenes. Initial low count of a susceptible E. coli and an ESBL-producing K. pneumoniae at 30℃ gradually increased with continued subculture.
Conclusion: Growth of not all resistant bacteria are slower and the growth improves withcontinued subculture. Coexistence of a susceptible bacteria with resistant bacteria in GLMS medium both at 30℃ and 37℃ does not reduce the number of
resistant bacteria.
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Keywords : Antimicrobial resistance, Cost of resistance, Fitness |
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