1986
DOI: 10.1128/aac.29.3.418
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Discrepancies between MBC and actual killing of viridans group streptococci by cell-wall-active antibiotics

Abstract: We determined the MBC of amoxicillin and vancomycin, two antibiotics advocated for treatment and prophylaxis of bacterial endocarditis, for 24 strains of viridans group streptococci isolated from patients with endocarditis. We found that the MIC of amoxicillin for all strains was <0.25 ,ug/ml and the MBC was either low (<0.5 ,ug/ml) in 6 nontolerant strains or high (>128 pg/ml) in 18 tolerant strains. The MIC of vancomycin for the 24 strains was '1 ,ug/ml, and the MBC was either low (<1 tig/ml) for 3 nontolera… Show more

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Cited by 39 publications
(28 citation statements)
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“…In an in vitro test, some of the bacterial cells may be dormant or replicating slowly and thus are not killed by the otherwise bactericidal agent. These "persisters" usually constitute Ͻ0.1% of the final inoculum but will be apparent as growth on agar medium during the course of time-kill or MBC testing (8,26,49,53,79,88). Notably, when retested these persisters appear just as susceptible as the parent strain and do not constitute a resistant subpopulation (8).…”
Section: Problems With Bactericidal Determinationsmentioning
confidence: 99%
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“…In an in vitro test, some of the bacterial cells may be dormant or replicating slowly and thus are not killed by the otherwise bactericidal agent. These "persisters" usually constitute Ͻ0.1% of the final inoculum but will be apparent as growth on agar medium during the course of time-kill or MBC testing (8,26,49,53,79,88). Notably, when retested these persisters appear just as susceptible as the parent strain and do not constitute a resistant subpopulation (8).…”
Section: Problems With Bactericidal Determinationsmentioning
confidence: 99%
“…(i) Persisters. The bactericidal activity of certain antimicrobial agents, notably ␤-lactams, is directly related to the rate of bacterial growth (10,26,30,49,53,58,61,79,81,88). The lower the rate of growth, the slower the bactericidal effect.…”
Section: Problems With Bactericidal Determinationsmentioning
confidence: 99%
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“…In the latter condition, endocarditis can be prevented only by prolonged levels of antibiotics, such as are achievable after multiple doses [18; R. M., P. Francioli, M. r.o, unpublished observations]. Because most strains of viridans streptococci appear to be poorly susceptible to the bactericidal action of cell wall-active antibiotics [4,5], drugs providing high and prolonged serum antibiotic activity after a single dose should be investigated for preventing experimental bacterial endocarditis after challenge with heavy loads of bacteria.…”
Section: Discussionmentioning
confidence: 99%
“…When these antibiotics do not rapidly kill the bacteria used for challenge, however, the efficacy of singledose prophylaxis is limited to the animals challenged with the lowest bacterial inoculum that infects 90070 of controls (ID 9o ) [1][2][3]. Isolates of viridans streptococci poorly susceptible to the bactericidal action of cell wall-active antibiotics are increasingly reported from patients with endocarditis [4] and among other clinical isolates of a-hemolytic streptococci [5]. Against these bacteria, even a single dose of a synergistic combination of amoxicillin plus gentamicin failed to protect animals challenged with inocula exceeding the ID 9o [6], and successful prevention of endocarditis could only be achieved by administering multiple doses of antibiotics that provide sustained blood levels after bacterial challenge (R. M., P. Francioli, M. P. G., unpublished observations).…”
mentioning
confidence: 99%