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Antimicrobial Agents and Chemotherapy logoLink to Antimicrobial Agents and Chemotherapy
. 1980 Oct;18(4):579–581. doi: 10.1128/aac.18.4.579

Antimicrobial susceptibility testing of Streptococcus pneumoniae by micro-broth dilution.

M M Tarpay, D F Welch, M I Marks
PMCID: PMC284052  PMID: 6905715

Abstract

Thirty-three clinical isolates of Streptococcus pneumoniae were tested for susceptibility to penicillin and ampicillin by a standard agar dilution method. Results were compared to those obtained using a micro-broth dilution technique in which Mueller-Hinton broth was supplemented with 5% difibrinated whole sheep blood. Among the 33 strains, 2 were resistant (minimal inhibitory concentration, 8 micrograms/ml), 10 were relatively resistant (minimal inhibitory concentration, 0.12 to 0.5 micrograms/ml), and 20 were susceptible (minimal inhibitory concentration, less than or equal to 0.06 micrograms/ml) to penicillin by both methods. Only one stain showed a two-dilutional-step difference by micro-broth and agar dilution testing resulting in categorization as relatively resistant by the former method but susceptible by the latter. A 1-microgram oxacillin disk correctly identified 11 of the 12 resistant strains. The micro-broth dilution technique is a reliable, simple method for penicillin or ampicillin susceptibility testing of pneumococci and economically feasibile to perform manually or with a semiautomated system.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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