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PubMed · 6546491

Penicillin-resistant pneumococci.

D K Oxley
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Abstract

Because of reports documenting the occurrence of pneumococci resistant to penicillin, the Microbiology Resource Committee of the College of American Pathologists studied the accuracy of various Kirby-Bauer disks in identifying a pneumococcal organism known to be clinically resistant to penicillin. The only disk that showed acceptable performance was the 1-microgram oxacillin disk, using the inhibition diameter of 19 mm or less as the criterion for predicting clinical penicillin resistance. It is particularly important to understand that, at present, penicillin disks do not provide acceptable predictive accuracy.

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MethicillinNafcillinOxacillinPenicillin ResistancePenicillinsStreptococcus pneumoniaeJournal Article

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D K Oxley. 1984. Penicillin-resistant pneumococci.. https://pubmed.ncbi.nlm.nih.gov/6546491/

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PubMed1994

[Multi-center evaluation to discriminate between the strains of methicillin-resistant Staphylococcus aureus (MRSA) and those susceptible (MSSA) by Showa oxacillin and methicillin disk susceptibility tests].

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Methicillin↗
PubMed1992

Correlation between regulation of mecA transcription and expression of methicillin resistance in staphylococci.

Total RNA was used to study the effect of penicillinase plasmid pI524 and of mecR, the regulatory region located on the methicillin resistance determinant (mec), on the expression of mecA, the gene coding for the low-affinity penicillin-binding protein PBP2', in methicillin-resistant staphylococci. In the present report, we show that the regulation of methicillin resistance occurs primarily at the level of mecA transcription and that in the presence of intact plasmid pI524 or mecR, the gene undergoes negative control. The relative amount of mecA mRNA present during exponential growth in uninduced cultures matches the type of mecA regulation and decreases in the following order: constitutive greater than pI524 greater than mecR-dependent mecA expression. Induction of mecA by methicillin is faster in pI524- than in mecR-controlled strains. The overall mRNA half-life is similar for all strains analyzed. Our results indicate that methicillin resistance under mecR control in certain staphylococcal strains could escape detection by the standard disk diffusion test and broth microdilution test because of the very slow derepression of the mecA gene. This finding is of importance for the clinical detection of this type of methicillin resistance.

Methicillin↗