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Resistance of Staphylococcus aureus to semisynthetic penicillins and cephalothin
Abstract:
Six strains of Staphylococcus aureus resistant to semisynthetic penicillins were recovered from clinical sources during a two-month period. Resistance was detected by standard disk sensitivity tests at 37 C. Two resistant strains were responsible for infections (one of which was fatal), and five strains were susceptible only to phage type 92. All of the strains produced penicillinase, which did not destroy oxacillin, and each was resistant to oxacillin at low inocula. Relative resistance to cephalosporin was demonstrable by the tube dilution assay but not by standard disk tests. The strains susceptible to phage type 92 were susceptible to vancomycin and to the synergistic action of oxacillin or cephalothin plus gentamicin.
Insights
Six Staphylococcus aureus strains resistant to semisynthetic penicillins were identified. These resistant strains caused infections, with one fatality, and showed varied susceptibility to antibiotics like vancomycin and gentamicin.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Emergence of antibiotic resistance in Staphylococcus aureus poses a significant public health threat.
- Semisynthetic penicillins are commonly used antibiotics, making resistance to them a critical concern.
Purpose of the Study:
- To identify and characterize strains of Staphylococcus aureus resistant to semisynthetic penicillins.
- To evaluate the susceptibility of these resistant strains to other antibiotics.
Main Methods:
- Isolation of Staphylococcus aureus from clinical sources over a two-month period.
- Detection of penicillin resistance using standard disk sensitivity tests at 37°C.
- Assessment of antibiotic susceptibility using tube dilution assays and disk tests.
Main Results:
- Six strains of Staphylococcus aureus resistant to semisynthetic penicillins were recovered.
- Two strains were associated with infections, including one fatal case.
- All strains produced penicillinase, were resistant to oxacillin at low inocula, and showed relative cephalosporin resistance by tube dilution but not disk tests.
- Strains susceptible to phage type 92 were susceptible to vancomycin and synergistic combinations of oxacillin/cephalothin plus gentamicin.
Conclusions:
- The study identified clinically significant strains of Staphylococcus aureus resistant to semisynthetic penicillins.
- These resistant strains exhibit complex resistance patterns, necessitating careful antibiotic selection.
- Vancomycin and combination therapies show promise against specific phage types of resistant Staphylococcus aureus.