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Occurrence of quinolone resistance in Staphylococcus aureus from nosocomial infection
1Robert Koch Institute of the Federal Bureau of Health, Branch Wernigerode, Germany.
Abstract:
Among 63 Staphylococcus aureus isolates (one isolate per one patient) counted from infections (from August to November 1991) in hospital T., eight exhibited resistance to fluoroquinolones. Seven of these quinolone-resistant isolates were multiply- and methicillin-resistant S. aureus (QR-MRSA). The results of phage-, plasmid- and genotyping (pulsed field electrophoresis) revealed that six different strain-clones of these MRSA were spread in the hospital. In vitro spontaneous mutants resistant to fluoroquinolones are 10-100-fold more frequent in MRSA than in other S. aureus when selected on isosensitest-agar containing 1 microgram/ml of ciprofloxacin. However, the same mutant frequencies were found in strain 8325-4 with and without the mecA-determinant. The resistance phenotype was stable over 30 generations of subculture in nutrient broth as well in natural quinolone resistant MRSA as in mutants of other types of S. aureus selected in vitro. The phenotypic association of quinolone resistance and MRSA is rather likely due to a higher frequency of spontaneous resistant mutants which are present in natural populations of MRSA. Data of chemotherapy prior to the isolation of S. aureus show that three of seven patients from whom QR-MRSA were isolated were treated with a quinolone. In eight cases of infections with non-MRSA and quinolone treatment the isolated S. aureus strains were in vitro sensitive to quinolones.
Insights
Quinolone resistance is more frequent in methicillin-resistant Staphylococcus aureus (MRSA) due to a higher rate of spontaneous mutations. This finding is crucial for understanding and combating antibiotic resistance in hospital settings.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Staphylococcus aureus is a common cause of hospital-acquired infections.
- Methicillin-resistance (MRSA) is a significant challenge in treating S. aureus infections.
- Fluoroquinolone antibiotics are frequently used to treat S. aureus infections.
Purpose of the Study:
- To investigate the prevalence and characteristics of fluoroquinolone resistance in Staphylococcus aureus isolates from a hospital setting.
- To determine the relationship between methicillin resistance and fluoroquinolone resistance in S. aureus.
- To explore the mechanisms underlying fluoroquinolone resistance in MRSA.
Main Methods:
- Isolation and characterization of Staphylococcus aureus from patient infections.
- Antimicrobial susceptibility testing for fluoroquinolones.
- Genotyping techniques including phage, plasmid, and pulsed-field gel electrophoresis.
- In vitro selection of spontaneous fluoroquinolone-resistant mutants.
Main Results:
- Eight out of 63 S. aureus isolates exhibited fluoroquinolone resistance; seven were identified as quinolone-resistant MRSA (QR-MRSA).
- Six distinct strain-clones of QR-MRSA were identified within the hospital.
- Spontaneous fluoroquinolone-resistant mutants occurred 10-100 times more frequently in MRSA compared to other S. aureus strains in vitro.
- The presence of the mecA determinant (conferring methicillin resistance) did not influence spontaneous fluoroquinolone resistance mutation frequency.
- The resistance phenotype was stable over prolonged subculturing.
Conclusions:
- The phenotypic association between quinolone resistance and MRSA is likely due to a higher frequency of spontaneous resistant mutants in natural MRSA populations.
- Understanding these resistance mechanisms is vital for effective treatment strategies against MRSA infections.
- Further research into the genetic and molecular basis of this increased mutation frequency is warranted.