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Therapeutic implications in the treatment of aural Pseudomonas infections based on in vitro susceptibility patterns
J E Dohar1, M A Kenna, R M Wadowsky
1Department of Otolaryngology, University of Pittsburgh School of Medicine, Pa, USA.
Insights
Pseudomonas aeruginosa ear infection susceptibility remained stable over four years, except for ticarcillin and mezlocillin. Tobramycin and piperacillin showed excellent susceptibility for treating ear infections.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Otolaryngology
Background:
- Pseudomonas aeruginosa is a common cause of ear infections, particularly in children.
- Understanding antibiotic susceptibility patterns is crucial for effective treatment.
- Monitoring changes in susceptibility over time helps guide empirical therapy.
Purpose of the Study:
- To analyze the in vitro antibiotic susceptibility of aural Pseudomonas aeruginosa isolates.
- To detect any shifts in susceptibility patterns over a four-year period.
Main Methods:
- Retrospective case series conducted at a tertiary pediatric hospital.
- Analyzed susceptibility of P. aeruginosa ear isolates from children under 18.
- Tested in vitro susceptibility against a range of antibiotics including penicillins, cephalosporins, aminoglycosides, and others.
Main Results:
- Overall susceptibility patterns showed little change over the four years.
- Ticarcillin and mezlocillin exhibited decreased susceptibility in 1989 compared to other years.
- Piperacillin (96%) and tobramycin (94%) demonstrated high susceptibility among intravenous and aminoglycoside agents, respectively.
Conclusions:
- Antibiotic susceptibility of P. aeruginosa ear isolates was largely stable, with notable exceptions for specific semisynthetic penicillins.
- The observed changes in ticarcillin and mezlocillin susceptibility may be due to altered breakpoint definitions.
- Tobramycin and piperacillin are effective options for empirical treatment of P. aeruginosa ear infections.
Objective:
To examine the in vitro susceptibility patterns of aural isolates of Pseudomonas aeruginosa and to identify changes over a 4-year period.
Design:
Retrospective case series.
Setting:
The outpatient department at Children's Hospital of Pittsburgh (Pa), a tertiary referral center.
Patients:
Ambulatory children younger than 18 years from whose ears P aeruginosa was isolated.
Outcome Measures:
The in vitro susceptibility of aural isolates of P aeruginosa to ampicillin, cefotaxime, chloramphenicol, sulfisoxazole, ticarcillin, mezlocillin, gentamicin, tobramycin, cefazolin, tetracycline, piperacillin, nitrofurantoin, cephalexin hydrochloride, ceftriaxone, cefuroxime axetil, and sulfamethoxazole-trimethoprim.
Results And Conclusions:
No changes were found in the trends of the susceptibility patterns over the 4-year study period, with the exception of the semisynthetic penicillins, ticarcillin and mezlocillin. These two agents were found to be relatively ineffective against the strains of P aeruginosa isolated in 1989 (59% and 18% susceptibility, respectively). This finding is in contrast to their effectiveness over the remainder of the study period (96% and 90% susceptibility, respectively), which was excellent. These observations likely reflect a change in the breakpoints for the minimal inhibitory concentrations between these periods. The intravenous agent with the best susceptibility profile was piperacillin (96%). Of the aminoglycosides tested, 94% of the isolates were sensitive to tobramycin, as opposed to only 79% for gentamicin. This finding may have significance when one is empirically selecting ototopical therapy, since both tobramycin and gentamicin are available as topical preparations. Of the oral agents, the combination of sulfamethoxazole-trimethoprim was most effective (46%).