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Gentamicin- and silver-resistant pseudomonas in a burns unit
Abstract:
In 1977-8 gentamicin-resistant strains of Pseudomonas aeruginosa became very common in a burns unit, over 90% being resistant at the peak of the outbreak. Some strains were also resistant to silver nitrate, though silver resistance was not found in any other strains of Ps aeruginosa isolated. Unlike the gentamicin resistance, the silver resistance was unstable, and strains became sensitive on repeated subculture. All the gentamicin-resistant strains of Ps aeruginosa were of the same serotype (O:11, H:2,5). Though gentamicin resistance could be transferred in vitro from resistant strains of Ps aeruginosa to one sensitive strain of Ps aeruginosa, there was no evidence of in-vivo transfer of gentamicin resistance between strains of pseudomonas in the patients' burns, nor was there evidence of transfer of gentamicin resistance between Ps aeruginosa and enterobacteria. Carbenicillin-resistant and gentamicin-resistant Ps aeruginosa were sometimes found in the same burns, but no gentamicin-carbenicillin (doubly) resistant strains were found among the 986 strains tested during the outbreak. The outbreak of gentamicin-resistant Ps aeruginosa from burns was not reduced by stopping treatment with gentamicin and its analogues but only by segregating all patients with Ps aeruginosa in one of the two wards of the unit and admitting new patients only to the other ward.
Insights
Gentamicin-resistant Pseudomonas aeruginosa outbreaks in burns units are challenging. Patient segregation, not antibiotic changes, effectively controlled a 1977-8 gentamicin-resistant Pseudomonas aeruginosa outbreak.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Hospital Epidemiology
Background:
- Gentamicin-resistant Pseudomonas aeruginosa (Ps aeruginosa) emerged as a significant issue in a hospital burns unit during 1977-8.
- High prevalence (over 90%) of gentamicin resistance was observed in Ps aeruginosa strains during the outbreak's peak.
Purpose of the Study:
- To investigate the characteristics and control of a gentamicin-resistant Ps aeruginosa outbreak in a burns unit.
- To determine the transferability and stability of gentamicin resistance and identify effective control measures.
Main Methods:
- Serotyping of Ps aeruginosa strains to identify common characteristics.
- In vitro and in vivo studies to assess gentamicin resistance transfer.
- Monitoring of antibiotic resistance patterns, including silver nitrate and carbenicillin resistance.
- Evaluation of different infection control strategies, including antibiotic treatment changes and patient segregation.
Main Results:
- All gentamicin-resistant Ps aeruginosa strains belonged to a single serotype (O:11, H:2,5).
- Silver nitrate resistance was observed in some strains but was unstable upon subculture.
- In vitro transfer of gentamicin resistance was demonstrated, but no evidence of in vivo transfer was found between Ps aeruginosa strains or with enterobacteria.
- No doubly resistant (gentamicin-carbenicillin) strains were identified.
- Stopping gentamicin treatment did not reduce the outbreak; patient segregation into separate wards was effective.
Conclusions:
- The outbreak was caused by a specific, highly prevalent strain of gentamicin-resistant Ps aeruginosa.
- Antibiotic resistance transfer mechanisms require further investigation, but in vivo transfer was not evident in this study.
- Patient segregation proved to be the most effective control strategy for this outbreak, highlighting the importance of non-pharmacological interventions in managing hospital-acquired infections.