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Development of trimethoprim-resistance in Salmonella typhi during therapy
Abstract:
A typhoid patient was infected with a fully-sensitive, plasmidless strain of Salmonella typhi which acquired resistance to kanamycin, sulfamethoxazole and trimethoprim during cotrimoxazole therapy. The resistant post-treatment strain harboured 4 plasmids of 62, 4.1, 3.8 and 3.0 Md in size. Kanamycin-, sulfamethoxazole- and trimethoprim-resistance were borne on a transferable 62 Md plasmid which was compatible with groups FI, FIme, FII, FIV, H1, H2, B, I1, I2, J, K, M, N, T, X, W and P. Sulfamethoxazole-resistance was also borne on the 4.1 Md plasmid. The 3.8 Md plasmid was not transferable; the 3.0 Md plasmid was transferable but did not confer antibiotic resistance. Excluding the strain described here, only 5 out of 35 other S typhi isolates contained plasmids. This is the first report of trimethoprim-resistant S typhi in Hong Kong.
Insights
A Salmonella typhi strain developed resistance to multiple antibiotics, including trimethoprim, during treatment. This resistance was linked to a transferable plasmid, a first for Hong Kong.
Area of Science:
- Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Salmonella typhi is a significant human pathogen causing typhoid fever.
- Antibiotic resistance in S. typhi poses a major public health threat.
- Understanding the genetic basis of antibiotic resistance is crucial for effective treatment.
Observation:
- A patient's Salmonella typhi strain acquired resistance to kanamycin, sulfamethoxazole, and trimethoprim during cotrimoxazole therapy.
- The resistant strain possessed four plasmids, with a 62 megadalton (Md) plasmid mediating resistance to all three antibiotics.
- Sulfamethoxazole resistance was also found on a 4.1 Md plasmid, and a 3.0 Md plasmid was transferable without conferring resistance.
Findings:
- The 62 Md plasmid, carrying kanamycin, sulfamethoxazole, and trimethoprim resistance, was transferable and compatible with numerous plasmid groups.
- This study reports the first instance of trimethoprim-resistant S. typhi identified in Hong Kong.
- Plasmids were uncommon in other S. typhi isolates examined, with only 5 out of 35 containing them.
Implications:
- The emergence and transferability of multi-drug resistance plasmids in S. typhi highlight the need for continuous surveillance.
- This finding underscores the importance of monitoring antibiotic resistance patterns, especially for drugs like trimethoprim.
- Effective strategies are needed to combat the spread of antibiotic-resistant typhoid strains globally.