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S. typhi with transferable chloramphenicol resistance isolated in Chandigarh during 1983-87
A Kapil1, A Ayyagari, R K Garg
1Dept. of Medical Microbiology, P.G.I.M.E.R., Chandigarh.
Abstract:
Plasmid mediated chloramphenicol resistance in S. Typhi has been reported since the outbreak in Kerala in 1972 from India. 876 strains of S. typhi isolated at Chandigarh during Jan 1983 to July 1987 were investigated for the incidence of chloramphenicol resistance. In 1983 34% of the total isolated were resistant to chloramphenicol, in 1984 24%, during 1985 5% & while in 1986 2% of the strains showed chloramphenicol resistance. The resistant strain showed chloramphenicol resistance. The resistant strains had an minimum inhibitory concentration of 64-128 ug/ml for chloramphenicol. All the resistant strains showed multiple drug resistance with the resistance pattern CSSuT. Of these 50 strains were studied for their mechanism of resistance by conjugation experiments which showed that CSSUT pattern could be transferred to E. coli J-53 and E. coli J-62 in primary and secondary transfer experiments indicating that the resistance was carried on a transferable plasmid.
Insights
Plasmid-mediated chloramphenicol resistance in Salmonella Typhi strains decreased significantly in Chandigarh from 1983 to 1986. This resistance, linked to multiple drug resistance, was found to be transferable via plasmids.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Plasmid-mediated chloramphenicol resistance in Salmonella Typhi (S. Typhi) was first documented in India during a 1972 outbreak.
- Chloramphenicol resistance poses a significant challenge in treating typhoid fever.
Purpose of the Study:
- To investigate the incidence and trends of chloramphenicol resistance in S. Typhi strains isolated in Chandigarh, India.
- To characterize the resistance patterns and mechanisms in these strains.
Main Methods:
- Analysis of 876 S. Typhi strains isolated between January 1983 and July 1987.
- Determination of chloramphenicol minimum inhibitory concentrations (MICs).
- Conjugation experiments to assess plasmid-mediated resistance transfer.
Main Results:
- A marked decline in chloramphenicol resistance was observed, from 34% in 1983 to 2% in 1986.
- Resistant strains exhibited high MICs (64-128 µg/ml) and multiple drug resistance (CSSuT pattern).
- Conjugation experiments confirmed that the CSSuT resistance pattern was transferable via plasmids to E. coli strains.
Conclusions:
- The incidence of plasmid-mediated chloramphenicol resistance in S. Typhi in Chandigarh decreased substantially during the study period.
- The observed multiple drug resistance is plasmid-borne and transferable, highlighting the potential for further dissemination.
- Continued surveillance of antimicrobial resistance in S. Typhi is crucial.