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Published on: August 11, 2014
Emerging resistance in Salmonella enterica serotype Typhi in Hong Kong
1Department of Microbiology, The Chinese University of Hong Kong, The Prince of Wales Hospital, Shatin, New Territories, Hong Kong, ROC.
Abstract:
A total of 182 Salmonella enterica serotype Typhi isolated from three hospitals in Hong Kong from 1986 to 1992 were tested for their susceptibility to 21 antimicrobial agents. Four percent or less were resistant to chloramphenicol, ampicillin, some of the cephalosporins, nalidixic acid, tetracycline and trimethoprim and 6% to 1024 mg/l sulfamethoxazole. All were susceptible to the aminoglycosides and the 4-quinolones. Nineteen isolates were resistant to at least 1, and up to 9, antibiotics. Of 8 chloramphenicolor multiply-resistant isolates studied, only 3 could transfer their resistances while resistance of one could only be mobilized. Four of 5 ampicillin-resistant strains produced a beta-lactamase of pI 5.5. Antibiotic resistances were mediated by plasmids of 106, 116 or 221 kb of incompatibility groups H, I1 and K. Three resistant isolates did not harbour any plasmid. A total of 43 (24%) S. Typhi harboured plasmids ranging in size from 4.3 to 221 kb. Plasmids of 106 kb and 8.5 kb were found in 17 and 10 isolates, respectively. Restriction enzyme digestion of these two plasmids showed that each could be differentiated into 3 types. Of 89 isolates that were phage typed, 38% were untypable, while 17% and 12% were of phage types E1 and A, respectively, and the rest belonged to 17 other types.
Insights
Salmonella Typhi in Hong Kong showed low resistance to many antibiotics between 1986-1992, but some strains exhibited multi-drug resistance. Plasmids mediated these antibiotic resistances, with varying phage types observed.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Salmonella enterica serotype Typhi (S. Typhi) is a significant human pathogen.
- Understanding antimicrobial susceptibility patterns is crucial for effective treatment and public health.
- Data on S. Typhi antibiotic resistance in Hong Kong during the late 20th century is important for historical context.
Purpose of the Study:
- To determine the antimicrobial susceptibility profile of S. Typhi isolates from Hong Kong.
- To investigate the mechanisms of antibiotic resistance, including plasmid mediation and beta-lactamase production.
- To characterize the phage types of the S. Typhi isolates.
Main Methods:
- Antimicrobial susceptibility testing against 21 agents.
- Plasmid analysis, including transferability, mobilization, and characterization by size and incompatibility groups.
- Detection of beta-lactamase production.
- Phage typing of S. Typhi isolates.
Main Results:
- Low resistance rates (<4%) were observed for chloramphenicol, ampicillin, some cephalosporins, nalidixic acid, tetracycline, and trimethoprim.
- High susceptibility was noted for aminoglycosides and 4-quinolones.
- Nineteen isolates displayed multi-drug resistance (1 to 9 antibiotics).
- Plasmid-mediated resistance was identified, with specific plasmid sizes (106, 116, 221 kb) and incompatibility groups (H, I1, K).
- Beta-lactamase production was found in ampicillin-resistant strains.
- Phage typing revealed a significant proportion of untypable strains (38%) and common types E1 (17%) and A (12%).
Conclusions:
- S. Typhi isolates in Hong Kong during 1986-1992 generally remained susceptible to many key antibiotics.
- Plasmid-mediated resistance and beta-lactamase production were mechanisms contributing to observed multi-drug resistance.
- The prevalence of specific phage types suggests potential epidemiological patterns.
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