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Plasmid analysis of Shigella dysenteriae type 1 isolates obtained from widely scattered geographical locations
K Haider1, B A Kay, K A Talukder
1International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka.
Abstract:
Plasmid profiles and antimicrobial susceptibility patterns of 343 strains of Shigella dysenteriae type 1, obtained from 18 different geographical locations, were analyzed. Three plasmids, with molecular sizes of 140, 6, and 2 megadaltons (MDa), were present in 94, 98, and 96%, respectively, of the 343 strains isolated during either epidemic or nonepidemic periods from 1965 to 1987. In addition to these plasmids, 83% of the strains harbored a 4-MDa plasmid and 25% harbored a 20-MDa plasmid. Various plasmid profiles were observed in which the 140-, 6-, and 2-MDa plasmids occurred commonly, irrespective of the place of isolation and drug resistance pattern of the strains. Certain profiles showed significant association with drug resistance patterns. These findings suggest that three plasmids, of molecular sizes 140, 6, and 2 MDa, are unique to S. dysenteriae type 1 strains and may indicate the global spread of a pathogenic bacterial clone. Additionally, these core plasmids, plus plasmids of various other sizes, could be used to identify emerging subclones which are causing both epidemic and sporadic disease. Thus, plasmid profiles of S. dysenteriae type 1 strains can be used to monitor possible pandemic strains as well as individual epidemic strains.
Insights
Plasmid profiles of Shigella dysenteriae type 1 strains reveal unique core plasmids (140, 6, and 2 megadaltons) common globally. These genetic markers aid in tracking pandemic strains and emerging subclones.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Shigella dysenteriae type 1 is a significant cause of bacterial dysentery.
- Understanding the genetic basis of its pathogenicity and spread is crucial for public health.
Purpose of the Study:
- To analyze plasmid profiles and antimicrobial susceptibility of Shigella dysenteriae type 1 strains.
- To identify unique plasmids associated with this pathogen and their potential role in global dissemination.
Main Methods:
- Analysis of plasmid DNA from 343 Shigella dysenteriae type 1 strains.
- Determination of molecular sizes of plasmids using established methods.
- Correlation of plasmid profiles with geographical origin and antimicrobial resistance patterns.
Main Results:
- Three plasmids (140, 6, and 2 megadaltons) were consistently present in 94-98% of strains.
- Additional plasmids (4-MDa and 20-MDa) were found in a subset of strains.
- The 140-, 6-, and 2-MDa plasmids were common across diverse locations and resistance profiles, suggesting they are unique to S. dysenteriae type 1.
Conclusions:
- The 140-, 6-, and 2-MDa plasmids are likely unique to Shigella dysenteriae type 1, indicating a potential global spread of a common pathogenic clone.
- Plasmid profiling can serve as a tool to monitor pandemic strains and identify emerging subclones responsible for both epidemic and sporadic disease.
- These findings support the use of plasmid profiles for epidemiological surveillance of Shigella dysenteriae type 1.