Salmonella enteritidis outbreak in Thailand: study by random amplified polymorphic DNA (RAPD) analysis

Area of Science:

• Microbiology
• Epidemiology
• Molecular Biology

Background:

• A significant outbreak of Salmonella enteritidis occurred in Thailand starting in 1990.
• Salmonella enteritidis isolates were predominantly found in chicken and human sources nationwide.
• The sustained high rate of spread necessitated an investigation into potential clonal origins.

Purpose of the Study:

• To investigate clonal involvement in the 1990 Salmonella enteritidis outbreak in Thailand.
• To identify the specific clones responsible for the ongoing epidemic.
• To determine the potential source and invasive characteristics of Salmonella enteritidis during the outbreak.

Main Methods:

• Clonal identification of 125 Salmonella enteritidis isolates from 1990-1993.
• Utilized Random Amplified Polymorphic DNA (RAPD) analysis for genotyping.
• Analysis of isolate distribution across different sources (chicken, human, blood).

Main Results:

• Eight distinct clones (profiles no. 1-8) were identified using RAPD analysis.
• A single predominant clone, profile no. 4, accounted for 93.6% of all isolates.
• This dominant clone was prevalent in both chicken and human isolates, suggesting chickens as the primary source.
• Nearly 40% of Salmonella enteritidis isolates were from blood cultures, indicating potential invasiveness.

Conclusions:

• The Salmonella enteritidis outbreak in Thailand was largely driven by a single clone (RAPD profile no. 4).
• Chickens are strongly implicated as the source of this dominant Salmonella enteritidis clone.
• The high proportion of blood isolates suggests significant invasiveness of Salmonella enteritidis in the Thai population during the epidemic.