Pg. 88-92 Absence of Staphylococcus aureus in the litchi export chain

Staphylococcus aureus is an opportunistic human pathogen capable of causing numerous human diseases. The majority of nosocomial infections as well as food poisoning incidences worldwide are due to S. aureus. In this study, 18 isolates obtained from a litchi export chain study was identified using biochemical as well as molecular methods. These isolates were selected based on their characteristic growth on Staphylococcus selective medium and was therefore presumed to be potential foodborne pathogens. Biochemical tests utilised included catalase, DNase, mannitol, alkaline phosphatase and coagulase tests. Molecular identification methods used were PCR-RFLPs, with cleavage by HindiII. No isolates from the litchi export chain were identified as S. aureus pathogens.

Summary:

• Staphylococcus aureus is a significant human pathogen responsible for food poisoning and nosocomial infections worldwide.
• The study aimed to determine the presence of S. aureus in the South African litchi export chain, given the high likelihood of contamination from food handlers who may carry the bacteria.
• Eighteen bacterial isolates suspected to be Staphylococcus spp. were collected from various points in the litchi export chain, including packhouse surfaces, handlers’ hands, cold rooms, and transport crates.
• Biochemical tests (catalase, DNase, mannitol, coagulase, and phosphatase) were used to identify isolates and differentiate S. aureus from other Staphylococcus species.
• Molecular identification using PCR-RFLP with HindIII enzyme confirmed none of the isolates matched the genetic profile of S. aureus.
• Although some isolates showed partial similarity to S. aureus, they were determined to be other Staphylococcus species.
• The coagulase test, a key diagnostic for pathogenic S. aureus, was negative for the majority of isolates, indicating a low risk of pathogenic contamination.
• The study emphasizes the importance of molecular techniques alongside biochemical tests for accurate identification of S. aureus.
• Results suggest that the litchi export chain represents a low risk for S. aureus contamination, likely due to good hygiene practices and maintained cold chain conditions.
• Despite possible temperature fluctuations during transport, which could increase survival risk, no pathogenic S. aureus was found in a comprehensive two-year study.
• This finding supports the safety of the South African litchi industry’s export practices under Eurepgap, HACCP, and BRC certification standards.
• The study highlights that reliance solely on selective media and biochemical tests may be inadequate without molecular verification for pathogen identification.