Fermentation of raw fish is a common process in Asia for improvement of shelf life and safety, however, little
is known about the survival of pathogenic bacteria in these products. Raw fish may be contaminated with
Salmonella and Vibrio species. The purpose of this study was to determine survival and potential growth
of Salmonella enterica serovar Weltevreden, S. enterica serovar Enteritidis, Vibrio cholerae and V.
parahaemolyticus as influenced by the preservation parameters (sodium chloride, garlic and lactic acid)
present in the Thai fermented fish product som-fak. The inhibitory effects of sodium chloride (0–4%), garlic
(0–10%) and lactic acid (pH levels as in som-fak) were measured in modified brain heart infusion (BHI) broth
at 30 °C. All bacteria were inhibited by 8–10% sodium chloride. Salmonella grew in all concentrations of garlic
whereas Vibrio spp. were inhibited by 1.0–1.5%. Lactic acid was inhibitory at levels above 1.5%. The
combinations of sodium chloride, lactic acid and garlic showed a distinct hurdle effect in the broth system.
Neither S. Enteritidis, V. cholerae nor V. parahaemolyticus grew in garlic (0.5–1%), regardless of the level of
sodium chloride (0.5–4% (w/v)), when lactic acid (0.5–2%) was present. S. Weltevreden was the least
inhibited of the four bacteria and grew in the combination of 0.5% garlic and 0.5% lactic acid regardless of the
NaCl level (0.5–4% (w/v)). Som-fak with 0 to 10% garlic or 2% glucose was inoculated with either (i) 103 CFU/
g Salmonella Weltevreden, (ii) 106 CFU/g garlic fermenting Lactobacillus plantarum strain 509 or (iii) a
combination of the two strains and stored at 30 °C. The Salmonella count increased to N108 CFU/g (N106 CFU/
g for 10% garlic) in all types of som-fak inoculated with S. Weltevreden within the first day. Only a
combination of at least 6% garlic and L. plantarum 509 was enough to prevent growth of the inoculated
Salmonella whereas adding the Lactobacillus strain alone or in combination with glucose was insufficient
to prevent growth. Our results show that Salmonella Weltevreden can grow in som-fak independently of the
inhibitory substances normally present in this type of product, emphasising the importance of preventing
contamination. However, our results also suggest that the use of garlic fermenting starter cultures in
combination with garlic could improve safety of fermented fish products.