Effect of NaCl, high iron, iron chelator and antibiotics on growth, virulence gene expression and drug susceptibility in non-typhoidal Salmonella: an in vitro fitness study.

Salmonella is one among the most versatile and resilient enteric pathogens that is known to have developed various survival strategies within the host system. The ability of the bacteria to circumvent the physiological parameters as well as dodge the antimicrobial stress environment within the host is one of the most crucial steps in establishing an infection. With an alarming rise in multi-drug resistant serovars of non-typhoidal Salmonella and lack of vaccine for combatting the infections, behaviour of the bacteria in the presence of host physiological conditions (NaCl, high and low iron) and antibiotics will help in understanding the survival strategies as well as mechanisms of resistance. Two multi-drug resistant and two sensitive serovars of Salmonella Weltevreden and Salmonella Newport isolated from poultry and seafood were used for growth kinetics and virulence gene expression study. The results obtained revealed that despite similar resistance pattern, effect of individual class of antibiotics on the growth of serovars varied. On the contrary, no significant difference was observed in growth pattern on exposure to these in vitro experimental conditions. Nevertheless, coupling these conditions with antibiotics drastically reduced the minimum inhibitory concentration (MIC) of antibiotics in resistant strains. A first of its kind study that draws attention on the significant effect of antibiotics and physiological conditions on MIC between resistant and sensitive non-typhoidal Salmonella serovars and expression of virulence genes from Salmonella pathogenicity island (SPI) 1 and 2 (invA, hilC, fliC2, sseA and ssrB).