AUTHOR=Ghoshal Mrinalini , Bechtel Tyler D. , Gibbons John G. , McLandsborough Lynne 

TITLE=Adaptive laboratory evolution of Salmonella enterica in acid stress

JOURNAL=Frontiers in Microbiology

VOLUME=Volume 14 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1285421

DOI=10.3389/fmicb.2023.1285421

ISSN=1664-302X

ABSTRACT=Adaptive Laboratory Evolution (ALE) studies play a crucial role in understanding the adaptation and evolution of different bacterial species. In this study, we have investigated the adaptation and evolution of Salmonella enterica serovar Enteritidis to acetic acid using ALE. Acetic acid concentrations below the minimum inhibitory concentration (sub-MIC) were used. Four evolutionary lineages (EL) EL1, EL2, EL3 and EL4 of S. Enteritidis were developed, each demonstrating varying levels of resistance to acetic acid. The acetic acid MIC of EL1 remained constant at 27mM throughout 70 days while the MIC of EL2, EL3 and EL4 increased throughout the 70 days. EL4 was adapted to the highest concentration of acetic acid (30mM) and demonstrated the highest increase in its MIC against acetic acid throughout the study, reaching an MIC of 35mM on day 70.  The growth rates of the evolved lineages increased over time and was dependent on the concentration of acetic acid used during the evolutionary process. EL4 had the greatest increase in growth rate, reaching 0.33(h-1) after 70 days in the presence of 30mM acetic acid as compared to EL1, which had a growth rate of 0.2 after 70 days with no exposure to acetic acid. Long-term expo-sure to acetic acid led to an increased MIC of human antibiotics such as ciprofloxacin and meropenem against the S. enterica evolutionary lineages. The MIC of ciprofloxacin for EL1 stayed constant at 0.016 throughout 70 days while that of EL4 increased to 0.047. Bacterial whole genome sequencing revealed single nucleotide polymorphisms in the ELs in various genes known to be involved in S. enterica virulence, pathogenesis and stress response including phoP, phoQ and fhuA. We also observed genome deletions in some of ELs as compared to the wild-type S. Enteritidis which may have contributed to the bacterial acid adaptation. This study highlights the potential for bacterial adaptation and evolution under environmental stress and underscores the importance of understanding the development of cross-resistance to antibiotics in S. enterica populations. This study serves to enhance our understanding of the pathogenicity and survival strategies of S. enterica under acetic acid stress.