The Global Regulator CcpA of Listeria monocytogenes Confers Sensitivity to Antimicrobial Fatty Acids

Abstract

Free fatty acids (FFAs) are known to exhibit antimicrobial and anti-virulent properties against bacterial pathogens. Specific FFAs, such as lauric acid (LA; C12:0), exert both effects against the foodborne pathogen Listeria monocytogenes: at low levels, LA acts to inhibit the activity of the virulence regulator PrfA, whereas at higher levels, LA inhibits bacterial growth. Deletion of prfA is known to promote tolerance toward antimicrobial FFAs, suggesting that the response of L. monocytogenes to anti-virulent and antimicrobial FFAs could be linked. In this study, we explored the response of L. monocytogenes toward antimicrobial FFAs holding an anti-virulence activity by isolating strains that can grow at high concentrations of LA. We found that LA-tolerant isolates carry mutations in the gene encoding the global regulator CcpA. Importantly, we discovered that mutation or deletion of ccpA protect L. monocytogenes against the antimicrobial activity of FFAs, whereas the ccpA mutants remain sensitive toward FFA’s PrfA inhibitory effect. A regulatory link involving CcpA, connecting the response toward the antimicrobial and anti-virulence activities of FFAs, is therefore unlikely. To further study how deletion of ccpA promotes FFA tolerance, we performed a transcriptomic analysis of the response to LA. Our data indicated that the FFA-tolerant phenotype of the ∆ccpA strain is not induced upon LA exposure but appears to be an inherent phenotypic trait of the ccpA deletion mutation. Interestingly, we found that the bacterial surface of L. monocytogenes becomes more hydrophilic upon deletion of ccpA, and we demonstrate that CcpA plays a role in the response of L. monocytogenes to other stress conditions, including low pH and antibiotics. Altogether, our study revealed that regulatory activities of CcpA lead to an increased hydrophobicity of the bacterial surface, which may confer sensitivity of L. monocytogenes against the antimicrobial activity of FFAs. Notably, CcpA is not involved in responding to the PrfA inhibitory effect of FFAs, showing that FFA-tolerant strains can still be targeted by the anti-virulent activity of FFAs.

Ultrasound-assisted extraction of emodin from Rheum officinale Baill and its antibacterial mechanism against Streptococcus suis based on CcpA

“…These results confirmed that emodin may play an antibacterial role by binding and interacting with CcpA in S. suis . Analogously, CcpA in Listeria monocytogenes was involved in the response to antimicrobial free fatty acids [74] .…”

Anti-infective activities of long-chain fatty acids against foodborne pathogens

“…Not surprisingly, bacteria are capable of developing resistance against the antimicrobial activity of FFAs. Indeed, FFA-tolerant strains were readily isolated by serial passage of L. monocytogenes in broth with increasing concentrations of antimicrobial medium- and long-chain FFAs (Thomasen et al 2022a , b ). Genome sequencing of FFA-tolerant isolates revealed mutations in genes involved in glycosylation of wall teichoic acids (WTAs) (Thomasen et al 2022a ).…”

“…4 ). A different subset of FFA-tolerant isolates was found to carry mutations in the ccpA gene encoding the catabolite control protein A, CcpA, a major transcriptional regulator of carbon catabolite repression in L. monocytogenes (Thomasen et al 2022b ). Inactivation of ccpA promotes growth in the presence of lauric acid (C12:0) and palmitic acid (C16:1) and results in a more hydrophilic cell surface.…”

“…Inactivation of ccpA promotes growth in the presence of lauric acid (C12:0) and palmitic acid (C16:1) and results in a more hydrophilic cell surface. Notably, mutations conferring tolerance toward antimicrobial medium- and long-chain FFAs also support growth of L. monocytogenes at low pH (Thomasen et al 2022a , b ).…”

“…palmitoleic acid (C16:1) and lauric acid (C12:0)]. Importantly, mutant strains that grow in the presence of high levels of antimicrobial medium- and long-chain FFAs remain susceptible to the PrfA-inhibitory activity of FFAs (Thomasen et al 2022a , b ). Thus, although L. monocytogenes becomes resistant to the antimicrobial activity of FFAs, it can still be targeted by their antivirulent activity.…”