Metabolic basis for the differential susceptibility of Gram-positive pathogens to fatty acid synthesis inhibitors

Abstract

Bacterial fatty acid synthesis (FASII) is an attractive target for treatment of Gram‐positive pathogens. The value of FASII inhibitors was recently questioned based on the ability of Streptococcus agalactiae to circumvent inhibition by utilizing exogenous fatty acids (FA) for phospholipid synthesis. This study compares the efficacy of FASII inhibitors against Staphylococcus aureus and Streptococcus pneumoniae grown in media containing FA. Exogenous FA overcame inhibition in S. pneumoniae, but not S. aureus. Neither the substrate specificities of the acyltransferases, nor the divergent modes of transcriptional regulation accounted for this difference. Exogenous FA strongly suppressed malonyl‐CoA production in S. pneumoniae but not S. aureus, indicating biochemical regulation at the acetyl‐CoA carboxylase in S. pneumoniae is the key difference between the two species. The lack of feedback regulation of malonyl‐CoA formation results in the accumulation of short chain acyl‐ACP and a block in exogenous FA uptake in S. aureus treated with FASII inhibitors. The ability of exogenous FA to biochemically inhibit the initiation of FASII determines whether FASII inhibitors will be effective against Gram‐Positive bacteria in the presence of exogenous FA. Supported by NIH GM034496 and ALSAC.

Activation of Exogenous Fatty Acids to Acyl-Acyl Carrier Protein Cannot Bypass FabI Inhibition in Neisseria

“…However, our experiments establish that Neisseria cannot circumvent FabI inhibition by scavenging fatty acids from the environment. In S. aureus, FabI inhibition blocks the uptake of fatty acids due to the depletion of cellular ACP as the initiation module of FASII continues to feed acyl-ACP into the elongation cycle and the enoyl-ACP intermediates accumulate at the inhibited step (35). AFN-1252 also inhibits the incorporation of extracellular fatty acids into Neisseria consistent with the blockade at the FabI step triggering the same imbalance in fatty acid metabolism in both organisms.…”

“…Lipoic acid was provided because it is an essential cofactor for ketoacid dehydrogenases and is derived from octanoyl-ACP arising from FASII (52)(53)(54). S. aureus lacking FASII require exogenous lipoate in addition to fatty acids to support maximum growth (35,55). These experiments showed that exogenous fatty acids cannot bypass the inhibition of FabI by AFN-1252 in both N. gonorrhoeae and N. meningitidis.…”

“…Strain JP1111 is viable at 30°C but nonviable at 42°C without fabI gene complementation. The JP1111 cells were transformed with the pPJ131-NgfabI plasmid, the pPJ131 parent plasmid, and the pBluescript plasmids expressing fabI from E. coli and S. aureus (35) and then plated on Luria-Bertani (10 g of tryptone, 5 g of yeast extract, and 5 g of NaCl in 1 liter of distilled water for liquid media with an additional 7.5 g of agarose for plates) plates at 30°C with 100 g/ml carbenicillin. The transformed cells were restreaked onto Luria-Bertani plates with 100 g/ml carbenicillin and grown at 30 or 42°C to determine whether the N. gonorrhoeae fabI complements the E. coli fabI activity.…”

Identification of a two-component fatty acid kinase responsible for host fatty acid incorporation by Staphylococcus aureus

“…In species related to Streptococcus agalactiae, extracellular FA can completely replace endogenously synthesized FA, rendering the FASII inhibitors ineffective growth inhibitors if sufficient FA are present (1,2). In contrast, FASII inhibitors exemplified by the enoyl-acyl carrier protein (ACP) reductase therapeutic AFN-1252 are effective against Staphylococcus aureus, even when extracellular FA are abundant (2,3). A major impediment to our understanding of this diversity is that the pathway and enzymes responsible for the incorporation of extracellular FA is not established in the Firmicutes.…”

Prospects of a new antistaphylococcal drug batumin revealed by molecular docking and analysis of the complete genome sequence of the batumin-producer Pseudomonas batumici UCM B-321

“…This physiologically process is not critical for many bacteria, as they can compensate the lack of synthesized fatty acids by uptake of exogenous molecules. However, suppression of fatty acid synthesis 8 becomes lethal for S. aureus because of a peculiarity of the regulation of fatty acid metabolism in this bacterium suppressing at the same time both the synthesis and incorporation of exogenous fatty acids [19]. In the latter paper it was explained why FabI inhibitors were much more toxic to S. aureus than to other micro-organisms.…”