Daptomycin Tolerance in the Staphylococcus aureus pitA6 Mutant Is Due to Upregulation of the dlt Operon

Abstract

dUnderstanding the mechanisms of how bacteria become tolerant toward antibiotics during clinical therapy is a very important object. In a previous study, we showed that increased daptomycin (DAP) tolerance of Staphylococcus aureus was due to a point mutation in pitA (inorganic phosphate transporter) that led to intracellular accumulation of both inorganic phosphate (P i ) and polyphosphate (polyP). DAP tolerance in the pitA6 mutant differs from classical resistance mechanisms since there is no increase in the MIC. In this follow-up study, we demonstrate that DAP tolerance in the pitA6 mutant is not triggered by the accumulation of polyP. Transcriptome analysis revealed that 234 genes were at least 2.0-fold differentially expressed in the mutant. Particularly, genes involved in protein biosynthesis, carbohydrate and lipid metabolism, and replication and maintenance of DNA were downregulated. However, the most important change was the upregulation of the dlt operon, which is induced by the accumulation of intracellular P i . The GraXRS system, known as an activator of the dlt operon (D-alanylation of teichoic acids) and of the mprF gene (multiple peptide resistance factor), is not involved in DAP tolerance of the pitA6 mutant. In conclusion, DAP tolerance of the pitA6 mutant is due to an upregulation of the dlt operon, triggered directly or indirectly by the accumulation of P i .

A FASII inhibitor prevents staphylococcal evasion of daptomycin by inhibiting phospholipid decoy production

“…5B,C,D,E,F,G) indicated that AFN-1252 and daptomycin still had bacteriostatic activity. It is therefore likely that this increase in survival after 3 exposures was due to the acquisition of tolerance to daptomycin, which is consistent with a previous study [29].…”

“…Although the combination of daptomycin and AFN-1252 prevented the acquisition of resistance to either antibiotic, we did observe the emergence of tolerance to the lipopeptide antibiotic after the third exposure to the drugs. The acquisition of daptomycin tolerance has been reported previously and was found to occur via increased expression of the dltABCD operon, although the mechanism by which this reduced susceptibility was unclear [29]. Crucially, however, whilst this tolerance phenotype reduces the ability of the daptomycin/AFN-1252 combination to kill S. aureus , the antibiotics are still able to inhibit bacterial growth.…”

Salt-Induced Stress Stimulates a Lipoteichoic Acid-Specific Three-Component Glycosylation System in Staphylococcus aureus

“…Modification of both WTA and LTA parent polymers can have vast impact on function. For instance, D-alanine (D-Ala) ester addition by the dltABCD operon has been shown to regulate autolysis during cell wall remodeling (16), localize penicillin-binding proteins (17), and confer resistance to antibiotics such as daptomycin (18) and antimicrobial peptides (19)(20)(21). The D-alanylation pathway is currently the most well defined (20,22,23), whereby DltA loads the carrier protein DltC with D-Ala.…”

Genetic and Transcriptomic Analyses of Ciprofloxacin-Tolerant Staphylococcus aureus Isolated by the Replica Plating Tolerance Isolation System (REPTIS)

“…The same antibiotics that kill susceptible cells by targeting active metabolic processes (15) are unlikely to kill tolerant variants with a reduced metabolism (16). Therefore, it is not surprising that even strains with antibiotic MICs below susceptibility breakpoints can be drug tolerant, as previously shown by our group (13) and others (12).…”

“…However, a heteroresistant strain contains cell subpopulations with different levels of antibiotic resistance (10). The mechanism of tolerance is completely different from that of resistance (11)(12)(13)(14). For example, quinolone persistence in S. aureus is attributed to a decrease in ATP levels (8).…”