Search for a command to run...
<i>Acinetobacter baumannii</i> is a Gram-negative bacterial pathogen that poses a major health concern due to increasing multidrug resistance. The Gram-negative cell envelope is a key barrier to antimicrobial entry and includes an inner and outer membrane. The maintenance of lipid asymmetry (Mla) system is the main homeostatic mechanism by which Gram-negative bacteria maintain outer membrane asymmetry. Loss of the Mla system in <i>A. baumannii</i> results in attenuated virulence and increased susceptibility to membrane stressors and some antibiotics. We recently reported two strain variants of the <i>A. baumannii</i> type strain ATCC 17978: 17978VU and 17978UN. Here, ∆<i>mlaF</i> mutants in the two ATCC 17978 strains display different phenotypes for membrane stress resistance, antibiotic resistance, and pathogenicity in a murine pneumonia model. Although allele differences in <i>obgE</i> were previously reported to synergize with ∆<i>mlaF</i> to affect growth and stringent response, <i>obgE</i> alleles do not affect membrane stress resistance. Instead, a single-nucleotide polymorphism (SNP) in the essential gene encoding undecaprenyl pyrophosphate (Und-PP) synthase, <i>uppS</i>, results in decreased enzymatic rate and decrease in total Und-P levels in 17978UN compared to 17978VU. The UppS<sup>UN</sup> variant synergizes with ∆<i>mlaF</i> to reduce capsule and lipooligosaccharide (LOS) levels, increase susceptibility to membrane stress and antibiotics, and reduce persistence in a mouse lung infection. Und-P is a lipid glycan carrier required for the biosynthesis of <i>A. baumannii</i> capsule, cell wall, and glycoproteins. These findings uncover synergy between Und-P and the Mla system in maintaining the <i>A. baumannii</i> cell envelope and antibiotic resistance.IMPORTANCE<i>Acinetobacter baumannii</i> is a critical threat to global public health due to its multidrug resistance and persistence in hospital settings. Therefore, novel therapeutic approaches are urgently needed. We report that a defective undecaprenyl pyrophosphate synthase (UppS) paired with a perturbed Mla system leads to synthetically sick cells that are more susceptible to clinically relevant antibiotics and show reduced virulence in a lung infection model. These results suggest that targeting UppS or undecaprenyl species and the Mla system may resensitize <i>A. baumannii</i> to antibiotics in combination therapies. This work uncovers a previously unknown synergistic relationship in cellular envelope homeostasis that could be leveraged for use in combination therapy against <i>A. baumannii</i>.