The UDP‐GalNAcA biosynthesis genes gna‐gne2 are required to maintain cell envelope integrity and in vivo fitness in multi‐drug resistant Acinetobacter baumannii

Abstract

Acinetobacter baumannii infects a wide range of anatomic sites including the respiratory tract and bloodstream. Despite its clinical importance, littleis known about the molecular basis of A. baumannii pathogenesis. We previously identified the UDP-N-acetyl-d-galactosaminuronic acid (UDP-GalNAcA) biosynthesis genes, gna-gne2, as being critical for survival in vivo. Herein, we demonstrate that Gna-Gne2 are part of a complex network connecting in vivo fitness, cell envelope homeostasis and resistance to antibiotics. The ∆gna-gne2 mutant exhibits a severe fitness defect during bloodstream infection. Capsule production is abolished in the mutant strain, which is concomitant with its inability to survive in human serum. In addition, the ∆gna-gne2 mutant was more susceptible to vancomycin and unable to grow on MacConkey plates, indicating an alteration in cell envelope integrity. Analysis of lipid A by mass spectrometry showed that the hexa-and hepta-acylated species were affected in the gna-gne2 mutant. Finally, the ∆gna-gne2 mutant was more susceptible to several classes of antibiotics. Together, this study demonstrates the importance of UDP-GalNAcA in the pathobiology of A. baumannii. By interrupting its biosynthesis, we showed that this molecule plays a critical role in capsule biosynthesis and maintaining the cell envelope homeostasis.

Characterization of Acinetobacter baumannii core oligosaccharide synthesis reveals novel aspects of lipooligosaccharide assembly

“…The UDP-GlcNAcA substrate is predicted to be generated via dehydrogenase activity at the C-6 position of UDP-GlcNAc by Gna, a homolog of WbpA in Pseudomonas aeruginosa and TviB in Salmonella enterica serovar Typhi ( 25 , 38 , 39 ). Previous reports have shown that the deletion of gna along with a downstream UDP-GlcNAcA C-4 epimerase gene, gne2 , results in partial truncation of the core oligosaccharide ( 40 ). Importantly, this GlcNAc precursor is an essential component of the peptidoglycan cell wall ( 41 ).…”

Genetic Dissection of Antibiotic Adjuvant Activity

“…We suspect that lptE mutations only partially impair LOS transport, as has been observed in other bacteria ( 45 , 46 ). Other top meropenem sensitive mutants (classes 1 and 2 in Table S2 ) inactivated the genes for β-lactamase OXA-23, LOS modification enzymes ( lpxL and lpsB ), capsule synthesis genes ( wzy , wzb , and wzc ), a capsule biosynthetic enzyme also involved in LOS synthesis ( gna ) ( 47 ), and genes needed for disulfide bond formation ( dsbAB ), zinc transport ( znuABC and zurA ), regulation ( rpoE and rseP ), or peptidoglycan metabolism ( pbpG and ampG ). For the three β-lactamases other than OXA-23, only mutations inactivating GES-14 increased meropenem sensitivity, although the phenotype was relatively weak (class 4).…”

The Capsule of <b><i>Acinetobacter baumannii</i></b> Protects against the Innate Immune Response

“…The capsule of A. baumannii has been shown to play significant roles in protection against several host processes. The capsule aids in resistance to desiccation, disinfectants, antimicrobials, and antibiotics, consequently mutations in genes responsible for capsule production severely affect virulence in vivo [ 15 , 16 , 17 , 18 , 19 ]. Similarly, alteration in capsule structure can impact virulence [ 20 ].…”