An Acinetobacter baumannii nasal carriage isolate recovered from an asymptomatic patient in Vietnam is extensively antibiotic resistant and produces a rare K71 type capsule

Acinetobacter baumannii is a leading cause of multidrug-resistant bacterial infections worldwide, and the capsular polysaccharide (CPS) is a major virulence determinant. A previous study of A. baumannii from intubated and asymptomatic patients admitted to the intensive care unit (ICU) at the Hospital for Tropical Diseases in Ho Chi Minh City in Vietnam revealed multiple lineages with diverse antibiotic resistance profiles and CPS biosynthesis loci. Here, we show that 48_n, an asymptomatic nasal carriage isolate belonging to ST142, is extensively antibiotic resistant and carries acquired resistance determinants accounting for the resistance profile. 48_n carries the novel KL71 CPS biosynthesis locus in the chromosome. The structure of the CPS produced by 48_n was established using ¹H and ¹³C nuclear magnetic resonance spectroscopy, including two-dimensional ¹Н,¹Н COSY, ¹Н,¹Н TOCSY, ¹Н,¹Н ROESY, ¹Н,¹³C HSQC, and ¹Н,¹³C HMBC experiments, and confirmed by Smith degradation. Consistent with the genetic content of KL71, the K71 CPS was found to be made up of octasaccharide K units containing six l-rhamnose residues and one residue each of N-acetyl-d-glucosamine and d-glucuronic acid. K71 CPS was branched and closely related to the K74 CPS produced by BAL_309, an antibiotic susceptible ST142 isolate recovered from an intubated patient in the same ICU 7 years later. K71 and K74 differ only in the linkage between K units, and this is due to the replacement of a single gene at the K locus that codes for the Wzy polymerase.

Importance: The majority of Acinetobacter baumannii genomes sequenced and analyzed to develop an understanding of extensively drug-resistant (XDR) isolates belong to the globally disseminated CC2 clonal complex. While XDR isolates belonging to rarer lineages are often unexplored, detailed analyses could provide novel insights into the spread of resistance, as well as cell surface features such as the CPS that determine the specificity of non-antibiotic therapeutics required to treat XDR infections that resist antimicrobial chemotherapy. Here, we describe the properties of an XDR asymptomatic nasal carriage isolate recovered in Vietnam that belongs to ST142, a rarely encountered sequence type. We report the resistance profile and correlate this with detected resistance determinants. We also solve the structure of the CPS and reveal its relationship with CPS produced by other A. baumannii isolates.