The K46 and K5 capsular polysaccharides produced by Acinetobacter baumannii NIPH 329 and SDF have related structures and the side-chain non-ulosonic acids are 4-O-acetylated by phage-encoded O-acetyltransferases

Abstract

Acinetobacter baumannii isolate NIPH 329 carries a novel capsular polysaccharide (CPS) gene cluster, designated KL46, that is closely related to the KL5 locus in A . baumannii isolate SDF but includes genes for synthesis of 5,7-diacetamido-3,5,7,9-tetradeoxy- l - glycero - l - manno -non-2-ulosonic (di- N -acetylpseudaminic) acid (Pse5Ac7Ac) instead of the corresponding D - glycero - D - galacto isomer (di- N -acetyllegionaminic acid) (Leg5Ac7Ac). In agreement with the genetic content of KL46, chemical studies of the K46 CPS produced by NIPH 329 revealed a branched tetrasaccharide repeat (K unit) with an overall structure the same as K5 from SDF but with â-Pse5Ac7Ac replacing α-Leg5Ac7Ac. As for K5, the K46 unit begins with d -Gal p NAc and includes α- d -Glc p NAc-(1→3)- d -Gal p NAc and α- d -Gal p -(1→6)- d -Glc p NAc linkages, formed by Gtr14 and Gtr15 glycosyltransferases, respectively. The Gtr94 K46 glycosyltransferase, which is related to Gtr13 K5, links Pse5Ac7Ac to d -Gal p in the growing K unit via a â-(2→6) linkage. Nearly identical Wzy enzymes connect the K46 and K5 units via a α-D-Gal p NAc-(1→3)-α-D-Gal p linkage to form closely related CPSs. Both Pse5Ac7Ac in K46 and Leg5Ac7Ac in K5 are acetylated at O4 but no acetyltransferase gene is present in KL46 or KL5. Related acetyltransferases were found encoded in the NIPH 329 and SDF genomes, but not in other strains carrying an unacetylated Pse or Leg derivative in the CPS. The genes encoding the acetyltransferases were in different putative phage genomes. However, related acetyltransferases were rare among the >3000 publically available genome sequences.

Diversity of carbapenem-resistant Acinetobacter baumannii and bacteriophage-mediated spread of the Oxa23 carbapenemase

“…Reports of the carriage of antibiotic-resistance genes in prophages have become more common in recent years [79][80][81], but it is thought that this is generally a rare occurrence [82]. However, recent evidence from studies focusing on A. baumannii have suggested that carriage of both virulence and antibiotic-resistance genes by prophages is relatively common in this species and may be a major mechanism of horizontal transfer of these genes [83][84][85][86][87]. It was recently noted that prophages appeared to be more common in IC5 isolates than in those belonging to IC1 or IC2 [85], and it is an intriguing possibility that prophages may be a major factor in the evolution of different ICs.…”

Acinetobacter baumannii K106 and K112: Two Structurally and Genetically Related 6-Deoxy-l-talose-Containing Capsular Polysaccharides

“…In this study, both K106 and K112 lack O -acetylation like K11, suggesting either that atr8 may be inactive in these strains or that the atr gene responsible for acetylation of K83 resides elsewhere. Further work will be needed to confirm the differential expression and/or activity of these acetyltransferases, or if an acetyltransferase is encoded elsewhere in the genome as has been observed for other strains [ 12 ].…”

“…The K units made by different A. baumannii strains may differ in sugar composition, sugar linkages, and/or linkages between the K units in the CPS polymer. K units may also be variously decorated with acetyl, acyl, pyruvyl groups, or other moieties (for examples, see [ 8 , 9 , 10 , 11 , 12 ]). This high structural diversity in the species is predominantly due to extensive variation in the genetic content at the chromosomal K locus (KL) that drives CPS biosynthesis [ 13 ], and to date, more than 140 KL gene clusters have been identified at this location [ 14 ].…”

“…(for examples, see [8][9][10][11][12]). This high structural diversity in the species is predominantly due to extensive variation in the genetic content at the chromosomal K locus (KL) that drives CPS biosynthesis [13], and to date, more than 140 KL gene clusters have been identified at this location [14].…”

Diversity of carbapenem-resistant Acinetobacter baumannii and bacteriophage-mediated spread of the Oxa23 carbapenemase

“…However, recent evidence from studies focusing on A. baumannii have suggested that carriage of both virulence and antibiotic resistance genes by prophages is relatively common in this species and may be a major mechanism of horizontal transfer of these genes (79)(80)(81)(82)(83). It was recently noted that prophages appeared to be more common in IC5 isolates than in those belonging to IC1 or IC2 (81) and it is an intriguing possibility that prophages may be a major factor in the evolution of different international clones.…”