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In this study, we report the identification of genes required for the biosynthesis of the core lipopolysaccharides (LPSs) of two strains of Proteus mirabilis. Since P. mirabilis and Klebsiella pneumoniae share a core LPS carbohydrate backbone extending up to the second outer-core residue, the functions of the common P. mirabilis genes was elucidated by genetic complementation studies using well-defined mutants of K. pneumoniae. The functions of strain-specific outer-core genes were identified by using as surrogate acceptors LPSs from two well-defined K. pneumoniae core LPS mutants. This approach allowed the identification of two new heptosyl-transferases (WamA and WamC), a galactosyltransferase (WamB), and an N-acetylglucosaminyltransferase (WamD). In both strains, most of these genes were found in the so-called waa gene cluster, although one common core biosynthetic gene (wabO) was found outside this cluster. doi: 10.1128/JB.00494-10

Aeromonas caviae Sch3N possesses a small genomic island that is involved in both flagellin glycosylation and lipopolysaccharide (LPS) O-antigen biosynthesis. This island appears to have been laterally acquired as it is flanked by insertion element-like sequences and has a much lower G+C content than the average aeromonad G+C content. Most of the gene products encoded by the island are orthologues of proteins that have been shown to be involved in pseudaminic acid biosynthesis and flagellin glycosylation in both Campylobacter jejuni and Helicobacter pylori. Two of the genes, 1st and lsg, are LPS specific as mutation of them results in the loss of only a band for the LPS O-antigen. Lsg encodes a putative Wzx flippase, and mutation of Lsg affects only LPS; this finding supports the notion that flagellin glycosylation occurs within the cell before the flagellins are exported and assembled and not at the surface once the sugar has been exported. The proteins encoded by flmA, flmB, neuA, flmD, and neuB are thought to make up a pseudaminic acid biosynthetic pathway, and mutation of any of these genes resulted in the loss of motility, flagellar expression, and a band for the LPS O-antigen. Furthermore, pseudaminic acid was shown to be present on both flagellin subunits that make up the polar flagellum filament, to be present in the LPS O-antigen of the A. caviae wild-type strain, and to be absent from the A. caviae flmD mutant strain.

Motility is an essential characteristic for mesophilic Aeromonas strains. We identified a new polar flagellum region (region 6) in the A. hydrophila AH-3 (serotype 034) chromosome that contained two additional polar stator genes, named pom[A.sub.2] and pom[B.sub.2]. A. hydrophila Pom[A.sub.2] and Pom[B.sub.2] are highly homologous to other sodium-conducting polar flagellum stator motors as well as to the previously described A. hydrophila AH-3 PomA and PomB. pomAB and pom[A.sub.2][B.sub.2] were present in all the mesophilic Aeromonas strains tested and were independent of the strains' ability to produce lateral flagella. Unlike MotX, which is a stator protein that is essential for polar flagellum rotation, here we demonstrate that PomAB and Pom[A.sub.2][B.sub.2] are redundant sets of proteins, as neither set on its own is essential for polar flagellum motility in either aqueous or high-viscosity environments. Both PomAB and Pom[A.sub.2][B.sub.2] are sodium.coupled stator complexes, although Pom[A.sub.2][B.sub.2] is more sensitive to low concentrations of sodium than PomAB. Furthermore, the level of transcription in aqueous and high-viscosity environments of pom[A.sub.2][B.sub.2] is reduced compared to that of pomAB. The A. hydrophila AH-3 polar flagellum is the first case described in which two redundant sodium-driven stator motor proteins (PomAB and Pom[A.sub.2][B.sub.2]) are found.

Comparison between the lipopolysaccharide (LPS) core structures of Aeromonas salmonicida subsp, salmonicida A450 and Aeromonas hydrophila AH-3 shows great similarity in the inner LPS core and part of the outer LPS core but some differences in the distal part of the outer LPS core (residues LD-Hep, D-Gal, and D-GalNAc). The three genomic regions encoding LPS core biosynthetic genes in A. salmonicida A450, of which regions 2 and 3 have genes identical to those of A. hydrophila AH-3, were fully sequenced. A. salmonicida A450 region 1 showed seven genes: three identical to those of A. hydrophila AH-3, three similar but not identical to those of A. hydrophila AH-3, and one without any homology to any well-characterized gene. A. salmonicida A450 mutants with alterations in the genes that were not identical to those of A. hydrophila AH-3 were constructed, and their LPS core structures were fully elucidated. At the same time, all the A. salmonicida A450 genes identical to those of A. hydrophila AH-3 were used to complement the previously obtained A. hydrophila AH-3 mutants for each of these genes. Combining the gene sequence and complementation test data with the structural data and phenotypic characterization of the mutant LPSs enabled a presumptive assignment of all LPS core biosynthesis gene functions in A. salmonicida A450. Furthermore, hybridization studies with internal probes for the A. salmonicida-specific genes using different A. salmonicida strains (strains of different subspecies or atypical strains) showed a unique or prevalent LPS core type, which is the one fully characterized for A. salmonicida A450.

Antimicrobial peptides (APs) are important host weapons against infections. Nearly all APs are cationic and their microbicidal action is initiated through interactions with the anionic bacterial surface. It is known that pathogens have developed countermeasures to resist these agents by reducing the negative charge of membranes, by active efflux and by proteolytic degradation. Here we uncover a new strategy of resistance based on the neutralization of the bactericidal activity of APs by anionic bacterial capsule polysaccharide (CPS). Purified CPSs from Klebsiella pneumoniae K2, Streptococcus pneumoniae serotype 3 and Pseudomonas aeruginosa increased the resistance to polymyxin B of an unencapsulated K. pneumoniae mutant. Furthermore, these CPSs increased the MICs of polymyxin B and human neutrophil [alpha]-defensin 1 (HNP-1) for unencapsulated K. pneumoniae, Escherichia coli and P. aeruginosa PAO1. Polymyxin B or HNP-1 released CPS from capsulated K. pneumoniae, S. pneumoniae serotype 3 and P. aeruginosa overexpressing CPS. Moreover, this material also reduced the bactericidal activity of APs. We postulate that APs may trigger in vivo the release of CPS, which in turn will protect bacteria against APs. We found that anionic CPSs, but not cationic or uncharged ones, blocked the bactericidal activity of APs by binding them, thereby reducing the amount of peptides reaching the bacterial surface. Supporting this, polycations inhibited such interaction and the bactericidal activity was restored. We postulate that trapping of APs by anionic CPSs is an additional selective virulence trait of these molecules, which could be considered as bacterial decoys for APs.

The Aeromonas hydrophila [wb.sub.*O34] gene cluster of strain AH-3 (serotype O34) was cloned and sequenced. This cluster contains genes necessary for the production of O34-antigen lipopolysaccharide (LPS) in A. hydrophila. We determined, using either mutation or sequence homology, roles for the majority of genes in the cluster by using the chemical O34-antigen LPS structure obtained for strain AH-3. The O34-antigen LPS export system has been shown to be a Wzy-dependent pathway typical of heteropolysaccharide pathways. Furthermore, the production of A. hydrophila O34-antigen LPS in Escherichia coli K-12 strains is dependent on incorporation of the Gne enzyme (UDP-N-acetylgalactosamine 4-epimerase) necessary for the formation of UDP-galactosamine in these strains. By using rapid amplification of cDNA ends we were able to identify a transcription start site upstream of the terminal wzz gene, which showed differential transcription depending on the growth temperature of the strain. The Wzz protein is able to regulate the O34-antigen LPS chain length. The differential expression of this protein at different temperatures, which was substantially greater at 20[degrees]C than at 37[degrees]C, explains the previously observed differential production of O34-antigen LPS and its correlation with the virulence of A. hydrophila serotype O34 strains.

By the isolation of three different Aeromonas hydrophila strain AH-3 (serotype O34) mutants with an altered lipopolysaccharide (LPS) migration in gels, three genomic regions encompassing LPS core biosynthesis genes were identified and characterized. When possible, mutants were constructed using each gene from the three regions, containing seven, four, and two genes (regions 1 to 3, respectively). The mutant LPS core structures were elucidated by using mass spectrometry, methylation analysis, and comparison with the full core structure of an O-antigen-lacking AH-3 mutant previously established by us. Combining the gene sequence and complementation test data with the structural data and phenotypic characterization of the mutant LPSs enabled a presumptive assignment of all LPS core biosynthesis gene functions in A. hydrophila AH-3. The three regions and the genes contained are in complete agreement with the recently sequenced genome of A. hydrophila ATCC 7966. The functions of the A. hydrophila genes waaC in region 3 and waaF in region 2 were completely established, allowing the genome annotations of the two heptosyl transferase products not previously assigned. Having the functions of all genes involved with the LPS core biosynthesis and most corresponding single-gene mutants now allows experimental work on the role of the LPS core in the virulence of A. hydrophila.

A mutation in galU that causes the lack of O34-antigen lipopolysaccharide (LPS) in Aeromonas hydrophila strain AH-3 was identified. It was proved that A. hydrophila GalU is a UDP-glucose pyrophosphorylase responsible for synthesis of UDP-glucose from glucose 1-phosphate and UTP. The galU mutant from this strain showed two types of LPS structures, represented by two bands on LPS gels. The first one (slow-migrating band in gels) corresponds to a rough strain having the complete core, with two significant differences: it lacks the terminal galactose residue from the LPS-core and 4-amino-4-deoxyarabinose residues from phosphate groups in lipid A. The second one (fast-migrating band in gels) corresponds to a deeply truncated structure with the LPS-core restricted to one 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) and three L-glycero-D-manno-heptose residues, galU mutants in several motile mesophilic Aeromonas strains from serotypes O1, O2, O11, O18, O21 and 044 were also devoid of the O-antigen LPS. The galU mutation reduced to less than 1% the survival of these Aeromonas strains in serum, decreased the ability of these strains to adhere and reduced by 1.5 or 2 log units the virulence of Aeromonas serotype O34 strains in a septicaemia model in either fish or mice. All the changes observed in the galU mutants were rescued by the introduction of the corresponding single wild-type gene.

An Aeromonas hydrophila AH-3 miniTn5 mutant unable to produce polar and lateral flagella was isolated, in which the transposon was inserted into a gene whose encoded protein was an orthologue of the Campylobacter jejuni motility accessory factor (Mar) protein. In addition to this gene, several other related genes were found in this cluster that was adjacent to the region 2 genes of the polar flagellum. Mutation of the A. hydrophila AH-3 mar-2, neuB-like, flmD or neuA-like genes resulted in non-motile cells that were unable to swim or swarm due to the absence of both polar and lateral flagella. However, both polar and lateral flagellins were present but were unglycosylated. Although the A. hydrophila AH-3 or Aeromonas caviae Sch3N genes did not hybridize with each other at the nucleotide level, the gene products were able to fully complement the mutations in either bacterium. Furthermore, well-characterized C. jejuni genes involved in flagella glycosylation (Cj1293, -1294 and -1317) were fully able to complement A. hydrophila mutants in the corresponding genes (flmA, flmB and neuB-like). It was concluded that the maf-2, neuB-like, flmD and neuA-like genes are involved in the glycosylation of both the polar and the lateral flagella in Aeromonas strains.

The core lipopolysaccharide (LPS) of Klebsiella pneumoniae contains two galacturonic acid (GalA) residues, but only one GalA transferase (WabG) has been identified. Data from chemical and structural analysis of LPS isolated from a wabO mutant show the absence of the inner core [beta]-Gala residue linked to e-glycero-D-manno-heptose III (L,D-Hep III). An in vitro assay demonstrates that the purified WabO is able to catalyze the transfer of GalA from UDP-GalA to the acceptor LPS isolated from the wabO mutant, but not to LPS isolated from waaQ mutant (deficient in L,D-Hep III). The absence of this inner core [beta]-GalA residue results in a decrease in virulence in a capsule-dependent experimental mouse pneumonia model. In addition, this mutation leads to a strong reduction in cell-bound capsule. Interestingly, a K66 Klebsiella strain (natural isolate) without a functional wabO gene shows reduced levels of cell-bound capsule in comparison to those of other K66 strains. Thus, the WabO enzyme plays an important role in core LPS biosynthesis and determines the level of cell-bound capsule in Klebsiella pneumoniae.

The mesophilic Aeromonas hydrophila AH-3 (serotype 034) strain shows two different UDP-hexose epimerases in its genome: GalE (EC 3.1.5.2) and Gne (EC 3.1.5.7). Similar homologues were detected in the different mesophilic Aeromonas strains tested. GalE shows only UDP-galactose 4-epimerase activity, while Gne is able to perform a dual activity (mainly UDP-N-acetyl galactosamine 4-epimerase and also UDP-galactose 4-epimerase). We studied the activities in vitro of both epimerases and also in vivo through the lipopolysaccharide (LPS) structure of A. hydrophila gne mutants, A. hydrophila gale mutants, A. hydrophila galE-gne double mutants, and independently complemented mutants with both genes. Furthermore, the enzymatic activity in vivo, which renders different LPS structures on the mentioned A. hydrophila mutant strains or the complemented mutants, allowed us to confirm a clear relationship between the virulence of these strains and the presence/absence of the O34 antigen LPS.

The complete structures of LPS core types 1 and 2 from Klebsiella pneumoniae have been described by other authors. They are characterized by a lack of phosphoryl residues, but they contain galacturonic acid (GalA) residues, which contribute to the necessary negative charges. The presence of a capsule was determined in core-LPS non-polar mutants from strains 52145 (O1 :K2), DL1 (O1 :K1) and C3 (O8 : K66). O-antigen ligase (waaL) mutants produced a capsule. Core mutants containing the GalA residues were capsulated, while those lacking the residues were non capsulated. Since the proteins involved in the transfer of GalA (WabG) and glucosamine residues (WabH) are known, the chemical basis of the capsular-K2-cell-surface association was studied. Phenol/water extracts from K. pneumoniae 52145[DELTA]wabH waaL and 52145[DELTA]waaL mutants, but not those from from K. pneumoniae 52145[DELTA]wabG waaL mutant, contained both LPS and capsular polysaccharide, even after hydrophobic chromatography. The two polysaccharides were dissociated by gel-filtration chromatography, eluting with detergent and metal-ion chelators. From these results, it is concluded that the K2 capsular polysaccharide is associated by an ionic interaction to the LPS through the negative charge provided by the carboxyl groups of the GalA residues.

Mesophilic Aeromonas strains express a polar flagellum in all culture conditions, and certain strains produce lateral flagella on semisolid media or on surfaces. Although Aeromonas lateral flagella have been described as a colonization factor, little is known about their organization and expression. Here we characterized the complete lateral flagellar gene cluster of Aeromonas hydrophila AH-3 containing 38 genes, 9 of which (lafA-U) have been reported previously. Among the flg[L.sub.L] and lafA structural genes we found a modification accessory factor gene (maf-5) that is involved in formation of lateral flagella; this is the first time that such a gene has been described for lateral flagellar gene systems. All Aeromonas lateral flagellar genes were located in a unique chromosomal region, in contrast to Vibrio parahaemolyticus, in which the analogous genes are distributed in two different chromosomal regions. In A. hydrophila mutations in flh[A.sub.L], lafK, fli[J.sub.L], flg[N.sub.L], flg[E.sub.L], and maf-5 resulted in a loss of lateral flagella and reductions in adherence and biofilm formation, but they did not affect polar flagellum synthesis. Furthermore, we also cloned and sequenced the A. hydrophila AH-3 alternative sigma factor [[sigma].sup.54] (rpoN); mutation of this factor suggested that it is involved in expression of both types of flagella.

Mesophilic Aeromonas spp. constitutively express a single polar flagellum that helps the bacteria move to more favorable environments and is an important virulence and colonization factor. Certain strains can also produce multiple lateral flagella in semisolid media or over surfaces. We have previously reported 16 genes (flgN to flgL) that constitute region 1 of the Aeromonas hydrophila AH-3 polar flagellum biogenesis gene clusters. We identified 39 new polar flagellum genes distributed in four noncontiguous chromosome regions (regions 2 to 5). Region 2 contained six genes (flaA to maf-1), including a modification accessory factor gene (maf-1) that has not been previously reported and is thought to be involved in glycosylation of polar flagellum filament. Region 3 contained 29 genes (filE to orf29), most of which are involved in flagellum basal body formation and chemotaxis. Region 4 contained a single gene involved in the motor stator formation (motX), and region 5 contained the three master regulatory genes for the A. hydrophila polar flagella (flrA to flrC). Mutations in the flaH, maf-1, fliM, flhA, fliA, and flrC genes, as well as the double mutant flaA flaB, all caused loss of polar flagella and reduction in adherence and biofilm formation. A defined mutation in the pomB stator gene did not affect polar flagellum motility, in contrast to the motX mutant, which was unable to swim even though it expressed a polar flagellum. Mutations in all of these genes did not affect lateral flagellum synthesis or swarming motility, showing that both A. hydrophila flagellum systems are entirely distinct.

Up to now only one major type of core oligosaccharide has been found in the lipopolysaccharide of all Klebsiella pneumoniae strains analyzed. Applying a different screening approach, we identified a novel Klebsiella pneumoniae core (type 2). Both Klebsiella core types share the same inner core and the outer-core-proximal disaccharide, GlcN-(1,4)-GalA, but they differ in the GlcN substituents. In core type 2, the GlcpN residue is substituted at the O-4 position by the disaccharide [beta]-Glcp(1-6)-[alpha]-Glcp(1, while in core type 1 the GlcpN residue is substituted at the 0-6 position by either the disaccharide [alpha]-Hep(1-4)-[alpha]-Kdo(2 or a Kdo residue (Kdo is 3-deoxy-d-manno-octulosonic acid). This difference correlates with the presence of a three-gene region in the corresponding core biosynthetic clusters. Engineering of both core types by interchanging this specific region allowed studying the effect on virulence. The replacement of Klebsiella core type 1 in a highly type 2 virulent strain (52145) induces lower virulence than core type 2 in a murine infection model.

The existence and genetic organization of a functional type III secretion system (TTSS) in a mesophilic Aeromonas strain by initially using the aeromonas hydrophila strain AH-3 is discussed. Results suggest that it seems logical to conclude that the mesophilic aeromonas strains that possess TTSS genes have a complete TTSS.

The gene cluster (waa) involved in Serratia marcescens N28b core lipopolysaccharide (LPS) biosynthesis was identified, cloned, and sequenced. Complementation analysis of known waa mutants from Escherichia coli K-12, Salmonella enterica, and Klebsiella pneumoniae led to the identification of five genes coding for products involved in the biosynthesis of a shared inner core structure: [L,D-HeppIII[alpha](1 [right arrow] 7)-L,D-HeppII[alpha](1[arrow right] 3)-L,D-Hepp[alpha](1[right arrow] 5)-KdopI(4 [left arrow] 2)[alpha]KdopII] (L,D-Hepp, L-glycero-D-manno-eptopyranose; Kdo, 3-deoxy-D-manno-oct2-ulosonic acid). Complementation and/or chemical analysis of several nonpolar mutants within the S. marcescens waa gene cluster suggested that in addition, three waa genes were shared by S. marcescens and K. pneumoniae, indicating that the core region of the LPS of S. marcescens and K. pneumoniae possesses additional common features. Chemical and structural analysis of the major oligosaccharide from the core region of LPS of an O-antigen-deficient mutant of S. marcescens N28b as well as complementation analysis led to the following proposed structure: [beta]-Glc- (1 [right arrow] 6)-[alpha]-Glc-(1 [right arrow] 4))-[alpha]-D-GlcN-(1 [right arrow] 4)-[alpha]-D-GalA-[(2 [left arrow] 1) -[alpha]-D,D-Hep- (2[left arrow] 1)-[alpha]Hep]-(1 [right arrow] 3)-[alpha]-L,D-Hep[(7 [left arrow] 1)-[alpha]-L,D-Hep]-(1 [right arrow] 3)-[alpha]-L,D-Hep-[(4 [left arrow] 1)-[beta]-D-Glc]-(1 [right arrow] 5)-Kdo. The D configuration of the [beta]-Glc, [alpha]-GclN, and [alpha]-GalA residues was deduced from genetic data and thus is tentative. Furthermore, other oligosaccharides were identified by ion cyclotron resonance-Fourier-transformed electrospray ionization mass spectrometry, which presumably contained in addition one residue of D-glycero-D-talooct-2-ulosonic acid (Ko) or of a hexuronic acid. Several ions were identified that differed from others by a mass of +80 Da, suggesting a nonstoichiometric substitution by a monophosphate residue. However, none of these molecular species could be isolated in substantial amounts and structurally analyzed. On the basis of the structure shown above and the analysis of nonpolar mutants, functions are suggested for the genes involved in core biosynthesis.

To determine the function of the wabG gene in the biosynthesis of the core lipopolysaccharide (LPS) of Klebsiella pneumoniae, we constructed wabG nonpolar mutants. Data obtained from the comparative chemical and structural analysis of LPS samples obtained from the wild type, the mutant strain, and the complemented mutant demonstrated that the wabG gene is involved in attachment to [alpha]-L-glycero-D-manno-heptopyranose II (L,D-HeppII) at the O-3 position of an [alpha]-D-galactopyranosyluronic acid ([alpha]-D-GalAp) residue. K. pneumoniae nonpolar wabG mutants were devoid of the cell-attached capsular polysaccharide but were still able to produce capsular polysaccharide. Similar results were obtained with K. pneumoniae nonpolar waaC and waaF mutants, which produce shorter LPS core molecules than do wabG mutants. Other outer core K. pneumoniae nonpolar mutants in the waa gene cluster were encapsulated. K. pneumoniae waaC, waaF, and wabG mutants were virulent when tested in different animal models. Furthermore, these mutants were more sensitive to some hydrophobic compounds than the wild-type strains. All these characteristics were rescued by reintroduction of the waaC, waaF, and wabG genes from K. pneumoniae.

Research reveals that Aeromonas salmonicida strains hybridize with lateral flagellum gene DNA probe but cannot produce lateral flagella. Data indicate that the lateral flagellin gene A is inactivated in this specialized pathogen.

Results show that a recombinat cosmid carries the waa gene cluster mediating Klebsiella pneumoniae C3 core lipopolysaccharide biosynthesis as revealed by genetic complementation analyses of waa mutants.

The Serratia marcescens N28b wbbL gene complements the rfb-50 mutation of Escherichia coli K-12 derivatives and a wbbL mutant has been found to be damaged in O4-antigen biosynthesis. A recombinant cosmid containing the wbbL gene was examined by subcloning and determination of O-antigen production phenotype in E. coli DH5alpha. Findings revealed that a recombinant plasmid (pSUB6) containing approximately 10 kb of DNA insert is sufficient to induce O4-antigen biosynthesis.

Two porins, OmpK36 and OmpK35, have been previously isolated from Klebsiella pneumoniae, and they are homologous to the Escherichia coli porins OmpC and OmpF, respectively. Identification of the two porins revealed that most isolates lacking expression of extended-spectrum beta-lactamases express the two porins, while most isolates producing these beta-lactamases express only porin OmpK36, and the OmpK35 porin is either very low or not expressed.

The 282-residue WbbL protein is a rhammosyltransferase capable of complementing the rfb-50 mutation in Escherichia coli K-12 derivatives. The Serratia marcescens mutants were constructed through the mobilization of suicide plasmids containing a portion of rmlD or wbbL. The nucleotide sequence of the plasmid pJT101 insert was determined to identify the S. marcescens genes conferring serum resistance. However, the insertion mutants were not capable of producing O antigens.

The expression of the type II secretion system (T3SS) regulon from Aeromonas hydrophila was analyzed by examining the activity of the aopN-aopD and aexT promoters via means of two different techniques, promoterless gfp fusions and real-time PCR. The results for both axsA and aopN mutants which are described as T3SS regulators in other species provided insight into their function as the major transcription regulator and valve of the T3SS, in Aeromonas hydrophila.

The article presents a new method for the evaluation of Aeromonas virulence by using Dictyostelium amoebae as an alternative host model.

The symbiotic association between Hirudo medicinalis and Aeromonas veronii bv. sorbia and colonization by the latter require the presence of serum complement system. A. veronii mutants lacking the complement system cannot colonize H. medicinalis but aquires the ability to colonize if the complement system is restored.

Results show that eight open reading frames of wb(sub)012 gene cluster code for Klebsiella pneumoniae O12-antigen lipopolysaccharide in Escherichia coli K-12. The wb gene cluster belongs to ABC 2 transporter-dependent pathways mediating O-antigen heteropolysaccharides synthesis.

The authors discuss their research on Klebsiella pneumoniae waaE gene. The functions of this gene in inner-core lipopolysaccharide biosynthesis and its role in motility and biofilm formation have been investigated, and the details are reported.

Introduction: Though eukaryotic glycoproteins have been studied since their discovery in the 1930s, the first bacterial glycoprotein was not identified until the 1970s. As a result, their role in bacterial pathogenesis is still not well understood and they remain an understudied component of bacterial virulence. In recent years, mass spectrometry has emerged as a leading technology for the study of bacterial glycoproteins, largely due to its sensitivity and versatility.Areas covered: Identification and comprehensive characterization of bacterial glycoproteins usually requires multiple complementary mass spectrometry approaches, including intact protein analysis, top-down analysis, and bottom-up methods used in combination with specialized liquid chromatography. This review provides an overview of liquid chromatography separation technologies, as well as current and emerging mass spectrometry approaches used specifically for bacterial glycoprotein identification and characterization.Expert commentary: Bacterial glycoproteins may have significant clinical utility as a result of their unique structures and exposure on the surface of the cells. Better understanding of these glycoconjugates is an essential first step towards that goal. These often unique structures, and by extension the key enzymes involved in their synthesis, represent promising targets for novel antimicrobials, while unique carbohydrate structures may be used as antigens in vaccines or as biomarkers. [ABSTRACT FROM AUTHOR]