Structural and Biological Characterization of a Capsular Polysaccharide Produced by Staphylococcus haemolyticus

Abstract

The DNA sequence of the genome of Staphylococcus haemolyticus JCSC1435 revealed a putative capsule operon composed of 13 genes in tandem. The first seven genes (capABCDEFG Sh ) showed >57% similarity with the Staphylococcus aureus cap5 or cap8 locus. However, the capHIJKLM Sh genes are unique to S. haemolyticus and include genes encoding a putative flippase, an aminotransferase, two glycosyltransferases, and a transcriptional regulator. Capsule-like material was readily apparent by immunoelectron microscopy on bacteria harvested in the postexponential phase of growth. Electron micrographs of a JCSC1435 mutant with a deleted cap region lacked the capsule-like material. Both strains produced small amounts of surface-associated material that reacted with antibodies to polyglutamic acid. S. haemolyticus cap genes were amplified from four of seven clinical isolates of S. haemolyticus from humans, and three of these strains produced a serologically cross-reactive capsular polysaccharide. In vitro assays demonstrated that the acapsular mutant strain showed greater biofilm formation but was more susceptible to complement-mediated opsonophagocytic killing than the parent strain. Structural characterization of capsule purified from S. haemolyticus strain JCSC1435 showed a trisaccharide repeating unit: ؊3-␣-L- FucNAc-3-(2-NAc-4-N-Asp-2,4,6-trideoxy-␤-D-Glc)-4-␣-D-GlcNAc-. This structure is unique among staphylococcal polysaccharides in that its composition includes a trideoxy sugar residue with aspartic acid as an N-acyl substituent.Among the coagulase-negative staphylococci (CoNS), Staphylococcus haemolyticus plays an important role in hospital-acquired opportunistic infections. S. haemolyticus is second only to Staphylococcus epidermidis in its frequency of isolation from human blood cultures (7, 9), and it may also cause peritonitis, otitis, urinary tract infections, and septicemia. Methicillin-resistant S. haemolyticus strains have been associated with foreign body infections (7), and S. haemolyticus is notorious for its multidrug-resistant phenotype, with decreased susceptibility to methicillin, teicoplanin, and vancomycin (24). S. haemolyticus was the first species of CoNS sharing teicoplanin and vancomycin resistance (23).The genome of the human-pathogenic S. haemolyticus strain JCSC1435 was sequenced in 2005 (25). At least 57 open reading frames (ORFs) associated with virulence were reported. As suggested by its species name, S. haemolyticus carries three candidate ORFs encoding hemolysins; other putative virulence factors include adhesins, exonucleases, proteases, and genes encoding a capsular polysaccharide (CP). Although slime production by S. haemolyticus has been reported (4), biofilm formation and adherence to acrylic by S. haemolyticus are significantly reduced compared to those of Staphylococcus epidermidis (2, 3). Moreover, the biofilm-associated ica locus, present in S. epidermidis and Staphylococcus aureus, is absent from strain JCSC1435 and other clinical isolates of S. haemolyticus (2, 6).Previous repo...

Characterization of the Structure and Biological Functions of a Capsular Polysaccharide Produced by Staphylococcus saprophyticus

“…CP was purified by methods similar to those we have described previously (7,59). Briefly, S. saprophyticus ATCC 15305 was cultivated on TSA medium overlaid with a dialysis membrane with a molecular size cutoff of 12,000 to 14,000 Da.…”

“…saprophyticus strain 15305 does not produce PNAG or polyglutamic acid (28,29), but this uropathogenic species is encapsulated. CP are lacking in isolates of S. epidermidis, the most common of the coagulase-negative species, but genomic evidence indicates that Staphylococcus haemolyticus (7,57), S. saprophyticus (29), and Staphylococcus carnosus (47) carry capsule loci with genetic similarity to the Staphylococcus aureus cap5 (cap8) gene locus. In this study, we purified and characterized the CP produced by S. saprophyticus ATCC 15305 and investigated the CP phenotype of S. saprophyticus clinical isolates.…”

Staphylococcus haemolyticus – an emerging threat in the twilight of the antibiotics age

“…Most S. haemolyticus strains seem to lack the important virulence attributes. However, some enzymes, cytolysins or surface substances are indicated in the literature as factors contributing to its virulence (Daniel et al, 2014;Flahaut et al, 2008;Simango, 2005), but none of them was identified as a crucial and determinative factor (Fredheim et al, 2009). Despite this, S. haemolyticus is, after S. epidermidis, the second most frequently isolated CNS from clinical cases, particularly from blood infections, including sepsis (Becker et al, 2014;Klingenberg et al, 2007;Liakopoulos et al, 2008;Silva et al, 2013).…”

Biofilm Formation by Staphylococcus haemolyticus

“…Both antimicrobial resistance and genetic rearrangements are probably mediated by insertion elements, which are abundant in S. haemolyticus (49). Recently, a capsular polysaccharide was proposed to be an important virulence factor in S. haemolyticus (16). S. haemolyticus biofilm formation in vitro has been reported, but the molecular mechanisms involved were not elu-cidated.…”