Molecular Characteristics, Virulence Gene and Wall Teichoic Acid Glycosyltransferase Profiles of Staphylococcus aureus: A Multicenter Study in China

Wall teichoic acid glycosylation of bovine-associated Staphylococcus aureus strains

Staphylococcus aureus (S. aureus) is one of the major causes of bovine mastitis, a disease with detrimental effects on health and wellbeing. Current control measures are costly, laborious and not always effective in eradicating S. aureus. The cell wall-linked polysaccharide wall teichoic acid (WTA) is highly immunogenic in humans and is considered as a prospective vaccine antigen based on promising pre-clinical studies in animals. WTA consist of polymerized ribitol-phosphate backbone that is modified with N-acetylglucosamine (GlcNAc) moieties in different configurations by the glycosyltransferases TarS (β-1,4-GlcNAc), TarM (α-1,4-GlcNAc) and TarP (β-1,3-GlcNAc). This study aimed to characterize the presence and genetic variation in tarS, tarM and tarP in bovine-associated S. aureus strains and how this impacts WTA-glycoprofile. Bioinformatic analyses of a whole genome sequence database consisting of 1047 S. aureus, 10 S. schweitzeri, and 6 S. argenteus strains showed that over 99% of strains contained tarS, 34 % also contained tarM, while 5 % of the strains encoded tarP in addition to tarS. The distribution of WTA-glycosyltransferase genes was similar to what has been reported for human-associated S. aureus strains. Phenotypic analysis of WTA glycosylation by flow cytometry corroborated with tarS/tarM/tarP gene presence. The WTA glycoprofile was variable between bovine-associated strains and the levels and ratios of GlcNAcylation were affected by growth conditions. Interestingly, a divergent tarM allele was present in strains of clonal complexes (CC) 49 and the mastitis-associated CC151, but its function was similar to canonical tarM. In conclusion, we demonstrated that bovine-associated S. aureus strains show similar variation in WTA GlcNAc decoration as human S. aureus strains, despite the presence of a divergent tarM allele.

Synthesis of structure-defined β-1,4-GlcNAc-modified wall teichoic acids as potential vaccine against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a high priority pathogen due to its life-threating infections to human health. Development of prophylactic or therapeutic anti-MRSA vaccine is a potential approach to treat S. aureus infections and overcome the resistance crisis. β-1,4-GlcNAc glycosylated wall teichoic acids (WTAs) derived from S. aureus are a new type of antigen that is closely associated with β-lactam resistance. In this study, structure-defined β-1,4-GlcNAc-modified WTAs varied in chain length and numbers of GlcNAc modification were synthesized by an ionic liquid-supported oligosaccharide synthesis (ILSOS) strategy in high efficiency and chromatography-free approach. Then the obtained WTAs were conjugated with tetanus toxin (TT) as vaccine candidates and were further evaluated in a mouse model to determine the structure-immunogenicity relationship. In vivo immunological studies revealed that the WTAs-TT conjugates provoked robust T cell-dependent responses and elicited high levels of specific anti-WTAs IgG antibodies production associated with the WTAs structure including chain length as well as the β-1,4-GlcNAc modification pattern. Heptamer WTAs conjugate T6, carrying three copy of β-1,4-GlcNAc modified RboP, was identified to elicit the highest titers of specific antibody production. The T6 antisera exhibited the highest recognition and binding affinity and the most potent OP-killing activities to MSSA and MRSA cells. This study demonstrated that β-1,4-GlcNAc glycosylated WTAs are promising antigens for further development against MRSA.

ST7 Becomes One of the Most Common Staphylococcus aureus Clones After the COVID-19 Epidemic in the City of Wuhan, China

Background

Staphylococcus aureus (S. aureus) was able to rapidly evolve and adapt under the pressure of antibiotics, host immune and environmental change. After Corona Virus Disease 2019 (COVID-19) epidemic in Wuhan, China, a large number of disinfectants were used, which might result in rapid evolution of S. aureus.

Methods

A total of 619 S. aureus isolates were collected from Zhongnan Hospital, Wuhan University from 2018 to 2021, including group BEFORE (309 strains collected before COVID-19 pandemic) and group AFTER (310 strains collected after COVID-19 pandemic), for comparing the changes of molecular epidemiology. The molecular characteristics of isolates were analyzed by Multi-locus sequence typing (MLST), spa, chromosomal cassette mec (SCCmec) typing, virulence genes were screened by the PCR, antibiotic susceptibility test was carried out by the VITEK system.

Results

Thirty-six sequence types (STs) belonging to 14 clone complexes (CCs) were identified. ST5 was the most prevalent clone in both groups, and ST7, ranking the sixth in group BEFORE, became the second dominant clone in group AFTER (6.5% vs 10.0%), whereas ST239 decreased from the seventh to the fourteenth (5.8% vs 1.9%). ST7 in group AFTER had a higher positive rate of virulence genes, including hlb, fnbB, seb, lukDE, sdrE and the proportion of ST7-t091 MRSA strains increased from 19.1% to 50% compared with group BEFORE. Though no significant difference of MRSA proportion was found between two groups, SCCmec type-III in group AFTER decreased (p<0.01). Though the rate of multidrug-resistance (MDR) decreased, the virulence genes hlb, hlg, fnbB, seb and pvl carrying rates were significantly elevated in MRSA strains of group AFTER.

Conclusion

After COVID-19 pandemic, ST7 becomes one of the predominant S. aureus clones in Wuhan and the carrying rate of SCCmec and virulence genes is on the rise. Therefore, it is essential to strengthen the surveillance of ST7 S. aureus clone.

Escalation of antimicrobial resistance among MRSA part 1: focus on global spread

INTRODUCTION

Staphylococcus aureus produce numerous virulence factors that influence tissue invasion, cytotoxicity, membrane damage, and intracellular persistence allowing them to be very common human pathogens. S. aureus isolates exhibit considerable diversity though specific genotypes have been associated with antimicrobial resistance (AMR) and toxin gene profiles. MRSA is an important pathogen causing both community-acquired (CA) and healthcare-acquired (HCA) infections. Importantly, over the past several decades, both HCA-MRSA and CA-MRSA have spread all over the globe. Even more concerning is that CA-MRSA clones have disseminated into hospitals and HCA-MRSA have entered the community. Factors that enhance spread of MRSA include: poor antimicrobial stewardship and inadequate infection control. The emergence and spread of multidrug resistant (MDR) MRSA has limited therapeutic options.

AREAS COVERED

The authors discuss the escalation of MRSA, both HCA-MRSA and CA-MRSA across the globe. A literature search of MRSA was performed via PubMed (up to September 2022), using the key words: antimicrobial resistance; β-lactams; community-associated MRSA; epidemiology; infection; multidrug resistance; Staphylococcus aureus.

EXPERT OPINION

Over the past several decades, MRSA has spread all over the globe. We encourage the judicious use of antimicrobials in accordance with antimicrobial stewardship programs along with infection control measures to minimize the spread of MRSA.

Genetic diversity of Staphylococcus aureus wall teichoic acid glycosyltransferases affects immune recognition

Staphylococcus aureus is a leading cause of skin and soft tissue infections and systemic infections. Wall teichoic acids (WTAs) are cell wall-anchored glycopolymers that are important for S. aureus nasal colonization, phage-mediated horizontal gene transfer, and antibiotic resistance. WTAs consist of a polymerized ribitol phosphate (RboP) chain that can be glycosylated with N-acetylglucosamine (GlcNAc) by three glycosyltransferases: TarS, TarM, and TarP. TarS and TarP modify WTA with β-linked GlcNAc at the C-4 (β1,4-GlcNAc) and the C-3 position (β1,3-GlcNAc) of the RboP subunit, respectively, whereas TarM modifies WTA with α-linked GlcNAc at the C-4 position (α1,4-GlcNAc). Importantly, these WTA glycosylation patterns impact immune recognition and clearance of S. aureus. Previous studies suggest that tarS is near-universally present within the S. aureus population, whereas a smaller proportion co-contain either tarM or tarP. To gain more insight into the presence and genetic variation of tarS, tarM and tarP in the S. aureus population, we analysed a collection of 25 652 S. aureus genomes within the PubMLST database. Over 99 % of isolates contained tarS. Co-presence of tarS/tarM or tarS/tarP occurred in 37 and 7 % of isolates, respectively, and was associated with specific S. aureus clonal complexes. We also identified 26 isolates (0.1 %) that contained all three glycosyltransferase genes. At sequence level, we identified tar alleles with amino acid substitutions in critical enzymatic residues or with premature stop codons. Several tar variants were expressed in a S. aureus tar-negative strain. Analysis using specific monoclonal antibodies and human langerin showed that WTA glycosylation was severely attenuated or absent. Overall, our data provide a broad overview of the genetic diversity of the three WTA glycosyltransferases in the S. aureus population and the functional consequences for immune recognition.

Horizontal transfer and phylogenetic distribution of the immune evasion factor tarP

Methicillin-resistant Staphylococcus aureus (MRSA), a major human pathogen, uses the prophage-encoded tarP gene as an important immune evasion factor. TarP glycosylates wall teichoic acid (WTA) polymers, major S. aureus surface antigens, to impair WTA immunogenicity and impede host defence. However, tarP phages appear to be restricted to only a few MRSA clonal lineages, including clonal complexes (CC) 5 and 398, for unknown reasons. We demonstrate here that tarP-encoding prophages can be mobilized to lysogenize other S. aureus strains. However, transfer is largely restricted to closely related clones. Most of the non-transducible clones encode tarM, which generates a WTA glycosylation pattern distinct from that mediated by TarP. However, tarM does not interfere with infection by tarP phages. Clonal complex-specific Type I restriction-modification systems were the major reasons for resistance to tarP phage infection. Nevertheless, tarP phages were found also in unrelated S. aureus clones indicating that tarP has the potential to spread to distant clonal lineages and contribute to the evolution of new MRSA clones.

Genomic Analysis of the Unusual Staphylococcus aureus ST630 Isolates Harboring WTA Glycosyltransferase Genes tarM and tagN

Staphylococcus aureus (S. aureus) can cause a broad spectrum of diseases ranging from skin infections to life-threatening diseases in both community and hospital settings. The surface-exposed wall teichoic acid (WTA) has a strong impact on host interaction, pathogenicity, horizontal gene transfer, and biofilm formation in S. aureus. The unusual S. aureus ST630 strains containing both ribitol-phosphate (RboP) WTA glycosyltransferase gene tarM and glycerol-phosphate (GroP) WTA glycosyltransferase gene tagN have been found recently. Native PAGE analysis showed that the WTA of tagN, tarM-encoding ST630 strains migrated slower than that of non-tagN-encoding ST630 strains, indicating the differences in WTA structure. Some mobile genetic elements (MGEs) such as the unique GroP-WTA biosynthetic gene cluster (SaGroWI), SCCmec element, and prophages that probably originated from the CoNS were identified in tagN, tarM-encoding ST630 strains. The SaGroWI element was first defined in S. aureus ST395 strain, which was refractory to exchange MGEs with typical RboP-WTA expressing S. aureus but could undergo horizontal gene transfer events with other species and genera via the specific bacteriophage Φ187. Overall, our data indicated that this rare ST630 was prone to acquire DNA from CoNS and might serve as a novel hub for the exchange of MGEs between CoNS and S. aureus. IMPORTANCE The structure of wall-anchored glycopolymers wall teichoic acid (WTA) produced by most Gram-positive bacteria is highly variable. While most dominant Staphylococcus aureus lineages produce poly-ribitol-phosphate (RboP) WTA, the tagN, tarM-encoding ST630 lineage probably has a poly-glycerol-phosphate (GroP) WTA backbone like coagulase-negative staphylococci (CoNS). There is growing evidence that staphylococcal horizontal gene transfer depends largely on transducing helper phages via WTA as the receptor. The structural difference of WTA greatly affects the transfer of mobile genetic elements among various bacteria. With the growing advances in sequencing and analysis technologies, genetic analysis has revolutionized research activities in the field of the important pathogen S. aureus. Here, we analyzed the molecular characteristics of ST630 and found an evolutionary link between ST630 and CoNS. Elucidating the genetic information of ST630 lineage will contribute to understanding the emergence and diversification of new pathogenic strains in S. aureus.

Molecular characteristics and risk factor analysis of Staphylococcus aureus colonization put insight into CC1 colonization in three nursing homes in Shanghai

Research indicates that Staphylococcus aureus colonization in the elderly with predisposing risks is associated with subsequent infection. However, the molecular epidemiology and risk factors for S. aureus colonization among residents and staff in nursing homes (NHs) in China remain unclear. A multicenter study was conducted in three NHs in Shanghai between September 2019 and October 2019. We explored the prevalence, molecular epidemiology, and risk factors for S. aureus colonization. All S. aureus isolates were characterized based on antimicrobial resistance, virulence genes, multilocus sequence typing (MLST), staphylococcus protein A (spa) typing, and staphylococcal cassette chromosome mec (SCCmec) typing. NH records were examined for potential risk factors for S. aureus colonization. S. aureus and methicillin-resistant S. aureus (MRSA) isolates were detected in 109 (100 residents and 9 staff, 19.8%, 109/551) and 28 (24 residents and 4 staff, 5.1%, 28/551) subjects among 496 residents and 55 staff screened, respectively. Compared to methicillin-susceptible S. aureus isolates, all 30 MRSA isolates had higher resistance rates to most antibiotics except minocycline, rifampicin, linezolid, vancomycin, and teicoplanin. Sequence type (ST) 1 (21.3%) was the most common sequence type, and t127 (20.5%) was the most common spa type among 122 S. aureus isolates. SCCmec type I (70%) was the dominant clone among all MRSA isolates. CC1 (26/122, 21.3%) was the predominant complex clone (CC), followed by CC398 (25/122, 20.5%), CC5 (20/122, 16.4%) and CC188 (18/122, 14.8%). Female sex (OR, 1.70; 95% CI, 1.04-2.79; P = 0.036) and invasive devices (OR, 2.19; 95% CI, 1.26-3.81; P = 0.006) were independently associated with S. aureus colonization.

The Role of hlb-Converting Bacteriophages in Staphylococcus aureus Host Adaption

As an opportunistic pathogen of humans and animals, Staphylococcus aureus asymptomatically colonizes the nasal cavity but is also a leading cause of life-threatening acute and chronic infections. The evolution of S. aureus resulting from short- and long-term adaptation to diverse hosts is tightly associated with mobile genetic elements. S. aureus strains can carry up to four temperate phages, many of which possess accessory genes encoding staphylococcal virulence factors. More than 90% of human nasal isolates of S. aureus have been shown to carry Sa3int phages, whereas invasive S. aureus isolates tend to lose these phages. Sa3int phages integrate as prophages into the bacterial hlb gene, disrupting the expression of the sphingomyelinase Hlb, an important virulence factor under specific infection conditions. Virulence factors encoded by genes carried by Sa3int phages include staphylokinase, enterotoxins, chemotaxis-inhibitory protein, and staphylococcal complement inhibitor, all of which are highly human specific and probably essential for bacterial survival in the human host. The transmission of S. aureus from humans to animals is strongly correlated with the loss of Sa3int phages, whereas phages are regained once a strain is transmitted from animals to humans. Thus, both the insertion and excision of prophages may confer a fitness advantage to this bacterium. There is also growing evidence that Sa3int phages may perform "active lysogeny," a process during which prophages are temporally excised from the chromosome without forming intact phage particles. The molecular mechanisms controlling the peculiar life cycle of Sa3int phages remain largely unclear. Nevertheless, their regulation is likely fine-tuned to ensure bacterial survival within different hosts.

Impact of Glycan Linkage to Staphylococcus aureus Wall Teichoic Acid on Langerin Recognition and Langerhans Cell Activation

Staphylococcus aureus is the leading cause of skin and soft tissue infections. It remains incompletely understood how skin-resident immune cells respond to invading S. aureus and contribute to an effective immune response. Langerhans cells (LCs), the only professional antigen-presenting cell type in the epidermis, sense S. aureus through their pattern-recognition receptor langerin, triggering a proinflammatory response. Langerin recognizes the β-1,4-linked N-acetylglucosamine (β1,4-GlcNAc) but not α-1,4-linked GlcNAc (α1,4-GlcNAc) modifications, which are added by dedicated glycosyltransferases TarS and TarM, respectively, on the cell wall glycopolymer wall teichoic acid (WTA). Recently, an alternative WTA glycosyltransferase, TarP, was identified, which also modifies WTA with β-GlcNAc but at the C-3 position (β1,3-GlcNAc) of the WTA ribitol phosphate (RboP) subunit. Here, we aimed to unravel the impact of β-GlcNAc linkage position for langerin binding and LC activation. Using genetically modified S. aureus strains, we observed that langerin similarly recognized bacteria that produce either TarS- or TarP-modified WTA, yet tarP-expressing S. aureus induced increased cytokine production and maturation of in vitro-generated LCs compared to tarS-expressing S. aureus. Chemically synthesized WTA molecules, representative of the different S. aureus WTA glycosylation patterns, were used to identify langerin-WTA binding requirements. We established that β-GlcNAc is sufficient to confer langerin binding, thereby presenting synthetic WTA molecules as a novel glycobiology tool for structure-binding studies and for elucidating S. aureus molecular pathogenesis. Overall, our data suggest that LCs are able to sense all β-GlcNAc-WTA producing S. aureus strains, likely performing an important role as first responders upon S. aureus skin invasion.

The Prevalence of Staphylococcus aureus and the Occurrence of MRSA CC398 in Monkey Feces in a Zoo Park in Eastern China

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the important antibiotic resistant pathogens causing infections in humans and animals. The increasing observation of MRSA in wildlife species has raised the concern of its impact on animal health and the potential of zoonotic transmission. This study investigated the prevalence of S. aureus in fecal samples from non-human primates in a zoo located in Jiangsu, China, in which 6 out of 31 (19.4%) fecal samples, and 2 out of 14 (14.3%) indoor room floor swab samples were S. aureus-positive. The antibiotic susceptibility tests of the eight isolates showed that the two isolates were resistant to both penicillin and cefoxitin, the three isolates were resistant only to penicillin, while three isolates were susceptible to all detected antibiotics. The two isolates resistant to cefoxitin were further identified as MRSA by the presence of mecA. Five different spa types were identified including t034 of two MRSA isolates from Trachypithecus francoisi, t189 of two methicillin-susceptible S. aureus (MSSA) isolates from Rhinopithecus roxellana, t377 of two MSSA isolates from Colobus guereza, and two novel spa types t19488 and t19499 from Papio anubis. Whole genome sequencing analysis showed that MRSA t034 isolates belonged to ST398 clustered in clonal complex 398 (CC398) and carried the type B ΦSa3 prophage. The phylogenetic analysis showed that the two MRSA t034/ST398 isolates were closely related to the human-associated MSSA in China. Moreover, two MRSA isolates contained the virulence genes relating to the cell adherence, biofilm formation, toxins, and the human-associated immune evasion cluster, which indicated the potential of bidirectional transfer of MRSA between monkeys and humans. This study is the first to report MRSA CC398 from monkey feces in China, indicating that MRSA CC398 could colonize in monkey and have the risk of transmission between humans and monkeys.