GltS regulates biofilm formation in methicillin-resistant Staphylococcus aureus

2023 Neer Award for Basic Science: Genetics of Cutibacterium acnes in revision shoulder arthroplasty: a large-scale bacterial whole-genome sequencing study

BACKGROUND

Cutibacterium acnes is the bacterium most commonly responsible for shoulder periprosthetic joint infection (PJI) and is often cultured from samples obtained at the time of revision for failed shoulder arthroplasty. We sought to determine whether these bacteria originate from the patient or from exogenous sources. We also sought to identify which C. acnes genetic traits were associated with the development of shoulder PJI.

METHODS

We performed bacterial whole-genome sequencing of C. acnes from a single-institution repository of cultures obtained before or during primary and revision shoulder arthroplasty and correlated the molecular epidemiology and genetic content of strains with clinical features of infection.

RESULTS

A total of 341 isolates collected over a 4-year period from 88 patients were sequenced. C. acnes cultured from surgical specimens demonstrated significant similarity to the strains colonizing the skin of the same patient (P < .001). Infrequently, there was evidence of strains shared across unrelated patients, suggesting that exogenous sources of C. acnes culture-positivity were uncommon. Phylotypes IB and II were modestly associated with clinical features of PJI, but all phylotypes appeared inherently capable of causing disease. Chronic shoulder PJI was associated with the absence of common C. acnes genes involved in bacterial quorum-sensing (luxS, tqsA).

CONCLUSION

C. acnes strains cultured from deep intraoperative sources during revision shoulder arthroplasty demonstrate strong genetic similarity to the strains colonizing a patient's skin. Some phylotypes of C. acnes commonly colonizing human skin are modestly more virulent than others, but all phylotypes have a capacity for PJI. C. acnes cultured from cases of PJI commonly demonstrated genetic hallmarks associated with adaptation from acute to chronic phases of infection. This is the strongest evidence to date supporting the role of the patient's own, cutaneous C. acnes strains in the pathogenesis of shoulder arthroplasty infection. Our findings support the importance of further research focused on perioperative decolonization and management of endogenous bacteria that are likely to be introduced into the arthroplasty wound at the time of skin incision.

Differential expression of small RNAs in biofilm-producing clinical methicillin-susceptible Staphylococcus aureus recovered from human urine

Bacterial small RNAs (sRNAs) play crucial roles in coordinating gene regulatory networks in various physiological processes, including biofilm formation. In this study, RNA sequencing was performed on biofilm (n = 4) and planktonic (n = 4) cells harvested at 10 h (pre-stationary phase of biofilm development) to identify biofilm-associated sRNAs in human methicillin-susceptible Staphylococcus aureus (MSSA) recovered from urine isolate. A total of 56 highly expressed sRNAs were identified with 15 overlapping sRNA genes (srn_9348, sprD, sRNA205, sRNA288, srn_2467, Sau-25, srn_2468, sRNA260, sRNA200, RsaE, sRNA397, Teg55, Teg60, RsaX05 and Teg140). Further validation through RT-qPCR analysis of nine sRNAs revealed that srn_9348 and sRNA260 were significantly expressed in the biofilm cells of urine sample. Both sRNAs were predicted to interact with mRNA genes including intracellular adhesin A (icaA) and host factor protein (hfq) involved in biofilm formation via cis-acting and trans-acting using CopraRNA analysis. Therefore, both sRNAs merit further investigations via reverse genetic approaches to elucidate their mechanism of translational regulation. In summary, the transcriptomic analysis conducted in this study offers new insights into the potential regulatory roles of sRNAs in MSSA biofilm development within the urinary environment.

Streptokinase reduces Streptococcus dysgalactiae subsp. equisimilis biofilm formation

BACKGROUND

Streptococcus dysgalactiae subspecies equisimilis (SDSE) is increasingly recognized as an emerging cause of invasive diseases including necrotizing soft tissue infections (NSTIs). In contrast to the closely related Streptococcus pyogenes, SDSE infections mainly affect older and comorbid patients. Biofilm formation has been demonstrated in soft tissue biopsies of S. pyogenes NSTI cases.

RESULTS

Here, we show that bacterial aggregations indicative of biofilms are also present in SDSE NSTI. Although streptokinase (Ska) activity and biofilm formation did not correlate in a diverse set of clinical SDSE isolates, addition of exogenous Ska at an early time point prevented biofilm formation for selected strains. Deletion of ska in SDSE S118 strain resulted in increased biofilm forming capacity. Ska-deficient mutant strain was characterized by a higher metabolic activity and consequent metabolome profiling of biofilms identified higher deposition of a wide range of metabolites as compared to the wild-type.

CONCLUSIONS

Our results argue that Ska suppresses biofilm formation in SDSE independent of its original plasminogen converting activity. However, the impact of biofilms and its consequences for patient outcomes in streptococcal NSTIs remain to be elucidated.

Bacterial single-cell RNA sequencing captures biofilm transcriptional heterogeneity and differential responses to immune pressure

Biofilm formation is an important mechanism of survival and persistence for many bacterial pathogens. These multicellular communities contain subpopulations of cells that display vast metabolic and transcriptional diversity along with high recalcitrance to antibiotics and host immune defenses. Investigating the complex heterogeneity within biofilm has been hindered by the lack of a sensitive and high-throughput method to assess stochastic transcriptional activity and regulation between bacterial subpopulations, which requires single-cell resolution. We have developed an optimized bacterial single-cell RNA sequencing method, BaSSSh-seq, to study Staphylococcus aureus diversity during biofilm growth and transcriptional adaptations following immune cell exposure. We validated the ability of BaSSSh-seq to capture extensive transcriptional heterogeneity during biofilm compared to planktonic growth. Application of new computational tools revealed transcriptional regulatory networks across the heterogeneous biofilm subpopulations and identification of gene sets that were associated with a trajectory from planktonic to biofilm growth. BaSSSh-seq also detected alterations in biofilm metabolism, stress response, and virulence that were tailored to distinct immune cell populations. This work provides an innovative platform to explore biofilm dynamics at single-cell resolution, unlocking the potential for identifying biofilm adaptations to environmental signals and immune pressure.

Glutamate-dependent arginine biosynthesis requires the inactivation of spoVG, sarA, and ahrC in Staphylococcus aureus

Genome sequencing has demonstrated that Staphylococcus aureus encodes arginine biosynthetic genes argDCJBFGH synthesizing proteins that mediate arginine biosynthesis using glutamate as a substrate. Paradoxically, however, S. aureus does not grow in a defined, glutamate-replete medium lacking arginine and glucose (CDM-R). Studies from our laboratory have found that specific mutations are selected by S. aureus that facilitate growth in CDM-R. However, these selected mutants synthesize arginine utilizing proline as a substrate rather than glutamate. In this study, we demonstrate that the ectopic expression of the argDCJB operon supports the growth of S. aureus in CDM-R, thus documenting the functionality of this pathway. Furthermore, suppressor mutants of S. aureus JE2 putA::Tn, which is defective in synthesizing arginine from proline, were selected on CDM-R agar. Genome sequencing revealed that these mutants had compensatory mutations within both spoVG, encoding an ortholog of the Bacillus subtilis stage V sporulation protein, and sarA, encoding the staphylococcal accessory regulator. Transcriptional studies document that argD expression is significantly increased when JE2 spoVG sarA was grown in CDM-R. Lastly, we found that a mutation in ahrC was required to induce argD expression in JE2 spoVG sarA when grown in an arginine-replete medium (CDM), suggesting that AhrC also functions to repress argDCJB in an arginine-dependent manner. In conclusion, these data indicate that the argDCJB operon is functional when transcribed in vitro and that SNPs within potential putative regulatory proteins are required to alleviate the repression.IMPORTANCEAlthough Staphylococcus aureus has the capability to synthesize all 20 amino acids, it is phenotypically auxotrophic for several amino acids including arginine. This work identifies putative regulatory proteins, including SpoVG, SarA, and AhrC, that function to inhibit the arginine biosynthetic pathways using glutamate as a substrate. Understanding the ultimate mechanisms of why S. aureus is selected to repress arginine biosynthetic pathways even in the absence of arginine will add to the growing body of work assessing the interactions between metabolism and S. aureus pathogenesis.

Volatile anesthetic isoflurane exposure facilitates Enterococcus biofilm infection

Enterococcus faecalis (E. faecalis) is one of the major pathogenic bacteria responsible for surgical site infections. Biofilm infections are major hospital-acquired infections. Previous studies suggested that ions could regulate biofilm formation in microbes. Volatile anesthetics, frequently administered in surgical setting, target ion channels. Here, we investigated the role of ion channels/transporters and volatile anesthetics in the biofilm formation by E. faecalis MMH594 strain and its ion transporter mutants. We found that a chloride transporter mutant significantly reduced biofilm formation compared to the parental strain. Downregulation of teichoic acid biosynthesis in the chloride transporter mutant impaired biofilm matrix formation and cellular adhesion, leading to mitigated biofilm formation. Among anesthetics, isoflurane exposure enhanced biofilm formation in vitro and in vivo. The upregulation of de novo purine biosynthesis pathway by isoflurane exposure potentially enhanced biofilm formation, an essential process for DNA, RNA, and ATP synthesis. We also demonstrated that isoflurane exposure to E. faecalis increased cyclic-di-AMP and extracellular DNA production, consistent with the increased purine biosynthesis. We further showed that isoflurane enhanced the enzymatic activity of phosphoribosyl pyrophosphate synthetase (PRPP-S). With the hypothesis that isoflurane directly bound to PRPP-S, we predicted isoflurane binding site on it using rigid docking. Our study provides a better understanding of the underlying mechanisms of E. faecalis biofilm formation and highlights the potential impact of an ion transporter and volatile anesthetic on this process. These findings may lead to the development of novel strategies for preventing E. faecalis biofilm formation and improving patient outcomes in clinical settings.

Comparative Proteomic Analysis of Protein Patterns of Stenotrophomonas maltophilia in Biofilm and Planktonic Lifestyles

Stenotrophomonas maltophilia is a clinically relevant bacterial pathogen, particularly in cystic fibrosis (CF) patients. Despite the well-known ability to form biofilms inherently resistant to antibiotics and host immunity, many aspects involved in S. maltophilia biofilm formation are yet to be elucidated. In the present study, a proteomic approach was used to elucidate the differential protein expression patterns observed during the planktonic-to-biofilm transition of S. maltophilia Sm126, a strong biofilm producer causing chronic infection in a CF patient, to identify determinants potentially associated with S. maltophilia biofilm formation. In all, 57 proteins were differentially (3-fold; p < 0.01) expressed in biofilm cells compared with planktonic counterparts: 38 were overexpressed, and 19 were down-expressed. It is worth noting that 34 proteins were exclusively found in biofilm, mainly associated with quorum sensing-mediated intercellular communication, augmented glycolysis, amino acid metabolism, biosynthesis of secondary metabolites, phosphate signaling, response to nutrient starvation, and general stress. Further work is warranted to evaluate if these proteins can be suitable targets for developing anti-biofilm strategies effective against S. maltophilia.