Dynamic in vivo mutations within the ica operon during persistence of Staphylococcus aureus in the airways of cystic fibrosis patients

Various mutations in icaR, the repressor of the icaADBC locus, occur in mucoid Staphylococcus aureus isolates recovered from the airways of people with cystic fibrosis

Staphylococcus aureus is one of the major pathogens isolated from the airways of people with cystic fibrosis (pwCF). Recently, we described a mucoid S. aureus phenotype from respiratory specimens of pwCF, which constitutively overproduced biofilm that consisted of polysaccharide intercellular adhesin (PIA) due to a 5bp-deletion (5bp-del) in the intergenic region of the intercellular adhesin (ica) locus. Since we were not able to identify the 5bp-del in mucoid isolates of two pwCF with long-term S. aureus persistence and in a number of mucoid isolates of pwCF from a prospective multicenter study, these strains were (i) characterized phenotypically, (ii) investigated for biofilm formation, and (iii) molecular typed by spa-sequence typing. To screen for mutations responsible for mucoidy, the ica operon of all mucoid isolates was analyzed by Sanger sequencing. Whole genome sequencing was performed for selected isolates. For all mucoid isolates without the 5 bp-del, various mutations in icaR, which is the transcriptional repressor of the icaADBC operon. Mucoid and non-mucoid strains belonged to the same spa-type. Transformation of PIA-overproducing S. aureus with a vector expressing the intact icaR gene restored the non-mucoid phenotype. Altogether, we demonstrated a new mechanism for the emergence of mucoid S. aureus isolates of pwCF.

Characterization of Staphylococcus Species Isolates from Sheep Milk with Subclinical Mastitis: Antibiotic Resistance, Enterotoxins, and Biofilm Production

Subclinical mastitis represents one of the most contagious diseases affecting animals involved in dairy production systems. Although coagulase-negative staphylococci (CoNSs) have been considered minor pathogens for many years, they have recently emerged as opportunistic pathogens in mastitis disorders. The objectives of this work were to assess the antimicrobial resistance profile and the ability to produce a biofilm in comparison with a reference strain and to search for genes related to biofilm production, antimicrobial resistance, and enterotoxins in 18 isolates of Staphylococcus species from the milk of sheep with subclinical mastitis, collected from different Sicilian farms. This knowledge is essential to provide basic information on the pathogenicity and virulence of staphylococcal species and their impact on animal health. All isolates were resistant to ampicillin, 88.8% to streptomycin, 77.7% to gentamicin, 44.4% to chloramphenicol, 27.7% to erythromycin, and 11.1% to tetracycline, and two isolates were strong biofilm producers. Antibiotic resistance gene profiling showed that 16.6% of isolates possess the blaZ gene, whereas the search of biofilm-associated genes revealed the occurrence of the sasC gene in 33.3% of isolates, the ica gene in 27.7%, and bap and agr (accessory gene regulator) genes in 16.6% of isolates. Altogether, the results of this study indicate that CoNSs can acquire virulence genes and could have a role as pathogens in subclinical mastitis.

Airway environment drives the selection of quorum sensing mutants and promote Staphylococcus aureus chronic lifestyle

Staphylococcus aureus is a predominant cause of chronic lung infections. While the airway environment is rich in highly sialylated mucins, the interaction of S. aureus with sialic acid is poorly characterized. Using S. aureus USA300 as well as clinical isolates, we demonstrate that quorum-sensing dysfunction, a hallmark of S. aureus adaptation, correlates with a greater ability to consume free sialic acid, providing a growth advantage in an air-liquid interface model and in vivo. Furthermore, RNA-seq experiment reveals that free sialic acid triggers transcriptional reprogramming promoting S. aureus chronic lifestyle. To support the clinical relevance of our results, we show the co-occurrence of S. aureus, sialidase-producing microbiota and free sialic acid in the airway of patients with cystic fibrosis. Our findings suggest a dual role for sialic acid in S. aureus airway infection, triggering virulence reprogramming and driving S. aureus adaptive strategies through the selection of quorum-sensing dysfunctional strains.

Transposon sequencing identifies genes impacting Staphylococcus aureus invasion in a human macrophage model

Staphylococcus aureus is a facultative intracellular pathogen in many host cell types, facilitating its persistence in chronic infections. The genes contributing to intracellular pathogenesis have not yet been fully enumerated. Here, we cataloged genes influencing S. aureus invasion and survival within human THP-1 derived macrophages using two laboratory strains (ATCC2913 and JE2). We developed an in vitro transposition method to produce highly saturated transposon mutant libraries in S. aureus and performed transposon insertion sequencing (Tn-Seq) to identify candidate genes with significantly altered abundance following macrophage invasion. While some significant genes were strain-specific, 108 were identified as common across both S. aureus strains, with most (n = 106) being required for optimal macrophage infection. We used CRISPR interference (CRISPRi) to functionally validate phenotypic contributions for a subset of genes. Of the 20 genes passing validation, seven had previously identified roles in S. aureus virulence, and 13 were newly implicated. Validated genes frequently evidenced strain-specific effects, yielding opposing phenotypes when knocked down in the alternative strain. Genomic analysis of de novo mutations occurring in groups (n = 237) of clonally related S. aureus isolates from the airways of chronically infected individuals with cystic fibrosis (CF) revealed significantly greater in vivo purifying selection in conditionally essential candidate genes than those not associated with macrophage invasion. This study implicates a core set of genes necessary to support macrophage invasion by S. aureus, highlights strain-specific differences in phenotypic effects of effector genes, and provides evidence for selection of candidate genes identified by Tn-Seq analyses during chronic airway infection in CF patients in vivo.

Carvacrol inhibits bacterial polysaccharide intracellular adhesin synthesis and biofilm formation of mucoid Staphylococcus aureus: an in vitro and in vivo study

Staphylococcus aureus (S. aureus) is one of the important human pathogens and causes both superficial and systemic infections. More importantly, the formation of S. aureus biofilms, a main cause of its pathogenicity and drug resistance, has been a critical challenge in clinical treatment. Carvacrol, a plant-based natural product, has gained great interest for therapeutic purposes due to its effective biological activity with low cytotoxicity. The present study aimed to investigate the effect of carvacrol on anti-biofilm activity. Growth curve analysis showed that applying a sub-inhibitory concentration of carvacrol (4 μg mL-1) was not lethal to S. aureus SYN; however, the inhibition rate of biofilm formation was as high as 63.6%, and the clearance rate of mature biofilms was as high as 30.7%. In addition, carvacrol effectively reduced the production of biofilm-associated extracellular polysaccharides and showed no effect on eDNA release. Furthermore, qPCR analysis revealed that carvacrol significantly down-regulated the expression of icaA, icaB, icaC, agrA, and sarA (P < 0.05). The in vivo efficacy of carvacrol against biofilm infection was further verified with a biological model of G. mellonella larvae. The results showed that carvacrol was non-toxic to the larvae and can effectively increase the survival rate of the larvae infected with S. aureus strain SYN.

In Vitro Selection Identifies Staphylococcus aureus Genes Influencing Biofilm Formation

Staphylococcus aureus generates biofilms during many chronic human infections, which contributes to its growth and persistence in the host. Multiple genes and pathways necessary for S. aureus biofilm production have been identified, but knowledge is incomplete, and little is known about spontaneous mutations that increase biofilm formation as infection progresses. Here, we performed in vitro selection of four S. aureus laboratory strains (ATCC 29213, JE2, N315, and Newman) to identify mutations associated with enhanced biofilm production. Biofilm formation increased in passaged isolates from all strains, exhibiting from 1.2- to 5-fold the capacity of parental lines. Whole-genome sequencing identified nonsynonymous mutations affecting 23 candidate genes and a genomic duplication encompassing sigB. Six candidate genes significantly impacted biofilm formation as isogenic transposon knockouts: three were previously reported to impact S. aureus biofilm formation (icaR, spdC, and codY), while the remaining three (manA, narH, and fruB) were newly implicated by this study. Plasmid-mediated genetic complementation of manA, narH, and fruB transposon mutants corrected biofilm deficiencies, with high-level expression of manA and fruB further enhancing biofilm formation over basal levels. This work recognizes genes not previously identified as contributing to biofilm formation in S. aureus and reveals genetic changes able to augment biofilm production by that organism.

Biology and Regulation of Staphylococcal Biofilm

Despite continuing progress in medical and surgical procedures, staphylococci remain the major Gram-positive bacterial pathogens that cause a wide spectrum of diseases, especially in patients requiring the utilization of indwelling catheters and prosthetic devices implanted temporarily or for prolonged periods of time. Within the genus, if Staphylococcus aureus and S. epidermidis are prevalent species responsible for infections, several coagulase-negative species which are normal components of our microflora also constitute opportunistic pathogens that are able to infect patients. In such a clinical context, staphylococci producing biofilms show an increased resistance to antimicrobials and host immune defenses. Although the biochemical composition of the biofilm matrix has been extensively studied, the regulation of biofilm formation and the factors contributing to its stability and release are currently still being discovered. This review presents and discusses the composition and some regulation elements of biofilm development and describes its clinical importance. Finally, we summarize the numerous and various recent studies that address attempts to destroy an already-formed biofilm within the clinical context as a potential therapeutic strategy to avoid the removal of infected implant material, a critical event for patient convenience and health care costs.

New Molecular Mechanism of Superbiofilm Elaboration in a Staphylococcus aureus Clinical Strain

Previously, we reported a novel regulator of biofilm (rob) with a nonsense mutation in the superbiofilm-elaborating strain JP080. Intriguingly, the complementation of JP080 with wild-type rob did not completely abolish its superbiofilm-elaborating phenotype. Therefore, we searched for other possible mutation(s) using complete genome sequence data and found a missense mutation in the gene icaR, which altered its 35th amino acid (Ala35Thr). To further study the mechanism of superbiofilm elaboration in JP080, we reconstructed the same mutations of rob and icaR in the strain FK300 and analyzed the phenotypes. The mutation of rob (A331T) increased biofilm elaboration, as previously demonstrated; similarly, an icaR mutation increased poly-N-acetylglucosamine and biofilm production in strain FK300. Furthermore, our analyses indicated that the double mutant of rob and icaR produced significantly more biofilms than the single mutants. Additionally, gel shift analysis revealed that the icaR from JP080 lost its ability to bind to the ica promoter region. These findings suggest that the icaR mutation in JP080 may result in a nonfunctional protein. We compared ica operon expression in an icaR single mutant, rob single mutant, and rob and icaR double mutant to the wild type. The rob and icaR mutants showed increased ica operon transcription by approximately 19- and 79-fold, respectively. However, the rob and icaR double mutant showed an approximately 350-fold increase, indicating the synergistic effects of icaR and rob on JP080 biofilm elaboration. Consequently, we concluded that the double mutations rob and icaR synergistically increased ica operon transcription, resulting in a superbiofilm phenotype in Staphylococcus aureus. IMPORTANCE Poly-N-acetylglucosamine (PNAG) is a major component of S. aureus biofilm. PNAG production is mediated by the products of four genes, icaADBC encoded in the ica operon, and the major negative regulator of this operon is IcaR encoded just upstream of icaADBC. Previously, we reported another negative regulator, Rob, through gene expression analysis of clinically isolated superbiofilm-elaborating strain JP080. The rob gene is encoded at different loci distant from the ica operon. Here, we report that JP080 also carried a mutation in icaR and demonstrated that IcaR and Rob synergistically regulate PNAG production. We successfully reconstructed these mutations in a wild type, and the double mutant resulted in superbiofilm-elaborating phenotype. We clearly show that loss of function of both IcaR and Rob is the very reason that JP080 is showing the superbiofilm-elaborating phenotype. This study clearly demonstrated there are at least two independent regulators synergistically fine-tuning PNAG production and suggested the complex regulatory mechanism of biofilm production.

Biofilm Formation by Staphylococcus aureus in the Specific Context of Cystic Fibrosis

Staphylococcus aureus is a major human pathogen whose characteristics support its success in various clinical settings including Cystic Fibrosis (CF). In CF, S. aureus is indeed the most commonly identified opportunistic pathogen in children and the overall population. S. aureus colonization/infection, either by methicillin-susceptible or methicillin-resistant strains, will become chronic in about one third of CF patients. The persistence of S. aureus in CF patients' lungs, despite various eradication strategies, is favored by several traits in both host and pathogen. Among the latter, living in biofilm is a highly protective way to survive despite deleterious environmental conditions, and is a common characteristic shared by the main pathogens identified in CF. This is why CF has earned the status of a biofilm-associated disease for several years now. Biofilm formation by S. aureus, and the molecular mechanisms governing and regulating it, have been extensively studied but have received less attention in the specific context of CF lungs. Here, we review the current knowledge on S. aureus biofilm in this very context, i.e., the importance, study methods, molecular data published on mono- and multi-species biofilm and anti-biofilm strategies. This focus on studies including clinical isolates from CF patients shows that they are still under-represented in the literature compared with studies based on reference strains, and underlines the need for such studies. Indeed, CF clinical strains display specific characteristics that may not be extrapolated from results obtained on laboratory strains.

A Review of Biofilm Formation of Staphylococcus aureus and Its Regulation Mechanism

Bacteria can form biofilms in natural and clinical environments on both biotic and abiotic surfaces. The bacterial aggregates embedded in biofilms are formed by their own produced extracellular matrix. Staphylococcus aureus (S. aureus) is one of the most common pathogens of biofilm infections. The formation of biofilm can protect bacteria from being attacked by the host immune system and antibiotics and thus bacteria can be persistent against external challenges. Therefore, clinical treatments for biofilm infections are currently encountering difficulty. To address this critical challenge, a new and effective treatment method needs to be developed. A comprehensive understanding of bacterial biofilm formation and regulation mechanisms may provide meaningful insights against antibiotic resistance due to bacterial biofilms. In this review, we discuss an overview of S. aureus biofilms including the formation process, structural and functional properties of biofilm matrix, and the mechanism regulating biofilm formation.

Lung-adapted Staphylococcus aureus isolates with dysfunctional agr system trigger a proinflammatory response

BACKGROUND

Staphylococcus aureus (Sa) dominates the lung microbiota of Cystic Fibrosis (CF) children and persistent clones are able to establish chronic infection for years, having a direct deleterious impact on lung function. However, in this context, the exact contribution of Sa to the decline in respiratory function in CF children is not elucidated.

METHODS

To investigate the contribution of persistent S. aureus clones in CF disease, we undertook the analysis of sequential isogenic isolates recovered from 15 young CF patients.

RESULTS

Using an Air-Liquid infection model, we observed a strong correlation between Sa adaption in the lung (late isolates), low toxicity and pro-inflammatory cytokine secretion. Conversely, early isolates appeared to be highly cytotoxic but did not promote cytokine secretion. We found that cytokine secretion was dependent on Staphylococcal protein A (Spa), which was selectively expressed in late compared to early isolates as a consequence of dysfunctional agr quorum-sensing system. Finally, we demonstrated the involvement of TNF-α receptor 1 signaling in the inflammatory response of airway epithelial cells to these lung-adapted Sa isolates.

CONCLUSION

Our results suggest an unexpected direct role of bacterial lung adaptation in the progression of chronic lung disease by promoting a pro-inflammatory response through acquired agr dysfunction.

Experimental Polymorphism Survey in Intergenic Regions of the icaADBCR Locus in Staphylococcus aureus Isolates from Periprosthetic Joint Infections

Staphylococcus aureus is a leading cause of prosthetic joint infections (PJI) characterized by bacterial biofilm formation and recalcitrance to immune-mediated clearance and antibiotics. The molecular events behind PJI infection are yet to be unraveled. In this sense, identification of polymorphisms in bacterial genomes may help to establish associations between sequence variants and the ability of S. aureus to cause PJI. Here, we report an experimental nucleotide-level survey specifically aimed at the intergenic regions (IGRs) of the icaADBCR locus, which is responsible for the synthesis of the biofilm exopolysaccharide PIA/PNAG, in a collection of strains sampled from PJI and wounds. IGRs of the icaADBCR locus were highly conserved and no PJI-specific SNPs were found. Moreover, polymorphisms in these IGRs did not significantly affect transcription of the icaADBC operon under in vitro laboratory conditions. In contrast, an SNP within the icaR coding region, resulting in a V176E change in the transcriptional repressor IcaR, led to a significant increase in icaADBC operon transcription and PIA/PNAG production and a reduction in S. aureus virulence in a Galleria mellonella infection model. In conclusion, SNPs in icaADBCR IGRs of S. aureus isolates from PJI are not associated with icaADBC expression, PIA/PNAG production and adaptation to PJI.

Molecular Basis of Wrinkled Variants Isolated From Pseudoalteromonas lipolytica Biofilms

Many Pseudoalteromonas species are dominant biofilm-forming Gammaproteobacteria in the ocean. The formation of Pseudoalteromonas biofilms is often accompanied by the occurrence of variants with different colony morphologies that may exhibit increased marine antifouling or anticorrosion activities. However, the genetic basis of the occurrence of these variants remains largely unexplored. In this study, we identified that wrinkled variants of P. lipolytica mainly arose due to mutations in the AT00_08765, a wspF-like gene, that are associated with decreased swimming motility and increased cellulose production. Moreover, we found that the spontaneous mutation in flhA, encoding a flagellar biosynthesis protein, also caused a wrinkled colony morphology that is associated with cellulose overproduction, indicating that flhA plays a dual role in controlling flagellar assembly and polysaccharide production in P. lipolytica. Investigation of wrinkled variants harboring spontaneous mutation in dgcB, encoding a GGDEF domain protein, also demonstrated dgcB plays an important role in regulating cellulose production and swimming motility. In addition, by screening the suppressor of the AT00_08765 variant strain, we also identified that the spontaneous mutation in cheR and bcsC directly abolished the wrinkled phenotype of the AT00_08765 variant strain, suggesting that the chemosensory signaling transduction and cellulose production are crucial for the determination of the wrinkled phenotype in P. lipolytica. Taken together, this study provides insights into the genetic variation within biofilms of P. lipolytica.

The Role of Staphylococcus aureus YycFG in Gene Regulation, Biofilm Organization and Drug Resistance

Antibiotic resistance is a serious global health concern that may have significant social and financial consequences. Methicillin-resistant Staphylococcus aureus (MRSA) infection is responsible for substantial morbidity and leads to the death of 21.8% of infected patients annually. A lack of novel antibiotics has prompted the exploration of therapies targeting bacterial virulence mechanisms. The two-component signal transduction system (TCS) enables microbial cells to regulate gene expression and the subsequent metabolic processes that occur due to environmental changes. The YycFG TCS in S. aureus is essential for bacterial viability, the regulation of cell membrane metabolism, cell wall synthesis and biofilm formation. However, the role of YycFG-associated biofilm organization in S. aureus antimicrobial drug resistance and gene regulation has not been discussed in detail. We reviewed the main molecules involved in YycFG-associated cell wall biosynthesis, biofilm development and polysaccharide intercellular adhesin (PIA) accumulation. Two YycFG-associated regulatory mechanisms, accessory gene regulator (agr) and staphylococcal accessory regulator (SarA), were also discussed. We highlighted the importance of biofilm formation in the development of antimicrobial drug resistance in S. aureus infections. Data revealed that inhibition of the YycFG pathway reduced PIA production, biofilm formation and bacterial pathogenicity, which provides a potential target for the management of MRSA-induced infections.

An Innovative Protocol for Metaproteomic Analyses of Microbial Pathogens in Cystic Fibrosis Sputum

Hallmarks of cystic fibrosis (CF) are increased viscosity of mucus and impaired mucociliary clearance within the airways due to mutations of the cystic fibrosis conductance regulator gene. This facilitates the colonization of the lung by microbial pathogens and the concomitant establishment of chronic infections leading to tissue damage, reduced lung function, and decreased life expectancy. Although the interplay between key CF pathogens plays a major role during disease progression, the pathophysiology of the microbial community in CF lungs remains poorly understood. Particular challenges in the analysis of the microbial population present in CF sputum is (I) the inhomogeneous, viscous, and slimy consistence of CF sputum, and (II) the high number of human proteins masking comparably low abundant microbial proteins. To address these challenges, we used 21 CF sputum samples to develop a reliable, reproducible and widely applicable protocol for sputum processing, microbial enrichment, cell disruption, protein extraction and subsequent metaproteomic analyses. As a proof of concept, we selected three sputum samples for detailed metaproteome analyses and complemented and validated metaproteome data by 16S sequencing, metabolomic as well as microscopic analyses. Applying our protocol, the number of bacterial proteins/protein groups increased from 199-425 to 392-868 in enriched samples compared to nonenriched controls. These early microbial metaproteome data suggest that the arginine deiminase pathway and multiple proteases and peptidases identified from various bacterial genera could so far be underappreciated in their contribution to the CF pathophysiology. By providing a standardized and effective protocol for sputum processing and microbial enrichment, our study represents an important basis for future studies investigating the physiology of microbial pathogens in CF in vivo – an important prerequisite for the development of novel antimicrobial therapies to combat chronic recurrent airway infection in CF.

Staphylococcus aureus and Cystic Fibrosis-A Close Relationship. What Can We Learn from Sequencing Studies?

Staphylococcus aureus is next to Pseudomonas aeruginosa the most isolated pathogen from the airways of cystic fibrosis (CF) patients, who are often infected by a dominant S. aureus clone for extended periods. To be able to persist, the pathogen has to adapt to the hostile niche of the airways to counteract host defence, antibiotic therapy and the competition with coinfecting pathogens. S. aureus is equipped with many virulence factors including adhesins, toxins that are localized on the chromosome, on plasmids or are phage-related. S. aureus is especially versatile and adaptation and evolution of the pathogen occurs by the acquisition of new genes by horizontal gene transfer (HGT), changes in nucleotides (single nucleotide variations, SNVs) that can cause a selective advantage for the bacteria and become fixed in subpopulations. Methicillin-resistant S. aureus are a special threat to CF patients due to the more severe lung disease occurring in infected patients. Today, with decreasing costs for sequencing, more and more studies using S. aureus isolates cultured from CF patients are being published, which use whole genome sequencing (WGS), multilocus sequence typing (MLST) or spa-sequence typing (spa-typing) to follow the population dynamics of S. aureus, elucidate the underlying mechanisms of phenotypic variants, newly acquired resistance or adaptation to the host response in this particular niche. In the first part of this review, an introduction to the genetic make-up and the pathogenesis of S. aureus with respect to CF is provided. The second part presents an overview of recent studies and their findings using genotypic methods such as single or multilocus sequencing and whole genome sequencing, which identify factors contributing to the adaptation of S. aureus and its evolution in the airways of individuals with CF.

Genomic analysis of Staphylococcus aureus from the West African Dwarf (WAD) goat in Nigeria

Background

Staphylococcus aureus can colonize various host species, and human-animal interaction is a significant factor for cross-species transmission. However, data on S. aureus colonization in animals, particularly on ruminants in close contact with humans, is limited. The West African Dwarf (WAD) goat is among the earliest domesticated ruminant associated with rural dwellers and small-holder farmers in sub-Saharan Africa. This study aimed to investigate the population structure, antibiotic resistance, and virulence gene determinants of S. aureus from the WAD goat in Nigeria.

Methods

Nasal samples were obtained from the WAD goat in five markets in Osun State, South-West Nigeria. S. aureus was characterized by antibiotic susceptibility testing, detection of virulence determinants, spa typing, and multilocus sequence typing (MLST). Representative isolates were selected for whole-genome sequencing, biofilm, and cytotoxicity assay.

Results

Of the 726 nasal samples obtained from the WAD goat, 90 S. aureus (12.4%) were recovered. Overall, 86 isolates were methicillin-susceptible, and four were mecA-positive (i.e., methicillin-resistant S. aureus [MRSA]). A diverse S. aureus clonal population was observed (20 sequence types [STs] and 37 spa types), while 35% (13/37) and 40% (8/20) were new spa types and STs, respectively. Eleven MLST clonal complexes (CC) were identified (CC1, CC5, CC8, CC15, CC30, CC45, CC97, CC121, CC133, CC152, CC522). The MRSA isolates were designated as t127-ST852-CC1-SCCmec type VII, t4690-ST152-CC152-SCCmec type Vc, and t8821-ST152-CC152-SCCmec type Vc. Phylogenetic analysis revealed that 60% (54/90) of all isolates were associated with ruminant lineages (i.e., CC133, CC522). Panton-Valentine Leukocidin (PVL)-positive S. aureus was identified in CC1, CC30, CC121, and CC152. For the CC522 isolates, we illustrate their pathogenic potential by the detection of the toxic shock syndrome gene and hemolysins, as well as their strong cytotoxicity and ability to form biofilms.

Conclusions

This is the first detailed investigation on the genomic content of S. aureus from the WAD goat in Nigeria. The S. aureus population of the WAD goat consists mainly of ruminant-associated lineages (e.g., CC133, CC522), interspersed with human-associated clones, including PVL-positive MRSA CC1 and CC152.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-021-00987-8.

Common Adaptive Strategies Underlie Within-Host Evolution of Bacterial Pathogens

Within-host adaptation is a hallmark of chronic bacterial infections, involving substantial genomic changes. Recent large-scale genomic data from prolonged infections allow the examination of adaptive strategies employed by different pathogens and open the door to investigate whether they converge toward similar strategies. Here, we compiled extensive data of whole-genome sequences of bacterial isolates belonging to miscellaneous species sampled at sequential time points during clinical infections. Analysis of these data revealed that different species share some common adaptive strategies, achieved by mutating various genes. Although the same genes were often mutated in several strains within a species, different genes related to the same pathway, structure, or function were changed in other species utilizing the same adaptive strategy (e.g., mutating flagellar genes). Strategies exploited by various bacterial species were often predicted to be driven by the host immune system, a powerful selective pressure that is not species specific. Remarkably, we find adaptive strategies identified previously within single species to be ubiquitous. Two striking examples are shifts from siderophore-based to heme-based iron scavenging (previously shown for Pseudomonas aeruginosa) and changes in glycerol-phosphate metabolism (previously shown to decrease sensitivity to antibiotics in Mycobacterium tuberculosis). Virulence factors were often adaptively affected in different species, indicating shifts from acute to chronic virulence and virulence attenuation during infection. Our study presents a global view on common within-host adaptive strategies employed by different bacterial species and provides a rich resource for further studying these processes.

Association of Diverse Staphylococcus aureus Populations with Pseudomonas aeruginosa Coinfection and Inflammation in Cystic Fibrosis Airway Infection

Staphylococcus aureus is one of the most common pathogens isolated from the airways of cystic fibrosis (CF) patients and often persists for extended periods. There is limited knowledge about the diversity of S. aureus in CF. We hypothesized that increased diversity of S. aureus would impact CF lung disease. Therefore, we conducted a 1-year observational prospective study with 14 patients with long-term S. aureus infection. From every sputum, 40 S. aureus isolates were chosen and characterized in terms of phenotypic appearance (size, hemolysis, mucoidy, and pigmentation), important virulence traits such as nuclease activity, biofilm formation, and molecular typing by spa sequence typing. Data about coinfection with Pseudomonas aeruginosa and clinical parameters such as lung function, exacerbation, and inflammatory markers in blood (C-reactive protein [CRP], interleukin 6 [IL-6], and S100A8/9 [calprotectin]) were collected. From 58 visits of 14 patients, 2,319 S. aureus isolates were distinguished into 32 phenotypes (PTs) and 50 spa types. The Simpson diversity index (SDI) was used to calculate the phenotypic and genotypic diversity, revealing a high diversity of PTs ranging from 0.19 to 0.87 among patients, while the diversity of spa types of isolates was less pronounced. The SDI of PTs was positively associated with P. aeruginosa coinfection and inflammatory parameters, with IL-6 being the most sensitive parameter. Also, coinfection with P. aeruginosa was associated with mucoid S. aureus and S. aureus with high nuclease activity. Our analyses showed that in CF patients with long-term S. aureus airway infection, a highly diverse and dynamic S. aureus population was present and associated with P. aeruginosa coinfection and inflammation. IMPORTANCE Staphylococcus aureus can persist for extended periods in the airways of people with cystic fibrosis (CF) in spite of antibiotic therapy and high numbers of neutrophils, which fail to eradicate this pathogen. Therefore, S. aureus needs to adapt to this hostile niche. There is only limited knowledge about the diversity of S. aureus in respiratory specimens. We conducted a 1-year prospective study with 14 patients with long-term S. aureus infection and investigated 40 S. aureus isolates from every sputum in terms of phenotypic appearance, nuclease activity, biofilm formation, and molecular typing. Data about coinfection with Pseudomonas aeruginosa and clinical parameters such as lung function, exacerbation, and inflammatory markers in blood were collected. Thirty-two phenotypes (PTs) and 50 spa types were distinguished. Our analyses revealed that in CF patients with long-term S. aureus airway infection, a highly diverse and dynamic S. aureus population was associated with P. aeruginosa coinfection and inflammation.

Plasmid-Chromosome Crosstalk in Staphylococcus aureus: A Horizontally Acquired Transcription Regulator Controls Polysaccharide Intercellular Adhesin-Mediated Biofilm Formation

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) of clonal complex CC398 typically carry various antimicrobial resistance genes, many of them located on plasmids. In the bovine LA-MRSA isolate Rd11, we previously identified plasmid pAFS11 in which resistance genes are co-localized with a novel ica-like gene cluster, harboring genes required for polysaccharide intercellular adhesin (PIA)-mediated biofilm formation. The ica genes on pAFS11 were acquired in addition to a pre-existing ica locus on the S. aureus Rd11 chromosomal DNA. Both loci consist of an icaADBC operon and icaR, encoding a corresponding icaADBC repressor. Despite carrying two biofilm gene copies, strain Rd11 did not produce PIA and transformation of pAFS11 into another S. aureus strain even slightly diminished PIA-mediated biofilm formation. By focusing on the molecular background of the biofilm-negative phenotype of pAFS11-carrying S. aureus, we identified the pAFS11-borne ica locus copy as functionally fully active. However, transcription of both plasmid- and core genome-derived icaADBC operons were efficiently suppressed involving IcaR. Surprisingly, although being different on the amino acid sequence level, the two IcaR repressor proteins are mutually replaceable and are able to interact with the icaA promoter region of the other copy. We speculate that this regulatory crosstalk causes the biofilm-negative phenotype in S. aureus Rd11. The data shed light on an unexpected regulatory interplay between pre-existing and newly acquired DNA traits in S. aureus. This also raises interesting general questions regarding functional consequences of gene transfer events and their putative implications for the adaptation and evolution of bacterial pathogens.

How Bacterial Adaptation to Cystic Fibrosis Environment Shapes Interactions Between Pseudomonas aeruginosa and Staphylococcus aureus

Pseudomonas aeruginosa and Staphylococcus aureus are the two most prevalent bacteria species in the lungs of cystic fibrosis (CF) patients and are associated with poor clinical outcomes. Co-infection by the two species is a frequent situation that promotes their interaction. The ability of P. aeruginosa to outperform S. aureus has been widely described, and this competitive interaction was, for a long time, the only one considered. More recently, several studies have described that the two species are able to coexist. This change in relationship is linked to the evolution of bacterial strains in the lungs. This review attempts to decipher how bacterial adaptation to the CF environment can induce a change in the type of interaction and promote coexisting interaction between P. aeruginosa and S. aureus. The impact of coexistence on the establishment and maintenance of a chronic infection will also be presented, by considering the latest research on the subject.

Comparative genomics of ST5 and ST30 methicillin-resistant Staphylococcus aureus sequential isolates recovered from paediatric patients with cystic fibrosis

Staphylococcus aureus chronic airway infection in patients with cystic fibrosis (CF) allows this pathogen to adapt over time in response to different selection pressures. We have previously shown that the main sequence types related to community-acquired methicillin-resistant S. aureus (MRSA) infections in Argentina - ST5 and ST30 - are also frequently isolated from the sputum of patients with CF, but in these patients they usually display multi-drug antimicrobial resistance. In this study, we sequenced the genomes of MRSA from four paediatric CF patients with the goal of identifying mutations among sequential isolates, especially those possibly related to antimicrobial resistance and virulence, which might contribute to the adaptation of the pathogen in the airways of patients with CF. Our results revealed genetic differences in sequential MRSA strains isolated from patients with CF in both their core and accessory genomes. Although the genetic adaptation of S. aureus was distinct in different hosts, we detected independent mutations in thyA, htrA, rpsJ and gyrA - which are known to have crucial roles in S. aureus virulence and antimicrobial resistance - in isolates recovered from multiple patients. Moreover, we identified allelic variants that were detected in all of the isolates recovered after a certain time point; these non-synonymous mutations were in genes associated with antimicrobial resistance, virulence, iron scavenging and oxidative stress resistance. In conclusion, our results provide evidence of genetic variability among sequential MRSA isolates that could be implicated in the adaptation of these strains during chronic CF airway infection.

The staphylococcal exopolysaccharide PIA - Biosynthesis and role in biofilm formation, colonization, and infection

Exopolysaccharide is a key part of the extracellular matrix that contributes to important mechanisms of bacterial pathogenicity, most notably biofilm formation and immune evasion. In the human pathogens Staphylococcus aureus and S. epidermidis, as well as in many other staphylococcal species, the only exopolysaccharide is polysaccharide intercellular adhesin (PIA), a cationic, partially deacetylated homopolymer of N-acetylglucosamine, whose biosynthetic machinery is encoded in the ica locus. PIA production is strongly dependent on environmental conditions and controlled by many regulatory systems. PIA contributes significantly to staphylococcal biofilm formation and immune evasion mechanisms, such as resistance to antimicrobial peptides and ingestion and killing by phagocytes, and presence of the ica genes is associated with infectivity. Due to its role in pathogenesis, PIA has raised considerable interest as a potential vaccine component or target.

Staphylococcus aureus and its Effects on the Prognosis of Bronchiectasis

Bronchiectasis, which is an abnormal and irreversible dilation of one or several bronchial segments, causes significant morbidity and impaired quality of life to patients, mainly as the result of recurrent and chronic respiratory infections. Staphylococcus aureus is a microorganism known for its high infectious potential related to the production of molecules with great pathogenic power, such as enzymes, toxins, adhesins, and biofilm, which determine the degree of severity of systemic symptoms and can induce exacerbated immune response. This review highlighted the clinical significance of S. aureus colonization/infection in bronchiectasis patients, since little is known about it, despite its increasing frequency of isolation and potential serious morbidity.

The staphylococcal exopolysaccharide PIA - Biosynthesis and role in biofilm formation, colonization, and infection

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PIA is a key extracellular matrix component in staphylococci and other bacteria.

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PIA is a cationic, partially deacetylated N-acetylglucosamine polymer.

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PIA has a major role in bacterial biofilms and biofilm-associated infection.

Exopolysaccharide is a key part of the extracellular matrix that contributes to important mechanisms of bacterial pathogenicity, most notably biofilm formation and immune evasion. In the human pathogens Staphylococcus aureus and S. epidermidis, as well as in many other staphylococcal species, the only exopolysaccharide is polysaccharide intercellular adhesin (PIA), a cationic, partially deacetylated homopolymer of N-acetylglucosamine, whose biosynthetic machinery is encoded in the ica locus. PIA production is strongly dependent on environmental conditions and controlled by many regulatory systems. PIA contributes significantly to staphylococcal biofilm formation and immune evasion mechanisms, such as resistance to antimicrobial peptides and ingestion and killing by phagocytes, and presence of the ica genes is associated with infectivity. Due to its role in pathogenesis, PIA has raised considerable interest as a potential vaccine component or target.

An injectable self-healing anesthetic glycolipid-based oleogel with antibiofilm and diabetic wound skin repair properties

Globally, wound infections are considered as one of the major healthcare problems owing to the delayed healing process in diabetic patients and microbial contamination. Thus, the development of advanced materials for wound skin repair is of great research interest. Even though several biomaterials were identified as wound healing agents, gel-based scaffolds derived from either polymer or small molecules have displayed promising wound closure mechanism. Herein, for the first time, we report an injectable and self-healing self-assembled anesthetic oleogel derived from glycolipid, which exhibits antibiofilm and wound closure performance in diabetic rat. Glycolipid derived by the reaction of hydrophobic vinyl ester with α-chloralose in the presence of novozyme 435 undergoes spontaneous self-assembly in paraffin oil furnished an oleogel displaying self-healing behavior. In addition, we have prepared composite gel by encapsulating curcumin in the 3D fibrous network of oleogel. More interestingly, glycolipid in its native form demoed potential in disassembling methicillin-resistant Staphylococcus aureus, methicillin-susceptible Staphylococcus aureus, and Pseudomonas aeruginosa biofilms. Both oleogel and composite gel enhanced the wound skin repair in diabetic induced Wistar rats by promoting collagen synthesis, controlling free radical generation and further regulating tissue remodeling phases. Altogether, the reported supramolecular self-assembled anesthetic glycolipid could be potentially used for diabetic skin wound repair and to treat bacterial biofilm related infections.

Development of a vaccine against Staphylococcus aureus invasive infections: Evidence based on human immunity, genetics and bacterial evasion mechanisms

Invasive Staphylococcus aureus infections are a leading cause of morbidity and mortality in both hospital and community settings, especially with the widespread emergence of virulent and multi-drug resistant methicillin-resistant S. aureus strains. There is an urgent and unmet clinical need for non-antibiotic immune-based approaches to treat these infections as the increasing antibiotic resistance is creating a serious threat to public health. However, all vaccination attempts aimed at preventing S. aureus invasive infections have failed in human trials, especially all vaccines aimed at generating high titers of opsonic antibodies against S. aureus surface antigens to facilitate antibody-mediated bacterial clearance. In this review, we summarize the data from humans regarding the immune responses that protect against invasive S. aureus infections as well as host genetic factors and bacterial evasion mechanisms, which are important to consider for the future development of effective and successful vaccines and immunotherapies against invasive S. aureus infections in humans. The evidence presented form the basis for a hypothesis that staphylococcal toxins (including superantigens and pore-forming toxins) are important virulence factors, and targeting the neutralization of these toxins are more likely to provide a therapeutic benefit in contrast to prior vaccine attempts to generate antibodies to facilitate opsonophagocytosis.

Chronic Staphylococcus aureus Lung Infection Correlates With Proteogenomic and Metabolic Adaptations Leading to an Increased Intracellular Persistence

BACKGROUND

Chronic lung infection in cystic fibrosis (CF) patients by Staphylococcus aureus is a well-established epidemiological fact. Indeed, S. aureus is the most commonly identified pathogen in the lungs of CF patients. Improving our understanding of the mechanisms associated with the persistence of S. aureus is therefore an important issue.

METHODS

We selected pairs of sequential S. aureus isolates from 3 patients with CF and from 1 patient with non-CF chronic lung disease. We used a combination of genomic, proteomic, and metabolomic approaches with functional assays for in-depth characterization of S. aureus long-term persistence.

RESULTS

In this study, we show that late S. aureus isolates from CF patients have an increased ability for intracellular survival in CF bronchial epithelial-F508del cells compared to ancestral early isolates. Importantly, the increased ability to persist intracellularly was confirmed for S. aureus isolates within the own-patient F508del epithelial cells. An increased ability to form biofilm was also demonstrated. Furthermore, we identified the underlying genetic modifications that induce altered protein expression profiles and notable metabolic changes. These modifications affect several metabolic pathways and virulence regulators that could constitute therapeutic targets.

CONCLUSIONS

Our results strongly suggest that the intracellular environment might constitute an important niche of persistence and relapse necessitating adapted antibiotic treatments.

A pursuit of Staphylococcus aureus continues: a role of persister cells

Staphylococcus aureus is a pathogen that causes critical diseases, such as pneumonia, endocarditis, and bacteremia, upon gaining access to the bloodstream of the host. Because host innate immunity alone cannot fight against this rapidly expanding pathogen, the use of antibiotic agents is necessary to clear out S. aureus. However, sub-populations of S. aureus fail to respond to the antibiotics resulting in ineffective clearance of the bacteria. One mechanism by which S. aureus does not respond to the antibiotics is by developing resistance through alterations in its genetic makeup, and genetic studies have revealed a major portion of mechanisms that are responsible for the rise of these antibiotic-resistant strains. Another sub-population that fails to respond to the antibiotics is called persister cells. There is a mounting clinical evidence that these persister cells significantly contribute to the antibiotic failure and persistent infection, but a clear mechanistic picture of the formation of the S. aureus persister cells is unavailable. This review focuses on drawing out a mechanistic map of factors that contribute to the formation of S. aureus persister cells. Understanding the mechanism will provide future direction for the development of novel antibiotic strategies to more efficiently tackle infections caused by S. aureus.

Genotypic and Phenotypic Diversity of Staphylococcus aureus Isolates from Cystic Fibrosis Patient Lung Infections and Their Interactions with Pseudomonas aeruginosa

Staphylococcus aureus has recently overtaken Pseudomonas aeruginosa as the most commonly recognized bacterial pathogen that infects the respiratory tracts of individuals with the genetic disease cystic fibrosis (CF) in the United States. Most studies of S. aureus in CF patient lung infections have focused on a few isolates, often exclusively laboratory-adapted strains, and how they are killed by P. aeruginosa Less is known about the diversity of S. aureus CF patient lung isolates in terms of both their virulence and their interaction with P. aeruginosa To begin to address this gap, we recently sequenced 64 clinical S. aureus isolates and a reference isolate, JE2. Here, we analyzed the antibiotic resistance genotypes, sequence types, clonal complexes, spa types, agr types, and presence/absence of other known virulence factor genes of these isolates. We hypothesized that virulence phenotypes of S. aureus, namely, toxin production and the mucoid phenotype, would be lost in these isolates due to adaptation in the CF patient lung. In contrast to these expectations, we found that most isolates can lyse both rabbit and sheep blood (67.7%) and produce polysaccharide (69.2%), suggesting that these phenotypes were not lost during adaptation to the CF lung. We also identified three distinct phenotypic groups of S. aureus based on their survival in the presence of nonmucoid P. aeruginosa laboratory strain PAO1 and its mucoid derivative. Altogether, our work provides greater insight into the diversity of S. aureus isolates from CF patients, specifically the distribution of important virulence factors and their interaction with P. aeruginosa, all of which have implications in patient health.IMPORTANCEStaphylococcus aureus is now the most frequently detected recognized pathogen in the lungs of individuals who have cystic fibrosis (CF) in the United States, followed closely by Pseudomonas aeruginosa When these pathogens are found to coinfect the CF lung, patients have a significantly worse prognosis. While P. aeruginosa has been rigorously studied in the context of bacterial pathogenesis in CF, less is known about S. aureus Here, we present an in-depth study of 64 S. aureus clinical isolates from CF patients, for which we investigated genetic diversity utilizing whole-genome sequencing, virulence phenotypes, and interactions with P. aeruginosa We found that S. aureus isolated from CF lungs are phylogenetically diverse; most retain known virulence factors and vary in their interactions with P. aeruginosa (i.e., they range from being highly sensitive to P. aeruginosa to completely tolerant to it). Deepening our understanding of how S. aureus responds to its environment and other microbes in the CF lung will enable future development of effective treatments and preventative measures against these formidable infections.

Genotypic and Phenotypic Diversity of Staphylococcus aureus Isolates from Cystic Fibrosis Patient Lung Infections and Their Interactions with Pseudomonas aeruginosa

Staphylococcus aureus has recently overtaken Pseudomonas aeruginosa as the most commonly recognized bacterial pathogen that infects the respiratory tracts of individuals with the genetic disease cystic fibrosis (CF) in the United States. Most studies of S. aureus in CF patient lung infections have focused on a few isolates, often exclusively laboratory-adapted strains, and how they are killed by P. aeruginosa Less is known about the diversity of S. aureus CF patient lung isolates in terms of both their virulence and their interaction with P. aeruginosa To begin to address this gap, we recently sequenced 64 clinical S. aureus isolates and a reference isolate, JE2. Here, we analyzed the antibiotic resistance genotypes, sequence types, clonal complexes, spa types, agr types, and presence/absence of other known virulence factor genes of these isolates. We hypothesized that virulence phenotypes of S. aureus, namely, toxin production and the mucoid phenotype, would be lost in these isolates due to adaptation in the CF patient lung. In contrast to these expectations, we found that most isolates can lyse both rabbit and sheep blood (67.7%) and produce polysaccharide (69.2%), suggesting that these phenotypes were not lost during adaptation to the CF lung. We also identified three distinct phenotypic groups of S. aureus based on their survival in the presence of nonmucoid P. aeruginosa laboratory strain PAO1 and its mucoid derivative. Altogether, our work provides greater insight into the diversity of S. aureus isolates from CF patients, specifically the distribution of important virulence factors and their interaction with P. aeruginosa, all of which have implications in patient health.IMPORTANCEStaphylococcus aureus is now the most frequently detected recognized pathogen in the lungs of individuals who have cystic fibrosis (CF) in the United States, followed closely by Pseudomonas aeruginosa When these pathogens are found to coinfect the CF lung, patients have a significantly worse prognosis. While P. aeruginosa has been rigorously studied in the context of bacterial pathogenesis in CF, less is known about S. aureus Here, we present an in-depth study of 64 S. aureus clinical isolates from CF patients, for which we investigated genetic diversity utilizing whole-genome sequencing, virulence phenotypes, and interactions with P. aeruginosa We found that S. aureus isolated from CF lungs are phylogenetically diverse; most retain known virulence factors and vary in their interactions with P. aeruginosa (i.e., they range from being highly sensitive to P. aeruginosa to completely tolerant to it). Deepening our understanding of how S. aureus responds to its environment and other microbes in the CF lung will enable future development of effective treatments and preventative measures against these formidable infections.

The Virulence Potential of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Cultured from the Airways of Cystic Fibrosis Patients

Staphylococcus aureus is one of the most common pathogens that infects the airways of patients with cystic fibrosis (CF) and contributes to respiratory failure. Recently, livestock-associated methicillin-resistant S. aureus (LA-MRSA), usually cultured in farm animals, were detected in CF airways. Although some of these strains are able to establish severe infections in humans, there is limited knowledge about the role of LA-MRSA virulence in CF lung disease. To address this issue, we analyzed LA-MRSA, hospital-associated (HA-) MRSA and methicillin-susceptible S.aureus (MSSA) clinical isolates recovered early in the course of airway infection and several years after persistence in this hostile environment from pulmonary specimens of nine CF patients regarding important virulence traits such as their hemolytic activity, biofilm formation, invasion in airway epithelial cells, cytotoxicity, and antibiotic susceptibility. We detected that CF LA-MRSA isolates were resistant to tetracycline, more hemolytic and cytotoxic than HA-MRSA, and more invasive than MSSA. Despite the residence in the animal host, LA-MRSA still represent a serious threat to humans, as such clones possess a virulence potential similar or even higher than that of HA-MRSA. Furthermore, we confirmed that S. aureus individually adapts to the airways of CF patients, which eventually impedes the success of antistaphylococcal therapy of airway infections in CF.

Staphylococcus aureus Pathogenicity in Cystic Fibrosis Patients-Results from an Observational Prospective Multicenter Study Concerning Virulence Genes, Phylogeny, and Gene Plasticity

Staphylococcus aureus and cystic fibrosis (CF) are closely interlinked. To date, however, the impact of S. aureus culture in CF airways on lung function and disease progression has only been elucidated to a limited degree. This analysis aims to identify bacterial factors associated to clinical deterioration. Data were collected during an observational prospective multi-center study following 195 patients from 17 centers. The average follow-up time was 80 weeks. S. aureus isolates (n = 3180) were scanned for the presence of 25 virulence genes and agr-types using single and multiplex PCR. The presence of specific virulence genes was not associated to clinical deterioration. For the agr-types 1 and 4, however, a link to the subjects’ clinical status became evident. Furthermore, a significant longitudinal decrease in the virulence gene quantity was observed. Analyses of the plasticity of the virulence genes revealed significantly increased plasticity rates in the presence of environmental stress. The results suggest that the phylogenetic background defines S. aureus pathogenicity rather than specific virulence genes. The longitudinal loss of virulence genes most likely reflects the adaptation process directed towards a persistent and colonizing rather than infecting lifestyle.

Antibiotic Treatment and Age Are Associated With Staphylococcus aureus Carriage Profiles During Persistence in the Airways of Cystic Fibrosis Patients

Background

Staphylococcus aureus is one of the most isolated pathogens from the airways of cystic fibrosis (CF) patients. There is a lack of information about the clonal nature of S. aureus cultured from CF patients and their impact on disease. We hypothesized that patients would differ in their clinical status depending on S. aureus clonal carriage profiles during persistence.

Methods

During a 21-months prospective observational multicenter study (Junge et al., 2016), 3893 S. aureus isolates (nose, oropharynx, and sputa) were cultured from 183 CF patients (16 German centers, 1 Austrian center) and subjected to spa-sequence typing to assess clonality. Data were associated to lung function, age, gender, and antibiotic treatment by multivariate regression analysis.

Results

Two hundred and sixty-five different spa-types were determined with eight prevalent spa-types (isolated from more than 10 patients): t084, t091, t008, t015, t002 t012, t364, and t056. We observed different carriage profiles of spa-types during the study period: patients being positive with a prevalent spa-type, only one, a dominant or related spa-type/s. Patients with more antibiotic cycles were more likely to be positive for only one spa-type (p = 0.005), while older patients were more likely to have related (p = 0.006), or dominant spa-types (p = 0.026). Two percent of isolates were identified as methicillin-resistant S. aureus (MRSA) and evidence of transmission of clones within centers was low.

Conclusion

There was a significant association of antibiotic therapy and age on S. aureus carriage profiles in CF patients indicating that antibiotic therapy prevents acquisition of new clones, while during aging of patients with persisting S. aureus, dominant clones were selected and mutations in the spa-repeat region accumulated.

High Nuclease Activity of Long Persisting Staphylococcus aureus Isolates Within the Airways of Cystic Fibrosis Patients Protects Against NET-Mediated Killing

Staphylococcus aureus is one of the first and most prevalent pathogens cultured from the airways of cystic fibrosis (CF) patients, which can persist there for extended periods. Airway infections in CF patients are characterized by a strong inflammatory response of highly recruited neutrophils. One killing mechanism of neutrophils is the formation of neutrophil extracellular traps (NETs), which capture and eradicate bacteria by extracellular fibers of neutrophil chromatin decorated with antimicrobial granule proteins. S. aureus secretes nuclease, which can degrade NETs. We hypothesized, that S. aureus adapts to the airways of CF patients during persistent infection by escaping from NET-mediated killing via an increase of nuclease activity. Sputum samples of CF patients with chronic S. aureus infection were visualized by confocal microscopy after immuno-fluorescence staining for NET-specific markers, S. aureus bacteria and overall DNA structures. Nuclease activity was analyzed in sequential isogenic long persisting S. aureus isolates, as confirmed by whole genome sequencing, from an individual CF patient using a FRET-based nuclease activity assay. Additionally, some of these isolates were selected and analyzed by qRT-PCR to determine the expression of nuc1 and regulators of interest. NET-killing assays were performed with clinical S. aureus isolates to evaluate killing and bacterial survival depending on nuclease activity. To confirm the role of nuclease during NET-mediated killing, a clinical isolate with low nuclease activity was transformed with a nuclease expression vector (pCM28nuc). Furthermore, two sputa from an individual CF patient were subjected to RNA-sequence analysis to evaluate the activity of nuclease in vivo. In sputa, S. aureus was associated to extracellular DNA structures. Nuclease activity in clinical S. aureus isolates increased in a time-and phenotype-dependent manner. In the clinical isolates, the expression of nuc1 was inversely correlated to the activity of agr and was independent of saeS. NET-mediated killing was significantly higher in S. aureus isolates with low compared to isolates with high nuclease activity. Importantly, transformation of the clinical isolate with low nuclease activity with pCM28nuc conferred protection against NET-mediated killing confirming the beneficial role of nuclease for protection against NETs. Also, nuclease expression in in vivo sputa was high, which underlines the important role of nuclease within the highly inflamed CF airways. In conclusion, our data show that S. aureus adapts to the neutrophil-rich environment of CF airways with increasing nuclease expression most likely to avoid NET-killing during long-term persistence.

The prevalence of Staphylococcus aureus with mucoid phenotype in the airways of patients with cystic fibrosis-A prospective study

BACKGROUND

Staphylococcus aureus is one of the most frequently isolated pathogens in the respiratory tract of CF patients. Recently, we characterized peculiar mucoid S. aureus isolates, which are excessive biofilm formers and which carried a 5bp-deletion within the intergenic region of the ica operon. In this prospective study, we determined the prevalence of mucoid S. aureus-isolates in the airways of CF-patients during a 3-months period.

METHODS

We analyzed specimens (sputa, throat swabs) from 81 CF patients who attended two CF centers in Münster, Germany. Ten S. aureus isolates were randomly picked from every S. aureus-positive airway specimen and evaluated for mucoidy using Congo Red agar and phenotypic tests. Mucoid isolates were characterized by spa sequence typing, biofilm production and sequencing of the intergenic region of the ica operon to screen for the 5bp-deletion.

RESULTS

In 7 of 81 examined patients (8.6%), we detected mucoid S. aureus phenotypes (37 out of 1050 isolates; 3.5%). Twenty-five mucoid isolates carried the 5bp-deletion. Mucoid isolates produced excessive biofilm and were significantly more resistant to certain antibiotics.

CONCLUSIONS

In our prospective study, mucoid S. aureus was present in 8.6% of S. aureus-positive CF-patients. In 6 of 7 patients, mucoid isolates carried the 5bp-deletion, indicating that also other so far not identified mechanisms cause excessive biofilm formation. Further studies are necessary to ascertain the clinical impact of mucoid S. aureus phenotypes on the severity of the CF disease.

Staphylococcus aureus in the airways of cystic fibrosis patients - A retrospective long-term study

BACKGROUND

Cystic fibrosis (CF) is an autosomal recessive disease associated with chronic airway infections by Staphylococcus aureus as one of the earliest and most prevalent pathogens. We conducted a retrospective study to determine the S. aureus infection status of CF patients treated since 1994 at two certified CF-centres in Münster, Germany, to get insights into the dynamics of S. aureus airway infection and the clinical impact on lung function on a long-term perspective.

MATERIALS AND METHODS

We used data from our microbiological database collected between 1994 and 2016 for patients treated at two centres in Münster, Germany, respectively, to determine the infection status for S. aureus. Furthermore, the resistance to selected antibiotics was determined for all patients' isolates and for 15 patients on a longitudinal basis. In addition, the prevalence of adaptive phenotypes such as small colony variants (SCVs) and mucoid S. aureus was assessed.

RESULTS

For this study, 2867 patient years with respiratory specimens (mean of 9.3 years for every patient, range 1-22 years) were evaluated for 283 CF patients (median age of 7 years at the beginning of the observation period, range 0-57 years, 51% male). 18% of patients were rarely infected by S. aureus (≤24% of observation years), 20% of patients intermittently (25-49%) and 61% persistently (≥50% of observation period). Susceptibility testing for 12969 S. aureus isolates resulted in resistance to methicillin in 9%, trimethoprim/sulfamethoxazole in 10%, levofloxacin in 14%, gentamicin in 20%, erythromycin and/or clindamycin in 30% and penicillin in 80% of all isolates. S. aureus isolates of 15 patients revealed dynamics of resistance with increase, decrease and loss of resistant isolates to the analysed antibiotics during the study period. SCVs were isolated at least once from 42% (n = 118) of patients and mucoid isolates from 2% (n = 7) of patients. In the last study year, 89 patients were infected by S. aureus only, 44 patients by S. aureus and Pseudomonas aeruginosa and 18 by P. aeruginosa only. Patients infected by S. aureus only were younger and had better lung function compared to the other two groups.

CONCLUSIONS

We determined a high percentage of patients with persistent S. aureus infection. During persistence, mostly fluctuation of resistance against various antibiotics was observed in the isolates indicating acquisition and loss of resistance genes by S. aureus. The prevalence of adaptive phenotypes during long-term persistence was high for SCVs (42% of patients), but low for mucoid isolates (2% of patients), which might be underestimated for mucoid phenotypes due to the retrospective study design and the difficulty to detect mucoid isolates in primary cultures. While patients with S. aureus only had better lung function and were younger, no difference was found between the group of P. aeruginosa and S. aureus co-infection and P. aeruginosa only with previous S. aureus infection.

A Novel Repressor of the ica Locus Discovered in Clinically Isolated Super-Biofilm-Elaborating Staphylococcus aureus

Staphylococcus aureus TF2758 is a clinical isolate from an atheroma and a super-biofilm-elaborating/polysaccharide intercellular adhesin (PIA)/poly-N-acetylglucosamine (PNAG)-overproducing strain (L. Shrestha et al., Microbiol Immunol 60:148–159, 2016, https://doi.org/10.1111/1348-0421.12359). A microarray analysis and DNA genome sequencing were performed to identify the mechanism underlying biofilm overproduction by TF2758. We found high transcriptional expression levels of a 7-gene cluster (satf2580 to satf2586) and the ica operon in TF2758. Within the 7-gene cluster, a putative transcriptional regulator gene designated rob had a nonsense mutation that caused the truncation of the protein. The complementation of TF2758 with rob from FK300, an rsbU-repaired derivative of S. aureus strain NCTC8325-4, significantly decreased biofilm elaboration, suggesting a role for rob in this process. The deletion of rob in non-biofilm-producing FK300 significantly increased biofilm elaboration and PIA/PNAG production. In the search for a gene(s) in the 7-gene cluster for biofilm elaboration controlled by rob, we identified open reading frame (ORF) SAOUHSC_2898 (satf2584). Our results suggest that ORF SAOUHSC_2898 (satf2584) and icaADBC are required for enhanced biofilm elaboration and PIA/PNAG production in the rob deletion mutant. Rob bound to a palindromic sequence within its own promoter region. Furthermore, Rob recognized the TATTT motif within the icaR-icaA intergenic region and bound to a 25-bp DNA stretch containing this motif, which is a critically important short sequence regulating biofilm elaboration in S. aureus. Our results strongly suggest that Rob is a long-sought repressor that recognizes and binds to the TATTT motif and is an important regulator of biofilm elaboration through its control of SAOUHSC_2898 (SATF2584) and Ica protein expression in S. aureus.

During the search for molecular mechanisms underlying biofilm overproduction of Staphylococcus aureus TF2758, we found a putative transcriptional regulator gene designated rob within a 7-gene cluster showing a high transcriptional expression level by microarray analysis. The deletion of rob in non-biofilm-producing FK300, an rsbU-repaired derivative of NCTC8325-4, significantly increased biofilm elaboration and PIA/PNAG production. The search for a gene(s) in the 7-gene cluster for biofilm elaboration controlled by rob identified ORF SAOUHSC_2898. Besides binding to its own promoter region to control ORF SAOUHSC_2898 expression, Rob recognized the TATTT motif within the icaR-icaA intergenic region and bound to a 25-bp DNA stretch containing this motif, which is a critically important short sequence regulating biofilm elaboration in S. aureus. Our results strongly suggest that Rob is a long-sought repressor that recognizes and binds to the TATTT motif and is a new important regulator of biofilm elaboration through its control of SAOUHSC_2898 and Ica protein expression in S. aureus.