Successful eradication of newly acquired MRSA in six of seven patients with cystic fibrosis applying a short-term local and systemic antibiotic scheme

Host-derived protease promotes aggregation of Staphylococcus aureus by cleaving the surface protein SasG

Staphylococcus aureus is one of the leading causes of hospital-acquired infections, many of which begin following attachment and accumulation on indwelling medical devices or diseased tissue. These infections are often linked to the establishment of biofilms, but another often overlooked key characteristic allowing S. aureus to establish persistent infection is the formation of planktonic aggregates. Such aggregates are physiologically similar to biofilms and protect pathogens from innate immune clearance and increase antibiotic tolerance. The cell-wall-associated protein SasG has been implicated in biofilm formation via mechanisms of intercellular aggregation but the mechanism in the context of disease is largely unknown. We have previously shown that the expression of cell-wall-anchored proteins involved in biofilm formation is controlled by the ArlRS-MgrA regulatory cascade. In this work, we demonstrate that the ArlRS two-component system controls aggregation, by repressing the expression of sasG by activation of the global regulator MgrA. We also demonstrate that SasG must be proteolytically processed by a non-staphylococcal protease to induce aggregation and that strains expressing functional full-length sasG aggregate significantly upon proteolysis by a mucosal-derived host protease found in human saliva. We used fractionation and N-terminal sequencing to demonstrate that human trypsin within saliva cleaves within the A domain of SasG to expose the B domain and induce aggregation. Finally, we demonstrated that SasG is involved in virulence during mouse lung infection. Together, our data point to SasG, its processing by host proteases, and SasG-driven aggregation as important elements of S. aureus adaptation to the host environment.IMPORTANCEHere, we demonstrate that the Staphylococcus aureus surface protein SasG is important for cell-cell aggregation in the presence of host proteases. We show that the ArlRS two-component regulatory system controls SasG levels through the cytoplasmic regulator MgrA. We identified human trypsin as the dominant protease triggering SasG-dependent aggregation and demonstrated that SasG is important for S. aureus lung infection. The discovery that host proteases can induce S. aureus aggregation contributes to our understanding of how this pathogen establishes persistent infections. The observations in this study demonstrate the need to strengthen our knowledge of S. aureus surface adhesin function and processing, regulation of adhesin expression, and the mechanisms that promote biofilm formation to develop strategies for preventing chronic infections.

Current and Emerging Inhaled Antibiotics for Chronic Pulmonary Pseudomonas aeruginosa and Staphylococcus aureus Infections in Cystic Fibrosis

Characterized by impaired mucus transport and subsequent enhanced colonization of bacteria, pulmonary infection causes major morbidity and mortality in patients with cystic fibrosis (CF). Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) are the two most common types of bacteria detected in CF lungs, which undergo multiple adaptational mechanisms such as biofilm formation resulting in chronic pulmonary infections. With the advantages of greater airway concentration and minimized systemic toxicity, inhaled antibiotics are introduced to treat chronic pulmonary infection in CF. Inhaled tobramycin, aztreonam, levofloxacin, and colistin are the four most common discussed inhaled antibiotics targeting P. aeruginosa. Additionally, inhaled liposomal amikacin and murepavadin are also in development. This review will discuss the virulence factors and adaptational mechanisms of P. aeruginosa and S. aureus in CF. The mechanism of action, efficacy and safety, current status, and indications of corresponding inhaled antibiotics will be summarized. Combination therapy and the strategies to select an optimal inhaled antibiotic protocol will also be discussed.

High prevalence of heterogeneous mupirocin-resistant Staphylococcus aureus and its molecular characterization

BACKGROUND

Mupirocin resistance of methicillin-resistant Staphylococcus aureus (MRSA) was frequently reported, but heterogeneous mupirocin resistance in Staphylococcus aureus (S. aureus) was rarely recognized. This study aims to investigate the prevalence of mupirocin heteroresistance among clinical S. aureus isolates and its possible molecular mechanism.

METHODS

Disk diffusion and agar dilution were used to detect the resistance features of mupirocin resistant S. aureus isolates collected form a tertiary teaching hospital in China. Population analysis profiling was used to identify the mupirocin heteroresistant isolates. Multi locus sequence typing and Staphylococcus protein A gene molecular typing were used to discriminate the genetic features of the heteroresistant isolates. Mutations in the isoleucyl tRNA synthetase (ileS) gene of S. aureus isolates were detected by gene sequencing technique.

RESULTS

Mupirocin heteroresistant isolates were identified in 27.67% (83/300) strains. The dominant clones with mupirocin heteroresistance were ST239-t030 MRSAs (25.30%, 21/83). Mutations of G1762T and A637G in ileS gene could be detected in the mupirocin resistant and heteroresistant isolates. The resistance of resistant subpopulations with mutation of G1762T in ileS gene could stabilize for at least 25 passages.

CONCLUSIONS

This study first revealed a higher prevalence of mupirocin heteroresistance in S. aureus. The mutation of G1762T in ileS gene is closely correlated with both mupirocin resistant and heteroresistant S. aureus isolates, supportingo ileS as a potential marker for fast identification of mupirocin resistant S. aureus.

Methicillin-Resistant Staphylococcus aureus Hospital-Acquired Pneumonia/Ventilator-Associated Pneumonia

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP). MRSA pneumonia is associated with significant morbidity and mortality. Several virulence factors allow S. aureus to become an effective pathogen. The polysaccharide intracellular adhesin allows for the production of biofilms, some strains can produce capsular polysaccharides that protect against phagocytosis, microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) allow for colonization of epithelial surfaces, and S. aureus secretes several exotoxins that aid in tissue destruction. The α-hemolysin exotoxin secreted by S. aureus is one of the most important virulence factors for the bacteria. The diagnosis of MRSA pneumonia can be challenging; the infection may present as a mild respiratory infection or severe respiratory failure and septic shock. Many individuals are colonized with MRSA and thus a positive nasopharyngeal swab does not confirm infection in the lower respiratory tract. The management of MRSA pneumonia has evolved. Historically, vancomycin has been the primary antibiotic used to treat MRSA pneumonia. Over the past decade, prospective studies have shown that linezolid leads to higher rates of clinical cure. Monoclonal antibodies are being studied as potential therapeutic options. MRSA is an important cause of HAP/VAP; novel diagnostics may facilitate rapid diagnosis of this infection and the available literature should be used to make informed decisions on management.

Not a wild goose chase: long-lasting MRSA negative status following eradication therapy for chronic MRSA infection in patients with cystic fibrosis

OBJECTIVES

Prevalence of MRSA in patients with CF has risen over the past decades, and chronic infection with MRSA is associated with worse outcome in this patient group.

METHODS

This retrospective observational study investigated long-term eradication rate in pediatric and adult CF patients with chronic MRSA infection, using a 6-month eradication regimen containing 2 oral antibiotics, combined with topical decolonisation measures. Respiratory tract cultures were performed at least every three months, from the first MRSA-positive culture onwards.

RESULTS

A total of 24 patients with chronic MRSA infection were identified from our CF patient registry, of which 13 patients underwent an eradication attempt. The regimen consisted of 2 oral antibiotics: a combination of rifampicin, fusidic acid, clindamycin and co-trimoxazol, based on the sensitivity pattern of the MRSA strain. At the end of the study period (median 8.2 years), 12 out of 13 patients (92%) were MRSA negative. None of the patients interrupted treatment due to side-effects.

CONCLUSIONS

Eradication of chronic MRSA infection is feasible, well-tolerated and highly successful, and can offer a long-lasting MRSA-negative status, obviating the need for patient segregation.

Cystic Fibrosis: Recent Insights into Inhaled Antibiotic Treatment and Future Perspectives

Although new inhaled antibiotics have profoundly improved respiratory diseases in cystic fibrosis (CF) patients, lung infections are still the leading cause of death. Inhaled antibiotics, i.e., colistin, tobramycin, aztreonam lysine and levofloxacin, are used as maintenance treatment for CF patients after the development of chronic Pseudomonas aeruginosa (P. aeruginosa) infection. Their use offers advantages over systemic therapy since a relatively high concentration of the drug is delivered directly to the lung, thus, enhancing the pharmacokinetic/pharmacodynamic parameters and decreasing toxicity. Notably, alternating treatment with inhaled antibiotics represents an important strategy for improving patient outcomes. The prevalence of CF patients receiving continuous inhaled antibiotic regimens with different combinations of the anti-P. aeruginosa antibiotic class has been increasing over time. Moreover, these antimicrobial agents are also used for preventing acute pulmonary exacerbations in CF. In this review, the efficacy and safety of the currently available inhaled antibiotics for lung infection treatment in CF patients are discussed, with a particular focus on strategies for eradicating P. aeruginosa and other pathogens. Moreover, the effects of long-term inhaled antibiotic therapy for chronic P. aeruginosa infection and for the prevention of pulmonary exacerbations is reviewed. Finally, how the mucus environment and microbial community richness can influence the efficacy of aerosolized antimicrobial agents is discussed.

The first report of Methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF) patients in Saudi Arabia

Introduction

Methicillin-resistant Staphylococcus aureus infections have been increasingly reported in patients with cystic fibrosis (CF) who have progressive deterioration in their pulmonary function.

Objectives

To determine the prevalence of MRSA infections in CF in a tertiary care center in Saudi Arabia.

Methodology

This is a retrospective chart review conducted as part of the CF registry data from 1 January 2002 to 1 June 2016. All patients with confirmed CF of all age groups who had a respiratory culture positive for MRSA were included in the study.

Results

Among 385 patients with CF who had respiratory samples, 43 (11%) were positive for MRSA at a mean age of 10.4 ± 7.2 years. Twenty-two patients out of the 43 (51%) were treated with different regimens: nasal Bactroban in 13/22 (59%); a combination of nasal Bactroban, oral vancomycin, and rifampicin for 2 weeks in 5 patients (23%); Bactroban and linezolid in one patient (5%); and oral vancomycin and rifampicin in 3 patients (14%). Eight out of the 22 treated patients (36%) achieved MRSA eradication. Six out of the 22 treated (27%) had experienced MRSA recurrence within 3–6 months, and another 5/22 (23%) continued to have MRSA colonization up to 2–4 years of follow-up despite using a proper eradication protocol. Twelve out of the 43 (28%) patients with MRSA infection died.

Conclusion

MRSA infection in our population with CF is common. Therefore, an eradication protocol should be instituted at an early stage to prevent chronic colonization. Children with persistent MRSA colonization have high morbidity and mortality rate.

Methicillin-Resistant Staphylococcus aureus Infection and Treatment Options

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of infection worldwide, including a wide array of both hospital- and community-acquired infections-most commonly bacteremia, upper and lower respiratory tract infection, skin and soft-tissue infection, osteomyelitis, and septic arthritis. This chapter describes the epidemiology of MRSA infection, its ability to confer antibiotic resistance and produce a wide array of virulence factors, and its pivotal role in human infection, especially cystic fibrosis. It also provides an introduction to the strategies for treatment of both chronic and acute MRSA infections.

Antimicrobial resistance in cystic fibrosis: A Delphi approach to defining best practices

BACKGROUND

Antimicrobial susceptibility testing (AST) is a cornerstone of infection management in cystic fibrosis. However, there is little evidence that AST predicts the clinical outcome of CF antimicrobial treatment. It has been suggested there is a need for careful consideration of current AST use by the CF community.

METHODS

We engaged a group of experts consisting of pulmonary (adult and pediatric) and infectious disease clinicians, microbiologists, and pharmacists representing a broad international experience. We conducted an iterative systematic survey (Delphi) to determine and quantify consensus regarding key questions facing CF clinicians in the use of respiratory culture results including what tests to order, when to obtain them, and how to act upon the results of the testing.

RESULTS

Consensus was reached for many questions but there was not universal agreement to the questions that were addressed. There were some differences with respect to cultures obtained for surveillance compared to when there is clinical worsening. Areas of general consensus include when and how respiratory cultures should be performed, what information should be reported, and when AST should be performed. A key finding is that clinical response to treatment is used to guide treatment decisions rather than AST results.

CONCLUSIONS

Recommendations are presented regarding questions related to microbiology testing for patients with CF. We have also offered recommendations for priority research questions.

Intermittent colonisation with Methicillin-Resistant Staphylococcal aureus can be eradicated from the Airways of Adults with Cystic Fibrosis

The airways of people with cystic fibrosis (CF) are chronically colonised with different pathogens. With recent interest in methicillin-resistant Staphylococcusaureus (MRSA), we have recently examined the rates of MRSA colonisation in different groups within our CF Service. This paper now examines the effectiveness of eradication strategies to clear the MRSA colonisation.