Methicillin-resistant Staphylococcus aureus in cystic fibrosis: how should it be managed?

Antibiotics and outcomes of CF pulmonary exacerbations in children infected with MRSA and Pseudomonas aeruginosa

BACKGROUND

Limited data exist to inform antibiotic selection among people with cystic fibrosis (CF) with airway infection by multiple CF-related microorganisms. This study aimed to determine among children with CF co-infected with methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (Pa) if the addition of anti-MRSA antibiotics to antipseudomonal antibiotic treatment for pulmonary exacerbations (PEx) would be associated with improved clinical outcomes compared with antipseudomonal antibiotics alone.

METHODS

Retrospective cohort study using data from the CF Foundation Patient Registry-Pediatric Health Information System linked dataset. The odds of returning to baseline lung function and having a subsequent PEx requiring intravenous antibiotics were compared between PEx treated with anti-MRSA and antipseudomonal antibiotics and those treated with antipseudomonal antibiotics alone, adjusting for confounding by indication using inverse probability of treatment weighting.

RESULTS

943 children with CF co-infected with MRSA and Pa contributed 2,989 PEx for analysis. Of these, 2,331 (78%) PEx were treated with both anti-MRSA and antipseudomonal antibiotics and 658 (22%) PEx were treated with antipseudomonal antibiotics alone. Compared with PEx treated with antipseudomonal antibiotics alone, the addition of anti-MRSA antibiotics to antipseudomonal antibiotic therapy was not associated with a higher odds of returning to ≥90% or ≥100% of baseline lung function or a lower odds of future PEx requiring intravenous antibiotics.

CONCLUSIONS

Children with CF co-infected with MRSA and Pa may not benefit from the addition of anti-MRSA antibiotics for PEx treatment. Prospective studies evaluating optimal antibiotic selection strategies for PEx treatment are needed to optimize clinical outcomes following PEx treatment.

Antimicrobial susceptibility and genotyping of microorganisms isolated from sputum culture of children with cystic fibrosis in an Iranian referral children's hospital

BACKGROUND

Chronic bacterial infections of the airways are present in most patients with cystic fibrosis (CF). Although most pathogens are acquired from the environment, there is great evidence of patient-to-patient transmission. Therefore, evaluating the genetic variation of strains isolated from CF patients is recommended for the purpose of examining hospital infection.

AIM

The aim of this study was to determine the antibiotic susceptibility pattern and genotyping of Staphylococcus aureus and Pseudomonas aeruginosa strains isolated from sputum samples of children with CF referred to a single pediatric CF center in Tehran, Iran.

METHODS

In this cross-sectional study, the antimicrobial susceptibility profiles of strains isolated from patients with CF during 1 year were determined. Pseudomonas aeruginosa and S. aureus isolates were genotyped using the random amplified polymorphic DNA polymerase chain reaction method and were analyzed using GelCompar II software.

RESULTS

Of 534 patients with CF, 384 had negative sputum cultures (72%), and 94 strains of P. aeruginosa (18%) and 53 strains of S. aureus (10%) were isolated. The mean age of the patients was 8.22 ± 5.7 years (range, 2 months to 18 years). The P. aeruginosa strains showed high sensitivity to ceftazidime (96%), piperacillin/tazobactam (96%), and imipenem (94%). All strains of S. aureus were susceptible to vancomycin, and 13% of the strains were methicillin-resistant S. aureus. High resistance to penicillin (92%) and erythromycin (88.5%) were reported. The results of P. aeruginosa genotyping revealed that there were six major clusters in this hospital. Also, based on the analysis of genotyping results, S. aureus strains were obtained from five clusters, most of which were located in cluster B1 (34 isolates, 64%).

CONCLUSION

The results of this study show the possibility of strains being transferred from one part of the hospital to another (especially from the respiratory ward to other areas). Hence, high attention should be paid to the basic methods of preventing infection.

Tedizolid is a promising antimicrobial option for the treatment of Staphylococcus aureus infections in cystic fibrosis patients

BACKGROUND

Tedizolid is a protein synthesis inhibitor in clinical use for the treatment of Gram-positive infections. Pulmonary MRSA infections are a growing problem in patients with cystic fibrosis (CF) and the efficacy of tedizolid-based therapy in CF pulmonary infections is unknown.

OBJECTIVES

To evaluate the in vitro and in vivo activity of tedizolid and predict the likelihood of tedizolid resistance selection in CF-background Staphylococcus aureus strains.

METHODS

A collection of 330 S. aureus strains (from adult and paediatric patients), either of normal or small colony variant (SCV) phenotypes, gathered at three CF centres in the USA was used. Tedizolid activity was assessed by broth microdilution, Etest and time-kill analysis. In vivo tedizolid efficacy was tested in a murine pneumonia model. Tedizolid in vitro mutants were obtained by 40 days of exposure and progressive passages. Whole genome sequencing of clinical S. aureus strains with reduced susceptibility to tedizolid was performed.

RESULTS

MRSA strain MIC90s were tedizolid 0.12-0.25 mg/L and linezolid 1-2 mg/L; for MSSA strains, MIC90s were tedizolid 0.12 mg/L and linezolid 1-2 mg/L. Two strains, WIS 441 and Seattle 106, with tedizolid MICs of 2 mg/L and 1 mg/L, respectively, had MICs above the FDA tedizolid breakpoint (0.5 mg/L). Tedizolid at free serum concentrations exhibited a bacteriostatic effect. Mean bacterial burdens in lungs (log10 cfu/g) for WIS 423-infected mice were: control, 11.2±0.5; tedizolid-treated (10 mg/kg), 3.40±1.87; linezolid-treated (40 mg/kg), 4.51±2.1; and vancomycin-treated (30 mg/kg), 5.21±1.93. For WIS 441-infected mice the (log10 cfu/g) values were: control, 9.66±0.8; tedizolid-treated, 3.18±1.35; linezolid-treated 5.94±2.19; and vancomycin-treated, 4.35±1.7.

CONCLUSIONS

These results suggest that tedizolid represents a promising therapeutic option for the treatment of CF-associated MRSA/MSSA infections, having potent in vivo activity and low resistance potential.

Isolation and first draft genome sequence of a linezolid-dependent Staphylococcus aureus clinical strain

Background: Antibiotic-dependent pathogenic bacteria are sporadically isolated from patients that received prolonged antibiotic treatments. Evolution of antibiotics dependence and its clinical implications are scarcely studied. Materials & methods: A linezolid-dependent Staphylococcus aureus strain was isolated from a cystic fibrosis patient. A draft genome sequence was obtained and searched for known antibiotics resistance determinants and virulence factors. Results: The genome was assembled into 79 contigs for a total of 2.83 Mbp. This strain is a sequence type 5 methicillin-resistant Staphylococcus aureus with a type I SCCmec cassette also conserving the Panton-Valentine leukocidin. The G2576T substitution, conferring linezolid resistance, was harbored by all five copies of the 23S rRNA. Conclusion: The linezolid-dependent strain is related to a strain circulating in Latin America that acquired a mutation conferring linezolid resistance.

Comparative Effectiveness of Vancomycin Versus Linezolid for the Treatment of Acute Pulmonary Exacerbations of Cystic Fibrosis

Background: Data are limited regarding the preferred antibiotics for treatment of acute pulmonary exacerbations (APEs) of cystic fibrosis (CF), when methicillin-resistant Staphylococcus aureus (MRSA) is suspected. Objective: To compare the rate of return to baseline lung function among individuals with APEs of CF treated with either vancomycin or linezolid. Methods: This retrospective study included individuals hospitalized for APEs of CF from May 1, 2015, to April 30, 2017 who were infected with MRSA and treated with vancomycin or linezolid. The primary outcome was the return to baseline lung function, as measured by forced expiratory volume in 1 s (FEV1). Descriptive and inferential statistics were used. All tests were 2-tailed with α set at 0.05. Results: A total of 122 encounters were included (vancomycin: n = 66; linezolid: n = 66). No difference existed in return to baseline FEV1 between vancomycin (53 [80.3%]) and linezolid (50 [75.8%]; P = 0.53); nor was there a difference in median percentage change in FEV1 from admission to follow-up between vancomycin (24.7%) and linezolid (20.7%; P = 0.61). Adverse drug events occurred more frequently in patient encounters treated with vancomycin (10 [15.2%]) compared with linezolid (2 [3%]; P = 0.002). Conclusion and Relevance: Our study observed no difference in the effectiveness of vancomycin compared with linezolid in terms of change in lung function for APEs of CF. The rate of adverse drug events was low. In individuals with CF infected with MRSA who are experiencing an APE, either vancomycin or linezolid appear to be viable treatment options.

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.

Antimicrobial Treatment of Staphylococcus aureus in Patients With Cystic Fibrosis

Staphylococcus aureus is a ubiquitous human commensal pathogen. It is commonly isolated in cystic fibrosis (CF) patients and is considered one of the main causes of the recurrent acute pulmonary infections and progressive decline in lung function that characterize this inherited life-threatening multisystem disorder. However, the true role of S. aureus in CF patients is not completely understood. The main aim of this narrative review is to discuss the present knowledge of the role of S. aureus in CF patients. Literature review showed that despite the fact that the availability and use of drugs effective against S. aureus have coincided with a significant improvement in the prognosis of lung disease in CF patients, clearly evidencing the importance of S. aureus therapy, how to use old and new drugs to obtain the maximal effectiveness has not been precisely defined. The most important problem remains that the high frequency with which S. aureus is carried in healthy subjects prevents the differentiation of simple colonization from infection. Moreover, although experts recommend antibiotic administration in CF patients with symptoms and in those with persistent detection of S. aureus, the best antibiotic approach has not been defined. All these problems are complicated by the evidence that the most effective antibiotic against methicillin-resistant S. aureus (MRSA) cannot be used in patients with CF with the same schedules used in patients without CF. Further studies are needed to solve these problems and to assure CF patients the highest level of care.

Staphylococcus aureus in cystic fibrosis: pivotal role or bit part actor?

PURPOSE OF REVIEW

The cystic fibrosis (CF) lung has long been appreciated as a competitive niche for complex interactions between bacterial species. The individual relationships between effects on the host, and thereafter clinical outcomes, has been poorly understood. We aim to describe the role of Staphyloccus aureus, one of the most commonly encountered bacteria cultured from the respiratory tracts of people with CF, and it's complex interplay with other organisms, with particular attention to Pseudomonas aeruginosa.

RECENT FINDINGS

We describe the challenges posed in understanding the role that S. aureus plays in the CF lung, including the difficulties in interpreting culture results depending upon sampling technique, relationships with P. aeruginosa and the rest of the microbiome, as well as discussing the relative merits and potential harms of antibiotic prophylaxis. Finally, we describe the particular challenge of methicillin-resistant S. aureus.

SUMMARY

We describe research underway that will address the long-held contentious issues of antibiotic prophylaxis. We also describe the emerging research interest in determining whether, at differences phases in the evolution of CF airways infection, S. aureus infection can have both harmful and protective effects for the host.

Methicillin-resistant Staphylococcus aureus in solid organ transplantation-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the American Society of Transplantation Infectious Diseases Community of Practice review the epidemiology, diagnosis, prevention, and management of methicillin-resistant Staphylococcus aureus (MRSA) infections in solid organ transplantation. Despite an increasing armamentarium of antimicrobials active against MRSA, improved diagnostic tools, and overall declining rates of infection, MRSA infections remain a substantial cause of morbidity and mortality in solid organ transplant recipients. Pre- and post-transplant MRSA colonization is a significant risk factor for post-transplant MRSA infection. The preferred initial treatment of MRSA bacteremia remains vancomycin. Hand hygiene, chlorhexidine bathing in the ICU, central-line bundles that focus on reducing unnecessary catheter use, disinfection of patient equipment, and the environment along with antimicrobial stewardship are all aspects of an infection prevention approach to prevent MRSA transmission and decrease healthcare-associated infections.

Pharmacokinetic Monitoring of Vancomycin in Cystic Fibrosis: Is It Time to Move Past Trough Concentrations?

BACKGROUND

A correlation between vancomycin (VAN) trough concentrations (VTC) and area under the curve (AUC) to minimum inhibitory concentration (MIC) ratio (AUC/MIC) has not been established in children/adolescents with cystic fibrosis (CF). The primary objective of this study was to determine the correlation between measured VTCs and AUC/MIC using population-based pharmacokinetics.

METHODS

A retrospective cohort study of children/adolescents diagnosed with CF, 6 to <18 years of age, treated with VAN for methicillin-resistant Staphylococcus aureus infection was conducted. The relationship between final VTCs and calculated AUC/MIC was assessed using Pearson and Spearman correlations. All tests were 2-tailed with alpha set at 0.05.

RESULTS

Thirty children/adolescents, 7 to 17 years of age (median age 15 year; interquartile range: 9-17 years), were included. The mean final VAN dose was 58.03 ± 18.58 mg/kg/d, and the median final VTC was 12.6 (11-13.6) mg/L. The mean AUC/MIC was 355.34 ± 138.46 (Le model) versus 426.79 ± 178.92 (Stockmann model; P = 0.089). No correlation existed between VTCs and AUC/MIC using either the model by Le (r = 0.140; P = 0.461) or Stockmann (r = 0.115; P = 0.564). Using the Stockmann model, VAN dose (mg/kg/dose) was found to have a strong positive correlation with AUC (r = 0.8874; P < 0.0001) and AUC/MIC (r = 0.7877; P < 0.0001).

CONCLUSIONS

VTCs did not correlate with AUC or AUC/MIC. Further research is needed to determine which estimate of VAN treatment efficacy is most appropriate for children and adolescents with CF infected with methicillin-resistant Staphylococcus aureus.

Synthesis and antibiotic activity of novel acylated phloroglucinol compounds against methicillin-resistant Staphylococcus aureus

The rise in antibiotic resistance among pathogenic microorganisms has created an imbalance in the drugs available for treatment, in part due to the slow development of new antibiotics. Cystic fibrosis (CF) patients are highly susceptible to antibiotic-resistant pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Phloroglucinols and related polyketide natural products have demonstrated antimicrobial activity against a number of Gram-positive bacteria including S. aureus. In this study, we investigated a series of acylated phloroglucinol derivatives to determine their potential as lead compounds for the design of novel therapeutics. To assess the activity of these compounds, we determined the minimum inhibitory and bactericidal concentration (MIC and MBC, respectively), the minimum biofilm inhibitory and biofilm eradication concentration (MBIC and MBEC, respectively), and evaluated hemolytic activity, as well as their interaction with clinically relevant antibiotics. Of the 12 compounds tested against MRSA and methicillin-susceptible strains, four showed MIC values ranging from 0.125 to 8 µg ml^-1 and all of them were bactericidal. However, none of the compounds were able to eradicate biofilms at the concentrations tested. Three of the four did not display hemolytic activity under the conditions tested. Further studies on the interactions of these compounds with clinically relevant antibiotics showed that phlorodipropanophenone displayed synergistic activity when paired with doxycycline. Our results suggest that these acylated phloroglucinols have potential for being further investigated as antibacterial leads.

Biology and management of methicillin resistant Staphylococcus aureus in cystic fibrosis

Staphylococcus aureus is one of the earliest bacteria isolated from the respiratory tract in people with cystic fibrosis (CF). Its methicillin resistant form, MRSA, has gained attention due to the rapid increase in the last decades and worse outcomes with chronic infection. In the United States, prevalence of MRSA in CF is around 27%, but is much lower (3-18%) in most other countries. Methicillin is typically genetically encoded by the mecA gene, which encodes for an alternative penicillin binding protein (PRBa). This PRBa has low affinity to β-lactams, thereby enabling growth of S. aureus in the presence of penicillinase resistant penicillins and most other β-lactams. Non-mecA positive strains of MRSA, so-called borderline resistant (BORSA) have also been described. In addition to production of toxins, the virulence of S. aureus is conferred by its adaptability allowing persistence in face of antibiotic therapies and host defense. These adaptive growth mechanisms include small colony variants, biofilms, and growth under anaerobic conditions. Several reports have described successful eradication of MRSA, yet only two randomized trials of eradication during early infection have been conducted. A list of MRSA specific antibiotics with dosing relevant to CF patients is presented here. Many of these require special dosing in people with CF. Novel antibiotics are in trials for skin and soft tissue infections and it is unclear if and when those might be available for lung infections. Thus the best strategies for MRSA would be primary prevention.

Activity of Telavancin against Staphylococcus aureus Isolates, Including Those with Decreased Susceptibility to Ceftaroline, from Cystic Fibrosis Patients

Methicillin-resistant Staphylococcus aureus (MRSA) acquisition in cystic fibrosis (CF) patients confers a clinical outcome worse than that in non-CF patients with an increased rate of declined lung function. Telavancin, an approved lipoglycopeptide used to treat infections due to S. aureus, has a dual mode of action causing inhibition of peptidoglycan synthesis and membrane depolarization. MRSA infections in CF patients remain an important problem with no foreseeable decline in prevalence rates. Although telavancin is currently in clinical use for the treatment of complicated skin infections and hospital-acquired pneumonia, the activity against S. aureus infections in CF patients has not been investigated. In this work, we studied the activity of telavancin against CF patient-derived S. aureus strains collected from geographically diverse CF centers in the United States. We found that the telavancin MIC90 was 0.06 μg/ml, 8-fold lower than the ceftaroline or daptomycin MIC90 and 25-fold lower than the linezolid and vancomycin MIC90 We demonstrate that telavancin at serum free concentrations has rapid bactericidal activity, with a decrease of more than 3 log10 CFU/ml being achieved during the first 4 to 6 h of treatment, performing better in this assay than vancomycin and ceftaroline, including against S. aureus strains resistant to ceftaroline. Telavancin resistance was infrequent (0.3%), although we found that it can occur in vitro in both CF- and non-CF patient-derived S. aureus strains by progressive passages with subinhibitory concentrations. Genetic analysis of telavancin-resistant in vitro mutants showed gene polymorphisms in cell wall and virulence genes and increased survival in a Galleria mellonella infection model. Thus, we conclude that telavancin represents a promising therapeutic option for infections in CF patients with potent in vitro activity and a low resistance development potential.

Detection of Bacteriophage Particles Containing Antibiotic Resistance Genes in the Sputum of Cystic Fibrosis Patients

Cystic fibrosis (CF) is a chronic disease in which the bacterial colonization of the lung is linked to an excessive inflammatory response that leads to respiratory failure. The microbiology of CF is complex. Staphylococcus aureus is the first bacterium to colonize the lungs in 30% of pediatric CF patients, and 80% of adult patients develop a chronic Pseudomonas aeruginosa infection, but other microorganisms can also be found. The use of antibiotics is essential to treat the disease, but antibiotic performance is compromised by resistance mechanisms. Among various mechanisms of transfer of antibiotic resistance genes (ARGs), the recently been reported bacteriophages are the least explored in clinical settings. To determine the role of phages in CF as mobile genetic elements (MGEs) carrying ARGs, we evaluated their presence in 71 CF patients. 71 sputum samples taken from these patients were screened for eight ARGs (bla_TEM, bla_CTX-M-1-group, bla_CTX-M-9-group, bla_OXA-48, bla_VIM, mecA, qnrA, and qnrS) in the bacteriophage DNA fraction. The phages found were also purified and observed by electron microscopy. 32.4% of CF patients harbored ARGs in phage DNA. β-lactamase genes, particularly bla_VIM and bla_TEM, were the most prevalent and abundant, whereas mecA, qnrA, and qnrS were very rare. Siphoviridae phage particles capable of infecting P. aeruginosa and Klebsiella pneumoniae were detected in CF sputum. Phage particles harboring ARGs were found to be abundant in the lungs of both CF patients and healthy individuals and could contribute to the colonization of multiresistant strains.