The Effects of Antibiotic Combination Treatments on Pseudomonas aeruginosa Tolerance Evolution and Coexistence with Stenotrophomonas maltophilia

The Pseudomonas aeruginosa bacterium is a common pathogen of cystic fibrosis (CF) patients due to its ability to evolve resistance to antibiotics during treatments. While P. aeruginosa resistance evolution is well-characterized in monocultures, it is less well-understood in polymicrobial CF infections. Here, we investigated how exposure to ciprofloxacin, colistin, or tobramycin antibiotics, administered at sub-minimum inhibitory concentration (MIC) doses, both alone and in combination, shaped the tolerance evolution of P. aeruginosa (PAO1 lab and clinical CF LESB58 strains) in the absence and presence of a commonly co-occurring species, Stenotrophomonas maltophilia. The increases in antibiotic tolerances were primarily driven by the presence of that antibiotic in the treatment. We observed a reciprocal cross-tolerance between ciprofloxacin and tobramycin, and, when combined, the selected antibiotics increased the MICs for all of the antibiotics. Though the presence of S. maltophilia did not affect the tolerance or the MIC evolution, it drove P. aeruginosa into extinction more frequently in the presence of tobramycin due to its relatively greater innate tobramycin tolerance. In contrast, P. aeruginosa dominated and drove S. maltophilia extinct in most other treatments. Together, our findings suggest that besides driving high-level antibiotic tolerance evolution, sub-MIC antibiotic exposure can alter competitive bacterial interactions, leading to target pathogen extinctions in multispecies communities. IMPORTANCE Cystic fibrosis (CF) is a genetic condition that results in thick mucus secretions in the lungs that are susceptible to chronic bacterial infections. The bacterial pathogen Pseudomonas aeruginosa is often associated with morbidity in CF and is difficult to treat due to its high resistance to antibiotics. The resistance evolution of Pseudomonas aeruginosa is poorly understood in polymicrobial infections that are typical of CF. To study this, we exposed P. aeruginosa to sublethal concentrations of ciprofloxacin, colistin, or tobramycin antibiotics in the absence and presence of a commonly co-occurring CF species, Stenotrophomonas maltophilia. We found that low-level antibiotic concentrations selected for high-level antibiotic resistance. While P. aeruginosa dominated in most antibiotic treatments, S. maltophilia drove it into extinction in the presence of tobramycin due to an innately higher tobramycin resistance. Our findings suggest that, besides driving high-level antibiotic tolerance evolution, sublethal antibiotic exposure can magnify competition in bacterial communities, which can lead to target pathogen extinctions in multispecies communities.

Investigating the potential for reversal of myofibroblast activation in human cardiac fibroblasts in 2D culture

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): BHF MRC

Introduction

Cardiac fibroblasts (cFbs) are responsible for deposition of extracellular matrix in the heart, providing support to the contracting myocardium and contributing to a myriad of physiological signalling processes. Prolonged and excessive activation of cFbs, via stimulation by transforming growth factor β (TGF-β), causes conversion of cFbs into myofibroblasts. Myofibroblasts are believed to cause pathological cardiac remodelling and to contribute to heart failure and arrhythmias. Reversion of myofibroblasts into cFbs has been demonstrated in rodent cells; it has yet to be explored in human cells.

Purpose

To characterise the effects of long-term 2D standard culture on the activation status of human cFbs. To identify the potential for human myofibroblasts to dedifferentiate back to cFbs.

Methods

Primary human cFbs were cultured in Corning Costar flasks (Young’s modulus E = ∼3GPa) for up to 10 passages. Cells were subsequently plated onto dishes with a Young’s modulus of ∼3GPa, 25kPa and 2kPa in the presence or absence of TGF-β (10ng/ml) and/or TGF-β receptor I inhibitor SD208 (10nM) for up to 4 days. The proliferative capacity of the cells was assessed using the CyQUANT NF® assay. Cells were assessed for mRNA and protein expression of myofibroblast activation markers α-smooth muscle actin (α-SMA) and collagen-1 by qPCR and western blotting. The localised distribution of α-SMA was assessed by confocal microscopy.

Results

Human cardiac fibroblasts robustly expressed α-SMA. Proliferation was significantly decreased at 2kPa compared to higher Young’s moduli (mean percentage change over 2 days: 2kPa = 115.1, 25kPa = 191.4, 3GPa = 205.9, p < 0.0001). qPCR analysis revealed no significant changes in expression of myofibroblast gene markers α-SMA and collagen 1 at either ∼3GPa, 25kPa or 2kPa Young’s Moduli in the presence or absence of TGF-β treatment (median fold change (interquartile range [IQR]) versus control: TGF-β(α-SMA, 3GPa) = 1.226 (0.820); TGF-β(Collagen 1, 3GPa) = 1.636 (1.403); TGF-β(α-SMA, 25kPa) = 1.069 (7.030); TGF-β(Collagen 1, 25kPa) = 1.103 (0.411); TGF-β(α-SMA, 2kPa) = 0.800 (5.021); TGF-β(Collagen 1, 2kPa) = 1.629 (7.092); n = 2-3). These data was confirmed by western blotting (median relative protein expression (IQR) versus control: TGF-β(α-SMA, 3GPa) = 1.012 (0.500); TGF-β(Collagen 1, 3GPa) = 1.008 (1.466); TGF-β(α-SMA, 25kPa) = 1.321 (2.282); TGF-β(Collagen 1, 25kPa) = 0.944 (1.125); TGF-β(α-SMA, 2kPa) = 1.142 (0.705); TGF-β(Collagen 1, 2kPa) = 0.283 (1.127), p > 0.05; n = 2-3). TGF-β or SD208 treatment did not affect α-SMA expression when assessed by confocal microscopy.

Conclusions

Long-term culture of human cFbs in 2D format leads to a robust and persistent activation of myofibroblasts that is unresponsive to TGF-ß activation or inhibition. Ongoing work is focussed on investigating whether human myofibroblast de-differentiation is possible.

Anaemia and coronary microvascular dysfunction in end-stage renal disease

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): (1) University Hospitals Birmingham Charity (2) Metchley Park Medical Society

Introduction

 

Coronary microvascular dysfunction (CMD) is common among patients with end-stage renal disease (ESRD) and confers poor prognosis. Coronary flow velocity reserve (CFVR) is a marker of coronary microvascular function and can be reliably measured using Doppler echocardiography. Reduced CFVR in ESRD has been attributed to factors such as hypertension and left ventricular hypertrophy (LVH). Anaemia is prevalent in ESRD but the association between haemoglobin and CFVR in ESRD has not been studied. 

Purpose

 

To assess if CFVR is related to haemoglobin among patients with ESRD. 

Methods

 

22 subjects with ESRD and awaiting kidney transplant (8 pre-dialysis and 14 on peritoneal dialysis) were studied with adenosine myocardial contrast echocardiography, Doppler CFVR assessment and serum multiplex immunoassay analysis. Individuals with diabetes, uncontrolled hypertension or ischaemic heart disease were excluded.

Results 

7/22 (32%) of subjects had CMD (defined as CFVR <2). Age (47 years ± 15 vs 55 ± 10, p = 0.177), estimated glomerular filtration rate [7ml/min/1.73m² (5-11) vs 9 (7-10), p = 0.837], systolic blood pressure (129mmHg ± 25 vs 137 ± 20, p = 0.398) and left ventricular mass index (98g/m² ± 31 vs 98 ± 28, p = 0.936) did not significantly differ between subjects with or without CMD. There were no significant differences in other demographic, haemodynamic, laboratory or echocardiographic variables between the two groups.  A panel of biomarkers of inflammation, myocardial stretch, cardiac fibrosis and LVH studied by multiplex immunoassay also did not show any significant differences between the two groups. No subjects had wall motion abnormalities or perfusion defects on myocardial contrast echocardiography.

CFVR was significantly lower in subjects with CMD (1.6 ± 0.2 vs 3.2 ± 0.9, p < 0.001). Subjects with CMD had significantly lower haemoglobin than subjects without CMD (102g/L ± 12 vs 117g/L ± 11, p = 0.008). There was a moderate positive correlation between haemoglobin and CFVR (r = 0.65, p = 0.001) – figure 1. In a stepwise multiple regression model with CFVR as the dependent variable and age, haemoglobin, systolic blood pressure, left ventricular mass index and estimated glomerular filtration rate as independent variables, only haemoglobin was an independent predictor of CFVR (β=0.051 95%CI 0.023-0.079, p = 0.001). 

Conclusions 

Among our cohort of ESRD patients awaiting kidney transplant, there was a high prevalence of CMD despite well controlled blood pressure and no significant LVH. Subjects with CMD had significantly lower haemoglobin than subjects without CMD. Reduced haemoglobin causes impaired oxygen carrying capacity to the myocardium, which may lead to microvascular ischaemia and adverse microvascular remodelling, causing CMD. Thus, anaemia may be a potentially correctible driver of CMD in ESRD.  This association needs to be confirmed in larger studies.

Abstract Figure 1