What Do We Know So Far About Ventricular Arrhythmias and Sudden Cardiac Death Prediction in the Mitral Valve Prolapse Population? Could Biomarkers Help Us Predict Their Occurrence?

PURPOSE OF THE REVIEW

To summarize currently available data on the topic of mitral valve prolapse (MVP) and its correlation to the occurrence of atrial and ventricular arrhythmias. To assess the prognostic value of several diagnostic methods such as transthoracic echocardiography, transesophageal echocardiography, cardiac magnetic resonance, cardiac computed tomography, electrocardiography, and electrophysiology concerning arrhythmic episodes. To explore intra and extracellular biochemistry of the cardiovascular system and its biomarkers as diagnostic tools to predict rhythm disturbances in the MVP population.

RECENT FINDINGS

MVP is a common and mainly benign valvular disorder. It affects 2-3% of the general population. MVP is a heterogeneous and highly variable phenomenon with three structural phenotypes: myxomatous degeneration, fibroelastic deficiency, and forme fruste. Exercise intolerance, supraventricular tachycardia, and chest discomfort are the symptoms that are often paired with psychosomatic components. Though MVP is thought to be benign, the association between isolated MVP without mitral regurgitation (MR) or left ventricle dysfunction, with ventricular arrhythmia (VA) and sudden cardiac death (SCD) has been observed. The incidence of SCD in the MVP population is around 0.6% per year, which is 6 times higher than the occurrence of SCD in the general population. Often asymptomatic MVP population poses a challenge to screen for VA and prevent SCD. Therefore, it is crucial to carefully assess the risk of VA and SCD in patients with MVP with the use of various tools such as diagnostic imaging and biochemical and genetic screening.

Systematic whole-genome sequencing reveals an unexpected diversity among actinomycetoma pathogens and provides insights into their antibacterial susceptibilities

Mycetoma is a neglected tropical chronic granulomatous inflammatory disease of the skin and subcutaneous tissues. More than 70 species with a broad taxonomic diversity have been implicated as agents of mycetoma. Understanding the full range of causative organisms and their antibiotic sensitivity profiles are essential for the appropriate treatment of infections. The present study focuses on the analysis of full genome sequences and antibiotic inhibitory concentration profiles of actinomycetoma strains from patients seen at the Mycetoma Research Centre in Sudan with a view to developing rapid diagnostic tests. Seventeen pathogenic isolates obtained by surgical biopsies were sequenced using MinION and Illumina methods, and their antibiotic inhibitory concentration profiles determined. The results highlight an unexpected diversity of actinomycetoma causing pathogens, including three Streptomyces isolates assigned to species not previously associated with human actinomycetoma and one new Streptomyces species. Thus, current approaches for clinical and histopathological classification of mycetoma may need to be updated. The standard treatment for actinomycetoma is a combination of sulfamethoxazole/trimethoprim and amoxicillin/clavulanic acid. Most tested isolates had a high IC (inhibitory concentration) to sulfamethoxazole/trimethoprim or to amoxicillin alone. However, the addition of the β-lactamase inhibitor clavulanic acid to amoxicillin increased susceptibility, particularly for Streptomyces somaliensis and Streptomyces sudanensis. Actinomadura madurae isolates appear to have a particularly high IC under laboratory conditions, suggesting that alternative agents, such as amikacin, could be considered for more effective treatment. The results obtained will inform future diagnostic methods for the identification of actinomycetoma and treatment.

Isolation of L-form Bacteria from Urine using Filtration Method

Transition of bacteria to the L-form state is thought to play a possible role in immune evasion and bacterial persistence during treatment with cell wall-targeting antibiotics. However, isolation and handling of L-form bacteria is challenging, mainly due to their high sensitivity to changes in osmolarity. Here, we describe detailed protocols for the preparation of L-form medium, isolation of L-forms from urine using a filtration method, detection of L-forms in urine samples by phase contrast microscopy and induction of L-forms in vitro. The exact requirements for survival and growth of L-forms may vary from strain to strain. Therefore, the methods presented here are intended to act as basic guidelines for establishing L-form protocols within individual laboratories, rather than as precise instructions. The filtration method can lead to a reduction in the number of L-forms in a sample and should not be used for quantification. However, it is the only method used so far for effective separation of cell wall-deficient variants from their walled counterparts and for identification of bacterial strains, which are capable of L-form switching in patients with urinary tract infections. The filtration method has the potential to be adapted for the isolation of L-forms from patients with other categories of bacterial infections and from environmental samples.

P1789 Stress echocardiography in patients with pulmonary arterial hypertension - a pilot study

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare, progressive disease with poor prognosis. Stress echocardiography (SE) gives an important data on hemodynamic response to exercise. In patients with PAH SE may be useful for the diagnosis and risk assessment but data are lacking.

AIM OF STUDY

The aim of the study was to analyze exercise-induced response of right heart function and pulmonary artery pressure in patients with PAH.

MATERIALS AND METHODS

Study group consisted of 15 hemodynamically stable patients, 9 women, aged 22-73 (median- 50), diagnosed with PAH treated at Cardiology Department. The patients were subjected to stress echocardiography on supine cycloergometer and underwent assessment before and at peak-exercise. Moreover the standard parameters of clinical assessment: NT-proBNP, WHO functional class, and 6-minute walk test were analyzed.

RESULTS

Nine patients were in WHO class III, 4 of them- WHO class II and 2- WHO class I. The median NT-proBNP concentration was 169.3 (IQR 151.2-989.5) pg/ml. 6-Minute Walk Test distance was 455 (428-489) meters. The median workload was 75 (IQR 50-100) Watts and it was the median 54% (IQR 37-62%) of predicted.

The echocardiographic parameters assessed in SE at rest and shortly after peak-exercise revealed that RV systolic volume did not significantly differ: 70 (49.8-112.3) vs 71.5 (36.6-110) ml, p = 0.3. Right atrial area decreased from median 21.9 (17.4-27.3) to 19.8 (16.4-22.1) cm2, p = 0.05, whereas right atrial volume did not significantly changed - 80 (47.5-99.5) vs 68 (47.3-78.8) ml, p = 0.13. Further, shortly after exercise tricuspid regurgitation peak gradient (TRPG) significantly increased - 43 (25-76.5) vs 71 (50.5-102) mmHg, p = 0.002.

CONCLUSIONS

In stable PAH patients supine SE is feasible. Even in advanced WHO functional classes patients were able to exercise. Among echocardiographic parameters TRPG reflecting systolic pulmonary artery pressure showed the biggest difference between baseline and peak-exercise values. SE and seems to be a valuable tool in PAH patients’ assessment.

Crucial role for central carbon metabolism in the bacterial L-form switch and killing by β-lactam antibiotics

The peptidoglycan (PG) cell wall is an essential structure for the growth of most bacteria. However, many are capable of switching into a wall-deficient L-form state, which is resistant to antibiotics that target cell wall synthesis, under osmoprotective conditions, including host environments. L-form cells might have an important role in chronic or recurrent infections. Crucially, the cellular pathways involved in switching to and from the L-form state are still poorly understood. This work shows that the lack of cell wall or blocking its synthesis by β-lactam antibiotics, results in an increased flux through glycolysis. This leads to the production of reactive oxygen species (ROS) from the respiratory chain (RC), which prevents L-form growth. Compensation for the metabolic imbalance by slowing down glycolysis, activating gluconeogenesis, or depleting oxygen, enables L-form growth in Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus. These effects do not occur in Enterococcus faecium, which lacks the RC pathway. Our results collectively show that when cell wall synthesis is blocked under aerobic and glycolytic conditions the perturbation of cellular metabolism causes cell death. We provide a mechanistic framework for many anecdotal descriptions of the optimal conditions for L-form growth and non-lytic killing by β-lactam antibiotics.

Lysozyme Counteracts β-Lactam Antibiotics by Promoting the Emergence of L-Form Bacteria

β-lactam antibiotics inhibit bacterial cell wall assembly and, under classical microbiological culture conditions that are generally hypotonic, induce explosive cell death. Here, we show that under more physiological, osmoprotective conditions, for various Gram-positive bacteria, lysis is delayed or abolished, apparently because inhibition of class A penicillin-binding protein leads to a block in autolytic activity. Although these cells still then die by other mechanisms, exogenous lytic enzymes, such as lysozyme, can rescue viability by enabling the escape of cell wall-deficient "L-form" bacteria. This protective L-form conversion was also observed in macrophages and in an animal model, presumably due to the production of host lytic activities, including lysozyme. Our results demonstrate the potential for L-form switching in the host environment and highlight the unexpected effects of innate immune effectors, such as lysozyme, on antibiotic activity. Unlike previously described dormant persisters, L-forms can continue to proliferate in the presence of antibiotic.

L-form bacteria, chronic diseases and the origins of life

The peptidoglycan cell wall is widely conserved across the bacterial domain, suggesting that it appeared early in the evolution of bacteria. It is normally essential but under certain conditions wall-deficient or ‘L-form’ bacteria can be isolated. In Bacillus subtilis this normally requires two genetic changes. The first, exemplified by mutations shutting down wall precursor synthesis, works by increasing membrane synthesis. This promotes the unusual form of proliferation used by L-forms, involving a range of relatively disorganized membrane blebbing or vesiculation events. The secondary class of mutations probably work by relieving oxidative stress that L-forms may incur due to their unbalanced metabolism. Repression or inhibition of cell wall precursor synthesis can stimulate the L-form transition in a wide range of bacteria, of both Gram-positive and -negative lineages. L-forms are completely resistant to most antibiotics working specifically on cell wall synthesis, such as penicillins and cephalosporins, consistent with the many reports of their involvement in various chronic diseases. They are potentially important in biotechnology, because lack of a wall can be advantageous in a range of production or strain improvement applications. Finally, L-forms provide an interesting model system for studying early steps in the evolution of cellular life.

This article is part of the themed issue ‘The new bacteriology’.