Author Interviews, Hospital Acquired, Infections, Nature / 24.02.2016
Marine Microbial Cahuitamycins as Biofilm Inhibitors For Medical Devices
MedicalResearch.com Interview with:
[caption id="attachment_21986" align="alignleft" width="200"]
Dr. Ashootosh Tripathi[/caption]
Ashootosh Tripathi, PhD
Postdoctoral Research Fellow
Life Sciences Institute I Sherman lab
University of Michigan
Ann Arbor, MI, USA
MedicalResearch: What is the background for this study? What are the main findings?
Dr. Tripathi: Acinetobacter baumannii is a nosocomial opportunistic and resistant pathogen that can spread epidemically among patients causing ventilator-associated pneumonia and bacteremia. The mortality rates associated with it can be as high as 60%, representing a paradigm of pathogenesis, transmission and resistance. In addition, numerous reports have shown the startling emergence of multidrug-resistant A. baumannii in hospitals as well as the identification of pan-drug-resistant strains at some locations. Among the various reasons for the antibiotic resistance of this pathogenic microbe, perhaps the most significant is mediated by its tendency to form biofilms (a highly structured extracellular polymeric matrix), which provide the microbe with the alarming ability to colonize medical devices. Interestingly, despite the well-understood role of bacterial biofilm behind aggravating antimicrobial resistance, there are currently no drugs specifically targeting biofilms in clinical trials to date. The study sought to solve this problem through the development of a biofilm inhibitor as a precision medicine, directed towards vulnerable patients, to avoid potential life-threatening infections.
A crystal-violet based high throughput in vitro screen was developed to identify inhibitors of A. baumannii biofilms against our natural products extract (NPE) library. The vast NPE library of ~42,000 extracts has been under constant development in Prof David H. Sherman laboratory at University of Michigan, Ann Arbor, for over the past decade, from a relatively underexplored marine microbiome collected from different part of world viz., Costa Rica, Panama, Papua New Guinea, etc., and is available for any research group with a robust high-throughput screening (HTS) assay (http://www.lsi.umich.edu/centers/center-for-chemical-genomics). The HTS assay that was queried against a library of 9,831 NPEs aimed to identify extracts inhibiting biofilm formation as a primary screening. Further secondary screening and activity threshold optimization revealed the extract from Streptomyces gandocaensis (collected from Costa Rica) to be of particular interest due to its ability to inhibit biofilm formation and had a limited effect on A. baumannii growth. Activity based chromatographic separation and analysis of extracts derived from S. gandocaensis resulted in the discovery of three peptidic metabolites (cahuitamycins A–C), with cahuitamycin C being the most effective biofilm inhibitor (IC50 =14.5 µM) with negligible A. baumannii growth inhibition (an important trait for ideal biofilm inhibitor). Following up on the exciting discovery, we also completely characterized the biosynthetic machinery involved in making the active molecules by S. gandocaensis, using sophisticated bioinformatics and molecular biology techniques. The knock out analysis revealed that the biosynthesis of cahuitamycin C proceeds via a convergent biosynthetic pathway, with one of the steps apparently being catalyzed by an unlinked gene encoding a 6-methylsalicylate synthase. Efforts to assess starter unit diversification through selective mutasynthesis led to production of unnatural analogues cahuitamycins D and E with increased potency (IC50=8.4 and 10.5 µM) against A. baumannii biofilm.
Dr. Ashootosh Tripathi[/caption]
Ashootosh Tripathi, PhD
Postdoctoral Research Fellow
Life Sciences Institute I Sherman lab
University of Michigan
Ann Arbor, MI, USA
MedicalResearch: What is the background for this study? What are the main findings?
Dr. Tripathi: Acinetobacter baumannii is a nosocomial opportunistic and resistant pathogen that can spread epidemically among patients causing ventilator-associated pneumonia and bacteremia. The mortality rates associated with it can be as high as 60%, representing a paradigm of pathogenesis, transmission and resistance. In addition, numerous reports have shown the startling emergence of multidrug-resistant A. baumannii in hospitals as well as the identification of pan-drug-resistant strains at some locations. Among the various reasons for the antibiotic resistance of this pathogenic microbe, perhaps the most significant is mediated by its tendency to form biofilms (a highly structured extracellular polymeric matrix), which provide the microbe with the alarming ability to colonize medical devices. Interestingly, despite the well-understood role of bacterial biofilm behind aggravating antimicrobial resistance, there are currently no drugs specifically targeting biofilms in clinical trials to date. The study sought to solve this problem through the development of a biofilm inhibitor as a precision medicine, directed towards vulnerable patients, to avoid potential life-threatening infections.
A crystal-violet based high throughput in vitro screen was developed to identify inhibitors of A. baumannii biofilms against our natural products extract (NPE) library. The vast NPE library of ~42,000 extracts has been under constant development in Prof David H. Sherman laboratory at University of Michigan, Ann Arbor, for over the past decade, from a relatively underexplored marine microbiome collected from different part of world viz., Costa Rica, Panama, Papua New Guinea, etc., and is available for any research group with a robust high-throughput screening (HTS) assay (http://www.lsi.umich.edu/centers/center-for-chemical-genomics). The HTS assay that was queried against a library of 9,831 NPEs aimed to identify extracts inhibiting biofilm formation as a primary screening. Further secondary screening and activity threshold optimization revealed the extract from Streptomyces gandocaensis (collected from Costa Rica) to be of particular interest due to its ability to inhibit biofilm formation and had a limited effect on A. baumannii growth. Activity based chromatographic separation and analysis of extracts derived from S. gandocaensis resulted in the discovery of three peptidic metabolites (cahuitamycins A–C), with cahuitamycin C being the most effective biofilm inhibitor (IC50 =14.5 µM) with negligible A. baumannii growth inhibition (an important trait for ideal biofilm inhibitor). Following up on the exciting discovery, we also completely characterized the biosynthetic machinery involved in making the active molecules by S. gandocaensis, using sophisticated bioinformatics and molecular biology techniques. The knock out analysis revealed that the biosynthesis of cahuitamycin C proceeds via a convergent biosynthetic pathway, with one of the steps apparently being catalyzed by an unlinked gene encoding a 6-methylsalicylate synthase. Efforts to assess starter unit diversification through selective mutasynthesis led to production of unnatural analogues cahuitamycins D and E with increased potency (IC50=8.4 and 10.5 µM) against A. baumannii biofilm.

Dr. Martin Hoenigl[/caption]
Martin Hoenigl, MD
Postdoctoral Fellow
AntiViral Research Center, Department of Medicine
University of California, San Diego
Medical Research: What is the background for this study?
Response: The detection of acute HIV infection (AHI) is critical to HIV prevention and treatment strategies. Many field-based testing programs rely on point-of-care HIV antibody testing, which will reliably identify persons with established infection, but fail to detect persons with AHI. In many of these programs additional tests for AHI are only performed / recommended in persons presenting with signs and symptoms consistent with an acute retroviral syndrome (ARS). These signs and symptoms are unspecific and include fatigue, headache, pharyngitis, skin rash, GI symptoms, night sweats and others. However, the proportion of persons with 
Dr. Robert Friedland[/caption]
Dr. Robert Friedland MD
Mason C. and Mary D. Rudd Endowed Chair In Neurology
Professor, Dept. of Neurology
University of Louisville Health Care Outpatient Center
Louisville, KY 40292
Medical Research: What is the background for this study? What are the main findings?
Dr. Robert Friedland: Oral infectious diseases are associated with stroke. Previous research by this group has shown that oral bacteria, cnm-positive Streptococcus mutans, was associated with cerebral microbleeds and intracerebral hemorrhage. We developed this study to investigate the roles of this bacteria in patients entering the hospital for all types of stroke. Among the patients who experienced intracerebral hemorrhage (ICH), 26 percent were found to have a specific bacterium in their saliva, cnm-positive S. mutans. Among patients with other types of stroke, only 6 percent tested positive for the bacterium. We also evaluated MRIs of study subjects for the presence of cerebral microbleeds (CMB), small brain hemorrhages which may cause dementia and also often underlie ICH. We found that the number of CMBs was significantly higher in subjects with cnm-positive S. mutans than in those without.

















Dr. Ephraim Tsalik
Dr. Ilir Agalliu[/caption]
