51
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Mehanna MM, Mneimneh AT, Abed El Jalil K. Levofloxacin-loaded naturally occurring monoterpene-based nanoemulgel: a feasible efficient system to circumvent MRSA ocular infections. Drug Dev Ind Pharm 2020; 46:1787-1799. [PMID: 32896171 DOI: 10.1080/03639045.2020.1821048] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Staphylococcus aureus is a leading cause of ocular keratitis worldwide, and the upsurge of Methicillin-resistant Staphylococcus Aureus (MRSA) strains necessitated the development of new antimicrobial agents. D-limonene is the major constituent of oil extracted from citrus peel, which has been utilized for its gastroprotective, antifungal, antitumor, and antibacterial effects. The present study aimed to develop an effective in-situ ocular limonene-based nanoemulgel to enhance the efficacy of fluoroquinolones against MRSA associated ocular biofilm infection. The nanoemulsion composed of limonene, Tween®80, propylene glycol at a ratio of 5:4:1 loaded with levofloxacin. The formulated levofloxacin-loaded limonene-based nanoemulsion physiochemical properties namely; droplet size, polydispersity index, zeta potential, and in-vitro drug release were studied and stability over three months was assessed. Furthermore, in-vitro antimicrobial susceptibility was investigated on biofilm-forming MRSA strain through kinetics of killing and biofilm assay. The in-situ nanoemulgel ocular irritation was studied by HET-CAM test. The results demonstrated that levofloxacin-loaded limonene-based nanoemulsion had a particle size of 119 ± 0.321 nm with improved eradicating efficacy of MRSA biofilm, where the MIC of the loaded nanoemulgel was 3.12 mg/ml significantly less than that of drug alone (6.25 mg/ml). HET-CAM test showed no signs of hemorrhage, coagulation, or lysis for the loaded nanoemulgel same as sodium chloride solution (negative control) where its irritation score was zero compared to 9.87 for the positive irritant group (1%w/v sodium lauryl sulfate). In conclusion, the current investigation provided a strong foundation for further studies of limonene nanoemulgel as a potential complementary therapeutic agent against resistant bacterial strains.
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Affiliation(s)
- Mohammed M Mehanna
- Pharmaceutical Technology Department, Faculty of Pharmacy, Beirut Arab University, Beirut, Lebanon.,Industrial Pharmacy Department, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt
| | - Amina Tarek Mneimneh
- Pharmaceutical Technology Department, Faculty of Pharmacy, Beirut Arab University, Beirut, Lebanon
| | - Khaled Abed El Jalil
- Pharmaceutical Sciences Department, Faculty of Pharmacy, Beirut Arab University, Beirut, Lebanon
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52
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Mao T, Fang F. Biomimetic Functional Surfaces towards Bactericidal Soft Contact Lenses. MICROMACHINES 2020; 11:E835. [PMID: 32878284 PMCID: PMC7569848 DOI: 10.3390/mi11090835] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Revised: 08/24/2020] [Accepted: 08/31/2020] [Indexed: 12/26/2022]
Abstract
The surface with high-aspect-ratio nanostructure is observed to possess the bactericidal properties, where the physical interaction between high-aspect-ratio nanostructure could exert sufficient pressure on the cell membrane eventually lead to cell lysis. Recent studies in the interaction mechanism and reverse engineering have transferred the bactericidal capability to artificial surface, but the biomimetic surfaces mimicking the topographical patterns on natural resources possess different geometrical parameters and surface properties. The review attempts to highlight the recent progress in bactericidal nanostructured surfaces to analyze the prominent influence factors and cell rupture mechanism. A holistic approach was utilized, integrating interaction mechanisms, material characterization, and fabrication techniques to establish inclusive insights into the topographical effect and mechano-bactericidal applications. The experimental work presented in the hydrogel material field provides support for the feasibility of potentially broadening applications in soft contact lenses.
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Affiliation(s)
- Tianyu Mao
- Centre of Micro/Nano Manufacturing Technology (MNMT-Dublin), University College Dublin, D04 V1W8 Dublin, Ireland;
| | - Fengzhou Fang
- Centre of Micro/Nano Manufacturing Technology (MNMT-Dublin), University College Dublin, D04 V1W8 Dublin, Ireland;
- State Key Laboratory of Precision Measuring Technology and Instruments, Centre of Micro/Nano Manufacturing Technology (MNMT), Tianjin University, Tianjin 300072, China
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53
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Dosler S, Hacioglu M, Yilmaz FN, Oyardi O. Biofilm modelling on the contact lenses and comparison of the in vitro activities of multipurpose lens solutions and antibiotics. PeerJ 2020; 8:e9419. [PMID: 32612893 PMCID: PMC7320721 DOI: 10.7717/peerj.9419] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 06/03/2020] [Indexed: 01/31/2023] Open
Abstract
During the contact lens (CL) usage, microbial adhesion and biofilm formation are crucial threats for eye health due to the development of mature biofilms on CL surfaces associated with serious eye infections such as keratitis. For CL related eye infections, multi drug resistant Pseudomonas aeruginosa or Staphylococcus aureus (especially MRSA) and Candida albicans are the most common infectious bacteria and yeast, respectively. In this study, CL biofilm models were created by comparing them to reveal the differences on specific conditions. Then the anti-biofilm activities of some commercially available multipurpose CL solutions (MPSs) and antibiotic eye drops against mature biofilms of S. aureus, P. aeruginosa, and C. albicans standard and clinical strains were determined by the time killing curve (TKC) method at 6, 24 and 48 h. According to the biofilm formation models, the optimal biofilms occurred in a mixture of bovine serum albumin (20% v/v) and lysozyme (2 g/L) diluted in PBS at 37 °C for 24 h, without shaking. When we compared the CL types under the same conditions, the strongest biofilms according to their cell density, were formed on Pure Vision ≥ Softens 38 > Acuve 2 ∼ Softens Toric CLs. When we compared the used CLs with the new ones, a significant increase at the density of biofilms on the used CLs was observed. The most active MPS against P. aeruginosa and S. aureus biofilms at 24 h was Opti-Free followed by Bio-True and Renu according to the TKC analyses. In addition, the most active MPS against C. albicans was Renu followed by Opti-Free and Bio-True at 48 h. None of the MPSs showed 3 Log bactericidal/fungicidal activity, except for Opti-Free against S. aureus and P. aeruginosa biofilms during 6 h contact time. Moreover, all studied antibiotic eye drops were active against S. aureus and P. aeruginosa biofilms on CLs at 6 h and 24 h either directly or as 1/10 concentration, respectively. According to the results of the study, anti-biofilm activities of MPSs have changed depending on the chemical ingredients and contact times of MPSs, the type of infectious agent, and especially the CL type and usage time.
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Affiliation(s)
- Sibel Dosler
- Department of Pharmaceutical Microbiology, Istanbul University, Faculty of Pharmacy, Istanbul, Turkey
| | - Mayram Hacioglu
- Department of Pharmaceutical Microbiology, Istanbul University, Faculty of Pharmacy, Istanbul, Turkey
| | - Fatima Nur Yilmaz
- Department of Pharmaceutical Microbiology, Istanbul University, Faculty of Pharmacy, Istanbul, Turkey
| | - Ozlem Oyardi
- Department of Pharmaceutical Microbiology, Istanbul University, Faculty of Pharmacy, Istanbul, Turkey
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54
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Microscopic characterization of biofilm in mixed keratitis in a novel murine model. Microb Pathog 2020; 140:103953. [DOI: 10.1016/j.micpath.2019.103953] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 12/17/2019] [Accepted: 12/27/2019] [Indexed: 12/17/2022]
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55
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Di Onofrio V, Gesuele R, Maione A, Liguori G, Liguori R, Guida M, Nigro R, Galdiero E. Prevention of Pseudomonas aeruginosa Biofilm Formation on Soft Contact Lenses by Allium sativum Fermented Extract (BGE) and Cannabinol Oil Extract (CBD). Antibiotics (Basel) 2019; 8:antibiotics8040258. [PMID: 31835470 PMCID: PMC6963262 DOI: 10.3390/antibiotics8040258] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/03/2019] [Accepted: 12/09/2019] [Indexed: 01/09/2023] Open
Abstract
Two natural mixtures, Allium sativum fermented extract (BGE) and cannabinol oil extract (CBD), were assessed for their ability to inhibit and remove Pseudomonas aeruginosa biofilms on soft contact lenses in comparison to a multipurpose Soft Contact Lens-care solution present on the Italian market. Pseudomonas aeruginosa (ATCC 9027 strain) and Pseudomonas aeruginosa clinical strains isolated from ocular swabs were tested. Quantification of the biofilm was done using the microtiter plate assay and the fractional inhibitory concentration index was calculated. Both forms of Pseudomonas aeruginosa generated biofilms. BGE at minimal inhibitory concentration (MIC) showed inhibition percentages higher than 55% for both strains, and CBD inhibited biofilm formation by about 70%. The care solution at MIC inhibited biofilm formation by about 50% for both strains tested. The effect of BGE on the eradication of the microbial biofilm on soft contact lenses at MIC was 45% eradication for P. aeruginosa ATCC 9027 and 36% for P. aeruginosa clinical strain. For CBD, we observed 24% biofilm eradication for both strains. For the care solution, the eradication MICs were 43% eradication for P. aeruginosa ATCC 9027 and 41% for P. aeruginosa clinical strain. It was observed that both the test soft contact lenses solution/BGE (fractional inhibitory concentration index: 0.450) and the test soft contact lenses solution/CBD (fractional inhibitory concentration index: 0.153) combinations exhibited synergistic antibiofilm activity against most of the studied bacteria. The study showed that BGE and CBD have good effect on inhibition of biofilm formation and removal of preformed biofilms, which makes them promising agents that could be exploited to develop more effective care solutions.
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Affiliation(s)
- Valeria Di Onofrio
- Department of Sciences and Technologies, University of Naples “Parthenope”, Business District, Block C4, 80143 Naples, Italy;
- Correspondence:
| | - Renato Gesuele
- Department of Biology, University of Naples “Federico II”, Via Cinthia, 80126 Naples, Italy; (R.G.); (A.M.); (M.G.); (E.G.)
| | - Angela Maione
- Department of Biology, University of Naples “Federico II”, Via Cinthia, 80126 Naples, Italy; (R.G.); (A.M.); (M.G.); (E.G.)
| | - Giorgio Liguori
- Department of Movement Sciences and Wellbeing, University of Naples “Parthenope”, Via Medina 40, 80133 Naples, Italy;
| | - Renato Liguori
- Department of Sciences and Technologies, University of Naples “Parthenope”, Business District, Block C4, 80143 Naples, Italy;
| | - Marco Guida
- Department of Biology, University of Naples “Federico II”, Via Cinthia, 80126 Naples, Italy; (R.G.); (A.M.); (M.G.); (E.G.)
| | - Roberto Nigro
- Department of Chemical, Material and Production Engineering, University of Naples “Federico II”, Piazzale V. Tecchio 80, 80125 Naples, Italy;
| | - Emilia Galdiero
- Department of Biology, University of Naples “Federico II”, Via Cinthia, 80126 Naples, Italy; (R.G.); (A.M.); (M.G.); (E.G.)
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56
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Decreased expression of femXAB genes and fnbp mediated biofilm pathways in OS-MRSA clinical isolates. Sci Rep 2019; 9:16028. [PMID: 31690794 PMCID: PMC6831631 DOI: 10.1038/s41598-019-52557-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2018] [Accepted: 10/01/2019] [Indexed: 02/03/2023] Open
Abstract
Methicillin-Resistant Staphylococcus aureus (MRSA) is a significant threat to human health. Additionally, biofilm forming bacteria becomes more tolerant to antibiotics and act as bacterial reservoir leading to chronic infection. In this study, we characterised the antibiotic susceptibility, biofilm production and sequence types (ST) of 74 randomly selected clinical isolates of S. aureus causing ocular infections. Antibiotic susceptibility revealed 74% of the isolates as resistant against one or two antibiotics, followed by 16% multidrug-resistant isolates (MDR), and 10% sensitive. The isolates were characterized as MRSA (n = 15), Methicillin-sensitive S. aureus (MSSA, n = 48) and oxacillin susceptible mecA positive S. aureus (OS-MRSA, n = 11) based on oxacillin susceptibility, mecA gene PCR and PBP2a agglutination test. All OS-MRSA would have been misclassified as MSSA on the basis of susceptibility test. Therefore, both phenotypic and genotypic tests should be included to prevent strain misrepresentation. In addition, in-depth studies for understanding the emerging OS-MRSA phenotype is required. The role of fem XAB gene family has been earlier reported in OS-MRSA phenotype. Sequence analysis of the fem XAB genes revealed mutations in fem × (K3R, H11N, N18H and I51V) and fem B (L410F) genes. The fem XAB genes were also found down-regulated in OS-MRSA isolates in comparison to MRSA. In OS-MRSA isolates, biofilm formation is regulated by fibronectin binding proteins A & B. Molecular typing of the isolates revealed genetic diversity. All the isolates produced biofilm, however, MRSA isolates with strong biofilm phenotype represent a worrisome situation and may even result in treatment failure.
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57
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Sapi E, Kasliwala RS, Ismail H, Torres JP, Oldakowski M, Markland S, Gaur G, Melillo A, Eisendle K, Liegner KB, Libien J, Goldman JE. The Long-Term Persistence of Borrelia burgdorferi Antigens and DNA in the Tissues of a Patient with Lyme Disease. Antibiotics (Basel) 2019; 8:antibiotics8040183. [PMID: 31614557 PMCID: PMC6963883 DOI: 10.3390/antibiotics8040183] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 10/06/2019] [Accepted: 10/09/2019] [Indexed: 01/29/2023] Open
Abstract
Whether Borrelia burgdorferi, the causative agent of Lyme disease, can persist for long periods in the human body has been a controversial question. The objective of this study was to see if we could find B. burgdorferi in a Lyme disease patient after a long clinical course and after long-term antibiotic treatment. Therefore, we investigated the potential presence of B. burgdorferi antigens and DNA in human autopsy tissues from a well-documented serum-, PCR-, and culture-positive Lyme disease patient, a 53-year-old female from northern Westchester County in the lower Hudson Valley Region of New York State, who had received extensive antibiotic treatments during extensive antibiotic treatments over the course of her 16-year-long illness. We also asked what form the organism might take, with special interest in the recently found antibiotic-resistant aggregate form, biofilm. We also examined the host tissues for the presence of inflammatory markers such as CD3+ T lymphocytes. Autopsy tissue sections of the brain, heart, kidney, and liver were analyzed by histological and immunohistochemical methods (IHC), confocal microscopy, fluorescent in situ hybridization (FISH), polymerase chain reaction (PCR), and whole-genome sequencing (WGS)/metagenomics. We found significant pathological changes, including borrelial spirochetal clusters, in all of the organs using IHC combined with confocal microscopy. The aggregates contained a well-established biofilm marker, alginate, on their surfaces, suggesting they are true biofilm. We found B. burgdorferi DNA by FISH, polymerase chain reaction (PCR), and an independent verification by WGS/metagenomics, which resulted in the detection of B. burgdorferi sensu stricto specific DNA sequences. IHC analyses showed significant numbers of infiltrating CD3+ T lymphocytes present next to B. burgdorferi biofilms. In summary, we provide several lines of evidence that suggest that B. burgdorferi can persist in the human body, not only in the spirochetal but also in the antibiotic-resistant biofilm form, even after long-term antibiotic treatment. The presence of infiltrating lymphocytes in the vicinity of B. burgdorferi biofilms suggests that the organism in biofilm form might trigger chronic inflammation.
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Affiliation(s)
- Eva Sapi
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Rumanah S Kasliwala
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Hebo Ismail
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Jason P Torres
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Michael Oldakowski
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Sarah Markland
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Gauri Gaur
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Anthony Melillo
- Department of Biology and Environmental Science, University of New Haven, West Haven, CT 06516, USA.
| | - Klaus Eisendle
- Central Teaching Hospital Bolzano L Böhlerstr, 539100 Bolzano, Italy.
| | - Kenneth B Liegner
- Private practice, 592 Route 22, Suite 1B, Pawling, NY 12564, USA.
- Northwell System, Northern Westchester Hospital, Mount Kisco, NY 10549, USA.
- Health Quest System, Sharon Hospital, Sharon, CT 06069, USA.
| | - Jenny Libien
- Department of Pathology, SUNY Downstate Health Sciences University, Brooklyn, NY 11203, USA.
| | - James E Goldman
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10031, USA.
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58
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Badenoch PR. A turning point for contact lens-associated microbial keratitis? Clin Exp Ophthalmol 2019; 47:701-703. [PMID: 31339224 DOI: 10.1111/ceo.13584] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Paul R Badenoch
- Department of Ophthalmology, Flinders Medical Centre, Adelaide, South Australia, Australia.,College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
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59
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Abstract
Food and beverage industries operate their production units under stringent hygiene standards to verify high-quality products. However, the presence of biofilms can cause hygienic problems in the industries in the case of pathogenic organisms. Microorganisms can form biofilms, which are resistant to cleaning and disinfection. Microorganisms in biofilms are closely packed in a matrix that acts as a barrier to cleaning and disinfection. Biofilms are observed in processing equipment and open surfaces, resulting in food safety problems or weakening of production efficiency. This review provides a recap of the biofouling process, including the production mechanisms and control techniques of microbial adhesion. Microbial adhesion and colonization are the sine qua non of the establishment of bacterial pathogenesis and this report focuses on their prevention.
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60
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Gangrade A, Parchand SM, Chatterjee S, Gangwe A, Agrawal D. Fulminant scleral abscess secondary to infected scleral buckle with Moraxella species. Indian J Ophthalmol 2019; 67:1214-1216. [PMID: 31238471 PMCID: PMC6611322 DOI: 10.4103/ijo.ijo_43_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Abstract
We here report a case of scleral buckle infection with fulminant scleral abscess secondary to Moraxella species. A 54-year-old chronic alcoholic male with a history of retinal detachment repair, with scleral buckle 8 years prior, presented with complaints of severe pain, redness, and swelling in the right eye since 2 weeks. The patient was diagnosed with scleral buckle infection, the buckle was removed, and cultures revealed Moraxella species. The postoperative course included fulminant scleral abscess treated with dual antibiotic therapy that included ceftriaxone and moxifloxacin. All systemic antibiotics were discontinued after 3 weeks, retina remained attached, and no recurrence occurred over a 1-year follow-up. Moraxella, though commonly associated with bacterial keratitis, can also lead to buckle infection, especially in chronic alcoholic and immunocompromised patients. In buckle infection, infected buckle along with sutures should be immediately removed without damaging underlying compromised sclera. Lastly, culture and drug sensitivity play a very important role in buckle infections.
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Affiliation(s)
| | | | - Samrat Chatterjee
- Cornea and Anterior Segment Services, MGM Eye Institute, Raipur, India
| | - Anil Gangwe
- Vitreo Retina Services, MGM Eye Institute, Raipur, India
| | - Deepshika Agrawal
- Cornea and Anterior Segment Services, MGM Eye Institute, Raipur, India
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61
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Córdova-Alcántara IM, Venegas-Cortés DL, Martínez-Rivera MÁ, Pérez NO, Rodriguez-Tovar AV. Biofilm characterization of Fusarium solani keratitis isolate: increased resistance to antifungals and UV light. J Microbiol 2019; 57:485-497. [DOI: 10.1007/s12275-019-8637-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 01/23/2019] [Accepted: 01/28/2019] [Indexed: 12/27/2022]
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62
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Mitra S, Chayani N, Mohapatra D, Barik MR, Sharma S, Basu S. High Prevalence of Biofilm-Forming MRSA in the Conjunctival Flora in Chronic Dacryocystitis. Semin Ophthalmol 2019; 34:74-79. [PMID: 30794029 DOI: 10.1080/08820538.2019.1578382] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
OBJECTIVES To report the microbiological spectrum of conjunctival flora and prevalence of biofilm-forming Methicillin-resistant Staphylococcus aureus (MRSA) in conjunctival flora in chronic dacryocystitis. DESIGN Prospective, case-control study. METHODS We included patients with unilateral chronic dacryocystitis, and their unaffected eyes as control. Microbiological profile and antibiotic susceptibility of the isolates was determined by standard microbiological procedures. S. aureus isolates were further evaluated for Methicillin resistance by Oxacillin resistance screening agar method and mecA polymerase chain reaction (PCR) and for biofilm synthesis by Congo red agar method, Microtitre plate (MTP) assay, and ica A and ica D PCR. RESULTS We found 95 patients with unilateral chronic dacryocystitis. Aerobic Gram-positive isolates (74.2%, n = 72) were more than Gram-negative (25.7%, n = 25) or anaerobic isolates (20.5%, n = 25). S. aureus was most common (46.4%, n = 45), followed by Pseudomonas aeruginosa (10.3%, n = 10). Gram-positive isolates showed highest sensitivity to Linezolid (100%) and higher generation fluoroquinolones. Gram-negative isolates showed good sensitivity (>90%) to all tested antibiotics. S. aureus isolates showed MRSA prevalence as 93.5% and 96.9% by Oxacillin resistance screening agar method and mecA PCR, respectively. Biofilm formation was found in 71.8% MRSA isolates by MTP assay and 58.1% MRSA isolates were resistant to ≥3 classes of antibiotics. CONCLUSIONS Gram-positive organisms, specifically S. aureus, are the major etiological agent in chronic dacryocystitis. There is high prevalence of MRSA in these isolates and concurrent biofilm formation.
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Affiliation(s)
- Sanchita Mitra
- a Ocular Microbiology Service , L V Prasad Eye Institute , Bhubaneswar and Hyderabad , India
| | - Nirupama Chayani
- b Department of Microbiology , SCB Medical College , Cuttack , India
| | | | - Manas Ranjan Barik
- a Ocular Microbiology Service , L V Prasad Eye Institute , Bhubaneswar and Hyderabad , India
| | - Savitri Sharma
- a Ocular Microbiology Service , L V Prasad Eye Institute , Bhubaneswar and Hyderabad , India
| | - Soumyava Basu
- c Retina and Uveitis Services , L V Prasad Eye Institute , Bhubaneswar , India
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63
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Yong YY, Dykes GA, Choo WS. Biofilm formation by staphylococci in health-related environments and recent reports on their control using natural compounds. Crit Rev Microbiol 2019; 45:201-222. [PMID: 30786799 DOI: 10.1080/1040841x.2019.1573802] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Staphylococci are Gram-positive bacteria that are ubiquitous in the environment and able to form biofilms on a range of surfaces. They have been associated with a range of human health issues such as medical device-related infection, localized skin infection, or direct infection caused by toxin production. The extracellular material produced by these bacteria resists antibiotics and host defence mechanism which complicates the treatment process. The commonly reported Staphylococcus species are Staphylococcus aureus and S. epidermidis as they inhabit human bodies. However, the emergence of other staphylococci, such as S. haemolyticus, S. lugdunensis, S. saprophyticus, S. capitis, S. saccharolyticus, S. warneri, S. cohnii, and S. hominis, is also of concern and they have been associated with biofilm formation. This review critically assesses recent cases on the biofilm formation by S. aureus, S. epidermidis, and other staphylococci reported in health-related environments. The control of biofilm formation by staphylococci using natural compounds is specifically discussed as they represent potential anti-biofilm agents which may reduce the burden of antibiotic resistance.
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Affiliation(s)
- Yi Yi Yong
- a School of Science , Monash University Malaysia , Selangor , Malaysia
| | - Gary A Dykes
- b School of Public Health , Curtin University , Bentley , Australia
| | - Wee Sim Choo
- a School of Science , Monash University Malaysia , Selangor , Malaysia
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64
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Hong HJ, Yun JM, Park DJ. Infectious Crystalline Keratopathy Caused by Alternaria. JOURNAL OF THE KOREAN OPHTHALMOLOGICAL SOCIETY 2019. [DOI: 10.3341/jkos.2019.60.11.1112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Hye Jin Hong
- Department of Ophthalmology, Daegu Fatima Hospital, Daegu, Korea
| | - Jong Myoung Yun
- Department of Ophthalmology, Daegu Fatima Hospital, Daegu, Korea
| | - Dae Jin Park
- Department of Ophthalmology, Daegu Fatima Hospital, Daegu, Korea
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65
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Shahrour H, Ferrer-Espada R, Dandache I, Bárcena-Varela S, Sánchez-Gómez S, Chokr A, Martinez-de-Tejada G. AMPs as Anti-biofilm Agents for Human Therapy and Prophylaxis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1117:257-279. [PMID: 30980362 DOI: 10.1007/978-981-13-3588-4_14] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Microbial cells show a strong natural tendency to adhere to surfaces and to colonize them by forming complex communities called biofilms. In this growth mode, biofilm-forming cells encase themselves inside a dense matrix which efficiently protects them against antimicrobial agents and effectors of the immune system. Moreover, at the physiological level, biofilms contain a very heterogeneous cell population including metabolically inactive organisms and persisters, which are highly tolerant to antibiotics. The majority of human infectious diseases are caused by biofilm-forming microorganisms which are responsible for pathologies such as cystic fibrosis, infective endocarditis, pneumonia, wound infections, dental caries, infections of indwelling devices, etc. AMPs are well suited to combat biofilms because of their potent bactericidal activity of broad spectrum (including resting cells and persisters) and their ability to first penetrate and then to disorganize these structures. In addition, AMPs frequently synergize with antimicrobial compounds and were recently reported to repress the molecular pathways leading to biofilm formation. Finally, there is a very active research to develop AMP-containing coatings that can prevent biofilm formation by killing microbial cells on contact or by locally releasing their active principle. In this chapter we will describe these strategies and discuss the perspectives of the use of AMPs as anti-biofilm agents for human therapy and prophylaxis.
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Affiliation(s)
- Hawraa Shahrour
- Department of Microbiology and Parasitology, University of Navarra, Pamplona, Spain.,Laboratory of Microbiology, Department of Life & Earth Sciences, Faculty of Sciences I, Lebanese University, Hadat campus, Beirut, Lebanon.,Platform of Research and Analysis in Environmental Sciences (PRASE), Doctoral School of Sciences and Technologies, Lebanese University, Hadat Campus, Beirut, Lebanon
| | - Raquel Ferrer-Espada
- Department of Microbiology and Parasitology, University of Navarra, Pamplona, Spain.,Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Israa Dandache
- Laboratory of Microbiology, Department of Life & Earth Sciences, Faculty of Sciences I, Lebanese University, Hadat campus, Beirut, Lebanon.,Platform of Research and Analysis in Environmental Sciences (PRASE), Doctoral School of Sciences and Technologies, Lebanese University, Hadat Campus, Beirut, Lebanon
| | | | | | - Ali Chokr
- Laboratory of Microbiology, Department of Life & Earth Sciences, Faculty of Sciences I, Lebanese University, Hadat campus, Beirut, Lebanon.,Platform of Research and Analysis in Environmental Sciences (PRASE), Doctoral School of Sciences and Technologies, Lebanese University, Hadat Campus, Beirut, Lebanon
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66
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Antibacterial layer-by-layer coatings to control drug release from soft contact lenses material. Int J Pharm 2018; 553:186-200. [DOI: 10.1016/j.ijpharm.2018.10.041] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 10/15/2018] [Accepted: 10/16/2018] [Indexed: 11/15/2022]
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Biofilm Formation on Bandage Contact Lenses Worn by Patients with the Boston Type 1 Keratoprosthesis: A Pilot Comparison Study of Prophylactic Topical Vancomycin 15 mg/mL and Linezolid 0.2%. Eye Contact Lens 2018; 44 Suppl 1:S106-S109. [DOI: 10.1097/icl.0000000000000337] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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68
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Doustdar F, Karimi F, Abedinyfar Z, Amoli FA, Goudarzi H. Genetic features of Pseudomonas aeruginosa isolates associated with eye infections referred to Farabi Hospital, Tehran, Iran. Int Ophthalmol 2018; 39:1581-1587. [PMID: 29982958 DOI: 10.1007/s10792-018-0980-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 06/18/2018] [Indexed: 11/30/2022]
Abstract
BACKGROUND Pseudomonas is the most common cause of microbial keratitis especially in people who use contact lens. The virulence of Pseudomonas aeruginosa in different eye infections is associated with different virulence factors . METHODS In this study, 54 P. aeruginosa isolates including 39 isolates from keratitis and 15 isolates from conjunctivitis were evaluated for their ability to form biofilm, production of protease, elastase, alkaline protease and their antibiotic-resistant patterns. The distribution of the exoS and exoU genes in the test strains were determined using PCR assays. RESULTS Most of the eye infections (90.74%) were seen in people who used contact lenses, and in most of patients (72.22%), the infection was presented as keratitis. None of the isolates were resistant to a single antibiotic as tested. Multidrug resistance (MDR) was detected in two isolates (3.5%) which were resistant to more than one category of antibiotics. The exoU+/exoS+ isolates were in majority although in total, compared to exoS, there were more exoU in a greater number of samples. Most of the strains produce elastase but among all of ocular isolates, only 5.8% of the strains showed alkaline protease activity. Most of the ocular isolates were not capable of producing biofilm. CONCLUSIONS In our study, a high prevalence of virulence factors was observed in P. aeruginosa isolates from contact lens wearer with keratitis. As the P. aeruginosa isolates from different infection origins and different geographic region may have different virulence factors, having a better perception of these differences could help to improve development of clinical instructions for the control of keratitis.
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Affiliation(s)
- Farahnoosh Doustdar
- Department of Microbiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
| | - Fatemeh Karimi
- Department of Biology, Faculty of Science, Azarbaijan Shahid Madani University, Tabriz, Iran
| | - Zohreh Abedinyfar
- Department of Microbiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Fahimeh Asadi Amoli
- Department of Pathology, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Hossein Goudarzi
- Department of Microbiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Magana M, Sereti C, Ioannidis A, Mitchell CA, Ball AR, Magiorkinis E, Chatzipanagiotou S, Hamblin MR, Hadjifrangiskou M, Tegos GP. Options and Limitations in Clinical Investigation of Bacterial Biofilms. Clin Microbiol Rev 2018; 31:e00084-16. [PMID: 29618576 PMCID: PMC6056845 DOI: 10.1128/cmr.00084-16] [Citation(s) in RCA: 113] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.
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Affiliation(s)
- Maria Magana
- Department of Clinical Microbiology, Athens Medical School, Aeginition Hospital, Athens, Greece
| | - Christina Sereti
- Department of Clinical Microbiology, Athens Medical School, Aeginition Hospital, Athens, Greece
- Department of Microbiology, Thriassio General Hospital, Attiki, Greece
| | - Anastasios Ioannidis
- Department of Clinical Microbiology, Athens Medical School, Aeginition Hospital, Athens, Greece
- Department of Nursing, Faculty of Human Movement and Quality of Life Sciences, University of Peloponnese, Sparta, Greece
| | - Courtney A Mitchell
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Anthony R Ball
- Gliese 623b, Mendon, Massachusetts, USA
- GAMA Therapeutics LLC, Pepperell, Massachusetts, USA
| | - Emmanouil Magiorkinis
- Department of Hygiene, Epidemiology and Medical Statistics, Medical School, University of Athens, Athens-Goudi, Greece
| | | | - Michael R Hamblin
- Harvard-MIT Division of Health Science and Technology, Cambridge, Massachusetts, USA
- Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA
- Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Maria Hadjifrangiskou
- Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - George P Tegos
- Gliese 623b, Mendon, Massachusetts, USA
- GAMA Therapeutics LLC, Pepperell, Massachusetts, USA
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70
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Species-specific characteristics of the biofilm generated in silicone tube: an in vitro study. BMC Ophthalmol 2018; 18:85. [PMID: 29614999 PMCID: PMC5883301 DOI: 10.1186/s12886-018-0750-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 03/23/2018] [Indexed: 11/23/2022] Open
Abstract
Background To investigate characteristics of biofilm which is usually found in silicone tube for nasolacrimal duct surgery and can be the root of chronic bacterial infections eventually resulted in surgical failure. Methods To form a biofilm, sterile silicone tube was placed in culture media of Staphylococcus aureus, Corynebacterium matruchotii, Pseudomonas aeruginosa, or Streptococcus pneumonia. Biofilms formed on these silicone tubes were fixed with 95% ethanol and stained with 0.1% crystal violet. After staining, the optical densities of biofilms were measured using spectrophotometer on a weekly basis for 12 weeks. Results Staphylococcus aureus group and Pseudomonas aeruginosa group formed significantly more amounts of biofilms compared to the control group. The maximum optical densities of the two groups were found on week 3–4 followed by a tendency of decrease afterwards. However, the amounts of biofilms formed in other groups of silicone tubes were not statistically significant from that of the control group. Conclusions Bacterial species that could form biofilm on silicone tube included Staphylococcus aureus (week 3) and Pseudomonas aeruginosa (Week 4). It is important to first consider that the cause of infection around 1 month after silicone tube intubation can be Staphylococcus aureus and Pseudomonas aeruginosa.
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71
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Sharma U, Vipra A, Channabasappa S. Phage-derived lysins as potential agents for eradicating biofilms and persisters. Drug Discov Today 2018; 23:848-856. [PMID: 29326076 DOI: 10.1016/j.drudis.2018.01.026] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 11/17/2017] [Accepted: 01/04/2018] [Indexed: 01/21/2023]
Abstract
Bacterial biofilms are highly resistant to the action of antibiotics. Presence of persisters, phenotypically resistant populations of bacterial cells, is thought to contribute toward recalcitrance of biofilms. The phage-derived lysins, by virtue of their ability to cleave the peptidoglycan of bacterial cells in an enzymatic manner, have the unique ability to kill dormant cells. Several lysins have shown potent antibiofilm activity in vitro. The fact that lysins have shown better efficacy than conventional drugs in animal models of endocarditis and other infections involving biofilms suggests that the lysins can potentially be developed against difficult-to-treat bacterial infections.
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Affiliation(s)
- Umender Sharma
- GangaGen Biotechnologies Pvt. Ltd., No 12, 5th cross, Raghavendra Layout, Tumkur Road, Yeshwantpur, Bangalore, 560022, India.
| | - Aradhana Vipra
- GangaGen Biotechnologies Pvt. Ltd., No 12, 5th cross, Raghavendra Layout, Tumkur Road, Yeshwantpur, Bangalore, 560022, India
| | - Shankaramurthy Channabasappa
- GangaGen Biotechnologies Pvt. Ltd., No 12, 5th cross, Raghavendra Layout, Tumkur Road, Yeshwantpur, Bangalore, 560022, India
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Clemens LE, Jaynes J, Lim E, Kolar SS, Reins RY, Baidouri H, Hanlon S, McDermott AM, Woodburn KW. Designed Host Defense Peptides for the Treatment of Bacterial Keratitis. Invest Ophthalmol Vis Sci 2017; 58:6273-6281. [PMID: 29242901 PMCID: PMC5730364 DOI: 10.1167/iovs.17-22243] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 11/08/2017] [Indexed: 11/24/2022] Open
Abstract
Purpose To limit corneal damage and potential loss of vision, bacterial keratitis must be treated aggressively. Innovation in antimicrobials is required due to the need for empirical treatment and the rapid emergence of bacterial resistance. Designed host defense peptides (dHDPs) are synthetic analogues of naturally occurring HDPs, which provide defense against invading pathogens. This study investigates the use of novel dHDPs for the treatment of bacterial keratitis. Methods The minimum inhibitory concentrations (MICs) were determined for dHDPs on both Gram-positive and -negative bacteria. The minimum biofilm eradication concentrations (MBEC) and in vitro time-kill assays were determined. The most active dHDP, RP444, was evaluated for propensity to induce drug resistance and therapeutic benefit in a murine Pseudomonas aeruginosa keratitis model. Results Designed HDPs were bactericidal with MICs ranging from 2 to >64 μg/mL and MBEC ranging from 6 to 750 μg/mL. In time-kill assays, dHDPs were able to rapidly reduce bacterial counts upon contact with as little as 2 μg/mL. RP444 did not induce resistance after repeated exposure of P. aeruginosa to subinhibitory concentrations. RP444 demonstrated significant efficacy in a murine model of bacterial keratitis as evidenced by a significant dose-dependent decrease in ocular clinical scores, a significantly reduced bacterial load, and substantially decreased inflammatory cell infiltrates. Conclusions Innovative dHDPs demonstrated potent antimicrobial activity, possess a limited potential for development of resistance, and reduced the severity of murine P. aeruginosa keratitis. These studies demonstrate that a novel dHDP may have potential to treat patients with sight-threatening bacterial keratitis.
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Affiliation(s)
| | - Jesse Jaynes
- Integrative Biosciences, Tuskegee University, Tuskegee, Alabama, United States
| | - Edward Lim
- Lumigenics LLC, Richmond, California, United States
| | - Satya S. Kolar
- The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States
| | - Rose Y. Reins
- The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States
| | - Hasna Baidouri
- The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States
| | - Samuel Hanlon
- The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States
| | - Alison M. McDermott
- The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States
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Kim DJ, Park JH, Kim M, Park CY. The Antibiofilm efficacy of nitric oxide on soft contact lenses. BMC Ophthalmol 2017; 17:206. [PMID: 29162075 PMCID: PMC5696802 DOI: 10.1186/s12886-017-0604-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Accepted: 11/15/2017] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND To investigate the antibiofilm efficacy of nitric oxide (NO) on soft contact lenses. METHODS Nitrite (NO precursor) release from various concentrations (0-1000 μM) of sodium nitrite (NaNO2, NO donor) was measured by Griess Assay. Cell viability assay was performed using human corneal epithelial cell under various concentration (0-1000 μM) of NaNO2. Biofilm formation on soft contact lenses was achieved by adding Staphylococcus aureus or Pseudomonas aeruginosa to the culture media. Various concentrations of NaNO2 (0-1000 μM) were added to the culture media, each containing soft contact lens. After incubation in NaNO2 containing culture media for 1, 3, or 7 days, each contact lens was transferred to a fresh, bacteria-free media without NaNO2. The bacteria in the biofilm were dispersed in the culture media for planktonic growth. After reculturing the lenses in the fresh media for 24 h, optical density (OD) of media was measured at 600 nm and colony forming unit (CFU) was counted by spreading media on tryptic soy agar plate for additional 18 h. RESULTS Nitrite release from NaNO2 showed dose-dependent suppressive effect on biofilm formation. Most nitrite release from NaNO2 tended to occur within 30 min. The viability of human corneal epithelial cells was well maintained at tested NaNO2 concentrations. The bacterial CFU and OD showed dose-dependent decrease in the NaNO2 treated samples on days 1, 3 and 7 for both Staphylococcus aureus and Pseudomonas aeruginosa. CONCLUSIONS NO successfully inhibited the biofilm formation by Staphylococcus aureus or Pseudomonas aeruginosa on soft contact lenses in dose-dependent manner.
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Affiliation(s)
- Dong Ju Kim
- Department of Ophthalmology, Dongguk University, Ilsan Hospital, 814, Siksadong, Ilsan-dong-gu, Goyang, Gyunggido, 410-773, South Korea
| | - Joo-Hee Park
- Department of Ophthalmology, Dongguk University, Ilsan Hospital, 814, Siksadong, Ilsan-dong-gu, Goyang, Gyunggido, 410-773, South Korea
| | - Marth Kim
- Department of Ophthalmology, Dongguk University, Ilsan Hospital, 814, Siksadong, Ilsan-dong-gu, Goyang, Gyunggido, 410-773, South Korea
| | - Choul Yong Park
- Department of Ophthalmology, Dongguk University, Ilsan Hospital, 814, Siksadong, Ilsan-dong-gu, Goyang, Gyunggido, 410-773, South Korea.
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74
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Infectious crystalline keratopathy. Surv Ophthalmol 2017; 63:480-499. [PMID: 29097211 DOI: 10.1016/j.survophthal.2017.10.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Revised: 10/15/2017] [Accepted: 10/19/2017] [Indexed: 01/07/2023]
Abstract
Infectious crystalline keratopathy was first reported by Gorovoy and colleagues in 1983 when they identified bacteria colonizing a cornea after a penetrating keratoplasty. Subsequent cases have elaborated on the organisms responsible and the management outcomes. Patients present with a white or gray branching opacity originating from an epithelial defect, commonly after a penetrating keratoplasty. Local immunosuppression contributes to the quiescent nature and the limited inflammatory response associated with infectious crystalline keratopathy. Diagnosis of the infective pathogens may be difficult, with a corneal scraping often being too superficial to obtain an adequate specimen. A biofilm is present that advantages microorganism survival, reduces antibiotic bioavailability, and inhibits diagnostic microbial detection. Treatment begins with topical antimicrobials, initially broad spectrum and then targeted to microorganism sensitivity. Adjunctive therapies to enhance the efficacy of treatment include disruption of the microorganism biofilm by laser, intrastromal antibiotics, and keratectomy. In recalcitrant cases, or where corneal scarring ensues, corneal transplantation is required.
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Yadav MK, Go YY, Kim SH, Chae SW, Song JJ. Antimicrobial and Antibiofilm Effects of Human Amniotic/Chorionic Membrane Extract on Streptococcus pneumoniae. Front Microbiol 2017; 8:1948. [PMID: 29089928 PMCID: PMC5641382 DOI: 10.3389/fmicb.2017.01948] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 09/22/2017] [Indexed: 01/11/2023] Open
Abstract
Background:Streptococcus pneumoniae colonize the human nasopharynx in the form of biofilms. The biofilms act as bacterial reservoirs and planktonic bacteria from these biofilms can migrate to other sterile anatomical sites to cause pneumonia, otitis media (OM), bacteremia and meningitis. Human amniotic membrane contains numerous growth factors and antimicrobial activity; however, these have not been studied in detail. In this study, we prepared amniotic membrane extract and chorionic membrane extract (AME/CME) and evaluated their antibacterial and antibiofilm activities against S. pneumoniae using an in vitro biofilm model and in vivo OM rat model. Materials and Methods: The AME/CME were prepared and protein was quantified using DCTM (detergent compatible) method. The minimum inhibitory concentrations were determined using broth dilution method, and the synergistic effect of AME/CME with Penicillin-streptomycin was detected checkerboard. The in vitro biofilm and in vivo colonization of S. pneumoniae were studied using microtiter plate assay and OM rat model, respectively. The AME/CME-treated biofilms were examined using scanning electron microscope and confocal microscopy. To examine the constituents of AME/CME, we determined the proteins and peptides of AME/CME using tandem mass tag-based quantitative mass spectrometry. Results: AME/CME treatment significantly (p < 0.05) inhibited S. pneumoniae growth in planktonic form and in biofilms. Combined application of AME/CME and Penicillin-streptomycin solution had a synergistic effect against S. pneumoniae. Biofilms grown with AME/CME were thin, scattered, and unorganized. AME/CME effectively eradicated pre-established pneumococci biofilms and has a bactericidal effect. AME treatment significantly (p < 0.05) reduced bacterial colonization in the rat middle ear. The proteomics analysis revealed that the AME/CME contains hydrolase, ribonuclease, protease, and other antimicrobial proteins and peptides. Conclusion: AME/CME inhibits S. pneumoniae growth in the planktonic and biofilm states via its antimicrobial proteins and peptides. AME/CME are non-cytotoxic, natural human product; therefore, they may be used alone or with antibiotics to treat S. pneumoniae infections.
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Affiliation(s)
- Mukesh K Yadav
- Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea.,Institute for Medical Device Clinical Trials, Korea University College of Medicine, Seoul, South Korea
| | - Yoon Y Go
- Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea
| | - Shin Hye Kim
- Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea
| | - Sung-Won Chae
- Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea
| | - Jae-Jun Song
- Department of Otorhinolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea
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SaeRS Is Responsive to Cellular Respiratory Status and Regulates Fermentative Biofilm Formation in Staphylococcus aureus. Infect Immun 2017; 85:IAI.00157-17. [PMID: 28507069 DOI: 10.1128/iai.00157-17] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Accepted: 05/08/2017] [Indexed: 01/12/2023] Open
Abstract
Biofilms are multicellular communities of microorganisms living as a quorum rather than as individual cells. The bacterial human pathogen Staphylococcus aureus uses oxygen as a terminal electron acceptor during respiration. Infected human tissues are hypoxic or anoxic. We recently reported that impaired respiration elicits a programmed cell lysis (PCL) phenomenon in S. aureus leading to the release of cellular polymers that are utilized to form biofilms. PCL is dependent upon the AtlA murein hydrolase and is regulated, in part, by the SrrAB two-component regulatory system (TCRS). In the current study, we report that the SaeRS TCRS also governs fermentative biofilm formation by positively influencing AtlA activity. The SaeRS-modulated factor fibronectin-binding protein A (FnBPA) also contributed to the fermentative biofilm formation phenotype. SaeRS-dependent biofilm formation occurred in response to changes in cellular respiratory status. Genetic evidence presented suggests that a high cellular titer of phosphorylated SaeR is required for biofilm formation. Epistasis analyses found that SaeRS and SrrAB influence biofilm formation independently of one another. Analyses using a mouse model of orthopedic implant-associated biofilm formation found that both SaeRS and SrrAB govern host colonization. Of these two TCRSs, SrrAB was the dominant system driving biofilm formation in vivo We propose a model wherein impaired cellular respiration stimulates SaeRS via an as yet undefined signal molecule(s), resulting in increasing expression of AtlA and FnBPA and biofilm formation.
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Land AD, Penno KL, Brzezinski JL. Identification of Microorganisms Isolated From Counterfeit and Unapproved Decorative Contact Lenses. J Forensic Sci 2017; 63:635-639. [PMID: 28542816 DOI: 10.1111/1556-4029.13553] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 04/18/2017] [Accepted: 04/19/2017] [Indexed: 12/29/2022]
Abstract
All contact lenses (corrective/noncorrective) are considered Class II or Class III medical devices under the Federal Food, Drug, and Cosmetic Act, which also states that contact lenses can only be obtained with a prescription. The Forensic Chemistry Center of the US Food & Drug Administration has examined over 300 decorative, noncorrective contact lenses obtained without a prescription. Our observations indicate that 60% of the counterfeit lenses and 27% of the unapproved lenses examined were positive for microbial contamination. Twenty-nine different brands of noncorrective contact lenses were examined, and 48% of them had at least one sample positive for microbial contamination. Each microorganism was further identified using DNA sequencing. Contaminated contact lenses are associated with numerous health risks, including ocular infections and conjunctivitis leading to permanent visual impairment or blindness. These results support the contention that acquiring contact lenses without a prescription is a considerable threat to consumer health and safety.
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Affiliation(s)
- Adrian D Land
- Forensic Chemistry Center, United States Food and Drug Administration, 6751 Steger Drive, Cincinnati, OH, 45237
| | - Katie L Penno
- Forensic Chemistry Center, United States Food and Drug Administration, 6751 Steger Drive, Cincinnati, OH, 45237
| | - Jennifer L Brzezinski
- Forensic Chemistry Center, United States Food and Drug Administration, 6751 Steger Drive, Cincinnati, OH, 45237
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El-Ganiny AM, Shaker GH, Aboelazm AA, El-Dash HA. Prevention of Bacterial Biofilm Formation on Soft Contact Lenses Using Natural Compounds. J Ophthalmic Inflamm Infect 2017; 7:11. [PMID: 28421562 PMCID: PMC5395510 DOI: 10.1186/s12348-017-0129-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2016] [Accepted: 03/31/2017] [Indexed: 01/24/2023] Open
Abstract
Purpose In eye care field, contact lenses (CL) have a great impact on improving vision, but their use can be limited by ocular infection. CL- associated infections can be reduced by good attention to CL storage case practice. CL-care solutions should be able to control microbial growth on CL. The aim of the study was to evaluate and compare the efficacy of CL-care solutions (found in Egyptian market) with some natural compounds in removal and inhibition of bacterial biofilm formed on soft CL. Clinical isolates were recovered from patients having conjunctivitis from Benha University Hospital and identified microbiologically. Quantification of biofilm was done using microtiter plate assay. Three multipurpose CL-care solutions were examined for their ability to remove and inhibit biofilm. Also four natural extracts having antibacterial activity and are safe on eye were tested for their anti-biofilm activity. Results The major bacterial isolates from eye infections were Pseudomonas aeruginosa (36%) and Staphylococcus spp. (37.8%). Only 33.3% of isolates showed ability to produce weak to moderate biofilm. The tested multi-purpose CL-care solutions showed moderate ability to remove preformed biofilm. Among the tested natural compounds, Calendula officinalis and Buddleja salviifolia extracts showed an excellent efficacy in inhibition of biofilm and also removal of preformed biofilm. Conclusion This study demonstrated that isolates from infected eye and CL-cases showed weak to moderate biofilm formation. Calendula officinalis and Buddleja salviifolia extracts showed excellent effect on inhibition and removal of biofilm, these extracts could be added into CL-care solutions which could markedly reduce eye-infections during CL-wear.
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Affiliation(s)
- Amira M El-Ganiny
- Microbiology and Immunology Department, Faculty of Pharmacy, Zagazig University, Zagazig, Egypt.
| | - Ghada H Shaker
- Microbiology and Immunology Department, Faculty of Pharmacy, Zagazig University, Zagazig, Egypt
| | - Abeer A Aboelazm
- Microbiology and Immunology Department, Faculty of Medicine, Benha University, Benha, Egypt
| | - Heba A El-Dash
- Microbiology and Immunology Department, Faculty of Pharmacy, Zagazig University, Zagazig, Egypt
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79
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Mashruwala AA, Guchte AVD, Boyd JM. Impaired respiration elicits SrrAB-dependent programmed cell lysis and biofilm formation in Staphylococcus aureus. eLife 2017; 6. [PMID: 28221135 PMCID: PMC5380435 DOI: 10.7554/elife.23845] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2016] [Accepted: 02/20/2017] [Indexed: 01/25/2023] Open
Abstract
Biofilms are communities of microorganisms attached to a surface or each other. Biofilm-associated cells are the etiologic agents of recurrent Staphylococcus aureus infections. Infected human tissues are hypoxic or anoxic. S. aureus increases biofilm formation in response to hypoxia, but how this occurs is unknown. In the current study we report that oxygen influences biofilm formation in its capacity as a terminal electron acceptor for cellular respiration. Genetic, physiological, or chemical inhibition of respiratory processes elicited increased biofilm formation. Impaired respiration led to increased cell lysis via divergent regulation of two processes: increased expression of the AtlA murein hydrolase and decreased expression of wall-teichoic acids. The AltA-dependent release of cytosolic DNA contributed to increased biofilm formation. Further, cell lysis and biofilm formation were governed by the SrrAB two-component regulatory system. Data presented support a model wherein SrrAB-dependent biofilm formation occurs in response to the accumulation of reduced menaquinone. DOI:http://dx.doi.org/10.7554/eLife.23845.001 Millions of bacteria live on the human body. Generally these bacteria co-exist with us peacefully, but sometimes certain bacteria may enter the body and cause infections, such as gum disease or a bone infection called osteomyelitis. Many of these infections are thought to occur when the bacteria become able to form complex communities called biofilms. Bacteria living in a biofilm cooperate and make lifestyle choices as a community, so in this way, they behave like a single organism containing many cells. A sticky glue-like material called the matrix holds the bacteria in a biofilm together. This matrix protects the bacteria in the biofilm from both the human immune system and antibiotics, allowing infections to develop and making them difficult to treat. Previous research has shown that the supply and level of oxygen in infected tissues decreases as an infection gets worse. One bacterium that typically lives peacefully on our bodies, called Staphylococcus aureus, can sometimes cause serious biofilm-associated infections. S. aureus forms biofilms more readily when oxygen is in short supply, but it was not known how these biofilms form. Understanding how S. aureus forms biofilms could help scientists develop better treatments for bacterial infections. Most bacterial cells have a cell wall to provide them with structural support. Mashruwala et al. found that, when oxygen levels are low, S. aureus decreases the production of a type of sugar that makes up the cell wall. At the same time, the bacteria produce more of an enzyme that breaks down cell walls. Together, these processes cause some of the bacteria cells to break open. The contents of these broken cells, including their DNA, help form the matrix that will hold together and protect the other bacterial cells in the biofilm. The experiments also identified a protein called SrrAB that switches on the process that ruptures the cells when oxygen is low. The findings of Mashruwala et al. show how bacteria grown in the laboratory form biofilms when they are starved of oxygen. The next steps following on from this work are to find out whether the same thing happens when bacteria infect animals and whether drugs that block the rupturing of bacterial cells could be used to treat infections. DOI:http://dx.doi.org/10.7554/eLife.23845.002
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Affiliation(s)
- Ameya A Mashruwala
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, United States
| | - Adriana van de Guchte
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, United States
| | - Jeffrey M Boyd
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, United States
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Balasubramanian S, Othman EM, Kampik D, Stopper H, Hentschel U, Ziebuhr W, Oelschlaeger TA, Abdelmohsen UR. Marine Sponge-Derived Streptomyces sp. SBT343 Extract Inhibits Staphylococcal Biofilm Formation. Front Microbiol 2017; 8:236. [PMID: 28261188 PMCID: PMC5311426 DOI: 10.3389/fmicb.2017.00236] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 02/03/2017] [Indexed: 01/22/2023] Open
Abstract
Staphylococcus epidermidis and Staphylococcus aureus are opportunistic pathogens that cause nosocomial and chronic biofilm-associated infections. Indwelling medical devices and contact lenses are ideal ecological niches for formation of staphylococcal biofilms. Bacteria within biofilms are known to display reduced susceptibilities to antimicrobials and are protected from the host immune system. High rates of acquired antibiotic resistances in staphylococci and other biofilm-forming bacteria further hamper treatment options and highlight the need for new anti-biofilm strategies. Here, we aimed to evaluate the potential of marine sponge-derived actinomycetes in inhibiting biofilm formation of several strains of S. epidermidis, S. aureus, and Pseudomonas aeruginosa. Results from in vitro biofilm-formation assays, as well as scanning electron and confocal microscopy, revealed that an organic extract derived from the marine sponge-associated bacterium Streptomyces sp. SBT343 significantly inhibited staphylococcal biofilm formation on polystyrene, glass and contact lens surfaces, without affecting bacterial growth. The extract also displayed similar antagonistic effects towards the biofilm formation of other S. epidermidis and S. aureus strains tested but had no inhibitory effects towards Pseudomonas biofilms. Interestingly the extract, at lower effective concentrations, did not exhibit cytotoxic effects on mouse fibroblast, macrophage and human corneal epithelial cell lines. Chemical analysis by High Resolution Fourier Transform Mass Spectrometry (HRMS) of the Streptomyces sp. SBT343 extract proportion revealed its chemical richness and complexity. Preliminary physico-chemical characterization of the extract highlighted the heat-stable and non-proteinaceous nature of the active component(s). The combined data suggest that the Streptomyces sp. SBT343 extract selectively inhibits staphylococcal biofilm formation without interfering with bacterial cell viability. Due to absence of cell toxicity, the extract might represent a good starting material to develop a future remedy to block staphylococcal biofilm formation on contact lenses and thereby to prevent intractable contact lens-mediated ocular infections.
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Affiliation(s)
| | - Eman M Othman
- Institute of Pharmacology and Toxicology, University of WürzburgWürzburg, Germany; Department of Analytical Chemistry, Faculty of Pharmacy, Minia UniversityMinia, Egypt
| | - Daniel Kampik
- Department of Ophthalmology, University Hospital Würzburg Würzburg, Germany
| | - Helga Stopper
- Institute of Pharmacology and Toxicology, University of Würzburg Würzburg, Germany
| | - Ute Hentschel
- GEOMAR Helmholtz Centre for Ocean Research, RD3 Marine Microbiology, and Christian-Albrechts University of Kiel Kiel, Germany
| | - Wilma Ziebuhr
- Institute for Molecular Infection Biology, University of Würzburg Würzburg, Germany
| | | | - Usama R Abdelmohsen
- Department of Botany II, Julius-von-Sachs Institute for Biological Sciences, University of WürzburgWürzburg, Germany; Department of Pharmacognosy, Faculty of Pharmacy, Minia UniversityMinia, Egypt
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81
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Kackar S, Suman E, Kotian MS. Bacterial and Fungal Biofilm formation on Contact Lenses and their Susceptibility to Lens Care Solutions. Indian J Med Microbiol 2017; 35:80-84. [DOI: 10.4103/ijmm.ijmm_16_273] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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82
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Infections in Ocular Prosthesis. CURRENT OPHTHALMOLOGY REPORTS 2016. [DOI: 10.1007/s40135-016-0104-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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83
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Scanning Electron Microscopic Analysis of Biofilm Formation in Explanted Human Boston Type I Keratoprostheses. Cornea 2016; 35:25-9. [PMID: 26562818 DOI: 10.1097/ico.0000000000000674] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE To describe the morphological distribution of host tissue and microbial biofilms on the intraocular surfaces of Boston type I keratoprostheses (KPros) explanted because of corneal melt. METHODS Retrospective study of scanning electron microscopy (SEM) images from 4 explanted Boston type I KPros composed of polymethylmethacrylate and titanium. SEM images of KPro-associated ocular surfaces were reviewed for the presence of inflammatory cells, microbes, and/or biofilm formation. One sterile type I KPro was also imaged to serve as a (device only) control. RESULTS All 4 KPros were explanted because of culture-negative, clinically "sterile" donor corneal melt with impending KPro extrusion. In all cases, the rough, irregular surfaces of the device harbored more adherent corneal epithelium and stromacytes, inflammatory cells, and bacteria than the smooth, polished surface of the KPro optic. Two KPros showed not only evidence of prior bacterial colonization but marked biofilm formation. CONCLUSIONS SEM images of explanted KPros explanted for "sterile" corneal melt demonstrated evidence of biofilm formation despite negative donor corneal cultures and the absence of clinical suspicion for infection. These results suggest that "sterile" corneal melt may be due to inflammatory host responses to low microbial burdens as seen in biofilms and/or released antigens after antibiotic-induced lysis. There was increased adherence of host tissue cells and microbial biofilms on the nonpolished surfaces of the KPro. Polishing the intraocular polymethylmethacrylate and titanium KPro surfaces may decrease microbial adhesion and biofilm formation in human subjects with KPros, but what impact this will have on rates of postoperative endophthalmitis is unknown.
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84
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Biofilms of Pathogenic Nontuberculous Mycobacteria Targeted by New Therapeutic Approaches. Antimicrob Agents Chemother 2015; 60:24-35. [PMID: 26459903 PMCID: PMC4704195 DOI: 10.1128/aac.01509-15] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 09/21/2015] [Indexed: 12/04/2022] Open
Abstract
Microbial infections of the cornea are potentially devastating and can result in permanent visual loss or require vision-rescuing surgery. In recent years, there has been an increasing number of reports on nontuberculous mycobacterial infections of the cornea. Challenges to the management of nontuberculous mycobacterial keratitis include delayed laboratory detection, low index of clinical suspicion, poor drug penetration, slow response to therapy, and prolonged use of antibiotic combinations. The ability of nontuberculous mycobacteria to evade the host immune response and the ability to adhere and to form biofilms on biological and synthetic substrates contribute to the issue. Therefore, there is an urgent need for new antimicrobial compounds that can overcome these problems. In this study, we evaluated the biofilm architectures for Mycobacterium chelonae and Mycobacterium fortuitum in dynamic flow cell chamber and 8-well chamber slide models. Our results showed that mycobacterial biofilms were quite resistant to conventional antibiotics. However, DNase treatment could be used to overcome biofilm resistance. Moreover, we successfully evaluated a new antimicrobial compound (AM-228) that was effective not only for planktonic mycobacterial cells but also for biofilm treatment and was compared favorably with the most successful “fourth-generation” fluoroquinolone, gatifloxacin. Finally, a new treatment strategy emerged: a combination of DNase with an antibiotic was more effective than an antibiotic alone.
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85
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Saraswathi P, Beuerman RW. Corneal Biofilms: From Planktonic to Microcolony Formation in an Experimental Keratitis Infection with Pseudomonas Aeruginosa. Ocul Surf 2015. [DOI: 10.1016/j.jtos.2015.07.001 [pii]] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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86
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Saraswathi P, Beuerman RW. Corneal Biofilms: From Planktonic to Microcolony Formation in an Experimental Keratitis Infection with Pseudomonas Aeruginosa. Ocul Surf 2015. [PMID: 26220579 DOI: 10.1016/j.jtos.2015.07.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
PURPOSE Microbial biofilms commonly comprise part of the infectious scenario, complicating the therapeutic approach. The purpose of this study was to determine in a mouse model of corneal infection if mature biofilms formed and to visualize the stages of biofilm formation. METHODS A bacterial keratitis model was established using Pseudomonas aeruginosa ATCC 9027 (1 × 10(8) CFU/ml) to infect the cornea of C57BL/6 black mouse. Eyes were examined post-infection (PI) on days 1, 2, 3, 5, and 7, and imaged by slit lamp microscopy, and light, confocal, and electron microscopy to identify the stages of biofilm formation and the time of appearance. RESULTS On PI day 1, Gram staining showed rod-shaped bacteria adherent on the corneal surface. On PI days 2 and 3, bacteria were seen within webs of extracellular polymeric substance (EPS) and glycocalyx secretion, imaged by confocal microscopy. Scanning electron microscopy demonstrated microcolonies of active infectious cells bound with thick fibrous material. Transmission electron microscopy substantiated the formation of classical biofilm architecture with P. aeruginosa densely packed within the extracellular polymeric substances on PI days 5 and 7. CONCLUSION Direct visual evidence showed that biofilms routinely developed on the biotic surface of the mouse cornea. The mouse model can be used to develop new approaches to deal therapeutically with biofilms in corneal infections.
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Affiliation(s)
| | - Roger W Beuerman
- Singapore Eye Research Institute (SERI), Singapore; Duke-NUS SRP Neuroscience and Behavioural Disorders and Emerging Infectious Diseases, Singapore; Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
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