Displaying publications 1 - 20 of 152 in total

  1. Siddiqui R, Khan NA
    Exp Parasitol, 2017 Dec;183:133-136.
    PMID: 28807757 DOI: 10.1016/j.exppara.2017.08.006
    Bacterial infections have remained significant despite our advances in the development of a plethora of disinfectants as well as antimicrobial chemotherapy. This is in part due to our incomplete understanding of the prevalence of bacterial pathogens in the environmental and clinical settings. Several lines of evidence suggest that Acanthamoeba is one of the most ubiquitous/resilient protists that also acts as a host/reservoir for pathogenic microbes. Thus targeting the hardy host, which harbour microbial pathogens, offer a potential avenue to counter infection transmission, particularly hospital/community-acquired infections. This will complement existing approach of applying disinfectants that are targeted against bacterial pathogens directly.
  2. Baig AM, Khan NA
    Microb Pathog, 2015 Nov;88:48-51.
    PMID: 26276705 DOI: 10.1016/j.micpath.2015.08.005
    Granulomatous amoebic encephalitis due to Acanthamoeba is a chronic disease that almost always results in death. Hematogenous spread is a pre-requisite followed by amoebae invasion of the blood-brain barrier to enter the central nervous system. Given the systemic nature of this infection, a significant latent period of several months before the appearance of clinical manifestations is puzzling. Based on reported cases, here we propose pathogenetic mechanisms that explain the above described latency of the disease.
  3. Soopramanien M, Khan NA, Siddiqui R
    J Appl Microbiol, 2021 Sep;131(3):1039-1055.
    PMID: 33368930 DOI: 10.1111/jam.14981
    Cancer is a prominent cause of morbidity and mortality worldwide, in spite of advances in therapeutic interventions and supportive care. In 2018 alone, there were 18·1 million new cancer cases and 9·6 million deaths indicating the need for novel anticancer agents. Plant-based products have often been linked with protective effects against communicable and non-communicable diseases. Recently, we have shown that animals such as crocodiles thrive in polluted environments and are often exposed to carcinogenic agents, but still benefit from prolonged lifespan. The protective mechanisms shielding them from cancer could be attributed to the immune system, and/or it is possible that their gut microbiota produce anticancer molecules. In support, several lines of evidence suggest that gut microbiota plays a critical role in the physiology of its host. Here, we reviewed the available literature to assess whether the gut microbiota of animals thriving in polluted environment possess anticancer molecules.
  4. Siddiqui R, Aqeel Y, Khan NA
    Cont Lens Anterior Eye, 2016 Oct;39(5):389-93.
    PMID: 27133448 DOI: 10.1016/j.clae.2016.04.004
    Acanthamoeba castellanii is the causative agent of blinding keratitis. Though reported in non-contact lens wearers, it is most frequently associated with improper use of contact lens. For contact lens wearers, amoebae attachment to the lens is a critical first step, followed by amoebae binding to the corneal epithelial cells during extended lens wear. Acanthamoeba attachment to surfaces (biological or inert) and migration is an active process and occurs during the trophozoite stage. Thus retaining amoebae in the cyst stage (dormant form) offers an added preventative measure in impeding parasite traversal from the contact lens onto the cornea. Here, we showed that as low as 3% DMSO, abolished A. castellanii excystation. Based on the findings, it is proposed that DMSO should be included in the contact lens disinfectants as an added preventative strategy against contracting Acanthamoeba keratitis.
  5. Siddiqui R, Saleem S, Khan NA
    Exp Parasitol, 2016 Jun 18;168:16-24.
    PMID: 27327524 DOI: 10.1016/j.exppara.2016.06.006
    The treatment of Acanthamoeba infections remains problematic, suggesting that new targets and/or chemotherapeutic agents are needed. Bioassay-guided screening of drugs that are clinically-approved for non-communicable diseases against opportunistic eukaryotic pathogens is a viable strategy. With known targets and mode of action, such drugs can advance to clinical trials at a faster pace. Recently Bortezomib (proteasome inhibitor) has been approved by FDA in the treatment of multiple myeloma. As proteasomal pathways are well known regulators of a variety of eukaryotic cellular functions, the overall aim of the present study was to study the effects of peptidic and non-peptidic proteasome inhibitors on the biology and pathogenesis of Acanthamoeba castellanii of the T4 genotype, in vitro. Zymographic assays revealed that inhibition of proteasome had detrimental effects on the extracellular proteolytic activities of A. castellanii. Proteasome inhibition affected A. castellanii growth (using amoebistatic assays), but not viability of A. castellanii. Importantly, proteasome inhibitors affected encystation as determined by trophozoite transformation into the cyst form, as well as excystation, as determined by cyst transformation into the trophozoite form. The ability of proteasome inhibitor to block Acanthamoeba differentiation is significant, as it presents a major challenge in the successful treatment of Acanthamoeba infection. As these drugs are used clinically against non-communicable diseases, the findings reported here have the potential to be tested in a clinical setting against amoebic infections.
  6. Soo ZMP, Khan NA, Siddiqui R
    Acta Trop, 2020 Jan;201:105183.
    PMID: 31542372 DOI: 10.1016/j.actatropica.2019.105183
    Leptospirosis is a zoonotic disease caused by the pathogenic helical spirochetes, Leptospira. Symptoms include sudden-onset fever, severe headaches, muscle pain, nausea and chills. Leptospirosis is endemic in developing countries such as Malaysia, India, Sri Lanka, and Brazil where thousands of cases are reported annually. The disease risk factors include the high population of reservoirs, environmental factors, recreational factors, and occupational factors. To end the endemicity of leptospirosis, these factors need to be tackled. The management of leptospirosis needs to be refined. Early diagnosis remains a challenge due to a lack of clinical suspicion among physicians, its non-specific symptoms and a limited availability of rapid point-of-care diagnostic tests. The purpose of this review is to provide insight into the status of leptospirosis in developing countries focusing on the risk factors and to propose methods for the improved management of the disease.
  7. Jeyamogan S, Khan NA, Siddiqui R
    Arch Med Res, 2021 02;52(2):131-142.
    PMID: 33423803 DOI: 10.1016/j.arcmed.2020.10.016
    The number of cancer cases worldwide in terms of morbidity and mortality is a serious concern, despite the presence of therapeutic interventions and supportive care. Limitations in the current available diagnosis methods and treatments methods may contribute to the increase in cancer mortality. Theranostics, is a novel approach that has opened avenues for the simultaneous precise diagnosis and treatment for cancer patients. Although still in the early development stage, theranostic agents such as quantum dots, radioisotopes, liposomes and plasmonic nanobubbles can be bound to anticancer drugs, cancer cell markers and imaging agents, with the support of available imaging techniques, provide the potential to facilitate diagnosis, treatment and management of cancer patients. Herein, we discuss the potential benefits of several theranostic tools for the management of cancer. Specifically, quantum dots, radio-labelled isotopes, liposomes and plasmonic nanobubbles coupled with targeting agents and/or anticancer molecules and imaging agents as theranostic agents are deliberated upon in this review. Overall, the use of theranostic agents shows promise in cancer management. Nevertheless, intensive research is required to realize these expectations.
  8. Yousuf FA, Siddiqui R, Khan NA
    Rev Inst Med Trop Sao Paulo, 2017 Jun 01;59:e32.
    PMID: 28591260 DOI: 10.1590/S1678-9946201759032
    Rotavirus and pathogenic free-living amoebae are causative agents of important health problems, especially for developing countries like Pakistan where the population has limited access to clean water supplies. Here, we evaluated the prevalence of rotavirus and free-living amoebae (Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri) in drinking water supplies of Karachi, Pakistan. Six water filtration plants that supply drinking water to the population of Karachi were investigated. Additionally, drinking water samples from households were analyzed for the presence of rotavirus and free-living amoebae. Rotavirus was present in 35% of the water samples collected from water filtration plants; however, domestic tap water samples had a prevalence of only 5%. Out of 20 water samples from filtration plants, 13 (65%) were positive for Acanthamoeba spp., and one (5%) was positive for B. mandrillaris. Out of 20 drinking water samples collected from different areas of Karachi, 35% were positive for Acanthamoeba spp. Rotavirus was detected in 5% of the drinking water samples tested. Overall, these findings showed for the first time the presence of rotavirus, in addition to pathogenic free-living amoebae in drinking water supplies of Karachi that could be an important public health risk for the affected population.
  9. Akbar N, Siddiqui R, Iqbal M, Sagathevan K, Khan NA
    Lett Appl Microbiol, 2018 May;66(5):416-426.
    PMID: 29457249 DOI: 10.1111/lam.12867
    Here, we hypothesized that the microbial gut flora of animals/pests living in polluted environments, produce substances to thwart bacterial infections. The overall aim of this study was to source microbes inhabiting unusual environmental niches for potential antimicrobial activity. Two cockroach species, Gromphadorhina portentosa (Madagascar) and Blaptica dubia (Dubia) were selected. The gut bacteria from these species were isolated and grown in RPMI 1640 and conditioned media were prepared. Conditioned media were tested against a panel of Gram-positive (Methicillin-resistant Staphylococcus aureus, Streptococcus pyogenes, Bacillus cereus) and Gram-negative (Escherichia coli K1, Salmonella enterica, Serratia marcescens, Pseudomonas aeruginosa, Klebsiella pneumoniae) bacteria, as well as the protist pathogen, Acanthamoeba castellanii. The results revealed that the gut bacteria of cockroaches produce active molecule(s) with potent antibacterial properties, as well as exhibit antiamoebic effects. However, heat-inactivation at 95°C for 10 min had no effect on conditioned media-mediated antibacterial and antiamoebic properties. These results suggest that bacteria from novel sources i.e. from the cockroach's gut produce molecules with bactericidal as well as amoebicidal properties that can ultimately lead to the development of therapeutic drugs.

    SIGNIFICANCE AND IMPACT OF THE STUDY: The bacteria isolated from unusual dwellings such as the cockroaches' gut are a useful source of antibacterial and antiamoebal molecules. These are remarkable findings that will open several avenues in our search for novel antimicrobials from unique sources. Furthermore studies will lead to the identification of molecules to develop future antibacterials from insects.

  10. Baig AM, Lalani S, Khan NA
    J Basic Microbiol, 2017 Jul;57(7):574-579.
    PMID: 28466971 DOI: 10.1002/jobm.201700025
    Here we describe features of apoptosis in unicellular Acanthamoeba castellanii belonging to the T4 genotype. When exposed to apoptosis-inducing compounds such as doxorubicin, A. castellanii trophozoites exhibited cell shrinkage and membrane blebbing as observed microscopically, DNA fragmentation using agarose gel electrophoresis, and phosphatidylserine (PS) externalization using annexin V immunostaining. Overall, these findings suggest the existence of apoptosis in A. castellanii possibly mediated by intrinsic apoptotic cascade. Further research in this field could provide avenues to selectively induce apoptosis in A. castellanii by triggering intrinsic apoptotic cascade.
  11. Akbar N, Siddiqui R, Sagathevan K, Khan NA
    Int Microbiol, 2020 Nov;23(4):511-526.
    PMID: 32124096 DOI: 10.1007/s10123-020-00123-3
    Infectious diseases, in particular bacterial infections, are the leading cause of morbidity and mortality posing a global threat to human health. The emergence of antibiotic resistance has exacerbated the problem further. Hence, there is a need to search for novel sources of antibacterials. Herein, we explored gut bacteria of a variety of animals living in polluted environments for their antibacterial properties against multi-drug resistant pathogenic bacteria. A variety of species were procured including invertebrate species, Blaptica dubia (cockroach), Gromphadorhina portentosa (cockroach), Scylla serrata (crab), Grammostola rosea (tarantula), Scolopendra subspinipes (centipede) and vertebrate species including Varanus salvator (water monitor lizard), Malayopython reticulatus (python), Cuora amboinensis (tortoise), Oreochromis mossambicus (tilapia fish), Rattus rattus (rat), Gallus gallus domesticus (chicken) and Lithobates catesbeianus (frog). Gut bacteria of these animals were isolated and identified using microbiological, biochemical, analytical profiling index (API) and through molecluar identification using 16S rRNA sequencing. Bacterial conditioned media (CM) were prepared and tested against selected Gram-positive and Gram-negative pathogenic bacteria as well as human cells (HaCaT). The results revealed that CM exhibited significant broad-spectrum antibacterial activities. Upon heat inactivation, CM retained their antibacterial properties suggesting that this effect may be due to secondary metabolites or small peptides. CM showed minimal cytotoxicity against human cells. These findings suggest that gut bacteria of animals living in polluted environments produce broad-spectrum antibacterial molecule(s). The molecular identity of the active molecule(s) together with their mode of action is the subject of future studies which could lead to the rational development of novel antibacterial(s).
  12. Ong TYY, Khan NA, Siddiqui R
    J Clin Microbiol, 2017 07;55(7):1989-1997.
    PMID: 28404683 DOI: 10.1128/JCM.02300-16
    Acanthamoeba spp. and Balamuthia mandrillaris are causative agents of granulomatous amoebic encephalitis (GAE), while Naegleria fowleri causes primary amoebic meningoencephalitis (PAM). PAM is an acute infection that lasts a few days, while GAE is a chronic to subacute infection that can last up to several months. Here, we present a literature review of 86 case reports from 1968 to 2016, in order to explore the affinity of these amoebae for particular sites of the brain, diagnostic modalities, treatment options, and disease outcomes in a comparative manner.
  13. Siddiqui R, Aqeel Y, Khan NA
    Antimicrob Agents Chemother, 2016 11;60(11):6441-6450.
    PMID: 27600042 DOI: 10.1128/AAC.00686-16
    For the past several decades, there has been little improvement in the morbidity and mortality associated with Acanthamoeba keratitis and Acanthamoeba encephalitis, respectively. The discovery of a plethora of antiacanthamoebic compounds has not yielded effective marketed chemotherapeutics. The rate of development of novel antiacanthamoebic chemotherapies of translational value and the lack of interest of the pharmaceutical industry in developing such chemotherapies have been disappointing. On the other hand, the market for contact lenses/contact lens disinfectants is a multi-billion-dollar industry and has been successful and profitable. A better understanding of drugs, their targets, and mechanisms of action will facilitate the development of more-effective chemotherapies. Here, we review the progress toward phenotypic drug discovery, emphasizing the shortcomings of useable therapies.
  14. Khan NA, Anwar A, Siddiqui R
    Curr Med Chem, 2018 May 10.
    PMID: 29745319 DOI: 10.2174/0929867325666180510125633
    BACKGROUND: First discovered in the early 1970s, Acanthamoeba keratitis has remained a major eye infection and presents a significant threat to the public health, especially in developing countries. The aim is to present a timely review of our current understanding of the advances made in this field in a comprehensible manner and includes novel concepts and provides clear directions for immediate research priorities.

    METHOD: We undertook a search of bibliographic databases for peer-reviewed research literature and also summarized our published results in this field.

    RESULTS: The present review focuses on novel diagnostic and therapeutic strategies in details which can provide access to management and treatment of Acanthamoeba keratitis. This coupled with the recently available genome sequence information together with high throughput genomics technology and innovative approaches should stimulate interest in the rational design of preventative and therapeutic measures. Current treatment of Acanthamoeba keratitis is problematic and often leads to infection recurrence. Better understanding of diagnosis, pathogenesis, pathophysiology and therapeutic regimens, would lead to novel strategies in treatment and prophylaxis.

  15. Anwar A, Siddiqui R, Khan NA
    ACS Chem Neurosci, 2019 01 16;10(1):6-12.
    PMID: 30149693 DOI: 10.1021/acschemneuro.8b00321
    Pathogenic free-living amoebae including Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri cause infections of the central nervous system (CNS), which almost always prove fatal. The mortality rate is high with the CNS infections caused by these microbes despite modern developments in healthcare and antimicrobial chemotherapy. The low awareness, delayed diagnosis, and lack of effective drugs are major hurdles to overcome these challenges. Nanomaterials have emerged as vital tools for concurrent diagnosis and therapy, which are commonly referred to as theranostics. Nanomaterials offer highly sensitive diagnostic systems and viable therapeutic effects as a single modality. There has been good progress to develop nanomaterials based efficient theranostic systems against numerous kinds of tumors, but this field is yet immature in the context of infectious diseases, particularly parasitic infections. Herein, we describe the potential value of theranostic applications of nanomaterials against brain infections due to pathogenic amoebae.
  16. Anwar A, Khan NA, Siddiqui R
    ACS Chem Neurosci, 2020 08 19;11(16):2378-2384.
    PMID: 32073257 DOI: 10.1021/acschemneuro.9b00613
    Brain-eating amoebae including Acanthamoeba spp., Naegleria fowleri, and Balamuthia mandrillaris cause rare infections of the central nervous system that almost always result in death. The high mortality rate, lack of interest for drug development from pharmaceutical industries, and no available effective drugs present an alarming challenge. The current drugs employed in the management and therapy of these devastating diseases are amphotericin B, miltefosine, chlorhexidine, pentamidine, and voriconazole which are generally used in combination. However, clinical evidence shows that these drugs have limited efficacy and high host cell cytotoxicity. Repurposing of drugs is a practical approach to utilize commercially available, U.S. Food and Drug Administration approved drugs for one disease against rare diseases caused by brain-eating amoebae. In this Perspective, we highlight some of the success stories of drugs repositioned against neglected parasitic diseases and identify future potential for effective and sustainable drug development against brain-eating amoebae infections.
  17. Gabriel S, Khan NA, Siddiqui R
    J Water Health, 2019 Feb;17(1):160-171.
    PMID: 30758312 DOI: 10.2166/wh.2018.164
    The aim of this study was to determine the occurrence of free-living amoebae (FLA) in Peninsular Malaysia and to compare different methodologies to detect them from water samples. Water samples were collected from tap water, recreational places, water dispensers, filtered water, etc. and tested for FLA using both cultivation and polymerase chain reaction (PCR) via plating assays and centrifugation methods. Amoebae DNA was extracted using Instagene matrix and PCR was performed using genus-specific primers. Of 250 samples, 142 (56.8%) samples were positive for presence of amoebae, while 108 (43.2%) were negative. Recreational water showed higher prevalence of amoebae than tap water. PCR for the plating assays revealed the presence of Acanthamoeba in 91 (64%) samples and Naegleria in 99 (70%) of samples analysed. All samples tested were negative for B. mandrillaris. In contrast, the centrifugation method was less effective in detecting amoebae as only one sample revealed the presence of Acanthamoeba and 52 (29%) samples were positive for Naegleria. PCR assays were specific and sensitive, detecting as few as 10 cells. These findings show the vast distribution and presence of FLA in all 11 states of Peninsular Malaysia. Further studies could determine the possible presence of pathogenic species and strains of free-living amoebae in public water supplies in Malaysia.
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