Research Our laboratory focuses on two topics: Molecular biology of antimicrobial resistance among bacteria and genetic characterization of bacterial exotoxins. Antimicrobial resistance is of growing global concern in human and veterinary medicine. Understanding the role of various environmental (ecological) and intrinsic factors that lead to prevalence, amplification and spread of antibiotic resistance is vital. In our lab, we develop quantitative (real-time) PCR assays and microarrays to monitor development and amplification of antimicrobial resistance genes and identify modes of spread of these genetic elements in the environment. We primarily utilize the feedlot industry as a model to understand the role of animal industry in amplification and spread of antimicrobial resistance genetic elements. We have considerable interest in identifying non-traditional selection pressures (factors other than exposure to antibiotics) that contribute towards multi-drug resistance among intestinal commensals and food-borne pathogens. We are also studying the molecular structure and expression of leukotoxin in Fusobacterium necrophorum. Leukotoxin is one of the major virulence factors of F. necrophorum and plays a critical role in causing multifocal coagulative necrosis of the liver in bovines. The leukotoxin is a large secreted exotoxin (approximately 336 KDa) which causes apoptosis of target cells at lower concentrations and necrosis at higher concentrations. Leukotoxin gene (lktA) is part of a multigene operon consisting of upstream lktB gene (which encodes a bacterial cell-associated protein) and a downstream lktC which encodes an uncharacterized protein. Efforts are on to elucidate the role of the promoter in variable expression of leukotoxin among subspecies and strains of F. necrophorum. Flow-cytometry, electron microscopy and biochemical assays, are used to investigate the mode of action of leukotoxin. We also investigate factors that affect the expression of shigatoxins in E. coli O157:H7. Teaching I teach two sophomore pathology courses (DMP 715 and DMP 720) and one graduate course (DMP 860). I coordinate Systemic Pathology Course (DMP 720; Spring) in which I teach 25 lectures and approximately 30 labs. I primarily focus on pathologies of cardiovascular, nervous, urinary, reproductive, and musculoskeletal systems. I teach 6-8 lectures and approximately 10 to 12 labs in General Pathology course (DMP 715; Fall) including pathology of the hemolymphatic system. Pathogenic Mechanisms (DMP 860) is a higher level graduate course designed to understand the mechanisms by which microbes (Viruses, Bacteria, Fungi and Protozoans) alter the host systems to their advantage and cause disease. The first half of the course will focus on learning host environment in health and disease and the second half will address microbial pathogenesis in host disease. Selected publications T. G. Nagaraja, S. K. Narayanan, G. C. Stewart, and M. M. Chengappa. 2005. Fusobacterium necrophorum infections in animals: Pathogenesis and pathogenic mechanisms. Anaerobe. 11: 239-246. Narayanan, S., M. M. Chengappa, G. C. Stewart, and T. G. Nagaraja. 2003. Immunogenicity and protective effects of truncated recombinant leukotoxin proteins of Fusobacterium necrophorum in mice. Vet. Microbiol. 93(4) 335-347. Narayanan, S., G. C. Stewart, M. M. Chengappa, L. Willard, W. Shuman, M. Wilkerson, and T. G. Nagaraja. 2002. Fusobacterium necrophorum Leukotoxin Induces Activation and Apoptosis of Bovine Leukocytes. Infect. Immun. 70(8):4609-4620. Narayanan, S., T. G. Nagaraja, M. M. Chengappa, and G. C. Stewart. 2002. Leukotoxins in Gram-negative bacteria. Vet. Microbiol. 84(4):337-356. Narayanan, S., T. G. Nagaraja, M. M. Chengappa, and G. C. Stewart. 2001. Cloning, Sequencing and Expression of Leukotoxin gene from Fusobacterium necrophorum. Infect. Immun. 69(9):5447-5455. Narayanan, S., T. G. Nagaraja, M. M. Chengappa, and G. C. Stewart. 2001. Electrophoretic mobility anomalies associated with PCR amplification of the intergenic spacer region between 16S and 23S ribosomal RNA genes of Fusobacterium necrophorum. J. Microbiol. Methods. 46(2):165-169. Stewart G. C. and S. Narayanan. 1999. Recombinant DNA principles and methodologies. (Eds.) J. J. Greene and V. B. Rao. ISBN No. 0-8247-9989-5. Marcel Dekker, Inc. NY. Invited review in Journal of Microbiological Methods. Narayanan, S., T. G. Nagaraja, J. Staats, M. M. Chengappa, and R. D. Oberst. 1998. Biochemical and biological characterizations and ribotyping of Actinomyces pyogenes and Actinomyces pyogenes-like organisms from liver abscesses in cattle. Vet Microbiol. 61(4): 289-303 Narayanan S., T. G. Nagaraja, N. Wallace, J. Staats, M. M. Chengappa, R. D. Oberst. 1998. Biochemical and ribotypic comparison of Actinomyces pyogenes and A pyogenes-like organisms from liver abscesses, ruminal wall, and ruminal contents of cattle. Am. J. Vet. Res. 59(3): 271-6 Narayanan, S., T. G. Nagaraja, O. Okwumabua, J. Staats, M. M. Chengappa, and R. D. Oberst. 1997. Ribotyping to compare Fusobacterium necrophorum from bovine liver abscesses, ruminal wall and ruminal contents. Appl. Environ. Microbiol. 63(12): 4671-8. Chandrasekar, V., S. Narayanan, P. S. Lalitha, and C. Vijayaragavan. 1993. The distribution of chromaffin cells in the adrenal gland of Japanese quail (Coturnix coturnix japonica). J. Vet. Anim. Sci. 24(8): 53-56. Narayanan, S., P. S. Lalitha, and C. Vijayaragavan. 1992. Histochemical observations on the urinary bladder of Indian buffaloes (Bubalus bubalis). Indian J. Vet. Anat. 4(1): 33-36.
Chandrasekar, V.,
S. Narayanan, and P. S. Lalitha. 1990. Histology and histochemistry of the uropygial gland of the Japanese quail (Coturnix coturnix japonica). J. Vet. Anim. Sci. 21(1): 77-82.
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