Stephen J. Knabel, Ph.D.

Complete 6-page Vitae (pdf)

Research Interests:

Detection, tracking and control of foodborne pathogens: Listeria monocytogenes, E. coli O157:H7, Salmonella and Campylobacter. Development of novel methods for the recovery of injured foodborne pathogens and detection by conventional and molecular methods. Contamination of raw animal foods by gram-negative foodborne pathogens and destruction by high pH. Understanding and enhancing the mechanisms of action of foodgrade microbial inhibitors. Metal ion interactions with spoilage and pathogenic microorganisms. Role of heat shock proteins in induced thermotolerance. Research on the long-term-survival phase of Listeria monocytogenes and its effect on changes in barotolerance, thermotolerance and cellular morphology.

Recent Publications:

 1.  Parameswaran, S., R. B. Guyer and S. J. Knabel.  2004.  Simple oPSU Broth-Bax PCR-PicoGreen system for rapid detection of Listeria monocytogenes in pasteurized milk and hot dogs.  J. Food Safety 23:233-248.

 2.  Zhang, W., B. Jayarao, and S. J. Knabel.  2004.  Multi-Virulence-Locus-Sequence Typing of Listeria monocytogenes.  Appl. Environ. Microbiol. 70: 913-920.

 3.  Knabel, S. J.  2004.  Food biosecurity in the U.S.  Microbiology Australia 25:10-16.

 4.  Zhang, W., G. Wilt, A. Hughs, and S. J. Knabel.  2004.  The BAX PCR for screening Listeria monocytogenes targets a partial putative gene lmo 2234 similar to iolE.  J. Food Prot. 67:1507-1511.

 5.  Bull, M. K., M. M. Hayman, C. M. Stewart, E. A. Szabo and S. J. Knabel.  2005.  Effect of prior growth temperature, type of enrichment medium, and temperature and time of storage on recovery of Listeria monocytogenes following high pressure processing of milk.  Int. J. Food Microbiol. 101:53-61

 6.  Zhang, W. and S. J. Knabel. 2005. Development of a multiplex PCR assay for simultaneous species- and serotype-specific detection, and DNA sequence-based subtyping of Listeria monocytogenes. J. Food Prot. 68:1907-1910.

 7.  Chen, Y., Zhang W. and S. J. Knabel.  2005.  Multi-virulence-locus sequence typing clarifies the epidemiology of two recent listeriosis outbreaks.  J. Clin. Microbiol. 43:5291-5294.

 8.  Fatemi, P., L. F. LaBorde, B. A. Annous, G. M. Sapers, J. F. Patton and S. J. Knabel.  2006.  Evaluation of sanitizer penetration and its effect on destruction of E. coli O157:H7 on/in Golden Delicious apples.  J. Food Prot. 69:548-555.

 9.  Fatemi, P and S. J. Knabel.  2006.  Influence of Punctures, Cuts and Apple Surface Morphologies on Penetration and Growth of E.  coli O157:H7. J. Food Protect. 69:267-275(9).

 10.  Chen, Y., W. Zhang, and S. J. Knabel.  2007.  Multi-Virulence-Locus Sequence Typing identifies single nucleotide polymorphisms that differentiate epidemic clones and outbreak strains of Listeria monocytogenes.  J. Clin. Microbiol. 45:835-846.

 11.  Chen, Y. and S. J. Knabel.  2007.  Multiplex PCR for simultaneous detection of bacteria of the genus Listeria, Listeria monocytogenes, and major serotypes and epidemic clones and outbreak clones of L. monocytogenes.  Appl. Environ. Microbiol. 73:6299-6304.

 12.  Sawant, A. A., N. V. Hegde, B. A. Straley, S. C. Donaldson, B. C. Love, S. J. Knabel, and B. M. Jayarao.  2007.  Antimicrobial-resistant enteric bacteria from dairy cattle.   Appl. Environ. Microbiology 73:156-163. 

 13.  Hayman, M. M., R. C. Anantheswaran and S. J. Knabel.  2007.  The effects of growth temperature and growth phase on the inactivation of Listeria monocytogenes in whole milk subject to high pressure processing.  Inter. J. Food Microbiol. 115-220-226. 

 14.  Kouassi, G. K., R. C. Anantheswaran, S. J. Knabel, and J. D. Floros.  2007.  Effect of high-pressure processing on activity and structure of alkaline phosphatase and lactate dehydrogenase in buffer and milk.  J. Agric. Food Chem. 55:9520-9529.

 15.  Hayman, M. M., G. K. Kouassi, R. C. Anantheswaran, J. D. Floros and S. J. Knabel.  2008.  Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing.  Int. J. Food Microbiol. 10:21-26.

 16.  Hayman, M. M., R. C. Anantheswaran, and S. J. Knabel.  2008.  Heat shock induces barotolerance in Listeria monocytogenes.  J. Food Prot. 71: 426-430.

 17.  Chen, Y. and S. J. Knabel.  2008.  Prophages in Listeria monocytogenes contain single nucleotide polymorphisms that differentiate outbreak clones within epidemic clones.  J. Clin. Microbiol. 46:1478-1484.

 18.  Chen, Y. and S. J. Knabel.  2008.  Strain Typing.  In Handbook of Listeria monocytogenes, Dongyou Liu (Ed.), CRC Press, New York.

 19.  Lomonaco, S., Y. Chen and S. J. Knabel.  2008.  Analysis of additional virulence genes and gene regions in Listeria monocytogenes confirms the epidemiological relevance of multi-virulence-locus sequence typing.  J. Food Prot. 71(12):2559-2566.

 20.  Wen, J., R. Anantheswaran and S. J. Knabel.  2009.  Changes in barotolerance, thermotolerance and cellular morphology throughout the life cycle of Listeria monocytogenes.  Appl. Environ. Microbiol. 75:1581-1588.

 21.  Liu, K, S. J. Knabel, and E. G. Dudley.  2009.  Rearrangement hot spot (rhs) genes are potential markers for multilocus sequence typing of Escherichia coli O157:H7.  Appl. Environ. Microbiol. 75:5853-5862.

 22.  Floros, J. D., et al. 2010.  Feeding the world today and tomorrow: The importance of food science and technology.  Comprehensive Reviews in Food Science and Food Safety 9:573-599.

 23.  NACMCF New Technologies Subcommittee (includes S. J. Knabel).  2010.  Response to the questions posed by the Food Safety and Inspection Service regarding determination of the most appropriate technologies to adopt for FSIS routine and baseline microbiological analysis.  J. Food Prot. 61:1075-1086.

 24.  Chen, Y. and S. J. Knabel.  2011.  Molecular Epidemiology of Foodborne Pathogens.  In, Genomics of Foodborne Pathogens, W. Zhang and M. Weidmann (eds.), Springer, N.Y., USA.

 25.  Verghese, B., M. Lok, J. Wen, V. Alessandria, Y. Chen, S. Kathariou and S. J. Knabel. 2011.  comK prophage junction fragments as markers for Listeria monocytogenes genotypes unique to individual meat and poultry processing plants and a model for rapid niche-specific adaptation, biofilm formation and persistence.  Appl. Environ. Microbiol. 77:3279-3292.

 26.  Liu F, R. Barrangou, P. Gerner-Smidt, E. M. Ribot, S. J. Knabel, and E. G. Dudley. 2011. Novel virulence gene and clustered regularly interspaced short palindromic repeat (CRISPR) multilocus sequence typing scheme for subtyping of the major serovars of Salmonella enterica subsp. enterica. Appl. Environ. Microbiol. 77:1946-1956.

 27.  Liu, F., S. Kariyawasam, B. M. Jayarao, R. Barrangou, P. Gerner-Smidt, E. M. Ribot, S. J. Knabel, E. G. Dudley. 2011. Subtyping Salmonella serovar Enteritidis isolates from different sources using sequence typing based on virulence genes and CRISPRs. Appl. Environ. Microbiol. 77:4520-4526.

 28.  Schwalm, N., B. Verghese, and S. J. Knabel.  2011.  A novel multiplex PCR protocol for detection and differentiation of the major clonal complexes of methicillin-resistant Staphylococcus aureus.  J. Microbiol. Methods. 86:379-382

 29.  Lomonaco, S., S. J. Knabel, A. Dalmasso, T. Civera, and M. T. Bottero.  2011.  A novel multiplex SNP-based method for identifying the epidemic clones of Listeria monocytogenes. Appl. Environ. Microbiol. 77:6290-6294.

 30. Wen, J., X. Deng, Z. Li, E. G. Dudley, R. C. Anantheswaran, S. J. Knabel and W. Zhang.  2011.  Transcriptomic response of Listeria monocytogenes during transition into the long-term-survival phase. Appl. Environ. Microbiol. 77:5966-72.

 31.  Knabel, S. J., A. Reimer, B. Verhese, M. Lok, J. Ziegler, J. Farber, F. Pagotto, M. Graham, C. A. Nadon, the Canadian Public Health Laboratory Network (CPHLN) and M. W. Gilmour.  2012.  Sequence typing confirms that a predominant Listeria monocytogenes clone caused human listeriosis cases and outbreaks in Canada from 1988-2010.  J. Clin. Microbiol. (published online ahead of print).

 32.  Verghese, B. and S. J. Knabel.  2012.  Multi-virulence-locus sequence typing of methicillin-resistant Staphylococcus aureus (MRSA) isolates from a Pennsylvania healthcare facility reveals genetic diversity that may enhance our understanding of its epidemiology.  Infection, genetics and evolution (in preparation).

 33.  Lomonaco, S., B. Verghese, P. Gerner-Smidt, C. Tarr, L. Katz, M. Berrang, R. Meinersmann, Y. Chen, E. Brown and S. J. Knabel.  2012.  Molecular characterization of Listeria monocytogenes isolates from the recent U.S. listeriosis outbreak linked to cantaloupe provides evidence for one novel outbreak strain and two novel epidemic clones.  New England Journal of Medicine (in preparation).

 Selected Funding Sources:

Grant on Milk Safety Program, Pennsylvania Department of Agriculture Research

Grant Program, Various Food Industry Grants