Stephen J. Knabel, Ph.D.

Professor Emeritus of Food Science

407 Rodney A. Erickson Food Science Building
University Park, PA 16802

Education

Iowa State University, Microbiology and Food Technology, Ph.D., 1989
Iowa State University, Food Technology, M.S., 1986
Iowa State University, Food Technology, B.S., 1973

Reseach 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

Murugesan, L., K. Zuzana, S. J. Knabel and L. F. LaBorde. 2015. Predominance and distribution of a persistent Listeria monocytogenes clone in a commercial fresh mushroom processing environment. J. Food Prot.78:88-98.

Knabel, S. J. 2014. “Multilocus Sequence Typing: An Adaptable Tool for Understanding the Global Epidemiology of Bacterial Pathogens" in DNA Methods in Food Safety: Molecular Typing of Foodborne and Waterborne Bacterial Pathogens, O. Oyarzabal and S. Kathariou (Eds), Wiley.

Doijad, S., S. Lomonaco, K. Poharkar, S. Garg, S. Knabel, S. Barbuddhe and B. Jayarao. 2014. Multi-Virulence-Locus Sequence typing of 4b Listeria monocytogenes isolates obtained from different sources in India over a 10-year period. Appl. Environ. Microbiol. 7:511-516.

Wood, T. K., S. J. Knabel and B. W. Kwan. 2013. Bacterial persister cell formation and dormancy. Appl. Environ. Microbiol. 79:7116-7121

Wen, J., S. Karthikeyan, R. C. Anantheswaran, and S. J. Knabel. 2013. Listeria monocytogenes responds to cell density as it transitions to the long-term-survival phase. Int. J. Food Microbiol. 165:326-331.

Rocha, P. R., S. Lomonaco, M. T. Botero, A. Dalmasso, A. Dondo, C. Grattanola, F. Zuccon, B. Julini, S. J. Knabel, M. T., Caupucchio and C. Casalone. 2013. Listeria monocytogenes strains from ruminant rhombencephalitis constitute a genetically homogeneous group related to human outbreak strains. Appl. Environ. Microbiol. 79: 3059-3066.

Viswanath P, Murugesan L, Knabel SJ, Verghese B, Chikthimmah N, LaBorde LF. 2013. Incidence of Listeria monocytogenes and Listeria spp. in a small-scale mushroom production facility. Journal of Food Protection. 76(4):608-615.

NACMCF. 2013. Expedited response to the questions posed by the United States Department of Agriculture Marketing Service to support ground beef purchanse for the Federal Food and Nutrition Assistance Programs. J. Food Prot. 70:523-537.

Lomonaco, S., B. Verghese, P. Gerner-Smidt, C. Tarr, L. Katz, M. Berrang, R. Meinersmann, Y. Chen, E. Brown and S. J. Knabel. 2012. Novel epidemic clones of Listeria monocytogenes, United States, 2011. Emerg. Infect. Dis. 19:147-150.

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. 50:1748-1752.

Prema Viswanath, Bindhu Verghese, Naveen Chikthimmah, Luke Laborde and Stephen. J. Knabel. 2012. Longitudinal study of Listeria species and Listeria monocytogenes in a small-scale commercial mushroom production facility. Food Control. (accepted)

Lomonaco, S., R. Patti, S. J. Knabel and T. Civera. 2012. Detection of virulence-associated genes and epidemic clone markers in Listeria monocytogenes isolates from PDO Gorganzola cheese. Int. J. Food Microbiol. 160:76-79.

Verghese, B., N. D. Schwalm III, E. G. Dudley and S. J. Knabel. 2012. A combined multi-virulence-locus sequence typing and Staphylococcus Cassette Chromosome mec typing scheme possesses enhanced discriminatory power for subtyping MRSA. Infect. Gen. Evol. 12:1816-1821.

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).

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. 50:1748-1752.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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

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.

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

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

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.

Selected Funding Sources

Grant on Milk Safety Program, Pennsylvania Department of Agriculture Research

Grant Program, Various Food Industry Grants