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:

Teo, Y.-L. and S. J. Knabel. 2000. Development of a Simple Recovery-Enrichment System for Enhanced Detection of Heat-Injured Listeria monocytogenes in Pasteurized Milk. J. Food Prot. 63:441-444.

Suh, J.-H., and S. J. Knabel. 2000. Comparison of different reducing agents for enhanced detection of heat-injured Listeria monocytogenes. J. Food Prot. 63:1058-1063.

Suh, J.-H, and S. J. Knabel. 2001. Comparison of different enrichment broths and background flora for detection of heat-injured Listeria monocytogenes in whole milk. J. Food Prot. 64:30-36.

Chikthimmah, N., R. B. Guyer, and S. J. Knabel. 2001. Validation of a 5-Log10 reduction of Listeria monocytogenes following simulated commercial processing of Lebanon bologna in a model system. J. Food Prot. 64:873-876.

Chikthimmah, N. and S. J. Knabel. 2001. Survival of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in and on vacuum-packaged Lebanon bologna stored at 3.6 and 13.0°C. J. Food Prot. 64:958-963.

Teo, A. Y.-L., G. R. Ziegler, and S. J. Knabel. 2001. Optimizing detection of heat-injured Listeria monocytogenes in pasteurized milk. J. Food Prot. 64:1000-1011.

Chikthimmah, N., R. Anantheswaran, R. F. Roberts, E. W. Mills and S. J. Knabel. 2001. Influence of sodium chloride on growth of lactic acid bacteria and subsequent destruction of Escherichia coli 0157:H7 during processing of Lebanon bologna. J. Food Prot. 64:1145-1150.

Chen, H., R. C. Anantheswaran, and S. J. Knabel. 2001. Optimization of iron supplementation for enhanced detection of Salmonella enteritidis in eggs. J. Food Prot. 64:1279-1285.

Knabel, S. J. 2002. Optimized one-step, recovery-enrichment broth for enhanced detection of Listeria monocytogenes in pasteurized milk and hot dogs. J. AOAC Int. 85:501-504.

Chen, H., R. C. Anantheswaran, and S. J. Knabel. 2002. Effect of rapid cooling on the growth and penetration of Salmonella Enteritidis into egg contents. J. Food Safety 22:255-271.

Kieras, S. J., E. W. Mills, S. J. Knabel, and A. N. Maretzki. 2003. Validation of pathogen destruction during manufacture of a meat-based potato snack (Chiparoo). J. Food Processing Preservation 26:385-399.

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.

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

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

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.

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., 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.

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.

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.

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.

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

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.

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

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.

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(3).

Selected Funding Sources:

Grant on Milk Safety Program, Pennsylvania Department of Agriculture Research

Grant Program, Various Food Industry Grants