Microbiologist — Division of Microbiology

Ashraf Khan, Ph.D.
(870) 543-7121
NCTRResearch@fda.hhs.gov  

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 About  |  Publications  |  Lab Member

Background

Dr. Ashraf Khan received his Master of Science in philosophy and Ph.D. in biochemistry from the Central Drug Research Institute, Lucknow, India in 1987. Following this, Dr. Khan completed a postdoctoral fellowship at Oakland University from 1987-1992. In 1992, Dr. Khan joined the Division of Microbiology at NCTR as a research microbiologist and since then he has been working on projects in food safety, antimicrobial-resistance mechanism, method development, environmental biotechnology, and microbial genetics of foodborne pathogens. Dr. Khan has authored more than 91 peer-reviewed papers and book chapters, and he is also a reviewer for several peer-reviewed journals.
 

Research Interests

Dr. Khan’s research is focused on understanding the role of cytolethal distending toxins (CDT) in non-typhyoidal Salmonella enterica (NTS). His laboratory has identified three genes cdtB, pltA, and pltB which encodes CDT from several food and clinical NTS isolates. Nucleotide sequence analysis of these genes (cdtB, pltA, and pltB) showed 100% similarity with Salmonella Typhi cdtB, pltA, and pltB genes. To elucidate the roles of CdtB, PltA, and PltB in NTS, his laboratory has constructed deletion mutants of CDT in NTS. Some of his preliminary results have shown that in vitro cultured HeLa cell lines infected with a wild type strain caused cytolethal distending intoxication, including cell cycle arrest, cytoplasmic distension, and nuclear enlargement of host target cells. Salmonella infection is one of the major foodborne illnesses in the United States. Several gram-negative bacterial pathogens, including Salmonella Typhi, produce CDT, which arrests growth, induces apoptosis of infected host cells, and extends persistence of pathogenic bacteria in the host. Nontyphoidal Salmonella serovars are important food pathogens that can lead to an infection causing mild and self-limiting diarrhea in both humans and animals. CDT, a conserved virulence factor in S. Typhi, is known to transfer horizontally between bacterial species, thus presenting a health risk. Dr. Khan’s other research projects include:

• The function efflux pump genes and its regulation in multidrug resistant Salmonella enterica and E. coli;
• Whole genome sequencing of multidrug resistant Salmonella spp. isolated from imported foods
• Characterization of enterotoxigenic Bacillus cereus from dietary supplements. 
   

Professional Societies Membership

American Society for Microbiology
Member
1988 — Present
 

Selected Publications

Draft Genome Sequences of Ciprofloxacin-Resistant Salmonella enterica Strains with Multiple-Antibiotic Resistance, Isolated from Imported Foods.
Khan A.A., Khajanchi B.K., Khan S.A., Elkins C.A., and Foley S.L.
Genome Announc. 2017, 5(45).
 

Isolation and Characterization of Antimicrobial-Resistant Nontyphoidal Salmonella enterica Serovars from Imported Food Products.
Bae D., Kweon O., and Khan A.A.
J Food Prot. 2016, 79(8):1348-54.
 

Characterization of Extended-Spectrum Beta-Lactamase (ESBL) Producing Non-Typhoidal Salmonella (NTS) from Imported Food Products.
Bae D., Cheng C., and Khan A.
Int J Food Microbiol. 2015, 214:12-7.
 

Detection and Functionality of the CdtB, PltA, and PltB from Salmonella Enterica Serovar Javiana.
Mezal E., Bae D., and Khan A.
Pathog Dis. 2014, 72(2):95-103.
 

The Sub-Species Characterization and Antimicrobial Resistance of Listeria Monocytogenes Isolated from Domestic and Imported Food Products from 2004 to 2011.
Bae D., Mezal E., Smiley R., Cheng C., and Khan A.
Food Res Int. 2014, 64;656-63.
 

Isolation and Molecular Characterization of Salmonella Enterica Serovar Enteritidis from Poultry House and Clinical Samples During 2010.
Mezal E., Sabol A., Khan M., Ali N., Stefanova R., and Khan A.
Food Microbiol. 2014, 38;67-74.
 

The tetA Gene Decreases Tigecycline Sensitivity of Salmonella Enterica Isolates.
Akiyama T., Presedo J., and Khan A.
Int J Antimicrob Agents. 2013, 42(2):133-40.
 

Isolation and Molecular Characterization of Salmonella Enterica Serovar Javiana from Food, Environmental and Clinical Samples.
Mezal E., Stefanova R., and Khan A.
Int J Food Microbiol. 2013, 164(1):113-8.
 

Identification and Molecular Characterization of Class 1 Integrons in Multiresistant Escherichia Coli Isolates from Poultry Litter.
Ponce-Rivas E., Munoz-Marquez M., and Khan A.
Appl Environ Microbiol. 2012, 78(15):5444-7.
 

Isolation and Characterization of Small qnrS1-Carrying Plasmids from Imported Seafood Isolates of Salmonella Enterica that are Highly Similar to Plasmids of Clinical Isolates.
Akiyama T. and Khan A.
FEMS Immunol Med Microbiol. 2012 Apr, 64(3):429-32.
 

Molecular Characterization of Strains of Fluoroquinolone-Resistant Salmonella Enterica Serovar Schwarzengrund Carrying Multidrug Resistance Isolated from Imported Foods.
Akiyama T. and Khan A.
J Antimicrob Chemother. 2012, 67(1):101-10.
 

Molecular Characterization of Salmonella Enterica Serovar Saintpaul Isolated from Imported Seafood, Pepper, Environmental and Clinical Samples.
Akiyama T., Khan A., Cheng C., and Stefanova R.
Food Microbiol. 2011, 28(6):1124-8.
 

Identification and Characterization of Class 1 Integron Resistance Gene Cassettes Among Salmonella Strains Isolated from Imported Seafood.
Khan A., Ponce E., Nawaz M., Cheng C., Khan J., and West C.
Appl Environ Microbiol. 2009, 75(4):1192-6.
 

Prevalence and Characterization of Salmonella Enterica Serovar Weltevreden from Imported Seafood.
Ponce E., Khan A., Cheng C., Summage-West C., and Cerniglia C.
Food Microbiol. 2008, 25(1):29-35.
 

Identification and Molecular Characterization of Salmonella spp. from Unpasteurized Orange Juices and Identification of New Serotype Salmonella Strain S. enterica Serovar Tempe.
Khan A., Melvin C., and Dagdag E.
Food Microbiol. 2007, 24(5):539-43.
 

Occurrence of Non-O157 Shiga Toxin-Producing Escherichia Coli in Ready-To-Eat Food from Supermarkets in Argentina.
Balague C., Khan A., Fernandez L., Redolfi A., Aquili V., Voltattorni P., Hofer C., Ebner G., Duenas S., and Cerniglia C.
Food Microbiol. 2006, 23(3):307-13.
 

Novel Organization of Genes in a Phthalate Degradation Operon of Mycobacterium Vanbaalenii PYR-1.
Stingley R., Brezna B., Khan A., and Cerniglia C.
Microbiology. 2004, 150(Pt 11):3749-61.
 

Classification of a Polycyclic Aromatic Hydrocarbon-Metabolizing Bacterium, Mycobacterium sp. Strain PYR-1, as Mycobacterium Vanbaalenii sp. nov.
Khan A., Kim S., Paine D., and Cerniglia C.
Int J Syst Evol Microbiol. 2002, 52(Pt 6):1997-2002.
 

Characterization of United States Outbreak Isolates of Vibrio Parahaemolyticus Using Enterobacterial Repetitive Intergenic Consensus (ERIC) PCR and Development of a Rapid PCR Method for Detection of O3:K6 Isolates.
Khan A., McCarthy S., Wang R., and Cerniglia C.
FEMS Microbiol Lett. 2002, 206(2):209-14.
 

Identification of Predominant Human and Animal Anaerobic Intestinal Bacterial Species by Terminal Restriction Fragment Patterns (TRFPs): a Rapid, PCR-Based Method.
Khan A., Nawaz M., Robertson L., Khan S., and Cerniglia C.
Mol Cell Probes. 2001, 15(6):349-55.
 

Detection of Multidrug-Resistant Salmonella Typhimurium DT104 by Multiplex Polymerase Chain Reaction.
Khan A., Nawaz M., Khan S., and Cerniglia C.
FEMS Microbiol Lett. 2000, 182(2):355-60.
 

Lab Member

Contact information for all lab members:
(870) 543-7121
NCTRResearch@fda.hhs.gov  

Ms. Khulud Alotaibi
Graduate Student