About

Dr. Ahmed Yousef earned his Ph.D. in Food Science from the University of Wisconsin-Madison and worked as a postdoctoral researcher there before joining Ohio State University as an Assistant Professor in 1991. Since his appointment, he has focused on searching for natural alternatives to synthetic food preservatives. His team discovered potent antimicrobial agents produced by beneficial bacteria, which are suitable for applications in food preservation. Since the late 1990s, Dr. Yousef and his research team have developed methods to pasteurize shell eggs and decontaminate fresh produce while maintaining their fresh qualities. His breakthrough involves using a combination of mild heat and pressurized ozone to pasteurize shell eggs, effectively eliminating Salmonella and other pathogens inside raw eggs. His ozone research has also led to methods for decontaminating spinach, apples, and other fresh produce. As a result, he established the largest ozone research laboratory in the U.S. at Ohio State. Due to his expertise in food safety, Dr. Yousef frequently appears in media to discuss issues related to foodborne disease outbreaks and product recalls. His area of expertise includes food microbiology, focusing on decontamination of food with gaseous sanitizers, discovery of novel antimicrobial preservatives, and ensuring the safety of food processed by emerging technology.

Research topics

• Microbiology
• Biology
• Molecular biology
• Food science
• Genetics
• Chemistry
• Materials science
• Biochemistry
• Nanotechnology

Selected publications

• Draft genome of <i>Streptomyces globosus</i> OSY-MM, a broad-spectrum antimicrobial producer isolated from a cave in South Central Kentucky

  Microbiology Resource Announcements · 2026-05-18

  articleOpen accessSenior author

  ABSTRACT Streptomyces globosus OSY-MM was originally isolated from a soil sample collected from a cave in South Central Kentucky and was found to display strong, broad-spectrum antimicrobial activity. S. globosus OSY-MM has a 7,277,920 bp genome with 6,476 genes, including biosynthetic gene clusters encoding the production of streptothricin, kirromycin, and venezuelin-like antibiotics.

  PublisherDOI

• Synergistic inactivation of Clostridium sporogenes PA 3679 spores by pressure-assisted thermal processing and cationic antimicrobials in a low-acid food matrix

  Food Control · 2026-04-19

  articleOpen access

  The high processing resistance of spores formed by Clostridium botulinum and its surrogate C. sporogenes PA 3679, presents a major challenge to food safety of low-acid foods. This study investigated the inactivation of C. sporogenes spores in carrot puree by pressure-assisted thermal processing (PATP; 600 MPa, 105 °C, 10 min), applied alone or in combination with cationic antimicrobials: chitosan (10 mg/mL), epsilon polylysine (0.2 mg/mL), and lauric arginate (0.2 mg/mL), followed by microbial stability evaluation during storage at 23 °C for 35 days. Additionally, spore response in HEPES buffer was evaluated after pressure-only (600 MPa, 27 °C, 10 min) and PATP treatment. Survivors were enumerated by the 3-tube most probable number method. PATP treatment resulted in a 4-log reduction of spores in carrot puree but allowed a 1-log increase during storage. Adding chitosan achieved a 6.5-log reduction, while incorporation of epsilon polylysine or lauric arginate achieved >6.5-log reduction, maintaining the spore population below detection levels (<0.48 Log MPN/ml) throughout storage. In buffer, pressure-only treatment was ineffective, whereas PATP yielded a 5.7-log reduction without recovery, highlighting nutrient availability as one critical factor in post-treatment spore recovery. Zeta potential results revealed that PATP increased surface charge of both the antimicrobials and spores, suggesting electrostatic interactions that may lead to spore death. The study demonstrates that PATP, in combination with these cationic antimicrobials, acts as an effective hurdle, providing both sporicidal activity during treatment and sporostatic effects during storage, thereby enhancing the safety and shelf-stability of a low-acid food like carrot puree. • PATP (600 MPa, 105 °C, 10 min) inactivated C. sporogenes PA 3679 spores. • Combined with cationic antimicrobials, PATP showed strong sporocidal effects. • Carrot puree stayed stable for 35 days at 23 °C after PATP and antimicrobial use. • Zeta potential shifts were linked to the extent of spore inactivation. • PATP with antimicrobials offers an effective hurdle against bacterial spores.

  PublisherDOI

• Data from: Combined effect of mechanical shear and moderate electric field on the inactivation of pathogenic bacteria in fresh orange juice

  Ag Data Commons · 2026-03-11

  datasetOpen access

  In response to the growing consumer demand for fresh-like products, the food and beverage industries are increasingly exploring innovative nonthermal technologies to effectively inactivate pathogenic bacteria while preserving product quality. Recently, we have examined the combined application of rotational shear stress and moderate electric fields (SS+MEF) to inactivate non-pathogenic microorganisms, including <i>Escherichia coli</i> K12 and <i>Listeria innocua</i>, under ambient temperature conditions. However, the effectiveness of SS+MEF treatments for inactivating pathogenic microorganisms in real food matrices remains largely unexplored. In this study, we investigated the inactivation of the pathogenic microorganisms <i>Escherichia coli</i> O157:H7, <i>Salmonella </i>Typhimurium, and <i>Listeria monocytogenes</i> in fresh orange juice with 5% pulp using simultaneous SS+MEF treatments under varying temperature conditions. Freshly squeezed orange juice samples were inoculated with bacteria and subjected to treatment using laboratory-scale batch shear-MEF device, and bacterial inactivation kinetics were analyzed through periodic sampling over a 30-minute treatment duration. A 5-log reduction in the pathogenic microorganism <i>E. coli</i> O157:H7 was achieved within 5 minutes of treatment at 45°C, while the same reduction was observed at 10 minutes for <i>S.</i> Typhimurium and <i>L. monocytogenes</i> at 55°C. The combined (SS+MEF) approach exhibited a significant advantage over conventional thermal pasteurization methods (70-80°C) for fruit and vegetable juices. These findings offer valuable insights for the food industry, which is increasingly seeking nonthermal alternatives for the effective inactivation of pathogenic microorganisms.

  PublisherDOI

• Ozone and non-thermal plasma as sustainable alternatives to chlorine for decontamination of alfalfa seeds and sprouts

  Food Research International · 2026-03-11

  articleOpen accessSenior author

  CFU/g) inoculum, and treated with aqueous ozone (5 ppm), non-thermal plasma (NTP; dry or in water mist), or calcium hypochlorite (20,000 ppm) for ≤15 min. At the high STEC inoculum, modest and comparable inactivation (1.1-1.7 log CFU/g reduction; p > 0.05) resulted from the 15-min treatments. In comparison, larger STEC inactivation (1.6-3.7 log CFU/g reduction) was observed at the lower inoculum, but inactivation magnitude depended on the antimicrobial treatment. Freshly prepared sprouts were similarly inoculated and treated for ≤15 min with aqueous ozone (5 ppm), NTP (dry or in mist), or calcium hypochlorite (50 ppm). The mild 2-min treatments were more effective at low (1.0-3.2 log CFU/g reduction) than at high (0.5-1.6 log CFU/g reduction) inoculum. None of these treatments adversely affected the quality of seeds or sprouts (p > 0.05). In conclusion, ozone, NTP, and chlorine reduced high STEC contamination on alfalfa seeds and sprouts to comparable levels, but chlorine outperformed ozone and NTP when the products received low STEC inocula before treatment. The expected minimal environmental and health impact of these chlorine-alternative technologies favors their future use, provided they are successfully optimized and validated at large-scale before implementation.

  PublisherDOI

• Data from: Combined effect of mechanical shear and moderate electric field on the inactivation of pathogenic bacteria in fresh orange juice

  Ag Data Commons · 2026-03-11

  datasetOpen access

  In response to the growing consumer demand for fresh-like products, the food and beverage industries are increasingly exploring innovative nonthermal technologies to effectively inactivate pathogenic bacteria while preserving product quality. Recently, we have examined the combined application of rotational shear stress and moderate electric fields (SS+MEF) to inactivate non-pathogenic microorganisms, including <i>Escherichia coli</i> K12 and <i>Listeria innocua</i>, under ambient temperature conditions. However, the effectiveness of SS+MEF treatments for inactivating pathogenic microorganisms in real food matrices remains largely unexplored. In this study, we investigated the inactivation of the pathogenic microorganisms <i>Escherichia coli</i> O157:H7, <i>Salmonella </i>Typhimurium, and <i>Listeria monocytogenes</i> in fresh orange juice with 5% pulp using simultaneous SS+MEF treatments under varying temperature conditions. Freshly squeezed orange juice samples were inoculated with bacteria and subjected to treatment using laboratory-scale batch shear-MEF device, and bacterial inactivation kinetics were analyzed through periodic sampling over a 30-minute treatment duration. A 5-log reduction in the pathogenic microorganism <i>E. coli</i> O157:H7 was achieved within 5 minutes of treatment at 45°C, while the same reduction was observed at 10 minutes for <i>S.</i> Typhimurium and <i>L. monocytogenes</i> at 55°C. The combined (SS+MEF) approach exhibited a significant advantage over conventional thermal pasteurization methods (70-80°C) for fruit and vegetable juices. These findings offer valuable insights for the food industry, which is increasingly seeking nonthermal alternatives for the effective inactivation of pathogenic microorganisms.

  PublisherDOI

• Ozone degradation of structurally distinct pesticides: A non-linear kinetic modeling approach

  The Science of The Total Environment · 2025-09-22 · 2 citations

  articleOpen accessSenior authorCorresponding

  The study was initiated to characterize the degradation of four pesticides, which target different pest categories, by aqueous ozone and to define their degradation kinetics. Pesticide's degradation was quantified using liquid chromatographic-mass spectrometric technique and residual level served as models' dependent variable. Applied ozone dose, measured as concentration–time ( Ct , min·mg/L) values, served as the independent variable. Ozone degraded the pesticides at different efficiencies, which were elucidated by data modeling. The first-order reaction kinetic model was inadequate for all tested compounds ( R 2 , 0.1355–0.7413). Degradation kinetics of the fungicide, prochloraz, and the neonicotinoid insecticide, acetamiprid, were best described by the exponential decay model, where the rate constant, k , was 16.1 and 25.1, respectively. Notably, the offset parameter for acetamiprid kinetic model was 0.497, indicating a substantial fraction of the pesticide remaining undegraded even after prolonged exposure to ozone. Degradation of the organophosphorus insecticide, chlorpyrifos-methyl, was best fitted using an exponential-linear combination model, characterized by a dominant exponential decay with a small linear contribution. Degradation of the acaricide, fenbutatin oxide, followed Weibull decay model, indicating an initial lag before the onset of rapid degradation. Ozone Ct values for 50 % pesticides degradation (Ct 50 ), derived from best-fit non-linear kinetic models, were 0.045, 0.601, and 2.79 min·mg/L for prochloraz, chlorpyrifos-methyl, and fenbutatin oxide, respectively. These findings suggest that (i) ozone may be effective against pesticide residue in water and food, (ii) ozone efficacy depends on the structure of the pesticide, and (iii) compound-specific kinetic models for ozone-based pesticide residue removal need to be developed. • Aqueous ozone was tested against a fungicide, 2 insecticides, and an acaricide. • Pesticide degradation kinetics were best described using non-linear modeling. • Ozone dose for 50 % pesticide degradation (Ct 50 ) ranged from 0.045 to 2.79 min·mg/L.

  PublisherDOI

• Enhancing the destruction of Burkholderia cepacia biofilm on stainless steel coupons by combining matrix-degrading enzymes with antimicrobials

  Frontiers in Cellular and Infection Microbiology · 2025-11-10 · 3 citations

  articleOpen accessSenior authorCorresponding

  Burkholderia cepacia is an underexplored opportunistic pathogen and a food spoilage species. The bacterium may serve as an ideal model for biofilm formation and resilience. Herein, we explored the possibility of enhancing the destruction of preformed B. cepacia biofilm by combining enzymes (amylase, DNase, and protease) that potentially degrade biofilm matrices with diverse antimicrobials. Initially, the biofilm-forming ability of B. cepacia ATCC 25416 was assessed in two microbiological media. A nutrient-rich broth favored planktonic cell proliferation, whereas a nutrient-limited medium supported robust biofilm formation. The minimum inhibitory concentration (MIC) of the tested antimicrobials against planktonic cells (MIC-Plank) was determined. Ciprofloxacin and meropenem gave the smallest MIC-Plank of 4.0 and 8.0 μg/mL, respectively. The MIC of the two antimicrobials, when applied against preformed biofilm (MIC-Bio), increased to 16 μg/mL. Enzyme-antimicrobial combinations decreased the MIC-Bio of the antimicrobials to 4.0–8.0 μg/mL in a synergistic or additive manner, as measured by the fractional inhibitory concentration index (FICI). Among the tested combinations, α-amylase-ciprofloxacin exhibited a synergistic effect (FICI = 0.50), proteinase K-ciprofloxacin (FICI = 0.625), and α-amylase-meropenem (FICI = 0.750) showed an additive effect against B. cepacia biofilms. These combinations, at their MIC-Bio, were applied to preformed biofilms on stainless-steel coupons. Application of α-amylase, ciprofloxacin, and their combination significantly decreased ( p &amp;lt; 0.0001) the biofilm populations from 8.4 ± 0.2 (untreated coupons) to 6.03 ± 0.2, 5.3 ± 0.3, and 4.5 ± 0.4 log 10 CFU/coupon, respectively. Similarly, α-amylase, meropenem, and their combination significantly decreased ( p &amp;lt; 0.0001) the biofilm populations from 7.5 ± 0.5 (untreated coupons) to 5.8 ± 0.1, 5.6 ± 0.1, and 3.8 ± 1.0 log 10 CFU/coupon, respectively. These findings were confirmed when biofilms formed on stainless-steel coupons were examined through scanning electron microscopy. It is predicted that antimicrobial concentrations higher than MIC-Bio in the treatment combinations would eliminate residual biofilm on the coupons, but this needs to be studied. To conclude, enzyme-antimicrobial combinations offer a promising biofilm control strategy by mitigating B. cepacia preformed biofilm and minimizing risks associated with this potentially hazardous and spoilage bacterium. Such a strategy could be implemented in processing environments when food-grade antimicrobial additives are used instead of the currently tested antimicrobials.

  PublisherOA PDFDOI

• One-Health Approach to Determine and Tackle Antimicrobial Resistance in the Human Dairy Interface: A Case of Non-Typhoidal Salmonella and Lactose-Fermenting Enterobacteriaceae

  Journal of Clinical Medicine and Regenerative Medicine · 2025-08-31

  articleOpen access

  Background Antimicrobial resistance (AMR) is among the top public health concerns globally. Determining the susceptibility pattern of pathogens is important in designing strategies to combat AMR. Thus, this study was designed to determine the AMR pattern of non-typhoidal Salmonella (NTS) and lactose fermenting Enterobacteriaceae (LFE) isolated from the human-dairy interface in the northwestern part of Ethiopia, where such information is lacking. Methods The study analysed 362 samples collected from humans, animals, food (milk) and the environment (sewage). The bacteria were isolated from the samples using standardized bacteriological methods. The antimicrobial susceptibility patterns and extended-spectrum beta-lactamase (ESBL) production ability were screened and confirmed by using the Kirby-Bauer disk diffusion method. The isolates were further characterized genotypically using multiplex polymerase chain reaction targeting the three ESBL-encoding genes. Results A total of 28 and 375 NTS and LFE bacterial isolates were identified. Isolates were more resistant to ampicillin and tetracycline. Forty-six point four and 70.7% of NTS and LFE were multidrug resistant (MDR), respectively. None of NTS and 21.3% of LFE were ESBL-producing. Genotypically, the majority of the isolates (97.5%), which were positive on the phenotypic test, were carrying one or more ESBL encoding genes. In conclusion, a high proportion of the bacterial isolates were resistant to commonly used antimicrobials, MDR, and were positive for ESBL production. Conclusion The findings provide evidence that the human-dairy interface is one of the important reservoirs of AMR traits and intervention points to reduce AMR. Therefore, the implementation of AMR mitigation strategies in a one-health approach is highly needed in the area.

  PublisherDOI

• Ozone Basics and Applications in Food Decontamination

  2025-09-19

  other1st authorCorresponding

  Ozone gas is a powerful antimicrobial agent due to its strong oxidizing potential. The gas is produced commercially from air or oxygen using the chroma discharge technology or from water using electrolysis. In various applications, ozone can be used in its gaseous state or after dissolution in water using ozone-water contacting devices. During its action against the treated organic load, including microbial contaminants, ozone molecule decomposes to oxygen, leaving no undesirable residues in the treated product. These characteristics made ozone a desirable agent for the treatment of drinking water. The interest in using ozone in the decontamination of food or in the sanitization of processing equipment and environment has been increasing steadily. Gaseous and aqueous states of ozone are usable in the decontamination of raw foods such as fresh produce, shell eggs, seafoods, and nuts. Additionally, aqueous ozone is usable in the decontamination of food and water packaging materials, food contact surfaces, and the food processing environment. Ozone not only inactivates microorganisms on raw agricultural commodities, but it may also decompose their load of hazardous chemicals such as pesticides and myotoxins. Considering the strong reactivity of ozone, its industrial implementation should be planned carefully to ensure the safety of workers in the facility.

  PublisherDOI

• Understanding human adaptation to acoustic spaces towards clinical voice application

  The Journal of the Acoustical Society of America · 2025-04-01

  articleSenior author

  Effective speech production and general human communication depend on aligning communicative intent and the environment. This presentation will review our research on how individuals perceive and adapt their voices to various communication spaces and how these environments may influence voice analysis regardless of the talkers’ perception. While our studies have primarily been motivated by understanding schoolteachers and their vocal use in classrooms, we have examined test–retest variability and general speech production variability in actual and simulated room environments. Our findings indicate subtle dependencies on moderate changes in reverberation and noise, as well as significant dependencies on more substantial acoustic alterations. Beyond speech production dependencies, we have explored the perception of room changes and the sense of vocal effort required in different scenarios. The implications extend to practical applications in architectural design, particularly for spaces like classrooms, performance venues, and healthcare settings, where vocal performance and voice quantification are more critical. By understanding the relationship between human voice and architectural acoustics, we can create environments that support vocal health and communication effectiveness. This research bridges the gap between architectural science and human behavior, advancing our understanding of how built environments shape human communication.

  PublisherDOI

Frequent coauthors

• Ahmed G. Abdelhamid

  Ohio University

  44 shared

• Sudhir K. Sastry

  The Ohio State University

  29 shared

• En Huang

  University of Arkansas for Medical Sciences

  28 shared

• Elmer H. Marth

  26 shared

• V.M. Balasubramaniam

  The Ohio State University

  20 shared

• Luis A. Rodríguez-Romo

  15 shared

• David R. Kasler

  The Ohio State University

  13 shared

• Taras Pyatkovskyy

  I.Horbachevsky Ternopil National Medical University

  13 shared

Labs

• Yousef LabPI

Education

• Ph. D., Food Science

  University of Wisconsin–Madison

  1984

Awards & honors

• Hall of Distinction Award
• Inductees Ohio State Hall of Distinction