Related Experiment Video
Updated: Feb 26, 2026
Evaluation of Microbial Safety of Dairies using Bacterial Proteomic Profiling via MALDI Approach
Published on: October 7, 2025
Listeria monocytogenes in raw milk, milking equipment and dairy workers: Molecular characterization and antimicrobial
Asmaa B M B Tahoun1, Rasha M M Abou Elez2, Eman N Abdelfatah1
1Department of Food Control, Faculty of Veterinary Medicine, Zagazig University, Zagazig City 44511, Sharkia, Egypt.
Objectives:
The aim of this study was to evaluate the genetic relatedness and patterns of antimicrobial resistance amongst L. monocytogenes isolated from raw milk, milking equipment, and hand swabs from workers in dairy farms.
Methods:
A total of 300 samples of raw milk, milking equipment, and hand swabs were collected from four dairy farms to examine the presence of Listeria species. Suspected isolates were further identified by VITEK-2 system and Polymerase Chain Reaction (PCR). Antimicrobial susceptibility of the L. monocytogenes isolates was determined, and genotyping analysis was performed by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR).
Results:
Listeria spp. was isolated from 79 (26.3%) of the 300 samples, including 29 (36.7%), 32 (40.5%), and 18 (22.8%) isolates found in raw milk, milking equipment, and hand swabs, respectively. L. monocytogenes was the most common isolated (87.3%) species, while the remaining Listeria isolates were L. innocua (12.7%). Among the 69 L. monocytogenes isolates, 42 (60.8%) showed the mutual presence of hlyA, prfA, inlA, and inlB virulence-associated genes. L. monocytogenes isolates from raw milk, milking equipment, and hand swabs showed high genetic relatedness. The potentially virulent L. monocytogenes isolates were most frequently resistance to tetracycline and clindamycin (81%, each) followed by rifampicin (71.4%), whereas, antimicrobial susceptibility was most frequently observed for ampicillin, levofloxacin, moxifloxacin, linezolid, and tigecycline (100%, each). Furthermore, 88% of L. monocytogenes isolates showed multidrug-resistance.
Conclusions:
The findings of this study show that the contamination of dairy farms with L. monocytogenes is relatively high, and highlight the emergence of multi-drug resistant L. monocytogenes in dairy farms. However, ampicillin is a good choice for treatment of listeriosis in the study area.
Insights
This study found high contamination of dairy farms with multi-drug resistant Listeria monocytogenes. Ampicillin shows promise for treating listeriosis in the studied region.
Area of Science:
- Food safety and microbiology
- Veterinary public health
- Antimicrobial resistance surveillance
Background:
- Listeria monocytogenes is a significant foodborne pathogen.
- Dairy farms are potential reservoirs for L. monocytogenes.
- Understanding genetic relatedness and antimicrobial resistance is crucial for control.
Purpose of the Study:
- To assess genetic relatedness of L. monocytogenes isolates from dairy farms.
- To determine antimicrobial resistance patterns in L. monocytogenes.
- To identify sources of contamination (raw milk, equipment, workers).
Main Methods:
- Collected 300 samples (raw milk, equipment, hand swabs) from four dairy farms.
- Identified Listeria species using VITEK-2 and Polymerase Chain Reaction (PCR).
- Determined antimicrobial susceptibility and performed genotyping via ERIC-PCR.
Main Results:
- Listeria spp. found in 26.3% of samples; L. monocytogenes was the predominant species (87.3%).
- High genetic relatedness observed among L. monocytogenes isolates from different sources.
- Significant multidrug-resistance (88%) noted, particularly to tetracycline and clindamycin; high susceptibility to ampicillin.
Conclusions:
- Dairy farm environments show substantial L. monocytogenes contamination.
- Emergence of multidrug-resistant L. monocytogenes strains is a concern in dairy settings.
- Ampicillin is identified as a potentially effective treatment for listeriosis in the study area.
