Characterization and Antibiotic Resistance of Listeria monocytogenes Strains Isolated from Greek Myzithra Soft Whey Cheese and Related Food Processing Surfaces over Two-and-a-Half Years of Safety Monitoring in a Cheese Processing Facility

Abstract

Listeriosis is a serious infectious disease with one of the highest case fatality rates (ca. 20%) among the diseases manifested from bacterial foodborne pathogens in humans, while dairy products are often implicated as sources of human infection with Listeria monocytogenes. In this study, we characterized phenotypically and genetically by whole-genome sequencing (WGS) 54 L. monocytogenes strains isolated from Myzithra, a traditional Greek soft whey cheese (48 isolates), and swabs collected from surfaces of a cheese processing plant (six isolates) in the Epirus region of Greece. All but one strain of L. monocytogenes belonged to the polymerase chain reaction (PCR) serogroups IIa (16.7%) and IIb (81.5%), corresponding to serotypes 1/2a, 3a and 1/2b, 3b, 7, respectively. The latter was identified as a PCR-serogroup IVb strain (1.8%) of serotypes 4b, 4d, 4e. Bioinformatics analysis revealed the presence of five sequence types (STs) and clonal complexes (CCs); ST1, ST3, ST121, ST 155, ST398 and CC1, CC3, CC121, CC155, CC398 were thus detected in 1.9, 83.3, 11.0, 1.9, and 1.9% of the L. monocytogenes isolates, respectively. Antibiograms of the pathogen against a panel of seven selected antibiotics (erythromycin, tetracycline, benzylpenicillin, trimethoprim-sulfamethoxazole, ampicillin, ciprofloxacin, and meropenem) showed that 50 strains (92.6%), the six surface isolates also included, were intermediately resistant to ciprofloxacin and susceptible to the rest of the six antimicrobial agents tested, whereas strong resistance against the use of a single from three implicated antibiotics was recorded to four strains (7.4%) of the pathogen isolated from Myzithra cheese samples. Thence, the minimum inhibitory concentrations (MICs) were determined for erythromycin (MIC = 0.19 μg/mL), ciprofloxacin (MIC ≥ 0.19 μg/mL), and meropenem (MIC = 0.64 μg/mL), and finally, just one strain was deemed resistant to the latter antibiotic. The phylogenetic positions of the L. monocytogenes strains and their genetic variability were determined through WGS, whilst also stress response and virulence gene analysis for the isolates was conducted. Findings of this work should be useful as they could be utilized for epidemiological investigations of L. monocytogenes in the food processing environment, revealing possible contamination scenarios, and acquired antimicrobial resistance along the food production chain.

Listeria monocytogenes from Marine Fish and the Seafood Market Environment in Northern Greece: Prevalence, Molecular Characterization, and Antibiotic Resistance

“…Similarly, Angelidis et al [29] report that among six strains isolated from bulk milk tanks, all were resistant to penicillin and clindamycin, whereas no strain was characterized as being resistant to vancomycin. The resistance profiles of the present study are distinct from the ones reported by Andritsos and Mataragas [57] and Angelidis et al [29], which implies that the fish production chain is more susceptible to antibiotic-resistant Listeria monocytogenes strains; still, more research is needed on this topic. Although the rates of multidrug-resistant Listeria monocytogenes foodborne strains are low, there appears to be a significant increase in the emergence of resistant Listeria monocytogenes strains from food and its processing environment, which necessitates vigilance [55].…”

“…Antibiotic resistance profiles of foodborne Listeria monocytogenes strains from the same area have been reported in different food commodities. Specifically, Andritsos and Mataragas [57] reported that 92.6% of the strains isolated from cheese showed intermediate resistance to ciprofloxacin and 7.4% showed resistance to erythromycin, ciprofloxacin, or meropenem. Similarly, Angelidis et al [29] report that among six strains isolated from bulk milk tanks, all were resistant to penicillin and clindamycin, whereas no strain was characterized as being resistant to vancomycin.…”

Recurring food source‐based Listeria outbreaks in the United States: An unsolved puzzle of concern?

“…Hypervirulent L. monocytogenes strains with an ability to infect respiratory system (the lungs) was reported recently in a coronavirus disease‐19 (COVID‐19) pandemic patient 25 . The whole genome sequencing (WGS) of L. monocytogenes isolated from cheese revealed that it was resistant to antimicrobials (AMR) like ciprofloxacin and meropenem, assumed to have acquired along the food chain 26 …”

“… 25 The whole genome sequencing (WGS) of L. monocytogenes isolated from cheese revealed that it was resistant to antimicrobials (AMR) like ciprofloxacin and meropenem, assumed to have acquired along the food chain. 26 …”

Prevalence, Serotypes, Antimicrobial Resistance and Biofilm-Forming Ability of Listeria monocytogenes Isolated from Bulk-Tank Bovine Milk in Northern Greece

“…The Listeria spp.-specific marker prs was detected in all L. monocytogenes isolates. In Greece, a limited number of studies have provided characterization data (serotypic and genotypic diversity, carriage of virulence genes, antibiotic resistance or biofilm-forming ability) of L. monocytogenes strains isolated from different sources such as meat, meat products, meat-processing environment and vegetables [42,43], soft whey-cheese and related food-processing surfaces [44], veterinary samples and raw ovine milk [19] or human clinical cases [45]. However, to our knowledge, data on L. monocytogenes isolates from bovine milk in Greece are not available.…”