title: Estimation of Listeria monocytogenes and Escherichia coli O157:H7 prevalence and levels in naturally contaminated rocket and cucumber samples by deterministic and stochastic approaches.
abstract: The aims of the present study were to determine the prevalence and levels of Listeria monocytogenes and Escherichia coli O157:H7 in rocket and cucumber samples by deterministic (estimation of a single value) and stochastic (estimation of a range of values) approaches. In parallel, the chromogenic media commonly used for the recovery of these microorganisms were evaluated and compared, and the efficiency of an enzyme-linked immunosorbent assay (ELISA)-based protocol was validated. L. monocytogenes and E. coli O157:H7 were detected and enumerated using agar Listeria according to Ottaviani and Agosti plus RAPID' L. mono medium and Fluorocult plus sorbitol MacConkey medium with cefixime and tellurite in parallel, respectively. Identity was confirmed with biochemical and molecular tests and the ELISA. Performance indices of the media and the prevalence of both pathogens were estimated using Bayesian inference. In rocket, prevalence of both L. monocytogenes and E. coli O157:H7 was estimated at 7% (7 of 100 samples). In cucumber, prevalence was 6% (6 of 100 samples) and 3% (3 of 100 samples) for L. monocytogenes and E. coli O157:H7, respectively. The levels derived from the presence-absence data using Bayesian modeling were estimated at 0.12 CFU/25 g (0.06 to 0.20) and 0.09 CFU/25 g (0.04 to 0.170) for L. monocytogenes in rocket and cucumber samples, respectively. The corresponding values for E. coli O157:H7 were 0.59 CFU/25 g (0.43 to 0.78) and 1.78 CFU/25 g (1.38 to 2.24), respectively. The sensitivity and specificity of the culture media differed for rocket and cucumber samples. The ELISA technique had a high level of cross-reactivity. Parallel testing with at least two culture media was required to achieve a reliable result for L. monocytogenes or E. coli O157:H7 prevalence in rocket and cucumber samples.
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece. agni_xatz@aua.gr.
authors.forename: Agni
authors.initials: A
authors.lastname: Hadjilouka
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece.
authors.forename: Kyriaki-Sofia
authors.initials: KS
authors.lastname: Mantzourani
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Katsarou
authors.affiliation: Department of Agricultural and Environmental Sciences, Università degli Studi di Milano, via Celoria 2, 20133 Milano, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Cavaiuolo
authors.affiliation: Department of Agricultural and Environmental Sciences, Università degli Studi di Milano, via Celoria 2, 20133 Milano, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Ferrante
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece.
authors.forename: Spiros
authors.initials: S
authors.lastname: Paramithiotis
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece.
authors.forename: Marios
authors.initials: M
authors.lastname: Mataragas
authors.affiliation: Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, GR-118 55 Athens, Greece.
authors.forename: Eleftherios H
authors.initials: EH
authors.lastname: Drosinos
mesh_terms: D001499:Bayes Theorem; D001937:Brassica / Q000382:microbiology*; D015169:Colony Count, Microbial; D018553:Cucumis sativus / Q000382:microbiology*; D003470:Culture Media / Q000737:chemistry; D004797:Enzyme-Linked Immunosorbent Assay; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000302:isolation & purification*; D012680:Sensitivity and Specificity
chemical_list: D003470:Culture Media