Full
Outline
To investigate the contamination status, molecular characteristics, virulence genes, antibiotic resistance genes and resistance profiles of Listeria monocytogenes (Lm) in foods from Baoshan City.
Whole-genome sequencing was performed on Lm strains isolated from retail foods in Baoshan. The sequences were assembled using BioNumerics 7.6 software, and their molecular characteristics were subsequently analyzed. In parallel, antimicrobial susceptibility testing was conducted on the 12 Lm strains using the broth dilution method.
A total of 229 food samples were collected and analyzed, yielding 12 Lm isolates with an overall contamination rate of 5.24%. No statistically significant difference was observed in Lm detection rates among the 5 food categories (P>0.05), although numerical variations in contamination existed across categories. Similarly, the overall contamination rates across the 5 sampling regions showed no statistically significant difference (P>0.05), despite observable variations among individual regions. The Lm isolated were classified into 2 genetic lineages:Lineage I comprised 7 strains (58.33%), and Lineage II comprised 4 strains (33.33%). One strain isolated from raw meat products remained untyped. They were classified into 3 kinds of serogroups: 1/2a-3a (4 strains, 33.33%), 1/2b-3b-7 (4 strains, 33.33%) and 4b-4d-4e (4 strains, 33.33%). The 6 sequence types (STs) were identified, with ST8(25%) being the dominant type. The isolates fell into 6 clonal complexe (CC), with CC8 (25%) as the predominant group. All isolates carried key virulence genes, with 100% harboring complete LIPI-1 and LIPI-2 gene clusters, while LIPI-3 and LIPI-4 were less frequent (2 and 3 strains, respectively). All isolates carried major resistance genes fosX, mprF, lin and sul. Antimicrobial susceptibility testing revealed resistance rates of 83.33% (10/12) to erythromycin and 33.33% (4/12) to meropenem. The 2 kinds of resistance patterns were observed: 6 strains showed single-drug resistance, and 4 strains showed dual resistance, primarily to erythromycin and meropenem (33.33%, 4/12).
Lm contamination is detected in various retail foods in Baoshan. The isolates exhibits high genetic diversity and included common pathogenic sequence types. All strains universally carry key virulence genes, indicating strong pathogenicity and potential outbreak risk. Moreover, widespread resistance to clinically important antibiotics, such as erythromycin and meropenem, is observed. Strengthened food monitoring across the city, along with standardized clinical and veterinary antibiotic use, is recommended to prevent and control the associated risks.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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