OBJECTIVE To analyze the epidemiological characteristics of Listeria monocytogenes isolated from clinical specimens in a hospital.
METHODS A total of 84 strains of L. monocytogenes were collected between 2010 and 2025. Of these, 42 were isolated from clinical specimens at the First Medical Center of Chinese PLA General Hospital, and 42 were isolated from food samples obtained from a market. Following species confirmation, antimicrobial susceptibility testing was performed. Whole-genome sequencing was performed on all strains, followed by homologous analysis, lineage identification, serotyping, multilocus sequence typing （MLST） and virulence gene identification.
RESULTS Clinical infections were predominantly bloodstream infections （42.86%）, central nervous system infections （26.19%） and perinatal infections （26.19%）. 75.61% of non-perinatal cases had underlying diseases that caused immunosuppression. All strains were 100.00% susceptible to ampicillin, penicillin, meropenem, and erythromycin. The susceptibility rate of clinical isolates to trimethoprim-sulfamethoxazole was 95.24%, and 92.86% of the strains exhibited MIC values ≤1 μg/ml for tetracycline. The clinical strains predominantly belonged to Lineage I （23/42, 54.76%）. The most common serotype was 1/2a （19/42, 45.24%）, and a total of 15 sequence types （STs） were identified, with ST87 and ST8 being the predominant ones. Except for three drug-resistant clinical strains carrying dfrG and tet（M）, other strains did not carry drug resistance genes. No statistically significant differences were observed in the distribution of lineage, MLST, serotype and virulence genes between clinical strains and food-derived Listeria. All strains carried the virulence islands LIPI-1 and LIPI-2. LIPI-3 was detected in 11.90% of the strains, and LIPI-4 in 17.86%. The stress survival island SSI-1 was present in approximately 55.74% （34/61） of the strains, while only one strain harbored a complete SSI-2.
CONCLUSIONS Clinical isolated strains of L. monocytogenes from 2010 to 2025 are predominantly sporadic, with bloodstream infections, central nervous system infections and perinatal infections being the main types. The strains are generally susceptible to ampicillin, penicillin, meropenem and other antibiotics, although a few strains show resistance to tetracycline and sulfonamides. Clinical isolated strains and food-derived strains exhibit high genetic homology, suggesting that clinical infections mainly originate from food transmission. Therefore, it is necessary to strengthen food hygiene and the prevention and control of foodborne diseases, as well as to continue antimicrobial resistance surveillance.
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