Diversity of Listeria monocytogenes isolates of human and food origin studied by serotyping, automated ribotyping and pulsed-field gel electrophoresis

Abstract

Automated ribotyping, pulsed-field gel electrophoresis (PFGE) and serotyping were evaluated for the epidemiological study of isolates of Listeria monocytogenes collected in Finland in 1997-1999 from human blood (n = 116) and the food industry (n = 72). The isolates divided into six serotypes, 23 EcoRI ribotypes, 54 AscI PFGE types, and 57 final subtypes if all results were combined. The discrimination index of ribotyping was lower (0.873) than that of PFGE (0.946). Two final subtypes dominated among human isolates, and identical subtypes were also found among food industry isolates. All PFGE types were serotype-specific, whereas two ribotypes included isolates of two serotypes. Isolates of serotype 3a, involved in an outbreak in Finland in 1999, matched one of these ribotypes, which also included some food industry isolates of serotype 1/2a. Ribotyping with EcoRI would not have been sufficient to define the outbreak in Finland caused by serotype 3a isolates. Although ribotyping is applicable as the first method in outbreak situations, human and food isolates with identical ribotypes should be investigated further by PFGE.

Distribution and Characteristics of Listeria monocytogenes Isolates from Surface Waters of the South Nation River Watershed, Ontario, Canada

“…Serovar groups 1/2c and 3b were not detected in this study, indicating that these infrequently detected food and clinical serovars (26) are also absent or infrequent in surface waters. Our results confirm previously established relationships between serovar group, ribotypes, and pulsotypes (29). Both ribotyping and PFGE demonstrated, on the basis of the Simpson index of discrimination (23), that surface water populations were diverse, although PFGE was more discriminant than ribotyping.…”

Relatedness of Listeria monocytogenes Isolates Recovered from Selected Ready-To-Eat Foods and Listeriosis Patients in the United States

“…About 50% of our food isolates displayed only 13 pulsotypes, and 88% of the isolates belonged to serogroup 1/2 (60% belonged to serotype 1/2a, 27% belonged to serotype 1/2b, and 1.6% belonged to serotype 1/2c). One explanation for this is that specific subtypes of L. monocytogenes in food products may have originated as persistent strains in the food processing environment that subsequently contaminated the finished products; this possibility is supported by the results of a number of studies (9,16,18,20,21,22,24,28). Collectively, our results and those of other investigators indicate that serotype 1/2a isolates displaying a few pulsotypes represent the majority of isolates found in food and food processing environments.…”

Pulsed-Field Gel Electrophoresis (PFGE) Analysis of Temporally Matched Listeria monocytogenes Isolates from Human Clinical Cases, Foods, Ruminant Farms, and Urban and Natural Environments Reveals Source-Associated as Well as Widely Distributed PFGE Types

“…Rapid, discriminatory, and standardized molecular subtyping methods are critical for effective food-borne disease surveillance and outbreak investigations. While automated ribotyping provides superior standardization and speed compared to many other molecular subtyping methods for bacterial isolates (58), not surprisingly and consistent with the findings of a number of previous studies (1,5,24,32,56), two-enzyme PFGE using the standard PulseNet protocol provides significantly higher subtype discrimination than EcoRI ribotyping. While automated ribotyping is thus suitable for population-based studies or subtype characterization of large numbers of isolates (1), the discriminatory power of PFGE clearly is critical for human disease outbreak investigations.…”