U.S. flag

An official website of the United States government


Main content area

Population Structure of Listeria monocytogenes Serotype 4b Isolates from Sporadic Human Listeriosis Cases in the United States from 2003 to 2008

Lee, Sangmi, Ward, Todd J., Graves, Lewis M., Tarr, Cheryl L., Siletzky, Robin M., Kathariou, Sophia
Applied and environmental microbiology 2014 v.80 no.12 pp. 3632-3644
DNA probes, Listeria monocytogenes, arsenic, benzalkonium chloride, cadmium, clones, disease outbreaks, disinfectants, foodborne illness, genotyping, heavy metals, humans, hybridization, listeriosis, microbiology, monitoring, population structure, serotypes, virulent strains, United States
Listeria monocytogenes can cause severe foodborne disease (listeriosis). Serotype 4b strains have resulted in numerous outbreaks, repeatedly involving three epidemic clones (ECI, ECII, and ECIa). Little is known about population structure of L. monocytogenes serotype 4b from sporadic listeriosis, even though most listeriosis cases are sporadic. Here we analyzed 136 serotype 4b isolates from sporadic cases in the United States between the years 2003-2008. ECI, ECII, and ECIa accounted for 32, 17, and 7%, respectively, of the isolates. Even though outbreak-associated clonal groups were major contributors to sporadic illness, annually 30-68% of isolates were outside of these ECs and several novel clonal groups were identified based on multilocus genotyping (MLGT) and hybridization profiles with a panel of DNA probes. Resistance to benzalkonium chloride was uncommon (3%) while 33 and 17% of the isolates were resistant to cadmium and arsenic, respectively. Resistance to these heavy metals was primarily found among EC isolates. Our analysis suggests a complex population structure of serotype 4b L. monocytogenes from sporadic disease, with important contributions by outbreak-associated strain types and several novel clonal groups; continuous monitoring will be warranted to assess longer term trends in clonality patterns and resistance attributes (disinfectant and heavy metals) in serotype 4b strains from sporadic listeriosis.