Molecular characterization of Listeria monocytogenes isolates from pregnancy-related cases in Northern Italy

Background and aims Invasive listeriosis usually affects pregnant, newborns, the elderly, and immunocompromised individuals. In pregnant women Listeria monocytogenes may cause abortion, fetal death, or neonatal morbidity. The aim of this study was to characterize pregnancy-related isolates of L. monocytogenes observed in Lombardy, Italy, from 2005 to 2012. Methods Intragenic regions of six virulence and seven housekeeping genes of 19 pregnancy-related isolates were amplified and analyzed. Virulence gene sequences were compared to available data obtained from isolates representing major human listeriosis outbreaks worldwide, and other unrelated isolates. Housekeeping alleles and STs were assigned by the Pasteur Institute, France. Results On the whole, 15 VTs and 14 STs were identified. Based on the MVLST results 37% of isolates (n=7) belonged to one the seven currently known ECs of L. monocytogenes. Interestingly, two ECI isolates (VT20) corresponded to ST1 and ST595 both included in the same Clonal Complex (CC) 1 which includes also VT87 (ST1). A similar picture was recorded for CC 101 which included ST38 (n=2) and ST101 (n=1) that have been typed as VT80 and 100, respectively, presenting just a SNP for both the typing protocols. Eight isolates proved to belong to previously observed VTs-STs (Table 1). Conclusions Typing of L. monocytogenes isolates analyzed herein from apparently sporadic pregnancy-related cases of listeriosis showed a possible relation between them. Such data will be important to better determine how ECs are distributed and trace their long-term spread.