Ongoing outbreak of invasive listeriosis due to serotype 1 / 2 a Listeria monocytogenes , Ancona province , Italy , January 2015 to February 2016

In the first seven weeks of 2016, five serotype 1/2a Listeria monocytogenes isolates were collected from patients with invasive listeriosis in Ancona province in Italy. These strains and six 1/2a isolates identified in 2015 in the same area were typed by ERIC-PCR and PFGE. A clonal relationship, documented between the two sets of isolates, suggested a listeriosis outbreak in Ancona that started most probably in 2015. Investigation into the source of infection is still ongoing.

In the first seven weeks of 2016, five serotype 1/2a Listeria monocytogenes isolates were collected from patients with invasive listeriosis in Ancona province in Italy.These strains and six 1/2a isolates identified in 2015 in the same area were typed by ERIC-PCR and PFGE.A clonal relationship, documented between the two sets of isolates, suggested a listeriosis outbreak in Ancona that started most probably in 2015.Investigation into the source of infection is still ongoing.
In the first seven weeks of 2016, six cases of invasive listeriosis were recorded in Ancona province, Italy.Five strains of Listeria monocytogenes serotype 1/2a were isolated and typed by enterobacterial repetitive intergenic consensus (ERIC)-PCR and PFGE, indicating clonality.In addition, seven serotype 1/2a L. monocytogenes strains from cases of invasive listeriosis recorded in the same area in 2015 were also typed and showed relatedness.Here we provide details of the ongoing outbreak.
The 2015 and 2016 isolates were identified as L. monocytogenes by Gram staining and the Vitek MS system (bioMérieux Italia SpA, Firenze, Italy).Susceptibility to ampicillin, meropenem, erythromycin, and sulphamethoxazole-trimethoprim was tested by the E-Test (Liofilchem, Teramo, Italy) according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines [1].All strains were susceptible to all the antibiotics tested.

Molecular typing
In order to identify relatedness, the 2015 and 2016 L. monocytogenes isolates were sent to our laboratory (Unit of Microbiology, Department of Biomedical Sciences and Public Health, Polytechnic University of Marche, Ancona) for molecular typing.Multiplex PCR serotyping [2] assigned five 2016 isolates and seven 2015 isolates to serotype 1/2a; the remaining isolates were serotype 4b (2016) and serotype 1/2c (2015).

Background
L. monocytogenes is widely distributed in the environment and is frequently isolated from a variety of sources, including soil, vegetation, food of animal origin such as meat and dairy products, silage, fecal material, sewage, and water [5].Listeriosis is most often transmitted through food and primarily affects older adults, pregnant women, newborns, and adults with weakened immune systems [5].Serotyping is a universally accepted typing method for L. monocytogenes, with more than 14 serotypes being recognised according to variation in somatic (O) and flagellar (H) antigens [6].Multiplex PCR serotyping is a practical alternative to slide agglutination serotyping, since it differentiates among the five major serogroups, each of which  includes multiple serotypes: serogroup IVb (serotypes 4b, 4d and 4e), serogroup IIa (serotypes 1/2a and 3a), serogroup IIb (serotypes 1/2b, 3b and 7), serogroup IIc (serotypes 1/2c and 3c), and serogroup IVa (serotypes 4a and 4c).By use of suitably designed primer pairs, the four major serotypes 1/2a, 1/2b, 1/2c, and 4b produce four distinct PCR profiles [2].PFGE is considered as the gold standard molecular typing approach for L. monocytogenes, owing to its high reproducibility and discrimination ability [4].ERIC PCR is a relatively simple, cost-effective, and discriminatory typing method based on ERIC sequences, 124 to 127 base-long elements consisting of highly conserved central inverted repeats found in the extragenic regions of the bacterial genome [3].