Molecular diversity and antimicrobial susceptibility of Listeria monocytogenes isolates from invasive infections in Poland (1997-2013)

Abstract

The epidemiology of invasive listeriosis in humans appears to be weakly characterized in Poland, the sixth most populous member state of the European Union. We obtained antimicrobial susceptibility data, PCR-serogroups and genotypic profiles for 344 invasive isolates of Listeria monocytogenes, collected between 1997 and 2013 in Poland. All isolates were susceptible to the 10 tested antimicrobials, except one that was resistant to tetracycline and minocycline and harbored the tet(M), tet(A) and tet(C) genes. Overall, no increasing MIC values were observed during the study period. Four PCR-serogroups were observed: IVb (55.8%), IIa (34.3%), IIb (8.1%) and IIc (1.8%). We identified clonal complexes (CCs) and epidemic clones (ECs) previously involved in outbreaks worldwide, with the most prevalent CCs/ECs being: CC6/ECII (32.6%), CC1/ECI (17.2%), CC8/ECV (6.1%) and CC2/ECIV (5.5%). The present study is the first extensive analysis of Polish L. monocytogenes isolates from invasive infections.

Figure 1

Prevalence of different clonal complexes (CCs) observed in 344 Listeria monocytogenes clinical isolates from Poland, 1997–2013.

Figure 2

Distribution of the 344 Listeria monocytogenes isolates belonging to different age groups in relation to clinical presentation: blood stream infections (a) and meningitis (b); Poland, 1997–2013.

Figure 3

Minimum spanning tree of MLST data for 344 L. monocytogenes isolates. Each circle represents one ST and the fragment of pie chart corresponds to single isolates. The size of the circle is proportional to the number of isolates with that ST. Gray zones surrounding groups of STs represent CC. The CCs numbers are indicated by gray text for this represented by 10 and more isolates. Connecting lines infer phylogenetic relatedness in terms of number of allelic differences (thick solid, 1; thin solid, 2; dashed, 3; dotted, 4 and above).

Figure 4

Distribution of borderline MICs (MIC at the susceptibility breakpoint) of ampicillin, penicillin, meropenem and co-trimoxazole by year, Poland 1997–2013 (* indicates p-values ≤ 0.05).