The Pathogenic Potential of Different Pulsed-Field Gel Electrophoresis Types of Listeria monocytogenes Strains Isolated from Food in Northeast Bosnia and Herzegovina Snjezana Hod zic ´, 1 Mirsada Hukic ´, 2 Giovanna Franciosa, 3 and Paolo Aureli 3 Abstract Listeria monocytogenes is often present in meat and meat products that are sold in the area of northeast Bosnia and Herzegovina. The major objective of this study was to examine the virulence of L. monocytogenes strains isolated from these types of food in that geographic area. Polymerase chain reaction was used to detect eight genes responsible for virulence of this pathogen, namely, prfA, inlA, inlB, hly, plcA, plcB, actA, and mpl. All examined isolates were confirmed to possess the eight virulence genes. Ten different pulsed-field gel electrophoresis (PFGE) macrorestriction profiles were recognized among 19 L. monocytogenes strains after restriction with two different endonucleases (ApaI and AscI). The pathogenicity of three different PFGE types of L. monocytogenes was confirmed through in vivo tests, which were performed on female white mice (Pasteur strain), and it ranged from 3.55 · 10 8 LD 50 to 1.58 · 10 10 LD 50 . All of the three different PFGE types of L. monocytogenes were regarded as moderately virulent in relation to the reference strain L. monocytogenes Scott A. This result might be one of the reasons for the absence of reported listeriosis in northeast Bosnia and Herzegovina, despite the high degree of food contamination with this pathogen. Key Words: Listeria monocytogenes—PFGE types—virulence genes. Introduction L isteria monocytogenes is an ubiquitous, Gram- positive bacterium and can be isolated from almost all ca- tegories of food (Kozak et al. 1996). It is pathogenic for both domestic and wild animals and also for humans, by causing the serious disease listeriosis. The routes of transmission of listeri- osis are different, and most commonly, it is transmitted trans- placentally from mother to fetus and through ingestion of food contaminated with L. monocytogenes (Farber and Peterkin 1991). The primary site of entry of L. monocytogenes is the digestive tract: the pathogen penetrates very fast into the intestinal epithelium, where it is phagocytosed by macrophages (in humans, this phase is asymptomatic). Intracellular prolifera- tion occurs, with destruction of macrophages and a conse- quential septicemia (Cousens and Wing 2000). Certain segments of human population such as the elderly, infants, pregnant women, people with reduced immunity, and indi- viduals undergoing immunosuppressive therapy have an increased risk of infection. Ingestion of L. monocytogenes is very common considering the omnipresent distribution of these bacteria and the high incidence of contamination of raw and industrially processed food. Yet, the incidence of human listeriosis is very low, usually about 2–8 sporadic cases per annum on a million of inhabitants in Europe and the United States of America (Re- court et al. 2000). Despite the high percentage, 23.3% (42/180) of raw meat samples (Hod zic ´ and i Hukic ´ 2004) and 11.1% (10/90) of meat product samples contaminated by L. mono- cytogenes in the area of Bosnia and Herzegovina (Hod zic ´ and i Hukic ´ 2006), no cases of human listeriosis were reported in the past 10 years in the same area (Department of Health Statis- tics, 2009). Even though occurrence of listeriosis may be under- estimated, another plausible reason for such conflicting proofs may be the variability of virulence of L. monocytogenes. In fact, although L. monocytogenes is defined as a pathogen at the level of species, within this species a high degree of genetic diver- sity and an extremely variable pathogenic potential are present. Main genes responsible for virulence of this pathogen 1 Faculty of Science, University of Tuzla, Tuzla, Bosnia and Herzegovina. 2 The Institute of Clinical Microbiology, Clinical Center University of Sarajevo, Sarajevo, Bosnia and Herzegovina. 3 Istituto Superiore di Sanita, Rome, Italy. VECTOR-BORNE AND ZOONOTIC DISEASES Volume 11, Number 9, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089/vbz.2010.0208 1279