Part III: Conservation and Management440
spp. occurred in populations of wild boar at different prevalence
rates. In Italy, Salmonella spp. was isolated from 10.8 per cent
and 25 per cent of the wild boar in Latium and the northern
region, respectively (Chiari et al. 2013; Zottola et al. 2013). In
central Portugal, Dias et al. (2015) recorded a prevalence of 5 per
cent, while Vieira-Pinto et al. (2011) reported a prevalence of
22 per cent in the north of this country. Navarro-Gonzalez et al.
(2013) also found that 5 per cent of urban wild boar in Barcelona
(Spain) were Salmonella spp. carriers. In north-eastern Spain,
the prevalence of Salmonella spp. from natural environment in
cattle and cattle-free areas were compared (Navarro-Gonzalez
et al. 2012). Interestingly, the occurrence of Salmonella spp. in
wild boar from cattle areas was two times higher (35.67 per cent)
than in wild boar from cattle-free areas (17.54 per cent). Up
until now, the registered prevalence of Salmonella spp. in wild
boar that share their habitat with cattle is the highest reported in
the literature (Navarro-Gonzalez et al. 2012).
Likewise, E. coli isolates have also been reported in wild boar
with variable prevalence: in central Portugal, Dias et al. (2015)
reported prevalence up to 96 per cent, while Navarro-Gonzalez
et al. (2013) reported lower prevalence in north-eastern Spain
(13 per cent), and in central Europe, Literak et al. (2010) reported
prevalence up to 99 per cent.
Regarding Enterococcus spp., studies also reported its pres-
ence in wild boar with variable prevalence: in Portugal, Poeta
et al. (2007) reported prevalence up to 50 per cent, while
Navarro-Gonzalez et al. (2013) reported higher values in urban
wild boar (Barcelona).
Few studies have analysed Campylobacter spp. prevalence
in wild boar; however, the results also showed high variability
in the prevalence: no Campylobacter spp. were detected in sam-
ples collected from Italy (Decastelli et al. 2014) and in Sweden,
12 per cent of the samples were positive (Wahlstrom et al. 2003).
In Spain, it was identified in 4.88 per cent of urban wild boar
(Barcelona) (Navarro-Gonzalez et al. 2013) and in 66 per cent
in a south-central Spain population (Díaz-Sánchez et al. 2013).
When comparing studies across Europe, it is clear that the
prevalence of bacterial species of wild boar, such as E. coli,
Salmonella spp., Enterococcus spp., and Campylobacter spp., var-
ies, as well as their antibiotic susceptibility profiles. Comparison
of bacterial antibiotic susceptibility phenotypes in wild boar
from different geographic origins is difficult because different
susceptibility testing methods have been used. Recent studies
have interpreted the bacterial susceptibility to biocides based
on epidemiological cut-off values (ECOFFs) (e.g. Dias et al.
2015). ECOFFs allow distinguishing wild-type (WT) bacte-
ria from bacteria with acquired resistance mechanisms (non-
wild-type; NWT). The European Committee on Antimicrobial
Susceptibility Testing (EUCAST) established these cut-offs for a
large number of organisms and antibiotics based on the deter-
mination of the minimum inhibitory concentrations (MIC)
by broth microdilution and also by disk diffusion agar testing
(www.eucast.org/). Clinical breakpoints are essential to guide
therapy, but the use of ECOFFs as interpretation criteria is useful
for inferring whether an isolate (independently of its resistance
definition according to clinical breakpoints) owns phenotypi-
cally detectable resistance mechanisms (Kronvall et al. 2011).In the future, ECOFFs interpretation should always be included
in epidemiological studies.
Most of the studies performed so far tested the recovered
bacteria against several antimicrobial agents. They showed
that percentage of resistance associated with wild boar is vari-
able according to the geographical location, but also accord-
ing to the examined indicator strains. Presently, for E. coli, the
prevalence of AMR can vary between 6 per cent (Literak et al.
2010) and 25 per cent (Dias et al. 2015). For Salmonella spp.,
3 per cent (Navarro-Gonzalez et al. 2012) to 11 per cent (Zottola
et al. 2013) of the isolates are resistant to at least one antibi-
otic. For wild boar, the highest percentages of resistance have
been recorded for penicillins, tetracyclines and sulphonamides
(Zottola et al. 2013; Dias et al. 2015). Interestingly, the last report
of the European Surveillance of Veterinary Antimicrobial
Consumption (EMA & ESVAC 2016) precisely indicates peni-
cillins, tetracyclines and sulphonamides as the antibiotics with
highest sales for food-producing animals. Additionally, these
three classes of antibiotics represent more than half (range
53–88 per cent) of the total amount of antimicrobial agents sold
in 25 European countries (Grave et al. 2014). It is worth not-
ing that resistance to ‘critically important antimicrobials for
human medicine’ (WHO 2012) has also been associated with
wild boar isolates from different countries, including Spain,
Poland, Portugal, and Czech Republic. Examples include resist-
ance to third-generation cephalosporins (mostly cefotaxime),
fluoroquinolones and also linezolid (Poeta et al. 2007; Literak
et al. 2010; Mokracka et al. 2012; Navarro-Gonzalez et al. 2013).
The epidemiology of some resistance genetic markers has
also been investigated. Extended spectrum beta-lactamases
(ESBL)-producing E. coli isolates have been isolated from sam-
ples of wild boar in Portugal (Poeta et al. 2007) and central
Europe (Literak et al. 2010). ESBLs confer resistance to most
β-lactam antibiotics, including penicillins, cephalosporins,
and monobactams (Li et al. 2007). These are among the most
commonly prescribed drugs, being considered one of the most
clinically important antimicrobial classes in both human and
veterinary medicine (Li et al. 2007). The detection of ESBL-
producing E. coli in wildlife populations is relatively recent, with
first reports in 2006 (Costa et al. 2006) but since then it has been
isolated from livestock, food, pets and environmental samples in
different European countries (Poeta et al. 2007). The variants of
ESBLs already reported include blaCTX-M-1, blaTEM1-b and blaTEM-52b
(Poeta et al. 2007; Literak et al. 2010). Resistance to tetracyclines
in E. coli is mainly encoded by tetA, tetB and tetG genes (Literak
et al. 2010; Caleja et al. 2011) or by tetM, tetS and tetK in Gram-
positive bacteria (Poeta et al. 2007). Some reports have described
the association of these genes with mobile genetic elements such
as conjugative plasmids, transposons, or integrons. These ele-
ments play an important role in horizontal gene transfer, which
has been responsible for the dissemination of antimicrobial
resistance throughout diverse bacterial species (Barlow 2009).
These studies raised several concerns about the role of wild
boar as carriers, reservoirs, and even vehicles for the dissemina-
tion of AMR strains into the environment, but they are purely
descriptive. They did not investigate the effects of anthropo-
genic activities (i.e. livestock and human density and intensity of.04013:02:28