poster - International Conference of Agricultural Engineering

of faecal bacteria (Kummerer, 2004; Ding & He, 2010; Jury et al., 2010); although, the causal
relationship between the entry and spread of antibiotic resistance remains undetermined
(Ding & He, 2010).
The horizontal gene transference is the most common mechanism of prokaryote cells to
obtain and disseminate antibiotic-resistance genes (ARG) between microbial populations (Xi
et al., 2009). Resistance genes to different AB classes are usually gathered in cassettes
inserted in mobile genetic elements, such as plasmids, transposons and integrons, being
transferred together. This feature causes a progressive increase of multidrug-resistant
bacteria in the environment, such as vancomycin-resistant Enterococcus (VRE), methicillin
resistant Staphylococcus aureus (MRSA), particularly in clinical settings, where the available
AB are losing effectiveness (Finch & Hunter, 2006) and therefore the control of these hospital
infections is increasingly difficult (Kummerer, 2009b). Moreover, since 1962, the development
of novel classes of AB is almost stationary, which leads to the need of developing innovative
and effective therapies and pharmacological agents (Livermore et al., 2011).
The gastrointestinal tract of animals and humans (Falk et al., 1998) and the aquatic
ecosystems, generally contaminated with raw human and animal sewage, are reservoirs of
antibiotic resistance determinants (ARD) (ARG and ARB), having favourable conditions for
ARB exchanging their genes (Kummerer, 2004). It is not thus surprising that faecal coliforms
and enterococci are the eligible bacterial groups to study antibiotic resistance in aquatic
environments (Schwartz et al., 2003; West et al., 2010), neither that WWTPs are the selected
sampling locations. In fact, WWTP collect wastewaters rich in bacteria previously exposed to
AB, originated in hospitals, nursing homes, livestock, agriculture or industry, (Schluter et al.,
2003) reflected potential sites for horizontal ARG transference due to its microbial richness
and high nutritional. Some studies in the WWTP have identified mobile genetic elements
both in bacteria isolated from wastewater and in the activated sludge tanks, demonstrating
that even with the decrease of bacteria in treated wastewaters there is an increased
proportion of multiresistant bacteria to AB in effluent water (Silva et al., 2006; Kummerer,
2009b; West et al., 2010; Moura et al., 2011).
In Portugal, the water quality legislation for treated wastewater reuse (Marecos do Monte &
Albuquerque, 2010) or human consumption (DL 306/2007, August 27) has no mention to the
detection and quantification of ARD. The latter, although controlling other pesticide residues
used in agriculture does not refers to bactericides, which application is illicit (Oliveira &
Henriques, 2011). However, Kummerer (2009b) refers to AB as one of the most significantly
consumed pharmaceutical groups, which explains the recognised widespread distribution of
AB and their residues in different environmental ecosystems. It is also known their high
toxicity to algae and bacteria, the ability to interrupt bacterial life cycles responsible of
biogeochemical processes and its potential for cause resistance among environmental
bacterial populations (Watkinson et al., 2009). Due to this awareness, AB has being recently
classified as a priority risk group.
The consciousness of the scientific community to the gravity of this problem caused by the
uncontrolled discharges of urban and agricultural wastewater has resulted in an increase of
studies evaluating the spread of ARB in aquatic environments in the last decades (Xi et al.,
2009; Moore et al., 2010; West et al., 2010). Despite the knowledge on AB genetic
resistance mechanisms, their transference among bacteria and on mechanisms of ARG
entrance, maintenance and spread in the environment; the accurate global ecological impact
of ABs and ARD and the inherent risks to human and animal health is still undetermined
(Kummerer, 2009a; Ding & He, 2010; Moore et al., 2010; West et al., 2010). The prevention
of the ARD spread is sustained on two main strands: i) on the pre-emission side, the prudent
use of AB, the development of new effective and environmentally degradable drugs, and ii)
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