Author(s):
Martins, Tânia Maria Correia 
; Lopes, Susana Patrícia ; Ferreira, Vânia ; Pereira, M. O. ; Nicolau, Ana
Date: 2012
Persistent ID: http://hdl.handle.net/1822/28578
Origin: RepositóriUM - Universidade do Minho
Subject(s): Wastewater treatment; Environmental bacterial isolates; Antibiotic resistance; Biofilm formation; Virulence profiles
Description
The increased prevalence of antibiotic resistance is one of the main problems
faced by health professionals nowadays, consequently dealing with the expansion of
nosocomial infections in hospitals and other health institutions.
Wastewater Treatment Plants (WWTP) aim at the treatment of residual waters
ensuring the preservation of the environment and ultimately, human health.
Nevertheless, they also receive residual water from health institutions and research
centres that can significantly contribute to the presence of pathogenic and resistant
microorganisms in the sewage.
The aim of this study was the isolation of potential pathogenic bacteria (E.coli,
S.aureus, S.enterica, P.aeruginosa and K.pneumoniae) from the final effluent of four
WWTP in the north of Portugal to subsequently evaluate some known virulence
factors, such as their ability as biofilm formers and their susceptibility to different
antibiotics.
The amount of E. coli surpassed all the other species and S.aureus was the less
frequent, considering all samples. The ability of biofilm formation depended on the
species considered, but also on the sampled WWTP. For instance, S.enteritidis and
E.coli showed low capacity to form biofilm, but they appeared with high CFU values.
S.aureus showed a high capacity of biofilm formation but only a small number of CFU
was counted. These data seem to indicate that S.aureus biofilms contain a huge
amount of polymeric matrix, which could be an obstacle to antibiotic action. In one of
the WWTP, most isolated bacteria revealed the lowest capacity to form biofilms, but
they clearly had the highest antibiotic resistance profiles. In one of the WWTP, biofilm
formation was greater for all isolates; indeed, it was the only WWTP where all isolated
bacteria were capable to produce biofilm which was rated as moderately to strongly
adherent, but showed, on the other hand, significant sensitivity to the tested
antibiotics. For example, P.aeruginosa isolated in this WWTP revealed a significant
ability to develop biofilm but presented the profiles of highest antibiotic susceptibility.
Similar tendencies for S. enteritidis and K.pneumoniae in other WWTP were obtained.
Interestingly, it can be concluded that some species showed particular responses
independently from the sampling plant, but others depended on the WWTP where the
sample was collected. The data obtained also highlight that procedures used for waste
water treatment are not effective in the removal of pathogenic bacteria, which appear
in the final effluents and are subsequently discharged into a natural water body.
