166
directly kills bacteria, thereby disrupting the biofilm and is now approved by the US
Food and Drug Administration (FDA) for scanning in medical diagnostics during
treatment of hypercalcaemia (Bjarnsholt et al. 2013). Further, combination strategies have proved to be fruitful when high doses of antibiotics are used together with
drugs that targets biofilm leading to effective eradication. Candidate drugs of choice
that can be used in combination strategies are meropenem, colistin and azithromycin, which are active under reduced oxygen tension and low metabolic activity, a
condition which is more specific to deeper layers of biofilms. External metabolic
and chemical stimuli combined with the use of antibiotics or engineered bacteriophages can also be used as novel strategy for disrupting bacterial biofilms.
β-lactamase is reported to be entrapped in the biofilm matrix and can impair the
penetration of β-lactams into deeper layers of thick biofilms which indicates
β-lactamase stable antibiotics such as meropenem or β-lactamase inhibitors might
be more effective in combination strategies (Hengzhuang et al. 2012). Additionally,
use of efflux pump inhibitors like thioridazine, 1-(1-naphthylmethyl)-piperazine
and Phe-Arg-naphthylamide may also help to cope up with the tolerance to antibiotics in the P. aeruginosa, E. coli and S. aureus associated biofilms (Liu et al. 2010).
Another important aspect is oxidative stress mediated mutation in biofilm associated bacteria leading to development of antibiotic resistance. Thus, antioxidants
such as l-proline, N-acetylcysteine, β-carotene or l-cysteine can be used in combination with antibiotics to decrease the resistance in bacteria as evident from the reports
against P. aeruginosa (Boles and Singh 2008). N-acetylcysteine, a potent mucolytic
agent used for treatment of cystic fibrosis, is also considered as an enhancer of antibiotic activity.
7.5.7 Bacteriophages
Bacteriophages are viruses infecting bacteria, discovered independently by
Frederick Twort and Felix d’Hérelle and are now considered as potent biological
control agents against bacterial biofilms (Motlagh et al. 2016). Among several benefits of lytic phages, considerable host specificity, self-propagation at the site of
infection, rapid clearance, great diversity, relatively easy isolation for a range of
pathogens, and the opportunity to make genetic modifications are most notable
(Nobrega et al. 2015). Unlike lysogeny, during lytic cycles bacteriophages replicate
in the bacterial host cell interior producing large number of progeny phages which
are a function of phage type and host strain. Exopolysaccharide matrix degrading
enzymes like phage encoded depolymerases may lead to biofilm disruption facilitating phagocytosis by polymorphonuclear leukocytes and improved effects of antimicrobial drugs (Fig. 7.5). T4 phage can infect and replicate within E. coli biofilms
killing bacterial cells and disrupting biofilm morphology. Rationally engineered T7
phage encoding a matrix degrading depolymerase is reported to have both lytic
potential and enzymatic activity which was exploited owing to its enhanced efficiency of phage mediated eradication of bacterial cells as well as biofilm matrix (Lu
B. P. Singh et al.
directly kills bacteria, thereby disrupting the biofilm and is now approved by the US
Food and Drug Administration (FDA) for scanning in medical diagnostics during
treatment of hypercalcaemia (Bjarnsholt et al. 2013). Further, combination strategies have proved to be fruitful when high doses of antibiotics are used together with
drugs that targets biofilm leading to effective eradication. Candidate drugs of choice
that can be used in combination strategies are meropenem, colistin and azithromycin, which are active under reduced oxygen tension and low metabolic activity, a
condition which is more specific to deeper layers of biofilms. External metabolic
and chemical stimuli combined with the use of antibiotics or engineered bacteriophages can also be used as novel strategy for disrupting bacterial biofilms.
β-lactamase is reported to be entrapped in the biofilm matrix and can impair the
penetration of β-lactams into deeper layers of thick biofilms which indicates
β-lactamase stable antibiotics such as meropenem or β-lactamase inhibitors might
be more effective in combination strategies (Hengzhuang et al. 2012). Additionally,
use of efflux pump inhibitors like thioridazine, 1-(1-naphthylmethyl)-piperazine
and Phe-Arg-naphthylamide may also help to cope up with the tolerance to antibiotics in the P. aeruginosa, E. coli and S. aureus associated biofilms (Liu et al. 2010).
Another important aspect is oxidative stress mediated mutation in biofilm associated bacteria leading to development of antibiotic resistance. Thus, antioxidants
such as l-proline, N-acetylcysteine, β-carotene or l-cysteine can be used in combination with antibiotics to decrease the resistance in bacteria as evident from the reports
against P. aeruginosa (Boles and Singh 2008). N-acetylcysteine, a potent mucolytic
agent used for treatment of cystic fibrosis, is also considered as an enhancer of antibiotic activity.
7.5.7 Bacteriophages
Bacteriophages are viruses infecting bacteria, discovered independently by
Frederick Twort and Felix d’Hérelle and are now considered as potent biological
control agents against bacterial biofilms (Motlagh et al. 2016). Among several benefits of lytic phages, considerable host specificity, self-propagation at the site of
infection, rapid clearance, great diversity, relatively easy isolation for a range of
pathogens, and the opportunity to make genetic modifications are most notable
(Nobrega et al. 2015). Unlike lysogeny, during lytic cycles bacteriophages replicate
in the bacterial host cell interior producing large number of progeny phages which
are a function of phage type and host strain. Exopolysaccharide matrix degrading
enzymes like phage encoded depolymerases may lead to biofilm disruption facilitating phagocytosis by polymorphonuclear leukocytes and improved effects of antimicrobial drugs (Fig. 7.5). T4 phage can infect and replicate within E. coli biofilms
killing bacterial cells and disrupting biofilm morphology. Rationally engineered T7
phage encoding a matrix degrading depolymerase is reported to have both lytic
potential and enzymatic activity which was exploited owing to its enhanced efficiency of phage mediated eradication of bacterial cells as well as biofilm matrix (Lu
B. P. Singh et al.