42 4 ART for Antibacterial Infection
in 1990. Recently, a new antibiotic resistant gene, bla (^) NDM-1, that exists in a plas-
mid has been identified in G− bacteria, such as E. coli and Krebsiella pneumoniae.
NDM-1 that represents New Delhi metallo-β-lactamase 1 was nominated because it
was identified from antibiotic resistant bacteria in New Delhi, India (Kumarasamy
et al. 2010 ). A recent publication has described that aureusimines, a series of nonri-
bosomal peptidyl secondary metabolites, assist the productive infection by bla (^) NDM-1
bacteria (Wyatt et al. 2010 ).
It is known that G+ bacteria produce NO by activating bNOS, which can pro-
tect bacteria from antibiotics (Gusarov et al. 2009 ). Ultraviolet irradiation can
upregulate bNOS and elevate the protective NO level in bacteria (Patel et al. 2009 ).
Like mammals, NO is also synthesized from ARG in G+ bacteria. There are three
subtypes of bacterial NO-producing enzymes: (1) completely homologous to the
mammalian NOS with both a heme-binding region and a reductase domain, such as
bNOS in S. cellulosum (Agapie et al. 2009 ); (2) partially homologous to the mam-
malian NOS with a heme-binding region, but without a reductase domain, includ-
ing bNOS in Bacilus, Staphylococcus, and Streptomyces. So they need another
reductase for NO synthesis (Crane 2008 ); (3) bNOS-independent enzyme systems
as in E. coli, encompassing cytochrome c nitrite reductase, NO sensitivity regulon,
and flavin hemoglobin (Corker and Poole 2003 ; van Wonderen et al. 2008 ).
Considering the high cost and long time for developing new antibacterial drugs,
we could alternatively find out the inhibitors of bNOS to deprive the protective
NO and synergize the insensitive antibiotics. In history, antibiotic synergists were
developed to augment the antibacterial capacity of antibiotics. For example, clavu-
lanic acid as an inhibitor of β-lactamase has been widely used in combination with
penicillin to kill penicillin-resistant bacteria with an increased β-lactamase activity.
4.2 In Vitro Examination for ART Suppressing
NO-Conveyed Bacterial Antibiotic Tolerance
4.2.1 Purposes and Significance
A current challenge of coping with bacterial infection is bacterial pathogens are
becoming less susceptible to or more tolerant of commonly used antibiotics. The
occurrence of “super bugs” with MDR/EDR predisposes a necessity of solving the
more and more severe issue of bacterial resistance to wide-spectral antibiotics. For
this purpose, we could consider to sensitize antibiotics by exploiting bNOS inhibi-
tors to abrogate the cytoprotective role played by bacteria-produced NO.
Because either G+ bacteria or G− bacteria are capable of generating their own
NO, they should be vulnerable to the inhibition of NO production. However, G+
bacteria synthesize NO depending on bNOS, whereas G− bacteria are independ-
ent on bNOS for NO production. So bNOS inhibitors are only effective on bNOS-
harboring G+ bacteria.
ART possesses pleiotropic functions, including antimalaria, antitumor, and
anti-inflammation (Krishna et al. 2008 ), but there is no evidence regarding ART’s