الفهرس 
Biodegradation of Fluoroquinolones Microbial Isolates from Environmental Samples in Egypt
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Abstract
The increase in the volume of industrial and urban wastewater produced as it contains toxic pharmaceutical compounds is considered one of the most important environmental problems worldwide. Antimicrobial agents are among the most commonly used drugs. Beta-lactams, macrolides, sulphonamides, FQs, and tetracyclines are the most important antibiotic groups used in both human and veterinary medicine. The high global consumption and high percentage of antibiotics (up to 90%) that may be
excreted without undergoing metabolism have resulted in their widespread presence in the environment, and the widespread and improper use of antibiotics in livestock, human and pets have resulted in the development of antibiotic-resistant bacteria among pathogenic bacteria, rendering current antibiotics ineffective in the treatment of numerous diseases thus, the aim of
this study is to investigate the potential of CIP and LEV biodegradation by
microbial populations, and to identify the metabolites/transformation
products originated during biodegradation process. In addition, the current study aimed to shed some light on the enzymes involved in FQs
biodegradation and possible biodegradation pathways.
Two bacterial consortia that can degrade CIP and LEV were isolated
from wastewater, identified as E. miricola, A. baumannii and K. pneumoniae
the optimal conditions for maximum degradation were explored and we
found that the optimum degradation conditions for both CIP and LEV in
sample 1 (A. baumannii and K. pneumoniae) were temperature 30 ° C, pH 5,
agitation rate 180 rpm and without UV application. For sample 2 (E.
miricola and K. pneumoniae), temperature 30 °C, pH 7, agitation rate 180
rpm and without UV application represent the optimum conditions for both
CIP and LEV biodegradation. CIP was readily degraded by the two bacterial
consortia by 50 % while LEV was degraded by 50 % and 30 % for sample
one and two respectively at concentration 1 mg/L within 48 h of incubation
in liquid medium. The biodegradation products were identified by liquid
chromatography tandem mass spectrometry. Seven major metabolites were
revealed from the biodegradation of each FQ (CIP and LEV) by the two
bacterial consortia. The relative abundance between isolates of the two
bacterial consortia during the biodegradation of CIP and LEV was
investigated. The data revealed that in sample 1 initially, K. pneumoniae was
more abundant than A. baumannii. However, as the CIP and LEV
biodegradation process progressed, the ratio became the same. Interestingly,
the initial ratio between the bacterial isolates in sample 2 (K. pneumoniae
and E. miricola) was essentially the same, but as the biodegradation process
proceeded, the ratio was changed and E. miricola became the foremost
Summary
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abundant one. The individual bacterial isolates in both consortia were
molecularly screened for aac (6 ’) –Ib-cr gene that is involved in the
degradation of FQs. All four isolates were positives for the gene. The
aac(6′)-Ib-cr variant was distinguished from the wild type gene by direct
sequencing and confirming the absence of the BstF5I restriction site present
in the wild-type gene. The role of the enzyme cytochrome P450 in the
breakdown of FQS was investigated by the addition of CYP450 inhibitor
ABT. The concentration of CIP and LEV was measured by HPLC-DAD
after 48 hours of incubation in absence and presence of 1-
aminobenzotriazole. Complete inhibition of the biodegradation of CIP and
LEV in the presence of 1-aminobenzotriazole indicated the possible
involvement of CYP450 enzymes. According to our research, various
biodegradation pathways have been proposed, including cleavage of
piperazine ring, substitution of Flourine atom, acetylation, decarboxylation,
and hydroxylation, as the main transformation reactions catalyzed by
CYP450 and the (aac (6 ′) - Ib-cr). The results of the phytotoxicity assay
revealed that the two bacterial consortia can be used in the bioremediation of
CIP and LEV yielding non phytotoxic compounds, thus, providing an
environmentally safe approach for dealing with FQs environmental
pollution