Introduction bacteria resistant to fluoroquinolones and broad-spectrum beta-lactams


To date, the bacterial resistance to antibiotics is one of the most
important global health threat introduced by the World Health Organization  and  most annual mortality due to hospital
infections occurs because of this problem (1).The  Escherichia coli is one of the most
important causal agents of intestinal and extraintestinal infection belongs to Enterobacteriaceae family (2). It causes a wide range of infections including
septicemia, pneumonia, urinary tract infection, meningitis and abscess in the different
organs (3,4). Antimicrobial resistance has been reported in Escherichia coli
worldwide and has created a lot of worries in developing and
developed countries (5).

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Different antibiotics are used to treat infections of this bacterium,
but carbapenems such as imipenem and meropenem is a selective treatment for
progressive infections caused by Gram-negative bacteria resistant to
fluoroquinolones and broad-spectrum beta-lactams (6,7). Resistance to carbapenems has been reported in Escherichia coli
in different parts of the world (8-10).
Carbapenemase enzymes are one of the most important causes of resistance to
carbapenems antibiotics in gram-negative bacteria (11). A large number of Carbapenemase has been identified in recent years,
which are classified into three classes, A (Klebsiella pneumoniae
carbapenemase or KPC and Guiana
extended-spectrum ?-lactamase or GES ) ,class B metallo-beta-lactamases
(Verona integron-encoded ?-lactamase or VIM , Imipenemase or IMP  and
New Delhi Metallo-beta-lactamase or NDM) and class D (oxacillinase) (12).

The enzyme KPC is the most common carbapenemase among Enterobacteriaceae
in the United States that is evidently expanding somewhere else on the
world. Despite the fact that KPC has the highest prevalence in Klebsiella
pneumoniae, however, this enzyme has also been significantly observed in
other Enterobacteriaceae species, including Escherichia coli,
Proteus, Serattia, Salmonella and Citrobacter (13).
NDM-1 is a strong metallo-beta-lactamase that was discovered for the
first time in Klebsiella pneumoniae and Escherichia coli isolates
from Swedish patient who was traveled to New Delhi, India in 2008 (14). The NDM-1 coding gene is located on mobile plasmids that
capable of being transmitted to different bacterial strains, and promotes the spred of drug
resistance throughout the world (15).Hence, the early
diagnosis of these carbapenemases among clinical isolates is important for
controlling and preventing their spread.

Due to the limited epidemiologic data about the  KPC and 
NDM  carbapenemase-producing Escherichia
coli in our region, this study was conducted to investigate these enzymes
by combined disk test and amplification of blaKPC and blaNDM
gene using polymerase chain reaction (PCR) in clinical isolates of
carbapenem-resistant  Escherichia coli
from two university-affiliated hospitals in Ahvaz, southwest Iran.

Material & Methods

Study region , sample collection and bacteria identification

This cross-sectional study was performed on 376 isolates of Escherichia coli collected from  different clinical samples including urine, blood, tracheal tube, wound, discharge
and abscess of
hospitalized patients in two university-affiliated hospitals  Golestan and Emam Khomaini in Ahvaz, southwest
Iran from June 2014 to July2015.These two hospitals are the main hospitals of
the Ahvaz city. Ahvaz  is one of the major metropolises in Iran,
which is considered to be the seventh most populated city in Iran. All
specimens were transferred to the  microbiology department of Ahvaz Jundishapur
University of Medical Sciences and were identified by conventional microscopic and biochemical
methods including Gram stain,  lysin iron
agar (LIA), triple suger iron agar (TSI), sulfur indol motility medium (SIM), Simmon’s citrate agar and urea broth (Merck Co, Germany) (16). After the final diagnosis of bacteria , some of the pure colonies were suspended in a Tryptic Soy Broth (TSB) containing 15% glycerol and
placed in ?80°C for prolonged storage.

Antimicrobial susceptibility test

Susceptibility to antibiotics was assessed
using the Kirby-Bauer disc diffusion method and results were interpreted based
on the Clinical and Laboratory Standards Institute (CLSI) principles (17,18). 


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