Phenotypic detection of resistance in Staphylococcus aureus
isolates: Detection of (mec A and fem A) gene in methicillin
resistant Staphylococcus aureus (MRSA) by Polymerase Chain
Reaction
Hawraa Wahab Aziz1
, Tasahel Hamid Al-Dulaimi2
and Ali Hussein Al-Marzoqi3* (Corresponding author), Nada
Khalid Ahmed4
1. College of Science for women, Babylon University.
2. College of Science for women, Babylon University.
3. College of Science for women, Babylon University, PO box 435, Al-Hillah city, Babylon, Iraq. E-mail:
ali_almarzoqi@yahoo.co.uk
4. College of Science for women, Babylon University.
* E-mail of the corresponding author: ali_almarzoqi@yahoo.co.uk
Abstract:
Background:
The drug resistant phenomenon is being worldwide concern especially in the last 20 years. Among the most
threatening antibiotic-resistant pathogens known are strains of methicillin-resistant S. aureus (MRSA), they are
resistant to ?-lactams and other cell-wall-active agents. In many developing countries, the situation appears
gloomy due to inadequate or poor implementation of policy on infection control, lack of political will,
inadequate resources including shortage of skilled manpower, poor motivation of health care workers and
researchers.
Objective:
The present study tries to describe an accurate and quick detection for of clinically relevant antibiotic resistance
gene of Staphylococcus aureus using PCR technique.
Methodology:
The mec A gene was amplified to characterize MRSA isolates at species level. The S. aureus isolates were
analyzed for their susceptibility to different classes of antibiotics using the disk diffusion method.
Results:
Of the total 429 Staphylococcus aureus isolated, 114 (26.54%) strains were MRSA. MSRA strains were selected
for PCR assay. Eighty one MRSA strains (71.05%) were mecA gene positive and thirty three (28.95%) MRSA
strains were mecA negative visualized on 1% agarose gel electrophoresis.
Conclusions:
The PCR assay was rapid and accurate procedure for the detection mec A gene of MRSA strains as compared to
the conventional methods like cutler, biochemical and microscopically since the time was taken is less and can
help efficiently in infection management.
Keywords: mec A, fem A, MRSA, SCC, PBP2a, PCR, genes, Staphylococcus aureus
Introduction
Staphylococcus aureus is a versatile, opportunistic pathogen able to cause a wide range of diseases in humans,
from minor skin infections to severe illnesses such as septicemia, toxic shock, endocarditis and pneumonia. It is
also able to colonize and infect a variety of other host species, including farm and companion animals and
wildlife. The emergence and dissemination of methicillin-resistant S. aureus (MRSA) since the early 1960s has
posed a major challenge to the treatment of S. aureus infections (1, 2).
Methicillin resistant S. aureus (MRSA) has become a major public health problem worldwide (3). The burden of
MRSA continues to raise, with a growth rate of 14% of all S. aureus strains from clinically significant samples
in New South Wales, Australia (4). The rising colonization rates lead to the increasing of infection rates in the
community and in hospitals. The consequence to the health care system is longer hospital stays and greater costs,
which approximately double the expenditure per patient (5).
The resistance in MRSA is due to the expression of Penicillin binding protein (PBP2a) encoded by mecA genes
(6,7) which is located on the Staphylococcal cassette chromosome (SCC) (8), a large genetic mobile element
which differs in size and genetic composition among different strains of MRSA (9). Different types of SCC mec
cassettes were extensively studied by PCR techniques. The resistance mechanism involves changes or defects
brought about by mutation on mecA gene which results in the organism’s resistance to antibiotics. In addition,
other antibiotic resistance genes may also be present in the cassette rendering resistance to multiple antibiotics.
Journal of Natural Sciences Research www.iiste.org
ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online)
Vol.4, No.1, 2014
113
Detection of mecA gene by Polymerase chain reaction is considered as the gold standard (10, 11) for methicillin
resistance as these genes are highly conserved among Staphylococcal species. In the present study, the PCR
method was used for the detection of mecA genes among the MRSA strains.
Among the most important of these pathogens are vancomycin-resistant enterococci (VRE) and methicillinresistant
Staphylococcus aureus (MRSA). As summery; the majority of MRSA strains have been associated with
hospital-acquired colonization and infections. MRSA strains in nursing homes and long-term care facilities are
usually of nosocomial origin , and most MRSA strains isolat