Paper 29 issue_1_dr_salaw thabet

Glob. J. Agric. Food Safety Sci., Vol.1: pp. 317 - 325 (2014(
Phenotypic and Genotypic Methicillin resistant Staphylococcus
aureus (MRSA) isolated from raw milk and some Dairy products.
Salaw Sayed Thabet 1
, Manal M. Amin 1
, Walaa M. A. Elsherif 1
, Azhar
Mohamed Hasan 2
and Nahed Mohamad Wahba 1
1
Department of Food Hygiene, Animal Health Research Institute, ARC,
Assiut, Egypt.
2
Department of Bacteriology, Animal Health Research Institute, ARC,
Assiut, Egypt.
ABSTRACT
The aims of this study were to evaluate the occurrence of methicillin-
resistant Staphylococcus aureus (MRSA) in raw milk and milk products samples and
investigate the antimicrobial resistance and molecular characteristics of these strains
using PCR. A total of 90 samples comprising of raw milk, ice cream and Damietta
cheese were randomly collected during 2013 from supermarkets and shops in Assuit
(30 samples of each) and examined for presence of S. aureus. The results revealed
that Staph. aureus was isolated with a percentage of 26.6% in raw milk, 30% in ice
cream and 6.6% in Damietta cheese samples. The results of antibiogram testing
revealed that 3.3% and 6.6 % of the isolated strains from raw milk and ice cream,
respectively show complete resistance and 3.3% from both samples showed
intermediate resistance. However, the isolated strains from Damietta cheese were
sensitive to methicillin. The mecA gene was detected by polymerase chain reaction in
all strains that showed complete and intermediate resistance using antibiotic
sensitivity test (2 from raw milk and 3 from ice cream samples). Significance of
MRSA infection from food remains uncertain.
Keywords: Methicillin-resistant Staphylococcus aureus, milk, ice-cream, cheese,
PCR and mecA gene.
1-INTRODUCTION
Methicillin-resistant Staphylococcus aureus is an important hospital and
community- associated pathogen worldwide (Ho et al., 2008). Foods may serve as an
important reservoir and source of community-acquired MRSA (Jones et al., 2002). In
recent years, MRSA strains have been identified in various foods including bovine
milk, ice cream and ready-to-eat foods (Kwon et al., 2006; Fessler et al., 2011;
Gucukoglu et al., 2013). Therapeutic options for MRSA infections are currently very
limited due to the fact that most MRSA strains are resistant to commonly used
antibiotics such as lactams, macrolides, aminoglycosides, and fluoroquinolones
(Tacconelli et al., 2008). Vancomycin and other glycopeptide antibiotics are
Massive Publisher House M.P.H. Egypt www.mphegypt.com ISSN 2356-7775

Salaw Sayed Thabet, et al. (2014)
presently used for treatment of MRSA infections. Recent studies have shown genetic
similarity between MRSA isolates from food animals, including dairy cows and those
in humans, suggesting transmission between the species (Juhász -Kaszanyitzky et
al., 2007 and Moon et al., 2007). MRSA infections in dairy cattle have been ascribed
to human-to-animal transfer, but the direct transmission is not always known (Juhász
-Kaszanyitzky et al., 2007). Methicillin resistance is mediated by the mecA gene that
encodes penicillin- binding protein 2a, which has unusual low affinity for all beta-
lactam antimicrobials (Pinho et al., 2001). To detect MRSA in milk and milk
products, phenotypic and genotypic methods were used. Phenotypic detection was
based on plating of samples on a selective media, coagulase test and antimicrobial
assay. Genotypic detection of MRSA based on polymerase chain reaction using mecA
specific primer.
2-MATERIAL AND METHODS
2-1 Sample collection:
A total of 90 samples of milk, ice cream and Damietta cheese (30 samples of
each) were collected from shops and supermarkets in Assuit, Egypt).
2-2 Isolation and identification of Staph. aureus: according to Bennett and
Lancette (2001)
All the samples were prepared and enriched on Staphylococci broth for 20 h
at 35º C and then inoculated onto Baird Parker Medium (Oxide, Basingstoke,
England), and incubated aerobically at 37º C for 24 h. The isolates were identified
using established microbiological methods which included colony morphology, Gram
staining and biochemical testing [catalase, coagulase and sugar fermentation (glucose,
sucrose, lactose, mannitol)].
2-3 Antimicrobial resistance testing of coagulase positive S. aureus:
Antimicrobial susceptibility was tested by the single diffusion method
according to Amita et al., (2008). Sensitivity disc of methicillin (oxacillin) at
concentration of 1ug was used to determine the susceptibility of the isolated
Staphylococcus aureus organism (Difco Laboratories and BioMerieux, France).
The antimicrobial susceptibility test was applied according to the guidelines
stipulated by National Committee for Clinical Laboratory Standards "NCCLS"
(2001). The zones of inhibition (ZI) were measured and recorded after 24 h of
incubation at 35º C, and the observations were interpreted. The isolates that were
resistant to methicillin (ZI: 10 mm or less) was regarded as methicillin-resistant
Staphylococcus aureus (MRSA) while those with zone of inhibition (11-12mm) were
regarded as intermediate resistance and 13 mm or more were termed susceptible.
2-4 Polymerase Chain Reaction (PCR)
Primer sequences of Staph. aureus used for PCR identification system according to
Jonas et al., (2002):
62

Phenotypic and Genotypic Methicillin resistant Staphylococcus aureus.……
Application of PCR for identification of MRSA was performed essentially
by using primers (Pharmacia Biotech) for detection of the mecA gene at amplicon
length of 310 bp as shown in the following table.
Table 1. Detection of the mecA gene at amplicon length of 210 bp.
Target gene Oligonucleotide sequence (5′ → 3′)
MecA1 GTA GAA ATG ACT GAA CGT CCG ATA A
MecA2 CCA ATT CCA CAT TGT TTC GGT CTA A
2-5 DNA preparation from bacterial culture (Towner et al., 1998):
An overnight bacterial culture (200 µl) was mixed with 800 µl of distilled
water and boiled for 10 min. The resulting solution was centrifuged and the
supernatant was used as the DNA template.
2-6 DNA amplification reaction of Staph. aureus: according to Geha et al.,
(1994):
Multiplex PCR was used for demonstration of suspected Staph. aureus
isolates using 5X Taq master (Fermentas) containing polymerase enzyme, magnesium
chloride (Mg Cl2), Deoxynucleotide triphosphate (dNTP) and PCR grade water. The
bacterial genomic DNA samples were amplified by PCR in a reaction mixture (25µ l)
containing 13.25 ml of sterile distilled H2O, 2.5ml of 10 x buffer, 0.63 ml of 10m
MNTPs, 1 ml of 25 Mm MgCl2, 1.25 µl of primer F (20 pmol/ml), 1.25 µl of primer R
(20 pmol/ml) and filled up to 25 µl PCR grade water. PCR protocol consisted of the
following steps: an initial denaturation (2 min at 95° C) for 30 cycles, primer
denaturation (1 min at 95° C) for 1 cycle, primer annealing (1 min at 57° C), primer
extension (2 min at 72° C) and a final elongation (5 min at 72° C). PCR products
underwent electrophoresis in 2.5% agarose gel (BioshopR
, Canda inc.lot No:
OE16323) using gel loading buffer (6×stock solution) (Fermentas, lot No: ooo56239),
DNA ladder (molecular marker) 185 and 160 bp (Fermentas, lot No: 00052518) and
stained with ethidium bromide (Bioshop ® Canda Inc, Lot No: 0A14667) to be
visualized by UV light.
3-RESULTS
Table 2. Incidence of Staph. aureus in the examined samples.
Types of samples No. of samples No. of positive samples %
Raw milk 30 8 26.6
Ice cream 30 9 30
Damietta Cheese 30 2 6.6
63

Table 3. Antimicrobial susceptible profile of Staph. aureus isolated from
raw milk, ice cream and Damietta cheese samples.
Staph. aureus strains isolated
from
Resistant strains Intermediate strains Sensitive strains
No. % No. % No. %
Raw milk 1 3.3 1 3.3 6 20
Ice cream 2 6.6 1 3.3 6 20
Damietta Cheese 0 0 0 0 2 6.6
Figure 1. Agarose gel electrophoresis of PCR amplification products using mecA primers for
detection of MRSA (mecA1 and mecA2) showing:
Lane M: 310 bp ladder as molecular DNA marker.
Lane 1: control positive for MRSA gene.
Lane 2 and 3: strains isolated from ice cream samples (classified as resistant by sensitivity test).
Lane 4: strain isolated from raw milk samples (classified as resistant by sensitivity test).
Lane 5: strain isolated from ice cream samples (classified as intermediate by sensitivity test).
Lane 6: strain isolated from raw milk samples (classified as intermediate by sensitivity test).
4-DISCUSSION
Intensive farming with thousands of animals raised in cramped conditions
means faster spread of infections and a greater need for antibiotics consequently.
Three classes of antibiotics rated as “critically important to human medicine” by the
World Health Organisation (cephalosporins, fluoroquinolones and macrolides) have
witnessed an eightfold increase in use in the animal population in the last decade. The
more antibiotics are used, the greater the likelihood that antibiotic-resistant bacteria,
such as MRSA, will evolve. This study was designed to determine the prevalence of
MRSA in raw milk and some milk products such as ice cream and Damietta cheese.
The results revealed that coagulase positive Staphylococcus aureus could be isolated
from 26.6% of raw milk samples (Table 2). The results of antibiogram testing
revealed that 2 MRSA strains (with total percentage of 6.6%) were recovered from
64

raw milk 1 strain (3.3%) was resistant and the other (3.3%) showed intermediate
resistance (Table 3). This incidence was higher than that recorded in bovine milk in
Korea (0.18%), in raw milk in both Switzerland and in China (1.4%) (Kwon et al.
2006; Huber et al. 2009 and Wang et al. 2014). A high prevalence of MRSA in
bovine mastitic milk was reported from some countries such Belgium (9.3%)
(Vanderhaeghen et al. 2010), and Turkey (17.2%) (Türkyilmaz et al. 2010).
Although methicillin is not generally used for treatment of mastitis, MRSA has been
recovered from dairy cattle (Türkyilmaz et al., 2010; Vanderhaeghen et al., 2010).
Furthermore, horizontal transmission of MRSA between dairy cattle and farm
workers has been reported (Juhász-Kaszanyitzky et al., 2007), suggesting that
human contact with MRSA-positive animals or vice versa could provide opportunity
for transmission of MRSA between them. Moreover, MRSA was detected in milking-
associated environmental samples such as milk cup, floor, fence, and ventilation
instrument of the milking parlor in a MRSA-positive milk farm. Also, all MRSA
isolates from the farm environment were genetically identical to those of milk isolates
(Lim et al 2013).
MARSA present in food could potentially cause skin infection, in food
handlers. In some individuals (immmuno-compromised persons and elderly) may
cause Staphylococcal enterocolitis. If food is cooked properly, MARSA cells will be
killed however, as with enterotoxigenic MARSA strains, under condition of
temperature abuse MARSA cells could grow in food produce heat-stable enterotoxins
and cause foodborne intoxication. The difficulty in treating infections caused by
pathogen resistant to multiple antibiotics should motivate efforts to prevent
contamination of food with MARSA.
The antibiotic resistance profile results of MRSA isolates indicated that 2
strains (6.6%) isolated from raw milk samples (one was resistant to methicillin and
the other showed intermediate). Meanwhile, Three strains (9.9% 10%) isolated from̴
ice cream samples (2 were resistant to methicillin and the other showed intermediate
resistance). On the other hand, all the isolated strains from Damietta cheeses were
sensitive for methicillin (Table 3).
The significance of Staph. aureus is its presence in high count (more than
106
/ml or g) in food which may lead to staphylococcus food poisoning (food
intoxication). The staphylococcus enterotoxinis heat stable toxin. If the MARSA is
enterotoxigenic strain, it will be of concern in food, if not; the significance is only
food infection for the handlers and workers with cut wounds. From the present study,
it was noted that high percentage of MRSA isolated from ice cream (9.9% 10%) and̴
this poses a potential health risk to consumers. The possible explanation for the
significant occurrence of MRSA in the studied ice cream samples may be due to
unrestricted and uncontrolled use of antibiotics in animals and farming, besides
unsatisfactory health status of cattle herds. Secondly, a greater percentage of
contaminations during industry are extensively managed, but they still exist in the
contaminated environment (Le Loir et al., 2003; Lowy, 2003; Ono et al., 2008 and
Strastkova et al., 2009). The risk comes from farm workers, vets and abattoir
workers, who may become infected through contact with livestock. In another study,
Wang et al., (2014) stated that although MRSA prevalence in retail foods is relatively
65

low, the risk of its transmission through the food chain, especially by uncooked food,
cannot be disregarded.
mecA is responsible for resisting to methicillin and other beta lactam
antibiotics and is localized in the Staph. aureus chromosome. mecA encodes
penicillin-binding protein 2a (PBP2a), which differs from other penicillin-binding
proteins as its active site does not bind methicillin or other beta lactam antibiotics
(Lowy, 2003). As such, PBP2a can continue to catalyze the transpeptidation reaction
required for peptidoglycan cross-linking, enabling cell wall synthesis in the presence
of antibiotics. As a consequence of the inability of PBP2a to interact with beta
lactammoieties, acquisition of mecA confers resistance to all beta lactam antibiotics in
addition to methicillin (Lowy, 2003 and Sahebnasagh et al., 2011.(
Molecular analysis of the MRSA isolates by polymerase chain reaction
(PCR) was carried out to detect mecA, which is the gold standard for detecting
methicillin-resistance. Five isolates (2 from raw milk and 3 from ice cream) were
positive to the presence of mecA gene (Photo 1). These results go parallel to the
results of sensitivity test indicating that all strains that showed complete and
intermediate resistance carried mecA gene. On the other hand, Adesida et al. (2005)
stated that PCR assays for detection of MRSA do not always give indisputable results,
some isolates have been found to be mecA negative in the PCR, but resistant to
methicillin/oxacillin. Also, some isolates have been found to be mecA positive, but
susceptible to both methicillin and oxacillin (Olonitola et al., 2007). Finally,
measures should be taken to prevent the transmission of MRSA among animals,
humans, and the farm environment.
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68

‫الظاهري‬ ‫التوصيف‬‫و‬‫للمزيسلين‬ ‫المقاوم‬ ‫الذهبي‬ ‫العنقودي‬ ‫للمكور‬ ‫الجيني‬
.‫اللبان‬ ‫منتجات‬ ‫وبعض‬ ‫اللبن‬ ‫من‬ ‫المعزولة‬
‫ثابت‬ ‫سيد‬ ‫سلوى‬1
‫امين‬ ‫محمد‬ ‫منال‬ ,1
‫الشريف‬ ‫على‬ ‫محمود‬ ‫ول ء‬ ,1
‫حسن‬ ‫محمد‬ ‫أزهار‬ ,2
‫وهبه‬ ‫محمد‬ ‫وناهد‬1
1
‫مصر‬ ,‫اسيوط‬ ‫الحيوان‬ ‫صحة‬ ‫بحوث‬ ‫بمعهد‬ ‫الذغذية‬ ‫صحة‬ ‫قسم‬
2
‫مصر‬ ,‫اسيوط‬ ‫الحيوان‬ ‫صحة‬ ‫بحوث‬ ‫بمعهد‬ ‫البكتيريولوجى‬ ‫قسم‬
‫تجميع‬ ‫تم‬30‫محل ت‬ ‫من‬ ‫الدمياطي‬ ‫والجبن‬ ‫كريم‬ ‫واليس‬ ‫الخام‬ ‫اللبن‬ ‫من‬ ‫لكل‬ ‫عينة‬
‫المقاوم‬ ‫الذهبي‬ ‫العنقودي‬ ‫المكور‬ ‫تواجد‬ ‫مدي‬ ‫لمعرفة‬ ‫اسيوط‬ ‫بمدينة‬ ‫ماركت‬ ‫والسوبر‬ ‫البقالة‬
‫عام‬ ‫خل ل‬ ‫للميزيسلين‬2013‫ان‬ ‫البكتريولوجي‬ ‫الفحص‬ ‫من‬ ‫تبين‬ ‫وقد‬26.6‫اللبن‬ ‫عينا ت‬ ‫من‬ %
‫و‬ ‫الخام‬30‫و‬ ‫كريم‬ ‫اليس‬ ‫من‬ %6,6‫الذهبي‬ ‫العنقودي‬ ‫بالمكور‬ ‫ملوثة‬ ‫الدمياطي‬ ‫الجبن‬ ‫من‬ %
‫النتائج‬ ‫وكانت‬ ‫عزلها‬ ‫تم‬ ‫التي‬ ‫للسلل ت‬ ‫الميزيسلين‬ ‫باستخدام‬ ‫اختبارالحساسية‬ ‫اجراء‬ ‫وتم‬
:‫كلتي‬3,3,6,6‫التوالي‬ ‫علي‬ ‫كريم‬ ‫واليس‬ ‫الخام‬ ‫اللبن‬ ‫من‬ ‫عزلها‬ ‫تم‬ ‫التي‬ ‫السلل ت‬ ‫من‬ %
‫و‬ (‫)الميزيسلين‬ ‫الحيوية‬ ‫المضادا ت‬ ‫من‬ ‫النوع‬ ‫لهذا‬ ‫مقاومة‬ ‫كانت‬3,3‫المقاومة‬ ‫متوسطة‬ ‫كانت‬ %
‫حساسة‬ ‫العترا ت‬ ‫فكانت‬ ‫الدمياطي‬ ‫الجبن‬ ‫أما‬ ‫كريم‬ ‫واليس‬ ‫الخام‬ ‫اللبن‬ ‫من‬ ‫العينا ت‬ ‫نفس‬ ‫من‬
‫اللبن‬ ‫من‬ ‫المعزولة‬ ‫المقاومة‬ ‫المتوسطة‬ ‫و‬ ‫المقاومة‬ ‫العينا ت‬ ‫فحص‬ ‫تم‬ ‫وقد‬ .‫الحيوية‬ ‫للمضادا ت‬
‫البلمرة‬ ‫اختبار‬ ‫باستخدام‬ ‫للمزيسلين‬ ‫المقاوم‬ ‫الذهبي‬ ‫العنقودي‬ ‫للمكور‬ ‫كريم‬ ‫واليس‬ ‫الخام‬
‫عترا ت‬ ‫الخمس‬ ‫في‬ ‫المقاومة‬ ‫هذه‬ ‫عن‬ ‫المسئو ل‬ ‫الجين‬ ‫وجود‬ ‫النتائج‬ ‫وأوضحت‬ ‫المتسلسل‬
‫وبسترة‬ ‫ذغلي‬ ‫بضرورة‬ ‫نوصي‬ ‫الدراسة‬ ‫هذه‬ ‫من‬ .‫كريم‬ ‫واليس‬ ‫الخام‬ ‫اللبن‬ ‫عينا ت‬ ‫من‬ ‫المعزولة‬
‫من‬ ‫إل‬ ‫كريم‬ ‫اليس‬ ‫شراء‬ ‫عدم‬ .‫منتجاته‬ ‫تصنيع‬ ‫قبل‬ ‫البسترة‬ ‫استخدام‬ ‫وكذلك‬ ‫تناوله‬ ‫فبل‬ ‫اللبن‬
‫ليتعرض‬ ‫لكي‬ ‫اللبان‬ ‫منتجا ت‬ ‫سلمة‬ ‫لضمان‬ ‫الكبيرة‬ ‫كالشركا ت‬ ‫فيها‬ ‫موثوق‬ ‫مصادر‬
.‫الميكروبا ت‬ ‫من‬ ‫النوع‬ ‫هذا‬ ‫لخطورة‬ ‫المستهلك‬
69

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