Phenotypic and Genotypic Detection of Enterotoxigenic Staphylococcus aureus in Domestic Dairy Products in Port Said Governorate, Egypt

Abstract

Staphylococcus aureus is an important food- borne pathogen involved in a variety of invasive diseases.
So the current study aimed to detect the frequency of contaminated dairy products by S. aureus and the
presence of enterotoxins genes in the isolated S. aureus strains. One hundred samples of milk and milk
products were collected randomly of different areas in Prot Said governorate. Thirty milk samples;
twenty raw milk, six pasteurized. milk and four powdered milk. Thirty cheese samples; ten karish
cheese, five damitta cheese, five rommy cheese, five cheedar cheese and five cooked cheese. Twenty
Yoghurt samples; ten canned yoghurt pasteurized and ten hand-made yoghurt non-pasteurized.
Staphylococcus aureus strains were isolated by cultivation on two selective media, Baird-Parker agar
and Mannitol Salt agar . This study deteted no S. aureus growth at pasteurized milk , the organism in
pasteurized milk by a percentage of (70%) and attributed that to inefficacy of the thermal process. The
current study detected S. aureus in 50 % of the examined samples of cheese. S. aureus only in 10 % of
the cheese samples Karish cheese was the highest in S. aureus contamination (70%) among different
types included in the present study. Rommy and damitta cheese also show a high rate o contamination
(60%). The least percentage was in cheedar and cooked cheese (20%) each. This may be due to
unhygienic storage and handling of rommy and damaitta cheese while cooked and cheedar cheese
were sold sealed. Yoghurt is the most popular type of fermented milk in Egypt, the present study
detected S. aureus in 35% of all examined samples. Similar, S. aureus detected in 72% of yoghurt
samples collected from different dairy shops and supermarkets, in Prot Said governorate. The present
study detected S.aureus in 40% of the examined samples of both cream and butter, which came after
milk (53.5%) and cheese (50%). Percentage of positive samples for S. aureus were higher in milk (53.3
%), followed by cheese (50 %), cream and butter (40 %) and lately yoghurt (35 %).Staphylococcal
Enterotoxins are classified by serological criteria into types designated SEA to SEE and SEG to SEU
and encoded by sea to see and seg to seu genes. One of the goals of this study is to determine the
presence of enterotoxin genes among isolated strain of S. aureus from dairy Products. To achieve this
goal, Multiplex PCR technique was applied on -S. aureus colonies from each positive sample isolated
from culture on Baird- Parker agar. In the present study enterotoxin genes were detected in 19 isolated
strains of S. aureus out of 46 strains positive for S. aureus in a percent of (41.3 %). This result is higher
than that detected by enterotoxin gene in (31.1 %) in isolated S. .aureus colonies from milk and milk
products. On the other hand SE detected gene in 37 % of raw milk samples, SEB is also incriminated in food poisoning. Staphylococcal enterotoxin (A) gene was highly
reported (52,6%), while enterotoxin (B) gene was reported in (31.6%). Double enterotoxin genes (sea
and seb) were reported in (15.8%). Regarding genotypic findings by PCR, sea gene was isolated with a
higher frequency than seb gene as it was detected in 52.6% of all isolated enterotoxin genes, followed
by seb (31.6%) and lastly (sea+seb) (15.8%). agarose gel electrophoresis for PCR showing of 270. bp
sea gene and 165 bp seb gene. (Lane M) is the ( 100 bp ladder marker), (Lane 2) is for sea, (Lane 3) is for
seb, (Lane 4) is for both genes (sea& seb).