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Research Article

Detection the Staphylococcus aureus Producing Enterotoxin Isolated from Skin Infections in Hospitalized Patients

A.A. Imanifooladi, M. Sattari, Sh. Najar Peerayeh, Z.M. Hassan and S.R. Hossainidoust
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Staphylococcus aureus is a major human pathogen that produces a wide array of toxins, thus causing various type of disease symptoms. Staphyloceccal enterotoxins (SES), a family of 9 major serological types of heat-stable enterotoxins, are a main cause of gastroenteritis and skin infection. In this study to determine the extent of enterotoxin-producing S. aureus in skin infections of hospitalized patients, their samples were screened and the results showed that 42% of totally 200 patients studied in this research carried S. aureus and 45% of these S. aureus produced Staphylococcal enterotoxins. Twenty percent produced enterotoxin A, 25% produced enterotoxin B and 4.7% produced both enterotoxin A and B. The results demonstrated a high level of enterotoxigenic and multi drug resistance S. aureus in skin infections of hospitalized patients.

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A.A. Imanifooladi, M. Sattari, Sh. Najar Peerayeh, Z.M. Hassan and S.R. Hossainidoust, 2007. Detection the Staphylococcus aureus Producing Enterotoxin Isolated from Skin Infections in Hospitalized Patients. Pakistan Journal of Biological Sciences, 10: 502-505.

DOI: 10.3923/pjbs.2007.502.505



Staphylococcus aureus strains have long been recognized as an important pathogen in human disease. They populate the skin, mucous, membranes, anterior narse, eyes and gastrointestinal tract of asymptomatic individuals (Bradley et al., 2005; Marples et al., 1990; Heczko et al., 1990). They can exist in thesae domains as residents or as temporary members of normal flora without causing disease (Altoparlak et al., 2004). The mean carrier rate in general population were found as 37.2%, in health care worker as 26.6% and in patient pf admission as 35.7% (Kluitmans et al., 1997). However, some strains of S. aureus also cause infections in humans including skin infections and food poisoning (Bergdoll et al., 1979; Noble and White, 1987). S. aureus also account for about 47% of all nosocomial infections (Wieneke et al., 1993 ). S. aureus generates a wide range of toxins and enzymes that facilitate it in overcoming the host defenses. Some strains produce one or more of nine serologically related enterotoxins (type A to R) (Bradley et al., 2005; Balaban et al., 2000). The human anterior nares and finger tips are important sources of enterotoxigenic and non enterotoxigenic staphylococci (Balaban et al., 1990; Chow et al., 1989). Nasal carrier of antibiotic- resistant S. aureus among hospital workers and hospitalized patients has been widely studied, but data on the enterotoxigenic S. aureus is less extensive (Kluitmans et al., 1997). This study was designed to determine whether there was a high frequency of enterotoxin (SEA-SEB) producing strain S. aureus in hospitalized patients and try to establish whether the most of these strains were multidrug resistant. The results revealed a significant relation between enterotoxigenic S. aureus isolated from hospitalized patients and hospital workers carrying S. aureus.


Sample collection: Two hundred patients hospitalized with skin infections in Tehran during Feb. 2005 until Sep 2005 were selected. Sterile swabs moistened in sterile normal saline and secretion of lesions was collected. Swabs were rotated five to six times and used to inoculate Mannitol Salt Agar (MSA) and blood agar plates (Merck, Oxoid, High media) in duplicate and incubated at 37°C. Plates were examined after 24 and 48 h incubation. Isolates identified as S. areus by growth characteristics on blood agar and MSA, gram stain reaction, catalas test, tube coagulase test and DNase test. Pureculture of isolates were stored in skimed milk broth at -75°C. Working cultures were maintained on brain heart infusion agar slopes at 4°C.

Detection of enterotoxins: Staphylococcal enterotoxins were obtained by Sac-culture as published previously (Robbins et al., 1974). Detection of enterotoxins were evaluated with ochtorlony test (Braga et al., 2005). Reference antitoxins were provided from Sigma Company.

Antibiotic susceptibility testing: The antibiotic susceptibility was determined by agar disc diffusion method as recommended by the National Committee for Clinical Laboratory Standards (standard M-2 A5/1995) with the following discs (Table 2). The susceptibility tests were performed on Mueller-Hinton agar with S. aureus strain ATCC 25923 as a control. The Mast diagnostic instruction sheet was followed for the zone size interpretation.


Detection the S. aureus isolated from skin infections: To assess the S. aureus in the skin infection, 200 patients with skin diseases were estimated and the protocol in Table 1 was performed the results showed that 84 S. aureus were isolated from skin infections in hospitalized patients and 45% of the S. aureus produced staphylococcal enterotoxins, that 20% of them produced SEA, 25% of them produced SEB, 4.7% of them produced SEA+SEB. The hospital studied in this research is one of the reference center in Tehran.

Susceptibility of S. aureus isolated from skin infections to antibiotics: To assess the susceptibility of the isolated S. aureus in the skin infection 200 patients were estimated and the protocol in Table 2 was performed the results for susceptibility of the isolate to 12 different antibiotics are shown in Table 2. While 1% of strains are resistant to vancomycin.

Table 1:
Staphylococcal Enterotoxin (SE) from skin infections in hospitalized patients

Table 2:
Susceptibility of the Staphylococcus aureus isolates from skin infections in hospitalized patients

There were some variations in antibiotic sensitivity patterns, but there was no significant difference between extent of toxin production and antibiogram patterns, which was an important observation.


An intention of this study was to determine about the population enterotoxigen S. aureus from skin infection on the hospitalized patients. S. aureus produces a set of exotoxins including SEs and toxic shock syndrome toxine-1(TSST-1) which cause skin infections, food poisoning and a life threatening toxic shock syndrome (TSS), respectively (Edwards et al., 1996; Tomi et al., 2005). The results showed that 42% causes of skin infection was S. aureus, which is higher than reported by previous studies (Umolu et al., 2002). This frequency was high compared to carrier in the hospital workers and general population which is 25 and 38%, respectively (Heczko et al., 1990; Balaban et al., 1990; Paul Moeatl, 1982; Shanson et al., 1980). These toxins are intermediate Molecular Weight proteins (22-30 KD) that also act as superantigens due to their ability to bind to MHC-II molecules on APCs and stimulate all T-cells bearing particular Vβ on their T-cell receptors (White et al., 1989; Herman et al., 1991). Although these are two separate functions localized on separate domains between these activities and in most cases a loss of superantigen activity (because of genetic mutation) results in loss of enterotoxic activity as well (Harris et al., 1993). However 45% of the S. aureus strains produced enterotoxins. This figure was more compatible than that reported by Naidu (Naidu et al., 1989), but higher than that reported by Edward (Edwards et al., 1996) and lower than that reported by Tomi et al. (2005). Isolates from skin infection exhibited high degree of enterotoxigenicity compared to nasal carrier of enterotoxin-producing S. aureus (Al bustan et al., 1996) also, the relationship between S. aureus nasal carrier and staphylococcal skin infection was significance (Toshkova et al., 2001; Tulloch, 1954). It seems that there is a relation between productivity of enterotoxin by S. aureus and the intensity of skin infections. In order to establish the fact it requires more studies, because enterotoxigenic S. aureus was present in more than 50% of patients with Psoriasis and Atopic dermatitis significantly correlate to enterotoxin production of isolated S. aureus strains (Tomi et al., 2005). The result of antibiogram showed that more of enterotoxigen S. aureus that cause skin infection in comparison with Umolu study are more resistance while related to Vancomycin showed only 1% resistance (Table 2) (Umolu et al., 2002). This probably depends to the fact that isolates from skin infection in our study originate from hospital strains and/or infection from surgical procedure that Weinstein also established that (Toshkova et al., 2001; Weinstein, 1959). It seems that the nosocomial strains are more resistant than general or food poisoning stains. A possible explanation for this result is that resistance mutant strains may be produced due to continuous encounter of nosocomial strains with different antibiotic used in hospital (Essawi et al., 1998). The present findings strongly confirmed this explanation and suggest that only choice drug for treatment is Vancomycine. However it is recommended that treatment against these strains could be prescribed as multidrug (synergism). Several methods have proposed and are in use for production and analysis of the enterotoxins. In the analysis of a strain for enterotoxigenicity only a small amount of culture supernatant is needed thus methods have been provided that give a few milliliters of relatively concentrated enterotoxin. These methods including the Sac-culture, the semi- solid agar plate and shake-flask (Robbins et al., 1974). The results obtained from our previous study concerning a comparison of the above method production of enterotoxins supported that the sac-culture method was superior (Imanifooladi et al., 2004).


This study was supported as a grant of Ph.D Thesis in Medical Sciences School, Tarbiat Modares University.

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