PREVALENCE OF STAPHYLOCOCCUS AUREUS IN FISH PROCESSING FACTORY

The aim of the presented work was the risk assessment of distribution and prevalence of Staphylococcus aureus during processing of cold-smoked fish. There were totally analyzed 80 samples of fish and 50 swab samples at all stages of the processing. Staphylococcus aureus was detected in 74% of analyzed samples. Brining stage was the important critical control point in cold-smoked fish proceesing. doi:10.5219/47


INTRODUCTION
Safety of fish products and their quality assurance is one of the main problems of food industry today.The presence or absence of foodborn pathogens in a fish product is a function of the harvest environment, sanitary conditions, and practices associated with equipment and personnel in the processing environment (FDA, 2001;Huss, 2003).The handling of fish products during the manufacturing process involves a risk of contamination by Staphylococcus aureus, a Gram-positive microorganism causing foodborne human intoxication (Ash, 1997; Shena et al., 2007).These bacteria are salt-tolerant and therefore can contaminate all cured preparations such as cold smoked fish, caviar and fish-based preserves (Hayes, 1995).Fish contains large amount of proteins and their breakdown into amino acids support the growth of Staph.aureus.Staphylococcus spp.may be isolated from newly caught fish, especially in warm waters (Gram and Huss, 2000).Staphylococcus is not found in the normal microflora of fish.This microorganism could be associated with salt In smoked and dried king salmon processed by Alaska Natives, coagulase-negative Staphylococcus species comprised 75% of the staphylococci isolates (Himelbloom et al., 1998).Most of the species of staphylococci, that have been isolated from fish are coagulase negative, namely, Staphylococcus epidermidis, S. xylosus, S. lentus, S. capitis, S. lugdunensis, S. hominis, S. warneri, S. cohnii, S. chromogenes.High Staph.aureus counts (10 4 -10 5 .g - ) occurred and reached 5% of total staphylococci counts.Up to 10 4 Staph.aureus cells.g - can be tolerated in ready-toeat seafoods (FDA, 2004).Enterotoxin production is typically associated with coagulase-positive Staph.aureus when cell populations are 10 5 .g - (Jablonski and Bohach, 1997).
The aim of the study was the assessment of prevalence of Staph.aureus during manufacturing of cold smoked trout.

Sampling
There were totally analyzed 80 samples of fish and 50 swab samples.Fish samples were taken from every step of processing: receiving raw materials, cleaning, separation of fillets, brining, cold smoking, packaging, storing.All samples of fish were collected and placed in sterile polyethylene bags, transported to laboratory and analyzed immediately upon arrival (ISO, 6887-3:2003).Swab samples were taken from all surfaces and tools by Transport swabs (MS 651, Hi Media) (APHA,1992).Detection of Staph.aureus.
For determination of species of Staph.aureus, 10g of each samples of fish fillets were removed aseptically using a scalpel and forceps, and then transferred to sterile tubes with 90ml Baird Staphylococcus Enrichment Broth Salt (M-1091, Hi media) (ISO, 68881-1999).Tubes were incubated for 24 hours at 370C.Then samples from every tube were taken with microbiological loop and spread on the surface of solid media Baird-Parker agar (M-043, Hi Media) and Mannitol salt agar (MM-118, Hi Media).All plates were examined visually for typical colony types and morphological characteristics.For confirmation of S. aureus strains Hicrom Aureus agar (M1468, Hi Media) was used and following biochemical tests were provided.Those results were confirmed by HiStaph TMidentification kit (Hi Media).For confirmation of DNAase reaction of Staphylococcus aureus, 3M Petrifilm Rapid Staphylococcus aureus Count plate (3MPetriFilmTM) was used.

Physical-chemical analysis
Moisture was determined by drying oven with the plates being weight until constant weight was reached AOAC 950.46B ; Novoa et al., 1994)

RESULTS AND DISCUSSION
Contamination level of raw fish by Staphylococcus aureus was low (10 cfu.g -1 ).In samples of frozen fish there was no prevalence of Staph aureus.At the beginning of brining stage, contamination level of fish by Staph.aureus was 100 cfu.g -1 .On third day of brining the contamination level increased up to 3 x 10 2 cfu.g -1 .In the samples of brining solution quantity of Staphylococcus aureus reached 5x10 2 cfu.g -1 .At the smoking stage the further increase up to 10 3 cfu.g - was observed.After packaging and during storage, contamination level of the ready product was decreased to 6 x 10 2 cfu.g -1 .High level of contamination of ready product by Staph.aureus was observed in 74% of the analysed samples.
There was studied the distribution and prevalence of Staphylococcus aureus on skin, in gills, nasal and mouth cavities of live fish by swabbing method.Results have shown the presence of only coagulasenegative Staphylococci, particularly Staphylococcus epidermidis.
Swab samples were taken from all processing surfaces and tools (included hooks and racks).High contamination level of hooks and surfaces of tables was observed.Contamination level of hooks and surfaces of tables was 28 cfu.50cm - and 18 cfu.50cm - respectively.
In all stages the physicochemical parameters were exact and at the same favorable for prevalence of Staphylococcus spp.In accordance with Varnam and Evans (1991), the mentioned parameters have a following ratio -pH = 4; NaCl (%) = 10-15; aw = 0.83.
Increase in contamination level was observed at the beginning of brining process.During this stage the microorganisms which are not able to grow at high concentration of salt in comparison with Staph.aureus are destroyed.One of the primary sources of contamination of fish by Staphylococcus aureus was the multiple use of the same brine solution.Our experiments have shown, that using of the drysalting technology together with preservatives contributes to considerable decrease in the level of contamination of product after salting process.

CONCLUSION
The primary factors affecting on prevalence of Staphylococcus aureus and contamination level of ready to eat fish were identified in this study.
Results of our studies have shown that the brining stage is the important critical control point, during processing of cold smoked fish.Our experiments have shown, that using the drysalting technology together with preservatives contributes to considerable decrease in the level of contamination of product after salting process.When using liquid brine solution the contamination level of fish is 4х10 3 cfu/g, using the dry -salt mixture decreases in the contamination level to 10 cfu/g is occured.Observance of hygienic requirements while preparing liquid brine solution, and also frequencies of its use accordance with

Fig. 1
Fig. 1 Prevalence of Staphylococcus aureus at every technological step of manufacturing of cold smoked trout.

Fig. 2
Fig. 2 Distribution of Staphylococcus aureus on skin, in gills, nasal and mouth cavities of live fish.

(
Storey et al., 1882; CAC/RCP 25-1979) are the important conditions promoting prevention of development and prevalence of Staphylococcus aureus.

(Hansen et al., 1995) or the raw fish (Ferreira et al, 2007) used
in the processing.Contamination of fish products through contaminated surfaces has also been observed in many cases (

Reij et al., 2003). According to Basti et al., (2003) some
kinds of salt smoked fish may be considered as risk of L. monocytogenes and Staph.aureus

Table 1 :
Physical-chemical parameters of fish samples Recovery count number of Staphylococcus aureus from contact surfaces.