Effect of liquid nitrogen freezing and subsequent storage on survival of Staphylococcus aureus and Streptococcus pyogenes in treated prawn meat

Prawn meat treated with Streptococcus pyogenes B-49-2 culture and Staphylococcus aureus ATCC-12598 culture were frozen in conventional plate freezer at -40°C and by spray type liquid nitrogen freezer. The frozen products were stored at -18°C. Streptococcus pyogenes B-49-2 showed low sensitivity to cold injury during freezing and frozen storage. Staphylococcus aureus ATCC-12598 survived during the entire storage period of 240 days. Total bacterial count of untreated prawn meat was found to be always lesser in liquid nitrogen frozen products than that in plate frozen products.

Study of effect Rosmarinus officinalis oil and nisin on the growth of Streptococcus iniae in lab conditions and fillets of rainbow trout (Oncorhynchus mykiss)

Fish are an important part of a healthy diet since they contain high quality protein, but typically present a low fat percent when compared to other meats. Fish is an extremely perishable food commodity. On the other hand, food borne diseases are still a major problem in the world, even in well-developed countries. The increasing incidence of food borne diseases coupled with the resultant social and economic implications means there is a constant striving to produce safer food and to develop new antimicrobial agents concerns over the safety of some chemical preservatives and negative consumer reactions to preservatives they perceive as chemical and artificial, have prompted on increased interest in more ‘‘naturalgreen’’ alternatives for the maintenance or extension of product shelf-life. Particular interest has focused on the potential applications of plant essential oils. However, to establish the usefulness of natural antimicrobial preservatives, they must be evaluated alone and in combination with other preservation factors to determine whether there are synergistic effects and multiple hurdles can be devised. In this study, were evaluated the effects of different concentrations of Rosmarinus officinalis and nisin and storage time (15 days) on growth of Streptococcus iniae GQ850377 in a lab conditions and a food model system (fillets of rainbow trout) in 4 and 8 °C. In addition, we also studied multi factorial effects of four different concentration of rosemary, three different concentrations of nisin, two different levels of pH in 3 temperature 4,15 and 37 °C on log% of S.iniae during 43 days in BHI broth. The results on growth of S. iniae were evaluated using SPSS 20.0 statistical software and analyzed the logarithm of total count of the bacterial by Tukey Test. Results were considered statistically significant when P<0.05. MIC and MBC values of rosemary and nisin were 0.03, 0.075 % and 5, 40 μg/mL, respectively. The growth of S. iniae was effected significantly (P<0.05) by rosemary and nisin and also combination of rosemary and nisin in 4 and 8 °C. Samples treated with 0.135 and 0.405 % of rosemary showed a significant decrease on the growth of the bacteria compared with control sample(P<0.05). The most ١٤٦ inhibitory effects were seen in samples treated with 0.135 and 0.405% of rosemary until 9 days after storage. Also, the synergism effects of rosemary and nisin on the growth rate of bacteria was significant (P<0.05) compared with untreated samples and samples treated with the rosemary or nisin, only. Synergistic effects was observed at concentration of 0.405% rosemary and 0.75 μg/mL nisin in both temprature. Results of this study showed that different concentration of rosemary a significant inhibitory effect (P<0.05) on log% of S. iniae, in BHI broth in pH 5.5 and 7 in 4,15 and 37 °C during 43 days. In concentration of 0% rosemary (control) in pH 5.5 and 7 and 37°C, log% were 1.099 and 3.15, whereas in concentration of 0.015% rosemary were -4/241 and 1.454, respectively. The use of essential oils may improve food safety and overall microbial quality. If essential oils were to be more widely applied as antibacterials in foods, the organoleptic impact would be important. In addition, it is recommended to apply essential oils or their compounds as part of a hurdle system and to use it as an antimicrobial component along with other preservation techniques. Thus essential of R. officinalis with high antibacterial activity selected in this study could be a potential source for inhibitory substances against some food-borne pathogens and they may be candidates for using in foods or food-processing systems.

Pathogenesis of Yersinia ruckeri-like isolates and compared with Streptococcus sp. in rainbow trout, Onchorhyncus mykiss

Pathogenesis of an isolate of Yersinia rukeri-like bacterium was studied in rainbow trout weighting 8-12 g at 20C and acceptable water quality for 20 days.

An assessment to pathogenicity of Streptococcus iniae obtained from rainbow trout fish in Fars Province

In order to evaluating Streptoccocus iniae pathogenicity recovered from trout in Fars province a total number of 400 healthy (15-20g) fingerling fish specimens which were kept in 1000 liters ponds and after spending compatibility (adaptation) period in new environment and desired condition as aspect of temperature, pH, food and density relative to accomplish disease experiments in interamusclar injection method with 3 × 10 3 , 3 × 10 4, 3 × 10 5, 3 × 10 6 ,3 × 10 7 bacterium cell dilutions per each fish, interaperitonal method with 2 × 10 3 , 2 × 10 4, 2 × 10 5, 2 × 10 6 ,2 × 10 7 dilutions of bacterium cell and in water bath method with 2 × 10 3 , 2 × 10 4, 2 × 10 5, 2 × 10 6 2 × 107 dilutions in 20 degree centigrade temperature were used. Control groups according to above (mentioned) method with 0.1cc sterile physiological serum per each fish were injected. Clinical and autopsy signs that observed in injected groups were includes: body darkness, swelling of abdomen, exophthalmy sometime with eye ocular haemorrhagy, anal (rectal) prolaps, blood congestion and petechia in muscles and congestion and haemorrhagy in intestines. Infectious results in interamusclar injection shown that, mortality 22 hours after injection begans and in 3 × 107 cells dilution per each fish 30 hours pass the injection was reached above 50 percent, so that the amount of LD50/ 30h in 3 × 10 7 cells per each fish was estimated. In interaperitonal injection method was shown those 20 hours after injection mortality begins and up to maximum 80 hours after continued and 32 hours after injection in 2 × 10 7 cells dilution mortality was reached above 50 percent, so that LD50 /32 hour in 2 × 10 7 cell dilution per each fish estimated. In water bath method even after sparing 15 days mortality had been too low which indicating long process of disease. By microscopic study of tissues, dilatation of bowman capsule, shrinkage of glomerols, increasing of melano macrophage centers, degeneration, necrosis of urine tubules in kidney tissue, dilatation of sinusoids, congestion of hepatic vessels, increasing of melanoma macrophages and hepatocite vacuolization in liver tissue, spleen congestion, heart pericardit, ocular haemorrhagy, congestion, edema and separating of basement membrane from gill secondary lamellae can be referred.