ABSTRACT
A total of 20 L. monocytogenes strains isolated from some local fish from different shops and markets located in 5 towns in Egypt. The total incidence of L. monocytogenes in raw fish was 9.3%, it was predominated in Clarias [4.19%] followed by Saurus [2.79%] then Sardines [2.33%]. They were phenotypic characterized with respect to 8 characters, carbohydrate fermentation profiles showed variation in utilization of dalcite, lactose, maltose, mannitol, starch and xylose while glucose, salicin, sucrose, trehalose and rhaminose yielded positive in all strains. They were tolerant to NaCl at high salt concentrations ranged from 8% to 20%. The growth inhibition of L. monocytogenes in presence of organic acids not occurred within 5 and 10 minutes but occurred after 24 h incubation at 37°C even with different concentrations [0.5, 1, 2 and 5%]. The positive percent of Congo red binding activity and Lecithinase production were 90% and 85% respectively. The drug susceptibility characterization of L. monocytogenes cleared that all isolates were resistant [100%] to colistin Sulphate, enrofloxacin, nalidixic acid and oxolinic acid, but were susceptible to chloramphenicol [100%] followed by erythromycin [80%], amoxycillin [75%] then oxytetracycline [70%]and ciprofloxacin [65%]. Pathogenicity in laboratory animals showed that 20 strains caused keratoconjunctivities in G. pig and only 16 strains killed the mice within 7 days. All strains were haemolytic to RBCs of horse, sheep, G. pig and human and only showed change in haemolysis with addition of D-mannose as follows 85, 75, 50 and 50% in horse, sheep, G. pig and human RBCs respectively. The count of L. monocytogenes inoculated in Sardine was affected by heat treatment where increasing time of exposure and degree of temperature reduced count as 100°C for 20 minutes completely eliminated L. monocytogenes, while at 70°C for 20 minutes only reduced count and having no effect at 50°C even with increasing time. Whereas treatment with organic acids revealed that when the acid concentration increased, the growth rate of L. monocytogenes decreased and the relative inhibition effect was generally lactic> acetic> citric acid, form interest of this work that low concentration of organic acids [0.5%] enhanced growth of L monocytogenes. Application of antimicrobial ice on Sardine not completely eliminated but reduced L. monocytogenes count from 1 X 10[8] to 1.5 X 10[5] and 2 X 10[3] after 60 and 120 minutes exposure respectively