ISOLATION, IDENTIFICATION AND BIOCONTROL OF SALMONELLA TYPHIMURIUM IN KARIESH CHEESE BY BACTEIOPHAGE

Abstract

The study aims to assess the possibility of biological control on one of the most serious patho-genic microbes that found to infect Kariesh cheese, namely Salmonella typhimurium. To achieve this object, firstly a total of 20 Kari-esh cheese samples were collected randomly from various markets located at Cairo and exposed to microbiological isolation and identification of S. typhimurium. The obtained results revealed that, S. typhimurium was detected in 30% of surveyed market Kariesh cheese according to the strain identified by polymerase chain reaction (PCR) technique. Secondary, five sewage water samples were obtained from Fac. of Agric., Ain Shams Univ., and Shoubra EL-Kheima station of drinking and sewage water for specific bacteriophage isolation and morphology particles of Salmonella bacte-riophage was examined by transmission electron microscope. Third, pasteurized skimmed buffalo's milk was converted into experimental Kariesh cheese at 40 o C by milk inoculation with 2% of freshly activated yoghurt bacterial starter culture and then milk was divided into 5 equal portions. The 1 st portion considered as control. The 2 nd , 3 rd , 4 th and 5 th portions were contaminated with equal level (1%) of S. typhimurium suspension containing 10 5 colony forming units (CFU)/mL, previously isolated from foregoing surveyed Kariesh cheese samples, followed by adding phage suspension, from which isolated from sewage water, containing 10 8 plaque forming units (PFU)/mL at the levels of nil, 1, 2 and 3% respectively. All portions were separately incubated at the same temperature up to curdling. The curds were cut and individually filled into stainless steel moulds lined with cheese cloth and consolidated by a slight pressure for 24 h. The blocks of curd were then cut, dry salted using 2% NaCl (w/w) and packaged into plastic containers. Experimentally, there were proportional reductions in lactic acid bacteria (LAB) population as the level of phage spiked into cheese milk increased, as which the reduction rate of LAB count during cold storage period (CSP) prolonging was however declined.