[Isolation of shigatoxin-producing Escherichia coli [STEC] from meat samples by PCR in Tehran and evaluation of antibacterial patterns of isolated strains]

Shigatoxin-producing Escherichia coli [STEC] is an emerging foodborne pathogen of worldwide public health importance. This bacterium has been reported as an etiological agent of many outbreaks and sporadic cases. Studies in different countries have shown that food items maybe contaminated by this pathogen. The present study was carried out to determine the frequency of STEC contamination of meat samples, collected in Tehran, as well as defining genotype and antibiotic susceptibility patterns of isolated bacteria. In a period of one year [from 1 July 2004 to 30 June 200, 250 beef samples were collected from different markets of Tehran city. For detection and isolation of STEC from beef samples, conventional culture and PCR were applied. Then, Antibacterial resistance patterns of isolated strains were determined by standard disk diffusing method. Among 250 beef samples, 47[18.8%] were positive for stx genes by PCR. However, only 30[12%] successful isolations of bacteria were made. Of the 30 STEC isolates, 24 [80%] carried the stx2 gene only, while 2 [6.7%] isolates gave positive results for both stx1and stx2. Four isolates [13.3%] possessed stx2 and eae genes. According to the antibiotic resistance tests, all isolates were susceptible to Gentamicin, Imipenem, Norfluxacin, Enrofloxacin, Nalidixic acid, Ciprofluxacin and Ceftazidime. The percentages of isolates that were resistance to the other antibacterial agents were as following: Olendeomycin:100, Erythromycin:100, Cephalothin:67, Amoxycillin-Clavulanic acid: 46.6, Chlortetracycline: 13.3, Tetracycline: 10 and Streptomycin: 6.6. Results of this study indicate that retail raw meats may often be contaminated with antimicrobial-resistant STEC and cautionary efforts are necessary in order to prevent them from contaminating with this bacterium

Detection of listeria monocytogenes in milk by the polymerase chain reaction

Listeria monocytogenes may be the cause of meningitis and sepsis. It is transmitted via food products. Precise detection of this organism would undoubtedly play a significant role in prevention of this infection.Polymerase chain reaction method was developed for detection of Listeria monocytogenes in milk samples after enrichment culture. It consists of culturing samples in Listeria enrichment broth, followed by DNA extraction and detection of the organism sing PCR.Dilutions of Listeria monocytogenes in milk were subjected to PCR amplification after enrichment culture. When determining the sensitivity of the method, it was found to be possible to detect 37 colony forming unit of the bacterium in milk. When this PCR method was applied to extract of DNA from different bacteria no PCR products were observed.The method was assessed as a sensitive, specific and time-saving way of detecting L. monocytogenes in milk samples