C olorectal cancer has become predominant cancer and now accounts for approximately 10% of cancer-related mortality in western countries (Kuipers et al., 2015). Colorectal cancer is the second-and third-most common cancer in women and men, respectively (Kuipers et al., 2015, Kuipers et al., 2013). Colorectal cancer (CRC) is the third most common mortality factor in Iran (Dolatkhah et al., 2015). The rate of an outbreak of CRC depended on the geographical regions (Khosravi Shadmani et al., 2017, Dolatkhah et al., 2015, Johnson et al., 2013). A high incidence of CRC has been observed in developed nations, such as the US, and Canada, and developing countries also continue increasing outbreak rates (Jemal et al., 2010, Khosravi Shadmani et al., 2017). In Iran, the prevalence of the CRC has experienced the same growth as those of other Asian nations, with CRC accounting for 8.4% of all research Article Abstract | Background: Colorectal cancer is one of the most common cancers in Iran. There are many effective methods of treatment of it. As a conventional treatment, chemotherapy has become a part of treatment scheme for patients with colorectal cancer. Enterococci are intestinal commensals. They are opportunistic pathogens which cause millions of human and animal infections annually. The aim of this study was to investigate the side effects of chemotherapy of sufferers from colon cancer on the antibiotic resistance of microflora. Methods: In this study, participants were divided into three groups: Group A: 300 colorectal cancer patients before the start of the cancer chemotherapy, group B: 300 healthy people living with patients at least for recent 12 months and group C includes 300 patients with colorectal cancer after six weeks chemotherapy. RNA was extracted from the stool of all the participants of the study. Following the RNA extraction from stool samples, cDNA libraries were constructed. Eight virulent genes (vanA, vanB, gelE, esp, asa1, aggA, efaA and enlA) of E. faecalis were evaluated by real-time qPCR. results: The results were showed the expression level of the virulent genes in the group of the patients after chemotherapy was significantly higher than the two groups of B and C (P<0.05). Although the expression of these genes in the group of patients before chemotherapy was higher than that of the control group, this increase was not significant (P>0.05). conclusions: It seems that chemotherapy could change the balance of mRNA expression of microflora such as antibiotic resistance genes. These could be responsible for infections arisen after ending the chemotherapy of cancer.
