Phenotypic Characterization of Protease-Producing Enterobacter cloacae Isolates from Colorectal Cancer Patients and Their Association with Serum IL-6 and MMP-9

Abstract

Colorectal cancer (CRC) is one of the greatest global health burdens, and recent data indicate the possible involvement of bacterial virulence factors in tumor development. One of these factors is protease-producing Enterobacter cloacae, whose impact may be connected with the inflammatory process and tissue remodeling. To perform the phenotypical characterization of protease-producing Enterobacter cloacae strains isolated from colorectal cancer patients and investigate their connection with serum interleukin-6 (IL-6) and matrix metalloproteinase-9 (MMP-9). This is a hospital-based comparative cross-sectional study of 90 patients with histopathologically proven CRC. Isolation and identification of bacteria were done by classical microbiology procedures and VITEK-2 system. Protease production was investigated phenotypically by using skim milk agar. Concentrations of IL-6 and MMP-9 in serum were measured by ELISA. From all patients, Enterobacter cloacae was isolated in 32 (35.6%) cases, 21 (65.6%) of these isolates being protease producers. IL-6 and MMP-9 concentrations in serum samples were statistically higher in patients with protease-positive isolates (33.2±8.7 pg/mL and 8.42±1.36 ng/mL respectively) than in those with protease-negative isolates and those who did not have E. cloacae isolation (P<0.001). There was a positive correlation between protease production and IL-6 concentration (r=0.56), and MMP-9 concentration (r=0.63). Protease-positive isolates were found to be independent predictors of an advanced tumor stage (OR=3.28, P=0.009). Bacterial isolates producing proteases from E. cloacae are common among patients with CRC and are associated with increased biomarkers of inflammation and matrix destruction and with advanced tumor stage, which may indicate a link between the bacterial protease phenotype and inflammatory status and characteristics of advanced CRC.