Lactic Acid Bacteria Diversity In Fresh Cucumbers And Tomatoes: Implications For Food Safety And Preservation

This study investigated the occurrence, diversity, and antimicrobial potential of lactic acid bacteria (LAB) isolated from fresh cucumbers and tomatoes obtained from selected markets in Calabar. Microbial enumeration revealed that tomatoes consistently harbored higher LAB counts than cucumbers, with Atimbo Market tomatoes recording the highest load (8.7 × 10⁶ CFU/g) and Marian Market cucumbers the lowest (3.2 × 10⁵ CFU/g). The higher prevalence of LAB in tomatoes was attributed to their softer texture, elevated sugar content, and higher moisture levels, which provide a favorable environment for microbial proliferation. Morphological characterization showed the dominance of rod-shaped isolates (Lactobacillus spp.), while cocci (Lactococcus, Enterococcus, and Streptococcus spp.) were also detected across all samples, demonstrating a broad microbial diversity. Biochemical characterization confirmed the presence of four LAB genera, Lactobacillus, Lactococcus, Enterococcus, and Streptococcus, each exhibiting distinct physiological traits, including salt tolerance, growth at different temperatures, and arginine hydrolysis. Enterococcus and Lactococcus were more frequently associated with cucumber isolates, while Lactobacillus species were widely distributed across both vegetables. Antimicrobial screening revealed that only three isolates demonstrated inhibitory activity against foodborne pathogens. Lactococcus isolate CU3 inhibited Staphylococcus aureus, Salmonella typhi, and Klebsiella pneumoniae, while Enterococcus isolate TM2 showed modest inhibition against S. aureus and Escherichia coli. The most potent isolate, Lactobacillus CU8, exhibited broad-spectrum antagonism with inhibition zones of 14.0–22.0 mm against all tested pathogens. The findings demonstrated that cucumbers and tomatoes are natural reservoirs of diverse LAB communities, with Lactobacillus species showing the greatest potential for food preservation. The strong antimicrobial activity of selected isolates, particularly Lactobacillus CU8, highlights their potential as natural biopreservatives, offering sustainable alternatives to synthetic preservatives for enhancing food safety and extending the shelf life of fresh produce.