Isolation and Identification of Gram-Negative bacteria in soil samples of Koronadal City Sanitary Landfill

Sanitary landfills, designed to manage waste and minimize environmental impact, can inadvertently become reservoirs for pathogenic microorganisms, posing health risks. This study aimed to isolate and identify gram-negative bacteria in soil samples from the Koronadal City sanitary landfill, which processes 4 of its 15-ton daily capacity of residual and biodegradable waste through composting and plastic recycling. Sterile techniques, including the use of a Class II Biosafety Cabinet, ensured the accuracy of bacterial isolation using nutrient, tryptic soy, and MacConkey agar, with identification performed via the API 20E kit. The study revealed diverse bacterial colonies with varied morphological characteristics, including forms such as circular, convex, irregular, and spreading, and colors like white, off-white, yellow, and pink. There are eleven (11) gram-negative bacteria were identified such as Enterobacter cloacae, Serratia liquefaciens, Enterobacter aerogenes, Serratia plymuthica, Klebsiella pneumoniae ssp. rhinoscleromatis, Erwinia spp., and Pantoea spp., Stenotrophomonas maltophilia, Vibrio fluvialis, Pseudomonas fluorescens/putida, and Burkholderia cepacia, were isolated. Soil analysis showed an alkaline pH of 7.87, high phosphorus, sufficient potassium, and moderate salinity (158.27 µS/cm), creating conditions favorable for gram-negative bacteria. These bacteria possess adaptive traits such as metabolic versatility, stress responses, and a protective outer membrane, enabling survival. The presence of known human pathogens raises health concerns due to waste pollution. However, these bacteria also hold potential for genetic engineering to mitigate pathogenicity while enhancing plastic waste degradation.