ABSTRACT

This study investigated the isolation of microorganisms from used and unused engine oil samples. The major bacterial isolates from the engine oil samples belong to Bacillus sp., Staphylococcus aureus, Escherichia coli and Pseudomonas sp. respectively, whereas the fungal isolates includes Aspergillus niger, Aspergillus flavus, and Penicillium sp. The total heterotrophic plate count (THPC) for the used and unused engine oils ranged from 1.4 × 105cfu/ml to 4.4 × 105cfu/ml. The total coliform plate count (TCPC) of the used and unused engine oils ranged from 1.4 × 105cfu/ml to 4.1 × 105cfu/ml. The total fungal plate count (TFPC) of the used and unused engine oils ranged from 1.5 × 105cfu/ml to 4.0 × 105cfu/ml.It was observed that Pseudomonas sp. is the most frequently occurring bacteria isolate with a percentage occurrence of (35.0%) whereas Escherichia coli had the least percentage occurrence of (10.0%). Aspergillus niger is the most frequently occurring fungal isolate with a percentage occurrence of (41.7%) whereas Aspergillus flavus has the least percentage occurrence of (25.0%). Finding feasibility in utilization of engine oil by microbial groups revealed that the isolates utilized these oily materials. The isolates showed different degrees of turbidity with the highest turbidity showed in the used engine oil sample for some of the tested strains. Engine oils are prone to deterioration when they are exposed to microbial activities, especially when they are in-use as shown from the study. Therefore microbial growths are proxies for deterioration in engine oils. The introduction of preservatives, additives and biocides in the engine oil could prevent microorganisms from infesting the engine oil thereby increasing its shelf life and preventing the engine parts from touching each other.