Abstract

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One of the drawbacks of land application of digestate is the possibility to contaminate the environment with potentially pathogenic, virulent and antibiotic resistant bacteria. The present study examined specifically the occurrence of virulence markers, haemolytic patterns and antibiotic susceptibility profiles of putative bacterial pathogens encountered during anaerobic digestion of manure before possible land application. Digestates collected from lab-scale semi-batch type anaerobic digesters were evaluated for the detection and occurrence of virulent and antibiotic resistant bacterial pathogens using standard microbiological methods. A total of 75 bacterial isolates were identified from poultry and goat manure samples, which belonged to 10 genera consisting of 40 (53.3 %) gram-positive bacteria (GPB) and 35 (46.7 %) gram-negative bacteria (GNB). Out of the 75 bacterial isolates from both samples, Clostridium sp, B. subtilis and E. coli had the highest frequency of occurrence 10 (13.3 %) each, closely followed by Staphylococcus epidermidis and Pseudomonas aeruginosa 8 (10.6 %) each, Staphylococcus aureus 7(9.33 %), Vibrio cholerae and Salmonella sp 6(8.00 %) each, while E. faecium and Shigella sp had the least frequency of occurrences 5(6.66 %) each. The percentage occurrence of virulence attributes among encountered isolates were: 54.7% lecithinase; 56.0% gelatinase; 42.6% caseinase, and 52.0% amylase while haemolysin production were 35.0%, 29.3% and 36% for α-, β- and γ- haemolysis respectively. Among them, Bacillus species and Pseudomonas aeruginosa exhibited more virulence determinants. The susceptibility pattern of GPB and GNB showed 100 % sensitivity to ciprofloxacin, however, GPB displayed varied level of 100 % sensitivity to a single antibiotics ranging from two (2) antibiotics in S. aureus to eight (8) antibiotics each in B. subtilis and Clostridium sp. The survival and persistence of potentially pathogenic and virulent bacteria with antibiotic resistance traits is of public health significance. Hence, the need for continuous monitoring and microbiological evaluation of anaerobic digestate is highly recommended before application on arable land

Keywords: Virulence determinants, antibiogram, digestate, pathogens, occurrence, manure