The impact of the leather manufacturing process on bacterial growth

Hides and skins used as a raw material for leather manufacture may be contaminated with various microbial species including potential pathogens. Many bacterial species such as Bacillus, Staphylococcus, Micrococcus and Pseudomonas were isolated from raw hides/skins, and hides/skins at different stages of leather making process. The extreme environmental conditions present during a conventional tanning process due to hazardous chemicals may prevent the growth of bacteria present on hides/skins. On the other hand, partial or total replacement of the hazardous chemicals with non-hazardous chemicals, during a best available technologies (BAT) process, may provide suitable conditions for microbial growth in tannery effluent and hides/skins. Therefore, the aim of the project was to determine the survival and growth of the various bacterial species during the conventional and BAT leather-making processes. The beamhouse and tanning stages were studied, as the majority of the environmental pollution occurs during the early stages of the leather making process. Both the pre-soaking and soaking stages during the conventional and BAT leather-making processes provided suitable conditions for bacterial (Bacillus cereus, Pseudomonas aeruginosa and Staphylococcus spp.) growth and proliferation. The results showed a significant reduction in the number of B. cereus found during the conventional and BAT unhairing processes. Limited B. cereus growth was observed during the subsequent reliming process. Bacillus cereus growth also occurred during the deliming and bating processes (conventional and BAT), followed by a decrease during the conventional and BAT pickling processes. No B. cereus colonies were isolated during the chrome tanning process. Growth of P. aeruginosa was inhibited during both the unhairing and reliming stages of the conventional and BAT leather making processes. A reappearance and recovery of P. aeruginosa in the subsequent deliming and bating (conventional and BAT) processes, indicated that deliming and bating processes may provide suitable growth conditions for P. aeruginosa. On the other hand, both the conventional and BAT pickling processes, and the chrome tanning processes hindered P. aeruginosa growth. Staphylococcus spp. were present throughout the conventional and BAT leather-making processes. A large reduction in the number of Staphylococcus spp. was observed during the unhairing and reliming processes (conventional and BAT). Growth of Staphylococcus spp. occurred during the subsequent deliming, bating, pickling and chrome tanning stages for both the conventional and BAT leather-making processes. The biochemical assays for bacterial identification confirmed the presence of B. cereus, P. aeruginosa and Staphylococcus spp. during the leather processing. The pulsed-field gel electrophoresis (PFGE) method of DNA fingerprinting confirmed that the bacterial species isolated during the leather manufacturing processes were the inoculated B. cereus and P. aeruginosa, and no alteration of the DNA of above-mentioned bacteria occurred during the processing. Overall, the research showed that bacterial species are capable of surviving during both the conventional and BAT leather-manufacturing processes. The bacterial species prefer the environmental conditions during the pre-soaking and soaking processes, while the unhairing and reliming processes did not favour the growth of bacterial species. Bacterial colonies were enumerated during the deliming and bating processes indicating that the unhairing and reliming processes did not cause total destruction of the bacterial cells. Alternatively pickling and chrome tanning processes were found to have suppressed the growth of bacterial colonies.