Antibacterial Susceptibility of Heavy Metals Tolerant Bacteria Isolated from NILEST Tannery Effluent

Background: The emergence of multiple antibiotics resistance among bacterial population poses a potential threat to human health. The co-existence of metal/antibiotic resistance in bacterial strains suggests the role of heavy metals as a factor which can also contribute to drug resistance phenomenon since heavy metal pollution results in selective pressure that leads to the development of multiple drug resistance among bacterial populations probably through horizontal gene transfer.

Aim: This study was aimed to isolate, identify, and determine the antibiogram profile of heavy metals tolerant bacteria from the tannery effluent at Nigerian Institute of Leather and Science Technology (NILEST), Zaria, using standard microbiological methods.

Place of Study: Department of Science Laboratory Technology, Nigerian Institute of Leather and Science Technology (NILEST), Zaria, Kaduna-Nigeria.

Methodology: Tannery effluent was cultured on heavy metals incorporated nutrient agar. The resultant isolates were purified by sub-culturing on fresh heavy metals incorporated nutrient agar and the antibiogram profile was determined using agar diffusion method.

Results: The bacteria isolated include Bacillus cereus (18.75%), Escherichia coli (12.50%), Klebsiella aerogenes (18.75%), Klebsiella pneumoniae (6.25%), Pseudomonas aeruginosa (12.50%), Proteus mirabilis (6.25%), and Staphylococcus aureus (25.00%) with Staphylococcus aureus being the most prevalent. In this study, heavy metals tolerant bacteria isolated from the tannery effluent were multidrug resistant as each of the isolates was able to resist the activity of one or more of the antibiotics across the three classes of antibiotics studied. Gentamicin was highly resisted followed by ampicillin and amoxicillin. Kanamycin and Nalidixic acid were more effective followed by Ciprofloxacin and Streptomycin. The β-lactams/penicillins were generally not very effective as compared to the glycopeptides and the quinolones. Staphylococcus aureus and Escherichia coli were highly resistant to six (6) out of the nine (9) antibiotics tested with Escherichia coli showing 100% resistance to ampicillin and amoxicillin. However, Bacillus cereus was moderately resistant to seven (7) out of the nine (9) antibiotics tested but highly resistant to gentamicin. Ampicillin and cefixime showed no activity against Proteus mirabilis and Klebsiella pneumoniae. However, Proteus mirabilis and Klebsiella aerogenes were 100% resistant to gentamicin. Kanamycin was inactive against Klebsiella pneumoniae. The Multiple Antibiotic Resistance (MAR) indices of all isolates were greater than 0.2.

Conclusions: The recovery of heavy metals tolerant bacteria from the tannery effluent is an indication that the effluent is laden with heavy metals. The high antibiotic resistance profile of the isolates in this study is an indication of the correlation between heavy metals tolerance and antibiotic resistance. The identified heavy metals tolerant bacterial strains could be useful for bio-remediation of heavy metals contaminated wastewaters and soil environments even though they are potential threat to successful chemotherapy if incriminated in infections.