Physico-chemical analysis and antibiotic susceptibility profile of Gram-negative bacteria isolated from storage tanks water in a tertiary institution in Nigeria

The physicochemical parameters and antibiotic susceptibility profile of Gram-negative bacteria in storage tanks water samples were studied. The pH was measured with pH meter and Temperature using mercury-in-glass thermometer. The measurements of Conductivity and Total Dissolved Solid (TDS) in water samples were done using a Bantec-510 Electrical Conductivity meter, Biological Oxygen Demand (BOD5) and Dissolved Oxygen (DO) were tested using DO meter. Alkalinity and Acidity were measured using titrimetric method. Gram-negative bacteria were isolated by spread plate method and identified by cultural, morphological and biochemical characterization. Susceptibility of isolates to antibiotics was determined using Kirby-Bauer disc diffusion technique. Temperature of the water samples ranged from 24.0 - 27.5oC with an average value of 27.7oC. The pH value ranged between 5.7 and 9.4. Conductivity values ranged between 20.2 and 39.2 µS/cm respectively. DO values ranged from 0.8 to 1.9 mg/mL across the water samples. The BOD and TDS values ranged from 0.2 - 0.4 mg/mL and 18.3 – 30.2 mg/mL, respectively. Six (6) Gram negative bacteria were recovered and identified from the water samples. The frequency and percentage occurrence of the bacteria include Enterobacter intermedius {2(33%)}, Salmonella bongori {1(16.67%)}, Klebsiella pneumoniae {1(16.67%)}, Citrobacter diversus {1(16.67%)}, and Klebsiella sp. {1(16.67%)}. Antibiotic susceptibility greatly varied among the bacterial isolates as all displayed total sensitivity to ceftriaxone and ciprofloxacin, but were resistant to chloramphenicol. All the bacteria were sensitive to cefuroxime and cefotaxime except Klebsiella species. The isolates showed varying resistance against meropenem and ceftazidime. Five (83.33%) of the bacteria were multiple antibiotic-resistant types with multiple antibiotic resistance index (MARI) values greater than 0.2. and exhibited various MAR patterns. In conclusion, some of the physicochemical parameters analyzed fall within the permissible limit recommended for drinking water. However, the presence of multiple antibiotic resistant Gram negative - bacteria in the water samples analyzed may constitute health hazards in humans.