Microbial analysis of pond soil and pond water samples
The results of oxytetracycline hydrochloride, florfenicol, sulphadimethoxine and ormetoprim residues in pond soil and pond water samples by microbial screening using Bacillus subtilis
and Escherichia coli
as the test organisms are presented in the Fig 3, 4 and 5 and Tables 2, 3 and 4. A total number of 150 samples in which 75 samples were pond soil and 75 samples were pond water, were analysed for residues and among the same, 6 pond soil samples (8%) and 8 pond water samples (10.66%) were found to be positive for oxytetracycline hydrochloride and for the antibiotic florfenicol 3 pond soil samples (4%) and 5 pond water samples (6.66%) were found to be positive and for the antibiotic sulphadimethoxine and ormetoprim 10 samples (13.33%) were found to be positive in pond soil and 16 samples (21.33%) were positive in pond water. Overall, 14 samples (9.33%) were found positive for oxytetracycline hydrochloride residues, 8 samples (5.33%) were found positive for florfenicol residues and 26 samples (17.33%) were positive for sulphadimethoxine and ormetoprim residues out of 150 samples.
Fig 3: Screening of Oxytetracycline hydrochloride residues in pond soil/pond water samples by microbiological method using Bacillus subtilis as indicator microorganism.
Fig 4: Screening of Florfenicol residues in pond soil/pond water samples by microbiological method using Escherichia coli as indicator microorganism.
Cengiz et al., (2010)
Fig 5: Screening of sulphadimethoxine and ormetoprim residues in pond soil/pond water samples by microbiological method using Escherichia coli as indicator microorganism.
reported that 50% samples of soil were positive for antibacterial substances which were related to tetracycline group. It was higher than the results of the current study. Tetracycline was able to contaminate and remain in soil for long time because of their adsorptive character. Ibraheem (2012)
described that 62% of tetracycline, 25% of doxycycline, 12.5% of chlortetracycline residues were present in the water samples. This result was contrary to the present findings as only a smaller percentage of samples were found contaminated with oxytetracycline hydrochloride.
The present results were contrary to the findings of Zhao et al., (2016)
who reported that 33.3% of soil samples were positive to amphenicol groups. The higher percentage of positive samples were due to frequent use of the antibiotic. Similarly, He et al., (2014)
also reported that the percentage of positive samples for sulphonamide were high at 48%. Wei (2012)
reported that more than 90% of the animal waste water and water resource samples were found to contain ciprofloxacin, enrofloxacin and florfenicol residues that were also completely contradictory to the results obtained in the present study. This higher percentage of occurrence of antibiotics in water was due to the ability of the antibiotic to enter into soil, sediments, etc
The LOD was found to be 50 µg/kg for oxytetracycline hydrochloride and 100 µg/kg for florfenicol, sulphadimethoxine and ormetoprim which is below the accepted maximum residue level (MRL) for the antibiotics set by European Union.
The data were subjected to statistical analysis by Chi- square test and there existed a non-significant difference between pond soil and pond water for all the three antibiotics and the results are shown in Tables 2, 3 and 4.
Table 2: Microbial screening of pond soil/ pond water using Bacillus subtilis (MTCC 121T) for oxytetracycline hydrochloride.
Table 3: Microbial screening of pond soil/ pond water using Escherichia coli (MTCC 40) for florfenicol.
Table 4: Microbial screening of pond soil/ pond water using Escherichia coli (MTCC 40) for sulphadimethoxine and ormetoprim.
The lower level of positive samples of antibiotics in soil in the present study indicates that the usage of antibiotics for performance promotion in the areas of study has been much lower than the earlier reports which might be due to increasing awareness of the farmers on the after effects of continuous usage of antibiotics. However, as antibiotics like tetracycline can remain in soil for longer duration, it is more prudent to work towards zero level contamination of the pond soil.
Kabir et al., (2004)
reported that the variation in the occurrence of antibiotic residues in present study in comparison with former studies could be attributed to a difference in fish species, sampling, location, time of collection and type and level of antibiotics used, variations in experimental conditions and the sensitivity of the method used for analysis.
However, the results of the present study indicate that the usage of antibiotics in the areas under study were much lower than the earlier reports quoted from other parts of the world which is appreciable and the same needs to be taken forward through appropriate measures to ensure zero usage.