Short term conservation of human pathogenic Escherichia coli isolates in Phosphate Buffer Saline (PBS): An effective & economical method

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Introduction: Many different methods of bacterial conservation techniques have been used. Most of them require technical excellence andare costly. Thus a simpler cost effective technique has been evaluated using phosphate buffer saline (PBS). Materials and Methods: 135 isolates were collected during the study period. The isolates were subcultured on 5% sheep blood agar and incubated at 37?C for 18-24 hours. After incubation, isolates were inoculated into autoclaved Phosphate Buffered Saline (PBS) in a Labelled screw capped vial. The vials were incubated at 37?C overnight. Standardized protocols were followed for antibiotic sensitivity testing. The isolates were analyzed for their sensitivity to Ampicillin, Gentamicin, Tobramycin, Amikacin, Ciprofloxacin, Levofloxacin, Cotrimoxazole, Amox-Clavulanate, Piperacillin Tazobactum, Norfloxacin, Amikacin, Ceftriaxone, Ceftazidime, Ceftazidime-Clavulanic Acid, Cefotaxime, Imipenam, Tetracycline & Nitrofurantoin. Baseline Minimum Inhibitory Concentration (MIC) of Ceftazidime was done using the Epsilometer test (E-test). The vials were stored at room temperature inside a thermocol box to avoid exposure to sunlight. Subcultures from distilled water were done to look for ability to grow, reduction in colony counts and for checking the purity of the isolate. Six monthly MIC using E-test was done and compared with baseline values. Results: Out of the 135 samples, 6 isolates did not grow on subcultures. 10 isolates were contaminated. 119 isolates showed good growth till the end of 12 months study period. The Minimum Inhibitory Concentration (MIC) did not alter from the baseline MIC. Conclusion: This method is inexpensive, technically simple method of bacterial conservation and is ideal for short term storage. This method will prove to be useful for young researchers, Post graduate students and even in Microbiology labs with minimal facilities. Keywords: Antibiogram, Bacterial preservation, Escherichia coli, Minimum inhibitory Con