Fabrication of autoclavable bacteriologic loops for handling Mycobacterium tuberculosis isolates from recycled materials in a resource poor setting

Introduction

Tuberculosis is the second leading cause of infectious diseases associated deaths and the leading cause of death among HIV infected people. ¹ This treatable disease globally has killed more than 4.6 million people within the last 3 years and developing countries are disproportionately affected. ² Nine of the 22 high burden countries are in resource limited sub-Saharan African countries ² where research and control efforts are greatly impeded by limited funds.

Culture of Mycobacterium tuberculosis, which is the gold standard for diagnosis and susceptibility testing, requires the manipulation of life isolates using inoculation loops. Commercial disposable loops are generally recommended because of bio-safety concerns. ³ However, they are expensive as they have to be imported and, therefore, eat into already lean budgets. Commercial reusable wooden and metal wire loop handles are also relatively expensive. When flame sterilization and reuse of inoculation loop is an option, flaming in a hooded Bunsen burner or electric micro incinerator is recommended as open flames are discouraged due to their aerosol generation. ⁴ These items are usually unavailable in many resource limited settings.

We therefore decided to evaluate alternative and more cost effective ways of obtaining autoclavable bacteriologic inoculation loops from used materials in the laboratory.

Materials and method

Polypropylene automatic pipette tips and nichrome or platinum wires from electric stoves were used to fabricate autoclavable loops.

One millilitre polypropylene tips are used in our laboratory to mix reagents and several of these autoclave resistant tips are used daily and discarded. Platinum wires are used to repair electric stoves (hot plate) and can be recovered from old hot plates or bought for just 200 Naira (US$ 1.2) for the entire length used in hot plates.

Loops of appropriate diameter were prepared as previously described. ⁵ The loops were inserted into the opening of the automatic pipette tip and heated in a Bunsen flame to melt the plastic (Figure 1). The length of the loop handle was extended by the serial addition of tips to achieve the desired length.

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The volume calibration of the loops when required was done by making several vertical passes of the loop in 1 mL of previously weighted distilled water. The final loop volume was calculated thus:

Assume the initial volume of water = V_i

Each used loop was disinfected in a jar of disinfectant (Lysol or 10% sodium hypochlorite in our setting). The loops were then sterilized by autoclaving and reused several times.

Discussion

In resource limited settings, the appropriation of scarce resources requires ingenuity. There are a lack of readily available bacteriological loops for manipulating M. tuberculosis in our setting as in other facilities in Nigeria which attempt M. tuberculosis culture. The loops are usually sourced from outside the country with attendant high cost and delays in delivery.

Heat resistant polypropylene automatic pipette tips were used routinely to transfer reagents and biological samples and then discarded. In our recycling effort, in order to ensure biosafety, those used on biological samples were discarded and only those used on reagents were washed and recycled. Platinum wires were recovered from old electric stoves. Each roll was used to make 50 loops of 6 cm length.

Conclusion

The in-house recycling of pipette tips saved us an expenditure of about 5000 Naira (US$32) on a pack of 50 imported plastic disposable loops and 10,000 Naira (US$63) on wooden loop handles.

We therefore encourage laboratories in resource poor settings to save on wire loops by adopting pragmatic approaches of recycling materials.