Assessing Reuse of Hypodermic Needles in Mice by means of Digital Imaging, Photomicrography, Bacterial Culture, Analysis of Nest Building, and Animal Vocalization

Abstract

Hypodermic needles are sometimes reused in animal research settings to preserve the viability of and to conserve limited quantities of injected material. However, the reuse of needles is strongly discouraged in human medicine to prevent inju- ries and the spread of infectious disease. No official guidelines prohibit needle reuse in veterinary medicine, although the practice may be discouraged. We hypothesized that reused needles would be significantly more blunt than unused needles and that reuse for additional injections would cause more animal stress. To test these ideas, we evaluated mice that were injected subcutaneously in the flank or mammary fat pad to generate cell line xenograft and mouse allograft models. Needles were reused up to 20 times, based on an IACUC-approved protocol. A subset of reused needles was digitally imaged to determine needle dullness based on the area of deformation from the secondary bevel angle; this parameter was not different between new needles and needles that had been reused 20 times. In addition, the number of times a needle was reused was not significantly related to audible mouse vocalization during injection. Finally, nest building scores for mice that were injected with a needle used 0 through 5 times were similar to those of mice injected with a needle had been used 16 through 20 times. Among the 37 reused needles that were tested, 4 were positive for bacterial growth; the only organisms cultured were Staphylococcus spp. Contrary to our hypothesis, reusing needles for subcutaneous injections did not increase animal stress based on analysis of vocalization or nest building.