Cutaneous antimicrobial defense

Comparison of two in vivo and two ex vivo tests to assess the antibacterial activity of several antiseptics

An ex vivo test was adapted to mimic the in vivo conditions of testing antiseptic activity on human forearms and in the European Standard Hygienic Handwash Test (BSEN 1499). The study was to validate the ex vivo protocols using 4.8% (w/v) para-chloro-meta-xylenol (PCMX, neat Dettol), 0.5% (w/v) triclosan in 70% (v/v) isopropanol, and 2% (v/v) povidone-iodine against a high bacterial inoculum (>10(8) cfu/mL) of Escherichia coli NCTC 10538. Two ex vivo tests using human skin samples, including one introducing a mechanical rubbing effect, were compared with two corresponding in vivo tests (the forearm test and the BSEN handwashing test). All antiseptics assessed in vivo (forearm and handwash tests) produced reductions in bacterial counts that were significantly greater than those for the non-medicated soft soap control. When assessed ex vivo without rubbing, only PCMX and povidone-iodine achieved reductions significantly greater than soft soap. When assessed ex vivo with mechanical rubbing, only PCMX and triclosan achieved reductions significantly greater than soft soap. Overall, the antiseptics at the concentrations tested were more active when tested in vivo than ex vivo. The addition of a mechanical effect, either in vivo by the volunteers washing their hands or ex vivo by a drill rubbing two skin samples against each other, produced a significantly greater reduction in bacterial concentrations. The ex vivo tests were easily adapted to mimic in vivo protocols. The value of such tests, particularly the one that includes a rubbing effect, may be significant as they avoid the need for human volunteers.

Assessment of skin viability: is it necessary to use different methodologies?

BACKGROUND/AIM

Skin is complex and may display variable structural and metabolic change 'ex vivo'. The present study aimed to follow measures of skin viability and evaluate their usefulness as markers of viability.

MATERIALS AND METHODS

We evaluated the viability of skin samples fresh or after being frozen and subsequently thawed. Assessments included histopathological appearance, lactate dehydrogenase (LDH) activity, oxygen consumption and skin pH.

RESULTS

Morphological investigations of fresh and frozen skin samples using light and electron microscopy showed samples with relatively well-defined epidermis and dermis. Frozen samples showed some sign of stratum corneum fragmentation, although this was not obvious. LDH activity measured in fresh samples kept at 4 degrees C was low, but it was stable up to 7 days. Fresh samples kept at 32 degrees C had a comparable LDH activity to the ones kept in the fridge up to 4 days. Frozen samples, thawed and then kept at 4 degrees C showed a stable LDH activity after 24 h of incubation. However, frozen samples incubated at 32 degrees C demonstrated a high variability in results, with up to 800 U/L of LDH activity after 5 days of incubation. Freshly excised as well as freshly thawed samples showed the highest respiration rates. Fresh and thawed samples stored for a long period of time had a significantly lower (sometimes non-existent) oxygen consumption rate. Our results also showed an increase in the oxygen consumption rate of fresh samples being incubated at 32 degrees C for 24 h. The oxygen consumption rate for all samples reached a plateau within the 15-min measurement period and even the fresh samples did not deplete all the oxygen from the medium. Skin samples ex vivo showed a significantly higher pH than human skin in vivo, and when incubated for 46 h at 32 degrees C, fresh samples had a significantly lower pH than frozen samples. All protocols were reproducible and freshly excised and freshly thawed skin samples showed the highest rates of viability.

CONCLUSION

ex vivo skin shows variation of several parameters over time. It is recommended to use two or three techniques for evaluation of skin viability including at least oxygen measurement and an enzyme assay.