HE MAGNITUDE OF INVASIVEmethicillin-resistant Staphylococcus aureus (MRSA) infections as well as the emergence of community-onset MRSA infections in the United States has been well documented. [1][2][3][4] Commonly due to the pulsedfield type USA300 strain of MRSA, outbreaks of skin and soft tissue infections (SSTIs) have been observed in prisoners, athletes, and other risk groups. 5,6 In parallel with the emergence of community-onset MRSA infections in the US civilian population, SSTIs have become a significant public health issue for the US military. During military training, approximately 4% to 6% of all individuals may experience an SSTI. 7,8 Furthermore, S aureus has been isolated from 91% of such cases, with MRSA accounting for 70% of S aureus isolates. MRSA also has been shown to be a common cause of S aureus bacteremia and other infections in population-based studies from the United States, particularly health care-associated infections. [9][10][11]

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Background: Most molluscs forage with their radula, a chitinous membrane with embedded teeth. As teeth are interfaces between the individual and its ingesta, trophic specialisations can be reflected by morphology, composition, and mechanical properties of the radula. Adaptations to the ingesta – especially with regard to mechanisms contributing to the reduction of structural failure and wear – are well studied in the heavily mineralized teeth of Polyplacophora and Patellogastropoda. For the rather chitinous teeth of non-limpet snails, we are however confronted with a large gap of knowledge. Results: For this study, we selected nudibranch gastropods, which are of high interest, when studying trophic specialisations, because taxa are strongly adapted to forage on certain prey types. To shed some light on this type of radula, we here investigated two species – Felimare picta and Doris pseudoargus, which are similar with regard to their food preference (Porifera-consuming). Tooth morphologies were documented using scanning-electron-microscopy and mechanical properties were tested by nanoindentation, to develop hypotheses on functional adaptations of the radula to the ingesta. We found that tooth morphologies and mechanical properties are rather similar in both species, indicating that teeth are similar in their function. In the search for the reasons of the specific mechanical properties, we studied the material composition. Teeth were visualized using confocal laser scanning microscopy (CLSM), to determine the degree of tanning, and analysed with energy-dispersive X-ray spectroscopy (EDX), to determine the elemental composition. Our results show, that the inorganic content and the emitted autofluorescence signal differ between the species. This was especially prominent, when studying the inner and outer sides (leading and trailing edges) of teeth. In F. picta, we detected high proportions of Si, whereas teeth of D. pseudoargus contained high amounts of Ca, which influenced the autofluorescence signal in CLSM. Using nanoindentation we determined high Young’s modulus and hardness values for the leading edges of teeth, which seem to correlate with the Si- and Ca-content. Conclusions: This is a new set of data for non-limpet gastropods, rendering that their teeth can be mechanically enhanced via different chemical pathways to reach similar properties in reducing structural failure and abrasion.

Molluscs forage with their radula, a chitinous membrane with teeth. Adaptations to hard or abrasive ingesta were well studied in Polyplacophora and Patellogastropoda, but for other taxa there are large gaps in knowledge. Here, we investigated the nudibranch gastropods Felimare picta and Doris pseudoargus , both of which feed on Porifera. Tooth morphologies were documented by scanning electron microscopy, and mechanical properties were tested by nanoindentation. We found that these parameters are rather similar in both species, indicating that teeth are similar in their function. To study the composition, teeth were visualized using confocal laser scanning microscopy (CLSM), to determine the degree of tanning, and analysed with energy-dispersive X-ray spectroscopy, to test the elemental composition. The emitted autofluorescence signal and the inorganic content differed between the species. This was especially prominent when studying the inner and outer tooth surfaces (leading and trailing edges). In F. picta , we detected high proportions of Si, whereas teeth of D. pseudoargus contained high amounts of Ca, which influenced the autofluorescence signal in CLSM. Employing nanoindentation, we determined high Young's modulus and hardness values for the leading edges of teeth, which relate to the Si and Ca content. This highlights that teeth with a similar morphology and mechanical properties can be mechanically enhanced via different chemical pathways in Nudibranchia.