CRI is one of the most common nosocomial infections in clinical practice23. Pathogens in the skin appendages, such as the epidermis, sebaceous glands, and hair follicles, are all possible causes of CRI23,24. Candida is the third largest pathogen that causes CRI, in which Candida albicans was the most common type of biofilm infection25,26. Therefore, we aimed to build a relevant animal model of Candida albicans biofilm-related CRI so as to support the treatment and prevention of related CRI.
To construct the CRI model, a small amount of C. albicans was added to the dorsal skin of mice, which simulates the clinical situation in which part of the C. albicans cannot be fully eradicated in the deep tissues and appendages of the skin by routine sterilization. After the implantation of the catheter, C. albicans was re-inoculated to mimic the presence of C. albicans in the external environment during surgery.
In this study, a 3-day time point was selected for the model construction, which is lower than that of the traditional C. albicans biofilm-related animal models18,27 due to the difficulty in the biofilm formation. Post-infection, C. albicans adhesion and biofilm formation were visible on the catheter surface in this model, which was proved by the SEM and fluorescence microscopy results (Figure 3 and Figure 4). This may be due to the concentration of C. albicans in this study was 1 × 108 CFU/mL, which was much higher than that of other animal models18,27. Besides, the skin around the catheter is in constant contact with the external environment. To simulate the extreme environments that CRI may encounter, C. albicans were inoculated again after the surgery.
The recurrence of infection is often caused by pathogens that remain in surrounding tissues23,28,29. Therefore, the presence or absence of pathogens in tissues is important for CRI. In this paper, PAS staining was undertaken to investigate the residues of C. albicans in the skin tissues. This method could also be used to evaluate the clearance effect of new therapeutic drugs or methods for CRI.
In conclusion, a Candida albicans strain with eGFP was used to construct a mouse CRI model to facilitate the intuitive observation of Candida albicans colonization on catheters. This strain can also be used to evaluate the interaction between Candida albicans and host cells, for example, the invasion and adhesion of Candida albicans to the host, the anti-Candida albicans effect of therapeutics, and the immune response. Besides, a two-step inoculation method was used to simulate pathogens derived from the external environment and the body. It is worth noting that subsequent microbial culture after infection was not conducted. The presence of biofilms is an important factor in the low sensitivity of cultures30,31,32. Previous reports suggest that microbial culture after infection had low sensitivity, specificity, and accuracy30,31,32,33,34. Instead, the presence of biofilms on the implant is a more reliable index. Therefore, SEM and fluorescence microscopy were used in this study to visualize and identify Candida albicans forming biofilms.
However, this model did not simulate the interaction between the patient's weakened immunity and the Candida albicans infection observed in clinics. If the model could consider the immunocompromised treatments (such as continuous injections of glucocorticoids)35 before the Candida albicans inoculation, it would be possible to better simulate infections occurring in clinical situations.