Amongst the 136 studied cases, 59.9% (82) were colonized with at least one Candida species. Most of them were colonized with C. albicans 59 (72%). C. krusei, C. kefyr, C. glaberata, C. parapsilosis, C. tropicalis, and C. famata were the least common Candida species. Detail information regarding the colonization pattern of the studied cases can be found in our recently published paper [11].
According to the results, all C. krusei, C. glaberata, C. parapsilosis, and C. tropicalis isolates were susceptible to amphotericin B (the most active agent for the treatment of non-albicans Candida species). Caspofungin exhibited high resistance against C. krusei and C. glaberata isolates (28.6% and 25%, respectively). Accordingly, amphotericin B can be considered as a more active agent than caspofungin for the treatment of non-albicans Candida species, especially, C. krusei and C. glaberata.
Frequency of azoles, caspofungin and amphotericin B resistance amongst uncommon Candida spices
There are limited reports on azole MIC range for C. kefyr. However, based on a large epidemiological study in our region [8], the available MIC range in colonizing isolates were 0.064-2 (MIC 90%: 0.5 µg/ml); 0.032–0.25 (MIC 90%: 0.125 µg/ml); 0.032–0.125 (MIC 90%: 0.032 µg/ml) for fluconazole, itraconazole and voriconazole, respectively. The caspofungin MIC range was reported between 0.032-2 (MIC 50%: 0.15 µg/ml and MIC 90%: 0.03 µg/ml) [8, 15]. C. kefyr is generally considered susceptible to amphotericin B (MIC < 1 µg/ml); however, wide range of MICs have been reported worldwide (0.5–64) [16–18]. C. kefyr is usually considered susceptible to posaconazole (MIC 90%: 0.032 to 0.12 µg/ml) [8, 17].
The reported fluconazole MIC range for C. famata is 0.25–16 (MIC 50%: 2–4 µg/ml and MIC 90%: 16 µg/ml) [19]; for itraconazole is 0.06–2 (MIC 50%: 0.25 µg/ml and MIC 90%: 0.5 µg/ml) [20]; and for voriconazole is 0.032-1 (MIC 90%: 0.125 µg/ml) [8]. The caspofungin MIC ragne is 0.032–0.25 (MIC 50%: 0.5 µg/ml and MIC 90%: 1 µg/ml) [8, 15]. C. famata is generally considered susceptible to amphotericin B (MIC < 1 µg/ml) [8, 21]. While higher posaconazole MICs were reported for C. famata (0.015–1; MIC 50%: 0.25 µg/ml, and MIC 90%: 1 µg/ml) [22], we found lower MIC range in our study (0.032–0.125, MIC 50%: 0.032 µg/ml). It should be noted that MIC ranges are different between colonized and infected isolates [8].
Accordingly, in this study the colonized isolates of C. Kefyr and C. famata were susceptible to the tested antifungal agents.
Therapeutic options for fungal infections are limited even before the global rise of antifungal resistance [23, 24]; hence, judicious prescription of available choices, especially non-azole antifungals, should be considered in high-risk settings, such as oncology centers. Our results confirmed that caspofungin and amphotericin B are more active antifungal agents compare to azoles in some isolates, such as C. parapsilosis.
The emergence of azole-resistant C. glabrata is also of significant concern in the setting that use fluconazole prophylaxis [9].
Clinical impact of antifungal stewardship interventions on antifungal susceptibility of Candida species during the two study periods
Epidemiological changes in the Candida colonization pattern was described in our previous report. Briefly, we found a significant reduction in non-albicans species colonization after the implementation of AFS. During period 1 (p1), 46.5% (88) of the studied cases (n = 188) were colonized, while in the 2nd period, the colonization rate reached 59.9% (P value = 0. 0.017) [11]. In total, 25.3% (23) of the cases were receiving antifungal prophylaxis during the 2nd period, mainly with the liposomal formulation of amphotericin B, while 54% were on antifungal prophylaxis during p1, mostly with fluconazole or itraconazole [Difference 21.2%, 95% CI: 9.16–31.77%, P = 0.0007]. This success was achieved by controlling and restricting antifungal usage during p2.
In a study by Hadadi et al. during 2011-12 C. albicans was the most common species followed by C. krusei, C. glabrata, C. tropicalis, C. famata, C. parapsilosis, C. dubliniensis, and C. kefyr during the p1. C. glabrata was the most resistant isolated Candida species, showing 70% resistant to fluconazole and 50% to itraconazole, 7.5% to amphotericin B, and 14% to ketoconazole [25].
Frequency of azole and caspofungin resistance C. albicans
Amongst the 117 tested isolates of C. albicans, 52.5% (53) of the isolates were found to be azole-resistant during p1, while only 1.5% (2) were resistant during p2 (P value < 0.001). No fluconazole-resistant (MIC ≥ 8 µg/ml) C. albicans was detected during p2 (P value < 0.001). Multidrug-resistant strains, including azole, caspofungin and amphotericin B resistant isolates were not found within the two study periods (Table 4 and Fig. 2).
Frequency of amphotericin B resistance C. albicans
Despite the significant reduction in fluconazole and caspofungin-resistant, during p2, some increase in the incidence of amphotericin B-resistant C. albicans was detected during p2 (Table 5). A small but significant increase in amphotericin B-resistant C. albicans strains can be partially explained by changing antifungal preventive strategy to liposomal amphotericin B, since 2015. However, the frequency of amphotericin B-resistant C. albicans was not affected by liposomal amphotericin B prophylaxis between the two periods (p = 0.619).
Table 5
The sensitivity of isolated C. albicans against fluconazole, caspofungin, and amphotericin B, during 2011-12 (period 1) and 2017-18 (period 2), No. (%) of isolates
Antifungal agent | Sensitivity | Period 1 | Period 2* | p-value |
Fluconazole | Sensitive | 53 (67.1) | 102 (102) | < 0.001** |
Resistant | 26 (32.9) | 0 |
Caspofungin | Sensitive | 54 (83.1) | 99 (97.1) | < 0.001** |
Resistant | 11 (16.9) | 1 (1) |
Amphotericin B | Sensitive | 83 (100) | 95 (93.1) | < 0.001** |
Resistant | 0 | 7 (6.9) |
* No fluconazole-resistant isolates of C. albicans was found during period 2 (2017–2018) |
** Statistically significant by Fisher’s exact test |
Frequency of azoles, caspofungin, and amphotericin B resistance amongst the non -albicans colonized species
We also analyzed the rate of fluconazole, voriconazole, itraconazole, caspofungin and amphotericin B resistance amongst the non-albicans colonized species between the two study periods. Significant decrease in fluconazole, itraconazole and caspofungin resistance was found among the C. glaberata strains during the second study period compared with 2011-12. Also, a statistically significant reduction in amphotericin B resistance was found during p2 in C. krusei isolates (Table 6).
Clinical impact of Candida colonization in hospitalized patients with hematological malignancies
Most of Candida bloodstream infections, including central line-associated candidemia originate from endogenous host flora [26–28]. The clinical impact of Candida colonization on the short-term mortality rate of patients with hematological malignancies was reported in a previous study [29]. On the other hand, short-term survival was affected in patients with non-albicans species, including C. glabrata, C. kefyr, and C. krusei, compare with C. albicans [29, 30]. Azole prophylaxis has a critical role in the development of either unsusceptible strains or even in the selection of yeast with intrinsic azole-resistant, such as C. krusei [6, 9, 31, 32].
As discussed earlier, during p1, more than 35% of cases were colonized with non-albicans species, mostly C. glabrata and C. krusei. However, after the implementation of the AFS, non-albicans colonization decreased to less than 20%, mostly C. krusei and C. Parapsilosis, with a significant decrease in C. glabrata colonization [11]. C. glabrata is considered as the second most common gastrointestinal yeast flora, after C. albicans [33]. In our opinion, the shift toward more C. albicans colonization is the result of sustained adherence to the AFS and restricted azole prescription (Table 1).
Comparison of the mean minimum inhibitory concentration (MIC) value of the six antifungal drugs between different Candida spp. during the two study periods
In addition to the susceptibility results, we also compared the mean MIC value of each antifungal drug for C. albicans, C. glabrata, C. krusei, C. parapsilosis, C. tropicalis, C. famata, and C. kefyr during two study periods (Fig. 4). As shown in Fig. 4, a significant reduction in mean FCZ-MIC was found for C. albicans, C. glabrata, and C. tropicalis in p2 compare to p1.
There are lots of data with respect to the positive effect of stewardship program on bacterial resistance [34–37]; however, due to its multi-factorial development, antifungal resistance is more challenging to measure. Even in colonized patients, susceptibility patterns might change over time, especially in immunocompromised hosts [8]. Although the AFS has known short-term effects (e.g., reduction in antifungal consumption, costs and outcomes) on the management of IFDs and patient safety [38–41], its long-term effects has been described on resistance patterns [42]. Based on stewardship program metrics, change in resistance patterns, and pathogen-specific resistance is the most difficult target to reach [34]. To the best of our knowledge, there is a shortage of reports on the improvement of antifungal susceptibility of Candida species overtimes after the implementation of AFS. Hence, the results of our study highlight the importance of strict adherence to the stewardship programs amongst the cancer patients.