Table 4 Synergistic antifungal activity of ZnO-NPs with conventional antifungals against C. albicans and C. tropicalis. Data represent mean Inhibition zone diameters (mm ± SE, *n* = 3). Superscript letters (ᵃ, ᵇ) indicate statistical significance within columns (Tukey’s test, *p* < 0.05). IFA = Increase in fold area; ns = not significant (p ≥ 0.05). FICI (Fractional inhibitory concentration Index) interpretation: ≤0.5 synergistic, > 0.5–1.0 additive, > 1.0–4.0 indifferent, > 4.0 antagonistic.

Treatment

Ketoconazole

Fluconazole

Itraconazole

Nystatin

Terbinafine

Amphotericin B

Antifungal only

16.35 ± 0.41ᵃ

17.93 ± 0.29ᵃ

16.34 ± 0.54ᵃ

27.13 ± 0.51ᵃ

26.38 ± 0.51ᵃ

11.82 ± 0.58ᵃ

Antifungal + ZnONPs

19.83 ± 0.25ᵃ

22.81 ± 0.38ᵇ

17.15 ± 0.42ᵃ

36.92 ± 0.32ᵇ

35.14 ± 0.63ᵇ

12.45 ± 0.51ᵃ

IFA

0.47

0.62

0.10

0.85

0.77

0.11

P value

NS

0.0426

NS

0.0017

0.0031

NS

FICI

1.25

0.75

1.50

0.38

0.63

1.50

Interpretation

Indifferent

Additive

Indifferent

Synergistic

Additive

Indifferent

B. C. tropicalis

Treatment Ketoconazole Fluconazole Itraconazole Nystatin Terbinafine Amphotericin B

Antifungal only

15.82 ± 0.57^a

25.73 ± 0.35^a

21.63 ± 0.54^a

16.84 ± 0.46^a

38.64 ± 0.74^a

13.52 ± 0.42^a

Antifungal + ZnONPs

21.09 ± 0.21^b

34.38 ± 0.62^b

22.43 ± 0.32^a

23.78 ± 0.38^b

37.92 ± 0.32^a

16.97 ± 0.31^a

IFA

0.78

0.79

0.07

0.99

− 0.04

0.58

P value

0.0316

0.0011

NS

0.0096

NS

NS

FICI

0.75

0.63

1.25

0.25

4.00

1.25

Interpretation

Additive

Additive

Indifferent

Synergistic

Antagonistic

In different