Evaluation of the antibacterial activity of tilmicosin-SLN against Streptococcus agalactiae: in vitro and in vivo studies

Figures & data

Table 1 Characteristics of SLNs (mean ± SD, n=3)

	EE (%)	LC (%)	MD (nm)	PDI	ZP (mV)
Til-SLN	59.4±2.4	11.2±0.30	343±26	0.41±0.05	−7.9±0.4
RB-Til-SLN	57.4±3.8	10.8±0.24	365±49	0.45±0.18	−8.5±0.5

Abbreviations: EE, encapsulation efficiency; LC, loading capacity; MD, mean diameter; PDI, polydispersity index; RB-Til-SLN, rhodamine B labeled tilmicosin-SLN; SLN, solid lipid nanoparticle; Til-SLN, tilmicosin-SLN; ZP, zeta potential.

Figure 1 Photographs of tilmicosin-SLN and labeled tilmicosin-SLN (magnification was 10×40).

Notes: Left, optical microscopy image of tilmicosin-SLN; middle, optical microscopy image of labeled tilmicosin-SLN; and right, fluorescence microscopy image of labeled tilmicosin-SLN. The fluorescence microscopy image of labeled tilmicosin-SLN was obtained at the same area of normal light.

Abbreviation: SLN, solid lipid nanoparticle.

Table 2 MIC and MBC of native tilmicosin and tilmicosin-SLN

	MIC (µg/mL)	MBC (µg/mL)
Native tilmicosin	0.9	8
Tilmicosin-SLN	1.2	12.3

Abbreviations: MBC, minimum bactericidal concentration; MIC, minimal inhibitory concentration; SLN, solid lipid nanoparticle.

Figure 2 Sustained antibacterial activity of native tilmicosin and tilmicosin-SLN (drug concentration: 0.9 μg/mL).

Abbreviations: CFU, colony forming unit; SLN, solid lipid nanoparticle.

Table 3 Pharmacokinetic after s.c. injection in mice (mean ± SD, n=5)

Pharmacokinetic value	Tilmicosin-SLN	Native tilmicosin
AUC0–inf	11,815.91±5,652.70a	1,969.40±216.54
MRT (hours)	425.33±209.25a	100.73±23.31
Cmax (µg/g)	25.57±7.65b	32.37±5.81
Tmax (hours)	48b	48
T1/2 (hours)	363.28±170.26a	56.39±23.02
Fr	6.00a	1

Notes:

a Statistical significances compared with native tilmicosin are P<0.05.

b Statistical significances compared with native tilmicosin are P>0.05.

Abbreviations: AUC_0–inf, the area under the concentration–time curve; C_max, the values of maximum serum concentration; Fr, the relative bioavailability at infinity; MRT, mean residence time; s.c., subcutaneous; SLN, solid lipid nanoparticle; T_1/2, elimination half-life; T_max, time to peak mammary glands concentration.

Figure 3 Concentrations of tilmicosin in mammary glands after s.c. injection (60 mg/kg).

Abbreviations: s.c., subcutaneous; SLN, solid lipid nanoparticle.

Figure 4 Fluorescence microscopy images of mammary gland slices.

Notes: Left, treated with labeled tilmicosin-SLN; middle, injection site; and right, treated with rhodamine B solution.

Abbreviation: SLN, solid lipid nanoparticle.

Table 4 The number of Streptococcus agalactiae in mammary glands (CFU/g) after they are infected with different inoculation quantities at 1 day (mean ± SD, n=4)

Inoculums (CFU/100 µL)	CFU/g
10^5	(1.22±0.88) ×10^3
10^6	(1.52±0.98) ×10^4
10^7	(8.53±2.76) ×10^7
10^8	(7.48±3.83) ×10^7

Abbreviation: CFU, colony forming unit.

Figure 5 The number of Streptococcus agalactiae in mammary glands that were infected with 1×10⁷ CFU/100 µL per mammary gland at 1, 3, and 6 days (mean ± SD, n=5).

Abbreviation: CFU, colony forming unit.

Figure 6 CFU counts in mammary glands after treatment.

Note: The horizontal line indicates the CFU detection limit.

Abbreviations: CFU, colony forming unit; IC, infected control group and treated with 0.9% [w/v] NaCl solution; SLN, solid lipid nanoparticle.