Biosynthesis of silver nanoparticles by Novosphingobium sp. THG-C3 and their antimicrobial potential

Figures & data

Figure 1. Neighbor-joining phylogenetic tree based on 16S rRNA gene sequences showing the relationships of strain THG–C3 with related species. Bootstrap values (expressed as percentage of 1000 replications) are shown at branch points. Bar, 0.01 substitutions per nucleotide position.

Figure 2. UV-vis spectra of reaction mixture. The figure inset shows NB with AgNO₃ solution as control and synthesized AgNPs.

Figure 3. FE-TEM image of synthesized AgNPs (A), SAED pattern (B), and XRD spectra of synthesized AgNPs (C).

Figure 4. The elemental mapping of AgNPs. (A): TEM image used for mapping and (B): silver distributions. EDX. Spectrum of synthesized AgNPs (C).

Figure 5. Antimicrobial activities of synthesized AgNPs (30 μl) at 500 ppm concentrations in water against S. aureus, V. parahaemolyticus, B. cereus, P. aeruginosa, C. tropicalis, C. albicans, E. coli, B. subtilis, and S. enterica.

Figure 6. Antimicrobial activities against P. aeruginosa of standard antibiotics (A1) and antibiotics loaded with synthesized AgNPs 30 μl (500 ppm) (A2); against S. enterica (B1, B2); against V. parahaemolyticus (C1, C2); against E. coli (D1, D2), respectively. Abbreviation: E 15 (erythromycin, 15 μg/disc), NV 30 (novobiocin, 30 μg/disk), OL 15 (oleandomycin, 15 μg/disk), MY 15 (lincomycin, 15 μg/disc), P 10 (penicillin G, 10 Units/disc), VA 30 (vancomycin, 30 μg/disk).

Table 1. Antimicrobial activity of silver nanoparticles against selected pathogenic strains.

Bacterial cultures	Zone of inhibition (mm)
	AgNPs 30 μl (500 ppm)
S. aureus	15.3 ± 1.2
V. parahaemolyticus	16.3 ± 0.5
B. cereus	13.7 ± 1.9
P. aeruginosa	16.0 ± 0.8
C. tropicalis	18.7 ± 0.9
C. albicans	19.7 ± 0.5
B. subtilis	13.0 ± 0.8
S. enterica	12.7 ± 0.5
E. coli	13.0 ± 0.8

The experiments were done in triplets and the results were interpreted in terms of standard deviation of mean diameter of zone of inhibition.

Table 2. Individual and combined efficacy of synthesized AgNPs and antibiotics against selected pathogenic strains.

Antibiotics	Zone of inhibition (mm)
	P. aeruginosa			S. enterica			V. parahaemolyticus			E. coli
	a*	b§	FA†	a*	b§	FA†	a*	b§	FA†	a*	b§	FA†
E15	–	15.3	5.5	–	14.7	5.0	18.0	21.7	0.4	–	16.7	6.7
P 10	–	12.0	3.0	–	10.3	2.0	44.3	46.3	0.1	–	11.7	2.8
MY 15	–	16.3	6.4	–	14.3	4.7	20.7	21.7	0.1	–	11.7	2.8
OL 15	–	12.3	3.2	–	10.3	2.0	19.7	24.7	0.6	–	11.3	2.6
VA 30	–	12.3	3.2	–	10.3	2.0	11.3	18.3	1.6	–	11.7	2.8
NV 30	–	16.3	6.4	–	14.7	5.0	29.3	33.3	0.3	–	14.0	4.4

a* : the values of antibiotics.

b§ : the values of antibiotics containing AgNPs (15 μg/disc).

(–): no antibacterial activity.

FA†: the values of increase in fold area, was calculated as (b² – a²)/a², discs’ diameters (6 mm) were used to calculate the FA† in the absence of inhibition zone.

Abbreviation: E 15 (erythromycin, 15 μg/disc), NV 30 (novobiocin, 30 μg/disk), OL 15 (oleandomycin, 15 μg/disk), MY 15 (lincomycin, 15 μg/disc), P 10 (penicillin G, 10 Units/disc), VA 30 (vancomycin, 30 μg/disk).