Biologically rapid synthesis of silver nanoparticles by Sphingobium sp. MAH-11^T and their antibacterial activity and mechanisms investigation against drug-resistant pathogenic microbes

Figures & data

Figure 1. The neighbour-joining (NJ) tree based on 16S rRNA gene sequence analysis showing phylogenetic relationships of strain MAH-11 with related species. Bootstrap values more than 70% based on 1000 replications are shown at branching points. Scale bar, 0.05 substitutions per nucleotide position.

Table 1. Biochemical characterization of Sphingobium sp. MAH-11.

API 20 NE	Result	API ZYM	Result
Nitrate reduction	−	Alkaline phosphatase	+
Indole production	−	Esterase (C4)	w
Glucose fermentation	−	Esterase lipase (C8)	w
Hydrolysis of		Lipase (C-14)	w
L-arginine	−	Cystine arylamidase,	+
Urea	−	Valine arylamidase	+
Esculine	+	Leucine arylamidase	+
Gelatine	−	Trypsin	w
4-nitrophenyl-BD-galactopyranoside	+	α-chymotrypsin	+
Utilization of		Acid phosphatase	+
D-glucose	+	Naphthol-AS-BI-phosphohydrolase	+
D-mannitol	−	α-galactosidase	−
L-arabinose	−	β-galactosidase	+
D-mannose	−	β-glucuronidase	−
D-maltose	−	α-glucosidase	W
N-acetyl-glucosamine	−	β-glucosidase	+
Gluconate	−	N-acetyl-β-glucosaminidase	−
Adipic acid	−	α-mannosidase	−
Capric acid	−	α-fucosidase	−
Malic acid	−
Triosodium citrate	−
Phenylacetic acid	−

+: Positive; –: Negative; w: weakly positive.

Figure 2. R2A broth with AgNO₃ as control (A), biosynthesized AgNPs (B), UV–vis spectra (C), FE-TEM images (D and E) and histogram of different sizes of biosynthesized AgNPs (F).

Figure 3. EDX spectrum of biosynthesized AgNPs (A), TEM image (electron micrograph region) used for mapping (B) and distribution of silver in the elemental mapping (C).

Figure 4. X-ray diffraction pattern (A) and SAED pattern (B) of biosynthesized AgNPs.

Figure 5. FT-IR spectra of biosynthesized AgNPs (A), bacterial culture supernatant (B) and silver nitrate (C).

Figure 6. Particles size distribution of biosynthesized AgNPs according to intensity (A), number (B) and volume (C).

Figure 7. Zones of inhibition of biosynthesized AgNPs (30 μL) at 500 ppm and 1000 ppm concentrations in the water against P. aeruginosa, E. coli and S. aureus.

Figure 8. Zones of inhibition of commercial antibiotics against P. aeruginosa, E. coli and S. aureus. Abbreviation. E (erythromycin, 15 μg/disc), P (penicillin, G 10 μg/disc) and VA (vancomycin, 30 μg/disc).

Table 2. Antimicrobial activity of biosynthesized AgNPs against P. aeruginosa, E. coli and S. aureus.

Pathogenic species	Zone of inhibition (mm)
	1000 ppm	500 ppm
Pseudomonas aeruginosa [KACC14021]	15.7 ± 1.2	12.9 ± 1.1
Escherichia coli [CCARM 0237]	14.3 ± 1.0	11.5 ± 0.9
Staphylococcus aureus [KCTC3881]	13.2 ± 0.7	11.1 ± 0.8

Table 3. Antimicrobial activity of commercial antibiotics against P. aeruginosa, E.coli and S. aureus. -: No zone of inhibition.

Pathogenic species	Antibiotic	Zone of inhibition (mm)
Pseudomonas aeruginosa [KACC14021]	Erythromycin	-
	Vancomycin	-
	Penicillin G	-
Escherichia coli [CCARM 0237]	Erythromycin	-
	Vancomycin	-
	Penicillin G	-
Staphylococcus aureus [KCTC3881]	Erythromycin	-
	Vancomycin	-
	Penicillin G	-

Figure 9. Growth curves of E. coli (A) and S. aureus (B) cultured in R2A broth with different concentrations of the biosynthesized AgNPs.

Figure 10. MBC of biosynthesized AgNPs against E. coli (A) and S. aureus (B).

Figure 11. FE-SEM images of normal E. coli cells (A), 1 × MBC AgNPs treated E. coli cells (B), normal S. aureus cells (C), 1 × MBC AgNPs treated S. aureus cells (D).