Assessing the impact of heavy metal residues in food and drug packaging on the standard bacterial strains: a biofilm perspective

Figures & data

Table 1. Luria Bertani broth with different concentrations of digests of packaging material/heavy metal salt solution for the detection of biofilm production.

Name of heavy metal in the DPM/heavy metal salt solution	Amount of LB broth added to each well of microtiter plate (µl)	Amount of heavy metal salt solution/digests added to LB broth (µg/ml)	Final concentration of heavy metal in each well (µg/ml)
Vanadium/vanadium pentoxide	176.8	3.2	1.6
	176.4	3.6	1.8
	176	4	2.0
	175.6	4.4	2.2*
Arsenic/arsenic trioxide	178	2	1.0
	177.6	2.4	1.2
	177.2	2.8	1.4
	176.8	3.2	1.6*
Cadmium/cadmium acetate	166.8	13.2	6.6
	166.4	13.6	6.8
	166	14	7.0
	165.5	14.4	7.2*
Mercury/mercuric chloride	178	2	1
	177.6	2.4	1.2
	177.2	2.8	1.4*
	176.8	3.2	1.6

* Additional concentrations tested for some bacteria, as MIC value was different as stated in Table 2.

Table 2. Biofilm-forming ability of standard stains of bacterial isolates in the presence of standard heavy metal salts and heavy metal digests from packaging material.

Heavy metals tested (CAC permissible level)	ATCC strains tested (MIC values)	Concentration (µg/ml)	Type of heavy metal	Type of biofilm produced
Vanadium (V:1.8µg/ml)	E. coli (2 µg/ml)	1.6	Standard	Strong
			Digest	Moderate
		1.8	Standard	Moderate
			Digest	Moderate
		2.0	Standard	Weak*
			Digest	Weak
	P. aeruginosa (2 µg/ml)	1.6	Standard	Strong
			Digest	Strong
		1.8	Standard	No biofilm*
			Digest	No biofilm
		2.0	Standard	No biofilm
			Digest	No biofilm
	K. pneumoniae (2 µg/ml)	1.6	Standard	Moderate
			Digest	Moderate
		1.8	Standard	Moderate
			Digest	Moderate
		2.0	Standard	No biofilm
			Digest	No biofilm
	E. faecalis (2.2 µg/ml)	1.8	Standard	Strong
			Digest	Strong
		2.0	Standard	Weak
			Digest	Weak
		2.2	Standard	Weak
			Digest	Weak
Arsenic (As:1.6µg/ml)	E. coli (1.6 µg/ml)	1.2	Standard	No biofilm
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm
		1.6	Standard	No biofilm
			Digest	No biofilm
	P. aeruginosa (1.6 µg/ml)	1.2	Standard	No biofilm
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm
		1.6	Standard	No biofilm
			Digest	No biofilm
	K. pneumoniae (1.6 µg/ml)	1.2	Standard	No biofilm
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm
		1.6	Standard	No biofilm
			Digest	No biofilm
	E. faecalis (1.4 µg/ml)	1.0	Standard	Weak
			Digest	Weak
		1.2	Standard	No biofilm
			Digest	Weak
		1.4	Standard	No biofilm
			Digest	No biofilm
Cadmium (Cd:7.0µg/ml)	E. coli (7 µg/ml)	6.6	Standard	Moderate
			Digest	No biofilm
		6.8	Standard	Moderate
			Digest	No biofilm
		7.0	Standard	No biofilm
			Digest	No biofilm
	P. aeruginosa (7.2 µg/ml)	6.8	Standard	Moderate
			Digest	No biofilm
		7.0	Standard	No biofilm
			Digest	No biofilm
		7.2	Standard	No biofilm
			Digest	No biofilm
	K. pneumoniae (7 µg/ml)	6.6	Standard	Weak
			Digest	No biofilm
		6.8	Standard	Weak
			Digest	No biofilm
		7.0	Standard	Weak
			Digest	No biofilm
	E. faecalis (7 µg/ml)	6.6	Standard	Weak
			Digest	No biofilm
		6.8	Standard	Weak
			Digest	No biofilm
		7.0	Standard	Weak
			Digest	No biofilm
Mercury (Hg:1.4µg/ml)	E. coli (1.6 µg/ml)	1.2	Standard	Weak
			Digest	No biofilm
		1.4	Standard	Weak
			Digest	No biofilm
		1.6	Standard	No biofilm
			Digest	No biofilm
	P. aeruginosa (1.4 µg/ml)	1.0	Standard	No biofilm
			Digest	No biofilm
		1.2	Standard	No biofilm
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm
	K. pneumoniae (1.4 µg/ml)	1.0	Standard	No biofilm
			Digest	No biofilm
		1.2	Standard	No biofilm
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm
	E. faecalis (1.4 µg/ml)	1.0	Standard	Weak
			Digest	No biofilm
		1.2	Standard	Weak
			Digest	No biofilm
		1.4	Standard	No biofilm
			Digest	No biofilm

* Weak {O.Dc < O.D ≤ (2 · O.Dc)}, Moderate {(2 · O.Dc) < O.D ≤ (4 · O.Dc)}, Strong {(4 · O.Dc) < O.D}, and No biofilm producers {O.D ≤ O.Dc} (Walawalkar et al., 2016).

Walawalkar, Y. D., Vaidya, Y., & Nayak, V. (2016). Response of Salmonella typhi to bile-generated oxidative stress: Implication of quorum sensing and persisted cell populations. Pathogens and Disease, 74(8). https://doi.org/10.1093/FEMSPD/FTW090

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Data availability statement

Data can be made available upon request from the corresponding author.