AMERICAN JOURNAL OF FOOD AND NUTRITION Print: ISSN 2157-0167, Online: ISSN 2157-1317, doi:10.5251/ajfn.2013.3.2.53.57 © 2013, ScienceHuβ, http://www.scihub.org/AJFN Antimicrobial activity some transition metal picolinates Oladipo I. C.1, Adeoye I. O.2 Adeyemo A. A.3 1Department of Science Laboratory Technology, Ladoke Akintola University of Technology, Ogbomoso. Nigeria. 2Department of Science Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso. Nigeria. 3Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore. 560012. India. ABSTRACT Picolinic acid and its derivatives have been found to be good preservatives. This study is aimed at the evaluation of its antibacterial properties. The antibacterial properties of its Manganese, Copper, Zinc, Cobalt and Nickel derivatives were tested on selected bacteria including Serratia marcescens, Micrococcus luteus, Proteus vulgaris, Proteus mirabilis, Bacillus cereus, Bacillus subtilis, Klebsiella pneumoniae, Escherichia coli, Shigella flexneri, Lactococcus lactis, Enterobacter cloacae and Staphylococcus aureus. The results demonstrated that picolinates has strong antibacterial activity against the test bacteria that majorly affects food consumed by man. Copper and cobalt picolinates had antibacterial activity against M. luteus and S. marcensces with MIC of 0.5mg/mL, nickel and manganese picolinates had antibacterial activity against B. subtilis, M. luteus and K. pneumonia with MIC of 0.5mg/mL, zinc picolinate had antibacterial activity against B. subtilis, B. cereus, S. flexneri, L. lactis, K. pneumonia, P. mirabilis, P. vulgaris, E. coli, E. cloacae and S. aureus with MIC of 0.5mg/mL. The minimum bactericidal concentrations were discovered to be a 2 fold increase on those of the minimum inhibitory concentrations. This work also highlights the potential use of picolinates for food preservation. INTRODUCTION with activated macrophages, had significant increases in lifespan compared to control (Ruffman et Picolinates are group of esters that are formed by al., 1987). reaction of picolinic acid with alcohol. It is also an excellent π-acceptor ligand and it forms stable Shimizu and Tomioka (2006) studied the in vitro and complexes with various transition metal ions. The in vivo antimicrobial activities of picolinic acid (PA) in picolinate ligands are coordinated to the metal centre combination with the antiprotozoal drug quinacrine in a bidentate form, and it is interesting to note that against intramacrophage Mycobacterium avium the two donor sites of the picolinate ligand are of complex (MAC). Quinacrine significantly potentiated significantly different nature. The pyridine nitrogen is the anti-MAC activity of PA, suggesting the a soft donor and a recognized stabilizer of the lower usefulness of this combination in the clinical control oxidation states of transition metals, whereas the of MAC infection. Musk and Hergenrother (2008) carboxylate oxygen is a hard donor and is known to showed that ferric picolinate (also ferric stabilize transition metals in their higher oxidation acetohydroxamate) is effective against Pseudomonas states aeruginosa. The relationship between the chemical structures and antimicrobial activity of selected Picolinates are used in dietary supplements for obese alkaline metal p- and o-iodobenzoates, nicotinates, people, since it has a beneficial effect on reducing picolinates and isonicotinates have also been diabetes risk (Borawska et al., 2008). Zinc picolinate studied. Microbiological studies on alkaline (as a source of zinc) has an antioxidant effect and picolinates showed that some of them inhibit the may be used in patients with chronic obstructive growth of Escherichia coli (Koczoń et al., 2005, pulmonary disease. Picolinates has also been shown 2006). to affect tumour growth. In vivo studies on mice inoculated with tumour cells showed that those Recently, a comparative assessment of picolinic acid treated with injections of picolinates in combination with common chemical preservatives in ginger fruit Am. J. Food. Nutr, 2013, 3(2): 53-57 juice showed that it has a much better preservative 106 cfu/ml. The turbidity of the actively growing broth power than most common chemical preservatives culture was adjusted with sterile broth to obtain (Akinwande et al 2012). This study is aimed at turbidity comparable to that of the 0.5 McFarland evaluating the antibacterial properties of picolinates standards. against selected bacterial pathogen and to determine To standardize the inoculum density for a their minimum inhibitory concentration against the susceptibility test. BaSO turbidity standard selected bacterial pathogens. 4 equivalent to a 0.5 McFarland standard was used. A MATERIALS AND METHOD 0.5 McFarland standard was prepared as described in NCCLS (NCCLS 1997). 1% v/v solution of Sample collection: The test microorganisms were sulphuric acid was prepared by adding 1ml of water collected from the Department of Microbiology, and mixed well. A 1.175% w/v solution of barium University of Ibadan, Ibadan. The test organisms are: chloride was prepared by dissolving 2.35g of Serratia marcescens, Micrococcus luteus, Proteus dehydrated barium chloride (BaCl .H O) in 200ml of vulgaris, Proteus mirabilis, Bacillus cereus, Bacillus 2 2 distilled water. To make the turbidity standard, 0.5ml subtilis, Klebsiella pneumoniae, Escherichia coli, of barium chloride solution was added to 1% 99.5ml Shigella flexneri, Lactococcus lactis, Enterobacter sulphuric acid solution and mixed well. A small cloacae, and Staphylococcus aureus. volume of these turbid solutions was transferred to Preparation of complexes: The synthesis of the screw-capped tube of the same type as used for substituted methyl pyridine carboxylates from readily preparing the control inoculates and stored in the available starting materials using the method dark at room temperature. described by Orjiekwe at al (2005). The metal salts Antibacterial test: The picolinates was serially was added dropwisely to an ethanolic solution of 2- diluted and perforated filter disc were soaked in each picolinic acid in 1:1 mole ratio while stirring continued concentration of picolinates according to the modified under reflux at 60 °C for 30minutes. A coloured methods of Washington and Wood (1995). The precipitate was formed which was filtered and concentration of picolinates in different plates was washed with acetone and dried in the dessicator. 0.5mg/ml, 1.0mg/ml, 1.5mg/ml, 2.0mg/ml and This procedure was used to prepare the manganese, 2.5mg/ml. copper, zinc, cobalt and nickel picolinate derivatives used for this study. Antibacterial susceptibility test of the isolated organism was done by disc diffusion using the Kirby- Determination of mic by agar plate dilution Bauer technique (Bauer et al., 1966) and as per method: Agar diffusion method was used to recommendation of NCCLS (NCCLS 1997). Panel of determine the Minimum Inhibitory Concentration picolinates were used (Fig 4.1). All tests were (MIC) of the antimicrobial agents. The picolinates performed on Mueller Hilton agar. The surface was were dissolved in distilled water and the perforated lightly and uniformly inoculated by cotton swab. Prior filter paper soaked in it. Dilutions of picolinates were to inoculation, the swab stick was dipped into prepared in sterile distilled water. The MIC range bacterial suspension having visually equivalent varied with different complexes. All MIC range was turbidity to 0.5McFarland standard. The swab stick followed according to the NCCLS guidelines was then taken out and squeezed on the wall of the (NCCLS, 1997). Mueller Hilton (500ml ) agar of each test tube to discard extra suspension. flask was sterilized in a pressure pot and allowed to cool in water bath at 50ºC and Mueller Hilton agar The picolinate soaked paper discs were placed on media was immediately poured on to a plate. agar surface of the plates already swabbed with different selected bacteria. Inoculated agar plates Inoculates were obtained from an overnight agar were allowed to stand until the soaked paper disc culture of the test microorganism. Inoculums for the were completely absorbed and after then it was MIC test were prepared by taking at least three to five incubated at 35ºC overnight. On the next day, plates well-isolated colonies from an agar plate culture. The were read by taking measurement of zones of top of each colony was touched with a sterile loop inhibition. Result were recorded and graded as and the growth was transferred into a tube containing resistant (R) and sensitivity (S) according to the 20ml Mueller Hilton broth. The broth culture was reference zone of inhibition of particular picolinate. incubated at 35ºC until it achieved the turbidity of the 0.5 McFarland standards (usually 2 to 6 hours). This results in a suspension containing approximately 2 x 54 Am. J. Food. Nutr, 2013, 3(2): 53-57 RESULTS There were variations in the results of the Nickel picolinate had antibacterial activity against antibacterial activity of the picolinates against M.luteus, B. subtilis, S. marcensces, K. pneumonia selected bacterial pathogens. Zinc picolinate had and B. cereus with MIC of 0.5mg/mL. Also against P. antibacterial activity against B. cereus, S. flexneri, P. vulgaris, P. mirabilis and S. aureus with MIC of vulgaris, P. mirabilis, K. pneumonia, L. lactis, S. 1.0mg/ml and had antibacterial activity against L. aureus, E. cloacae and E. coli with minimum lactis, E. coli, E. cloacae and S. flexneri with MIC of inhibitory concentration of 0.5mg/mL and also against 2.0mg/mL. The zones of inhibition ranged between B. subtilis and S. marcensces with minimum 7.5 and 11.4mm as shown in Figure 3. inhibitory concentration of 1.5mg/mL. It also had antibacterial activity against M. luteus with MIC of 2.0mg/mL. The diameter of zones of inhibition ranged Nipi between 8.5mm and 16.5mm as shown in Figure 1. 3 2 Mnpi 1 0 Nipi 3 (mg/mL) 2 Concentration 1 0 Mnpi Fig 3: The MIC of nickel picolinate against test bacteria Copper picolinate had antibacterial activity against S. Concentratio (mg/mL) aureus, P. vulgaris, M. luteus, L. lactis, E. coli, S.