International Journal of Nutrition, Pharmacology, Neurological Diseases

: 2012  |  Volume : 2  |  Issue : 1  |  Page : 70--73

Morphological and biochemical characteristics and antibiotic resistance pattern of Staphylococcus aureus isolated from grapes

Sushma Konuku, Mahalakshmi Mangai Rajan, Sridevi Muruhan 
 Department of Biotechnology, Faculty of Engineering, Vinayaka Missions Engineering College, Vinayaka Missions University, Ariyanoor, Tamil Nadu, India

Correspondence Address:
Sridevi Muruhan
Department of Biotechnology, Faculty of Engineering, Vinayaka Missions Engineering College, Vinayaka Missions University, Salem, Tamil Nadu,


Aim: To determine the morphological and biochemical characteristics and antibiotic resistance pattern of Staphylococcus aureus isolated from grapes collected from different areas of Bangalore, Karnataka, India. Materials and Methods: Morphological studies of S. aureus by gram staining and further identification by various biochemical tests were performed. Resistance against various antibiotics, including methicillin, and its change under ultraviolet (UV) light was evaluated. Results and Conclusion: S. aureus was isolated and confirmed by the pour plate method and biochemical tests. Pure cultures of the organisms were prepared. The organisms were tested for resistance against ampicillin, tetracycline, kanamycin, and methicillin. The study offers evidence of the presence of S aureus in grapes and provides information on the antibiotic resistance of the organisms.

How to cite this article:
Konuku S, Rajan MM, Muruhan S. Morphological and biochemical characteristics and antibiotic resistance pattern of Staphylococcus aureus isolated from grapes.Int J Nutr Pharmacol Neurol Dis 2012;2:70-73

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Konuku S, Rajan MM, Muruhan S. Morphological and biochemical characteristics and antibiotic resistance pattern of Staphylococcus aureus isolated from grapes. Int J Nutr Pharmacol Neurol Dis [serial online] 2012 [cited 2021 Oct 16 ];2:70-73
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Staphylococcus aureus is considered the third most important cause of food-borne illnesses in the world. [1],[2]

It is estimated that in the US alone food-borne illnesses affect 6 million to 80 million people each year, causing up to 9000 deaths and costing about 5 billion US dollars. [3] S. aureus is an important cause of food poisoning, pneumonia, wound infections, and nosocomial bacteremia. S aureus can be transmitted by different foods, including milk [4],[5] and beef. [6] However, the antibiotic resistance, especially methicillin resistance, of S. aureus isolated from grapes has not been investigated. Hence, the objective of the present study was to investigate the antibiotic resistance of S. aureus strains isolated from grapes samples collected from various supermarkets.

 Materials and Methods

Sample collection

Greenish-white and purple colored grapes were collected from five different places in Bangalore city (Karnataka, India), i.e., Jayanagar, Madiwala, Silk Board, Singsandhra, and BTM layout. Damaged grapes, identified on the basis of the physical appearance (broken skin, shriveled, discolored, etc.), were removed.

Isolation and preparation of pure culture

S. aureus was isolated from grapes. [7] From each plate, typical colonies of S. aureus with similar morphologies were isolated and cultured separately on slants.

Morphological and biochemical studies of S. aureus

After culture and bacterial isolation, the isolates were identified by morphology of colony and gram staining and by standard biochemical tests. [8]

Antibiotic susceptibility test

S. aureus -positive samples were selected for susceptibility tests. Antimicrobial susceptibility testing was done by the Kirby-Bauer disc diffusion method using LB agar medium, according to the Clinical Laboratory Standards Institute guidelines. [9] The following antimicrobial-impregnated discs (HiMedia Laboratories) were used: Tetracycline (15 μg), ampicillin (10 μg), kanamycin, gentamycin, and methicillin. After incubation at 42°C for 48 h in a microaerophilic atmosphere, the susceptibility of the S. aureus to each antimicrobial agent was measured.

Changes by ultraviolet method

The samples that showed resistance to antibiotics were treated under ultraviolet (UV). Sterilized LB broth was taken in five Petri plates and allowed to solidify. Then the sample was added. The five plates were kept for varying periods (plate 1 for 5 min, plate 2 for 10 min, plate 3 for 15 min, plate 4 for 20 min, and plate 5 for 25 min) under UV.

 Results and Discussion

The results of this study showed the presence of S aureus in grapes from different places of Bangalore. [Figure 1] shows the formation of a S. aureus colony in the pour plate method. Organisms from grapes streaked on mannitol salt agar showed colonies that fermented mannitol and appeared golden yellow. Morphological characteristics showed the organism to be gram positive, spherical S. aureus.{Figure 1}

After 24 h, the organism was grown from purple grapes collected from four places and green grapes collected from two places (P1 - Jayanagar juice shop, P2 - Silk Board, P3 - Jayanagar market, P4 - Madiwala juice shop, G1 - Jayanagar juice shop, and G2 - BTM layout). The colony formation in plates can be seen in [Figure 1]. These colonies were further used for pure culture.

The isolated organism showed negative results for indole, methyl red, Voges-Proskauer reaction, hydrogen sulphide, gelatin liquefaction, and oxidase test and showed positive results with citrate, lactose, sucrose, glucose, lipid hydrolysis, catalase, and starch hydrolysis test [Table 1]. Similar biochemical results have been reported for S. aureus.[10] {Table 1}

Both purple (P1-4) and green (G1-2) grapes showed the same results.

The source of the samples was as follows: P1 - Jayanagar juice shop, P2 - Silk Board juice shop, P3 - Jayanagar market, P4 - Madiwala juice shop, G1 - Jayanagar juice shop, and G2 - BTM layout.

Bacterial resistance to antimicrobial agents is a growing problem. This is due to the alteration of resistance mechanisms, acquisition of resistance genetic element from other bacteria, and genetic changes in the bacteria. [11] S. aureus isolated from purple grapes showed more resistance to methicillin than to other antibiotics [Figure 2]. [12] Since methicillin resistance emerged, methicillin-resistant S. aureus (MRSA) has become widespread in hospitals worldwide, causing bacteremia, pneumonia, surgical site infections, and other nosocomial infections. [13] The S. aureus strains isolated from purple grapes (P1-4) and green grapes (G1) in our study were also resistant to methicillin. of purple grapes (P1) also showed resistance to kanamycin and ampicillin [Table 2]. Similar results have been reported by others. [14],[15],[16]{Figure 2} {Table 2}

After 24 h of incubation, among the six samples only one (P1) showed resistance to three antibiotics (methicillin, ampicillin, and kanamycin). The remaining showed resistance to methicillin but were sensitive to the other antibiotics.

As P1 showed resistance to three antibiotics, it was further subjected to mutational change study by the UV method. There was growth of S. aureus [Figure 3] in the plates after exposure to UV rays for different time intervals (5 min, 10 min, 15 min, 20 min, and 25 min (named as U1, U2, U3, U4, and U5, respectively). In some plates the growth of the organism was at the corners of the plate, while in others growth occurred all around the plate.

[Figure 4] shows antibiotic susceptibility test and [Table 3] shows the zone of inhibition.{Figure 3}{Figure 4}{Table 3}

S. aureus is one of the most frequent bacteria isolated from raw milk, meat and poultry products. But with the extensive research on the application of technologies such as pulsed electric fields (PEF), high hydrostatic pressure, UV irradiation and ultrasound [17],[18],[19] in industrial-scale food processing has shown that these technologies can combine the advantage of preserving 'freshness' with acceptable inactivation of spoilage-causing and pathogenic microorganisms.

Various studies have demonstrated the presence of fungal, yeast, and bacterial species [20],[21] as well as the mycotoxin ochratoxin A [22],[23] in grapes. Our study shows the multiple antibiotic-resistance exhibited by a strain of S. aureus isolated from grapes.


Further research is needed for molecular characterization of the S. aureus strains.


The authors thank Dr. M. Mahesh, MSc, M.Phil, PhD; CEO, Azyme Biosciences, Bangalore, India, for his support in the work.


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