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Year : 2014  |  Volume : 32  |  Issue : 1  |  Page : 90--91

In-vitro antibacterial activity of some essential oils against clinical isolates of Acinetobacter baumannii

Gopinath Prakasam, Manju Bhashini, Lakshmipriya, S Srivani Ramesh 
 Department of Microbiology, Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai, Tamil Nadu, India

Correspondence Address:
S Srivani Ramesh
Department of Microbiology, Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai, Tamil Nadu

How to cite this article:
Prakasam G, Bhashini M, Lakshmipriya, Ramesh S S. In-vitro antibacterial activity of some essential oils against clinical isolates of Acinetobacter baumannii.Indian J Med Microbiol 2014;32:90-91

How to cite this URL:
Prakasam G, Bhashini M, Lakshmipriya, Ramesh S S. In-vitro antibacterial activity of some essential oils against clinical isolates of Acinetobacter baumannii. Indian J Med Microbiol [serial online] 2014 [cited 2020 Jan 23 ];32:90-91
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Dear Editor,

Until 1970s, Acinetobacter baumannii was considered to be a rare cause of nosocomial infections. However, the incidence of Acinetobacter infections has reached a point of concern and poses a threat to debilitated patients around the world. [1] The clinical importance of Acinetobacter has improved rapidly in the last 20 years, due to the world-wide expression of intensive care units that led to a change in the type of infections and the emergence of multi drug resistant Acinetobacter isolates. [2] Essential oils have been implicated in a wide array of applications for several 1000 years owing to their antimicrobial properties as alternative medicine. [3] Thus, the development of resistance to antibiotics is believed to be counteracted by the use of natural herbal medicine are being considered to be the need of the hour. The present study was undertaken to determine the in-vitro antibacterial activity of clove, peppermint and eucalyptus oils against clinical isolates of A. baumannii. Essential oils were procured from Tegraj and Co (P) Ltd, India and their purity was about 99.9%. The major constituents were found to be eugenol (84.2%), eugenyl acetate (9.7%) for clove oil. P-menthone (19.5%), menthol (63.5%) and 1,8-cineole (74.3%), α-terpinenol (10.3%) for peppermint oil and eucalyptus oil respectively. We tested a total of 50 isolates of A. baumannii from different clinical specimens that includes blood (15), endotracheal aspirates (14), bronchoalveolar lavage (6), pus (6), urine (5) and sputum (4). Minimum inhibitory concentrations (MICs) were determined for these oils by agar dilution method. [3] The concentrations were ranging from 0.03 to 2% (v/v). A sterile Mueller Hinton Agar without oils served as control plate for bacterial growth. Overnight culture suspensions of A. baumannii isolates were adjusted to 0.5 McFarland standard for turbidity and 10 μL of suspension was spot inoculated onto plates with afore mentioned concentrations of clove, peppermint and eucalyptus oils. Experiments were carried out in triplicate. Inoculated plates were incubated at 37°C for 24 h and MIC was determined. The lowest concentration of oils that inhibited the growth of A. baumannii isolates were considered as MIC. All the isolates were not inhibited at a concentration of 0.03% of clove oil, 0.03-0.125% of peppermint oil and 0.03-0.06% of eucalyptus oil. Strains were inhibited from 0.06 to 0.25%, 0.25-1% and 0.125-1% for clove, peppermint and eucalyptus oils respectively. In clove oil, 14/50 (28%) isolates were inhibited at 0.06%, 25/50 (50%) at 0.125% and 11/50 (22%) at 0.25% of clove oil. In peppermint oil, 34/50 (68%) isolates were inhibited at 0.25%, 12/50 (24%) and 4/50 (8%) were at 0.5% and 1% concentrations of peppermint oil respectively. In eucalyptus oils, 10/50 (20%) isolates were inhibited at 0.125%, 18/50 (36%) at 0.25%, 16/50 (32%) and 6/50 (12%) were at 0.5% and 1% respectively. Thus, the MIC of clove oil was found to be 0.06%, 0.25% for peppermint oil and 0.125% for eucalyptus oil [Table 1]. Similarly study was performed by Hammer et al. in 1999 on antibacterial activity of essential oils found that the MIC values of 0.25%, 0.5% and 1% were determined for clove, peppermint and eucalyptus oils respectively. [3] These oils have been shown to be effective against clinical isolates of A. baumannii in in-vitro condition. Carbapenem group of antibiotics are used as the most effective drug to treat infections caused by this notorious pathogen. Thus, we have also tested susceptibility of the same isolates to meropenem (Meronem, Astra Zeneca, UK) by MIC method as per Clinical Laboratory Standards Institute guidelines. [4] A standard strain of Pseudomonas aeruginosa ATCC 27853 was also included as quality control. MIC of ≥ 16 was considered as resistant to meropenem. Out of 50, 21 (42%) isolates were found to be meropenem sensitive with MIC range of ≤ 4 μg/mL, 2/50 (4%) isolates were intermediate and 27/50 (54%) were resistant with MIC ranges of 8 μg/mL and ≥ 16 μg/mL respectively. The study conducted by Taneja et al. in 2003 documented an increased percentage of carbapenem resistant (>20%) Acinetobacter isolates. [5] Similarly, Corbella et al. found > 36% of Acinetobacter spp. were appeared to be carbapenem resistant. [6] These reports are in concordant with our data as increased percentage of isolates was found to be resistant to carbapenem. Moreover, these isolates were found to be resistant to other classes of antibiotics except colistin and tigecycline by MIC. High antibiotic pressure due to indiscriminate usage of such group of drugs in the clinical settings led to the marked resistance among A. baumannii. In some essential oils such as eucalyptus and clove oils, there has been much research and documented some toxic and irritant properties. [7] In spite of this, most of these oils are available as whole oils or as part of pharmaceutical and cosmetic products. However, the studies on toxic and irritant properties of essential oils are imperative, especially when considering any new products for human administration. Thus, we suggest that these three oils were found to have good antibacterial activity against A. baumannii. This can be used as alternative and complementary antibacterial agents for controlling the Acinetobacter infections.{Table 1}


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