Effectiveness of Lippia sidoides Cham. (Verbenaceae) essential oil in inhibiting the growth of Staphylococcus aureus strains isolated from clinical material

Atividade do óleo essencial de Lippia sidoides Cham. (Verbenaceae) na inibição do crescimento de Staphylococcus aureus isolados de material clínico

ARTIGO

Effectiveness of Lippia sidoides Cham. (Verbenaceae) essential oil in inhibiting the growth of Staphylococcus aureus strains isolated from clinical material

Atividade do óleo essencial de Lippia sidoides Cham. (Verbenaceae) na inibição do crescimento de Staphylococcus aureus isolados de material clínico

Fillipe Pereira de Oliveira^I; Edeltrudes de Oliveira Lima^I,*; José Pinto de Siqueira Júnior^II; Evandro Leite de Souza^III; Bernadete Helena Cavalcante Santos^IV; Humberto Medeiros Barreto^II

^ILaboratório de Micologia, Departamento de Ciências Farmacêuticas, Universidade Federal da Paraíba, 58051-970, João Pessoa, PB, Brasil

^IIDepartamento de Biologia Molecular, Centro de Ciências Exatas e da Natureza, Universidade Federal da Paraíba, 58051-970, João Pessoa, PB, Brasil

^IIIDepartamento de Nutrição, Centro de Ciências da Saúde, Universidade Federal da Paraíba, 58051-970, João Pessoa, PB, Brasil

^IVLaboratório de Bacteriologia Clínica, Departamento de Ciências Farmacêuticas, Universidade Federal da Paraíba, 58051-970, João Pessoa, PB, Brasil

ABSTRACT

Staphylococcus aureus is a classical pathogen microorganism and it is commonly recognized as etiological agent of many community and nosocomial infections. Regarding the knowledge about the biological properties of Lippia sidoides Cham. (Verbenaceae), this study aimed to evaluate the effectiveness of its essential oil in inhibiting the growth of S. aureus strains isolated from clinical materials and with different profiles of antibiotic resistance. The results showed prominent anti-S. aureus activity of L. sidoides essential oil noted by large growth inhibition zones (15-21 mm). MIC found was of 0.4 µL/mL for all assayed strains. MIC presented prominent effectiveness in inhibiting the viability of S. aureus in broth during twenty-four hours of exposure characterizing a bacteriostatic effect. These results show the promising anti-staphylococcal property of L. sidoides essential oil and support the possibility of its rational use as alternative antibacterial agent.

Keywords: Lippia sidoides, Staphylococcus aureus, essential oil, antimicrobial activity.

RESUMO

Staphylococcus aureus apresenta-se como um microrganismo patogênico clássico sendo comumente reconhecido como agente etiológico de infecções comunitárias e hospitalares. Considerando o conhecimento acerca das propriedades biológicas apresentadas por Lippia sidoides Cham. (Verbenaceae), este estudo teve como objetivo avaliar a efetividade de seu óleo essencial em inibir o crescimento de cepas de S. aureus com diferentes perfis de resistência antibiótica isoladas de material clínico. Os resultados mostraram destacável atividade anti-S. aureus do óleo essencial de L. sidoides notada por grandes halos de inibição do crescimento bacteriano (15-21 mm). A CIM encontrada foi de 0.4 µL/mL para todas as cepas ensaiada. A CIM apresentou destacável efetividade de inibição da viabilidade de S. aureus em caldo durante vinte e quatro horas de interação caracterizando um efeito bacteriostático. Estes resultados mostram a destacável atividade antiestafilocócica do óleo essencial de L. sidoides, bem como suportam a possibilidade de seu uso racional como agente antimicrobiano alternativo.

Unitermos: Lippia sidoides, Staphylococcus aureus, óleo essencial, atividade antimicrobiana.

INTRODUCTION

Staphylococcus genus is widely spread in nature being part of the indigenous micoflora of skin and mucosa of animal and birds. Some Staphylococcus species are frequently recognized as etiological agents of many animal and human opportunistic infections (Nostro et al., 2004). S. aureus, S. epidermidis, S. saprophyticus and S. haemolyticus are the most important species as community and nosocomial human infection causing agents. In addition of causing different kinds of intoxications, S. aureus has been the most common etiological agent of festering infections which can attack different tissues and/or organs (e.g. furuncle, carbuncle, abscess, myocarditis, endocarditis, pneumonia, meningitis, bacterial arthritis) (Verhoff et al., 1999; Pereira et al., 2004). Capsule, peptdioglican, teicoic acids, A protein, adesins and synthesis of enzymes and extracelullar toxins are some virulence attributes present in/on S. aureus cell (Nostro et al., 2004).

All bacterial species are described as possessing some potential to develop strains with high resistance to various antibiotics, so that many cellular mechanisms involved in the rising of this biological phenomenon have been elucidated (Woolhouse, 2002; Wright, 2003). Among the bacterial genera able to develop changes in their sensitivity to antimicrobials, staphylococcal species have been recognized as having increasing and worrying antimicrobial resistance (Georgopapadakou, 2002; Nostro et al., 2004).

Over fifty years antibiotics have been applied in industry, agricultural, livestock and domestic environment for treating or inhibiting quickly the most infections. This use and, many times, misuse of antimicrobials in both human and animal medicine has been responsible for an unprecedent selection in the microbial evolution (White et al., 2002). Consequently, the society is facing the most serious dilemma of public health: the rising of infectious diseases which present etiological agents resistant to many and, some times, all clinically used antimicrobials (Souza et al., 2005a). For patients, the antimicrobial resistance increases the morbidity and mortality, while for healthcare institutions it means increasing costs (Dancer, 2001; Kuner; Oho, 2003).

Regarding the increasing clinical importance given to nosocomial and community bacterial infections and the progressive development of antimicrobial resistance, a great number of scientific researches emphasizing the antibacterial properties of plant products has been carried out (Hernández et al., 2003; Silva-Santos et al., 2004; Duarte et al. 2005; Gayoso et al., 2005; Michelin et al., 2005; Lima et al., 2006a; Lima et al., 2006b). Filtrates, infusions, macerated, juices, extracts and cataplasms from plants with medicinal properties have been applied in the treatment of various diseases since antiquity (Annuk et al., 1999; Hernández et al., 2003).

Lippia sidoides Cham. (Verbenaceae) is a plant native from Brazilian northeastern and it has showed valuable biological properties rising as potential source of biologically active compounds (Matos, 1994). L. sidoides leaves by-products have been applied in folk medicine for acne, wounds, skin and scalp infections treatment. Still, their infusion has been used for treating allergic rhinitis and vaginal, buccal and oropharyngeal infections (Sousa et al., 1991; Martins et al., 1994).

This study was carried out with the purpose of evaluating the effectiveness of L. sidoides essential oil in inhibiting the growth and survival of S. aureus strains isolated from clinical samples, which presented different profiles of resistance to various antibiotics conventionally applied in clinical therapy.

MATERIAL AND METHODS

Essential oil

Lippia sidoides Cham. (Verbenaceae) essential oil was supplied by Laboratory of Pharmaceutic Technology, Department of Pharmaceutical Sciences, Health Sciences Center, Federal University of Paraíba and its extraction was performed by hidrodistillation procedure (Craveiro et al., 1981; Matos, 1988).

Essential oil solutions used in antimicrobial assays were obtained according to the following procedure: 600 µL of the essential oil, 40 µL of Tween 80 and q.s.f. 5 mL of sterile water were added in sterile assay tube and shaken for 5 minutes using Vortex (Fanem), obtaining a solution with final essential oil concentration of 120 µL/mL. Following serial dilution technique, it was obtained solutions with concentrations of 60, 30, 15, 0.8, 0.4, 0.2, 0.1, 0.05, 0.025, 0.12 and 0.06 µL/mL (Souza et al., 2005b).

Microorganisms

S. aureus strains used as test microorganisms were isolated from clinical material (Table 1) by standard procedures (Murray, 1999; Konneman, 2001). The most strains presented resistance profile to some antibiotics applied in clinical therapy (Table 2). Antibiotic resistance study was carried out according to NCCLS (1999). Stock cultures were maintained on Muller-Hinton agar slants at 7 °C (± 1 °C). Overnight cultures inoculated in Muller-Hinton agar slants at 37 °C were used to prepare the bacterial inoculum used in the antimicrobial assays. The inoculum was of 10⁶ colony forming units per mL (cfu/mL) prepared in sterile saline solution (0.85%) and standardized according to the turbidity of McFarland scale 0.5 tube and adjusted for presenting the wished microbial population (Fromtling et al., 1983).

Antimicrobial assays

Anti-staphylococcal effectiveness of L. sidoides essential oil was assessed in three steps: screening, determination of Minimum Inhibitory Concentration-MIC and MIC interference on the bacterial cell viability.

Solid medium diffusion technique using filter paper discs was used for screening the antibacterial activity. For this, 1 mL of the bacterium suspension (approximately 10⁶ cfu/mL) was uniformly spread on sterile agar Muller-Hinton Petri dishes. After bacterial suspension absorption by agar, filter paper discs (Whartman n. 1, diameter 6mm) were soaked with 20 µL of the essential oil and placed on the inoculated agar (Nair et al., 2005; Sahin et al., 2004). The system was incubated at 37 °C for 24 hours. At the end of the incubation period, the bacterial growth inhibition zone diameter was measured using calipers and expressed in millimeters. It was considered as positive antibacterial activity when observed growth inhibition zone with diameter equal to or higher than 10 mm diameter (Lima et al., 1993).

Control of sensitivity of the assayed strains to Tween 80 was carried out by solid medium diffusion technique using filter paper discs (Bauer; Kirby, 1966). Also, the viability of the bacterial strains was assessed by verifying their capacity to grow in Muller-Hinton agar without addition of essential oil.

Microplate bioassay was used to determine the essential oil MIC. For this was used a microplate with 96 wells (flatted bottom) and cap. The 96-well microplates were prepared dispensing into each well 100 µL of doubled strength Brain Heart Infusion broth inoculated with 1mL of the bacterium inoculum prior the assay (1:9 v/v). A 100 µL of the essential oil solution with their respective concentration was transferred into seven consecutive wells. Final volume in each well was 200 µL. The solution having the highest concentration was added into the first well and the smallest concentration was added into the penultimate well. The last well contained 200 mL of Brain Heart Infusion broth inoculated with the bacterium inoculum was used as positive control (strain viability). The microplate was aseptically sealed, followed by mixing on plate shaker (300 rpm) for 30s, and incubated at 28 – 30 °C/48hs (Viljoen et al., 2003; Sahin et al., 2004). Antibacterial activity was detected using a colorimetric method by adding 200 µL of resauzurin staining (0.1%) aqueous solution in each well at the end of the incubation period. MIC was defined as the lowest essential oil concentration able to inhibit the bacteria growth, as indicated by resauzurin staining (bacteria died cells are not able to change the staining color by visual observation – blue to red) (Palomino et al., 2002; Burt; Reinders, 2003).

Viable cells count method was used to carry out the study about the interference of the MIC essential oil on the bacterial cell viability. 5 mL of doubled strength Brain Heart Infusion broth was inoculated with 1 mL of the bacterium suspension. After that, 4 mL of the essential oil solution with concentration adjusted to provide an essential oil final concentration similar to the MIC previously determined, was added to the system and followed for shaking for 30s using Vortex. The system was incubated at 37 °C. At different time intervals (1, 2, 4, 8, 12 and 24 hs) of exposure, 1 mL of the suspension was serially diluted in PBS (10^-1 - 10^-5) and inoculated in sterile Muller-Hinton agar Petri dishes for 24 hs at 37 °C (Arora; Kaur, 1999; Viljohen et al., 2003). In the control assay, the essential oil solution was replaced by sterile distilled water. After the incubation period, the number of colonies (cfu/mL) was counted and expressed in log of cfu/mL.

All antimicrobial assays were performed twice and the results were expressed as average of the two repetitions.

Statistical analysis

Statistical analysis was carried out by descriptive statistic study and determination of statistically significant difference (P <0.05) by Tukey test to the bacteria viability study. For this was used Sigma stat 2.03 computer program

RESULTS AND DISCUSSION

In the last years there has been a great scientific interest in chemical and pharmacological investigations regarding the biological properties of medicinal plants (Silva et al., 2003; Rocha et al., 2005; Barbosa-Filho et al., 2005; Barbosa-Filho et al., 2006a; Barbosa-Filho et al., 2006b; Barbosa-Filho et al., 2006c). It is known that medicinal plants have been source of many drugs applied in clinical procedures (e.g morphine, emetine, rutine). Essential oils are involved in many important actions related to the plant survival, playing prominent role in its defense against microorganisms (Cechinel-Filho et al., 1998; Siqui et al., 2000). The use of essential oils as antimicrobial agents presents two principal characteristics: i) their natural origin meaning more safety for users and environment; ii)there is low risk of rising microbial resistance to their action because essential oils are mixtures of several compounds that, apparently, presents different antimicrobial action making more difficult the microbial adaptability (Daferera et al., 2003).

Table 3 shows the inhibitory activity of L. sidoides essential oil on S. aureus strains isolated from clinical material. As can be seen, the essential oil at absolute concentration showed effectiveness in inhibiting all bacteria strains with inhibition zones diameters between 15-21 mm (average: 17.3; s.d.:1.8). Seven out from the twelve assayed strains showed inhibition zones with diameter of 18 mm. Smallest inhibition zones (15 mm) were found to S. aureus BH8, BH13 and BH22, while the largest one (21 mm) was found to S. aureus BH19. MIC value was 0.4 µL/mL for all assayed strains. This MIC value is smaller than other found in some studies emphasizing the anti-S. aureus properties of medicinal plants (Carson et al., 1995; Caeli et al., 2000; McGaw et al., 2000; Hernández et al., 2003; Nostro et al., 2004). Antimicrobial effectiveness of L. sidoides essential oil on different pathogen microorganisms (e.g. P. aeruginosa, B. subtilis, S. aureus, E. coli, Streptococcus spp., Trichosporon spp.) also was reported by other researches (Lemos et al., 1990; Laxoste, 1994; Lima et al., 1994; Siani et al., 2000; Pontes, 2002; Costa et al., 2005; Oliveira et al, 2006). The essential oils of Lippia sidoides was active against larvae of Aedes aegypti and Culex quinquefasciatus (Costa et al., 2005).

Aligiannis et al. (2001) proposed a classification about the antimicrobial potential of plant products, based on MIC results: strong inhibitors – MIC up to 0.5 µL/mL; moderate inhibitors – MIC between 0.6 and 1.5 µL/mL; weak inhibitors – MIC above 1.6 µL/mL. Regarding the MIC values found for all assayed S. aureus strains, the classification criteria above cited confirms the strong anti-staphylococcal property of L. sidoides essential oil. Still, this intense anti-S. aureus activity becomes more important when regarded that the most assayed strains showed resistance to at least three clinically used antibiotics (Table 2).

Figure 1 shows the interference of L. sidoides essential oil MIC on the cell viability of S. aureus BH1. This strain was chosen for this assay because it presented high antibiotic resistance profile being resistant to twelve out from the fourteen tested antibiotics. MIC showed strong effectiveness in inhibiting the bacterial growth in broth with significant difference (P <0.05) with respect to the control assays. After twenty-four hours of exposure the control assay presented microbial count greater than 10⁹cfu/mL. On the other hand, the treated assay showed count around 10⁶cfu/mL (next to the initial inoculum). From two hours of exposure on the treated assay showed microbial count around 99.9% (1000 folds) smaller than the one found in the control assay.

Antimicrobial effect showed by L. sidoides essential oil on S. aureus can be recognized as bacteriostatic effect. Bacteriostatic property is characterized when some compound is able to cause the bacteria failure to grow in broth, but it is cultured when the broth is plated onto a suitable agar (Smith-Palmer et al, 1998; Burt, 2004). Thymol, carvacrol, p-pinene, a-pinene, mircene, 1,8 cineole, g-terpinene, p-metadiene, methyl-thymol, methyl-carvacrol, linalool, 4-terpineole, g-elemene are some compounds found in L. sidoides essential oil (Lemos et al., 1990; Matos; Oliveira, 1998; Leal et al., 2003). Thymol has been recognized as the active compound related to the antibacterial and antifungical property of L. sidoides essential oil (Matos; Oliveira, 1998). Thirteen compounds that don’t belong the class of the essential oils, 3-O-acetyloleanolic acid, methyl 3,4-dihydroxy benzoate, lapachenol, tecomaquinone, tectoquinone, tectol, acetilated tectol, quercetin, luteolin, glucoluteolin, lippisidoquinone, taxifolin and isolariciresinol, were isolated from ethanol extract of Lippia sidoides (Costa et al., 2002).

The results obtained in this study showed the strong anti-staphylococcal property of L. sidoides essential oil noted by small MIC value and effectiveness in inhibiting the microbial growth in broth. The MIC value found for all assayed strains was prominently smaller than other MIC values found by many researches emphasizing the antimicrobial potential of medicinal plants on S. aureus strains. These data are promising and could encourage further researches on phytochemical, toxicological and pharmacological aspects of L. sidoides by-products in order to support their possible rational use in the antimicrobial therapy, particularly, in anti-S. aureus therapy.

Received 03/25/06. Accepted 08/30/06

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Publication Dates

• Publication in this collection
  17 May 2007
• Date of issue
  Dec 2006

History

• Accepted
  30 Aug 2006
• Received
  25 Mar 2006