Chromolaenaodorata (Siam weed) is a fast-growing perennial and invasive weed native to South and Central America. It is a known Toxic weed that is widespread in many parts of the world, including Nigeria. It is a specie from the family Asteraceae. The weed goes by many common names such as devil weed, communist weed, hagonoy, Awolowo leaf etc. Away from its native range, Chromolaenaodorata is an important weed in tropical areas extending from west central and Southern Africa to India, Sri lanka, Bangladesh, Cambodia, China, Taiwan and Indonesia (Bani, 2002., Umukoro and Ashorobi, 2006 and Hung et al., 2011) [3, 10]. Chromolaenaodorata is an aggressive competitor that occupies different types of lands where it forms dense strands that prevent the establishment of other flora. It is a menace in plantations and other ecosystems. It suppresses young plantations, agricultural crops and smothers vegetation as it possesses allelopathic potentialities and growth inhibitors (Ambica and Jayachandra, 2003) [1]. The economic value of Chromolaenaodorata is low.

However, Chromolaenaodorata is a perennial shrub and it has become a serious pest in the humid tropics of South East Asia, African and pacific Islands. It spreads rapidly in lands used for forestry, pasture and plantation crops such as rubber, coffees, coconut, cocoa and cashew. The plant can be poisonous to livestock as it has exceptionally high level of nitrate in the leaves and young shoots; the cattle feeding on these die of tissue anoxia (Sajise et al; 2005) [2].

The plant of Chromolaenaodorata is hairy and glandular and the leaves give off a pungent, aromatic odour when crushed (Lalith, 2009). The seed of the plant regenerate from the roots and under favourable conditions the plant can grow more than 3cm a day (Lalith, 2009) [7].

Chromolaenaodorata is sometimes grown as a medicinal and ornamental plant. It is used as a traditional medicine in Indonesia. The young leaves are crushed, and the resulting liquid used to treat skin wounds (Iwu, 2000) [6]. It is also used as anti-diarrhea, anti-plasmotic, anti-hypertensive, anti-inflammatory, diuretic tonic, anti-pyretic and heart tonic (Vital and Windell, 2009) [11]. In some Countries the fresh leave extract are use for treatment of burns, soft tissue wounds and skin infections. (Ayyanaf and Ignacinuthu 2009) [5]. In Southern parts of Nigeria, the leaves are used for wound dressing, skin infection and to stop bleeding as an anticoagulant. The Juice of the crushed leaves is applied to cuts to arrest bleeding: According to Iwu (2000) [6]. The macerated leaves are usually applied to swollen part of the body to relieve inflammation amongst the rural population in Southern parts of Nigeria.

The Micro-organisms under investigation against Chromolaena odorata namely, Staphylococcus aureus, Esherichia coli Pseudomonalaeruginosa and Proteus Spp are potential human pathogens. These organisms exist in nature and have posed serious threat to man. The aim of the study is to determine the antimicrobial activity of Chromolaenaodorata leaf on common pathogenic bacteria that exist in nature.

The study revealed anti-microbial activities of Chromolaenaodorata. The inhibitory effect of the ethanol stock (80g/250ml) grounded extract of the leaf on the test organisms showed Staphylococcus aureus 15mm, Escherichia coli 10mm, Psendomonaaeruginosa 15mm and Proteus sp. 15mm. The aqueous stock of leaf showed to inhibitory effect against all the organisms. Ethanol alone showed minimal (insignificant) inhibitory effect of 0.4 – 0.8mm as shown in table 1.

Table 1: Comparative antimicrobial sensitivity of extracts of leaf of Chromolaena odorata .

Diluted Ethanol extract showed Zones of Inhibition at 1:10 with Staphylococcus aureus showing 12mm, Escherichia coli 11mm, Pseudomonas aeruginosa 12mm and Proteus Species 8mm. At 1:100 dilution only Proteus Species showed inhibition of 0.5mm while others showed no zone of inhibition as showed in table 2 and figure 1.

Table 2: Zone of Inh ibition in relation to dilution

Figure 1: Zone of Inhibition in relation to dilution