Latin name: Cynodon dactylon
Source material: Pollen
Sub family: Chloridoideae
Common names: Bermuda grass, Bermuda-grass, Bermudagrass, Scutch grass, Wire grass, Star grass, Bahama grass, Devil grass.
Synonyms: Panicum dactylon.
Bermuda grass is found in much of Europe though not Scandinavia, in the USA, South Africa, Australia, India, and Japan. It probably originated in India. It is the dominant forage grass of Brazil. It is the most common tropical lawn grass, especially in dry areas, and an important pasture grass in the southern US. It is considered to be one of the most allergenic grasses.
Bermuda grass is a creeping, low-growing, evergreen perennial usually growing to 0.3 m by 0.5 m at a medium rate. It is one of about 9 species of the genus Cynodon. Reproduction is mostly by means of long runners on top of the ground, but also through seeds and a vast system of hard, sharp-pointed rhizomes beneath the ground. The grayish leaves on the erect stems are 1.5 to 10 cm long, while those on the runners and rhizomes are very short, scaly, and not leaf-like. Roots are formed at the joints, and frequent erect stalks are produced, about 10 to 45 cm high. There are 3 to 5 very narrow 2 to 6 cm finger-like flowering spikes at the tip.
The grass flowers in North America from April/May to September/October. Around the Mediterranean, blooming occurs from May to August, and in other regions of the world from February to December. The flowers are hermaphrodite (have both male and female organs) and are pollinated by wind. The seeds, like the flowers, are tiny, with as many as 4.4 million seeds in one kilogram. In drought, the plant dies above ground but will re-grow from rhizomes.
Bermuda grasses vary greatly in size, shape and colour, but the distinguishing characteristics of Cynodon dactylon are the conspicuous ring of white hairs of the ligule, the fringe of hairs on the keel of the lemma, and the gray-green appearance of the foliage.
Bermuda grass occurs on waste places, roadsides, pastures and agricultural fields, in riparian areas adjacent to streams and marshes, and in the understory of open forests, orchards, and Pine (Pinus spp.) plantations. Unwanted spreading of the species is exacerbated by continued planting, as a turf and forage crop and especially for soil reclamation purposes. Bermuda grass is difficult to control once it has been nurtured and has become established.
Bermuda grass has no reported uses as a food, but is a folk remedy for a large number of ailments.
Bermuda grass pollen contains at least 12 IgE-binding proteins (1, 2) 2 of these allergens have been described as major allergenssince they reacted with IgE antibodies in more than 50% of sera in a study on 21 Bermuda grass-allergic individuals (3).
- Cyn d 1, a major allergen, has been characterised and consists of 11 isoforms(4, 5, 6, 7, 8). This allergen may occur as a single 34 kDa protein or as a mixture of 34 and 29 kDa proteins (isoforms) (9).
- Cyn d 7, a 12 kDa calcium binding protein (10-11)
- Cyn d 12, a profilin (12)
- Cyn d 1 only weakly precipitates allergens from other grass species in immunochemical studies, indicating that Cyn d 1 possesses some unique immunochemical properties. Four monoclonal antibodies of Bermuda grass have been shown to cross-react with pollen components from other grass species, especially Poa pratensis (Meadow grass) and Dactylis glomerata (Cocksfoot) (13).
Two isoallergens of Cyn d 1 isolated were designated Cyn d 1a and b. Cyn d 1a is a 32 kDa protein, and Cyn d 1b is a 31 kDa protein (14).
Approximately 10% of sera of Bermuda-allergic individuals showed IgE reactivity to Cyn d 7 (10).
A 46 kDa antigen of Bermuda grass pollen has been identified. The amino acid sequences of 4 internal peptide fragments were found to be 25-71% identical with those of cytochrome c oxidase III from Corn grass pollen (15). The clinical relevance has not yet been demonstrated.
Bermuda also contains species-specific allergen (16).
A cDNA clone coding for Birch pollen allergen, Bet v 4, a calcium-binding allergen, has significant sequence similarities extending outside the Ca2+-binding sites with pollen-specific allergens of Brassica and Bermuda grass (17). The clinical relevance has not yet been demonstrated.
The genus Cynodon comprises 9 species, which are geographically widely distributed and genetically diverse. Genetic relatedness among the species demonstrated that the strongest species similarities were between C. aethiopicus and C. arcuatus, C. transvaalensis and C. plectostachyus, and C. incompletus and C. nlemfuensis (18). Other studies have demonstrated complete cross-reactivity between Giant Bermuda grass extract and Bermuda grass (19).
There is not much cross-reactivity between Bermuda grass and temperate pasture grasses, due in part to the absence of Group 2, 3 and 5 antigens in the former. Cross-reactivity among the different individual species of the subfamily Chloridoideae could be expected (Bermuda, Buffalo, Windmill, and Grama grasses). (20-23). Extracts of Buffalo grass pollen were shown to significantly inhibit IgE binding to the Buffalo grass, Kikuyu, Eragrostis and Bermuda, but 100% inhibition was never achieved, indicating that cross-reactivity existed but also that unique epitopes are present in Buffalo grass (24). A study reported a close allergenic relationship between Salt, Grama and Bermuda grasses. Johnson grass appeared to also share some allergenicity with Bermuda grass (25).
This grass contains Group 1 allergens, to which more than 95% of patients allergic to grass pollen possess IgE antibodies. These are highly cross-reactive glycoproteins exclusively expressed in the pollen of many grasses (26-28).
Group 1 allergens are highly homologous, but not all of the antigenic epitopes are crossreactive (29). For example, Group 1 allergens from eight different clinically important grass pollens of the Pooideae (Rye grass, Canary grass, Meadow grass, Cocksfoot and Timothy), Chloridoideae (Bermuda grass) and Panicoideae (Johnson grass, Maize) were isolated, and IgE binding to an allergic human serum pool was conducted to determine the degree of antigenic and IgE-binding similarities. The highest IgE-binding similarity was observed between Cocksfoot and Rye grass (53%) and between Rye grass and Canary grass (43%). No IgE-binding similarity was observed between Maize and other grasses. The highest antigenic similarity was also observed between Rye grass and Cocksfoot grass (76%), and the lowest similarity between Maize (23%) and Bermuda (10%) (30). Monoclonal antibodies of Cyn d 1 (Bermuda grass) recognised cross-reactive epitopes on proteins from eight other grasses including Rye grass, Timothy grass, Meadow grass and Johnson grass(14).
Bermuda grass contains a profilin, which may contribute to cross-reactivity in pollen- and food-allergic patients. Pollen that contains profilin has been demonstrated in Phleum pratense (Timothy), Olea europaea (Olive), Cynodon dactylon (Bermuda grass), Parietaria judaica (Wall Pellitory), Sorghum halepense (Johnson grass), Poa pratensis (Meadow grass), Ambrosia elatior (a Ragweed), and Helianthus annuus (Sunflower) pollen (12, 31, 35).
A low degree of cross-reactivity was shown between Kikuyu grass and Bermuda grass (33).
IgG immunoblot analyses of Date Palm pollen (Phoenix dactylifera L.) showed varying degrees of cross-reactivity with Bermuda grass, but this cross-reactivity is generally of low intensity (34).
IgE mediated reactions
Bermuda grass pollen is a very common source of pollinosis throughout the world and is a potent inducer of asthma, allergic rhinitis and allergic conjunctivitis (35-37).
In northern New South Wales, Australia, an association between Bahia grass and asthma in children was reported, and between Bermuda grass and allergic rhinitis in adults (38).
Sandstorm dust has been shown to contain Bermuda grass pollen, and appears to be a prolific source of potential triggers of allergic and nonallergic respiratory ailments (39).
In Comarca Lagunera, Spain, of 101 patients with asthma, 70% were found to be highly sensitive to Cynodon dactylon on specific IgE determination (40).
Bermuda grass was shown to make a high contribution to overall pollen rain in the semiarid environment of Arizona (41). In children, the prevalence of physician-diagnosed asthma was 9.8% at age 6 (n = 948) and 15.5% at age 11 (n = 895).
Specific IgE tests for Bermuda grass demonstrated that it was the most prevalent allergen among children with allergic rhinitis (42). A further study confirmed the high prevalence of Bermuda grass sensitisation and found that Bermuda grass pollen was also significantly associated with sinusitis (43). In Orange County, California, in 271 patients identified by a group of local allergy specialists, tree pollen allergens were the most prevalent sensitising agents, followed in declining order by weed pollens, molds, environmentals, and grass pollen extracts. However, Bermuda grass pollen elicited the highest positive rate, with 85% of the group positive to this allergen (44).
In Mexico, Bermuda grass is a prominent aeroallergen (45). In Monclova, Coahuila, 4.9% of 247 patients were shown to be sensitised to Bermuda grass pollen(46). In Oaxaca, specific IgE determination in 138 patients with asthma, rhinitis and sinusitis showed that Bermuda and Rye grass were the most prevalent sensitising allergens after House Dust Mite (47).
Bermuda grass was shown by serumspecific IgE determination to be the most prevalent sensitising pollen in asthmatic children in Taiwan, with 8% of the children positive to this allergen (48).
In 100 Thai patients with allergic rhinitis, specific IgE tests were positive in 17% (49). In Kuala Lumpur, Malaysia, Bermuda grass pollen was recorded in aerobiological and clinical studies, and reported to be the most allergenic of the grass pollens (50).
Kuwait is a desert country where the prevailing high temperatures, low humidity, and scant vegetation suggest a low prevalence of allergy. In a study of allergen-specific IgE among 505 young adult blood donors with a mean age of 28.4 years, the Pharmacia CAP-RAST test showed that Bermuda grass, House Dust Mite, and Goosefoot were the most prevalent sensitising allergens, with frequencies of 53.6%, 52.7%, and 50.9%, respectively, among the sensitised subjects (51).
Furthermore, in 810 patients with extrinsic asthma or allergic rhinitis from Kuwait, specific IgE to Bermuda grass was detected in 54.6% of sera (52). Further studies confirmed the high prevalence of sensitisation. In 706 patients aged 6 to 64 years with allergic rhinitis, specific IgE to Bermuda grass was detected in 55.0% (53). In 553 asthmatics, serum-specific IgE to Bermuda grass was found in 62.9%.
Bermuda grass was imported for the purpose of "greening" the desert (54).
Similarly, in 263 United Arab Emirate nationals with a respiratory disease suspected of being of allergic origin, 33% were sensitised to Bermuda grass (55).
In Saudi Arabia, in both adults and children with asthma and/or allergic rhinitis, specific IgE determination found Bermuda grass to be one of the most common allergens (56-57). In the Eastern Province of Saudi Arabia, 29% of 1,159 patients were shown, through specific IgE tests, to be sensitised to Bermuda grass (58).
Bermuda grass has also been shown to be a prominent allergen in Africa. In Johannesburg and Cape Town, South Africa, Bermuda was shown by specific IgE tests to be one of the most prevalent sensitising allergens in children with asthma and allergic rhinitis (59-60).
In a general paediatric clinic in Zimbabwe, in 84 children aged below 12 years with atopic conditions, the commonest allergens identified were Dust Mite and Bermuda grass, as determined by specific IgE determination (61). In Nigeria, specific IgE tests confirmed that Bermuda grass was a major aeroallergen in both rural and urban asthmatics (62).
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