Evaluating and comparing the efficacy of two methods in isolation of Nocardia species from soil samples

Nocardia spp. are gram-positive, aerobic and weakly acid-fast bacteria, which can cause a wide range of acute and chronic infections in animals and humans. Soil and other environmental resources are natural habitat of this group of bacteria. Nocardia species can survive in the hospital's environmental resources and cause fatal infections in host immune-compromised patients. The purpose of this study was to evaluate and compare two methods of isolation of Nocardia species from the soil.
30 soil samples were collected from agricultural areas, parks, gardens and hospitals in Isfahan. Then, for isolation of Nocardia species, soil samples were studied using Serial dilution and Slip-buried methods. In both methods, samples were incubated at 30 ° C for 2-3 weeks. Then, resistance to lysozyme test was also used to confirm the genus Nocardia.
Of 30 samples, 7 (23.3%) strains were isolated using serial dilution method and 3 (10%) strains were isolated by the Slip-buried method.
The results of this study showed that serial dilution method was a suitable method. In the Slip-buried method, streptomycin and chloramphenicol antibiotics are used and due to the susceptibility of some Nocardia species to these antibiotics, this method is not appropriate; In addition, the Serial dilution method is more rapid and cheaper than the Slip-buried method.