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Brazilian Archives of Biology and Technology

Print version ISSN 1516-8913

Braz. arch. biol. technol. vol.57 no.2 Curitiba Mar./Apr. 2014

http://dx.doi.org/10.1590/S1516-89132014000200011 

BIOLOGICAL AND APPLIED SCIENCES

 

Antagonistic activity of antibiotic producing Streptomyces sp. against fish and human pathogenic bacteria

 

 

Md. Nazmul HossainI; Md. Mahbubur RahmanII, *

IDepartment of Genetic Engineering and Biotechnology; Shahjalal University of Science and Technology; Sylhet -Bangladesh
IIDepartment of Biotechnology; Bangabandhu Sheikh Mujibur Rahman Agricultural University; Gazipur - Bangladesh

 

 


ABSTRACT

In this study, attempts were made to isolate Streptomyces sp. from soil samples of two different regions of Bangladesh and evaluate their antagonistic activity against fish and human pathogenic bacteria. A total of 10 isolates were identified as Streptomyces sp. based on several morphological, physiological and biochemical tests. Cross streak method was used to observe the antagonistic activity of the Streptomyces sp. isolates against different fish pathogens belonging to the genus Aeromonas, Pseudomonas and Edwardsiella and human clinical isolates belonging to the genus Klebsiella, Salmonella and Streptococcus. Seven Streptomyces sp. isolates showed antagonism against both fish and human pathogenic bacteria. Four isolates viz., N24, N26, N28 and N47 showed broad spectrum of antagonistic activity (80-100%) against all genera of fish and human pathogenic bacteria. The isolate N49 exhibited highest spectrum of antagonism against all fish pathogens (90-100%) but comparatively lower degree of antagonism against human pathogens (50-60%). Rest of the two isolates (N21 and N23) showed variability in their antagonism. Results showed that broad spectrum antibiotic(s) could be developed from the isolates N24, N26, N28 and N47against several human and fish pathogens. The isolate N49 could be a potential source of antibiotic, especially for fish pathogenic bacteria.

Keywords: Streptomyces sp., antagonistic activity, cross streak method, antibiotic.


 

 

INTRODUCTION

Streptomyces are Gram-positive soil microbes represented as the largest number of species and varieties among the family Actinomycetaceae. Streptomyces species are the source of thousands of bioactive compounds and screening programs have shown that secondary metabolites can be isolated (Wendisch and Kutzner 1992; Santos 2012), which bind to active sites of enzyme organelles and receptors (William et al. 1983). Streptomyces sp. is responsible for the production 50% of clinically useful antibiotics (Miyadoh 1993).

Soil is a natural reservoir for the microorganisms with their antimicrobial products and provides an excellent resource for the isolation and identification of therapeutically important products (Dancer 2004). Among the soil microbes, Streptomyces sp. are the important group producing antibiotics of agricultural and medicinal importance and over 6,000 compounds have been reported to be produced by Streptomyces (Takahashi and Omura 2003; Kavitha et al. 2010). However, with the alarming increasing rate of drug resistance in pathogenic microorganisms throughout the world, the demand to discover newer and safer antibiotics with lesser side effects are increasing day-by-day (Gupte et al. 2002). But, the search for a new, safer, broad-spectrum antibiotic with greater potency has been progressing slowly. The present work was undertaken with an effort to isolate antibiotic producing Streptomyces from two different soil samples of Bangladesh and evaluate their antagonistic potentials against some fish and human pathogenic bacteria.

 

MATERIALS AND METHODS

Collection of soil samples

Soil samples were collected from two different regions of Bangladesh during June to August 2011. Samples were taken up from a depth of 10 cm form each area, placed in sterile plastic bags, transported to the laboratory under ambient condition and air-dried at room temperature. The samples were pretreated by drying at 70oC for 1h in a hot air dryer.

Isolation of and enumeration of microbes from soil

For isolation of Streptomyces sp., serial dilution technique was followed using different aqueous dilutions (10-1 to 10-4). Each diluted sample was inoculated by standard spread plate method on Starch-Casein Agar (SCA) medium containing (g/l) Glycerol 10, Casein 0.3, KNO3 2.0, K2HPO4 2.0, MgSO4 0.05, CaCO3 0.02, FeSO4 0.01, Agar 18 and distilled water 1L (pH 7.0± 0.1) (Kuster and Williams 1964). After incubation of the plates at 30o C for seven days, typical Streptomyces sp. colonies were selected (Shirling and Gottlieb 1966) and total number of bacteria as well as total number Streptomyces colonies (presumptive colonies) were counted and expressed as colony forming unit per gram of soil sample (CFU/g). The selected colonies were re-streaked on Streptomyces Agar Medium (SAM) containing (g/l) Glucose 10, Beef extract 4.0, Peptone 4.0, NaCl 2.5, Yeast extract 1.0 and Agar 20 (Atlas 1997) and incubated at 30o C to obtain the pure culture.

Identification of Streptomyces sp. isolates

Ten presumptive Streptomyces sp. isolates were characterized by morphological and physiological tests, which included colony characteristics (size, shape and color), Gram staining, presence of aerial mycelium, motility and spore formation, and biochemical tests, which included oxidase and catalase activity, H2S production, Methyl Red test (MR), Voges-Proskauer Test (VP), acid production from carbohydrates (glucose, lactose and sucrose), Indole test, hydrolysis of casein and starch, utilization of different carbon and nitrogen sources. The bacterial isolates were identified following the Bergey's Manual of Determinative Bacteriology (Bergey and John 1994).

Test microorganisms

Both fish pathogenic bacteria (viz., Aeromonas sp., Pseudomonas sp. and Edwardsiella sp.) and human clinical isolates (viz., Klebsiella sp., Salmonella sp. and Streptococcus sp.) were used as test organism to determine the antagonistic activity of the Streptomyces sp. isolates. Ten isolates from each bacterial genus were used to evaluate the antagonistic activity of the Streptomyces sp. isolates. All of the test isolates were obtained from the USDA project laboratory of the Department of Genetic Engineering and Biotechnology, Shahjalal University of Science and Technology, Sylhet, Bangladesh. The test organisms were cultured in Nutrient Broth (NB) at 27 and 37°C for 24h for fish and human pathogens, respectively.

Evaluation of antagonistic activity of Streptomyces sp. Isolates

The antagonistic activity of soil isolates was evaluated by Cross Streak method (Rahman et al. 2011). Each of the isolate was streaked on Streptomyces Agar Medium (SAM) as straight line and incubated at 30°C for six days. Then the plates were seeded with test organisms by a single streak at a 90° angle to the Streptomyces isolates and incubated at 37 and 27°C for 24 h for human and fish pathogenic bacteria, respectively. The antagonistic effect of Streptomyces sp. isolates on test organism was analyzed by the determination of size of inhibition zone. The percentage of antagonism of Streptomyces isolates to each genus of test organisms was estimated.

 

RESULTS AND DISCUSSION

Isolation and enumeration of microbes from soil

The colony forming unit (CFU) per gram of soil was estimated to know total bacterial load and load of presumptive Streptomyces sp. in different soil sample. The highest microbial count and Streptomyces count was 3.1×106 CFU/g of soil and 2.8×104 CFU/g of soil, respectively in the pond sediment sample of Sylhet region. The lowest bacterial count was 0.8×106 CFU/g of soil in the soil sample collected from the hill of Sylhet (Table 1).

In the present study, the highest load of Streptomyces sp. was obtained in the pond sediment sample of Sylhet region of Bangladesh. This pond was used for fish farming and was rich in organic compounds that might be the reason for highest count of Streptomyces sp.

Identification of Streptomyces sp. isolates

Baesd on the morphological, physiological and biochemical characteristics, all the isolates were identified as Streptomyces sp. All the isolates were Gram positive with aerial mycelium and most of them were filamentous with long chain of spores (Fig. 1A). The isolates were non-motile, catalase positive, oxidase positive, ureaese positive and positive for H2S production, but negative for nitrate reduction, MR test and VP test. Detailed results of morphological, physiological and biochemical tests of the isolates are shown in Tables 2 and 3. Similar methods were followed by Shirling and Gottlieb (1966); Berd (1973) and Rahman et al. (2011) for the identification of Streptomyces sp. from soil.

 

 

Antagonistic activity of Streptomyces sp. isolates

Among the ten Streptomyces sp. isolates, seven showed antagonistic activity against different fish pathogenic and human clinical isolates in cross streak method used in this study (Fig. 1B). Cross streak method is relatively easy and reliable method, especially for the screening program to test the antagonistic activity of antibiotic producing microbes, which is commonly used (Lemos et al. 1985; Ceylan et al. 2008; Arifuzzaman et al. 2010; Rahman et al. 2011; Valli et al. 2012). Determination of antagonism against different microorganisms is very important to determine the spectrum of antibiotic produced by an isolate. Here, the percentage of antagonism against different fish and human pathogenic bacteria were evaluated to measure the spectrum of antibiotic produced by the soil isolates. Similar type of study was also conducted by others (George et al. 2010). In this study, four of the seven antagonistic isolates viz., N24, N26, N28 and N47 showed broad spectrum of antagonistic activity (80-100%) against the test isolates belonging to all bacterial genera. The isolate N49 exhibited highest spectrum of antagonism against all fish pathogens (90-100%) but comparatively lower degree of antagonism against human pathogens (50-60%). Hence, the isolate N49 could be considered as a valuable source for the development of antibiotic against fish disease caused by Aeromonas sp., Pseudomonas sp. and Edwardsiella sp. The other two isolates N21 and N23 showed variability in their antagonism but maximum to fish pathogenic Pseudomonas sp. (80%) and Edwardsiella sp. (70%), respectively. The antagonistic activity of Streptomyces sp. isolates to different fish and human pathogenic bacteria has given in Table 4.

Various microorganisms have survived for thousands of years by their ability to adapt against antimicrobial drugs and this process enables some bacteria to develop resistance to certain antibiotics, rendering the antibiotics ineffective. As a result, most of the bacteria resistant to multiple antibiotics, causing a crucial threat for the treatment of diseases of human and animals (Bennett 2008). The increasing frequency of multi-drug resistant pathogenic bacteria in recent years has created an urgent demand in the pharmaceutical industry for screening of new antibiotics (George 2010; Foysal et al. 2011; Sharmeen et al. 2012; Fuad et al. 2012). The results of present study showed that broad spectrum antibiotic could be developed from the isolates N24, N26, N28 and N47, which could be effective against several human and fish diseases. The isolate N49 could be used as a better source to reduce the prevalence of fish disease.

 

CONCLUSION

Soil samples from two different parts of Bangladesh were evaluated for isolating potent Streptomyces sp strains. Results showed that these soils could be good source for isolating antibiotic producing Streptomyces but more studies should be carried out to find out valuable antibiotic producing bacteria. Further investigation is also necessary to purify the active novel metabolites from these isolates.

 

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Received: January 01, 2013
Accepted: November 23, 2013

 

 

* Author for correspondence: mahbub_biotech@yahoo.com

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