Structure elucidation and biological activity of antibacterial compound from Micromonospora auratinigra, a soil Actinomycetes.

AIMS: The aim of this study was to isolate and characterize the bioactive compound of Micromonospora auratinigra, HK-10 and its antibacterial inhibitory mechanism. METHODS AND RESULTS: An oily bioactive compound was extracted from HK-10 (GenBank accession no. JN381554) and found to have promising antibacterial activity. The compound was characterized as 2-methylheptylisonicotinate (1) by (1) H, (13) C NMR and mass spectroscopy. Minimum inhibitory concentration (MIC) of this molecule was tested by micro broth dilution method and was found to be 70, 40, 80, 60, 60 and 50 µg for Staphylococcus aureus, Bacillus subtilis, Proteus vulgaris, Echerichia coli, Pseudomonas aeruginosa and Mycobacterium abscessus respectively. The effects of compound 1 were studied on bacterial membrane structure using scanning electron microscopy. The results indicated a membrane-disrupting mechanism, resulting in the dysfunction of the cytoplasmic membrane structure and cell death of the pathogenic bacterial strains. Kinetics of growth of the test organisms was also analysed and indicated 2-methylheptylisonicotinate 1 as a bactericidal agent. Furthermore, we have studied the binding affinity of 1 towards different membrane proteins of pathogenic bacteria by in silico analysis. CONCLUSIONS: 2-methylheptylisonicotinate was isolated from M. auratinigra, a rare actinobacterial strain possessing antibacterial activity through a membrane-disrupting mechanism, and has MICs similar to standard antibiotic neomycin sulphate. It is the first report about a strain of M. auratinigra, isolated from Indo-Burma biodiversity hotspot of North-east India with new antimicrobial activities. In silico studies have also supported these results performed on various membrane targets of pathogenic bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: The antibacterial potential of M. auratinigra is reported for the first time. The results indicate the possible use of 2-methylheptylisonicotinate as a source of antibacterial agent against dreaded human pathogens.

Brevibacillus laterosporus strain BPM3, a potential biocontrol agent isolated from a natural hot water spring of Assam, India.

A bacterial strain designated as BPM3 isolated from mud of a natural hot water spring of Nambar Wild Life Sanctuary, Assam, India, strongly inhibited growth of phytopathogenic fungi (Fusarium oxysporum f. sp. ciceri, F. semitectum, Magnaporthe grisea and Rhizoctonia oryzae) and gram-positive bacterium (Staphylococcus aureus). The maximum growth and antagonistic activity was recorded at 30°C, pH 8.5 when starch and peptone were amended as carbon and nitrogen sources, respectively. In greenhouse experiment, this bacterium (BPM3) suppressed blast disease of rice by 30-67% and protected the weight loss by 35-56.5%. The maximum disease protection (67%) and weight loss protection (56.5%) were recorded when the bacterium was applied before 2 days of the pathogen inoculation. Antifungal and antibacterial compounds were isolated from the bacterium which also inhibited the growth of these targeted pathogens. The compounds were purified and on spectroscopic analysis of a purified fraction having R(f) 0.22 which showed strong antifungal and antibacterial activity indicated the presence of C-H, carbonyl group, dimethyl group, -CH(2) and methyl group. The bacterium was characterized by morphological, biochemical and molecular approaches and confirmed that the strain BPM3 is Brevibacillus laterosporus.

MRI findings of cerebral malaria. A report of two cases.

Cerebral malaria is a protozoal disease affecting the brain caused by Plasmodium falciparum. The hallmark of cerebral malaria is progressive decline in the sensorium leading to coma and in some cases death. MR findings reported in cerebral malaria are diffuse cerebral swelling / edema, bilateral nearly symmetrical T2 hyperintense lesions in basal ganglia and similar lesions in thalamus, pons and cerebellum. The imaging findings of cerebral malaria depend on the duration of the illness and time of MR examination. We describe two patients of cerebral malaria having mixed Plasmodium falciparum and Plasmodium vivex infestation showing bilateral basal ganglia infarcts with cerebral swelling in one patient and bilateral basal ganglia and cerebellar lesions in the other.

Klebsiella meningitis. A case report.

Acute bacterial meningitis is a severe CNS infection occurring mostly in infants and older children. Bacterial meningitis caused by gram-negative bacteria is usually fatal. Klebsiella pneumoniae is an uncommon gram-negative bacteria causing meningitis with a poor outcome. Though the commonest presentation of bacterial meningitis is fever, patients usually seek medical attention for uncontrolled seizure and features of raised ICP. The commonest complications of gram-negative bacterial meningitis including Klebsiella meningitis are subdural hygroma / empyema, hydrocephalus, infarcts (both arterial and venous) and cortical blindness due to hypoxic ischaemic insult. MRI is the best modality for evaluating these patients for early diagnosis. Early institution of treatment significantly reduces the mortality and morbidity. We describe a case of acute bacterial meningitis caused by Klebsiella pneumoniae with MR evidence of sinus thrombosis, venous infarcts and subdural hygroma.

Pseudomonas aeruginosa inducing rice resistance against Rhizoctonia solani: production of salicylic acid and peroxidases.

Three isolates of Pseudomonas aeruginosa were used for seed treatment of rice; all showed plant growth promoting activity and induced systemic resistance in rice against Rhizoctonia solani G5 and increased seed yield. Production of salicylic acid (Sal) by P. aeruginosa both in vitro and in vivo was quantified with high performance liquid chromatography. All three isolates produced more Sal in King's B broth than in induced roots. Using a split root system, more Sal accumulated in root tissues of bacterized site than in distant roots on the opposite site of the root system after 1 d, but this difference decreased after 3 d. Sal concentration 0-200 g/L showed no inhibition of mycelial growth of R. solani in vitro, while at > or =300 g/L it inhibited it. P. aeruginosa-pretreated rice plants challenged inoculation with R. solani (as pathogen), an additional increase in the accumulation of peroxidase was observed. Three pathogenesis-related peroxidases in induced rice plants were detected; molar mass of these purified peroxidases was 28, 36 and 47 kDa. Purified peroxidase showed antifungal activity against phytopathogenic fungi R. solani, Pyricularia oryzae and Helminthosporium oryzae.