In vitro antimicrobial activity of natural toxins and animal venoms tested against Burkholderia pseudomallei

BACKGROUND: Burkholderia pseudomallei are the causative agent of melioidosis. Increasing resistance of the disease to antibiotics is a severe problem in treatment regime and has led to intensification of the search for new drugs. Antimicrobial peptides are the most ubiquitous in nature as part of the innate immune system and host defense mechanism. METHODS: Here, we investigated a group of venoms (snakes, scorpions and honey bee venoms) for antimicrobial properties against two strains of Gram-negative bacteria Burkholderia pseudomallei by using disc-diffusion assay for in vitro susceptibility testing. The antibacterial activities of the venoms were compared with that of the isolated L-amino acid oxidase (LAAO) and phospholipase A(2 )(PLA(2)s) enzymes. MICs were determined using broth dilution method. Bacterial growth was assessed by measurement of optical density at the lowest dilutions (MIC 0.25 mg/ml). The cell viability was measured using tetrazolium salts (XTT) based cytotoxic assay. RESULTS: The studied venoms showed high antimicrobial activity. The venoms of C. adamanteus, Daboia russelli russelli, A. halys, P. australis, B. candidus and P. guttata were equally as effective as Chloramphenicol and Ceftazidime (30 μg/disc). Among those tested, phospholipase A(2 )enzymes (crotoxin B and daboiatoxin) showed the most potent antibacterial activity against Gram-negative (TES) bacteria. Naturally occurring venom peptides and phospholipase A(2 )proved to possess highly potent antimicrobial activity against Burkholderia pseudomallei. The XTT-assay results showed that the cell survival decreased with increasing concentrations (0.05–10 mg/mL) of Crotalus adamanteus venom, with no effect on the cell viability evident at 0.5 mg/mL. CONCLUSION: This antibacterial profile of snake venoms reported herein will be useful in the search for potential antibacterial agents against drug resistant microorganisms like B. pseudomallei

Fatal necrotizing pneumonia caused by group A streptococcus

Group A streptococcus (GAS) causes invasive, non-invasive and non-suppurative diseases. Pneumonia is one of the invasive infections caused by GAS. Although GAS is a significant and serious cause of childhood pneumonia, it is often overlooked clinically. Similarly, the recent literature is surprisingly scant on reports of GAS pneumonia and concentrates mainly on varicella-associated invasive GAS diseases. In this case report, we present a previously healthy 7-year-old child with community-acquired pneumonia that progressed rapidly and resulted in sepsis, respiratory failure and death. In both blood and pleural fluid cultures, Streptococcus pyogenes were isolated. On autopsy, macroscopic examination revealed that the lung tissue appeared to have lost its normal architecture. Necrosis was present and the lung had a spongy appearance with some solid areas. The light microscopy revealed massive oedema, haemorrhages, intense inflammatory cell infiltration and necrosis. This case report highlights the need for consideration of invasive GAS infection in the event of severe, rapidly progressing pneumonia in children