Shunmugiah Karutha Pandian

Antibiofilm activity of coral-associated bacteria against different clinical M serotypes of Streptococcus pyogenes

Streptococcus pyogenes is the frequent cause of purulent infections in humans. Formation of a biofilm is one of the important aspects of its pathogenicity. Streptococcus pyogenes biofilm communities tend to exhibit significant tolerance to antimicrobial challenge during infections. Exploring novel targets against biofilm-forming pathogens is therefore an important alternative treatment measure. We attempted to screen marine bacteria, especially coral-associated bacteria (CAB), for antibiofilm activity against streptococcal biofilm formation. The bacterial biofilms were quantified by crystal violet staining. Of 43 CAB isolates, nine clearly demonstrated antibiofilm activity. At biofilm inhibitory concentrations (BIC), biofilm formation was reduced up to 80%, and sub-BIC (0.5 and 0.25 BIC) significantly reduced biofilm formation by up to 60% and 40-60%, respectively. Extracts of Bacillus horikoshii (E6) displayed efficient antibiofilm activity. As quorum sensing (QS) and cell surface hydrophobicity (CSH) are crucial factors for biofilm formation in S. pyogenes, the CAB were further screened for QS inhibition properties and CSH reduction properties. This study reveals the antibiofilm and QS inhibition property of CAB.

Inhibition of biofilm development of uropathogens by curcumin - an anti-quorum sensing agent from Curcuma longa.

Urinary tract infection is caused primarily by the quorum sensing (QS)-dependent biofilm forming ability of uropathogens. In the present investigation, an anti-quorum sensing (anti-QS) agent curcumin from Curcuma longa (turmeric) was shown to inhibit the biofilm formation of uropathogens, such as Escherichia coli, Pseudomonas aeruginosa PAO1, Proteus mirabilis and Serratia marcescens, possibly by interfering with their QS systems. The antibiofilm potential of curcumin on uropathogens as well as its efficacy in disturbing the mature biofilms was examined under light microscope and confocal laser scanning microscope. The treatment with curcumin was also found to attenuate the QS-dependent factors, such as exopolysaccharide production, alginate production, swimming and swarming motility of uropathogens. Furthermore, it was documented that curcumin enhanced the susceptibility of a marker strain and uropathogens to conventional antibiotics.

Screening and evaluation of probiotics as a biocontrol agent against pathogenic Vibrios in marine aquaculture.

Aims:  The present work aims at finding potential probionts from marine sources as a biocontrol agent against pathogenic Vibrio species in shrimp larval culture.

Evaluation of anti-quorum-sensing activity of edible plants and fruits through inhibition of the N-acyl-homoserine lactone system in Chromobacterium violaceum and Pseudomonas aeruginosa.

Background: To find out an alternative strategy to antibiotic usage against bacterial infection. Materials and Methods: The purpose of this study is to describe the quorum-sensing (QS) inhibitory activity of edible plants and fruits against N-acyl-homoserine lactone (AHL)-mediated violacein production in Chromobacterium violaceum and virulence factor expression in Pseudomonas aeruginosa PAO1. Results: Aqueous extracts of Ananas comosus (Bromeliaceae), Musa paradiciaca (Musaceae), Manilkara zapota (Sapotaceae) and Ocimum sanctum (Lamiaceae) were prepared and anti-QS activity of each extract was tested against AHL-mediated phenotypic expressions of C. violaceum and PAO1. Most of these extracts showed significant reduction in AHL-mediated violacein production in C. violaceum as well as pyocyanin pigment, staphylolytic protease, elastase production and biofilm formation in PAO1. However, these extracts were not inhibitory to bacterial growth, revealing that the QS inhibition by the extracts is not related to static or killing effects on the bacteria. Conclusions: The present study identified the anti-QS activity of A. comosus, M. paradiciaca, M. zapota and O. sanctum. An AHL-inactivating compound from these plant sources can be used as an alternative to antibiotic compounds to prevent AHL-mediated bacterial infection in higher organisms.

In vitro and in vivo antibiofilm activity of a coral associated actinomycete against drug resistant Staphylococcus aureus biofilms

Staphylococcus aureus is now amongst the most important pathogenic bacteria responsible for bloodstream nosocomial infections and for biofilm formation on indwelling medical devices. Its increasing resistance to common antibiotics, partly attributed to its ability to form biofilms, is a challenge for the development of new antimicrobial agents. Accordingly, the goal of this study was to evaluate the effect of a coral associated actinomycete (CAA) - 3 on S. aureus biofilms both in vitro and in vivo. Methanolic extracts of CAA-3 showed a reduction in in vitro biofilm formation by S. aureus ATCC 11632, methicillin resistant S. aureus ATCC 33591 and clinical isolates of S. aureus at the biofilm inhibitory concentration (BIC) of 0.1 mg ml−1. Furthermore, confocal laser scanning microscope (CLSM) studies provide evidence of CAA-3 inhibiting intestinal colonisation of S. aureus in the nematode Caenorhabditis elegans. To conclude, this study for the first time, reports CAA as a promising source of anti-biofilm compounds, for developing novel drugs against highly resistant staphylococcal biofilms.

Bacillus pumilus of Palk Bay origin inhibits quorum-sensing-mediated virulence factors in Gram-negative bacteria.

The aim of the current study was to inhibit quoring-sensing(QS)-mediated virulence factors of representative Gram-negative bacteria by marine bacterial isolates. Bacteria isolated from Palk Bay sediments were screened for anti-QS activity. Eleven strains inhibited QS signals in Chromobacterium violaceum (ATCC 12472) and C. violaceum CV026. The marine bacterial strain S8-07 reduced the accumulation of N-acyl homoserine lactone (AHLs) and showed significant inhibition of LasA protease(76%), LasB elastase(84%), caseinase(70%), pyocyanin (84%), pyoverdin and biofilm formation(87%) in Pseudomonas aeruginosa PAO1. Strain S8-07 also showed highly significant reduction (90%) in prodigiosin, secreted casienase (92%), hemolytic activity (73%) and biofilm formation (61%) in Serratia marcescens. Strain S8-07, identified as Bacillus pumilus (accession number FJ584416), showed distinct profiles of inhibition against the virulence factors of both P. aeruginosa PAO1 (las, rhl) and S. marcescens (shl). Polar extraction and proteinase K treatment of the culture supernatant confirmed that the anti-QS activity of S8-07 was indeed due to a protein molecule. Acidification assay and HPLC analysis revealed that the degradation of AHL was not due to lactonase activity, but rather, was due to acylase activity of S8-07. Thus, novel anti-QS acylase activity is reported for the first time from a B. pumilus strain of marine origin.

Phylogenetic characterization of culturable bacterial diversity associated with the mucus and tissue of the coral Acropora digitifera from the Gulf of Mannar

Corals, considered the rainforests of the oceans, harbour an abundance of different bacterial populations throughout the coral structure. In the present study we attempted to characterize the cultivable bacterial population associated within the mucus and tissue of the coral Acropora digitifera from the Gulf of Mannar. 16S rRNA gene was amplified from the cultured mucus and tissue isolates. Amplified ribosomal DNA restriction analysis, performed with a combination of restriction enzymes to determine the polymorphic groups of bacteria, generated 19 distinct groups in the coral mucus and 17 distinct groups in the coral tissue. Phylogenetic analyses based on the full-length sequences of 16S rRNA gene sequences showed that the majority of bacterial isolates belonged to the group Firmicutes, followed by Gammaproteobacteria and Actinobacteria. On investigating their antimicrobial activity, mucus isolates showed about 25% activity and tissue isolates showed 48% activity. This study revealed the presence of actinomycetes in both the coral mucus and the coral tissue, which had high activity against pathogens. This study, for the first time, demonstrates that actinomycetes existing within corals also have potential antibacterial activity. This has been overlooked so far, and indicates that, in addition to mucus, bacteria within the tissue of corals might defend the coral host against pathogens.

A novel compound from the marine bacterium Bacillus pumilus S6-15 inhibits biofilm formation in Gram-positive and Gram-negative species

Biofilm formation is a critical problem in nosocomial infections and in the aquaculture industries and biofilms show high resistance to antibiotics. The aim of the present study was to reveal a novel anti-biofilm compound from marine bacteria against antibiotic resistant Gram-positive and Gram-negative biofilms. The bacterial extract (50 μg ml−1) of S6-01 (Bacillus indicus = MTCC 5559) showed 80–90% biofilm inhibition against Escherichia coli, Shigella flexneri, Proteus mirabilis and S6-15 (Bacillus pumilus = MTCC 5560) showed 80–95% biofilm inhibition against all the 10 tested organisms. Furthermore, they also reduced the hydrophobicity index and extracellular polymeric substances (EPS) production. Structural elucidation of the active principle in S6-15 using GC-MS, 1H NMR, and 13C NMR spectral data revealed it to be 4-phenylbutanoic acid. This is the first report of 4-phenylbutanoic acid as a natural product. The purified compound (10–15 μg ml−1) showed potential activity against a wide range of biofilms. This study for the first time, reports a novel anti-biofilm compound from a marine bacterium with wide application in medicine and the aquaculture industry.

The anti-biofilm potential of pomegranate (Punica granatum L.) extract against human bacterial and fungal pathogens

Infectious diseases caused by bacteria and fungi are the major cause of morbidity and mortality across the globe. Multi-drug resistance in these pathogens augments the complexity and severity of the diseases. Various studies have shown the role of biofilms in multi-drug resistance, where the pathogen resides inside a protective coat made of extracellular polymeric substances. Since biofilms directly influence the virulence and pathogenicity of a pathogen, it is optimal to employ a strategy that effectively inhibits the formation of biofilm. Pomegranate is a common food and is also used traditionally to treat various ailments. This study assessed the anti-biofilm activity of a methanolic extract of pomegranate against bacterial and fungal pathogens. Methanolic extract of pomegranate was shown to inhibit the formation of biofilms by Staphylococcus aureus, methicillin resistant S. aureus, Escherichia coli, and Candida albicans. Apart from inhibiting the formation of biofilm, pomegranate extract disrupted pre-formed biofilms and inhibited germ tube formation, a virulence trait, in C. albicans. Characterization of the methanolic extract of pomegranate revealed the presence of ellagic acid (2,3,7,8-tetrahydroxy-chromeno[5,4,3-cde]chromene-5,10-dione) as the major component. Ellagic acid is a bioactive tannin known for its antioxidant, anticancer, and anti-inflammatory properties. Further studies revealed the ability of ellagic acid to inhibit the growth of all species in suspension at higher concentrations (>75 μg ml−1) and biofilm formation at lower concentrations (<40 μg ml−1) which warrants further investigation of the potential of ellagic acid or peel powders of pomegranate for the treatment of human ailments.

Inhibition of Streptococcus pyogenes Biofilm Formation by Coral-Associated Actinomycetes

Streptococcus pyogenes biofilms tend to exhibit significant tolerance to antimicrobials during infections. We screened coral-associated actinomycetes (CAA) for antibiofilm activity against different biofilm forming M serotype of Streptococcus pyogenes. Actinomycetes isolated from the mucus of the coral Acropora digitifera were screened for antibiofilm activity against S. pyogenes biofilms wherein several isolates clearly demonstrated antibiofilm activity. The biofilm inhibitory concentrations (BICs) and the sub-BICs (1/2 and 1/4 BIC) of the extracts significantly prevented biofilm formation up to 60–80%. The extract of Streptomyces akiyoshinensis (A3) displayed efficient antibiofilm activity against all the biofilm forming M serotypes. All the five extracts efficiently reduced the cell surface hydrophobicity (a crucial factor for biofilm formation in S. pyogenes) of three M types and thus may inhibit biofilm formation. CAA represent an interesting source of marine invertebrates-derived antibiofilm agents in the development of new strategies to combat Streptococcal biofilms.