Biochemical analysis of leptospiral LPS explained the difference between pathogenic and non-pathogenic serogroups

Lipopolysaccharide (LPS) is the major surface antigen of Leptospira. In this study, the genes involved in the LPS biosynthesis were analyzed and compared by bioinformatics tools. Also, the chemical composition analysis of leptospiral lipopolysaccharides (LPS) extracted from 5 pathogenic serovars like Autumnalis, Australis, Ballum, Grippotyphosa, Pomona, and the nonpathogenic serovar Andamana was performed. Methods used were Limulus amebocyte lysate assay (LAL), gas chromatography-mass spectrometry (GC-MS), fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance spectroscopy (NMR). LAL assay showed a significantly higher level of endotoxicity among pathogenic serovars (~0.490 EU/mL) than that of nonpathogenic Andamana (~0.102 EU/mL). FAMES analysis showed the presence of palmitic acid (C16:0), hydroxy lauric acid (3-OH-C12:0), and oleic acid (C18:0). Palmitoleic acid (C16: 1), and 3- hydroxy palmitate (3-OH-C16:0) was detected only in pathogenic serovars. In contrast myristoleic acid (C14:1) and stearic acid (C18:0) were present in Andamana. FTIR analysis revealed C-O-C stretch of esters, 3°ROH functional groups and carbohydrate vibration range were similar among pathogenic serovars. The NMR analysis reveals similarity for 6 deoxy sugars and methyl groups of Autumnalis, Australis, and Ballum. Further, the presence of palmitoleic acid and 3-hydroxy palmitate may be the significant pathogen-associated predisposing factor. This mediates high osmolarity glycerol (HOG) mediated stress response in leptospiral LPS mediated pathogenesis.

Multilocus sequence typing (MLST) of leptospiral strains isolated from two geographic locations of Tamil Nadu, India

Here the rodent carrier status for the transmission of human leptospirosis in Tiruchirappalli, district, Tamil Nadu, India was assessed. The predominantly circulating leptospiral STs were recognized by multilocus sequence typing (MLST). A total of 113 rodents were trapped from different provinces of the Tiruchirappalli district. The most prevalent rodent was Bandicota bengalensis (37.2%), and of the total, 52.2% (n=59) rodents were found to be positive for leptospiral 16S rRNA. These results were validated with a leptospiral culture positivity of 45.8% (n=27). Three isolates from Chennai (2 rodents and 1 human) and 1 human isolate from Tiruchirappalli were included to understand the spatial variations and to track the source of human leptospirosis. The serogroup, serovar, and species level identification of all 31 isolates identified 28 to be Leptospira borgpetersenii serovar Javanica and three as Leptospira interrogans serovar Autumnalis. MLST analysis defined all isolates to the existing ST profiles (ST145 and ST27) with the exception of 6 L. borgpetersenii (ST DR) isolates that showed variations in the sucA and pfkB loci. The DR ST was locally confined to Chatram province of Tiruchirappalli suggesting an epidemiological link. The predominant STs, ST145 and ST-DR form a group, indicating the presence of original strain that subsequently diverged evolutionarily into two STs. The variations between L. borgpetersenii in sucA and pfkB loci may be an indication that evolutionary changes transpired in Tiruchirappalli.

Lipopolysaccharide Specific Immunochromatography Based Lateral Flow Assay for Serogroup Specific Diagnosis of Leptospirosis in India

BACKGROUND

Leptospirosis is a re-emerging infectious disease that is under-recognized due to low-sensitivity and cumbersome serological tests. MAT is the gold standard test and it is the only serogroup specific test used till date. Rapid reliable alternative serogroup specific tests are needed for surveillance studies to identify locally circulating serogroups in the study area.

METHODS/PRINCIPAL FINDINGS

In the present investigation the serological specificity of leptospiral lipopolysaccharides (LPS) was evaluated by enzyme linked immunosorbent assay (ELISA), dot blot assay and rapid immunochromatography based lateral flow assay (ICG-LFA). Sera samples from 120 MAT positive cases, 174 cases with febrile illness other than leptospirosis, and 121 seronegative healthy controls were evaluated for the diagnostic sensitivity and specificity of the developed assays. LPS was extracted from five locally predominant circulating serogroups including: Australis (27.5%), Autumnalis (11.7%), Ballum (25.8%), Grippotyphosa (12.5%), Pomona (10%) and were used as antigens in the diagnostics to detect IgM antibodies in patients' sera. The sensitivity observed by IgM ELISA and dot blot assay using various leptospiral LPS was >90% for homologous sera. Except for Ballum LPS, no other LPS showed cross-reactivity to heterologous sera. An attempt was made to develop LPS based ICG-LFA for rapid and sensitive serogroup specific diagnostics of leptospirosis. The developed ICG-LFA showed sensitivity in the range between 93 and 100% for homologous sera. The Wilcoxon analysis showed LPS based ICG-LFA did not differ significantly from the gold standard MAT (P>0.05).

CONCLUSION

The application of single array of LPS for serogroup specific diagnosis is first of its kind. The developed assay could potentially be evaluated and employed for as MAT alternative.

Bacteriocinogenic potential of a probiotic strain Bacillus coagulans [BDU3] from Ngari

Bacteriocin producing strain BDU3 was isolated from a traditional fermented fish of Manipur Ngari. The strain BDU3 was identified as Bacillus coagulans by phenotypic and genotypic characterization. The BDU3 produced novel bacteriocin, which showed an antimicrobial spectrum toward a wide spectrum of food borne, and closely related pathogens with a MIC that ranged between 0.5 and 2.5 μg/mL. The isolate was able to tolerate pH as low as 2.0 and up to 0.2% bile salt concentration. Three step purification was employed to increase the specific activity of the antimicrobial compound. The fractions were further chromatographed by Rp-HPLC C-18 column and the purified bacteriocin had a specific activity of ∼8500 AU/mg. However, the potency of bacteriocin was susceptible to digestion with Proteinase K, Pepsin, SDS, EDTA and Urea. Molecular mass of purified bacteriocin was found to be 1.4 kDa using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). The functional group was revealed by FTIR analysis. The cytotoxicity assay (MTT) using purified bacteriocin showed 2 times lower EC50 values compared to SDS. This is the smaller bacteriocin ever reported before from B. coagulans with greater antimicrobial potency with lower cytotoxicity. This bacteriocin raises the possibilities to be used as a biopreservative in food industries.

Development of species-specific primers for detection of Streptococcus pyogenes from throat swabs

A species-specific molecular marker has been developed to detect the human pathogen Streptococcus pyogenes from throat swabs. Streptococcus pyogenes is an important pathogen among Gram-positive organisms. A rapid and simple diagnostic tool is of utmost importance for the identification of this pathogen. The random amplified polymorphic DNA (RAPD) technique was used to differentiate the S. pyogenes strains. A differentially amplified fragment obtained from RAPD profiles was sequenced and characterized, which was developed into a sequence characterized amplified region (SCAR) marker to evaluate the specificity of S. pyogenes from other species of Streptococcus. The sensitivity of the SCAR primers was studied by qualitative PCR and the detection limit was found to be 10(-1) ng of genomic DNA or one to two cells of S. pyogenes. The specificity of the primers was assayed in 270 clinical throat swabs wherein 23 samples turned to be positive, which was highly significant over culture-based methods. This species-specific primer enables accurate detection of S. pyogenes from clinical samples and will be a useful tool in epidemiological studies.