Antibiotic Resistance of Salmonella enterica Serovar Typhi in Kolkata, India, and In Vitro Experiments on Effect of Combined Chemotherapy

This communication states the changing patterns of Salmonella enterica serovar Typhi (S. Typhi) isolates causing enteric fever in and around Kolkata, India. Among the isolates resistance to ampicillin (A), chloramphenicol (C), cotrimoxazole (Co) and tetracycline (T) were plasmid mediated; the plasmid was unstable in S. Typhi, and the other enteric bacteria like Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris were found to be the potential source of dissemination of such plasmids into S. Typhi. The infection with such S. Typhi strains were successfully treated with ciprofloxacin (Cp: MICs 0.0075–0.075 μg mL−1) and/or ofloxacin (Ofx: MICs 0.0125–0.075 μg mL−1), but in the later course, the S. Typhi strains, showing resistance to nalidixic acid, developed low level of resistance to Cp and Ofx, causing the treatment failure. Thus, the treatment regimen was shifted to the third generation cephalosporins like ceftriaxone (Ct) and cefotaxime (Cf). Keeping in mind the anticipation of development of resistance to Ct/Cf, we prepared the treatment regimen for MDR enteric fever, based on the double-drug synergy tests in vitro; Cp-gentamycin (FICI 0.121–0.216) and Cp-trimethoprim (FICI 0.14–0.483) combinations were found effective against S. Typhi isolates having decreased sensitivity to cp (MICs: 0.5–1.25 μg mL−1)

Kinetics of Dimethoate Biodegradation in Bacterial System

The present study is an investigation on the kinetics of dimethoate biodegradation and an estimation of residual dimethoate in bacterial culture by spectrophotometry. The methylene chloride extract of the culture medium was used for determination of dimethoate through its reaction with 1 chloro-2, 4 dinitrobenzene to produce methylamine whose absorbance at 505 nm gave an estimation of dimethoate content. The dimethoate standard curve follows Beer’s law at 505 nm with a slope of 0.0129 absorbance units per µg/mL. The regression equation relating concentration of dimethoate (x) with the absorbance is (y): y = 0.037 + 0.0129x. The amount of residual dimethoate after 7 days were 0, 4, 17, 28 and 29 µg/mL; the rate constants were 0.775, 0.305, 0.225, 0.167 and 0.127 each per day, and the efficiency of dimethoate degradation were 100%, 96%, 83%, 72% and 71%, for Bacillus licheniformis, Pseudomonas aeruginosa, Aeromonas hydrophila, Proteus mirabilis and Bacillus pumilus respectively. Dimethoate remediation could be attained through bacterial metabolism of the pesticide and colorimetric analysis might be useful in the estimation of dimethoate within a detection limit of 5–100 µg/mL

SYNERGISM BETWEEN MIMUSOPS ELENGI AND BAUHINIA VARIEGATA SEED EXTRACTS AGAINST SALMONELLA ENTERICA SEROVAR TYPHI AND VIBRIO CHOLERAE O1 BIOTYPE EL TOR SEROTYPE OGAWA ISOLATES

ABSTRACT The current communication evaluates the antibacterial activity of Mimusops elengi (M. elengi) and Bauhinia variegata (B. variegata) seed extracts, alone and in combination, against Salmonella enterica serovar Typhi (S. typhi) and Vibrio cholerae O1 biotype El Tor serotype Ogawa (V. cholerae) isolates. The antibacterial activity of ethanolic extracts of bakul, M. elengi, seed (MSE; 500 µg) and kanchan, B. variegata, seed (BSE; 500 µg), alone and in combination, was determined following agar diffusion method, for a total of 16 S. typhi and V. cholerae isolates. The zone diameter of inhibition (ZDI) for the agents was recorded, and growth inhibitory indices (GIIs) were calculated. The V. cholerae and S. Typhi isolates had BSE (500 µg) and MSE (500 µg) ZDIs 12-17 mm and 13-15 mm, respectively. The GIIs of the BSE-MSE combination ranged 0.654 -0.788 and 0.538 -0.759 for the isolates of S. typhi and V. cholerae, respectively. The combined activity of BSE and MSE was synergistic against the test bacterial isolates, and the test plant extracts are potential in combating S. typhi and V. cholerae drug resistance and hence are important sources for the development of non-antibiotic drug(s) against S. typhi and V. cholerae infection