In this work, a simple, safe and rapid method for enumerating nitrifying bacteria was used as an alternative to traditional harmful chemical methods. The enumeration of nitrifying bacteria was based upon the change of color of the growth media containing pH indicators in response to acid production during nitrification. The oxidation of ammonia to strong acids by nitrifiers leads to pH decrease, which can be detected by pH indicators such as methyl orange (MO), bromocresol green (BCG), methyl red (MR), bromothymol blue (BTB), and phenol red (PhR) using the Most Probable Number (MPN) technique. The use of these pH indicators revealed a higher estimate than the classical chemical methods in all tested samples. Ammonium oxidizer counts always exceeded those of nitrite oxidizers in the surveyed environments. The time required for the detection of growth (positive tubes in MPN) was descending in the following order: MO, BCG, MR, BTB and PhR. The time to detection was shorter for ammonium oxidizers than for nitrite oxidizers. Generally, nitrifier counts were very low in soils compared with farmyard manure or sewage effluent. Incubation periods for both organisms differed from 4 to 8 weeks depended upon the indicator used. Finally, it could be concluded that the use of pH indicators, especially phenol red, as proposed in this study was accurate, sensitive and successfully applicable for the enumeration of nitrifiers in different environments.

This study investigated different amino acid-based surfactants (AASs), also known as biosurfactants, including sodium N-dodecyl asparagine (AS), sodium N-dodecyl tryptophan (TS), and sodium N-dodecyl histidine (HS) for their potential anticorrosion, antibacterial, and antidermatophyte properties. The chemical and electrochemical techniques were employed to examine the copper corrosion inhibition efficacy in H2SO4 (1.0 M) solution at 298 K. The results indicated their promising corrosion inhibition efficiencies (% IEs), which varied with the biosurfactant structures and concentrations, and the concentrations of corrosive medium. Higher % IEs values were attributed to the surfactant adsorption on the copper surface and the production of a protective film. The adsorption was in agreement with Langmuir adsorption isotherm. The kinetics and mechanisms of copper corrosion and its inhibition by the examined AASs were illuminated. The surfactants behaved as mixed-kind inhibitors with minor anodic priority. The values of % IEs gained from weight loss technique at a 500 ppm of the tested surfactants were set to be 81, 83 and 88 for AS, HS and TS, respectively. The values of % IEs acquired from all the applied techniques were almost consistent which were increased in the order: TS > HS ≥ AS, establishing the validity of this study. These surfactants also exhibited strong broad-spectrum activities against pathogenic Gram-negative and Gram-positive bacteria and dermatophytes. HS exhibited the highest antimicrobial activity followed by TS, and AS. The sensitivity of pathogenic bacteria varied against tested AASs. Shigella dysenteriae and Trichophyton mantigrophytes were found to be the most sensitive pathogens. HS exhibited the highest antibacterial activity against Shigella dysenteriae, Bacillus cereus, E. coli, K. pneumoniae, and S. aureus through the formation of clear zones of 70, 50, 40, 39, and 35 mm diameters, respectively.AASs also exhibited strong antifungal activity against all the tested dermatophyte molds and fungi. HS caused the inhibition zones of 62, 57, 56, 48, and 36 mm diameters against Trichophyton mantigrophytes, Trichophyton rubrum, Candida albicans, Trichosporon cataneum, and Cryptococcus neoformans, respectively. AASs minimal lethal concentrations ranged between 16 to 128 µg/ml. HS presented the lowest value (16 µg/ml) against tested pathogens followed by TS (64 µg/ml), and AS (128 µg/ml). Therefore, AASs, especially HS, could serve as an effective alternative antimicrobial agent against food-borne pathogenic bacteria and skin infections-associated dermatophyte fungi.

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