A rapid colorimetric method for the detection of carminic acid in samples based on visible color change.

Carminic Acid (CA), an insect-derived red color, is widely used as a colorant and additive in food and non-food items. The detection of CA is of great concern since it is unacceptable for vegetarians and vegans consumers. Therefore, it is important for food authorities to have a rapid detection method for CA. We describe here a simple and rapid method for the qualitative detection of CA, using Pb2+ for complex formation. As a result, the sample solution shows a visible change from pink to purple (bathochromic shift) which could also be analyzed through a spectrophotometer at λmax = 605 nm. The structure of the CA-Pb2+ complex was also studied through advanced spectroscopic techniques. Moreover, the presence of iron results in the formation of a stable CA-Fe2+ complex without any significant color change, as Fe2+ has a stronger binding affinity with CA. Thus, sodium fluoride (NaF) was used to prevent CA-Fe2+ complex formation. Therefore, two methods were developed based on the absence (method I) and presence (method II) of NaF. The LOD and LOQ for the method I was 0.0025 and 0.0076 mg mL-1, and for method II, values were 0.0136 and 0.0415 mg mL-1, respectively. The methods were also validated by intra and inter-day analyses. A total of 45 commercials, including food and non-food samples, were screened for the detection of CA. The developed methods are applicable for the effective and rapid surveillance of CA in various samples without the use of high-tech instruments.

Untargeted metabolomics analysis of gentamicin-induced tolerant colonies of Klebsiella pneumoniae.

PURPOSE: Antibiotic resistance development in pathogenic bacteria like Klebsiella pneumoniae seriously threatens humankind. Therefore, it is important to understand the interaction of bacteria with antibiotic agents and how it acquires resistance at the molecular level. The current study describes metabolomics analysis of K. pneumoniae sensitive strains and its gentamicin-tolerant (resistant) strains. METHODS: K. pneumoniae strains were treated at five different concentrations of gentamicin, increasing from a low dose (16.2 µg/mL) to the highest dose (250 µg/mL) at three incubation time periods (24 h, 48 h, and 72 h). Colonies obtained at various concentrations and time intervals were subjected to metabolomic analysis using GC-MS. RESULTS: A drastic change was observed in the morphology of K. pneumoniae colonies with the increasing gentamicin concentration. Moreover, K. pneumoniae strains grown at the highest concentration (250 µg/mL) were found tolerant to 1 mg/mL gentamicin (4-folds) and considered resistant strains. A total of 459 metabolites were identified. A sequential down/up-regulation in 4, 3, and 4 metabolites were observed in association with the increasing gentamicin concentration at 24 h, 48 h, and 72 h, respectively. While with the comparative analysis of resistant and sensitive strains, a total of seven down- and sixteen up-regulated metabolites were observed. The concentration of some fatty acids and sugars have been found to increase while, a few metabolites like inosine, tyrosine, 1-propionylproline, and 2-hydroxyacetic acid have been found down-regulated in resistant samples. CONCLUSION: These regulator metabolites might be associated with resistance development in K. pneumoniae against gentamicin and might be helpful in the rapid detection of gentamicin-resistant clinical strains.