Highly Sensitive Immunochromatographic Identification of Tetracycline Antibiotics in Milk

Turn-off/turn-on biosensing of tetracycline and ciprofloxacin antibiotics using fluorescent iron oxide quantum dots

A fluorescence probe based on iron oxide quantum dots (IO-QDs) was synthesized using the hydrothermal method for the determination of tetracycline (TCy) and ciprofloxacin (CPx) in aqueous solution. The IO-QDs were characterized using high-resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), vibrating sample magnetometry (VSM), and Fourier-transform infrared spectroscopy (FTIR). The as-prepared IO-QDs are fluorescent, stable, and with a fluorescence quantum yield (QY) of 9.8 ± 0.12%. The fluorescence of IO-QDs was observed to be quenched and enhanced in the presence of TCy and CPx, respectively. The fluorescence intensity ratio shows linearity at concentrations from 1-100 μM and 5-100 μM for TCy and CPx, respectively; the detection limit for TCy and CPx was estimated to be 0.71 μM and 1.56 μM, respectively. The proposed method was also successfully utilized in the spiked samples of drinking water and honey with good recoveries. The method offered convenience, rapid detection, high sensitivity, selectivity, and cost-efficient alternative options for the determination of TCy and CPx in real samples.

Development of a Lateral-Flow Immunochromatographic Strip for the Detection of Oxytetracycline Residues in Biological Fluids

Oxytetracycline (OTC) is extensively used in veterinary medicine and for growth promotion around the globe. The indiscriminate use of OTC in food-producing animals leaves residues in animal products. The presence of these residues in animal products causes economic losses and harmful effects on consumers. Different regulatory bodies set maximum residue limits (MRLs) for different tetracyclines. To avoid harmful effects, there is a need for a simple, fast, and economical method for the screening of animal products. In this study, a fast, economical, and user-friendly lateral-flow immunochromatographic (LFIC) assay based on gold nanoparticles (AuNPs) was developed to detect the presence of OTC residues in biological fluids. AuNPs provided visual results as red lines in 6-15 min. Polyclonal rabbit IgG antibodies were produced using the immunogen of OTC. These antibodies were purified by the combined ammonium sulfate-octanoic acid precipitation method. Antibodies were conjugated to AuNPs as recognition biomolecules. A LFIC strip was optimized using borate buffer spiked with different concentrations of the OTC. The visual limit of detection (LOD) in different biological samples (milk, serum, and urine) was determined using samples spiked with OTC. The LOD was found to be 15 μg/L, which is very low from the MRL (100 μg/L) set by different regulatory authorities. This LFIC strip can be used to detect OTC residues in biological fluids for point-of-care testing (POCT). These strips are easy to use, cost-effective, and portable and provide quick results without the use of laboratory instruments.

Group-targeting sulfonamides via an evanescent-wave biosensor based on rational designed coating antigen

In order to effectively monitor a wide variety of sulfonamides residues in the environment, group-targeting immunoassay based on the group-specific antibodies has attracted great attentions, which can realize the detection of a group of contaminants in environment as many as possible even the unrecognized ones. Indirect competitive immunoassay is generally adopted for small molecule detection however the rational design of immobilized coating antigen for improved recognition capability on the solid surface is far from enough. To cover the research gap, we proposed the design criteria of coating antigen for surface-based indirect competitive immunoassay based on the molecular docking. Taking the group-specific antibodies against sulfonamides (SA) as a proof-of-concept, a hapten with a linking arm with 3 methyl groups was selected to synthesize the coating antigen. Through surface immobilization of coating antigen, a portable biosensor for group-targeting immunoassay of sulfonamides was developed and demonstrated excellent performance with detection limits lower than 0.6 μg/L for four SA variants, and the cross-reactivities of 148-215 % relative to sulfadiazine. The recovery rates of SAs in liquid milk ranges from 87 to 97 %, which confirmed the application potential of this method in the determination of SAs. Its capability to measure total SAs in a simple and low-cost way would pave the way for a variety of application fields.

Colorimetric aptasensor for on-site detection of oxytetracycline antibiotic in milk

Oxytetracycline (OTC), one of the largely used antibiotic in veterinary practice has been banned due to its potential side effects. Development of a field applicable and affordable kit to detect OTC will help to eliminate such milk from human consumption. An aptamer has been designed (27 nt; K_d = 29.2 ± 19.4 nM) through rational truncation. OTC interacts with this aptamer in G rich regions as confirmed by molecular modelling and circular dichroism spectroscopy. To develop a lateral flow based aptasensor, OTC was conjugated with a 7 kDa carrier protein to immobilize onto the nitrocellulose membrane. Using 0.125 µM aptamer-gold conjugate, assay could visually detects upto 5 ng/mL of OTC in spiked milk within 10 mins [Limit of quantitation (LOQ)-0.254 ± 1.62 ng/mL; permissible limit 100 ng/mL]. It showed no cross reactivity with components of milk and data correlated with analysis done through HPLC.

Indirect Competitive Determination of Tetracycline Residue in Honey Using an Ultrasensitive Gold-Nanoparticle-Linked Aptamer Assay

Tetracycline residue in honey has become an increasingly important food safety problem. In this work, an ultrasensitive gold nanoparticles (AuNPs)-linked aptamer assay was developed to determine the tetracycline residue in honey. First, a tetracycline–bovine serum albumin conjugate coating was applied to a microplate. Then, with the incubation of AuNPs-linked aptamer, the fixed tetracycline in the microplate competed for the limited aptamer with the free tetracycline in the sample. Higher amounts of free tetracycline in the sample were associated with more competitive binding of aptamer-AuNPs, and the aptamer-AuNPs binding with tetracycline-BSA was lower. Finally, as a kind of nanozyme, AuNPs exhibited peroxidase activity and oxidized 3,3′,5,5′-tetramethylbenzidine, transforming it from colorless to blue, and achieving the measurement at 652 nm. The analytical performance—including linearity, limit of detection, selectivity, precision, repeatability, and accuracy—has been investigated. It was successfully applied to the determination of tetracycline in honey samples with high accuracy and sensitivity.

Antimicrobial potential of lactic acid bacteria from domestic chickens (Gallus domesticus) from south Celebes, Indonesia, in different growth phases: in vitro experiments supported by computational docking

BACKGROUND AND OBJECTIVES

Pathogenic bacterial infection is one of the factors that can cause extensive losses in poultry farming. Pathogenic bacteria that infect domestic chickens (Gallus domesticus) include Escherichia coli. This study has investigated antimicrobial compounds from probiotic bacteria isolated from the digestive tract of domestic chickens originating from Takalar Regency, South Sulawesi, Indonesia.

MATERIALS AND METHODS

Lactic acid bacteria were grown on de Man-Ragosa-Sharpe agar medium for 24 hours. The bacterial isolate with the best inhibitory power was identified as Bacillus subtilis (B. subtilis), based on 16S RNA sequences. Antimicrobial activity of the selected lactic acid bacteria was tested on the pathogenic bacteria, E. coli and Staphylococcus aureus. Using well diffusion method. In this study, in silico study was conducted to examine the structure and binding affinity of lactic acid bacteria against E. coli and S. aureus. Molecular docking experiments were performed using the PyRx 0.8 software.

RESULTS

This study showed that the bacteria were B. subtilis strain PATA-5. The response of inhibition of antimicrobial compounds produced by B. subtilis strain PATA-5 maximum in the stationary phase. The bactericidal properties of B. subtilis strain PATA-5 were categorized as strong against Gram-negative E. coli, i.e., 30.5 mm, when compared to Gram-positive S. aureus, i.e., 17.5 mm.

CONCLUSION

B. subtilis strain PATA-5 is capable to produce natural antibiotic cyclic lipopeptides, namely surfactin.