Heavy Metal Tolerance Trend in Extended-Spectrum β-Lactamase Encoding Strains Recovered from Food Samples

This study evaluates bacteriological profiles in ready-to-eat (RTE) foods and assesses antibiotic resistance, extended-spectrum β-lactamase (ESBL) production by gram-negative bacteria, and heavy metal tolerance. In total, 436 retail food samples were collected and cultured. The isolates were screened for ESBL production and molecular detection of ESBL-encoding genes. Furthermore, all isolates were evaluated for heavy metal tolerance. From 352 culture-positive samples, 406 g-negative bacteria were identified. Raw food samples were more often contaminated than refined food (84.71% vs. 76.32%). The predominant isolates were Klebsiella pneumoniae (n = 76), Enterobacter cloacae (n = 58), and Escherichia coli (n = 56). Overall, the percentage of ESBL producers was higher in raw food samples, although higher occurrences of ESBL-producing E. coli (p = 0.01) and Pseudomonas aeruginosa (p = 0.02) were observed in processed food samples. However, the prevalence of ESBL-producing Citrobacter freundii in raw food samples was high (p = 0.03). Among the isolates, 55% were bla_CTX-M, 26% were bla_SHV, and 19% were bla_TEM. Notably, heavy metal resistance was highly prevalent in ESBL producers. These findings demonstrate that retail food samples are exposed to contaminants including antibiotics and heavy metals, endangering consumers.

Heavy metal content of produce grown in San Juan County (New Mexico, USA)

The Animas River Watershed has long received discharges of naturally occurring acid rock drainage; however, on August 5, 2015, three million gallons flowed into the agricultural region of Farmington, New Mexico and the Navajo Nation. Consumers and growers in the region were fearful that produce might absorb heavy metals from contaminated irrigation water originating from these rivers. Samples were collected from the region including corn (n = 30), pumpkin (n = 10), squash (n = 10), and cucumber (n = 10) then processed and tested using inductively coupled plasma-optical emission spectrometry (ICP-OES) for concentrations of nine metals of interest. These include toxic metals: Al, As, and Pb, which were compared to the World Health Organization limits, 18.29 mg d^-1, 0.192 mg d^-1, and 0.05 mg kg^-1, respectively and essential metals: Cr, Fe, Mn, Zn, Ca, and Cu whose levels were compared to the National Academies' dietary references for tolerable upper intake levels. Results indicate that produce grown in the region contained significantly less metal than the allowable limits, except for Pb in two corn samples. This research is the first attempt to monitor and analyze heavy metal absorption of produce in the area.

Occurrence of priority trace metals in tomatoes (Solanum lycopersicum L.) from some areas of Uasin Gishu County, Kenya

This study determined the concentration of zinc, lead and cadmium in tomatoes consumed in some areas of Uasin Gishu, Kenya. Samples were taken in quintuplicate from Huruma and Bahati estates (Eldoret) and Chebaiywo (Kesses) and their metalliferous content were determined by atomic absorption spectroscopy. All samples had detectable levels of trace metals, with lead recording the highest concentration of 43.20 ± 0.31 mg/kg. Zinc concentrations were below WHO guidelines. Daily intakes ranged from 8.25 × to 2.59 × mg/kg/day. Though there are no probable cancer risks, hazard quotients indicated that deleterious health effects could arise from daily consumption of tomatoes.

Recombinant Fusion Protein PbrD Cross-Linked to Calcium Alginate Nanoparticles for Pb Remediation

Lead (Pb) pollution arising from industrial and mining activities has led to widespread environmental toxicity, particularly in South Africa. Humans exposed to Pb are reported to suffer from detrimental health impacts that can lead to fatalities. As such, there is an urgent need to remediate Pb from the environment. In this study, we propose the use of a Pb-specific recombinant fusion metalloprotein, rPbrD surface-cross-linked onto calcium alginate nanoparticles (CANPs) for the biosorption of Pb(II) from aqueous solution. The prepared biosorbents were characterized using scanning electron microscopy, transmission electron microscopy, and dynamic light scattering. Their ability to biosorb soluble Pb(II) was determined by inductively coupled plasma mass spectroscopy and their adsorption mechanism was described according to the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms. The rate of Pb uptake for bare CANPs and rPbrD-CANPs at a concentration of 100 mg/L metal was 3.34 and 8.82 mg/g, respectively, within 30 min. The adsorption data for the bare CANPs best fit the Langmuir isotherm, whereas the adsorption data for rPbrD-CANPs best fitted the Freundlich isotherm. Based on the sorption intensity (n) and the separation factor (R _L), both biosorbents represent a favorable adsorption system. These findings suggest that the proposed nanobiosorbent is a promising candidate for the recovery of Pb ions present in high concentrations such as acid mine drainage or industrial effluent.

Isolation and Molecular Identification of Virulence, Antimicrobial and Heavy Metal Resistance Genes in Livestock-Associated Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is one of the most important pathogens of humans and animals. Livestock production contributes a significant proportion to the South African Gross Domestic Product. Consequently, the aim of this study was to determine for the first time the prevalence, virulence, antibiotic and heavy metal resistance in livestock-associated S. aureus isolated from South African livestock production systems. Microbial phenotypic methods were used to detect the presence of antibiotic and heavy metal resistance. Furthermore, molecular DNA based methods were used to genetically determine virulence as well as antibiotic and heavy metal resistance determinants. Polymerase chain reaction (PCR) confirmed 217 out of 403 (53.8%) isolates to be S. aureus. Kirby-Bauer disc diffusion method was conducted to evaluate antibiotic resistance and 90.8% of S. aureus isolates were found to be resistant to at least three antibiotics, and therefore, classified as multidrug resistant. Of the antibiotics tested, 98% of the isolates demonstrated resistance towards penicillin G. High resistance was shown against different heavy metals, with 90% (196/217), 88% (192/217), 86% (188/217) and 84% (183/217) of the isolates resistant to 1500 µg/mL concentration of Cadmium (Cd), Zinc (Zn), Lead (Pb) and Copper (Cu) respectively. A total of 10 antimicrobial resistance and virulence genetic determinants were screened for all livestock associated S. aureus isolates. Methicillin-resistant S. aureus (MRSA) isolates were identified, by the presence of mecC, in 27% of the isolates with a significant relationship (p < 0.001)) with the host animal. This is the first report of mecC positive LA-MRSA in South Africa and the African continent. The gene for tetracycline resistance (tetK) was the most frequently detected of the screened genes with an overall prevalence of 35% and the highest prevalence percentage was observed for goats (56.76%) followed by avian species (chicken, duck and wild birds) (42.5%). Virulence-associated genes were observed across all animal host species. The study reports the presence of luks/pv, a gene encoding the PVL toxin previously described to be a marker for community acquired-MRSA, suggesting the crossing of species between human and livestock. The high prevalence of S. aureus from the livestock indicates a major food security and healthcare threat. This threat is further compounded by the virulence of the pathogen, which causes numerous clinical manifestations. The phenomenon of co-selection is observed in this study as isolates exhibited resistance to both antibiotics and heavy metals. Further, all the screened antibiotic and heavy metal resistance genes did not correspond with the phenotypic resistance.

Nutrient and Antinutrient Compositions and Heavy Metal Uptake and Accumulation in S. nigrum Cultivated on Different Soil Types

Solanum nigrum cultivated on different soil texture types, sandy clay loam, silty clay loam, clay loam, loam, and control soils, were evaluated for proximate compositions, antinutrients, vitamins, and mineral composition with plant age using standard analytical methods. Accumulation of trace elements using translocation factor was studied to determine their toxic levels in plant tissues. Data were analysed by ANOVA and results expressed as means and standard deviation. Ash content, crude fibre, protein, alkaloid, phytate, and saponin ranged between 11.4 and 12%, 19.24 and 19.95%, 34.23 and 38.98, 42.08 and 45.76 mg/ml, 0.84 and 1.17%, and 94.10 and 97.00%, respectively. Vitamins A, C, and B were present in high quantity. Macro- and micronutrients recorded showed that S. nigrum is a potential reservoir of minerals. Accumulation of micronutrients was observed to be the highest at the flowering stage between the 4th and 5th weeks after transplanting. Plants cultivated on clay loam, silty clay loam, and loam soils accumulated elevated nutritional compositions and abundant antinutrients. However, the accumulated trace metals in the plants are within the recommended safe levels. All nutrient values are in the recommended requirements for daily consumption.