Copper tolerance and antibiotic resistance in soil bacteria from olive tree agricultural fields routinely treated with copper compounds.

BACKGROUND: Heavy metal pollution may act as persistent selective pressure that favors the spread of antimicrobial resistance in natural environments. The aim of this study was to isolate and identify metal-tolerant bacteria from soils in olive tree fields routinely treated with copper-derived compounds and to evaluate the tolerance of bacterial strains to other metals and their resistance to clinically relevant antibiotics. RESULTS: Five hundred and ninety-five bacterial isolates from 45 olive tree agricultural fields were studied. Minimum inhibitory concentrations (MICs) ≥ 16 mmol L-1 were detected for copper (57% of isolates), zinc (37%) and lead (62%), while only 3% had MICs ≥ 12 mmol L-1 for nickel. Ninety-six metal-tolerant strains were selected for identification and antibiotic resistance determination. Most isolates belonged to the genera Pseudomonas (37%), Bacillus (23%) and Chryseobacterium (20%), while 6% were identified as Variovorax, 4% as Stenotrophomonas and 2% as Serratia or Burkholderia. Highest copper tolerance was detected among Pseudomonas. Over 75% of the strains with high copper tolerance were also resistant to vancomycin, 50% to ampicillin and 40% to erythromycin or trimethoprim/sulfamethoxazole. CONCLUSION: Bacteria from olive soils are tolerant to metals, mainly copper, but also zinc and lead, as well as resistant to clinically important antibiotics, which could be a troublesome issue in clinical settings. © 2019 Society of Chemical Industry.

Aerobic and respirative growth of heterofermentative lactic acid bacteria: A screening study.

Heterofermentative lactic acid bacteria (76 strains) belonging to Lactobacillus, Leuconostoc and Weissella species which are important in fermentation, spoilage or as probiotics were screened in a factorial experiment for their ability to grow, produce catalase and consume oxygen in aerobiosis or in anaerobiosis, with or without supplementation with hemin and/or menaquinone in a medium containing glucose as a carbohydrate source. Aerobiosis improved growth with a few exceptions. The effect of supplementation with heme and/or menaquinone was strain specific and clear evidence of heme-boosted respiration was found in some cases. Heme-catalase was produced by strains of L. brevis, W. minor and Leuc. mesenteroides; some strains of the latter species produced non-heme catalase. Shaken flasks experiments showed that aerobic growth resulted in increased maximum growth rate and in a limited increase in biomass. Heme supplementation during aerobic growth resulted in a further increase in growth rate and final biomass only for a few strains; this was often related to catalase, which was also responsible for increased tolerance of H2O2. In both experiments we found evidence of heme toxicity, especially in anaerobiosis and in absence of menaquinone. Dose response curves for aerobic growth in the presence of combinations of hemin and menaquinone were non-monotonic, with growth stimulation at low doses of heme (<2.5 mg/l) and toxicity at higher doses. Menaquinone at 0.25-8 mg/l increased growth stimulation and partially reduced toxicity.

Genetic Determinants for Metal Tolerance and Antimicrobial Resistance Detected in Bacteria Isolated from Soils of Olive Tree Farms.

Copper-derived compounds are often used in olive tree farms. In a previous study, a collection of bacterial strains isolated from olive tree farms were identified and tested for phenotypic antimicrobial resistance and heavy metal tolerance. The aim of this work was to study the genetic determinants of resistance and to evaluate the co-occurrence of metal tolerance and antibiotic resistance genes. Both metal tolerance and antibiotic resistance genes (including beta-lactamase genes) were detected in the bacterial strains from Cu-treated soils. A high percentage of the strains positive for metal tolerance genes also carried antibiotic resistance genes, especially for genes involved in resistances to beta-lactams and tetracycline. Significant associations were detected between genes involved in copper tolerance and genes coding for beta-lactamases or tetracycline resistance mechanisms. A significant association was also detected between zntA (coding for a Zn(II)-translocating P-type ATPase) and tetC genes. In conclusion, bacteria from soils of Cu-treated olive farms may carry both metal tolerance and antibiotic resistance genes. The positive associations detected between metal tolerance genes and antibiotic resistance genes suggests co-selection of such genetic traits by exposure to metals.

Synthesis and Evaluation of Antimicrobial and Antibiofilm Properties of A-Type Procyanidin Analogues against Resistant Bacteria in Food.

Natural A-type procyanidins have shown very interesting biological activities, such as their proven antiadherence properties against pathogenic bacteria. In order to find the structural features responsible for their activities, we describe herein the design and synthesis of six A-type procyanidin analogues and the evaluation of their antimicrobial and antibiofilm properties against 12 resistant bacteria, both Gram positive and Gram negative, isolated from organic foods. The natural A-type procyanidin A-2, which had known antiadherence activity, was also tested as a reference compound for the comparative studies. Within the series, analogue 4, which had a NO2 group on ring A, showed the highest antimicrobial activity (MIC of 10 µg/mL) and was one of the best molecules at preventing biofilm formation (up to 40% decreases at 100 µg/mL) and disrupting preformed biofilms (up to 40% reductions at 0.1 µg/mL). Structure-activity relationships are also analyzed.

Adaptation to Biocides Cetrimide and Chlorhexidine in Bacteria from Organic Foods: Association with Tolerance to Other Antimicrobials and Physical Stresses.

Chlorhexidine (CH) and quaternary ammonium compounds (QAC), such as cetrimide (CE), are widely used as disinfectants because of their broad antimicrobial spectrum. However, their frequent use for disinfection in different settings may promote bacterial drug resistance against both biocides and clinically relevant antibiotics. This study analyzes the effects of stepwise exposure to cetrimide (CE) and chlorhexidine (CH) of bacteria from organic foods and previously classified as biocide-sensitive. Gradual exposure of these strains to biocides resulted in mainly transient decreased antimicrobial susceptibility to other antibiotics and to biocides. Biocide-adapted bacteria also exhibit alterations in physiological characteristics, mainly decreased heat tolerance, or gastric acid tolerance in CE-adapted strains, while bile resistance does not seem to be influenced by biocide adaptation. Results from this study suggest that changes in membrane fluidity may be the main mechanism responsible for the acquisition of stable tolerance to biocides.