Modelling of tetracycline resistance gene transfer by commensal Escherichia coli food isolates that survived in gastric fluid conditions

One Health-based management for sustainably mitigating tetracycline-resistant Aeromonas hydrophila-induced health risk

Aeromonas hydrophila has ability to spread tetracycline resistance (tetR) under stresses of oxytetracycline (OTC), one of the most important antibiotics in aquaculture industry. Even though environmental reservoir of Aeromonas allows it to be at interfaces across One Health components, a robust modelling framework for rigorously assessing health risks is currently lacking. We proposed a One Health-based approach and leveraged recent advances in quantitative microbial risk assessment appraised by available dataset to interpret interactions at the human-animal-environment interfaces in various exposure scenarios. The dose-response models were constructed considering the effects on mortality for aquaculture species and tetR genes transfer for humans. A scenario-specific risk assessment on pond species-associated A. hydrophila infection and human gut-associated tetR genes transfer was examined. Risk-based control strategies were involved to test their effectiveness. We showed that farmed shrimp exposed to tetracycline-resistant A. hydrophila in OTC-contaminated water experienced higher infection risk (relative risk: 1.25-1.34). The tetR genes transfer risk for farmers in shrimp ponds (∼2 × 10-4) and swimmers in coastal areas (∼4 × 10-6) during autumn exceeded acceptable risk (10-6). This cautionary finding underscores the importance of accounting for monitoring, assessing, and mitigating occupational health hazards among workers in shrimp farming sectors within future One Health-based strategies for managing water infection risks. We recommend that OTC emission rate together with A. hydrophila concentration should be reduced by up to 70-99% to protect human, farmed shrimp, and environmental health. Our predictive framework can be adopted for other systems and be used as a "risk detector" for assessing tetR-related health risks that invoke potential risk management on addressing sustainable mitigation on offsetting residual OTC emission and tetR genes spread in a species-human-environmental health system.

A Comprehensive Study on Antibiotic Resistance among Coagulase-Negative Staphylococci (CoNS) Strains Isolated from Ready-to-Eat Food Served in Bars and Restaurants

The present study aimed to characterize and assess the diversity of CoNS strains as potential vectors for the spread of resistance to antimicrobial agents from RTE foods served in bars and restaurants. Eighty-five CoNS strains, obtained from 198 RTE food samples, were investigated. Sixty-seven CoNS isolates (78.8%) were resistant to at least one antibiotic tested, and 37 (43.5%) were multidrug resistant (MDR-CoNS). Moreover, CoNS strains contained genes conferring resistance to antibiotics critically important in medicine, i.e., β-lactams [mecA (29.4%); blaZ (84.7%)], aminoglycosides [aac(6')-Ie-aph(2″)-Ia (45.9%); aph(2″)-Ic (3.5%)], macrolides, lincosamides and streptogramin B-MLS_B [msrA/B (68.2%); ermB (40%) and mphC (4.7%)], tetracyclines [tetK (31.8%); tetM (16.5%) and/or tetL (2.35%)]. We also found the fusB/C/D genes responsible for the acquired low-level fusidic acid resistance (17.6%) and streptogramin resistance determinant vgaA in 30.6% of isolates. In three linezolid resistant strains (2 S. epidermidis and 1 S. warneri), mutation was detected, as demonstrated by L101V and V188I changes in the L3 protein amino acid sequences. The high frequency in RTE food of MDR-CoNS including methicillin-resistant (MR-CoNS) strains constitutes a direct risk to public health as they increase the gene pool from which pathogenic bacteria can pick up resistance traits.

Multidrug-Resistant Biofilms (MDR): Main Mechanisms of Tolerance and Resistance in the Food Supply Chain

Biofilms are mono- or multispecies microbial communities enclosed in an extracellular matrix (EPS). They have high potential for dissemination and are difficult to remove. In addition, biofilms formed by multidrug-resistant strains (MDRs) are even more aggravated if we consider antimicrobial resistance (AMR) as an important public health issue. Quorum sensing (QS) and horizontal gene transfer (HGT) are mechanisms that significantly contribute to the recalcitrance (resistance and tolerance) of biofilms, making them more robust and resistant to conventional sanitation methods. These mechanisms coordinate different strategies involved in AMR, such as activation of a quiescent state of the cells, moderate increase in the expression of the efflux pump, decrease in the membrane potential, antimicrobial inactivation, and modification of the antimicrobial target and the architecture of the EPS matrix itself. There are few studies investigating the impact of the use of inhibitors on the mechanisms of recalcitrance and its impact on the microbiome. Therefore, more studies to elucidate the effect and applications of these methods in the food production chain and the possible combination with antimicrobials to establish new strategies to control MDR biofilms are needed.

Evaluation of the Stress Tolerance of Salmonella with Different Antibiotic Resistance Profiles

Disease caused by antibiotic-resistant Salmonella is a serious clinical problem that poses a great threat to public health. The present study is aimed at assessing differences in bacterial kinetics with different antibiotic resistance profiles under environmental stress and at developing microbial tolerance models in lettuce during storage from 4 to 36°C. The drug-resistance phenotypes of 10 Salmonella Typhimurium (S. Typhimurium) isolates were examined using the broth microdilution method. The results of 10 S. Typhimurium isolates in the suspensions showed that a slow trend towards reduction of drug-sensitive (DS) isolates in relation to the others though without statistical difference. Compared to DS S. Typhimurium SA62, greater bacterial reduction was observed in multidrug-resistant (MDR) S. Typhimurium HZC3 during lettuce storage at 4°C (P < 0.05). It was likely that a cross-response between antibiotic resistance and food-associated stress tolerance. The greater growth in lettuce at 12°C was observed for DS S. Typhimurium SA62 compared to MDR S. Typhimurium HZC3 and was even statistically different (P < 0.05), while no significant difference was observed for bacterial growth between MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 strains in lettuce storage from 16 to 36°C (P > 0.05). The goodness-of-fit indices indicated the Log-linear primary model provided a satisfactory fit to describe the MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 survival at 4°C. A square root secondary model could be used to describe the effect of temperature (12, 16, 28, and 36°C) on the growth rates of S. Typhimurium HZC3 (adj - R 2 = 0.91, RMSE = 0.06) and S. Typhimurium SA62 (adj - R 2 = 0.99, RMSE = 0.01) derived from the Huang primary model. It was necessary to pay attention to the tolerance of antibiotic resistant bacteria under environmental stress, and the generated models could provide parts of the input data for microbial risk assessment of Salmonella with different antibiotic resistance profile in lettuce.

Insights into Emergence of Antibiotic Resistance in Acid-Adapted Enterohaemorrhagic Escherichia coli

The emergence of multidrug-resistant pathogens presents a global challenge for treating and preventing disease spread through zoonotic transmission. The water and foodborne Enterohaemorrhagic Escherichia coli (EHEC) are capable of causing intestinal and systemic diseases. The root cause of the emergence of these strains is their metabolic adaptation to environmental stressors, especially acidic pH. Acid treatment is desired to kill pathogens, but the protective mechanisms employed by EHECs cross-protect against antimicrobial peptides and thus facilitate opportunities for survival and pathogenesis. In this review, we have discussed the correlation between acid tolerance and antibiotic resistance, highlighting the identification of novel targets for potential production of antimicrobial therapeutics. We have also summarized the molecular mechanisms used by acid-adapted EHECs, such as the two-component response systems mediating structural modifications, competitive inhibition, and efflux activation that facilitate cross-protection against antimicrobial compounds. Moving beyond the descriptive studies, this review highlights low pH stress as an emerging player in the development of cross-protection against antimicrobial agents. We have also described potential gene targets for innovative therapeutic approaches to overcome the risk of multidrug-resistant diseases in healthcare and industry.

Antibiotic-resistant bacteria and gut microbiome communities associated with wild-caught shrimp from the United States versus imported farm-raised retail shrimp

In the United States, farm-raised shrimp accounts for ~ 80% of the market share. Farmed shrimp are cultivated as monoculture and are susceptible to infections. The aquaculture industry is dependent on the application of antibiotics for disease prevention, resulting in the selection of antibiotic-resistant bacteria. We aimed to characterize the prevalence of antibiotic-resistant bacteria and gut microbiome communities in commercially available shrimp. Thirty-one raw and cooked shrimp samples were purchased from supermarkets in Florida and Georgia (U.S.) between March-September 2019. The samples were processed for the isolation of antibiotic-resistant bacteria, and isolates were characterized using an array of molecular and antibiotic susceptibility tests. Aerobic plate counts of the cooked samples (n = 13) varied from < 25 to 6.2 log CFU/g. Isolates obtained (n = 110) were spread across 18 genera, comprised of coliforms and opportunistic pathogens. Interestingly, isolates from cooked shrimp showed higher resistance towards chloramphenicol (18.6%) and tetracycline (20%), while those from raw shrimp exhibited low levels of resistance towards nalidixic acid (10%) and tetracycline (8.2%). Compared to wild-caught shrimp, the imported farm-raised shrimp harbored distinct gut microbiota communities and a higher prevalence of antibiotic-resistance genes in their gut. The presence of antibiotic-resistant strains in cooked shrimps calls for change in processing for their mitigation.

Transcriptome changes and polymyxin resistance of acid-adapted Escherichia coli O157:H7 ATCC 43889

Background

Acid treatment is commonly used for controlling or killing pathogenic microorganisms on medical devices and environments; however, inadequate acid treatment may cause acid tolerance response (ATR) and offer cross-protection against environmental stresses, including antimicrobials. This study aimed to characterise an Escherichia coli strain that can survive in the acidic gastrointestinal environment.

Results

We developed an acid-tolerant E. coli O157:H7 ATCC 43889 (ATCC 43889) strain that can survive at pH 2.75 via cell adaptation in low pH conditions. We also performed RNA sequencing and qRT-PCR to compare differentially expressed transcripts between acid-adapted and non-adapted cells. Genes related to stress resistance, including kdpA and bshA were upregulated in the acid-adapted ATCC 43889 strain. Furthermore, the polymyxin resistance gene arnA was upregulated in the acid-adapted cells, and resistance against polymyxin B and colistin (polymyxin E) was observed. As polymyxins are important antibiotics, effective against multidrug-resistant gram-negative bacterial infections, the emergence of polymyxin resistance in acid-adapted E. coli is a serious public health concern.

Conclusion

The transcriptomic and phenotypic changes analysed in this study during the adaptation of E. coli to acid environments can provide useful information for developing intervention technologies and mitigating the risk associated with the emergence and spread of antimicrobial resistance.

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY-Fullerene C60 Dyad as Potential Antimicrobial Agent

A covalently linked BODIPY-fullerene C₆₀ dyad (BDP-C₆₀ ) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C₆₀ to inactivate bacteria. The absorption spectrum of BDP-C₆₀ was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C₆₀ . Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP-C₆₀ exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP-C₆₀ turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP-C₆₀ is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.

Distribution of Transferable Antibiotic Resistance Genes in Laboratory-Reared Edible Mealworms (Tenebrio molitor L.)

In the present study, the distribution of antibiotic resistance genes in laboratory-reared fresh mealworm larvae (Tenebrio molitor L.), their feeding substrates (carrots and wheatmeal), and frass was assessed. Microbial counts on selective media added with antibiotics highlighted the presence of lactic acid bacteria resistant to ampicillin and vancomycin and, more specifically, enterococci resistant to the latter antibiotic. Moreover, staphylococci resistant to gentamicin, erythromycin, tetracycline, and vancomycin were detected. Enterobacteriaceae resistant to ampicillin and gentamicin were also found, together with Pseudomonadaceae resistant to gentamicin. Some of the genes coding for resistance to macrolide-lincosamide-streptogramin B (MLSB) [erm(A), erm(C)], vancomycin [vanA, vanB], tetracycline [tet(O)], and β-lactams [mecA and blaZ] were absent in all of the samples. For the feeding substrates, organic wheatmeal was positive for tet(S) and tet(K), whereas no AR genes were detected in organic carrots. The genes tet(M), tet(K), and tet(S) were detected in both mealworms and frass, whereas gene aac-aph, coding for resistance to amynoglicosides was exclusively detected in frass. No residues for any of the 64 antibiotics belonging to 10 different drug classes were found in either the organic wheatmeal or carrots. Based on the overall results, the contribution of feed to the occurrence of antibiotic resistance (AR) genes and/or antibiotic-resistant microorganisms in mealworm larvae was hypothesized together with vertical transmission via insect egg smearing.

Multidrug Resistance, Biofilm Formation, and Virulence of Escherichia coli Isolates from Commercial Meat and Vegetable Products

Escherichia coli is an important food safety and public health concern because of its pathogenicity and potential for antimicrobial resistance. E. coli isolates as food contaminants and their antimicrobial resistance, biofilm-forming ability, and virulence genes were analyzed to identify the potential of E. coli in food as a major transmission route for antimicrobial resistance and infectious agents. Among the 709 samples of minced meat and fresh vegetable products tested, 18.6% were positive for E. coli. One hundred nine (29.2%) out of 383 E. coli isolates were resistant to 1 or more of the 25 tested antimicrobials. Among the isolates from minced pork, the highest rate of resistance was observed for tetracycline (52.8%), followed by ampicillin (41.6%). The highest resistance rates against tetracycline were coincident with the high amount of tetracycline sold for veterinary use. Because penicillin is the most frequently used antimicrobial in humans, with 4.52 defined daily doses per 1000 people per day, the high rate of resistance to ampicillin (41.6%) supported the potential risk of E. coli food contaminants. However, only 1.3% of the isolates possessed the virulence genes commonly involved in foodborne outbreaks of E. coli. Sixty-seven isolates (17.5%) were multidrug-resistant (MDR), and the highest MDR was observed against 14 antimicrobials. Most of the MDR E. coli isolates showed biofilm-forming ability. Therefore, these isolates will have additional protection from environmental stresses, including antimicrobials. Given the importance of E. coli to food safety and public health, our results on the prevalence of antimicrobial resistance and virulence factors provide useful information for risk management options to protect public health.

Occurrence of transferable antibiotic resistances in commercialized ready-to-eat mealworms (Tenebrio molitor L.)

The present study aimed to assess the occurrence of transferable determinants conferring resistance to tetracyclines, macrolide-lincosamide-streptogramin B, vancomycin, beta-lactams, and aminoglycosides in 40 samples of commercialized edible mealworms (Tenebrio molitor L.) purchased from European Union (EU) and non-EU producers. A high prevalence of tet(K) was observed in all of the samples assayed, with percentages of PCR-based positivity that ranged from 80% (samples from Thailand) to 100% (samples from the Netherlands, Belgium and France). For macrolides, erm(B) prevailed, being detected in 57.5% of the samples assayed, whereas erm(A) and erm(C) were detected with lower frequencies. Genes for resistance to vancomycin were only detected in samples produced in France and Belgium, with 90% and 10% of the samples being positive for vanA, respectively. Beta-lactamase genes were found with low occurrence, whereas the gene aac-aph, conferring high resistance to aminoglycosides, was found in 40% of the samples produced in the Netherlands and Belgium and 20% of the samples produced in Thailand. The results of Principal Coordinate Analysis and Principal Component Analysis depicted a clean separation of the samples collected from the four producers based on the distribution of the 12 AR determinants considered. Given the growing interest on the use of mealworms as a novel protein source, AR detection frequencies found in the present study suggest further investigation into the use of antibiotics during rearing of this insect species and more extensive studies focused on the factors that can affect the diffusion of transferable ARs in the production chain. Until such studies are completed, prudent use of antibiotics during rearing of edible insects is recommended.