Metagenomics reveals the resistance patterns of electrochemically treated erythromycin fermentation residue.

Erythromycin fermentation residue (EFR) represents a typical hazardous waste produced by the microbial pharmaceutical industry. Although electrolysis is promising for EFR disposal, its microbial threats remain unclear. Herein, metagenomics was coupled with the random forest technique to decipher the antibiotic resistance patterns of electrochemically treated EFR. Results showed that 95.75% of erythromycin could be removed in 2 hr. Electrolysis temporarily influenced EFR microbiota, where the relative abundances of Proteobacteria and Actinobacteria increased, while those of Fusobacteria, Firmicutes, and Bacteroidetes decreased. A total of 505 antibiotic resistance gene (ARG) subtypes encoding resistance to 21 antibiotic types and 150 mobile genetic elements (MGEs), mainly including plasmid (72) and transposase (52) were assembled in EFR. Significant linear regression models were identified among microbial richness, ARG subtypes, and MGE numbers (r2=0.50-0.81, p< 0.001). Physicochemical factors of EFR (Total nitrogen, total organic carbon, protein, and humus) regulated ARG and MGE assembly (%IncMSE value = 5.14-14.85). The core ARG, MGE, and microbe sets (93.08%-99.85%) successfully explained 89.71%-92.92% of total ARG and MGE abundances. Specifically, gene aph(3')-I, transposase tnpA, and Mycolicibacterium were the primary drivers of the resistance dissemination system. This study also proposes efficient resistance mitigation measures, and provides recommendations for future management of antibiotic fermentation residue.

Clinical observation of topical antipruritic spray acting on epidermal growth factor receptor tyrosine kinase inhibitor in the treatment of dermatitis.

To observe the efficacy of topical antipruritic spray (TAS) in the treatment of epidermal growth factor receptor (EGFR) tyrosine kinase-related rashes, and to evaluate its efficacy and safety. 120 malignant tumor patients with confirmed pathological diagnosis and rash after EGFR application were selected and randomly divided into an experimental group of 60 cases and a control group of 60 cases. The 2 groups were intervened with self-made antipruritic spray and erythromycin ointment for 14 consecutive days. To observe the changes in rash, itching degree, and quality of life index of skin diseases in both groups of patients before and after treatment. The decrease in the number of itching cases in the experimental group reached 53.84%, and after 7 weeks of intervention, the total effective rate of rash treatment in this group of patients (91.67%) was significantly better than that in the control group (36.67%); The symptoms of the dermatology life quality index (DLQI) scale in the experimental group patient table after intervention showed significant changes compared to before intervention. After statistical testing, there was a significant difference between the groups and outside the group (R < 0.05). And the comprehensive effect of the experimental patients with external spray after 14 weeks of intervention reached 93.16%. The self-made antipruritic spray has significant effect on improving EGFR rash and itching, and there is no obvious adverse reaction.

Does exposure timing of macrolide antibiotics affect the development of river periphyton? Insights into the structure and function.

Discharged sewage is the dominant source of urban river pollution. Macrolide antibiotics have emerged as prominent contaminants, which are frequently detected in sewage and rivers and pose a threat to aquatic microbial community. As a typical primary producer, periphyton is crucial for maintaining the biodiversity and functions of aquatic ecosystem. However, effects of antibiotic exposure time as well as the recovery process of periphyton remain undetermined. In the present study, five exposure scenarios of two typical macrolides, erythromycin (ERY) and roxithromycin (ROX) were investigated at 50 µg/L, dose to evaluate their potential detrimental effects on the structure and function of periphyton and the subsequent recovery process in 14 days. Results revealed that the composition of periphytic community returned to normal over the recovery period, except for a few sensitive species. The antibiotics-caused significant photodamage to photosystem II, leading to continuous inhibition of the photosynthetic capacity of periphyton. Furthermore, no significant difference in carbon metabolism capacity was observed after direct antibiotic exposure, while the amine carbon utilization capacity of periphyton remarkably increased during the recovery process. These results indicated that periphyton community was capable of coping with the periodic exposure of antibiotic pollutants and recovering on its own. However, the ecological functions of periphyton can be permanently disturbed due to macrolide exposure. Overall, this study sheds light on the influence of macrolide exposure on the development, structure and function of the periphytic microbial community in rivers.

Inducible clindamycin-resistant and biofilm formation in the Staphylococcus aureus isolated from healthcare worker's anterior nasal carriage.

OBJECTIVE: The purpose of this study is a new update on the resistance profile, Macrolide-Lincosamide-Streptogramin B resistance mechanisms and biofilm formation in the Staphylococcus aureus isolated from health care workers (HCWs) nasal carriage at a children's teaching hospital in Babol (Northern Iran). RESULTS: A total of 143 non-repetitive nasal swab samples were collected from volunteers, where 53.8% (n; 77/143) were HCWs, 33.6% (n; 48/143) medical students, and 12.6% (n; 18/143) resident students. The prevalence of nasal carriers of S. aureus was 22.4% (n; 32/143), among them, 40.6% (n; 13/32) were identified as methicillin-resistant Staphylococcus aureus (MRSA( carriers. Antimicrobial susceptibility testing showed that erythromycin (68.8%, n; 22/32) and ciprofloxacin (15.6%, n; 5/32) had the highest and lowest resistance rate, respectively. The frequency of resistance genes in the strains was as follows; ermC (n; 17/32, 53.1%), ermA (n; 11/32, 34.4%), ermB (n; 6/32, 18.7%), ereA (n; 3/32, 9.4%). Moreover, 50.0% (n; 16/32), 28.1% (n; 9/32) and 21.8% (n; 7/32) of isolates were strongly, weakly and moderately biofilm producer, respectively. Macrolides-lincosamides-streptogramins B (MLSB) antibiotic resistance among S. aureus isolates from HCWs nasal carriage have found significant prevalence rates throughout the globe. It is crucial to remember that the development of biofilms and MLS B antibiotic resistance are both dynamic processes.

Erythromycin disrupts Acinetobacter baumannii biofilms through destruction of the quorum sensing system.

BACKGROUND: This study was conducted to explore the effects of erythromycin on biofilms comprising Acinetobacter baumannii (A baumannii). METHODS: To clarify the effect of erythromycin on the biofilms of A baumannii, we collected pure Ab strains isolated and identified from a variety of sample types extracted from patients in the microbiological laboratory of our hospital from April to August 2023, and divided them into an experimental group (treated with erythromycin) and a control group (without erythromycin). The morphology and quantity of A baumannii biofilm were observed at 24h, 48h, 72h, and 5d post-treatment, respectively, and the expression of quorum sensing (QS) system gene (abaI, abaR) mRNA was detected by fluorescence quantitative PCR. RESULTS: The results showed that A baumanniis are prone to form multiple drug-resistant (MDR) bacteria, against which the most commonly used clinical antibiotics are ineffective. Overall, we found that the number of bacteria, the number of bacteria in the biofilm, and the number of biofilms formed gradually increased over time, with a statistical difference (P < .05). After the addition of erythromycin, significant improvements in biofilm formation were achieved, indicating that erythromycin can destroy A baumannii biofilms, inhibiting bacterial growth to a certain extent. The expression levels of abaI and abaR gradually increased over time, indicating that the role of the QS system became more apparent over time. Biofilm formation is related to the QS system of A baumanniis. After erythromycin treatment, abaI and abaR mRNA expression was downregulated in the experimental group. CONCLUSION: Erythromycin disrupts A baumannii biofilms by destroying the quorum sensing system.

Portable smartphone-assisted amperometric immunosensor based on CoCe-layered double hydroxide for rapidly immunosensing erythromycin.

Herein, we have manufactured a newly designed bifunctional impedimetric and amperometric immunosensor for rapidly detecting erythromycin (ERY) in complicated environments and food stuffs. For this, bimetallic cobalt/cerium-layered double hydroxide nanosheets (CoCe-LDH NSs), which was derived from Co-based zeolite imidazole framework via the structure conversion, was simultaneously utilized as the bioplatform for anchoring the ERY-targeted antibody and for modifying the gold and screen printed electrode. Basic characterizations revealed that CoCe-LDH NSs was composed of mixed metal valences, enrich redox, and abundant oxygen vacancies, facilitating the adhesion on the electrode, the antibody adsorption, and the electron transfers. The manufactured impedimetric and amperometric immunosensor based on CoCe-LDH has showed the comparable sensing performance, having a wide linear detection range from 1.0 fg mL-1 to 1.0 ng mL-1 with the ultralow detection limit toward ERY. Also, the portable, visualized, and efficient analysis of ERY was then attained at the smartphone-assisted CoCe-LDH-based SPE.

Exploring naphthoquinone and anthraquinone derivatives as antibiotic adjuvants against Staphylococcus aureus biofilms: Synergistic effects of menadione.

Given the ability of Staphylococcus aureus to form biofilms and produce persister cells, making infections difficult to treat with antibiotics alone, there is a pressing need for an effective antibiotic adjuvant to address this public health threat. In this study, a series of quinone derivatives were evaluated for their antimicrobial and antibiofilm activities against methicillin-susceptible and methicillin-resistant S. aureus reference strains. Following analyses using broth microdilution, growth curve analysis, checkerboard assay, time-kill experiments, and confocal laser scanning microscopy, menadione was identified as a hit compound. Menadione exhibited a notable antibacterial profile (minimum inhibitory concentration, MIC = 4-16 µg/ml; minimum bactericidal concentration, MBC = 256 µg/ml) against planktonic S. aureus and its biofilms (minimum biofilm inhibitory concentration, MBIC50 = 0.0625-0.25 µg/ml). When combined with oxacillin, erythromycin, and vancomycin, menadione exhibited a synergistic or additive effect against planktonic cells and biofilms of two S. aureus reference strains and six clinical isolates, highlighting its potential as a suitable adjuvant for further development against S. aureus biofilm-associated infections.

Assessing and harnessing updated polyketide synthase modules through combinatorial engineering.

The modular nature of polyketide assembly lines and the significance of their products make them prime targets for combinatorial engineering. The recently updated module boundary has been successful for engineering short synthases, yet larger synthases constructed using the updated boundary have not been investigated. Here we describe our design and implementation of a BioBricks-like platform to rapidly construct 5 triketide, 25 tetraketide, and 125 pentaketide synthases to test every module combination of the pikromycin synthase. Anticipated products are detected from 60% of the triketide synthases, 32% of the tetraketide synthases, and 6.4% of the pentaketide synthases. We determine ketosynthase gatekeeping and module-skipping are the principal impediments to obtaining functional synthases. The platform is also employed to construct active hybrid synthases by incorporating modules from the erythromycin, spinosyn, and rapamycin assembly lines. The relaxed gatekeeping of a ketosynthase in the rapamycin synthase is especially encouraging in the quest to produce designer polyketides.

Effect of Stepwise Exposure to High-Level Erythromycin on Anaerobic Digestion.

High-level erythromycin (ERY) fermentation wastewater will pose serious threats to lake environments. Anaerobic digestion (AD) has advantages in treating high-level antibiotic wastewater. However, the fate of antibiotic resistance genes (ARGs) and microbial communities in AD after stepwise exposure to high-level ERY remains unclear. In this study, an AD reactor was first exposed to 0, 5, 10, 50, 100 and 200 mg/L ERY and then re-exposed to 0, 50, 200 and 500 mg/L ERY to investigate the effect of ERY on AD. The results show that AD could adapt to the presence of high-level ERY (500 mg/L) and could maintain efficient CH4 production after domestication with low-level ERY (50 mg/L). The AD process could achieve higher removal of ERY (>94%), regardless of the initial ERY concentration. ErmB and mefA, conferring resistance through target alteration and efflux pumps, respectively, were dominant in the AD process. The first exposure to ERY stimulated an increase in the total ARG abundance, while the AD process seemed to discourage ARG maintenance following re-exposure to ERY. ERY inhibited the process of acetoclastic methanogenesis, but strengthened the process of hydrogenotrophic methanogenesis. This work provides useful information for treating high-level ERY fermentation wastewater by the AD process.

Fabrication of graphitic carbon nitride/gum Arabic/potassium carrageenan composite for efficient adsorption of erythromycin: Kinetic and thermodynamic studies.

Erythromycin (ERY) molecules are robust to the environment and hard to remove due to their aromatic structure. Nowadays, numerous researches have reported that the ERY amount in water is above the standard level and its removal is necessary. Here, we prepared three solid adsorbents: graphitic carbon nitride (g-C3N4), potassium carrageenan beads (Cr), and graphitic carbon nitride/gum Arabic/potassium carrageenan composite (g-ACr). Several techniques such as XRD, SEM, TEM, TGA, ATR-FTIR, Zeta potential, and N2 adsorption were employed to characterize the fabricated adsorbents. Five essential factors of adsorbent dose, initial ERY concentration, contact time, temperature, and pH were optimized to investigate the batch adsorption of ERY. The maximum adsorption capacity of 356.12 mg/g was attained by g-ACr composite at an adsorbent dose of 1.25 g/L, contact time of 6 h, and pH 7 at 15 °C. The data showed that the experimental findings exhibited the best agreement with Langmuir, Temkin, and DR isotherm models, in addition to the kinetic models of pseudo-second-order, Elovich, and intra-particle diffusion. The evaluated thermodynamic factors designated that the ERY adsorption is endothermic, physisorption, favorable, and spontaneous process. The g-ACr reusability displayed a decline in the adsorption capacity after seven adsorption/desorption runs by 5.7 %. Finally, this work outcomes depict that g-ACr composite is an efficient reusable adsorbent for ERY elimination from wastewater.

Cryo-EM structures reveal the molecular mechanism of HflX-mediated erythromycin resistance in mycobacteria.

Mycobacterial HflX confers resistance against macrolide antibiotics. However, the exact molecular mechanism is poorly understood. To gain further insights, we determined the cryo-EM structures of M. smegmatis (Msm) HflX-50S subunit and 50S subunit-erythromycin (ERY) complexes at a global resolution of approximately 3 Å. A conserved nucleotide A2286 at the gate of nascent peptide exit tunnel (NPET) adopts a swayed conformation in HflX-50S complex and interacts with a loop within the linker helical (LH) domain of MsmHflX that contains an additional 9 residues insertion. Interestingly, the swaying of this nucleotide, which is usually found in the non-swayed conformation, is induced by erythromycin binding. Furthermore, we observed that erythromycin decreases HflX's ribosome-dependent GTP hydrolysis, resulting in its enhanced binding and anti-association activity on the 50S subunit. Our findings reveal how mycobacterial HflX senses the presence of macrolides at the peptide tunnel entrance and confers antibiotic resistance in mycobacteria.

A phase II, multicenter, nonblinded, randomized controlled trial for evaluating protective effects of ABPC/SBT plus, azithromycin versus erythromycin, in pregnant women with pPROM occurring at <28 weeks of gestation on the development of BPD in neonates: Study protocol.

This is a protocol for PPROM-AZM Study, phase II, nonblinded, randomized controlled trial. Bronchopulmonary dysplasia (BPD) at a postmenstrual age of 36 weeks (BPD36) is often observed in infants with preterm premature rupture of the membranes (pPROM). A regimen of ampicillin (ABPC) intravenous infusion for 2 days and subsequent amoxicillin (AMPC) oral administration for 5 days plus erythromycin (EM) intravenous infusion for 2 days followed by EM oral administration for 5 days is standard treatment for pPROM. However, the effect on the prevention of moderate/severe BPD36 using the standard treatment has not been confirmed. Recently, it is reported that ampicillin/sulbactam (ABPC/SBT) plus azithromycin (AZM) was effective for the prevention of moderate/severe BPD36 in pPROM patients with amniotic infection of Ureaplasma species. Therefore, our aim is to evaluate the occurrence rate of the composite outcome of "incidence rate of either moderate/severe BPD36 or intrauterine fetal death, and infantile death at or less than 36 weeks 0 days" comparing subjects to receive ABPC/SBT for 14 days plus AZM for 14 days (intervention group) and those to receive ABPC/SBT for 14 days plus EM for 14 days (control group), in a total of 100 subjects (women with pPROM occurring at 22-27 weeks of gestation) in Japan. The recruit of subjects was started on April 2022, and collection in on-going. We also investigate the association between the detection of Ureaplasma species and occurrence of BPD36. In addition, information on any adverse events for the mother and fetus and serious adverse events for infants are collected during the observation period. We allocate patients at a rate of 1:1 considering two stratification factors: onset of pPROM (22-23 or 24-27 weeks) and presence/absence of a hospital policy for early neonatal administration of caffeine. Trial registration: The trial number in the Japan Registry of Clinical Trials is jRCTs031210631.

Therapeutic Efficacy of an Erythromycin-Loaded Coaxial Nanofiber Coating in a Rat Model of S. aureus-Induced Periprosthetic Joint Infection.

Implant surface nanofiber (NF) coatings represent an alternative way to prevent/treat periprosthetic joint infection (PJI) via local drug release. We developed and characterized a coaxial erythromycin (EM)-doped PLGA/PCL-PVA NF coating. The purpose of this study was to determine the efficacy of EM-NF coatings (EM0, no EM, EM100 (100 mg/mL), and EM1000 (1000 mg/mL) wt/wt) in a rat PJI model. A strong bond of the EM-NF coating to the surface of titanium (Ti) pins was confirmed by in vitro mechanical testing. Micro-computed tomography (mCT) analysis showed that both EM100 and EM1000 NF effectively reduced periprosthetic osteolysis compared to EM0 at 8 and 16 weeks after implantation. Histology showed that EM100 and EM1000 coatings effectively controlled infection and enhanced periprosthetic new bone formation. The bone implant contact (BIC) of EM100 (35.08%) was higher than negative controls and EM0 (3.43% and 0%, respectively). The bone area fraction occupancy (BAFO) of EM100 (0.63 mm2) was greater than controls and EM0 (0.390 mm2 and 0.0 mm2, respectively). The BAFO of EM100 was higher than that of EM1000 (0.3 mm2). These findings may provide a basis for a new implant surface fabrication strategy aimed at reducing the risks of defective osseointegration and PJI.

Tracking trends in the Top End: clindamycin and erythromycin resistance in Group A Streptococcus in the Northern Territory, 2012-2023.

Abstract: This retrospective study reviewed the macrolide resistance rates of Group A Streptococcus (GAS) isolates in the Northern Territory from 2012 to 2023. Clindamycin and erythromycin resistance rates peaked in 2021, at 6.0% and 12.2% respectively, and then returned to near baseline at 1-2% in 2023. Increased resistance rates were identified in the Top End of Australia from mid-2020, followed 15 months later by high rates in central Australia in 2022. Factors associated with resistant isolates were living in a rural region and of age 18 years and older. Possible explanations include a transient clonal introduction of a resistant GAS strain to the Northern Territory from 2020 to 2022. Ongoing surveillance is required to monitor regional trends and identify temporal variations in resistant isolates.

[Occurrence and environmental risks of antibiotics in surface water of China].

Antibiotics as emerging pollutants are frequently detected in surface water, raising concerns about the associated risk of antibiotic resistance genes (ARGs). Despite the widespread apprehension, there are still research gaps in the occurrence of antibiotic pollution in surface water and the associated ecological risks to aquatic organisms in China. Here, we established a dataset of antibiotic pollution in surface water in China during 2018-2022, which encompassed 3 368 concentration values of 128 antibiotics reported in 124 articles. Our analysis showed that antibiotic concentrations were predominantly in the ng/L-µg/L range, reaching up to 26 µg/L. Notably, sulfonamides (e.g., sulfamethoxazole) and quinolones (e.g., ciprofloxacin) were frequently reported at high concentrations. The pollution degree of antibiotics represented by sulfamethoxazole, ciprofloxacin, roxithromycin, and tetracycline exhibited no significant variation across different years but was lower in summer than that in spring and autumn. Additionally, distinct spatial distribution characteristics of the pollution were observed. According to calculation results of the aquatic ecological risk assessment model and the weighted frequency, we proposed a list of priority antibiotics including clarithromycin, erythromycin, sulfamethoxazole, ofloxacin, and oxytetracycline in surface water. Last but not least, this study points out the deficiencies in current research on the occurrence and ecological risks of antibiotics in surface water of China and provides viable screening strategies and monitoring recommendations in this context.

Machine learning-based classification reveals distinct clusters of non-coding genomic allelic variations associated with Erm-mediated antibiotic resistance.

The erythromycin resistance RNA methyltransferase (erm) confers cross-resistance to all therapeutically important macrolides, lincosamides, and streptogramins (MLS phenotype). The expression of erm is often induced by the macrolide-mediated ribosome stalling in the upstream co-transcribed leader sequence, thereby triggering a conformational switch of the intergenic RNA hairpins to allow the translational initiation of erm. We investigated the evolutionary emergence of the upstream erm regulatory elements and the impact of allelic variation on erm expression and the MLS phenotype. Through systematic profiling of the upstream regulatory sequences across all known erm operons, we observed that specific erm subfamilies, such as ermB and ermC, have independently evolved distinct configurations of small upstream ORFs and palindromic repeats. A population-wide genomic analysis of the upstream ermB regions revealed substantial non-random allelic variation at numerous positions. Utilizing machine learning-based classification coupled with RNA structure modeling, we found that many alleles cooperatively influence the stability of alternative RNA hairpin structures formed by the palindromic repeats, which, in turn, affects the inducibility of ermB expression and MLS phenotypes. Subsequent experimental validation of 11 randomly selected variants demonstrated an impressive 91% accuracy in predicting MLS phenotypes. Furthermore, we uncovered a mixed distribution of MLS-sensitive and MLS-resistant ermB loci within the evolutionary tree, indicating repeated and independent evolution of MLS resistance. Taken together, this study not only elucidates the evolutionary processes driving the emergence and development of MLS resistance but also highlights the potential of using non-coding genomic allele data to predict antibiotic resistance phenotypes. IMPORTANCE: Antibiotic resistance (AR) poses a global health threat as the efficacy of available antibiotics has rapidly eroded due to the widespread transmission of AR genes. Using Erm-dependent MLS resistance as a model, this study highlights the significance of non-coding genomic allelic variations. Through a comprehensive analysis of upstream regulatory elements within the erm family, we elucidated the evolutionary emergence and development of AR mechanisms. Leveraging population-wide machine learning (ML)-based genomic analysis, we transformed substantial non-random allelic variations into discernible clusters of elements, enabling precise prediction of MLS phenotypes from non-coding regions. These findings offer deeper insight into AR evolution and demonstrate the potential of harnessing non-coding genomic allele data for accurately predicting AR phenotypes.

CRISPR/Cas9-Mediated Promoter Engineering in Saccharopolyspora erythraea.

In situ promoter engineering is an effective way to alter target gene expression without introducing excess DNA sequences. Recently, the CRISPR/Cas9 technologies have been proved to be efficient tools for genome editing in actinomycetes, making it easier and more efficient to perform gene insertion and substitution in actinomycetes in a scarless manner. In this chapter, we describe a routine protocol for CRISPR/Cas9-mediated promoter engineering in Saccharopolyspora erythraea NRRL 23338, which is the wild-type producer of erythromycin. This protocol can be adapted to CRISPR/Cas9-mediated gene editing, not limited to promoter engineering, in other actinomycetes, with modifications.

Implementation of temporal moments to elucidate the reactive transport of metformin and erythromycin in the saturated porous media.

This study investigates the fate and transport dynamics of metformin (MTN) and erythromycin (ETM), both classified as pharmaceutical and personal care products (PPCPs), in a saturated sandy soil column using temporal moment analysis (TMA). The key flow and transport parameters, including Darcy velocity, longitudinal dispersivity, adsorption, and degradation coefficients, were analyzed. The results reveal that MTN, a highly mobile contaminant, is eliminated from the column in approximately 40 days, while ETM shows significant adsorption due to its hydrophobic and adsorptive nature. Darcy velocity significantly affects PPCP transport; a one-order magnitude change alters contaminant mass recovery at the column outlet by 88% for MTN and 39-fold for ETM. Longitudinal dispersivity has minimal impact on the transport of PPCPs. However adsorption primarily governs the fate of PPCPs with high adsorption coefficients (Kd), and degradation rates control the fate of low-sorbing PPCPs. A one-order magnitude change in Kd results in a 55% change in the zeroth temporal moment (ZTM) of MTN and a 30-fold change in the case of ETM. Additionally, a one-order magnitude change in the degradation coefficient leads to a 60% variation in MTN's ZTM and a 5% variation in ETM's ZTM. Thus, TMA is a valuable tool for understanding PPCP dynamics in subsurface environments, providing critical insights for managing their increasing concentrations.

Activated carbon adsorption for mitigating the harmful effects of antibiotics on the biological activated sludge: Effect on heterotrophic kinetics through respirometry.

Conventional wastewater treatment plants (WWTPs) are not designed for the abatement of antibiotics, and their effluents are one of the main entry ways of these emerging contaminants to the aquatic environment, causing major concern due to their toxicity, persistence, and bioaccumulation. When wastewater containing antibiotics enters the bioreactor, they can impact microbial communities of the activated sludge, affecting biodegradation processes of organic matter and nutrients. There is scarce information about the effect of activated carbon on the activated sludge within the bioreactor in presence of antibiotics. In light of this, the effect of representative antibiotics, ciprofloxacin (CIP), nalidixic acid (NAL), and erythromycin (ERY), on the performance of a conventional activated sludge of a WWTP was analyzed by respirometry with and without activated carbon. NAL and ERY negatively affected the net heterotrophic biomass growth rate (r'x,H), with reduction percentages of 26%-90% and 31%-81%, respectively. The addition of activated carbon mitigated this effect, especially for ERY, with increments of even 8% in the r'x,H for the hybrid process when working with 5 ppm of ERY and 80 ppm of activated carbon compared with the value in the absence of antibiotic and activated carbon. This effect was attributed to the enhanced retention of ERY, in comparison to NAL, on the surface of the activated carbon, probably due to its higher molecular size and affinity towards the activated carbon (log Kow = 3.06). This effect was more marked at low sludge retention times (below 8 days). PRACTITIONER POINTS: Ciprofloxacin (CIP), nalidixic acid (NAL), and erythromycin (ERY) were studied. NAL and ERY exerted negative impact on heterotrophic growth rate. Effect of antibiotics on microorganisms in the presence of activated carbon was studied. Activated carbon was mainly relevant for ERY due to its adsorption retention. Enhancement by activated carbon was more significant at low sludge retention times.

Effect of erythromycin residuals in food on the development of resistance in Streptococcus pneumoniae: an in vivo study in Galleria mellonella.

Background: The use of antimicrobials to treat food animals may result in antimicrobial residues in foodstuffs of animal origin. The European Medicines Association (EMA) and World Health Organization (WHO) define safe antimicrobial concentrations in food based on acceptable daily intakes (ADIs). It is unknown if ADI doses of antimicrobials in food could influence the antimicrobial susceptibility of human-associated bacteria. Objectives: This aim of this study was to evaluate if the consumption of ADI doses of erythromycin could select for erythromycin resistance in a Galleria mellonella model of Streptococcus pneumoniae infection. Methods: A chronic model of S. pneumoniae infection in G. mellonella larvae was used for the experiment. Inoculation of larvae with S. pneumoniae was followed by injections of erythromycin ADI doses (0.0875 and 0.012 µg/ml according to EMA and WHO, respectively). Isolation of S. pneumoniae colonies was then performed on selective agar plates. Minimum inhibitory concentrations (MICs) of resistant colonies were measured, and whole genome sequencing (WGS) was performed followed by variant calling to determine the genetic modifications. Results: Exposure to single doses of both EMA and WHO ADI doses of erythromycin resulted in the emergence of erythromycin resistance in S. pneumoniae. Emergent resistance to erythromycin was associated with a mutation in rplA, which codes for the L1 ribosomal protein and has been linked to macrolide resistance in previous studies. Conclusion: In our in vivo model, even single doses of erythromycin that are classified as acceptable by the WHO and EMA induced significant increases in erythromycin MICs in S. pneumoniae. These results suggest the need to include the induction of antimicrobial resistance (AMR) as a significant criterion for determining ADIs.