Levels of antibiotic resistance genes (ARGs) and the fractions of antibiotic resistant bacteria (ARB) among culturable heterotrophic bacteria were compared in outdoor air near conventional (n = 3) and organic (n = 3) cattle rearing facilities. DNA extracts from filters taken from 18 locations were analyzed by quantitative polymerase chain reaction (qPCR) for five ARGs. At the reference (non-agricultural) site, all genes were below detection. ARGs sul1, bla SHV, erm(B), and bla TEM were more frequently detected and at higher levels (up to 870 copies m⁻³ for bla SHV and 750 copies m⁻³ for sul1) near conventional farms compared to organic locations while the opposite was observed for erm(F) (up to 210 copies m⁻³). Isolates of airborne heterotrophic bacteria (n = 1295) collected from the sites were tested for growth in the presence of six antibiotics. By disk diffusion on a subset of isolates, the fractions of ARB were higher for conventional sites compared to organic farms for penicillin (0.9 versus 0.63), cloxacillin (0.74 versus 0.23), cefoperazone (0.58 versus 0.14), and sulfamethazine (0.50 versus 0.33) for isolates on nutrient agar. All isolates’ ΔA600ₚᵣₑₛ/ΔA600ₐbₛ were measured for each of the six tested antibiotics; isolates from farms downwind of organic sites had a lower average ΔA600ₚᵣₑₛ/ΔA600ₐbₛ for most antibiotics. In general, all three analyses used to indicate microbial resistance to antibiotics showed increases in air samples nearby conventional versus organic cattle rearing facilities. Regular surveillance of airborne ARB and ARGs near conventional and organic beef cattle farms is suggested.

Listeria monocytogenes (L. monocytogenes) is frequently detected in ruminants, especially dairy cattle, and associated with the sporadic and epidemic outbreak of listeriosis in farms. In this epidemiological study, the prevalence, virulence, antibiotic resistance profiles, and genetic diversity of L. monocytogenes in three Egyptian dairy cattle farms were investigated. The risk factors associated with the fecal shedding of L. monocytogenes were analyzed. The L. monocytogenes strains from the three farms were categorized into distinct genotypes based on sampling site and sample type through enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). A total of 1896 samples were collected from animals, environments, and milking equipment in the three farms. Results revealed that 137 (7.23%) of these samples were L. monocytogenes positive. The prevalence of L. monocytogenes in the animal samples was high (32.1%), and the main environmental source of prevalent genotypes in the three farms was silage. For all sample types, L. monocytogenes was more prevalent in farm I than in farms II and III. Risk factor analysis showed seasonal variation in production hygiene. For all sample types, L. monocytogenes was significantly more prevalent in winter than in spring and summer. The level of L. monocytogenes fecal shedding was high likely because of increasing age, number of parities, and milk yield in dairy cattle. Two virulence genes, namely, hlyA & prfA, were also detected in 93 strains, whereas only one of these genes was found in 44 residual strains. Conversely, iap was completely absent in all strains. The strains exhibited phenotypic resistance to most of the tested antibiotics, but none of them was resistant to netilmicin or vancomycin. According to sample type, the strains from the animal samples were extremely resistant to amoxicillin (95.2%, 80/84) and cloxacillin (92.9%, 78/84). By comparison, the strains from the environmental samples were highly resistant to cefotaxime (86.95%, 20/23). Furthermore, 25 multi-antibiotic resistance (MAR) patterns were observed in L. monocytogenes strains. All strains had a MAR index of 0.22–0.78 and harbored antibiotic resistance genes, including extended-spectrum β-lactamase (blaCTX-M [92.7%] and blaDHA-1 [66.4%]), quinolones (qnrS [91.2%], qnrA [58.4%], parC [58.4%], and qnrB [51%]), macrolides (erm[B] [76.6%], erm(C) [1.5%], and msr(A) [27%]), trimethoprim (dfrD [65.7%]), and tetracyclines (tet(M) [41.6%], tet(S) [8%], and int-Tn [26.3%]). ERIC-PCR confirmed that the strains were genetically diverse and heterogeneous. A total of 137 isolated L. monocytogenes strains were classified into 22 distinct ERIC-PCR groups (A–V). Among them, ERIC E (10.2%) was the most prevalent group. These results indicated that environment and milking equipment served as reservoirs and potential transmission ways of virulent and multidrug-resistant L. monocytogenes to dairy animals, consequently posing threats to public health. Silage is the main environmental source of prevalent genotypes on all three farms. Therefore, hygienic measures at the farm level should be developed and implemented to reduce L. monocytogenes transmission inside dairy cattle farms.

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO₂ photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO₂ photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO₂ anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO₂ photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240 min, the TiO₂ photocatalysis and photo-Fenton processes achieved ∼45 and ∼15 % of mineralization, respectively. During the electrochemical treatment, 100 % of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO₂ photocatalysis.

This work studies the degradation of seven representative antibiotics (ciprofloxacin, norfloxacin, levofloxacin, oxacillin, cloxacillin, cefalexin, and cefadroxil) by solar photo-Fenton process. The removal of antibiotics by the individual components (i.e., light, H₂O₂, or Fe (II)) and the complete photochemical system (light/H₂O₂/Fe (II)) was initially evaluated. Then, the effect of citric acid addition to the photo-Fenton system was assessed. In the third place, the primary transformation products for two illustrative cases (ciprofloxacin and oxacillin treated by photo-Fenton) were determined. Also, photo-Fenton in the presence of citric acid was applied to remove antibiotics from a simulated hospital wastewater. It was found that the solar light component induced degradation of ciprofloxacin, norfloxacin, and levofloxacin, but the rest of the considered antibiotics were not reduced by photolysis. In turn, the photo-Fenton system showed a degrading action on all the tested antibiotics. The addition of citric acid to the system significantly increased the removal of antibiotics. Initial degradation products indicated that hydroxyl radical attacked moieties of antibiotics responsible for their antimicrobial activity. Finally, the treatment of hospital wastewater evidenced the high potentiality of photo-Fenton process for degrading antibiotics in aqueous matrices containing elevated concentrations of citric acid.