The Response of Pseudomonas aeruginosa PAO1 to UV-activated Titanium Dioxide/Silica Nanotubes.

Pseudomonas aeruginosa is a bacterium of high clinical and biotechnological importance thanks to its high adaptability to environmental conditions. The increasing incidence of antibiotic-resistant strains has created a need for alternative methods to increase the chance of recovery in infected patients. Various nanomaterials have the potential to be used for this purpose. Therefore, we aimed to study the physiological response of P. aeruginosa PAO1 to titanium dioxide/silica nanotubes. The results suggest that UV light-irradiated nanomaterial triggers strong agglomeration in the studied bacteria that was confirmed by microscopy, spectrophotometry, and flow cytometry. The effect was diminished when the nanomaterial was applied without initial irradiation, with UV light indicating that the creation of reactive oxygen species could play a role in this phenomenon. The nanocomposite also affected biofilm formation ability. Even though the biomass of biofilms was comparable, the viability of cells in biofilms was upregulated in 48-hour biofilms. Furthermore, from six selected genes, the mexA coding efflux pump was upregulated, which could be associated with an interaction with TiO2. The results show that titanium dioxide/silica nanotubes may alter the physiological and metabolic functions of P. aeruginosa PAO1.

Chitinase Expression in Listeria monocytogenes Is Influenced by lmo0327, Which Encodes an Internalin-Like Protein.

The chitinolytic system of Listeria monocytogenes thus far comprises two chitinases, ChiA and ChiB, and a lytic polysaccharide monooxygenase, Lmo2467. The role of the system in the bacterium appears to be pleiotropic, as besides mediating the hydrolysis of chitin, the second most ubiquitous carbohydrate in nature, the chitinases have been deemed important for the colonization of unicellular molds, as well as mammalian hosts. To identify additional components of the chitinolytic system, we screened a transposon mutant library for mutants exhibiting impaired chitin hydrolysis. The screening yielded a mutant with a transposon insertion in a locus corresponding to lmo0327 of the EGD-e strain. lmo0327 encodes a large (1,349 amino acids [aa]) cell wall-associated protein that has been proposed to possess murein hydrolase activity. The single inactivation of lmo0327, as well as of lmo0325 that codes for a putative transcriptional regulator functionally related to lmo0327, led to an almost complete abolishment of chitinolytic activity. The effect could be traced at the transcriptional level, as both chiA and chiB transcripts were dramatically decreased in the lmo0327 mutant. In accordance with that, we could barely detect ChiA and ChiB in the culture supernatants of the mutant strain. Our results provide new information regarding the function of the lmo0325-lmo0327 locus in L. monocytogenes and link it to the expression of chitinolytic activity.IMPORTANCE Many bacteria from terrestrial and marine environments express chitinase activities enabling them to utilize chitin as the sole source of carbon and nitrogen. Interestingly, several bacterial chitinases may also be involved in host pathogenesis. For example, in the important foodborne pathogen Listeria monocytogenes, the chitinases ChiA and ChiB and the lytic polysaccharide monooxygenase Lmo2467 are implicated in chitin assimilation but also act as virulence factors during the infection of mammalian hosts. Therefore, it is important to identify their regulators and induction cues to understand how the different roles of the chitinolytic system are controlled and mediated. Here, we provide evidence for the importance of lmo0327 and lmo0325, encoding a putative internalin/autolysin and a putative transcriptional activator, respectively, in the efficient expression of chitinase activity in L. monocytogenes and thereby provide new information regarding the function of the lmo0325-lmo0327 locus.

Antimicrobial resistance of Salmonella spp. isolated from food

This review summarizes current data on resistance among Salmonella spp. isolates of food origin from countries in different regions of the world. The mechanisms of resistance to different groups of antimicrobial compounds are also considered. Among strains resistant to quinolones and/or fluoroquinolones the most prevalent mechanism is amino acid substitutions in quinolone resistance-determining region (QRDR) of genes gyrA, parC but mechanism of growing importance is plasmid-mediated quinolone resistance (PMQR) associated with genes qnrA, qnrB, qnrC, qnrD, qnrS but frequency of their detection is different. Resistance to sulfonamides is mostly associated with genes sul1 and sul2, while resistance to trimethoprim is associated with various variants of dhfr ( dfr) genes. Taking into account Salmonella spp. strains isolated from food, resistance to ß-lactams is commonly associated with ß-lactamases encoding by blaTEM genes. However strains ESBL and AmpC ­ positive are also detected. Resistance to aminoglicosides is commonly result of enzymatic inactivation. Three types of aminoglycoside modifying enzyme are: acetyltransferases (AAC), adenyltransferases (ANT) and phosphotransferases (APH). Resistance to tetracyclines among Salmonella spp. isolated from food is most commonly associated with active efflux. Among numerous genetic determinants encoding efflux pumps tetA, tetB, tetC, tetD, tetE and tetG are reported predominatingly. One of the most common mechanisms of resistance against chloramphenicol is its inactivation by chloramphenicol acetyltrasferases (CATs), but resistance to this compound can be also mediated by chloramphenicol efflux pumps encoded by the genes cmlA and floR. It is important to monitor resistance of Salmonella isolated from food, because the globalization of trade, leading to the long-distance

Resistance to Sulfonamides and Dissemination of sul Genes Among Salmonella spp. Isolated from Food in Poland.

Antimicrobial resistance of pathogenic bacteria, including Salmonella spp., is an emerging problem of food safety. Antimicrobial use can result in selection of resistant organisms. The food chain is considered a route of transmission of resistant pathogens to humans. In many European countries, sulfonamides are one of the most commonly used antimicrobials. The aim of our investigation was to assess the prevalence of sul genes and plasmid occurrence among sulfonamide-resistant Salmonella spp. Eighty-four sulfonamide-resistant isolates were collected in 2008 and 2013 from retail products in Poland. Minimal inhibitory concentration of all of these isolates was ≥1024 µg/mL. Resistant isolates were tested for the presence of sul1, sul2, sul3, and int1 genes by using multiplex polymerase chain reaction. In total, 44.0% (37/84) isolates carried the sul1 gene, 46.4% (39/84) were sul2 positive, while the sul3 gene was not detected in any of the sulfonamide-resistant isolates tested. It was found that 3.6% (3/84) of resistant Salmonella spp. contained sul1, sul2, and intI genes. All 33 intI-positive isolates carried the sul1 gene. Eleven of the sulfonamide-resistant isolates were negative for all the sul genes. Most of the sulfonamide-resistant Salmonella spp. harbored plasmids; only in eight isolates were no plasmids detected. Generally, the size of the plasmids ranged from approximately 2 kb to ≥90 kb. Our results revealed a relatively a high prevalence of sulfonamides-resistant Salmonella spp. isolated from retail food. Additionally, we have detected a high dissemination of plasmids and class 1 integrons that may enhance the spread of resistance genes in the food chain.

Inactivation of the SecA2 protein export pathway in Listeria monocytogenes promotes cell aggregation, impacts biofilm architecture and induces biofilm formation in environmental condition.

Listeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic species and as an opportunistic intracellular pathogen. Besides its capacity to grow in a wide range of environmental and stressful conditions, L. monocytogenes has the ability to adhere to and colonize surfaces. Morphotype variation to elongated cells forming rough colonies has been reported for different clinical and environmental isolates, including biofilms. This cell differentiation is mainly attributed to the reduced secretion of two SecA2-dependent cell-wall hydrolases, CwhA and MurA. SecA2 is a non-essential SecA paralogue forming an alternative translocase with the primary Sec translocon. Following investigation at temperatures relevant to its ecological niches, i.e. infection (37°C) and environmental (20°C) conditions, inactivation of this SecA2-only protein export pathway led, despite reduced adhesion, to the formation of filamentous biofilm with aerial structures. Compared to the wild type strain, inactivation of the SecA2 pathway promoted extensive cell aggregation and sedimentation. At ambient temperature, this effect was combined with the abrogation of cell motility resulting in elongated sedimented cells, which got knotted and entangled together in the course of filamentous-biofilm development. Such a cell differentiation provides a decisive advantage for listerial surface colonization under environmental condition. As further discussed, this morphotypic conversion has strong implication on listerial physiology and is also of potential significance for asymptomatic human/animal carriage.

Effect of composting and storage on the microbiome and resistome of cattle manure from a commercial dairy farm in Poland.

Manure from food-producing animals, rich in antibiotic-resistant bacteria and antibiotic resistance genes (ARGs), poses significant environmental and healthcare risks. Despite global efforts, most manure is not adequately processed before use on fields, escalating the spread of antimicrobial resistance. This study examined how different cattle manure treatments, including composting and storage, affect its microbiome and resistome. The changes occurring in the microbiome and resistome of the treated manure samples were compared with those of raw samples by high-throughput qPCR for ARGs tracking and sequencing of the V3-V4 variable region of the 16S rRNA gene to indicate bacterial community composition. We identified 203 ARGs and mobile genetic elements (MGEs) in raw manure. Post-treatment reduced these to 76 in composted and 51 in stored samples. Notably, beta-lactam, cross-resistance to macrolides, lincosamides and streptogramin B (MLSB), and vancomycin resistance genes decreased, while genes linked to MGEs, integrons, and sulfonamide resistance increased after composting. Overall, total resistance gene abundance significantly dropped with both treatments. During composting, the relative abundance of genes was lower midway than at the end. Moreover, higher biodiversity was observed in samples after composting than storage. Our current research shows that both composting and storage effectively reduce ARGs in cattle manure. However, it is challenging to determine which method is superior, as different groups of resistance genes react differently to each treatment, even though a notable overall reduction in ARGs is observed.

A newly identified IncY plasmid from multi-drug-resistant Escherichia coli isolated from dairy cattle feces in Poland.

Comprehensive whole-genome sequencing was performed on two multi-drug-resistant Escherichia coli strains isolated from cattle manure from a typical dairy farm in Poland in 2020. The identified strains are resistant to beta-lactams, aminoglycosides, tetracyclines, trimethoprim/sulfamethoxazole, and fluoroquinolones. The complete sequences of the harbored plasmids revealed antibiotic-resistance genes located within many mobile genetic elements (e.g., insertional sequences or transposons) and genes facilitating conjugal transfer or promoting horizontal gene transfer. These plasmids are hitherto undescribed. Similar plasmids have been identified, but not in Poland. The identified plasmids carried resistance genes, including the tetracycline resistance gene tet(A), aph family aminoglycoside resistance genes aph(3″)-lb and aph (6)-ld, beta-lactam resistance genes blaTEM-1 and blaCTX-M-15, sulfonamide resistance gene sul2, fluoroquinolone resistance gene qnrS1, and the trimethoprim resistance gene dfrA14. The characterized resistance plasmids were categorized into the IncY incompatibility group, indicating a high possibility for dissemination among the Enterobacteriaceae. While similar plasmids (99% identity) have been found in environmental and clinical samples, none have been identified in farm animals. These findings are significant within the One Health framework, as they underline the potential for antimicrobial-resistant E. coli from livestock and food sources to be transmitted to humans and vice versa. It highlights the need for careful monitoring and strategies to limit the spread of antibiotic resistance in the One Health approach. IMPORTANCE: This study reveals the identification of new strains of antibiotic-resistant Escherichia coli in cattle manure from a dairy farm in Poland, offering critical insights into the spread of drug resistance. Through whole-genome sequencing, researchers discovered novel plasmids within these bacteria, which carry genes resistant to multiple antibiotics. These findings are particularly alarming, as these plasmids can transfer between different bacterial species, potentially escalating the spread of antibiotic resistance. This research underscores the vital connection between the health of humans, animals, and the environment, emphasizing the concept of One Health. It points to the critical need for global vigilance and strategies to curb the proliferation of antibiotic resistance. By showcasing the presence of these strains and their advanced resistance mechanisms, the study calls for enhanced surveillance and preventive actions in both agricultural practices and healthcare settings to address the imminent challenge of antibiotic-resistant bacteria.

The IncC and IncX1 resistance plasmids present in multi-drug resistant Escherichia coli strains isolated from poultry manure in Poland.

The study describes the whole-genome sequencing of two antibiotic-resistant representative Escherichia coli strains, isolated from poultry manure in 2020. The samples were obtained from a commercial chicken meat production facility in Poland. The antibiotic resistance profile was characterized by co-resistance to ß-lactam antibiotics, aminoglycosides, and fluoroquinolones. The three identified resistance plasmids (R-plasmids), pECmdr13.2, pECmdr13.3, and pECmdr14.1, harbored various genes conferring resistance to tetracyclines (tetR[A]) for, aminoglycoside (aph, aac, and aad families), ß-lactam (blaCMY-2, blaTEM-176), sulfonamide (sul1, sul2), fluoroquinolone (qnrS1), and phenicol (floR). These plasmids, which have not been previously reported in Poland, were found to carry IS26 insertion elements, the intI1-integrase gene, and conjugal transfer genes, facilitating horizontal gene transfer. Plasmids pECmdr13.2 and pECmdr14.1 also possessed a mercury resistance gene operon related to transposon Tn6196; this promotes plasmid persistence even without antibiotic selection pressure due to co-selection mechanisms such as co-resistance. The chicken manure-derived plasmids belonged to the IncX1 (narrow host range) and IncC (broad host range) incompatibility groups. Similar plasmids have been identified in various environments, clinical isolates, and farm animals, including cattle, swine, and poultry. This study holds significant importance for the One Health approach, as it highlights the potential for antibiotic-resistant bacteria from livestock and food sources, particularly E. coli, to transfer through the food chain to humans and vice versa.

Environmental microbiome diversity and stability is a barrier to antimicrobial resistance gene accumulation.

When antimicrobial resistant bacteria (ARB) and genes (ARGs) reach novel habitats, they can become part of the habitat's microbiome in the long term if they are able to overcome the habitat's biotic resilience towards immigration. This process should become more difficult with increasing biodiversity, as exploitable niches in a given habitat are reduced for immigrants when more diverse competitors are present. Consequently, microbial diversity could provide a natural barrier towards antimicrobial resistance by reducing the persistence time of immigrating ARB and ARG. To test this hypothesis, a pan-European sampling campaign was performed for structured forest soil and dynamic riverbed environments of low anthropogenic impact. In soils, higher diversity, evenness and richness were significantly negatively correlated with relative abundance of >85% of ARGs. Furthermore, the number of detected ARGs per sample were inversely correlated with diversity. However, no such effects were present in the more dynamic riverbeds. Hence, microbiome diversity can serve as a barrier towards antimicrobial resistance dissemination in stationary, structured environments, where long-term, diversity-based resilience against immigration can evolve.

Pig manure treatment strategies for mitigating the spread of antibiotic resistance.

Due to the risk of pathogenic antibiotic-resistant bacteria and their antibiotic-resistance genes transfer from livestock feces to the soil and cultivated crops, it is imperative to find effective on-farm manure treatments to minimize that hazardous potential. An introduced worldwide policy of sustainable development, focus on ecological agricultural production, and the circular economy aimed at reducing the use of artificial fertilizers; therefore, such treatment methods should also maximize the fertilization value of animal manure. The two strategies for processing pig manure are proposed in this study-storage and composting. The present study examines the changes in the physicochemical properties of treated manure, in the microbiome, and in the resistome, compared to raw manure. This is the first such comprehensive analysis performed on the same batch of manure. Our results suggest that while none of the processes eliminates the environmental risk, composting results in a faster and more pronounced reduction of mobile genetic elements harboring antibiotic resistance genes, including those responsible for multi-drug resistance. Overall, the composting process can be an efficient strategy for mitigating the spread of antibiotic resistance in the environment and reducing the risk of its transfer to crops and the food chain while providing essential fertilizer ingredients.

Influence of soil use on prevalence of tetracycline, streptomycin, and erythromycin resistance and associated resistance genes.

This study examined differences in antibiotic-resistant soil bacteria and the presence and quantity of resistance genes in soils with a range of management histories. We analyzed four soils from agricultural systems that were amended with manure from animals treated with erythromycin and exposed to streptomycin and/or oxytetracycline, as well as non-manure-amended compost and forest soil. Low concentrations of certain antibiotic resistance genes were detected using multiplex quantitative real-time PCR (qPCR), with tet(B), aad(A), and str(A) each present in only one soil and tet(M) and tet(W) detected in all soils. The most frequently detected resistance genes were tet(B), tet(D), tet(O), tet(T), and tet(W) for tetracycline resistance, str(A), str(B), and aac for streptomycin resistance, and erm(C), erm(V), erm(X), msr(A), ole(B), and vga for erythromycin resistance. Transposon genes specific for Tn916, Tn1549, TnB1230, Tn4451, and Tn5397 were detected in soil bacterial isolates. The MIC ranges of isolated bacteria for tetracycline, streptomycin, and erythromycin were 8 to >256 µg/ml, 6 to >1,024 µg/ml, and 0.094 to >256 µg/ml, respectively. Based on 16S rRNA gene similarity, isolated bacteria showed high sequence identity to genera typical of soil communities. Bacteria with the highest MICs were detected in manure-amended soils or soils from agricultural systems with a history of antibiotic use. Non-manure-amended soils yielded larger proportions of antibiotic-resistant bacteria, but these had lower MICs, carried fewer antibiotic resistance genes, and did not display multidrug resistance (MDR).

Re-evaluation of the significance of penicillin binding protein 3 in the susceptibility of Listeria monocytogenes to ß-lactam antibiotics.

BACKGROUND: Penicillin binding protein 3 (PBP3) of L. monocytogenes has long been thought of as the primary lethal target for ß-lactam antibiotics due to the excellent correlation between the MICs of different ß-lactams and their affinity for this protein. The gene encoding PBP3 has not yet been directly identified in this gram-positive bacterium, but based on in silico analysis, this protein is likely to be encoded by lmo1438. However, studies examining the effects of mutations in genes encoding known and putative L. monocytogenes PBPs have demonstrated that inactivation of lmo1438 does not affect sensitivity to ß-lactams. RESULTS: In this study, overexpression of lmo1438 was achieved using an inducible (nisin-controlled) expression system. This permitted the direct demonstration that lmo1438 encodes PBP3. PBP3 overexpression was accompanied by slightly elevated PBP4 expression. The recombinant strain overexpressing PBP3 displayed significant growth retardation and greatly reduced cell length in the stationary phase of growth in culture. In antibiotic susceptibility assays, the strain overexpressing PBP3 displayed increased sensitivity to subinhibitory concentrations of several ß-lactams and decreased survival in the presence of a lethal dose of penicillin G. However, the MIC values of the tested ß-lactams for this recombinant strain were unchanged compared to the parent strain. CONCLUSIONS: The present study allows a reevaluation of the importance of PBP3 in the susceptibility of L. monocytogenes to ß-lactams. It is clear that PBP3 is not the primary lethal target for ß-lactams, since neither the absence nor an excess of this protein affect the susceptibility of L. monocytogenes to these antibiotics. The elevated level of PBP4 expression observed in the recombinant strain overexpressing PBP3 demonstrates that the composition of the L. monocytogenes cell wall is subject to tight regulation. The observed changes in the morphology of stationary phase cells in response to PBP3 overexpression suggests the involvement of this protein in cell division during this phase of growth.

N-acetylglucosamine-6-phosphate deacetylase (NagA) of Listeria monocytogenes EGD, an essential enzyme for the metabolism and recycling of amino sugars.

The main aim of our study was to determine the physiological function of NagA enzyme in the Listeria monocytogenes cell. The primary structure of the murein of L. monocytogenes is very similar to that of Escherichia coli, the main differences being amidation of diaminopimelic acid and partial de-N-acetylation of glucosamine residues. NagA is needed for the deacetylation of N-acetyl-glucosamine-6 phosphate to glucosamine-6 phosphate and acetate. Analysis of the L. monocytogenes genome reveals the presence of two proteins with NagA domain, Lmo0956 and Lmo2108, which are cytoplasmic putative proteins. We introduced independent mutations into the structural genes for the two proteins. In-depth characterization of one of these mutants, MN1, deficient in protein Lmo0956 revealed strikingly altered cell morphology, strongly reduced cell wall murein content and decreased sensitivity to cell wall hydrolase, mutanolysin and peptide antibiotic, colistin. The gene products of operon 150, consisting of three genes: lmo0956, lmo0957, and lmo0958, are necessary for the cytosolic steps of the amino-sugar-recycling pathway. The cytoplasmic de-N-acetylase Lmo0956 of L. monocytogenes is required for cell wall peptidoglycan and teichoic acid biosynthesis and is also essential for bacterial cell growth, cell division, and sensitivity to cell wall hydrolases and peptide antibiotics.

Factors promoting and limiting antimicrobial resistance in the environment - Existing knowledge gaps.

The dissemination of multidrug-resistant bacteria strains and genes carrying antibiotic resistance is currently considered to be one of the most important global problem. The WHO calls for the need to contain the spread of Antimicrobial Resistance (AMR) from all possible sources. There have been many international actions grouping scientists studying this phenomenon, and quite a lot of scientific projects devoted to this problem have already been carried out. As well, so far several strategies have been developed that can inhibit the AMR spread. In this mini-review, we highlight overlooked aspects that seem to be crucial for creating a comprehensive picture of AMR, especially in the context of One Health approach.

A Comprehensive Study of the Microbiome, Resistome, and Physical and Chemical Characteristics of Chicken Waste from Intensive Farms.

The application of chicken waste to farmland could be detrimental to public health. It may contribute to the dissemination of antibiotic-resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) from feces and their subsequent entry into the food chain. The present study analyzes the metagenome and resistome of chicken manure and litter obtained from a commercial chicken farm in Poland. ARB were isolated, identified, and screened for antibiogram fingerprints using standard microbiological and molecular methods. The physicochemical properties of the chicken waste were also determined. ARGs, integrons, and mobile genetic elements (MGE) in chicken waste were analyzed using high-throughput SmartChip qPCR. The results confirm the presence of many ARGs, probably located in MGE, which can be transferred to other bacteria. Potentially pathogenic or opportunistic microorganisms and phytopathogens were isolated. More than 50% of the isolated strains were classified as being multi-drug resistant, and the remainder were resistant to at least one antibiotic class; these pose a real risk of entering the groundwater and contaminating the surrounding environment. Our results indicate that while chicken manure can be sufficient sources of the nutrients essential for plant growth, its microbiological aspects make this material highly dangerous to the environment.

Deep impact of the inactivation of the SecA2-only protein export pathway on the proteosurfaceome of Listeria monocytogenes.

Listeria monocytogenes presents a dimorphism associated to the SecA2 activity with cells having a normal rod shape or a dysmorphic elongated filamentous form. Besides variation of the cell and colony morphotype, this cell differentiation has profound ecophysiological and physiopathological implications with collateral effects on virulence and pathogenicity, biotope colonisation, bacterial adhesion and biofilm formation. This suggests the SecA2-only protein export could influence the listerial cell surface, which was investigated first by characterising its properties in L. monocytogenes wt and ΔsecA2. The degree of hydrophilicity and Lewis acid-base properties appeared significantly affected upon SecA2 inactivation. As modification of electrostatic properties would owe to modification in the composition of cell-surface proteins, the proteosurfaceome was further investigated by shotgun label-free proteomic analysis with a comparative relative quantitative approach. Following secretomic analysis, the protein secretion routes of the identified proteins were mapped considering the cognate transport and post-translocational maturation systems, as well as protein categories and subcellular localisation. Differential protein abundance profiles coupled to network analysis revealed the SecA2 dependence of 48 proteins, including some related to cell envelope biogenesis, translation and protein export, which could account for modifications of adhesion and surface properties of L. monocytogenes upon SecA2 inactivation. This investigation unravelled the profound influence of SecA2 activity on the cell surface properties and proteosurfaceome of L. monocytogenes, which provides advanced insights about its ecophysiopathology. SIGNIFICANCE: L. monocytogenes is a foodborne zoonotic pathogen and etiological agent of human listeriosis. This species presents a cellular dimorphism associated to the SecA2 activity that has profound physiopathological and ecophysiological implications with collateral effects on bacterial virulence and colonisation. To explore the influence of the SecA2-only protein export on the listerial cell, the surface properties of L. monocytogenes expressing or depleted of SecA2 was characterised by microelectrophoresis, microbial affinity to solvents and contact angles analyses. As modifications of hydrophilicity and Lewis acid-base electrostatic properties would owe to modification in the composition of cell-surface proteins, the proteinaceous subset of the surfaceome, i.e. the proteosurfaceome, was investigated further by shotgun label-free proteomic analysis. This subproteome appeared quite impacted upon SecA2 inactivation with the identification of proteins accounting for modifications in the cell surface properties. The profound influence of SecA2 activity on the cell surface of L. monocytogenes was unravelled, which provides advanced insights about its ecophysiopathology.

An update on some structural aspects of the mighty miniwall.

Peptidoglycan (PG), the mighty miniwall, is the main structural component of practically all bacterial cell envelopes and has been the subject of a wealth of research over the past 60 years, if only because its biosynthesis is the target of many antibiotics that have successfully been used in the treatment of bacterial infections. This review is mainly focused on the most recent achievements in research on the modification of PG glycan strands, which contribute to the resistance of bacteria to the host immune response to infection and to their own lytic enzymes, and on studies on the spatial organization of the macromolecule.

Antibiotics and Antibiotic Resistance Genes in Animal Manure - Consequences of Its Application in Agriculture.

Antibiotic resistance genes (ARGs) are a relatively new type of pollutant. The rise in antibiotic resistance observed recently is closely correlated with the uncontrolled and widespread use of antibiotics in agriculture and the treatment of humans and animals. Resistant bacteria have been identified in soil, animal feces, animal housing (e.g., pens, barns, or pastures), the areas around farms, manure storage facilities, and the guts of farm animals. The selection pressure caused by the irrational use of antibiotics in animal production sectors not only promotes the survival of existing antibiotic-resistant bacteria but also the development of new resistant forms. One of the most critical hot-spots related to the development and dissemination of ARGs is livestock and poultry production. Manure is widely used as a fertilizer thanks to its rich nutrient and organic matter content. However, research indicates that its application may pose a severe threat to human and animal health by facilitating the dissemination of ARGs to arable soil and edible crops. This review examines the pathogens, potentially pathogenic microorganisms and ARGs which may be found in animal manure, and evaluates their effect on human health through their exposure to soil and plant resistomes. It takes a broader view than previous studies of this topic, discussing recent data on antibiotic use in farm animals and the effect of these practices on the composition of animal manure; it also examines how fertilization with animal manure may alter soil and crop microbiomes, and proposes the drivers of such changes and their consequences for human health.

Oleanolic acid and ursolic acid affect peptidoglycan metabolism in Listeria monocytogenes.

The plant pentacyclic triterpenoids, oleanolic and ursolic acids, inhibit the growth and survival of many bacteria, particularly Gram-positive species, including pathogenic ones. The effect of these compounds on the facultative human pathogen Listeria monocytogenes was examined. Both acids affected cell morphology and enhanced autolysis of the bacterial cells. Autolysis of isolated cell walls was inhibited by oleanolic acid, but the inhibitory activity of ursolic acid was less pronounced. Both compounds inhibited peptidoglycan turnover and quantitatively affected the profile of muropeptides obtained after digestion of peptidoglycan with mutanolysin. These results suggest that peptidoglycan metabolism is a cellular target of oleanolic and ursolic acids.

The impact of environmental contamination with antibiotics on levels of resistance in soil bacteria.

This study examined the effects of tetracycline and streptomycin on microorganisms in three different soil habitats: forest soil, agricultural soil, and compost. These antibiotics are commonly used in both medical and veterinary therapy as well as in the production of plant biomass and until quite recently, the production of animal biomass. Microcosms were used as model systems in which the number of microorganisms in environments containing different amounts of antibiotics was analyzed. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of tetracycline and streptomycin were determined. The MIC and MBC values of tetracycline against the tested strains were 20 to 180 microg/ mL and 30 to 300 microg/mL, respectively, and of streptomycin, 360 to 500 microg/mL and > or =500 microg/mL, respectively. Resistant bacterial strains were identified and their physiological profiles assessed. Streptomycin and tetracycline were found to reduce the number of bacteria in the studied soils by between 50 and 80%. Soil bacteria were found to be more resistant to streptomycin than to tetracycline. The bacterial species showing the highest resistance to tetracycline were Rhizobium radiobacter, Burkholderia cepacia, Brevundimonas vesicularis, and Pasteurella multocida. Most soils with high concentrations of streptomycin (5 mg/kg) contained Rhizobium radiobacter, Burkholderia cepacia, and Sphingomonas multivorum, among others. The strains most resistant to tetracycline were isolated from agricultural soil that is constantly subjected to tetracycline pressure from animal manures and biosolids. Among resistant strains, opportunistic pathogens were identified.