Acquisition Of Antibiotic Resistance Research Articles

Evolution of Antibiotic Resistance in Surrogates of Francisella tularensis (LVS and Francisella novicida): Effects on Biofilm Formation and Fitness.

Francisella tularensis, the causative agent of tularemia, is capable of causing disease in a multitude of mammals and remains a formidable human pathogen due to a high morbidity, low infectious dose, lack of a FDA approved vaccine, and ease of aerosolization. For these reasons, there is concern over the use of F. tularensis as a biological weapon, and, therefore, it has been classified as a Tier 1 select agent. Fluoroquinolones and aminoglycosides often serve as the first line of defense for treatment of tularemia. However, high levels of resistance to these antibiotics has been observed in gram-negative bacteria in recent years, and naturally derived resistant Francisella strains have been described in the literature. The acquisition of antibiotic resistance, either natural or engineered, presents a challenge for the development of medical countermeasures. In this study, we generated a surrogate panel of antibiotic resistant F. novicida and Live Vaccine Strain (LVS) by selection in the presence of antibiotics and characterized their growth, biofilm capacity, and fitness. These experiments were carried out in an effort to (1) assess the fitness of resistant strains; and (2) identify new targets to investigate for the development of vaccines or therapeutics. All strains exhibited a high level of resistance to either ciprofloxacin or streptomycin, a fluoroquinolone and aminoglycoside, respectively. Whole genome sequencing of this panel revealed both on-pathway and off-pathway mutations, with more mutations arising in LVS. For F. novicida, we observed decreased biofilm formation for all ciprofloxacin resistant strains compared to wild-type, while streptomycin resistant isolates were unaffected in biofilm capacity. The fitness of representative antibiotic resistant strains was assessed in vitro in murine macrophage-like cell lines, and also in vivo in a murine model of pneumonic infection. These experiments revealed that mutations obtained by these methods led to nearly all ciprofloxacin resistant Francisella strains tested being completely attenuated while mild attenuation was observed in streptomycin resistant strains. This study is one of the few to examine the link between acquired antibiotic resistance and fitness in Francisella spp., as well as enable the discovery of new targets for medical countermeasure development.

A One-Health Quantitative Model to Assess the Risk of Antibiotic Resistance Acquisition in Asian Populations: Impact of Exposure Through Food, Water, Livestock and Humans.

Antimicrobial resistance (AMR) has become a major threat worldwide, especially in countries with inadequate sanitation and low antibiotic regulation. However, adequately prioritizing AMR interventions in such settings requires a quantification of the relative impacts of environmental, animal, and human sources in a One-Health perspective. Here, we propose a stochastic quantitative risk assessment model for the different components at interplay in AMR selection and spread. The model computes the incidence of AMR colonization in humans from five different sources: water or food consumption, contacts with livestock, and interhuman contacts in hospitals or the community, and combines these incidences into a per-year acquisition risk. Using data from the literature and Monte-Carlo simulations, we apply the model to hypothetical Asian-like settings, focusing on resistant bacteria that may cause infections in humans. In both scenarios A, illustrative of low-income countries, and B, illustrative of high-income countries, the overall individual risk of becoming colonized with resistant bacteria at least once per year is high. However, the average predicted incidence of colonization was lower in scenario B at 0.82 (CrI [0.13, 5.1]) acquisitions/person/year, versus 1.69 (CrI [0.66, 11.13]) acquisitions/person/year for scenario A. A high percentage of population with no access to improved water on premises and a high percentage of population involved in husbandry are shown to strongly increase the AMR acquisition risk. The One-Health AMR risk assessment framework we developed may prove useful to policymakers throughout Asia, as it can easily be parameterized to realistically reproduce conditions in a given country, provided data are available.

Combination Therapy Using Low-Concentration Oxacillin with Palmitic Acid and Span85 to Control Clinical Methicillin-Resistant Staphylococcus aureus.

The overuse of antibiotics has led to the emergence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MRSA is difficult to kill with a single antibiotic because it has evolved to be resistant to various antibiotics by increasing the PBP2a (mecA) expression level, building up biofilm, introducing SCCmec for multidrug resistance, and changing its membrane properties. Therefore, to overcome antibiotic resistance and decrease possible genetic mutations that can lead to the acquisition of higher antibiotic resistance, drug combination therapy was applied based on previous results indicating that MRSA shows increased susceptibility to free fatty acids and surfactants. The optimal ratio of three components and the synergistic effects of possible combinations were investigated. The combinations were directly applied to clinically isolated strains, and the combination containing 15 μg/mL of oxacillin was able to control SCCmec type III and IV isolates having an oxacillin minimum inhibitory concentration (MIC) up to 1024 μg/mL; moreover, the combination with a slightly increased oxacillin concentration was able to kill SCCmec type II. Phospholipid analysis revealed that clinical strains with higher resistance contained a high portion of 12-methyltetradecanoic acid (anteiso-C15:0) and 14-methylhexadecanoic acid (anteiso-C17:0), although individual strains showed different patterns. In summary, we showed that combinatorial therapy with a low concentration of oxacillin controlled different laboratory and highly diversified clinical MRSA strains.

Multidrug Resistance in Integron Bearing Klebsiella pneumoniae isolated from Alexandria University Hospitals, Egypt.

Klebsiella pneumoniae is by far one of the most common Enterobacteriaceae associated with hospital-acquired infections. The dissemination of multi drug resistant Klebsiella pneumoniae is causing difficulty to treat infections worldwide. Of additional concern, multi drug resistant Klebsiella pneumoniae acquires and transfers antibiotic resistance genes among other bacterial isolates. Integrons have the main role in the acquisition as well as dissemination of resistance genes. Accordingly we aimed to investigate the frequency of resistance genes sul1, sul2, tetA, tetB and aac (3) IIa, class one (int1 gene) and class two integrons(int2 gene) in Klebsiella pneumoniae clinical isolates from four major hospitals in Alexandria, Egypt using Polymerase Chain Reaction. In addition we aimed to evaluate the association between multidrug resistance and presence of integrons in hospital-acquired Klebsiella pneumoniae in our hospitals. To the best of our knowledge, there is little information about integrons and acquisition of multiple antibiotic resistance in Klebsiella pneumoniae in hospitals in Alexandria, Egypt. In this study 76 isolates were resistant to sulphamethoxazole /trimethoprim. Of these 38 isolates (50%) harbored both genes sul1 and sul2 genes. 42 isolates out of the 60 (70%) isolates that showed resistance to tetracycline were tetA or tetB positive. The prevalence of int1 gene among all isolates tested was 90%, while only one isolate harbored the int2 gene (1%). Our results were indicative of the high prevalence of multidrug resistant Klebsiella pneumoniae as well as integrons that were found to play an essential role in the dissemination of antibiotic resistance genes in our hospitals.

Association of Virulence and Antibiotic Resistance in Salmonella-Statistical and Computational Insights into a Selected Set of Clinical Isolates.

The acquisition of antibiotic resistance (AR) by foodborne pathogens, such as Salmonella enterica, has emerged as a serious public health concern. The relationship between the two key survival mechanisms (i.e., antibiotic resistance and virulence) of bacterial pathogens is complex. However, it is unclear if the presence of certain virulence determinants (i.e., virulence genes) and AR have any association in Salmonella. In this study, we report the prevalence of selected virulence genes and their association with AR in a set of phenotypically tested antibiotic-resistant (n = 117) and antibiotic-susceptible (n = 94) clinical isolates of Salmonella collected from Tennessee, USA. Profiling of virulence genes (i.e., virulotyping) in Salmonella isolates (n = 211) was conducted by targeting 13 known virulence genes and a gene for class 1 integron. The association of the presence/absence of virulence genes in an isolate with their AR phenotypes was determined by the machine learning algorithm Random Forest. The analysis revealed that Salmonella virulotypes with gene clusters consisting of avrA, gipA, sodC1, and sopE1 were strongly associated with any resistant phenotypes. To conclude, the results of this exploratory study shed light on the association of specific virulence genes with drug-resistant phenotypes of Salmonella. The presence of certain virulence genes clusters in resistant isolates may become useful for the risk assessment and management of salmonellosis caused by drug-resistant Salmonella in humans.

The impact of metal pipe materials, corrosion products, and corrosion inhibitors on antibiotic resistance in drinking water distribution systems.

Drinking water distribution systems (DWDS) are unique engineering environments that are important routes for the acquisition and dissemination of antibiotic resistance. Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in drinking water pose risks to human and environmental health. Metals are known stressors that can select for antibiotic resistance. The objective of this review was to assess the state of knowledge regarding the impact of metal pipe materials, corrosion products, and corrosion inhibitors on the prevalence of antibiotic resistance in DWDS. ARGs and mobile genetic elements (MGEs) have been detected in full-scale DWDS in concentrations ranging from ~ 101 to 1010 copies/L. Metal pipe materials can select for bacteria harboring ARGs and metal resistance genes (MRGs) through co-selection processes. Corrosion products that develop in metal drinking water pipes (Cu, Fe, and Pb oxides) may also stimulate antibiotic resistance selection during distribution. Different corrosion inhibitor regimes (phosphates, sodium silicates) may also have impacts on microbial communities and the abundance of resistance genes in DWDS. Research is needed to quantify how engineering decisions related to drinking water infrastructure and corrosion inhibitor practices impact the abundance and distribution of ARG, MRGs, and MGEs in potable water systems. KEY POINTS: • Lack of quantitative measurements of antibiotic and metal resistance genes in drinking water distribution systems. • Pipe materials and corrosion products that develop in pipe scales may impact antibiotic resistance. • Corrosion inhibitors with zinc or phosphate could alter antibiotic resistance. • Management decisions should consider antibiotic resistance ramifications. Graphical abstract.

Strong Environment-Genotype Interactions Determine the Fitness Costs of Antibiotic Resistance In Vitro and in an Insect Model of Infection.

The acquisition of antibiotic resistance commonly imposes fitness costs, a reduction in the fitness of bacteria in the absence of drugs. These costs have been quantified primarily using in vitro experiments and a small number of in vivo studies in mice, and it is commonly assumed that these diverse methods are consistent. Here, we used an insect model of infection to compare the fitness costs of antibiotic resistance in vivo to those in vitro Experiments explored diverse mechanisms of resistance in a Gram-positive pathogen, Bacillus thuringiensis, and a Gram-negative intestinal symbiont, Enterobacter cloacae Rifampin resistance in B. thuringiensis showed fitness costs that were typically elevated in vivo, although these were modulated by genotype-environment interactions. In contrast, resistance to cefotaxime via derepression of AmpC β-lactamase in E. cloacae resulted in no detectable costs in vivo or in vitro, while spontaneous resistance to nalidixic acid, and carriage of the IncP plasmid RP4, imposed costs that increased in vivo Overall, fitness costs in vitro were a poor predictor of fitness costs in vivo because of strong genotype-environment interactions throughout this study. Insect infections provide a cheap and accessible means of assessing the fitness consequences of resistance mutations, data that are important for understanding the evolution and spread of resistance. This study emphasizes that the fitness costs imposed by particular mutations or different modes of resistance are extremely variable and that only a subset of these mutations is likely to be prevalent outside the laboratory.

Broadscale phage therapy is unlikely to select for widespread evolution of bacterial resistance to virus infection.

Multi-drug resistant bacterial pathogens are alarmingly on the rise, signaling that the golden age of antibiotics may be over. Phage therapy is a classic approach that often employs strictly lytic bacteriophages (bacteria-specific viruses that kill cells) to combat infections. Recent success in using phages in patient treatment stimulates greater interest in phage therapy among Western physicians. But there is concern that widespread use of phage therapy would eventually lead to global spread of phage-resistant bacteria and widespread failure of the approach. Here, we argue that various mechanisms of horizontal genetic transfer (HGT) have largely contributed to broad acquisition of antibiotic resistance in bacterial populations and species, whereas similar evolution of broad resistance to therapeutic phages is unlikely. The tendency for phages to infect only particular bacterial genotypes limits their broad use in therapy, in turn reducing the likelihood that bacteria could acquire beneficial resistance genes from distant relatives via HGT. We additionally consider whether HGT of clustered regularly interspaced short palindromic repeats (CRISPR) immunity would thwart generalized use of phages in therapy, and argue that phage-specific CRISPR spacer regions from one taxon are unlikely to provide adaptive value if horizontally-transferred to other taxa. For these reasons, we conclude that broadscale phage therapy efforts are unlikely to produce widespread selection for evolution of bacterial resistance.

MrkD Gene as a Regulator of Biofilm Formation with Correlation to Antibiotic Resistance among Clinical Klebsiella pneumoniae Isolates from Menoufia University Hospitals

Background: Klebsiella pneumoniae (K. pneumoniae) is a common pathogen involved in a diverse array of life-threatening infections. Increasing frequent acquisition of antibiotic resistance by K. pneumoniae has given rise to multidrug-resistant pathogen mostly at the hospital level. Objectives: To assess the prevalence and antibiotic resistance pattern of the clinical K. pneumoniae isolates at Menoufia University Hospitals (MUHs) as well as to explore the role of mrkD gene as a regulator of biofilm formation. Methodology: A total of 340 different clinical samples were obtained from 270 patients who were admitted to MUHs and those from Outpatient clinics during the period from April 2018 to September 2019. 84 K. pneumoniae isolates were identified by the standard microbiological methods and vitek-2 system. The antimicrobial resistance pattern was determined by disk diffusion method. The biofilm-forming ability of all K. pneumoniae isolates was demonstrated phenotypically by the modified Congo red agar method (MCRA) and PCR assay verified the presence of mrkD gene as a genetic determinant of biofilm formation. Results: Klebsiella spp. represented 34.7% of the collected isolates and the predominant spp. was K. pneumoniae (91.3%). The highest resistance rates were for ceftriaxone (69%) followed by aztreonam (67.9%), 66.7% for each of piperacillin and ceftazidime, while the least resistance rate was for fosfomycin (8.3%). Biofilm production was detected among 83.3% of the isolates by MCRA method. A highly significant statistical difference was noted between biofilm- and non- biofilm - producing K. pneumoniae isolates regarding resistance to cefepieme and amikacin (P <0.001) and similarly regarding resistance to aztreonam, imipenem, meropenem, ertapenem and tobramycin (P<0.05). Conventional PCR assay showed that, 92% of the isolates harbored mrkD gene with a highly significant association with biofilm formation. Conclusion: The increasing prevalence and remarkable ability to acquire antibiotic resistance among K. pneumoniae isolates together with biofilm formation should alert even more regarding the hazard of this pathogen in hospital settings.

Variation of antibiotic resistance in Salmonella Enteritidis, Escherichia coliO157:H7, and Listeria monocytogenes after exposure to acid, salt, and cold stress

AbstractBacteria with antibiotic‐resistant could seriously threaten to human health, increasing the treatment cost for infections and negatively affecting treatment outcomes. Stress adaptation is one possible mechanism for the acquisition or enhancement of antibiotic resistance in bacteria as a result of cross‐protection. In this study, the effects of acid, salt, and cold stress on the antibiotic resistance of Salmonella Enteritidis, Listeria monocytogenes, and Escherichia coli O157:H7 were investigated using the disc diffusion method. For S. Enteritidis, acidic growth conditions increased resistance to ciprofloxacin and erythromycin (p < .05), and addition of 4% NaCl to growth media decreased resistance to chloramphenicol (p < .05). Irrespective of pH and the NaCl concentration of the growth medium, refrigerated E. coli O157:H7 showed increased resistance to amoxycillin, ciprofloxacin, gentamicin, streptomycin, and erythromycin (p < .05). Acid‐adapted L. monocytogenes showed decreased the resistance to amoxycillin, ampicillin, chloramphenicol, ciprofloxacin, erythromycin, gentamicin, streptomycin, and tetracycline (p < .05). In conclusion, prolonged exposure of foodborne pathogens to acid, salt, and cold stress alters their antibiotic resistance. However, the effect of acid, salt, and cold stress on bacterial antibiotic resistance depend on both the bacterial species and the specific antibiotic. Therefore, multiple factors need to be considered for a foodborne antimicrobial resistant risk assessment.

Co-selection of antibiotic-resistant bacteria in a paddy soil exposed to As(III) contamination with an emphasis on potential pathogens

The increased acquisition of antibiotic resistance by pathogens is a global health concern. The environmental selection of antibiotic resistance can be caused by either antibiotic residues or co-selecting agents such as toxic metal(loid)s. This study explored the potential role of As(III) as a co-selecting driver in the spread of antibiotic resistance in paddy soils. By applying high-throughput sequencing, we found that the diversity and composition of soil microbial communities was significantly altered by As(III) exposure, resulting in an increased proportion of potential pathogens (9.9%) compared to the control soil (0.1%). Meanwhile, a total of 46 As(III)-resistant isolates were obtained from As(III)-exposure soil, among which potential pathogens accounted for 54.3%. These As(III)-resistant bacteria showed a high incidence of resistance to sulfanilamide (100%) and streptomycin (88–93%). The association between antibiotic and As(III) resistances was further investigated in a potentially pathogenic isolate by whole-genome sequencing and a transcription assay. The results showed that As(III) and antibiotic resistance genes might co-occur in a mobile genomic island and be co-regulated by As(III), implying that antibiotic resistance could be co-selected by As(III) via co-resistance and co-regulation mechanisms. Overall, these results suggest that As(III) exposure provides a strong selective pressure for the expansion of soil bacterial resistome.

Chemiluminescent Carbapenem‐Based Molecular Probe for Detection of Carbapenemase Activity in Live Bacteria

Carbapenemase-producing organisms (CPOs) pose a severe threat to antibacterial treatment due to the acquisition of antibiotic resistance. This resistance can be largely attributed to the antibiotic-hydrolyzing enzymes that the bacteria produce. Current carbapenem "wonder drugs", such as doripenem, ertapenem, meropenem, imipenem, and so on, are resistant to regular β-lactamases, but susceptible to carbapenemases. Even worse, extended exposure of bacteria to these drugs accelerates the spread of resistance genes. In order to preserve the clinical efficacy of antibacterial treatment, carbapenem drugs should be carefully regulated and deployed only in cases of a CPO infection. Early diagnosis is therefore of paramount importance. Herein, we report the design, synthesis, and activity of the first carbapenemase-sensitive chemiluminescent probe, CPCL, which may be used to monitor CPO activity. The design of our probe enables enzymatic cleavage of the carbapenem core, which is followed by a facile 1,8-elimination process and the emission of green light through rapid chemical excitation. We have demonstrated the ability of the probe to detect a number of clinically relevant carbapenemases and the successful identification of CPO present in bacterial cultures, such as those used for clinical diagnosis. We believe that our use of "turn-on" chemiluminescence activation will find significant application in future diagnostic assays and improve antibacterial treatment.

The Manganese-Responsive Transcriptional Regulator MumR Protects Acinetobacter baumannii from Oxidative Stress.

Acinetobacter baumannii is an emerging opportunistic pathogen that primarily infects critically ill patients in nosocomial settings. Because of its rapid acquisition of antibiotic resistance, infections caused by A. baumannii have become extremely difficult to treat, underlying the importance of identifying new antimicrobial targets for this pathogen. Manganese (Mn) is an essential nutrient metal required for a number of bacterial processes, including the response to oxidative stress. Here, we show that exogenous Mn can restore A. baumannii viability in the presence of reactive oxygen species (ROS). This restoration is not dependent on the high-affinity Nramp family Mn transporter, MumT, as a ΔmumT mutant is no more sensitive to hydrogen peroxide (H2O2) killing than wild-type A. baumannii However, mumR, which encodes the transcriptional regulator of mumT, is critical for growth and survival in the presence of H2O2, suggesting that MumR regulates additional genes that contribute to H2O2 resistance. RNA sequencing revealed a role for mumR in regulating the activity of a number of metabolic pathways, including two pathways, phenylacetate and gamma-aminobutyric acid catabolism, which were found to be important for resisting killing by H2O2 Finally, ΔmumR exhibited reduced fitness in a murine model of pneumonia, indicating that MumR-regulated gene products are crucial for protection against the host immune response. In summary, these results suggest that MumR facilitates resistance to the host immune response by activating a transcriptional program that is critical for surviving both Mn starvation and oxidative stress.

Implications of bacteriophages on the acquisition and spread of antibiotic resistance in the environment.

Although bacteriophages (or simply phages) are the most abundant biological entities and have the potential to transfer genetic material between bacterial hosts, their contribution to the acquisition and spread of antibiotic resistance genes in the environment has not been extensively studied. The environment is continually exposed to a wide variety of pollutants from anthropogenic sources, which may promote horizontal gene transfer events, including those mediated by phages. Considering the significant and growing concern of antibiotic resistance, phages should be taken into consideration during the implementation of mitigation measures. This review is focused on the emergence and spread of antibiotic resistance in the environment, with a special emphasis on the role of phages.

Instances of altered gut microbiomes among Irish cricketers over periods of travel in the lead up to the 2016 World Cup: A sequencing analysis.

Changes and stresses experienced during travel have the potential to impact the gut microbiome, with travel implicated in the spread of antibiotic resistance genes across continents. The possibility of gut microbiome-mediated negative impacts arising from travel, and consequences for peak performance, would be of particular concern for elite athletes. Faecal samples were collected from male (N=14) and female (N=7) cricket players during the build-up to the 2016 Cricket World Cup. Baseline and post-travel samples were collected from all participants and subjected to 16S rRNA amplicon sequencing. Samples from a subset of participants (N=4) were also analysed by shotgun metagenomic sequencing. Analysis revealed a single travel time point as having the potential to have an impact on the gut microbiome. Reductions in alpha diversity following travel were observed, accompanied by shifts in the taxonomic profile of the gut microbiome. Antibiotic resistance and virulence genes were also identified as undergoing changes following travel. This study reveals that periods of travel, in particular following gastrointestinal distress, may result in gut microbiome disruption. While this analysis was completed in athletes, the findings are applicable to all travelling individuals and considerations should be made surrounding travel in an attempt to reduce these changes.

Targeting Antibiotic Resistance Genes Is a Better Approach to Block Acquisition of Antibiotic Resistance Than Blocking Conjugal Transfer by Recipient Cells: A Genome-Wide Screening in Escherichia coli.

The conjugal transfer is a major driving force in the spread of antibiotic resistance genes. Nevertheless, an effective approach has not yet been developed to target conjugal transfer to prevent the acquisition of antibiotic resistance by this mechanism. This study aimed to identify potential targets for plasmid transfer blockade by isolating mutants defective in the completion of the acquisition of antibiotic resistance via conjugal transfer. We performed genome-wide screening by combining an IncP1α-type broad host range plasmid conjugation system with a comprehensive collection of Escherichia coli gene knockout mutants (Keio collection; 3884 mutants). We followed a six-step screening procedure to identify the mutants showing conjugation deficiency precisely. No mutants defective in the conjugal transfer were isolated, strongly suggesting that E. coli cannot escape from being a recipient organism for P1α plasmid transfer. However, several mutants with low viability were identified, as well as mutants defective in establishing resistance to chloramphenicol, which was used for transconjugant selection. These results suggest that developing drugs capable of inhibiting the establishment of antibiotic resistance is a better approach than attempting to prevent the conjugal transfer to block the spread of antibiotic resistance genes. Our screening system based on the IncP1α-type plasmid transfer can be extended to isolation of target genes for other drugs. This study could be the foundation for further research to understand its underlying molecular mechanism through functional analysis of the identified genes.

A compartmental model for antibiotic resistant bacterial infections over networks

This paper presents a compartmental model for bacterial infections in a population distributed over a network of individuals. Within each node, individuals interact, bacteria can be transmitted and the disease may be spread; moreover, the acquisition of bacterial antibiotic resistance is considered. In addition, nodes are connected through weighted edges, and consequently individuals from different nodes may interact. As a result, the infection may be propagated over the network. We perform an analysis on this propagation as well as numerical simulations in order to illustrate the validity of the model.

Baicalin Inhibits Biofilm Formation and the Quorum-Sensing System by Regulating the MsrA Drug Efflux Pump in Staphylococcus saprophyticus.

Staphylococcus saprophyticus (S. saprophyticus) is one of the main pathogens that cause serious infection due to its acquisition of antibiotic resistance. The efflux pump decreases antibiotic abundance, and biofilm compromises the penetration of antibiotics. It has been reported that baicalin is a potential agent to inhibit efflux pumps, biofilm formation, and quorum-sensing systems. The purpose of this study was to investigate whether baicalin can inhibit S. saprophyticus biofilm formation and the quorum-sensing system by inhibiting the MsrA efflux pump. First, the mechanism of baicalin inhibiting efflux was investigated by the ethidium bromide (EtBr) efflux assay, measurement of ATP content, and pyruvate kinase (PK) activities. These results revealed that baicalin significantly reduced the efflux of EtBr, the ATP content, and the activity of PK. Moreover, its role in biofilm formation and the agr system was studied by crystal violet staining, confocal laser scanning microscopy, scanning electron microscopy, and real-time polymerase chain reaction. These results showed that baicalin decreased biofilm formation, inhibited bacterial aggregation, and downregulated mRNA transcription levels of the quorum-sensing system regulators agrA, agrC, RNAIII, and sarA. Correlation analysis indicated that there was a strong positive correlation between the efflux pump and biofilm formation and the agr system. We demonstrate for the first time that baicalin inhibits biofilm formation and the agr quorum-sensing system by inhibiting the efflux pump in S. saprophyticus. Therefore, baicalin is a potential therapeutic agent for S. saprophyticus biofilm-associated infections.

Understanding human health risks caused by antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) in water environments: Current knowledge and questions to be answered

Aquatic environments are identified as an ideal setting for acquisition and dissemination of antibiotic resistance, and human exposure to antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in aquatic environments may pose an additional health risk. Quantitative microbial risk assessment (QMRA) has been suggested as a suitable method to evaluate and quantify this health risk. However, information about the exposure to ARB and ARGs in aquatic environments is lacking for many scenarios and dose-response models regarding the ARB infections are not developed yet. This review summarizes the current knowledge regarding the ARB and ARGs in aquatic environments and highlights the challenging questions remaining to be answered to better forecast the health risks caused by ARB and ARGs in water environments. The questions include what are the missing information needed to quantify the human health risks caused by exposing to ARB and ARGs in aquatic environments? what are the suitable markers to evaluate the ARB/ARGs contamination in aquatic environments? how frequently do the ARG selection and propagation occur in aquatic environments? and are there any unknown hot spots? Studies on the above topics will contribute to better management of antibiotic resistance dissemination in water environments and its risks on human health.Abbreviations3GC3rd generation cephalosporinsARBAntibiotic resistant bacteriaARGAntibiotic resistance geneCFUColony forming unitDBPDisinfection by-productseDNAExtracellular DNAEPSExtracellular polymeric substancesHGTHorizontal gene transferISCRInsertion sequence common regionMARMultiple antibiotic resistantMICMinimum inhibitory concentrationMGEMobile genetic elementsMSWMunicipal solid wasteQMRAQuantitative microbial risk assessmentVBNCViable but non-culturableWWTPWastewater treatment plant

CRISPR-Cas influences the acquisition of antibiotic resistance in Klebsiella pneumoniae.

In the US Carbapenem resistance in Klebsiella pneumoniae (Kp) is primarily attributed to the presence of the genes blaKPC-2 and blaKPC-3, which are transmitted via plasmids. Carbapenem-resistant Kp (CR-Kp) infections are associated with hospital outbreaks. They are difficult to treat, and associated with high mortality rates prompting studies of how resistance is obtained. In this study, we determined the presence of CRISPR-Cas in 304 clinical Kp strains. The CRISPR-Cas system has been found to prevent the spread of plasmids and bacteriophages, and therefore limits the horizontal gene transfer mediated by these mobile genetic elements. Here, we hypothesized that only those Kp strains that lack CRISPR-Cas can acquire CR plasmids, while those strains that have CRISPR-Cas are protected from gaining these plasmids and thus maintain sensitivity to antimicrobials. Our results show that CRISPR-Cas is absent in most clinical Kp strains including the clinically important ST258 clone. ST258 strains that continue to be sensitive to carbapenems also lack CRISPR-Cas. Interestingly, CRISPR-Cas positive strains, all non-ST258, exhibit lower resistance rates to antimicrobials than CRISPR-Cas negative strains. Importantly, we demonstrate that the presence of CRISPR-Cas appears to inhibit the acquisition of blaKPC plasmids in 7 Kp strains. Furthermore, we show that strains that are unable to acquire blaKPC plasmids contain CRISPR spacer sequences highly identical to those found in previously published multidrug-resistance-containing plasmids. Lastly, to our knowledge this is the first paper demonstrating that resistance to blaKPC plasmid invasion in a CRISPR-containing Kp strain can be reversed by deleting the CRISPR-cas cassette.