Comparative Transcriptomics Reveals Distinct Gene Expressions of a Model Ciliated Protozoan Feeding on Bacteria-Free Medium, Digestible, and Digestion-Resistant Bacteria

Bacterivory is an important ecological function of protists in natural ecosystems. However, there are diverse bacterial species resistant to protistan digestion, which reduces the carbon flow to higher trophic levels. So far, a molecular biological view of metabolic processes in heterotrophic protists during predation of bacterial preys of different digestibility is still lacking. In this study, we investigated the growth performance a ciliated protozoan Tetrahymena thermophila cultivated in a bacteria-free Super Proteose Peptone (SPP) medium (control), and in the media mixed with either a digestion-resistant bacterial species (DRB) or a digestible strain of E. coli (ECO). We found the protist population grew fastest in the SPP and slowest in the DRB treatment. Fluorescence in situ hybridization confirmed that there were indeed non-digested, viable bacteria in the ciliate cells fed with DRB, but none in other treatments. Comparative analysis of RNA-seq data showed that, relative to the control, 637 and 511 genes in T. thermophila were significantly and differentially expressed in the DRB and ECO treatments, respectively. The protistan expression of lysosomal proteases (especially papain-like cysteine proteinases), GH18 chitinases, and an isocitrate lyase were upregulated in both bacterial treatments. The genes encoding protease, glycosidase and involving glycolysis, TCA and glyoxylate cycles of carbon metabolic processes were higher expressed in the DRB treatment when compared with the ECO. Nevertheless, the genes for glutathione metabolism were more upregulated in the control than those in both bacterial treatments, regardless of the digestibility of the bacteria. The results of this study indicate that not only bacterial food but also digestibility of bacterial taxa modulate multiple metabolic processes in heterotrophic protists, which contribute to a better understanding of protistan bacterivory and bacteria-protists interactions on a molecular basis.

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Development of an Immunochromatographic Strip Using Conjugated Gold Nanoparticles for the Rapid Detection of Klebsiella pneumoniae Causing Neonatal Sepsis

Pharmaceutics ◽

10.3390/pharmaceutics13081141 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1141

Author(s):

Noha M. Elhosseiny ◽

Tamer M. Samir ◽

Aliaa A. Ali ◽

Amani A. El-Kholy ◽

Ahmed S. Attia

Keyword(s):

Gold Nanoparticles ◽

Klebsiella Pneumoniae ◽

Causative Agent ◽

Neonatal Sepsis ◽

Bacterial Species ◽

Resistant Bacteria ◽

Immunochromatographic Strip ◽

Amino Acid Peptide ◽

Negative Results ◽

Drug Resistant Bacteria

Neonatal sepsis is a leading cause of death among newborns and infants, especially in the developing world. The problem is compounded by the delays in pinpointing the causative agent of the infection. This is reflected in increasing mortality associated with these cases and the spread of multi-drug-resistant bacteria. In this work, we deployed bioinformatics and proteomics analyses to determine a promising target that could be used for the identification of a major neonatal sepsis causative agent, Klebsiella pneumoniae. A 19 amino acid peptide from a hypothetical outer membrane was found to be very specific to the species, well conserved among its strains, surface exposed, and expressed in conditions simulating infection. Antibodies against the selected peptide were conjugated to gold nanoparticles and incorporated into an immunochromatographic strip. The developed strip was able to detect as low as 105 CFU/mL of K. pneumoniae. Regarding specificity, it showed negative results with both Escherichia coli and Enterobacter cloacae. More importantly, in a pilot study using neonatal sepsis cases blood specimens, the developed strip selectively gave positive results within 20 min with those infected with K. pneumoniae without prior sample processing. However, it gave negative results in cases infected with other bacterial species.

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Antimicrobial Resistance among Neonates with Bacterial Sepsis and Their Clinical Outcomes in a Tertiary Hospital in Kathmandu Valley, Nepal

Tropical Medicine and Infectious Disease ◽

10.3390/tropicalmed6020056 ◽

2021 ◽

Vol 6 (2) ◽

pp. 56

Author(s):

Bijendra Raj Raghubanshi ◽

Karuna D. Sagili ◽

Wai Wai Han ◽

Henish Shakya ◽

Priyanka Shrestha ◽

...

Keyword(s):

Antibiotic Resistance ◽

Neonatal Sepsis ◽

Bacterial Culture ◽

Bacterial Species ◽

Antibiotic Sensitivity ◽

College Teaching ◽

Hospital Treatment ◽

Resistant Bacteria ◽

Coagulase Negative Staphylococcus ◽

Cross Sectional

Globally, antibiotic resistance in bacteria isolated from neonatal sepsis is increasing. In this cross-sectional study conducted at a medical college teaching hospital in Nepal, we assessed the antibiotic resistance levels in bacteria cultured from neonates with sepsis and their in-hospital treatment outcomes. We extracted data of neonates with sepsis admitted for in-patient care from June 2018 to December 2019 by reviewing hospital records of the neonatal intensive care unit and microbiology department. A total of 308 neonates with sepsis were admitted of which, blood bacterial culture antibiotic sensitivity reports were available for 298 neonates. Twenty neonates (7%) had bacteriologic culture-confirmed neonatal sepsis. The most common bacterial species isolated were Staphylococcus aureus (8), followed by coagulase-negative Staphylococcus (5). Most of these bacteria were resistant to at least one first-line antibiotic used to manage neonatal sepsis. Overall, there were 7 (2%) deaths among the 308 neonates (none of them from the bacterial culture-positive group), and 53 (17%) neonates had left the hospital against medical advice (LAMA). Improving hospital procedures to isolate bacteria in neonates with sepsis, undertaking measures to prevent the spread of antibiotic-resistant bacteria, and addressing LAMA’s reasons are urgently needed.

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STUDIES ON THE BACTERIOPHAGE OF D'HERELLE

Journal of Experimental Medicine ◽

10.1084/jem.42.4.483 ◽

1925 ◽

Vol 42 (4) ◽

pp. 483-497 ◽

Cited By ~ 9

Author(s):

Jacques J. Bronfenbrenner ◽

Charles Korb

Keyword(s):

Quantitative Evaluation ◽

Bacterial Species ◽

Relative Concentration ◽

Serial Dilution ◽

The Other ◽

Resistant Bacteria ◽

Dilution Method ◽

High Concentration ◽

Average Size ◽

Broth Dilution

The experiments reported above confirm the fact that lytic principle is distributed in active solution in a state of indivisible units. This permits its quantitative evaluation by serial dilution, as well as by plating on agar. The latter method, however, often gives readings considerably lower than those obtained by the broth dilution method of titration. By varying the concentration of agar it has been possible to show that the discrepancy is due to adsorption of the lytic agent on agar. When the concentration of the latter is increased from 0.3 per cent to 2.5 per cent the number of plaques of lysis is reduced more than 100 times. At the same time the average size of the plaques also decreases approximately to one-tenth of the original. The size, as well as the number of plaques, has been found to depend also on the condition of the culture employed in titration. Thus, when the culture exposed to the action of lytic agent is composed of young susceptible bacteria, the greater the concentration of bacteria, the smaller the plaques. When the culture is composed partly of young and partly of old susceptible bacteria, both the size and the number of the plaques are diminished with the increase in the relative concentration of old bacteria. On the other hand, presence in the culture of resistant bacteria does not affect either the size or the number of the plaques so long as the relative concentration of susceptible bacteria in the culture is sufficient to allow formation of them. The plaques appearing in the presence of a high concentration of resistant variants in the culture are relatively indistinct owing to overgrowth. Under carefully controlled conditions the size of plaques is found to be determined by the character of the lytic filtrate. Thus in the case of lytic agents which act upon more than one bacterial species the size of the plaques remains constant, irrespective of the bacterial substratum used for the production of the active filtrate.

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Species, Risk Factors, and Antimicrobial Susceptibility Profiles of Bacterial Isolates from HIV-Infected Patients Suspected to Have Pneumonia in Mekelle Zone, Tigray, Northern Ethiopia

BioMed Research International ◽

10.1155/2019/8768439 ◽

2019 ◽

Vol 2019 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

Gebre Adhanom ◽

Dawit Gebreegziabiher ◽

Yemane Weldu ◽

Araya Gebreyesus Wasihun ◽

Tadele Araya ◽

...

Keyword(s):

Risk Factors ◽

Antimicrobial Susceptibility ◽

Bacterial Pneumonia ◽

Bacterial Infections ◽

Bacterial Species ◽

Diffusion Method ◽

Resistant Bacteria ◽

P Value ◽

Northern Ethiopia ◽

Hiv Patients

Background. Pneumonia is a condition, where bacterial infections are implicated as the most common causes of morbidity and mortality in humans. The actual burden of HIV-infected patients with pneumonia is not well documented in Mekelle region of Ethiopia. This study estimated the prevalence of bacterial pneumonia in HIV patients, antimicrobial susceptibility patterns of pathogens implicated in pneumonia, and associated risk factors in Mekelle zone, Tigray, Northern Ethiopia, during August-December 2016. Methods. Sputum specimens were collected from 252 HIV seropositive individuals with suspected pneumonia. Data on sociodemographics and risk factors were also collected using a structured questionnaire. Blood, Chocolate, and Mac Conkey agar plates (Oxoid, Hampshire, UK) were used to grow the isolates. The isolated colonies were identified based on Gram stain, colony morphology, pigmentation, hemolysis, and biochemical tests. The antimicrobial susceptibility test was performed using the modified Kirby-Bauer disc diffusion method. The analysis was performed using SPSS version 22 and p-value < 0.05 with corresponding 95% confidence interval (CI) was considered statistically significant. Results. Out of the 252 samples, 110 (43.7%) were positive for various bacterial species. The predominant bacterial species were Klebsiella pneumoniae (n=26, 23.6 %) followed by Streptococcus pneumoniae (n=17, 15.5 %), Escherichia coli (n=16, 14.5%), Klebsiella spp. (n=15, 13.6%), Staphylococcus aureus (n=9, 8.2%), Enterobacter spp. (n=7, 6.3%), Pseudomonas aeruginosa (4, n=3.6%), Proteus spp. (n=4, 3.6%), Citrobacter freundii (n=7, 6.3%), Streptococcus pyogenes (3, 2.7%), and Haemophilus influenzae (n=2, 1.8%). Young age (18-29), recent CD4+ count less than 350 cells/mL, alcohol consumption, and HIV WHO stage II showed significant association with the occurrence of bacterial pneumonia. Resistance to penicillin, co-trimoxazole, and tetracycline was observed in 81.8%, 39.8%, and 24.5% of the isolates, respectively. Conclusions. The problem of pneumonia among HIV patients was significant in the study area. The high prevalence of drug-resistant bacteria isolated from the patient’s samples possesses a health risk in immunocompromised HIV patients. There is a need to strengthen and expand culture and susceptibility procedures for the administration of appropriate therapy to improve patients management and care which may aid in decreasing the mortality.

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Evolution under low antibiotic concentrations: a risk for the selection of Pseudomonas aeruginosa multidrug resistant mutants in nature

10.1101/2021.04.21.440750 ◽

2021 ◽

Author(s):

Fernando Sanz-García ◽

Sara Hernando-Amado ◽

José Luis Martínez

Keyword(s):

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Polymyxin B ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

Published Data ◽

Natural Ecosystems ◽

Clinical Value ◽

Drug Concentrations ◽

Resistant Mutants

ABSTRACTBACKGROUNDAntibiotic pollution of non-clinical environments might have a relevant impact on human health if resistant pathogens are selected. However, this potential risk is often overlooked, since drug concentrations in nature are usually below their minimal inhibitory concentrations (MICs). Albeit, antibiotic resistant bacteria can be selected even at sub-MIC concentrations, in a range that is dubbed the sub-MIC selective window, which depends on both the antibiotic and the pathogen.OBJECTIVESDetermine the sub-MIC selective windows of seven antibiotics of clinical relevance in the opportunistic pathogen Pseudomonas aeruginosa and evaluate the risk for selecting resistant mutants in nature, based on published data about the amount of antimicrobials detected in natural environments.METHODSWe conducted evolution experiments of P. aeruginosa PA14 in presence of sub-MIC concentrations of ceftazidime, amikacin, levofloxacin, ciprofloxacin, tetracycline, polymyxin B or imipenem, and measured drug susceptibility of the evolved populations.RESULTSSub-MIC selective window of quinolones was the largest, and the ones of polymyxin B and imipenem, the narrowest. Clinically relevant multidrug resistant (MDR) mutants (presenting MICs above EUCAST clinical breakpoints) arose within the sub-MIC selective windows of the majority of antibiotics tested, being these phenotypes probably mediated by efflux pumps′ activity.DISCUSSIONOur data show that the concentration of antibiotics reported in aquatic ecosystems -colonizable by P. aeruginosa- are, in occasions, higher than the ones able to select MDR mutants. This finding has implications for understanding the role of different ecosystems and conditions in the emergence of antibiotic resistance from a One-Health point of view. Further, it highlights the importance of delineating the sub-MIC selective windows for drugs of clinical value in pathogens with environmental niches, in order to evaluate the health risks due to antibiotic pollution of natural ecosystems and ultimately tackle antibiotic resistance.

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Targeted-Antibacterial-Plasmids (TAPs) combining conjugation and CRISPR/Cas systems achieve strain-specific antibacterial activity

10.1101/2020.10.12.335968 ◽

2020 ◽

Author(s):

Audrey Reuter ◽

Cécile Hilpert ◽

Annick Dedieu-Berne ◽

Sophie Lematre ◽

Erwan Gueguen ◽

...

Keyword(s):

Antibacterial Activity ◽

Pathogenic Bacteria ◽

Bacterial Species ◽

Carbapenem Resistance ◽

Double Strand Breaks ◽

Resistant Bacteria ◽

Innovative Strategy ◽

Strand Breaks ◽

Drug Resistant Bacteria

AbstractThe global emergence of drug-resistant bacteria leads to the loss of efficacy of our antibiotics arsenal and severely limits the success of currently available treatments. Here, we developed an innovative strategy based on Targeted-Antibacterial-Plasmids (TAPs) that use bacterial conjugation to deliver CRISPR/Cas systems exerting a strain-specific antibacterial activity. TAPs are highly versatile as they can be directed against any specific genomic or plasmid DNA using the custom algorithm (CSTB) that identifies appropriate targeting spacer sequences. We demonstrate the ability of TAPs to induce strain-selective killing by introducing lethal double strand breaks (DSBs) into the targeted genomes. TAPs directed against a plasmid-born carbapenem resistance gene efficiently resensitise the strain to the drug. This work represents an essential step towards the development of an alternative to antibiotic treatments, which could be used for in situ microbiota modification to eradicate targeted resistant and/or pathogenic bacteria without affecting other non-targeted bacterial species.

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Merging Metagenomics and Spatial Epidemiology To Understand the Distribution of Antimicrobial Resistance Genes from Enterobacteriaceae in Wild Owls

Applied and Environmental Microbiology ◽

10.1128/aem.00571-20 ◽

2020 ◽

Vol 86 (20) ◽

Author(s):

Elizabeth A. Miller ◽

Julia B. Ponder ◽

Michelle Willette ◽

Timothy J. Johnson ◽

Kimberly L. VanderWaal

Keyword(s):

Antimicrobial Resistance ◽

Resistance Genes ◽

Spatial Epidemiology ◽

Anthropogenic Sources ◽

Resistant Bacteria ◽

Metagenomic Sequencing ◽

Wild Animals ◽

Natural Ecosystems ◽

Content Type ◽

Antimicrobial Resistance Genes

ABSTRACT Antimicrobial resistance (AMR) is a well-documented phenomenon in bacteria from many natural ecosystems, including wild animals. However, the specific determinants and spatial distribution of resistant bacteria and antimicrobial resistance genes (ARGs) in the environment remain incompletely understood. In particular, information regarding the importance of anthropogenic sources of AMR relative to that of other biological and ecological influences is lacking. We conducted a cross-sectional study of AMR in great horned owls (Bubo virginianus) and barred owls (Strix varia) admitted to a rehabilitation center in the midwestern United States. A combination of selective culture enrichment and shotgun metagenomic sequencing was used to identify ARGs from Enterobacteriaceae. Overall, the prevalence of AMR was comparable to that in past studies of resistant Enterobacteriaceae in raptors, with acquired ARGs being identified in 23% of samples. Multimodel regression analyses identified seasonality and owl age to be important predictors of the likelihood of the presence of ARGs, with birds sampled during warmer months being more likely to harbor ARGs than those sampled during cooler months and with birds in their hatch year being more likely to harbor β-lactam ARGs than adults. Beyond host-specific determinants, ARG-positive owls were also more likely to be recovered from areas of high agricultural land cover. Spatial clustering analyses identified a significant high-risk cluster of tetracycline resistance gene-positive owls in the southern sampling range, but this could not be explained by any predictor variables. Taken together, these results highlight the complex distribution of AMR in natural environments and suggest that both biological and anthropogenic factors play important roles in determining the emergence and persistence of AMR in wildlife. IMPORTANCE Antimicrobial resistance (AMR) is a multifaceted problem that poses a worldwide threat to human and animal health. Recent reports suggest that wildlife may play an important role in the emergence, dissemination, and persistence of AMR. As such, there have been calls for better integration of wildlife into current research on AMR, including the use of wild animals as biosentinels of AMR contamination in the environment. A One Health approach can be used to gain a better understanding of all AMR sources and pathways, particularly those at the human-animal-environment interface. Our study focuses on this interface in order to assess the effect of human-impacted landscapes on AMR in a wild animal. This work highlights the value of wildlife rehabilitation centers for environmental AMR surveillance and demonstrates how metagenomic sequencing within a spatial epidemiology framework can be used to address questions surrounding AMR complexity in natural ecosystems.

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The Inactivation of Enzymes Belonging to the Central Carbon Metabolism Is a Novel Mechanism of Developing Antibiotic Resistance

mSystems ◽

10.1128/msystems.00282-20 ◽

2020 ◽

Vol 5 (3) ◽

Author(s):

Teresa Gil-Gil ◽

Fernando Corona ◽

José Luis Martínez ◽

Alejandra Bernardini

Keyword(s):

Antibiotic Resistance ◽

Stenotrophomonas Maltophilia ◽

Bacterial Species ◽

Bacterial Metabolism ◽

Resistant Bacteria ◽

Uridine Diphosphate ◽

Biosynthesis Pathway ◽

Content Type ◽

Peptidoglycan Biosynthesis ◽

Central Carbon

ABSTRACT Fosfomycin is a bactericidal antibiotic, analogous to phosphoenolpyruvate, that exerts its activity by inhibiting the activity of MurA. This enzyme catalyzes the first step of peptidoglycan biosynthesis, the transfer of enolpyruvate from phosphoenolpyruvate to uridine-diphosphate-N-acetylglucosamine. Fosfomycin is increasingly being used, mainly for treating infections caused by Gram-negative multidrug-resistant bacteria. The mechanisms of mutational resistance to fosfomycin in Stenotrophomonas maltophilia, an opportunistic pathogen characterized by its low susceptibility to commonly used antibiotics, were studied in the current work. None of the mechanisms reported so far for other organisms, which include the production of fosfomycin-inactivating enzymes, target modification, induction of an alternative peptidoglycan biosynthesis pathway, and the impaired entry of the antibiotic, are involved in the acquisition of such resistance by this bacterial species. Instead, the unique cause of resistance in the mutants studied is the mutational inactivation of different enzymes belonging to the Embden-Meyerhof-Parnas central metabolism pathway. The amount of intracellular fosfomycin accumulation did not change in any of these mutants, showing that neither inactivation nor transport of the antibiotic is involved. Transcriptomic analysis also showed that the mutants did not present changes in the expression level of putative alternative peptidoglycan biosynthesis pathway genes or any related enzyme. Finally, the mutants did not present an increased phosphoenolpyruvate concentration that might compete with fosfomycin for its binding to MurA. On the basis of these results, we describe a completely novel mechanism of antibiotic resistance based on mutations of genes encoding metabolic enzymes. IMPORTANCE Antibiotic resistance has been largely considered a specific bacterial response to an antibiotic challenge. Indeed, its study has been mainly concentrated on mechanisms that affect the antibiotics (mutations in transporters, efflux pumps, and antibiotic-modifying enzymes, or their regulators) or their targets (i.e., target mutations, protection, or bypass). Usually, antibiotic resistance-associated metabolic changes were considered a consequence (fitness costs) and not a cause of antibiotic resistance. Herein, we show that alterations in the central carbon bacterial metabolism can also be the cause of antibiotic resistance. In the study presented here, Stenotrophomonas maltophilia acquires fosfomycin resistance through the inactivation of glycolytic enzymes belonging to the Embden-Meyerhof-Parnas pathway. Besides resistance to fosfomycin, this inactivation also impairs the bacterial gluconeogenic pathway. Together with previous work showing that antibiotic resistance can be under metabolic control, our results provide evidence that antibiotic resistance is intertwined with the bacterial metabolism.

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High Colonization Rate and Heterogeneity of ESBL- and Carbapenemase-Producing Enterobacteriaceae Isolated from Gull Feces in Lisbon, Portugal

Microorganisms ◽

10.3390/microorganisms8101487 ◽

2020 ◽

Vol 8 (10) ◽

pp. 1487

Author(s):

Marta Aires-de-Sousa ◽

Claudine Fournier ◽

Elizeth Lopes ◽

Hermínia de Lencastre ◽

Patrice Nordmann ◽

...

Keyword(s):

Escherichia Coli ◽

Staphylococcus Aureus ◽

Methicillin Resistant Staphylococcus Aureus ◽

Bacterial Species ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

Multidrug Resistant Bacteria ◽

Vancomycin Resistant Enterococci ◽

Vancomycin Resistant ◽

Encoding Genes

In order to evaluate whether seagulls living on the Lisbon coastline, Portugal, might be colonized and consequently represent potential spreaders of multidrug-resistant bacteria, a total of 88 gull fecal samples were screened for detection of extended-spectrum β-lactamase (ESBL)- or carbapenemase-producing Enterobacteriaceae for methicillin-resistant Staphylococcus aureus (MRSA) and for vancomycin-resistant Enterococci (VRE). A large proportion of samples yielded carbapenemase- or ESBL-producing Enterobacteriaceae (16% and 55%, respectively), while only two MRSA and two VRE were detected. Mating-out assays followed by PCR and whole-plasmid sequencing allowed to identify carbapenemase and ESBL encoding genes. Among 24 carbapenemase-producing isolates, there were mainly Klebsiella pneumoniae (50%) and Escherichia coli (33%). OXA-181 was the most common carbapenemase identified (54%), followed by OXA-48 (25%) and KPC-2 (17%). Ten different ESBLs were found among 62 ESBL-producing isolates, mainly being CTX-M-type enzymes (87%). Co-occurrence in single samples of multiple ESBL- and carbapenemase producers belonging to different bacterial species was observed in some cases. Seagulls constitute an important source for spreading multidrug-resistant bacteria in the environment and their gut microbiota a formidable microenvironment for transfer of resistance genes within bacterial species.

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HAMLET, a Protein Complex from Human Milk, Has Bactericidal Activity and Enhances the Activity of Antibiotics against Pathogenic Streptococci

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01193-19 ◽

2019 ◽

Vol 63 (12) ◽

Cited By ~ 5

Author(s):

Feiruz Alamiri ◽

Kristian Riesbeck ◽

Anders P. Hakansson

Keyword(s):

Human Milk ◽

Bactericidal Activity ◽

Combination Treatment ◽

Bacterial Species ◽

Penicillin G ◽

Resistant Bacteria ◽

Tumoricidal Activity ◽

Antibiotic Resistant ◽

Content Type ◽

Transport Inhibitors

ABSTRACT HAMLET (human alpha-lactalbumin made lethal to tumor cells) is a protein-lipid complex derived from human milk that was first described for its tumoricidal activity. Later studies showed that HAMLET also has direct bactericidal activity against select species of bacteria, with highest activity against Streptococcus pneumoniae. Additionally, HAMLET in combination with various antimicrobial agents can make a broad range of antibiotic-resistant bacterial species sensitive to antibiotics. Here, we show that HAMLET has direct antibacterial activity not only against pneumococci but also against Streptococcus pyogenes (group A streptococci [GAS]) and Streptococcus agalactiae (group B streptococci [GBS]). As with pneumococci, HAMLET treatment of GAS and GBS resulted in depolarization of the bacterial membrane, followed by membrane permeabilization and death, which was able to be inhibited by calcium and sodium transport inhibitors. Treatment of clinical antibiotic-resistant isolates of S. pneumoniae, GAS, and GBS with sublethal concentrations of HAMLET in combination with antibiotics decreased the MICs of the antibiotics into the sensitive range. This effect could also be blocked by ion transport inhibitors, suggesting that HAMLET’s bactericidal and combination treatment effects used similar mechanisms. Finally, we show that HAMLET potentiated the effects of erythromycin against erythromycin-resistant bacteria more effectively than penicillin G potentiated killing bacteria resistant to erythromycin. These results show that HAMLET effectively (i) kills three different species of pathogenic streptococci by similar mechanisms and also (ii) potentiates the activities of macrolides and lincosamides more effectively than combination treatment with beta-lactams. These findings suggest a potential therapeutic role for HAMLET in repurposing antibiotics currently causing treatment failures in patients.

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