Fosfomycin and tobramycin in combination downregulate nitrate reductase genes narG and narH, resulting in increased activity against Pseudomonas aeruginosa under anaerobic conditions

Combined analysis of transcriptomics and metabolomics provide insights into the antibacterial mechanism of bacteriocin XJS01 against multidrug-resistant Staphylococcus aureus

Multidrug-resistant (MDR) bacteria are widespread in the environment and pose a serious threat to public health. It has been shown that bacteriocins have a great potential in controlling MDR pathogens, including Staphylococcus aureus. A previously reported Lactobacillus salivarius bacteriocin XJS01 exhibited good antibacterial activity against MDR S. aureus 2612:1606BL1486 (henceforth referred to as S. aureus_26), but its molecular mechanism remains unknown. Herein, we investigated the antibacterial mechanism of XJS01 on S. aureus_26 using an approach combining transcriptomics and metabolomics. The results showed that XJS01 induced significant changes at both transcriptional and metabolic levels in S. aureus_26. In total, 231 differentially expressed genes (DEGs) and 206 differentially abundance metabolites (DAMs) were identified in S. aureus_26 treated with 1 × MIC (minimum inhibition concentration) XJS01 compared with untreated (XJS01-free) cells (control). Functional analysis revealed that these DEGs and DAMs, alone with the related pathways and biological processes, were typically involved in stress response, being primarily related to metal uptake, cell virulence, self-help mechanism, amino acid and energy metabolism, bacterial stress response (e.g., two-component system), and membrane transport (e.g., phosphotransferase system). Overall, this study uncovered the multi-target effects of bacteriocins against MDR S. aureus at the genome-wide transcriptional and metabolic levels. These findings might be useful in the development of bacteriocins for the control of MDR S. aureus and other drug-resistant bacteria.

Phage resistance mutation triggered by OmpC deficiency in Klebsiella pneumoniae induced limited fitness costs

Outer membrane proteins (OMPs) play an important role in bacterial fitness costs. Derived from the interaction between Klebsiella pneumoniae K7 and phage GH-K3, K7R^B is an outer membrane porin-deficient phage-resistant mutant strain triggered by ompC₇₁₂ deletion, exhibits expression inhibition of OmpC, OmpN, KPN_02430 and OmpF, but its fitness costs and regulatory mechanism remains unknown. In this study, compared with K7, K7R^B showed almost unaffected growth rate, slightly decreased virulence, and increased resistance to some antibiotics. Transcriptome analysis showed that the pathways of glycerolipid metabolism and nitrogen metabolism in K7R^B were significantly inhibited, while the transcription of permeases belonging to ABC transporters tended to be active, nutrient uptakes such as citrate and phenylalanine were also enhanced. However, transcriptional up-regulation in K7R^B was inhibited by overexpression of OmpC, OmpN, KPN_02430 and OmpF in general. Overexpression of OmpN, KPN_02430 and OmpF, respectively, restoring the sensitivity of strains to antibiotics to varying degrees, while OmpC overexpression aggravated the bacterial drug-resistance especially to β-lactam antibiotics. Besides, unlike OmpC and OmpF, overexpression of OmpN and KPN_02430 reduced bacterial virulence. In brief, by revealing the limited fitness costs of phage-resistant mutant K. pneumoniae with porin-deficiency, our study providing a reference for the design and development of drugs to inhibit the ways of bacterial metabolic rewiring and to increase fitness costs.

Mutational background influences P. aeruginosa ciprofloxacin resistance evolution but preserves collateral sensitivity robustness

Bacterial adaptation to the presence of an antibiotic often involves evolutionary trade-offs, such as increased susceptibility to other drugs (collateral sensitivity). Its exploitation to design improved therapeutic strategies is only feasible if collateral sensitivity is robust, reproducible, and emerges in resistant mutants; these issues are rarely addressed in available publications. We describe a robust collateral sensitivity phenotype that emerges in different antibiotic-resistance mutational backgrounds, due to different genetic events, and propose therapeutic strategies effective for treating infections caused by Pseudomonas aeruginosa antibiotic-resistant mutants. Since conserved collateral sensitivity phenotypes do not confer adaptation to the presence of antibiotics, our results are also relevant for understanding convergent evolution processes in which the force selecting the emerging phenotype remains unclear.

Collateral sensitivity is an evolutionary trade-off whereby acquisition of the adaptive phenotype of resistance to an antibiotic leads to the nonadaptive increased susceptibility to another. The feasibility of harnessing such a trade-off to design evolutionary-based approaches for treating bacterial infections has been studied using model strains. However, clinical application of collateral sensitivity requires its conservation among strains presenting different mutational backgrounds. Particularly relevant is studying collateral sensitivity robustness of already-antibiotic-resistant mutants when challenged with a new antimicrobial, a common situation in clinics that has hardly been addressed. We submitted a set of diverse Pseudomonas aeruginosa antibiotic-resistant mutants to short-term evolution in the presence of different antimicrobials. Ciprofloxacin selects different clinically relevant resistance mutations in the preexisting resistant mutants, which gave rise to the same, robust, collateral sensitivity to aztreonam and tobramycin. We then experimentally determined that alternation of ciprofloxacin with aztreonam is more efficient than ciprofloxacin–tobramycin alternation in driving the extinction of the analyzed antibiotic-resistant mutants. Also, we show that the combinations ciprofloxacin–aztreonam or ciprofloxacin–tobramycin are the most effective strategies for eliminating the tested P. aeruginosa antibiotic-resistant mutants. These findings support that the identification of conserved collateral sensitivity patterns may guide the design of evolution-based strategies to treat bacterial infections, including those due to antibiotic-resistant mutants. Besides, this is an example of phenotypic convergence in the absence of parallel evolution that, beyond the antibiotic-resistance field, could facilitate the understanding of evolution processes, where the selective forces giving rise to new, not clearly adaptive phenotypes remain unclear.

Comparative transcription analysis of resistant mutants against four different antibiotics in Pseudomonas aeruginosa

The emergence of antibiotic resistance has severely impaired the treatment of infections caused by Pseudomonas aeruginosa. There are few studies related to comparing the antibiotics resistance mechanisms of P. aeruginosa against different antibiotics. In this study, RNA sequencing was used to investigate the differences of transcriptome between wild strain and four antibiotics resistant strains of P. aeruginosa PAO1 (polymyxin B, ciprofloxacin, doxycycline, and ceftriaxone). Compared to the wild strain, 1907, 495, 2402, and 116 differentially expressed genes (DEGs) were identified in polymyxin B, ciprofloxacin, doxycycline, and ceftriaxone resistant PAO1, respectively. After analysis of genes related to antimicrobial resistance, we found genes implicated in biofilm formation (pelB, pelC, pelD, pelE, pelF, pelG, algA, algF, and alg44) were significantly upregulated in polymyxin B-resistant PAO1, efflux pump genes (mexA, mexB, oprM) and biofilm formation genes (pslJ, pslK and pslN) were upregulated in ciprofloxacin-resistant PAO1; other efflux pump genes (mexC, mexD, oprJ) were upregulated in doxycycline-resistant PAO1; ampC were upregulated in ceftriaxone-resistant PAO1. As a consequence of antibiotic resistance, genes related to virulence factors such as type Ⅱ secretion system (lasA, lasB and piv) were significantly upregulated in polymyxin B-resistant PAO1, and type Ⅲ secretion system (exoS, exoT, exoY, exsA, exsB, exsC, exsD, pcrV, popB, popD, pscC, pscE, pscG, and pscJ) were upregulated in doxycycline-resistant PAO1. While, ampC were upregulated in ceftriaxone-resistant PAO1. In addition, variants were obtained in wild type and four antibiotics resistant PAO1. Our findings provide a comparative transcriptome analysis of antibiotic resistant mutants selected by different antibiotics, and might assist in identifying potential therapeutic strategies for P. aeruginosa infection.

Rapid and robust evolution of collateral sensitivity in Pseudomonas aeruginosa antibiotic-resistant mutants

The analysis of trade-offs, as collateral sensitivity, associated with the acquisition of antibiotic resistance, is mainly based on the use of model strains. However, the possibility of exploiting these trade-offs for fighting already resistant isolates has not been addressed in depth, despite the fact that bacterial pathogens are frequently antibiotic-resistant, forming either homogeneous or heterogeneous populations. Using a set of Pseudomonas aeruginosa-resistant mutants, we found that ceftazidime selects pyomelanogenic tobramycin-hypersusceptible mutants presenting chromosomal deletions in the analyzed genetic backgrounds. Since pyomelanogenic resistant mutants frequently coexist with other morphotypes in patients with cystic fibrosis, we analyzed the exploitation of this trade-off to drive extinction of heterogeneous resistant populations by using tobramycin/ceftazidime alternation. Our work shows that this approach is feasible because phenotypic trade-offs associated with the use of ceftazidime are robust. The identification of conserved collateral sensitivity networks may guide the rational design of evolution-based antibiotic therapies in P. aeruginosa infections.

CFTR-PTEN-dependent mitochondrial metabolic dysfunction promotes Pseudomonas aeruginosa airway infection

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor best known for regulating cell proliferation and metabolism. PTEN forms a complex with the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) at the plasma membrane, and this complex is known to be functionally impaired in CF. Here, we demonstrated that the combined effect of PTEN and CFTR dysfunction stimulates mitochondrial activity, resulting in excessive release of succinate and reactive oxygen species. This environment promoted the colonization of the airway by Pseudomonas aeruginosa, bacteria that preferentially metabolize succinate, and stimulated an anti-inflammatory host response dominated by immune-responsive gene 1 (IRG1) and itaconate. The recruitment of myeloid cells induced by these strains was inefficient in clearing the infection and increased numbers of phagocytes accumulated under CFTR-PTEN axis dysfunction. This central metabolic defect in mitochondrial function due to impaired PTEN activity contributes to P. aeruginosa infection in CF.

Quantitative Proteomics Reveals the Mechanism of Silver Nanoparticles against Multidrug-Resistant Pseudomonas aeruginosa Biofilms

The decline of clinically effective antibiotics has made it necessary to develop more effective antimicrobial agents, especially for refractory biofilm-related infections. Silver nanoparticles (AgNPs) are a new type of antimicrobial agent that can eradicate biofilms and reduce bacterial resistance, but its anti-biofilm mechanism has not been elucidated. In this study, we investigated the molecular mechanism of AgNPs against multidrug-resistant Pseudomonas aeruginosa by means of anti-biofilm tests, scanning electron microscopy (SEM), and tandem mass tag (TMT)-labeled quantitative proteomics. The results of anti-biofilm tests demonstrated that AgNPs inhibited the formation of P. aeruginosa biofilm and disrupted its preformed biofilm. SEM showed that when exposed to AgNPs, the structure of the P. aeruginosa biofilm was destroyed, along with significant reduction of its biomass. TMT-labeled quantitative proteomic analysis revealed that AgNPs could defeat the P. aeruginosa biofilm in multiple ways by inhibiting its adhesion and motility, stimulating strong oxidative stress response, destroying iron homeostasis, blocking aerobic and anaerobic respiration, and affecting quorum sensing systems. Our findings offer a new insight into clarifying the mechanism of AgNPs against biofilms, thus providing a theoretical basis for its clinical application.

Oxygen Limitation Enhances the Antimicrobial Activity of Fosfomycin in Pseudomonas aeruginosa Following Overexpression of glpT Which Encodes Glycerol-3-Phosphate/Fosfomycin Symporter

Fosfomycin is resurfacing as a "last resort drug" to treat infections caused by multidrug resistant pathogens. This drug has a remarkable benefit in that its activity increases under oxygen-limited conditions unlike other commonly used antimicrobials such as β-lactams, fluoroquinolones and aminoglycosides. Especially, utility of fosfomycin has being evaluated with particular interest to treat chronic biofilm infections caused by Pseudomonas aeruginosa because it often encounters anaerobic situations. Here, we showed that P. aeruginosa PAO1, commonly used in many laboratories, becomes more susceptible to fosfomycin when grown anaerobically, and studied on how fosfomycin increases its activity under anaerobic conditions. Results of transport assay and gene expression study indicated that PAO1 cells grown anaerobically exhibit a higher expression of glpT encoding a glycerol-3-phosphate transporter which is responsible for fosfomycin uptake, then lead to increased intracellular accumulation of the drug. Elevated expression of glpT in anaerobic cultures depended on ANR, a transcriptional regulator that is activated under anaerobic conditions. Purified ANR protein bound to the DNA fragment from glpT region upstream, suggesting it is an activator of glpT gene expression. We found that increased susceptibility to fosfomycin was also observed in a clinical isolate which has a promoted biofilm phenotype and its glpT and anr genes are highly conserved with those of PAO1. We conclude that increased antibacterial activity of fosfomycin to P. aeruginosa under anaerobic conditions is attributed to elevated expression of GlpT following activation of ANR, then leads to increased uptake of the drug.

Use of Calgary and Microfluidic BioFlux Systems To Test the Activity of Fosfomycin and Tobramycin Alone and in Combination against Cystic Fibrosis Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is a major cause of morbidity and mortality in chronically infected cystic fibrosis patients. Novel in vitro biofilm models which reliably predict the therapeutic success of antimicrobial therapies against biofilm bacteria should be implemented. The activity of fosfomycin, tobramycin, and the fosfomycin-tobramycin combination against 6 susceptible P. aeruginosa strains isolated from respiratory samples from cystic fibrosis patients was tested by using two in vitro biofilm models: a closed system (Calgary device) and an open model based on microfluidics (BioFlux). All but one of the isolates formed biofilms. The fosfomycin and tobramycin minimal biofilm inhibitory concentrations (MBIC) were 1,024 to >1,024 μg/ml and 8 to 32 μg/ml, respectively. According to fractional inhibitory concentration analysis, the combination behaved synergistically against all the isolates except the P. aeruginosa ATCC 27853 strain. The dynamic formation of the biofilm was also studied with the BioFlux system, and the MIC and MBIC of each antibiotic were tested. For the combination, the lowest tobramycin concentration that was synergistic with fosfomycin was used. The captured images were analyzed by measuring the intensity of the colored pixels, which was proportional to the biofilm biomass. A statistically significant difference was found when the intensity of the inoculum was compared with the intensity of the microchannel in which the MBIC of tobramycin, fosfomycin, or their combination was used (P < 0.01) but not when the MIC was applied (P > 0.01). Fosfomycin-tobramycin was demonstrated to be synergistic against cystic fibrosis P. aeruginosa strains in the biofilm models when both the Calgary and the microfluidic BioFlux systems were tested. These results support the clinical use of this combination.

Fosfomycin

The treatment of bacterial infections suffers from two major problems: spread of multidrug-resistant (MDR) or extensively drug-resistant (XDR) pathogens and lack of development of new antibiotics active against such MDR and XDR bacteria. As a result, physicians have turned to older antibiotics, such as polymyxins, tetracyclines, and aminoglycosides. Lately, due to development of resistance to these agents, fosfomycin has gained attention, as it has remained active against both Gram-positive and Gram-negative MDR and XDR bacteria. New data of higher quality have become available, and several issues were clarified further. In this review, we summarize the available fosfomycin data regarding pharmacokinetic and pharmacodynamic properties, the in vitro activity against susceptible and antibiotic-resistant bacteria, mechanisms of resistance and development of resistance during treatment, synergy and antagonism with other antibiotics, clinical effectiveness, and adverse events. Issues that need to be studied further are also discussed.

Phenotypic shift in Pseudomonas aeruginosa populations from cystic fibrosis lungs after 2-week antipseudomonal treatment

BACKGROUND

The influence of suppressive therapy on the different P. aeruginosa phenotypes harbored in the lungs of cystic fibrosis (CF) patients remains unclear. Our aim was to investigate the phenotypic changes (mucoidy, hypermutability, antibiotic resistance, transcriptomic profiles and biofilm) in P. aeruginosa populations before and after a 2-week course of suppressive antimicrobial therapy in chronically infected CF patients in Denmark.

MATERIAL AND METHODS

Prospective observational clinical study. Sputum samples were assessed before and after treatment for P. aeruginosa, with regard to: a) colony-forming units (CFU/mL), b) frequency of mucoids and non-mucoids, c) resistance pattern to anti-pseudomonal drugs, d) hypermutability, e) transcriptomic profiles, and f) presence of biofilms.

RESULTS

We collected 23 sputum samples (12 before antibiotic treatment and 11 after) and 77 P. aeruginosa from different CF patients. After treatment, the P. aeruginosa burden diminished but antimicrobial resistance to aztreonam, tobramycin and ceftazidime rose; non-mucoid phenotypes presented increased resistance to colistin, tobramycin, meropenem, and ciprofloxacin, and hypermutable phenotypes to ciprofloxacin. In spite of biofilm persistence, a down-regulation of genes involved in denitrification was detected.

CONCLUSION

A 2-week course of suppressive therapy reduces P. aeruginosa lung colonization and influences nitrogen metabolism genes, but also promotes antimicrobial resistance while P. aeruginosa persists in biofilms.

Antimicrobial Activity of Fosfomycin-Tobramycin Combination against Pseudomonas aeruginosa Isolates Assessed by Time-Kill Assays and Mutant Prevention Concentrations

The antibacterial activity of fosfomycin-tobramycin combination was studied by time-kill assay in eight Pseudomonas aeruginosa clinical isolates belonging to the fosfomycin wild-type population (MIC = 64 μg/ml) but with different tobramycin susceptibilities (MIC range, 1 to 64 μg/ml). The mutant prevention concentration (MPC) and mutant selection window (MSW) were determined in five of these strains (tobramycin MIC range, 1 to 64 μg/ml) in aerobic and anaerobic conditions simulating environments that are present in biofilm-mediated infections. Fosfomycin-tobramycin was synergistic and bactericidal for the isolates with mutations in the mexZ repressor gene, with a tobramycin MIC of 4 μg/ml. This effect was not observed in strains displaying tobramycin MICs of 1 to 2 μg/ml due to the strong bactericidal effect of tobramycin alone. Fosfomycin presented higher MPC values (range, 2,048 to >2,048 μg/ml) in aerobic and anaerobic conditions than did tobramycin (range, 16 to 256 μg/ml). Interestingly, the association rendered narrow or even null MSWs in the two conditions. However, for isolates with high-level tobramycin resistance that harbored aminoglycoside nucleotidyltransferases, time-kill assays showed no synergy, with wide MSWs in the two environments. glpT gene mutations responsible for fosfomycin resistance in P. aeruginosa were determined in fosfomycin-susceptible wild-type strains and mutant derivatives recovered from MPC studies. All mutant derivatives had changes in the GlpT amino acid sequence, which resulted in a truncated permease responsible for fosfomycin resistance. These results suggest that fosfomycin-tobramycin can be an alternative for infections due to P. aeruginosa since it has demonstrated synergistic and bactericidal activity in susceptible isolates and those with low-level tobramycin resistance. It also prevents the emergence of resistant mutants in either aerobic or anaerobic environments.

Phylogenomics of Mycobacterium Nitrate Reductase Operon

NarGHJI operon encodes a nitrate reductase that can reduce nitrate to nitrite. This process enhances bacterial survival by nitrate respiration under anaerobic conditions. NarGHJI operon exists in many bacteria, especially saprophytic bacteria living in soil which play a key role in the nitrogen cycle. Most actinomycetes, including Mycobacterium tuberculosis, possess NarGHJI operons. M. tuberculosis is a facultative intracellular pathogen that expands in macrophages and has the ability to persist in a non-replicative form in granuloma lifelong. Nitrogen and nitrogen compounds play crucial roles in the struggle between M. tuberculosis and host. M. tuberculosis can use nitrate as a final electron acceptor under anaerobic conditions to enhance its survival. In this article, we reviewed the mechanisms regulating nitrate reductase expression and affecting its activity. Potential genes involved in regulating the nitrate reductase expression in M. tuberculosis were identified. The conserved NarG might be an alternative mycobacterium taxonomic marker.

Antimicrobial resistance, respiratory tract infections and role of biofilms in lung infections in cystic fibrosis patients

Lung infection is the main cause of morbidity and mortality in patients with cystic fibrosis and is mainly dominated by Pseudomonas aeruginosa. The biofilm mode of growth makes eradication of the infection impossible, and it causes a chronic inflammation in the airways. The general mechanisms of biofilm formation and antimicrobial tolerance and resistance are reviewed. Potential anti-biofilm therapeutic targets such as weakening of biofilms by quorum-sensing inhibitors or antibiotic killing guided by pharmacokinetics and pharmacodynamics of antibiotics are presented. The vicious circle of adaptive evolution of the persisting bacteria imposes important therapeutic challenges and requires development of new drug delivery systems able to reach the different niches occupied by the bacteria in the lung of cystic fibrosis patients.

Evidence for the efficacy of aztreonam for inhalation solution in the management of Pseudomonas aeruginosa in patients with cystic fibrosis

Chronic airway infection in cystic fibrosis (CF) is a main cause of the increased morbidity and mortality found with this disease. The most common cause of Gram-negative infection is Pseudomonas aeruginosa. The introduction of inhaled antibiotics has changed the lives of affected patients and the clinical outcome of this infection; this article focuses on the use of inhaled antibiotics in chronic P. aeruginosa infection in CF, and specifically on studies including the use of inhaled aztreonam lysine in P. aeruginosa infection. Studies were identified using PubMed and ClinicalTrials.gov, searching for ‘inhaled aztreonam’ and ‘cystic fibrosis’. Inhaled aztreonam is an important new treatment option for chronic P. aeruginosa infection in CF. Long-term studies have shown that the drug is safe and superior to inhaled tobramycin in these specific infections.

Nitrite modulates bacterial antibiotic susceptibility and biofilm formation in association with airway epithelial cells

Pseudomonas aeruginosa is the major pathogenic bacteria in cystic fibrosis and other forms of bronchiectasis. Growth in antibiotic-resistant biofilms contributes to the virulence of this organism. Sodium nitrite has antimicrobial properties and has been tolerated as a nebulized compound at high concentrations in human subjects with pulmonary hypertension; however, its effects have not been evaluated on biotic biofilms or in combination with other clinically useful antibiotics. We grew P. aeruginosa on the apical surface of primary human airway epithelial cells to test the efficacy of sodium nitrite against biotic biofilms. Nitrite alone prevented 99% of biofilm growth. We then identified significant cooperative interactions between nitrite and polymyxins. For P. aeruginosa growing on primary CF airway cells, combining nitrite and colistimethate resulted in an additional log of bacterial inhibition compared to treating with either agent alone. Nitrite and colistimethate additively inhibited oxygen consumption by P. aeruginosa. Surprisingly, whereas the antimicrobial effects of nitrite in planktonic, aerated cultures are nitric oxide (NO) dependent, antimicrobial effects under other growth conditions are not. The inhibitory effect of nitrite on bacterial oxygen consumption and biofilm growth did not require NO as an intermediate as chemically scavenging NO did not block growth inhibition. These data suggest an NO-radical independent nitrosative or oxidative inhibition of respiration. The combination of nebulized sodium nitrite and colistimethate may provide a novel therapy for chronic P. aeruginosa airway infections, because sodium nitrite, unlike other antibiotic respiratory chain "poisons," can be safely nebulized at high concentration in humans.

Physiological levels of nitrate support anoxic growth by denitrification of Pseudomonas aeruginosa at growth rates reported in cystic fibrosis lungs and sputum

Chronic Pseudomonas aeruginosa lung infection is the most severe complication in patients with cystic fibrosis (CF). The infection is characterized by the formation of biofilm surrounded by numerous polymorphonuclear leukocytes (PMNs) and strong O2 depletion in the endobronchial mucus. We have reported that O2 is mainly consumed by the activated PMNs, while O2 consumption by aerobic respiration is diminutive and nitrous oxide (N2O) is produced in infected CF sputum. This suggests that the reported growth rates of P. aeruginosa in lungs and sputum may result from anaerobic respiration using denitrification. The growth rate of P. aeruginosa achieved by denitrification at physiological levels (~400 μM) of nitrate (NO(-) 3) is however, not known. Therefore, we have measured growth rates of anoxic cultures of PAO1 and clinical isolates (n = 12) in LB media supplemented with NO(-) 3 and found a significant increase of growth when supplementing PAO1 and clinical isolates with ≥150 μM NO(-) 3 and 100 μM NO(-) 3, respectively. An essential contribution to growth by denitrification was demonstrated by the inability to establish a significantly increased growth rate by a denitrification deficient ΔnirS-N mutant at <1 mM of NO(-) 3. Activation of denitrification could be achieved by supplementation with as little as 62.5 μM of NO(-) 3 according to the significant production of N2O by the nitrous oxide reductase deficient ΔnosZ mutant. Studies of the promoter activity, gene transcripts, and enzyme activity of the four N-oxide reductases in PAO1 (Nar, Nir, Nor, Nos) further verified the engagement of denitrification, showing a transient increase in activation and expression and rapid consumption of NO(-) 3 followed by a transient increase of NO(-) 2. Growth rates obtained by denitrification in this study were comparable to our reported growth rates in the majority of P. aeruginosa cells in CF lungs and sputum. Thus, we have demonstrated that denitrification is required for P. aeruginosa growth in infected endobronchial CF mucus.

Mechanisms of reduced susceptibility and genotypic prediction of antibiotic resistance in Prevotella isolated from cystic fibrosis (CF) and non-CF patients

OBJECTIVES

To investigate mechanisms of reduced susceptibility to commonly used antibiotics in Prevotella cultured from patients with cystic fibrosis (CF), patients with invasive infection and healthy control subjects and to determine whether genotype can be used to predict phenotypic resistance.

METHODS

The susceptibility of 157 Prevotella isolates to seven antibiotics was compared, with detection of resistance genes (cfxA-type gene, ermF and tetQ), mutations within the CfxA-type β-lactamase and expression of efflux pumps.

RESULTS

Prevotella isolates positive for a cfxA-type gene had higher MICs of amoxicillin and ceftazidime compared with isolates negative for this gene (P < 0.001). A mutation within the CfxA-type β-lactamase (Y239D) was associated with ceftazidime resistance (P = 0.011). The UK CF isolates were 5.3-fold, 2.7-fold and 5.7-fold more likely to harbour ermF compared with the US CF, UK invasive and UK healthy control isolates, respectively. Higher concentrations of azithromycin (P < 0.001) and clindamycin (P < 0.001) were also required to inhibit the growth of the ermF-positive isolates compared with ermF-negative isolates. Furthermore, tetQ-positive Prevotella isolates had higher MICs of tetracycline (P = 0.001) and doxycycline (P < 0.001) compared with tetQ-negative isolates. Prevotella spp. were also shown, for the first time, to express resistance nodulation division (RND)-type efflux pumps.

CONCLUSIONS

This study has demonstrated that Prevotella isolated from various sources harbour a common pool of resistance genes and possess RND-type efflux pumps, which may contribute to tetracycline resistance. The findings indicate that antibiotic resistance is common in Prevotella spp., but the genotypic traits investigated do not reflect phenotypic antibiotic resistance in every instance.