Current therapies for pseudomonas aeruginosa

Atomic force microscopy analysis of Pel polysaccharide- and type IV pili-mediated adhesion of Pseudomonas aeruginosa PA14 to an abiotic surface

Type IV pili (TFP) contribute to the ability of microbes such as Pseudomonas aeruginosa to engage with and move across surfaces. We reported previously that P. aeruginosa TFP generate retractive forces of ∼30 pN and provided indirect evidence that TFP-mediated surface attachment was enhanced in the presence of the Pel polysaccharide. Here, we use different mutants defective in flagellar, Pel production or TFP production - alone or in combination - to decipher the relative contribution of these biofilm-promoting factors for P. aeruginosa adhesion. By means of atomic force microscopy (AFM), we show that mutating the flagellum (ΔflgK mutant) results in an increase in Pel polysaccharide production, but this increase in Pel does not result in an increase in surface adhesive properties compared to those previously described for the WT strain. By blocking Pel production in the ΔflgK mutant (ΔflgKΔpel), we directly show that TFP play a major role in the adhesion of the bacteria to hydrophobic AFM tips, but that the adhesion force is only slightly impaired by the absence of Pel. Inversely, performing single-cell force spectroscopy measurements with the mutant lacking TFP (ΔflgKΔpilA) reveals that the Pel can modulate the attachment of the bacteria to a hydrophobic substrate in a time-dependent manner. Finally, little adhesion was detected for the ΔflgKΔpilAΔpelA triple mutant, suggesting that both TFP and Pel polysaccharide make a substantial contribution to bacteria-substratum interaction events. Altogether, our data allow us to decipher the relative contribution of Pel and TFP in the early attachment by P. aeruginosa.

Pseudomonas Bacteremia in Children: Clinical and Microbiologic Features and Risk Factors of Mortality: A Retrospective Cohort Study

BACKGROUND

Pseudomonas bacteremia is most commonly acquired in hospital. The aim of this study was to investigate the clinical features and antibiotic susceptibility, mortality rate and risk factors of mortality in children with Pseudomonas bacteremia.

METHODS

A retrospective cohort study that included children 18 years of age or younger admitted to a tertiary hospital with Pseudomonas bacteremia between 2005 and 2020.

RESULTS

A total of 196 patients with Pseudomonas bacteremia were identified. The proportional rate of Pseudomonas bacteremia was 33.9/100,000 hospital days. Underlying disease was documented in 81.1% of patients, 61% had hemato-oncological disease. Pseudomonas bacteremia was healthcare related in 180 (91.8%) episodes. Multidrug-resistant (MDR) Pseudomonas accounted for 16 (8.2%) and difficult-to-treat organism to 3 (1.5%) of all isolates. Thirty-day mortality was reported in 27 (13.8%) patients, all had Pseudomonas aeruginosa. In multivariate regression analysis, the first model showed that younger age [P = 0.038, odds ratio (OR) = 1.095, 95% confidence interval (CI): 1.005-1.192] and inappropriate empiric antibiotic treatment (P = 0.004, OR = 3.584, 95% CI: 1.490-8.621) were significantly associated with higher mortality. The second model also showed higher morality in younger age (P = 0.021, OR = 1.114, 95% CI: 1.016-1.221) and MDR isolates (P = 0.001, OR = 9.725, 95% CI: 2.486-38.039).

CONCLUSIONS

Significant morbidity and mortality due to Pseudomonas bacteremia, but relatively lower mortality than previously published. Although young age, MDR isolates and inappropriate antibiotic treatment have been associated with increased mortality, these factors, especially with low prevalence of MDR isolates, may reflect the baseline mortality rate in vulnerable hosts with continuous contact with healthcare facilities facing such severe infection, and more efforts should be made to emphasize infection control practices to prevent such severe infection.

Metallacarborane Derivatives Effective against Pseudomonas aeruginosa and Yersinia enterocolitica

Pseudomonas aeruginosa is an opportunistic human pathogen that has become a nosocomial health problem worldwide. The pathogen has multiple drug removal and virulence secretion systems, is resistant to many antibiotics, and there is no commercial vaccine against it. Yersinia pestis is a zoonotic pathogen that is on the Select Agents list. The bacterium is the deadliest pathogen known to humans and antibiotic-resistant strains are appearing naturally. There is no commercial vaccine against the pathogen, either. In the current work, novel compounds based on metallacarborane cage were studied on strains of Pseudomonas aeruginosa and a Yersinia pestis substitute, Yersinia enterocolitica. The representative compounds had IC₅₀ values below 10 µM against Y. enterocolitica and values of 20–50 μM against P. aeruginosa. Artificial generation of compound-resistant Y. enterocolitica suggested a common mechanism for drug resistance, the first reported in the literature, and suggested N-linked metallacarboranes as impervious to cellular mechanisms of resistance generation. SEM analysis of the compound-resistant strains showed that the compounds had a predominantly bacteriostatic effect and blocked bacterial cell division in Y. enterocolitica. The compounds could be a starting point towards novel anti-Yersinia drugs and the strategy presented here proposes a mechanism to bypass any future drug resistance in bacteria.

Synthesis and antibacterial evaluation against resistant Gram-negative bacteria of monobactams bearing various substituents on oxime residue

Based on the structural characteristics of aztreonam (AZN) and its target PBP3, a series of new monobactam derivatives bearing various substituents on oxime residue were prepared and evaluated for their antibacterial activities against susceptible and resistant Gram-negative bacteria. Among them, compounds 8p and 8r displayed moderate potency with MIC values of 0.125-32 μg/mL against most tested Gram-negative strains, comparable to AZN. Meanwhile, the combination of 8p and 8r with avibactam as a β-lactamases inhibitor, in a ratio of 1:16, showed a promising synergistic effect against both ESBLs- and NDM-1-producing K. pneumoniae, with significantly reduced MIC values up to 8-fold and >256-fold respectively. Furthermore, both of them demonstrated excellent safety profiles both in vitro and in vivo. The results provided powerful information for further structural optimization of monobactam antibiotics to fight β-lactamase-producing resistant Gram-negative bacteria.

Characterization and structure determination of prolyl-tRNA synthetase from Pseudomonas aeruginosa and development as a screening platform

Pseudomonas aeruginosa is an opportunistic multi-drug resistant pathogen implicated as a causative agent in nosocomial and community acquired bacterial infections. The gene encoding prolyl-tRNA synthetase (ProRS) from P. aeruginosa was overexpressed in Escherichia coli and the resulting protein was characterized. ProRS was kinetically evaluated and the KM values for interactions with ATP, proline, and tRNA were 154, 122, and 5.5 μM, respectively. The turn-over numbers, kcatobs , for interactions with these substrates were calculated to be 5.5, 6.3, and 0.2 s-1 , respectively. The crystal structure of the α2 form of P. aeruginosa ProRS was solved to 2.60 Å resolution. The amino acid sequence and X-ray crystal structure of P. aeruginosa ProRS was analyzed and compared with homologs in which the crystal structures have been solved. The amino acids that interact with ATP and proline are well conserved in the active site region and overlay of the crystal structure with ProRS homologs conforms to a similar overall three-dimensional structure. ProRS was developed into a screening platform using scintillation proximity assay (SPA) technology and used to screen 890 chemical compounds, resulting in the identification of two inhibitory compounds, BT06A02 and BT07H05. This work confirms the utility of a screening system based on the functionality of ProRS from P. aeruginosa.

The Impact of using the term "Diabetic Ear" for the patients with Skull Base Osteomyelitis

BACKGROUND:

Diabetes and ear disease are some of the most widespread health concerns. The focus here is on the impact of using the term “Diabetic Ear” for patients with skull base osteomyelitis (SBM) in the context of malignant otitis externa (MOE). The aim of this study was to discover the awareness of general practitioners (GPs), residents, specialists, and consultants at Primary Health Care Centers about necrotizing otitis externa (NOE), also known previously as malignant external otitis (MOE), assess their deficiencies and provide solutions; also assist them for the early detection and possible prevention of diabetes- related ear diseases and their complications.

MATERIALS AND METHODS:

A cross-sectional study was conducted among a random sample of physicians (residents, specialists, and consultants) working at the Primary Health Care Centers in Al-Khobar and Dammam cities of the Eastern Province, Saudi Arabia. Data was collected using a standardized questionnaire. SPSS was used for data entry and analysis.

RESULTS:

The total number of medical practitioners was 84. Their mean age was 33.97 (±9.55). The proportion of females was higher than males, only 28.3% of the participants responded correctly when asked about MOE. Similarly, very few were aware of the risks of MOE (2.5%), complications associated with it (17.3%) and the necessary procedures for managing patients (24.2%). The awareness of doctors in the primary health clinics about MOE was significantly better than those in hospitals (P = 0.002).

CONCLUSION:

There was a significant deficiency in the knowledge of GPs on MOE. Therefore, health education and awareness programs on MOE are recommended. Furthermore, we recommend that it is necessary to encourage the use of the term “Diabetic EAR “to increase the level of awareness of physicians about MOE.

Identification and Characterization of Chemical Compounds that Inhibit Leucyl-tRNA Synthetase from Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is an opportunistic multi-drug resistance pathogen implicated as the causative agent in a high-percentage of nosocomial and community acquired bacterial infections. The gene encoding leucyl-tRNA synthetase (LeuRS) from P. aeruginosa was overexpressed in Escherichia coli and the resulting protein was characterized.

METHODS

LeuRS was kinetically evaluated and the KM values for interactions with leucine, ATP and tRNA were 6.5, 330, and 3.0 μM, respectively. LeuRS was developed into a screening platform using scintillation proximity assay (SPA) technology and used to screen over 2000 synthetic and natural chemical compounds.

RESULTS

The initial screen resulted in the identification of two inhibitory compounds, BT03C09 and BT03E07. IC50s against LeuRS observed for BT03C09 and BT03E07 were 23 and 15 μM, respectively. The minimum inhibitory concentrations (MIC) were determined against nine clinically relevant bacterial strains. In time-kill kinetic analysis, BT03C09 was observed to inhibit bacterial growth in a bacteriostatic manner, while BT03E07 acted as a bactericidal agent. Neither compound competed with leucine or ATP for binding LeuRS. Limited inhibition was observed in aminoacylation assays with the human mitochondrial form of LeuRS, however when tested in cultures of human cell line, BT03C09 was toxic at all concentration whereas BT03E07 only showed toxic effects at elevated concentrations.

CONCLUSION

Two compounds were identified as inhibitors of LeuRS in a screen of over 2000 natural and synthetic compounds. After characterization one compound (BT03E07) exhibited broad spectrum antibacterial activity while maintaining low toxicity against human mitochondrial LeuRS as well as against human cell cultures.

[Impact of duration of antibiotic therapy on the prognosis of patients with acute myeloid leukemia who had Gram-negative bloodstream infection in consolidation chemotherapy]

Objectives: To investigate the influence of duration of antibiotic therapy on the prognosis of patients with AML who had Gram-negative bloodstream infection during consolidation chemotherapy. Methods: Data were collected retrospectively from 591 patients enrolled from the registered "A Phase III study on optimizing treatment based on risk stratification for acute myeloid leukemia, ChiCTR-TRC-10001202" treatment protocol between September 2010 and January 2016 in different treatment cycles. Results: A total of 119 episodes of Gram-negative bloodstream infection occurred during consolidation chemotherapy. Excluding the 5 episodes in which fever lasted longer than 7 days, 114 episodes of infection were analyzed. The median neutrophil count was 0 (0-5.62)×10(9)/L, median neutropenia duration was 9 (3-26) days, median interval of antibiotics administration was 7 (4-14) days. Logistic regression analysis showed that there is no significant difference on 3-day recurrent fever rate and reinfection by the same type bacteria between antibiotics administration ≤7 days or >7 days (1.2% vs 3.0%, P=0.522, OR=0.400, 95% CI 0.024-6.591; 18.5% vs 21.2%, P=0.741, OR=0.844, 95% CI 0.309-2.307). Propensity score analysis confirmed there was no significant difference on same pathogen infection rate between antibiotics application time ≤ 7 days or >7 days (P=0.525, OR=0.663, 95% CI 0.187-2.352). No infection associated death occurred within 7 or 30 days in both groups. Conclusion: Discontinuation of therapy until sensitive antibiotics treated for 7 days does not increase the recurrent fever rate and the infection associated death rate. Indicating that, for AML who had Gram-negative bloodstream infection during consolidation chemotherapy, short courses of antibiotic therapy is a reasonable treatment option when the infection is controlled.

Identifying and exploiting genes that potentiate the evolution of antibiotic resistance

There is an urgent need to develop novel approaches for predicting and preventing the evolution of antibiotic resistance. Here we show that the ability to evolve de novo resistance to a clinically important β-lactam antibiotic, ceftazidime, varies drastically across the genus Pseudomonas. This variation arises because strains possessing the ampR global transcriptional regulator evolve resistance at a high rate. This does not arise because of mutations in ampR. Instead, this regulator potentiates evolution by allowing mutations in conserved peptidoglycan biosynthesis genes to induce high levels of β-lactamase expression. Crucially, blocking this evolutionary pathway by co-administering ceftazidime with the β-lactamase inhibitor avibactam can be used to eliminate pathogenic P. aeruginosa populations before they can evolve resistance. In summary, our study shows that identifying potentiator genes that act as evolutionary catalysts can be used to both predict and prevent the evolution of antibiotic resistance.

Molecular epidemiology of carbapenem-resistant Pseudomonas aeruginosa in an endemic area: comparison with global data

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is an endemic problem in certain countries including Greece. CRPA and multidrug-resistant P. aeruginosa (MDRPA) firstly emerged in our region during the 80s, right after the launch of imipenem and meropenem as therapeutic agents against P. aeruginosa infections. The role of outer membrane protein (Opr) inactivation has been known to contribute to imipenem resistance since many years, while efflux overexpression systems have been mainly associated with meropenem resistance. Among carbapenemases, metallo-β-lactamases (MBL) and mostly Verona integron-mediated (VIM) MBL's have played the most crucial role in CRPA emergence. VIM-2 and VIM-4 producing CRPA, usually belonging to clonal complexes (CC) 111 and 235 respectively, have most frequently been isolated. Bla_VIM-2 and bla_VIM-4 are usually associated with a class 1 integron. VIM-17 also has appeared in Greece. On the other hand, other VIM subtypes detected in a global level, such as VIM-3, VIM-5, VIM-6, VIM-7, VIM-11, VIM-14, VIM-15, VIM-16 and VIM-18 have not yet emerged in Greece. However, new VIM subtypes will probably emerge in the future. In addition, MBL carbapenemases other than VIM, detected worldwide have not yet appeared. A single CRPA isolate producing KPC has emerged in our region several years ago. The study of the molecular basis of Opr deficiency and efflux overexpression remains a challenge for the future. In this article, we review the molecular epidemiology of CRPA in an endemic area, compared to global data.

Factors associated with in-hospital mortality among critically ill surgical patients with multidrug-resistant Gram-negative infections

PURPOSE

Multidrug-resistant (MDR) Gram-negative infection increases risk of mortality, other complications, and costs. The objective of this study was to determine the prevalence of and identify factors associated with in-hospital mortality among critically ill surgical patients.

MATERIALS AND METHODS

This case-control study included critically ill surgical patients from 2011 to 2014 who had a carbapenem-resistant Enterobacteriaceae (CRE), MDR P. aeruginosa, or MDR Acinetobacter spp. infection. Characteristics of patients surviving to hospital discharge were compared to those of non-survivors.

RESULTS

Sixty-two patients were included. Of these, 21 (33.9%) died prior to discharge. Vasopressors and mechanical ventilation prior to index culture were more common in non-survivors vs. survivors (76.2% vs. 46.3%, p=0.03; and 100% vs. 63.4%, p=0.001). ICU and hospital LOS prior to index culture was longer in non-survivors vs. survivors (median 19 vs. 4days, p=0.001; and median 25 vs. 7days, p=0.009). In multivariate logistic regression, achievement of source control was the only variable associated with decreased in-hospital mortality [0.04 (95% CI 0.003-0.52); p=0.01].

CONCLUSIONS

MDR Gram-negative infection is associated with significant in-hospital mortality among critically ill surgical patients. Source control, along with prior ICU LOS, mechanical ventilation status, vasopressor use, and definitive antibiotic choice, are important predictors of survival in this population.

Label-free SRM-based relative quantification of antibiotic resistance mechanisms in Pseudomonas aeruginosa clinical isolates

Both acquired and intrinsic mechanisms play a crucial role in Pseudomonas aeruginosa antibiotic resistance. Many clinically relevant resistance mechanisms result from changes in gene expression, namely multidrug efflux pump overproduction, AmpC β-lactamase induction or derepression, and inactivation or repression of the carbapenem-specific porin OprD. Changes in gene expression are usually assessed using reverse-transcription quantitative real-time PCR (RT-qPCR) assays. Here, we evaluated label-free Selected Reaction Monitoring (SRM)-based mass spectrometry to directly quantify proteins involved in antibiotic resistance. We evaluated the label-free SRM using a defined set of P. aeruginosa isolates with known resistance mechanisms and compared it with RT-qPCR. Referring to efflux systems, we found a more robust relative quantification of antibiotic resistance mechanisms by SRM than RT-qPCR. The SRM-based approach was applied to a set of clinical P. aeruginosa isolates to detect antibiotic resistance proteins. This multiplexed SRM-based approach is a rapid and reliable method for the simultaneous detection and quantification of resistance mechanisms and we demonstrate its relevance for antibiotic resistance prediction.

Evaluation of tests to predict metallo-β-lactamase in cystic fibrosis (CF) and non-(CF) Pseudomonas

Double disks synergy test (DDST) and combined disks test (CD) were evaluated to predict the presence of metallo-β-lactamase in 70 Pseudomonas aeruginosa isolates recovered from cystic fibrosis and non-cystic fibrosis patients. DDST_{CAZ-EDTA 1 cm} and CD_IMP-EDTA tests showed the best accuracy (94.3%). Furthermore, for other combinations, accuracy unsatisfactory was obtained.

Antimicrobial and biocide resistance of bacteria in a Lebanese tertiary care hospital

The environment in a Lebanese tertiary-level care hospital was examined for bacterial contamination. In total, 8 open-air and 62 surface samples were taken and CFU were enumerated. Morphologically different isolates (n=104) were obtained and tested for resistance to a wide range of antibiotics by the Kirby-Bauer disc diffusion method. Minimum bactericidal concentrations of isolates to seven different biocides used within this facility were also determined using both qualitative and quantitative methods. Gram-positive bacteria (82.7% of isolates) were encountered more often than Gram-negative bacteria (17.3%), and the genus Staphylococcus was most prevalent among isolates (59.6% of the isolates). Gram-positive isolates showed the highest resistance to penicillin (60.6%), clindamycin (54.5%) and ceftazidime (39.4%); the lowest frequencies of resistance were seen with vancomycin (0% of isolates), nitrofurantoin (3.5%), tetracycline (12.1%) and ciprofloxacin (12.1%). The prevalence of meticillin-resistant Staphylococcus aureus (MRSA) and meticillin-resistant coagulase negative staphylococci among all environmental samples was 3.8% and 11.5% of isolates, respectively. All Gram-negative isolates were multidrug-resistant (MDR). With respect to biocides, the highest frequency of resistance was to quaternary ammonium compounds (QACs) (13.5% of isolates) and the lowest frequency of resistance was to QAC/biguanide complex (<1% of isolates) and Anios DVA (3.8%). MDR bacteria can pose a serious threat in the hospital environment, showing the need for prudent use of antibiotics and correct infection control procedures.

Role of Pseudomonas aeruginosa AmpR on β-lactam and non-β-lactam transient cross-resistance upon pre-exposure to subinhibitory concentrations of antibiotics

Pseudomonas aeruginosa is one of the most dreaded opportunistic pathogens accounting for 10 % of hospital-acquired infections, with a 50 % mortality rate in chronically ill patients. The increased prevalence of drug-resistant isolates is a major cause of concern. Resistance in P. aeruginosa is mediated by various mechanisms, some of which are shared among different classes of antibiotics and which raise the possibility of cross-resistance. The goal of this study was to explore the effect of subinhibitory concentrations (SICs) of clinically relevant antibiotics and the role of a global antibiotic resistance and virulence regulator, AmpR, in developing cross-resistance. We investigated the induction of transient cross-resistance in P. aeruginosa PAO1 upon exposure to SICs of antibiotics. Pre-exposure to carbapenems, specifically imipenem, even at 3 ng ml(-1), adversely affected the efficacy of clinically used penicillins and cephalosporins. The high β-lactam resistance was due to elevated expression of both ampC and ampR, encoding a chromosomal β-lactamase and its regulator, respectively. Differences in the susceptibility of ampR and ampC mutants suggested non-AmpC-mediated regulation of β-lactam resistance by AmpR. The increased susceptibility of P. aeruginosa in the absence of ampR to various antibiotics upon SIC exposure suggests that AmpR plays a major role in the cross-resistance. AmpR was shown previously to be involved in resistance to quinolones by regulating MexEF-OprN efflux pump. The data here further indicate the role of AmpR in cross-resistance between quinolones and aminoglycosides. This was confirmed using quantitative PCR, where expression of the mexEF efflux pump was further induced by ciprofloxacin and tobramycin, its substrate and a non-substrate, respectively, in the absence of ampR. The data presented here highlight the intricate cross-regulation of antibiotic resistance pathways at SICs of antibiotics and the need for careful assessment of the order of antibiotic regimens as this may have dire consequences. Targeting a global regulator such as AmpR that connects diverse pathways is a feasible therapeutic approach to combat P. aeruginosa pathogenesis.

Small molecule screen yields inhibitors of Pseudomonas homoserine lactone-induced host responses

Pseudomonas aeruginosa infections are commonly associated with cystic fibrosis, pneumonias, neutropenia and burns. The P. aeruginosa quorum sensing molecule N-(3-oxo-dodecanoyl) homoserine lactone (C12) cause multiple deleterious host responses, including repression of NF-κB transcriptional activity and apoptosis. Inhibition of C12-mediated host responses is predicted to reduce P. aeruginosa virulence. We report here a novel, host-targeted approach for potential adjunctive anti-Pseudomonal therapy based on inhibition of C12-mediated host responses. A high-throughput screen was developed to identify C12 inhibitors that restore NF-κB activity in C12-treated, lipopolysaccharide (LPS)-stimulated cells. Triazolo[4,3-a]quinolines with nanomolar potency were identified as C12-inhibitors that restore NF-κB-dependent luciferase expression in LPS- and TNF-stimulated cell lines. In primary macrophages and fibroblasts, triazolo[4,3-a]quinolines inhibited C12 action to restore cytokine secretion in LPS-stimulated cells. Serendipitously, in the absence of an inflammatory stimulus, triazolo[4,3-a]quinolines prevented C12-mediated responses, including cytotoxicity, elevation of cytoplasmic calcium, and p38 MAPK phosphorylation. In vivo efficacy was demonstrated in a murine model of dermal inflammation involving intradermalC12 administration. The discovery of triazolo[4,3-a]quinolines provides a pharmacological tool to investigate C12-mediated host responses, and a potential host-targeted anti-Pseudomonal therapy.

X-box binding protein 1 (XBP1s) is a critical determinant of Pseudomonas aeruginosa homoserine lactone-mediated apoptosis

Pseudomonas aeruginosa infections are associated with high mortality rates and occur in diverse conditions including pneumonias, cystic fibrosis and neutropenia. Quorum sensing, mediated by small molecules including N-(3-oxo-dodecanoyl) homoserine lactone (C12), regulates P. aeruginosa growth and virulence. In addition, host cell recognition of C12 initiates multiple signalling responses including cell death. To gain insight into mechanisms of C12-mediated cytotoxicity, we studied the role of endoplasmic reticulum stress in host cell responses to C12. Dramatic protection against C12-mediated cell death was observed in cells that do not produce the X-box binding protein 1 transcription factor (XBP1s). The leucine zipper and transcriptional activation motifs of XBP1s were sufficient to restore C12-induced caspase activation in XBP1s-deficient cells, although this polypeptide was not transcriptionally active. The XBP1s polypeptide also regulated caspase activation in cells stimulated with N-(3-oxo-tetradecanoyl) homoserine lactone (C14), produced by Yersinia enterolitica and Burkholderia pseudomallei, and enhanced homoserine lactone-mediated caspase activation in the presence of endogenous XBP1s. In C12-tolerant cells, responses to C12 including phosphorylation of p38 MAPK and eukaryotic initiation factor 2α were conserved, suggesting that C12 cytotoxicity is not heavily dependent on these pathways. In summary, this study reveals a novel and unconventional role for XBP1s in regulating host cell cytotoxic responses to bacterial acyl homoserine lactones.

Chronic and acute infections associated with P. aeruginosa constitute a major healthcare burden. Antimicrobial approaches are currently used against P. aeruginosa; however, infections are typically refractory to treatment and drug resistant strains have been isolated. As such, there is urgent need to understand mechanisms of P. aeruginosa virulence and for new strategies to fight infections. The P. aeruginosa-derived quorum-sensing molecule C12 is recognized by host cells and initiates stress responses including cytotoxicity. In this study, the X-box binding protein 1 transcription factor (XBP1s) was identified as a host factor critical for apoptotic responses initiated by C12 and other similar quorum sensing molecules. Additional C12-initiated host responses, including phosphorylation of p38 MAPK and eIF2α were found to be of lesser importance for C12-initiated cytotoxicity. These studies have broad implications for our understanding of bacterial virulence mechanisms and for development of potential new strategies to combat infections.

Malignant Otitis Externa

Objective

Malignant otitis externa (MOE) is a severe disease with varying outcomes. Despite advances in antibiotic treatment, a significant proportion still succumbs to this disease. We aimed to analyze the effect of clinical factors on prognosis and to review treatment outcomes in our institution.

Study Design

Case series with retrospective chart review of MOE cases from 2006 to 2011.

Setting

Department of Otolaryngology–Head and Neck Surgery, National University Hospital, Singapore, a tertiary referral center.

Subjects and Methods

Patients with MOE admitted for treatment were studied and divided into 2 outcome groups depending on response to a 6-week course of intravenous antibiotics. Demographic and disease factors were analyzed with regard to outcome.

Results

Nineteen cases were analyzed. Disease resolved in 63.2% after 6 weeks of antibiotics. Mortality was 21.1%. Age, diabetic control, duration of diagnostic delay, cranial nerve involvement, and inflammatory markers were not found to predict prognosis. Erythrocyte sedimentation rate and C-reactive protein levels correlated with disease activity and can be used to monitor progress. Clival involvement was associated with persistent disease ( P = .002). Only 63.2% of cases had positive cultures. Pseudomonas aeruginosa was the main organism, and 33.3% of isolates were multidrug resistant. Outcome was not different in cases where culture-directed therapy was employed vs those where empirical ceftazidime and fluoroquinolone were used ( P = .650).

Conclusion

Malignant otitis externa remains an insidious disease with significant mortality. Involvement of the clivus portends a poorer prognosis. Combination therapy with intravenous ceftazidime and oral fluoroquinolone remains relevant despite concerns of culture-negative cases and multidrug-resistant Pseudomonas.

Multidrug resistant bacteria isolated from cockroaches in long-term care facilities and nursing homes

Residents in long-term care facilities and nursing homes have a relative higher risk for infections. The nocturnal and filthy habits of cockroaches may be ideal disseminators of pathogenic microorganisms in these institutions. This study was designed to determine the infestation and vector potential of cockroaches under this institutional environment. Cockroaches were collected from 69 long-term care facilities and nursing homes in Kaohsiung City. Risk factors related to cockroach infestation were determined by questionnaire survey. In addition, bacteria were isolated and identified from the alimentary tract and external surface of these insects. Antibiotic resistances of these microorganisms were then determined. Cockroach infestation was found in 45 (65.2%) institutions and 558 cockroaches (119 Periplaneta americana and 439 Blattella germanica) were collected. A significant association was found between cockroach infestation and indoor environmental sanitation. From 250 adult cockroaches, 38 species of gram-negative bacteria, 20 species of glucose non-fermenter bacilli and 6 species of gram-positive bacteria were isolated. Moreover, antibiotic resistances were found among the bacteria isolated. These findings indicate that cockroaches have the potential in transmitting pathogenic bacteria with multidrug resistances in long-term care facilities and nursing homes.

Diphosphonium ionic liquids as broad-spectrum antimicrobial agents

PURPOSE

One of the most disturbing trends in recent years is the growth of resistant strains of bacteria with the simultaneous dearth of new antimicrobial agents. Thus, new antimicrobial agents for the use on the ocular surface are needed.

METHODS

We synthesized a variety of ionic liquid compounds, which possess 2 positively charged phosphonium groups separated by 10 methylene units in a "bola"-type configuration. We tested these compounds for antimicrobial activity versus a variety of ocular pathogens, as well as their cytoxicity, in vitro in a corneal cell line and in vivo in mice.

RESULTS

The ionic liquid Di-Hex C10 demonstrated broad in vitro antimicrobial activity at low micromolar concentrations versus gram-negative and gram-positive organisms, including methicillin-resistant Staphylococcus aureus strains and ocular fungal pathogens. Treatment with Di-Hex C10 resulted in bacterial killing in as little as 15 minutes in vitro. Di-Hex C10 showed little cytotoxicity at 1 μM versus a corneal epithelial cell line or at 10 μM in a mouse corneal wound model. We also show that this bis-phosphonium ionic liquid structure is a key because a comparable monophosphonium ionic liquid is cytotoxic to both bacteria and corneal epithelial cells.

CONCLUSIONS

Here, we report the first use of dicationic bis-phosphonium ionic liquids as antimicrobial agents. Our data suggest that diphosphonium ionic liquids may represent a new class of broad-spectrum antimicrobial agents for the use on the ocular surface.

Disposable vs Reusable Electrocardiography Leads in Development of and Cross-contamination by Resistant Bacteria

Hospital-acquired infections caused by antibacterial-resistant microorganisms are associated with high mortality and morbidity rates and markedly affect hospital economics. The expense became greater in 2008 when reimbursement for treatment of hospital-acquired infections was no longer provided by Medicare. Infections caused by cross-contamination with resistant bacteria can be eliminated by 3 methods: kill the bacteria before resistance develops, stop bacteria from communicating and acquiring resistance, and eliminate the pathway from one patient to another. Because electrocardiography wires cannot be completely disinfected 100% of the time, they may be contributing to the growth of resistant bacteria. The many pathways provided by reusable wires for cross-contamination with resistant bacteria increase the risk for hospital-acquired infection when these wires are used. Disposable electrocardiography leads eliminate risk of infection through these pathways. Adoption of disposable electrocardiography leads as an adjunct to an overall infection control program can decrease infection rates in acute health care facilities.

Structural basis for effectiveness of siderophore-conjugated monocarbams against clinically relevant strains of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes nosocomial infections for which there are limited treatment options. Penicillin-binding protein PBP3, a key therapeutic target, is an essential enzyme responsible for the final steps of peptidoglycan synthesis and is covalently inactivated by β-lactam antibiotics. Here we disclose the first high resolution cocrystal structures of the P. aeruginosa PBP3 with both novel and marketed β-lactams. These structures reveal a conformational rearrangement of Tyr532 and Phe533 and a ligand-induced conformational change of Tyr409 and Arg489. The well-known affinity of the monobactam aztreonam for P. aeruginosa PBP3 is due to a distinct hydrophobic aromatic wall composed of Tyr503, Tyr532, and Phe533 interacting with the gem-dimethyl group. The structure of MC-1, a new siderophore-conjugated monocarbam complexed with PBP3 provides molecular insights for lead optimization. Importantly, we have identified a novel conformation that is distinct to the high-molecular-weight class B PBP subfamily, which is identifiable by common features such as a hydrophobic aromatic wall formed by Tyr503, Tyr532, and Phe533 and the structural flexibility of Tyr409 flanked by two glycine residues. This is also the first example of a siderophore-conjugated triazolone-linked monocarbam complexed with any PBP. Energetic analysis of tightly and loosely held computed hydration sites indicates protein desolvation effects contribute significantly to PBP3 binding, and analysis of hydration site energies allows rank ordering of the second-order acylation rate constants. Taken together, these structural, biochemical, and computational studies provide a molecular basis for recognition of P. aeruginosa PBP3 and open avenues for future design of inhibitors of this class of PBPs.

Classification of 17 newly isolated virulent bacteriophages of Pseudomonas aeruginosa

Seventeen virulent bacteriophages specific to Pseudomonas aeruginosa strains were isolated by screening various environmental samples. These isolated bacteriophages were grouped based on results obtained from restriction fragment analysis of phage genomes, random amplification of polymorphic DNA (RAPD) typing, morphology observations under transmission electron microscope, and host range analysis. All 17 bacteriophages are double-stranded DNA viruses and can be divided into 5 groups based on DNA restriction profiles. A set of 10-mer primers was used in RAPD typing of phages, and similar conclusions were obtained as for restriction fragment analysis. One phage was randomly selected from each of the 5 groups for morphology observations. Four of them had an icosahedral head with a long contractile tail, belonging to the Myoviridae family, and one phage had an icosahedral head with a short tail, thereby belonging to the Podoviridae family. Host range experiments were conducted on 7 laboratory strains and 12 clinical strains of P. aeruginosa. The results showed that 13 phages had the same infection profile, killing 8 out of 19 tested P. aeruginosa strains, and the remaining 4 phages had different and unique infection profiles. This study highlights the diversity of bacteriophages specific to P. aeruginosa in the environment.

Infection and panniculitis

Infection-induced panniculitis may result from a number of microbes including bacteria, fungi, and parasites. Viruses have also been implicated as a cause. This type of panniculitis can occur as a primary infection by direct inoculation of infectious microorganisms into the subcutaneous tissue, or secondarily via microbial hematogenous dissemination with subsequent infection of the subcutaneous tissue. Panniculitis is rarely viewed solely in terms of infectious causes. Also, subcutaneous infections are infrequently viewed in terms of infection-induced panniculitis but rather as cutaneous infections with subcutaneous involvement. Little information exists specifically on the subject of infection-induced panniculitis outside of the realm of case reports and case series. In this review, the present authors address panniculitis from the vantage point of infectious causes, focusing on those microorganisms with infection-induced panniculitis reports in the literature. Diagnosis and treatment are also discussed.

Genetic determinants involved in the susceptibility of Pseudomonas aeruginosa to beta-lactam antibiotics

The resistome of P. aeruginosa for three β-lactam antibiotics, namely, ceftazidime, imipenem, and meropenem, was deciphered by screening a comprehensive PA14 mutant library for mutants with increased or reduced susceptibility to these antimicrobials. Confirmation of the phenotypes of all selected mutants was performed by Etest. Of the total of 78 confirmed mutants, 41 demonstrated a reduced susceptibility phenotype and 37 a supersusceptibility (i.e., altered intrinsic resistance) phenotype, with 6 mutants demonstrating a mixed phenotype, depending on the antibiotic. Only three mutants demonstrated reduced (PA0908) or increased (glnK and ftsK) susceptibility to all three antibiotics. Overall, the mutant profiles of susceptibility suggested distinct mechanisms of action and resistance for the three antibiotics despite their similar structures. More detailed analysis indicated important roles for novel and known β-lactamase regulatory genes, for genes with likely involvement in barrier function, and for a range of regulators of alginate biosynthesis.

Iron-Depletion prevents biofilm formation in Pseudomonas Aeruginosa through twitching mobility and quorum sensing

Influence of iron-depletion on twitching motility and quorum sensing (QS) system in P. aeruginosa was evaluated. The results demonstrated iron-depletion can retard biofilm formation and increase the twitching motility and expression of QS-related genes, suggesting a potential interaction between twitching motility and QS system in P. aeruginosa biofilm formation.

Current treatment of pseudomonal infections in the elderly

Pseudomonas aeruginosa infections have emerged as a major infectious disease threat in recent decades as a result of the significant mortality of pseudomonal pneumonia and bacteraemia, and the evolving resistance exhibited by the pathogen to numerous antibacterials. Pseudomonas possesses a large genome; thus, the pathogen is environmentally adaptable, metabolically flexible, able to overcome antibacterial pressure by selecting for resistant strains and even able to accumulate resistance mechanisms, leading to multidrug resistance (MDR), an increasingly recognized therapeutic challenge. In fact, most research currently does not focus on maximizing the efficacy of available antibacterials; rather, it focuses on maximizing their ecological safety. The elderly population may be particularly prone to pseudomonal infection as a result of increased co-morbidities (such as diabetes mellitus and structural lung disease), the presence of invasive devices such as urinary catheters and feeding tubes, polypharmacy that includes antibacterials, and immune compromise related to age. However, age per se, as well as residence in nursing homes, may not predispose individuals to an increased risk for pseudomonal infection. On the other hand, age has been repeatedly outlined as a risk factor for MDR pseudomonal infections. The severity of pseudomonal infections necessitates prompt administration of appropriate antibacterials upon suspicion. Progress has been made in recognizing risk factors for P. aeruginosa infections both in hospitalized and community-residing patients. Antimicrobial therapy may be instituted as a combination or monotherapy: the debate cannot be definitively resolved since the available data are extracted from studies with varying targeted populations and varying definitions of response, adequacy and MDR. Empirical combination therapy maximizes the chances of bacterial coverage and exerts a lower resistance selection pressure. Although associated with increased percentages of adverse events, mainly as a result of the included aminoglycosides, empirical combination therapy seems a reasonable choice. Upon confirmation of Pseudomonas as the causative agent and awareness of its susceptibility profile, monotherapy is advocated by many, but not all, experts. Infections involving MDR strains can be treated with colistin, which has adequate efficacy and few renal adverse events, or doripenem. In the elderly, in addition to making dose modifications that are needed because of loss of renal function, the prescriber should be more cautious about the use of aminoglycoside-containing regimens, possibly replacing them with a combination of quinolone and a beta-lactam, notwithstanding the possible increased pressure for selection of resistance with the latter combination.

Antimicrobial agents for surgical infections

Antimicrobial drugs are useful for the empiric and definitive treatment of infections in surgical patients. They are also important agents for perioperative antimicrobial prophylaxis. The proper selection and use of these drugs is a critical skill for surgeons. Although these agents have many beneficial effects, they also possess occasional adverse effects and should not be used indiscriminately.

Does the activity of the combination of imipenem and colistin in vitro exceed the problem of resistance in metallo-beta-lactamase-producing Klebsiella pneumoniae isolates?

Using time-kill methodology, we investigated the interactions of an imipenem-colistin combination against 42 genetically distinct Klebsiella pneumoniae clinical isolates carrying a bla(VIM-1)-type gene. Irrespective of the imipenem MIC, the combination was synergistic (50%) or indifferent (50%) against colistin-susceptible strains, while it was antagonistic (55.6%) and rarely synergistic (11%) against non-colistin-susceptible strains (with synergy being observed only against strains with colistin MICs of 3 to 4 microg/ml). The combination showed improved bactericidal activity against isolates susceptible either to both agents or to colistin.