Annie Wong-Beringer

Use of an Efflux Pump Inhibitor To Determine the Prevalence of Efflux Pump-Mediated Fluoroquinolone Resistance and Multidrug Resistance in Pseudomonas aeruginosa

ABSTRACT Fluoroquinolone-resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression (EPO) and/or target mutations. EPO can result in multidrug resistance (MDR) due to broad substrate specificity of the pumps. MC-04,124, an efflux pump inhibitor (EPI) shown to significantly potentiate activity of levofloxacin in P. aeruginosa, was used to examine the prevalence of EPO in clinical isolates. MICs were determined for ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin with or without EPI and for other antipseudomonal agents by using broth microdilution against P. aeruginosa isolates from adults (n = 119) and children (n = 24). The prevalence of the EPO phenotype (≥8-fold MIC decrease when tested with EPI) was compared among subgroups with different resistance profiles. The EPO phenotype was more prevalent among levofloxacin-resistant than levofloxacin-sensitive strains (61%, 48/79 versus 9%, 6/64). EPO was present in 60% of fluoroquinolone-resistant strains without cross-resistance, while it was present at variable frequencies among strains with cross-resistance to other agents: piperacillin-tazobactam (86%), ceftazidime (76%), cefepime (65%), imipenem (56%), gentamicin (55%), tobramycin (48%), and amikacin (27%). The magnitude of MIC decrease with an EPI paralleled the frequency of which the EPO phenotype was observed in different subgroups. EPI reduced the levofloxacin MIC by as much as 16-fold in eight strains for which MICs were 128 μg/ml. Efflux-mediated resistance appears to contribute significantly to fluoroquinolone resistance and MDR in P. aeruginosa. Our data support the fact that increased fluoroquinolone usage can negatively impact susceptibility of P. aeruginosa to multiple classes of antipseudomonal agents.

Vancomycin-associated nephrotoxicity: a critical appraisal of risk with high-dose therapy

The recent emergence of meticillin-resistant Staphylococcus aureus (MRSA) strains with reduced susceptibility to vancomycin has prompted clinicians to prescribe vancomycin therapy targeting high trough concentrations (15-20 mg/L). Relevant studies (n=12) analysing the occurrence of nephrotoxicity with high-dose therapy were reviewed. Most studies were retrospective and the temporal relationship between elevated trough levels and development of nephrotoxicity was unclear, precluding a definitive cause-effect analysis. Available data suggest an association between vancomycin trough level and risk of nephrotoxicity as a function of intensity and duration of therapy (>7 days), compounded by concomitant receipt of nephrotoxins, vasopressor therapy and underlying physiological impairment. In separate studies in which a high trough concentration was measured prior to the onset of nephrotoxicity, the frequency of occurrence was 21-28% in patients with concomitant risks compared with 7% in patients without risks. A similar comparison between risk and no-risk groups who attained a standard trough concentration (10-15 mg/L) indicates the rates of occurrence as 9-21% vs. 2%. Onset of nephrotoxicity ranged from 4 days to 8 days from the start of therapy. The degree of renal dysfunction was modest, with a reported decrease of 35-45% in creatinine clearance from baseline. Resolution occurred in >70% of patients by the time of discharge. Future studies should detail clearly the temporal relationship between drug exposure and onset of nephrotoxicity, confounding risk factors, extent of injury and time course of recovery, and should also determine the relative risk versus benefit of high-dose vancomycin versus alternative agents.

Regulatory Oversight and Safety of Probiotic Use

Saccharomyces boulardii probiotics should be used with caution for management of Clostridium difficile infections in hospitalized patients.

Systemic Antifungal Therapy: New Options, New Challenges

The frequency of invasive fungal infections has increased dramatically in recent decades because of an expanding population at risk. Until now, treatment options for invasive mycoses have been primarily amphotericin B and the azoles, fluconazole and itraconazole. Traditional agents are limited by an inadequate spectrum of activity, drug resistance, toxicities, and drug‐drug interactions. The recent approval of caspofungin and voriconazole clearly has expanded the number of existing antifungal drugs available. However, the enthusiasm that accompanies their availability is counterbalanced by limited clinical experience, high drug acquisition costs, and distinctive toxicities. The pharmacologic characteristics, extent of clinical experience (efficacy and toxicity), and drug acquisition costs among available systemic antifungal agents are compared, with emphasis on the new agents. Also, recommendations on the role of each agent are provided according to the most common indications for systemic antifungal therapy: invasive candidiasis, invasive aspergillosis, and febrile neutropenia.

A multicentre study to evaluate the impact of timing of caspofungin administration on outcomes of invasive candidiasis in non-immunocompromised adult patients

OBJECTIVES Candida non-albicans species cause an increasing proportion of invasive candidiasis (IC). Prompt initiation of effective antifungal therapy has been shown to positively impact the outcomes of IC. Caspofungin is often reserved as a second-line agent after suboptimal response to initial therapy. We determined the impact of the timing of caspofungin administration on outcomes of IC. METHODS Medical records were reviewed on all hospitalized adults who received >or=72 h of caspofungin for IC (isolation of Candida species from blood, intra-abdominal or other sterile sites). Clinical data were extracted from medical charts and recorded. Patients were classified based on delayed initiation (DI; >3 days) versus early initiation (EI; <or=3 days) of caspofungin relative to the time the culture was obtained. RESULTS A total of 169 patients received caspofungin for IC; Candida glabrata (n = 78, 46%) was the most common cause, followed by mixed species (n = 36, 21%), Candida albicans (n = 36, 21%), Candida parapsilosis (n = 9, 6%), Candida tropicalis (n = 6, 3%), Candida krusei and other species (n = 4, 2%). Infection sites were bloodstream related (n = 119, 71%), intra-abdominal (n = 44, 26%) and other sterile sites (n = 6, 3%). DI of caspofungin was associated with a lower response rate (35/62, 56% versus 82/107, 77%; P = 0.006), longer time to achieve clinical stability (10 versus 4 days; P = 0.002) and longer length of stay after isolation of the organism (28 versus 21 days; P = 0.007), compared with EI (n = 107). CONCLUSIONS Non-albicans Candida species accounted for the majority of IC in caspofungin-treated patients. Improved outcomes were observed for patients initiated with caspofungin within 72 h of positive culture compared with those who received delayed therapy.

Differentiation in quinolone resistance by virulence genotype in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a leading pathogen that has become increasingly resistant to the fluoroquinolone antibiotics due to widespread prescribing. Adverse outcomes have been shown for patients infected with fluoroquinolone-resistant strains. The type III secretion system (TTSS) is a major virulence determinant during acute infections through the injection of effector toxins into host cells. Most strains exhibit a unique TTSS virulence genotype defined by the presence of either exoS or exoU gene encoding two of the effector toxins, ExoS and ExoU, respectively. Specific TTSS effector genotype has been shown previously to differentially impact virulence in pneumonia. In this study, we examined the relationship between TTSS effector genotype and fluoroquinolone resistance mechanisms in a collection of 270 respiratory isolates. We found that a higher proportion of exoU+ strains were fluoroquinolone-resistant compared to exoS+ strains (63% vs 49%, p = 0.03) despite its lower overall prevalence (38% exoU+ vs 56% exoS+). Results from sequencing the quinolone resistance determining regions (QRDRs) of the 4 target genes (gyrA, gyrB, parC, parE) indicated that strains containing the exoU gene were more likely to acquire ≥2 mutations than exoS+ strains at MICs ≤8 µg/ml (13% vs none) and twice as likely to have mutations in both gyrA and parC than exoS+ strains (48% vs 24% p = 0.0439). Our findings indicate that P. aeruginosa strains differentially develop resistance-conferring mutations that correlate with TTSS effector genotype and the more virulent exoU+ subpopulation. Differences in mutational processes by virulence genotype that were observed suggest co-evolution of resistance and virulence traits favoring a more virulent genotype in the quinolone-rich clinical environment.

Absolute Bioavailability and Pharmacokinetics of Linezolid in Hospitalized Patients Given Enteral Feedings

ABSTRACT Linezolid is a new antimicrobial agent effective against drug-resistant gram-positive pathogens which are common causes of infections in hospitalized patients. Many such patients rely on the intravenous or enteral route for nutrition and drug administration. Therefore, the bioavailability of linezolid administered enterally in the presence of enteral feedings in hospitalized patients was examined. Eighteen subjects were assessed in a randomized single-dose crossover study; 12 received continuous enteral feedings, while 6 did not (controls). Both groups received linezolid 600 mg intravenously and orally (control) or enterally, with the alternate route of administration separated by a 24-h washout period. Pharmacokinetic parameters derived from noncompartmental and compartmental analysis incorporating linear and nonlinear elimination pathways were compared between groups: F, Ka, Vs, K23, K32, Vmax, Km, and K20 (bioavailability, absorption rate constant, volume of central compartment normalized to body weight, intercompartmental rate constants, maximum velocity, Michaelis-Menten constant, and elimination rate constant, respectively). Pharmacokinetic (PK) data were available from 17 patients. The linezolid oral suspension was rapidly and completely absorbed by either the oral or enteral route of administration. Bioavailability was unaltered in the presence of enteral feedings. PK estimates remain similar regardless of the model applied. At the therapeutic dose used, only slight nonlinearity in elimination was observed. A linezolid oral suspension may be administered via the enteral route to hospitalized patients without compromise in its excellent bioavailability and rapid rate of absorption. Compartmental pharmacokinetic analysis offers a more flexible study application, since bioavailability (F) can be estimated directly with intermixed intravenous/oral doses without a need for a washout period.

Risk of developing pneumonia is enhanced by the combined traits of fluoroquinolone resistance and type III secretion virulence in respiratory isolates of Pseudomonas aeruginosa.

Objectives:To determine the differential association of host characteristics, antimicrobial resistance, and type III secretion system virulence of Pseudomonas aeruginosa isolates with respiratory syndromes in hospitalized adult patients. Design:Retrospective, cohort study. Setting:Community teaching hospital. Patients:Two hundred eighteen consecutive adult patients with respiratory culture positive for P. aeruginosa between January 2005 to January 2010. Interventions:Medical charts were reviewed to obtain demographic, laboratory, radiographic, and clinical information. Isolates were assayed by polymerase chain reaction for genes encoding the type III secretion system effectors (ExoU, ExoS, and PcrV) and for strain relatedness using randomly amplified polymorphic DNA analysis. Levofloxacin susceptibility was determined by broth microdilution. Patients were grouped by colonization, bronchitis, or pneumonia and were compared for differential risk of developing the clinical syndrome with respect to host and microbial characteristics. Measurements and Main Results:Half of the study cohort (54%, 117 of 218) had pneumonia, 32% (70 of 218) had bronchitis, and 14% (31 of 218) had colonization; in-hospital mortality was 35%, 11%, and 0%, respectively. Host factors strongly associated with pneumonia development were residence in long-term care facility, healthcare-associated acquisition of P. aeruginosa, higher Acute Physiology and Chronic Health Evaluation II score, presence of enteral feeding tube, mechanical ventilation, and recent history of pneumonia. Fluoroquinolone-resistant (57% vs 34%, 16%; p < 0.0001) and multidrug-resistant (36% vs 26%, 7%; p = 0.0045) strains were more likely to cause pneumonia than bronchitis or colonization, respectively. Analysis of host and microbial factors in a multivariate regression model yielded the combined traits of fluoroquinolone resistance and gene encoding the type III secretion system ExoU effector in P. aeruginosa as the single most significant predictor of pneumonia development. Conclusions:These results suggest that fluoroquinolone-resistant phenotype in a type III secretion system exoU strain background contributes toward the pathogenesis of P. aeruginosa in pneumonia.

In Vitro Activity of Daptomycin in Combination with β-Lactams, Gentamicin, Rifampin, and Tigecycline against Daptomycin-Nonsusceptible Enterococci

ABSTRACT Enterococci that are nonsusceptible (NS; MIC > 4 μg/ml) to daptomycin are an emerging clinical concern. The synergistic combination of daptomycin plus beta-lactams has been shown to be effective against vancomycin-resistant Enterococcus (VRE) species in vitro. This study systematically evaluated by in vitro time-kill studies the effect of daptomycin in combination with ampicillin, cefazolin, ceftriaxone, ceftaroline, ertapenem, gentamicin, tigecycline, and rifampin, for a collection of 9 daptomycin-NS enterococci that exhibited a broad range of MICs and different resistance-conferring mutations. We found that ampicillin plus daptomycin yielded the most consistent synergy but did so only for isolates with mutations to the liaFSR system. Daptomycin binding was found to be enhanced by ampicillin in a representative isolate with such mutations but not for an isolate with mutation to the yycFGHIJ system. In contrast, ampicillin enhanced the killing of the LL-37 human antimicrobial peptide against daptomycin-NS E. faecium with either the liaFSR or yycFGHIJ mutation. Antagonism was noted only for rifampin and tigecycline and only for 2 or 3 isolates. These data add support to the growing body of evidence indicating that therapy combining daptomycin and ampicillin may be helpful in eradicating refractory VRE infections.

Reducing empirical use of fluoroquinolones for Pseudomonas aeruginosa infections improves outcome.

BACKGROUND We previously reported ciprofloxacin resistance (CR) and empirical use of fluoroquinolones as predictors of mortality in patients infected with Pseudomonas aeruginosa in a case-control study. Here, we assessed the clinical impact of reducing empirical fluoroquinolone use for P. aeruginosa infections in hospitalized patients by performing a follow-up study in 2005-06 [period 2 (P2)] and comparing this with prior data from 2001-02 [period 1 (P1)]. METHODS Medical charts of infected patients who received at least 72 h of antibiotic therapy were reviewed. Patients were subgrouped based on the susceptibility of infected strains into the CR or ciprofloxacin-susceptible group. Antibiograms, patient and treatment variables and outcome measures were compared between groups and between study periods. RESULTS Study patients were elderly (median age, 76 years), had a median of three co-morbidities and a median APACHE II score of 13. Most (75%) had pneumonia or urosepsis. Empirical use of fluoroquinolones was reduced by 30% in P2 versus P1, with a corresponding 39% increase in piperacillin/tazobactam use. The resultant positive impact observed in the CR group during P2 includes shortened delay to receipt of effective therapy (1 versus 3.5 days, P < 0.0001), reduced length of stay (13 versus 16 days, P = 0.03) and 2-fold lower mortality (9% versus 22%, P = 0.05). Susceptibility of P. aeruginosa improved by 10% to all antipseudomonal agents tested. CONCLUSIONS In settings where high rates of fluoroquinolone resistance exist, use of non-fluoroquinolone-based empirical regimens for P. aeruginosa infections improves patient outcomes and organism susceptibility over time.