Infections by pandrug-resistant gram-negative bacteria: clinical profile, therapeutic management, and outcome in a series of 21 patients

Emergence of colistin-resistant gram-negative rods in intensive care units: A cross-sectional study from a developing country

Objectives

To determine the clinical features, outcomes, and factors associated with the emergence of colistin-resistant gram-negative rods isolated from patients admitted to intensive care units.

Methods

This cross-sectional study was conducted at the intensive care units of Liaquat National Hospital, from April 2019 to February 2020. Gram-negative rods resistant to colistin with minimum inhibitory concentrations ⩾ 4 mcg/mL according to Clinical and Laboratory Standards Institute criteria as reported in cultures were included. Clinical, demographical data and treatment given were recorded and analyzed using SPSS version 25.

Results

A total of 93 patients were included; 58.1% were males. The mean age of patients was 59.48 ± 18.36 years. The most common organism isolated was Klebsiella pneumoniae (91.4%). The most common specimen was the tracheal (62.4%). Ventilator-acquired pneumonia was seen in 38.7%. The most common co-morbid disease seen in patients was diabetes (41%); 77% had a symptomatic infection and were treated with a combination of 2 or more antibiotics, most commonly meropenem plus fosfomycin. The most common susceptible antibiotics were fosfomycin (72%) and tigecycline (50.5%). Mean intensive care unit stay and total duration of hospital stay were prolonged (16.83 ± 12.93 and 23.34 ± 17.52 days, respectively). Forty-eight (62.3%) patients with symptomatic infection with colistin-resistant isolates were treated and discharged, and mortality was seen in 23 (29.9%). A significant association was found between mortality and symptomatic infection, endotracheal intubation with mechanical ventilation (p = 0.003), and a prolonged hospital stay of >20 days (p = 0.041).

Conclusion

Colistin-resistant gram-negative rods pose a significant problem especially in developing countries because of limited therapeutic options. Stringent infection control and comprehensive antimicrobial stewardship programs are needed to overcome this challenge.

Pandrug-resistant Gram-negative bacteria: a systematic review of current epidemiology, prognosis and treatment options

BACKGROUND

The literature on the epidemiology, mortality and treatment of pandrug-resistant (PDR) Gram-negative bacteria (GNB) is scarce, scattered and controversial.

OBJECTIVES

To consolidate the relevant literature and identify treatment options for PDR GNB infections.

METHODS

A systematic search in MEDLINE, Scopus and clinical trial registries was conducted. Studies reporting PDR clinical isolates were eligible for review if susceptibility testing for all major antimicrobials had been performed. Characteristics and findings of retrieved studies were qualitatively synthesized.

RESULTS

Of 81 studies reviewed, 47 (58%) were published in the last 5 years. The reports reflected a worldwide dissemination of PDR GNB in 25 countries in 5 continents. Of 526 PDR isolates reported, Pseudomonas aeruginosa (n=175), Acinetobacter baumannii (n=172) and Klebsiella pneumoniae (n=125) were most common. PDR GNB were typically isolated in ICUs, but several studies demonstrated wider outbreak potential, including dissemination to long-term care facilities and international spread. All-cause mortality was high (range 20%-71%), but appeared to be substantially reduced in studies reporting treatment regimens active in vitro. No controlled trial has been performed to date, but several case reports and series noted successful use of various regimens, predominantly synergistic combinations, and in selected patients increased exposure regimens and newer antibiotics.

CONCLUSIONS

PDR GNB are increasingly being reported worldwide and are associated with high mortality. Several treatment regimens have been successfully used, of which synergistic combinations appear to be most promising and often the only available option. More pharmacokinetic/pharmacodynamic and outcome studies are needed to guide the use of synergistic combinations.

Mortality of Pandrug-Resistant Klebsiella pneumoniae Bloodstream Infections in Critically Ill Patients: A Retrospective Cohort of 115 Episodes

BACKGROUND

The increased frequency of bacteraemias caused by pandrug-resistant Klebsiella pneumoniae (PDR-Kp) has significant implications. The aim of the present study was to identify predictors associated with mortality of PDR-Kp bacteraemias.

METHODS

Patients with monomicrobial bacteraemia due to PDR-Kp were included. K. pneumoniae was considered PDR if it showed resistance to all available groups of antibiotics. Primary outcome was 30-day mortality. Minimum inhibitory concentrations (MICs) of meropenem, tigecycline, fosfomycin, and ceftazidime/avibactam were determined by Etest, whereas for colistin, the broth microdilution method was applied. bla _KPC, bla _VIM, bla _NDM, and bla _OXA genes were detected by PCR.

RESULTS

Among 115 PDR-Kp bacteraemias, the majority of infections were primary bacteraemias (53; 46.1%), followed by catheter-related (35; 30.4%). All isolates were resistant to tested antimicrobials. bla _KPC was the most prevalent carbapenemase gene (98 isolates; 85.2%). Thirty-day mortality was 39.1%; among 51 patients with septic shock, 30-day mortality was 54.9%. Multivariate analysis identified the development of septic shock, Charlson comorbidity index, and bacteraemia other than primary or catheter-related as independent predictors of mortality, while a combination of at least three antimicrobials was identified as an independent predictor of survival.

CONCLUSIONS

Mortality of PDR-Kp bloodstream infections was high. Administration of at least three antimicrobials might be beneficial for infections in critically ill patients caused by such pathogens.

Excess mortality due to pandrug-resistant Acinetobacter baumannii infections in hospitalized patients

BACKGROUND

Pandrug-resistant Acinetobacter baumannii (PDRAB) is increasingly being reported as a nosocomial pathogen worldwide, but determining its clinical impact is challenging.

AIM

To assess the spectrum of excess mortality attributable to PDRAB infection in acute care settings.

METHODS

This four-year cohort study was conducted in a tertiary-care referral hospital in Greece to estimate excess in-hospital mortality due to PDRAB infection by comparing patients infected to those colonized with PDRAB by means of competing risks survival analysis.

FINDINGS

The study cohort comprised 91 patients (median age: 67 years; 77% men). For most patients, PDRAB was first isolated in the intensive care unit (ICU) (N = 51; 57%) or following ICU discharge (N = 26; 29%). Overall in-hospital mortality was 68% (95% confidence interval (CI): 57.5-77.5%). PDRAB-infected patients (N = 62; 68%) and PDRAB-colonized patients (N = 29; 32%) had similar baseline characteristics, but the absolute excess risk of 30-day mortality in infected patients compared to colonized patients was 34% (95% CI: 14-54%). Multivariable competing risks regression showed that PDRAB infection significantly increased the daily hazard of 30-day in-hospital death (cause-specific hazard ratio (csHR): 3.10; 95% CI: 1.33-7.21) while simultaneously decreasing the daily rate of discharge (csHR: 0.24; 95% CI: 0.08-0.74), thereby leading to longer hospitalization. Stronger effects were observed for bloodstream infections.

CONCLUSION

New effective antimicrobials would be expected to prevent mortality in one of every three patients treated for PDRAB infection and reduce their length of hospitalization. However, available therapeutic options remain extremely limited and emphasis on preventing healthcare-associated transmission of PDRAB is ever more important.

Retrospective analysis of colistin-resistant bacteria in a tertiary care centre in India

The incidence of carbapenem-resistant Enterobacteriaceae has been steadily rising. The morbidity, mortality and financial implications of such patients are significant. We did a retrospective analysis of the case records of 11 patients who had culture report positive for pan drug-resistant (PDR) organisms. There were total 15 isolates of PDR organisms in 11 patients. These were associated with catheter-associated urinary tract infections (7), tracheitis (4), bacteraemia (2), meningitis (1) and soft-tissue infection (1). Average APACHE II score was 23.72 (range 7-36) indicating patients with multiple co-morbidities and organ dysfunction. The average length of hospital stay was 60.72 (25-123) days. The overall mortality rate was 81.81 per cent, while PDR infection-related mortality was 18.18 per cent. Strict implementation of antibiotic stewardship programme is essential to limit use and prevent abuse of colistin.

Treatment pattern, prognostic factors, and outcome in patients with infection due to pan-drug-resistant gram-negative bacteria

The present study investigated the clinical course, treatment pattern, prognostic factors, and outcome of patients with pun-drug resistant (PDR) infections. This was a retrospective single-center cohort study including consecutive eligible patients with a PDR infection hospitalized at the University Hospital of Heraklion, Crete, Greece, between January 2010 and June 2018. In total, 65 patients with infections due to PDR gram-negative pathogens were identified. The median age was 64 years (interquartile range, IQR: 45.5-74.5) and the median Charlson comorbidity index 3.0 (IQR: 1.0-5.75). Of the 65 PDR isolates, 31 (48%) were Klebsiella pneumoniae, 28 (43%) Acinetobacter baumannii, and 6 (9%) Pseudomonas aeruginosa. The most common empirical therapy was colistin-based combination (n = 32; 49%), followed by non-colistin, non-tigecycline combination (n = 25; 39%), and carbapenemes + tigecycline (n = 8; 12%). The empirical therapy was effective in 50%, 37.5%, and 8% of patients receiving colistin combination, carbapenemes - tigecycline, and non-colistin, non-tigecycline combination, respectively (p value = 0.003). The infection-related in-hospital mortality was 32% (95% confidence interval, CI: 21-45%). Three factors were significantly associated with infection-related in-hospital mortality in multivariate analysis: Charlson comorbidity index (odds ratio, OR: 1.5, 95% CI: 1.0-2.3, p value = 0.030), prior steroid use (OR: 4.1, 95% CI: 1.0-17.0, p value = 0.049), and empirical treatment with non-colistin, non-tigecycline combination (OR: 7.5; 95% CI: 1.7-32.8, p value = 0.008). Infections due to PDR pathogens are associated with considerable mortality. Our results support the use of colistin and/or tigecycline-based combinations as empirical therapy when infection due to PDR pathogens is suspected.

Rational Combinations of Polymyxins with Other Antibiotics

Combinations of antimicrobial agents are often used in the management of infectious diseases. Antimicrobial agents used as part of combination therapy are often selected empirically. As regrowth and the emergence of polymyxin (either colistin or polymyxin B) resistance has been observed with polymyxin monotherapy, polymyxin combination therapy has been suggested as a possible means by which to increase antimicrobial activity and reduce the development of resistance. This chapter provides an overview of preclinical and clinical investigations of CMS/colistin and polymyxin B combination therapy. In vitro data and animal model data suggests a potential clinical benefit with many drug combinations containing clinically achievable concentrations of polymyxins, even when resistance to one or more of the drugs in combination is present and including antibiotics normally inactive against Gram-negative organisms. The growing body of data on the emergence of polymyxin resistance with monotherapy lends theoretical support to a benefit with combination therapy. Benefits include enhanced bacterial killing and a suppression of polymyxin resistant subpopulations. However, the complexity of the critically ill patient population, and high rates of treatment failure and death irrespective of infection-related outcome make demonstrating a potential benefit for polymyxin combinations extremely challenging. Polymyxin combination therapy in the clinic remains a heavily debated and controversial topic. When combinations are selected, optimizing the dosage regimens for the polymyxin and the combinatorial agent is critical to ensure that the benefits outweigh the risk of the development of toxicity. Importantly, patient characteristics, pharmacokinetics, the site of infection, pathogen and resistance mechanism must be taken into account to define optimal and rational polymyxin combination regimens in the clinic.

A Study of 24 Patients with Colistin-Resistant Gram-negative Isolates in a Tertiary Care Hospital in South India

BACKGROUND

As the use of colistin to treat carbapenem-resistant Gram-negative infections increases, colistin resistance is being increasingly reported in Indian hospitals.

MATERIALS AND METHODS

Retrospective chart review of clinical data from patients with colistin-resistant isolates (minimum inhibitory concentration >2 mcg/ml). Clinical profile, outcome, and antibiotics that were used for treatment were analyzed.

RESULTS

Twenty-four colistin-resistant isolates were reported over 18 months (January 2014-June 2015). A history of previous hospitalization within 3 months was present in all the patients. An invasive device was used in 22 (91.67%) patients. Urine was the most common source of the isolate, followed by blood and respiratory samples. Klebsiella pneumoniae constituted 87.5% of all isolates. Sixteen (66.6%) were considered to have true infection, whereas eight (33.3%) were considered to represent colonization. Susceptibility of these isolates to other drugs tested was tigecycline in 75%, chloramphenicol 62.5%, amikacin 29.17%, co-trimoxazole 12.5%, and fosfomycin (sensitive in all 4 isolates tested). Antibiotics that were used for treatment were combinations among the following antimicrobials-tigecycline, chloramphenicol, fosfomycin, amikacin, ciprofloxacin, co-trimoxazole, and sulbactam. Among eight patients who were considered to have colonization, there were no deaths. Bacteremic patients had a significantly higher risk of death compared to all nonbacteremic patients (P = 0.014).

CONCLUSIONS

Colistin resistance among Gram-negative bacteria, especially K. pneumoniae, is emerging in Indian hospitals. At least one-third of isolates represented colonization only rather than true infection and did not require treatment. Among patients with true infection, only 25% had a satisfactory outcome and survived to discharge. Fosfomycin, tigecycline, and chloramphenicol may be options for combination therapy.

Polymyxin combinations: pharmacokinetics and pharmacodynamics for rationale use

Since their reintroduction into the clinic in the 1980s, the polymyxin antibiotics colistin-administered intravenously as an inactive prodrug, colistin methanesulfonate (CMS)-and polymyxin B have assumed an important role as salvage therapy for otherwise untreatable gram-negative infections. However, the emerging pharmacodynamic and pharmacokinetic data on CMS/colistin and polymyxin B indicate that polymyxin monotherapy is unlikely to generate plasma concentrations that are reliably efficacious. Additionally, regrowth and the emergence of resistance with monotherapy are commonly reported even when concentrations exceed those achieved clinically. Given this situation, polymyxin combination therapy, which is increasingly being used clinically, has been suggested as a possible means of increasing antimicrobial activity and reducing the development of resistance. Although considerable in vitro data support this view, investigations of polymyxin combination therapy in patients have only recently commenced. The currently available clinical data for polymyxin combinations are generally limited to retrospective analyses and small, low-powered, prospective studies using traditional dosage regimens that achieve low plasma concentrations. Considering the potential for rapid development of resistance to polymyxins, well-designed clinical trials that include higher-dose polymyxin regimens are urgently required to provide a more definitive answer regarding the role of polymyxin combination therapy compared with monotherapy. In this article, we provide an overview of key in vitro and clinical investigations examining CMS/colistin and polymyxin B combination therapy.

Antibiotic regimens for treatment of infections due to multidrug-resistant Gram-negative pathogens: An evidence-based literature review

Evidences regarding the efficacy of different antibiotic regimens proposed for treatment of multidrug-resistant (MDR) Gram-negative pathogens have been reviewed. Available data in Scopus, Medline, EMBASE, the Cochrane central register of controlled trials, and Cochrane database of systematic reviews have been collected. Several antibiotic regimens are proposed for treatment of MDR Gram-negative infections (defined as nonsusceptibility to at least one agent in three or more antimicrobial categories). The most challenging issue is the treatment of carbapenem-resistant (CR) Gram-negative pathogens. A carbapenem plus either colistin or tigecycline was the most effective regimen for treatment of CR Gram-negative pathogens with low-level resistance (minimal inhibitory concentration [MIC] ≤ 8 mg/L). However, in high-level resistance (MIC > 8 mg/L), combination of colistin and tigecycline showed promising effect.

Global assessment of antimicrobial susceptibility among Gram-negative organisms collected from pediatric patients between 2004 and 2012: results from the Tigecycline Evaluation and Surveillance Trial

The Tigecycline Evaluation and Surveillance Trial (TEST) was designed to monitor susceptibility to commonly used antimicrobial agents among important pathogens. We report here on susceptibility among Gram-negative pathogens collected globally from pediatric patients between 2004 and 2012. Antimicrobial susceptibility was determined using guidelines published by the Clinical and Laboratory Standards Institute (CLSI). Most Enterobacteriaceae showed high rates of susceptibility (>95%) to amikacin, tigecycline, and the carbapenems (imipenem and meropenem); 90.8% of Acinetobacter baumannii isolates were susceptible to minocycline, and susceptibility rates were highest in North America, Europe, and Asia/Pacific Rim. Amikacin was the most active agent against Pseudomonas aeruginosa (90.4% susceptibility), with susceptibility rates being highest in North America. Extended-spectrum β-lactamases (ESBLs) were reported for 11.0% of Escherichia coli isolates and 24.2% of Klebsiella pneumoniae isolates globally, with rates reaching as high as 25.7% in the Middle East and >43% in Africa and Latin America, respectively. Statistically significant (P<0.01) differences in susceptibility rates were noted between pediatric age groups (1 to 5 years, 6 to 12 years, or 13 to 17 years of age), globally and in some regions, for all pathogens except Haemophilus influenzae. Significant (P<0.01) differences were reported for all pathogens globally and in most regions, considerably more frequently, when pediatric and adult susceptibility results were compared. Amikacin, tigecycline, and the carbapenems were active in vitro against most Gram-negative pathogens collected from pediatric patients; A. baumannii and P. aeruginosa were susceptible to fewer antimicrobial agents. Susceptibility rates among isolates from pediatric patients were frequently different from those among isolates collected from adults.

Clinical treatment of pandrug-resistant bacterial infection consulted by clinical pharmacist

Objective

Pandrug-resistant (PDR) bacterial infections are associated with considerable prolongation of hospitalization and mortality in clinical practice.

Method

This case-series study was conducted during a 3-year period from 2011 to 2013. A total of 30 PDR patients consulted by clinical pharmacist were recorded to evaluate the anti-infection treatment.

Results

All isolates of PDR bacteria from patients were identified as pan-drug resistant acine-tobacter baumannii (63.3%), pan-drug resistant klebsiella pneumonia (20.0%), and pandrug-resistant pseudomonas aeruginosa (16.7%). Of the 30 patients, 96.7% therapeutic regimens supposed by clinical pharmacists were applied to treat the infectious patients up to 82.8% clinical cure rates. 30 patients completed the prescribed treatment, of which 19 underwent monotherapy that the clinical cure rate was 78.9%, and 10 underwent combination therapy that the clinical cure rate was 90.0%. In the following therapy, doxycycline, cefoperazone shubatan and amikacin have the certain effect on anti-infection therapy. Combination therapy combined with doxycycline was better treatment option for PDR infectious patients.

Conclusion

In a word, it appears to be effective for the successful therapy of PDR infections upon tetracyclines administration.

Potent and broad-spectrum antibacterial activity of indole-based bisamidine antibiotics: synthesis and SAR of novel analogs of MBX 1066 and MBX 1090

The prevalence of drug-resistant bacteria in the clinic has propelled a concerted effort to find new classes of antibiotics that will circumvent current modes of resistance. We have previously described a set of bisamidine antibiotics that contains a core composed of two indoles and a central linker. The first compounds of the series, MBX 1066 and MBX 1090, have potent antibacterial properties against a wide range of Gram-positive and Gram-negative bacteria. We have conducted a systematic exploration of the amidine functionalities, the central linker, and substituents at the indole 3-position to determine the factors involved in potent antibacterial activity. Some of the newly synthesized compounds have even more potent and broad-spectrum activity than MBX 1066 and MBX 1090.

Synergistic activity of colistin and rifampin combination against multidrug-resistant Acinetobacter baumannii in an in vitro pharmacokinetic/pharmacodynamic model

Combination therapy may be required for multidrug-resistant (MDR) Acinetobacter baumannii. This study systematically investigated bacterial killing and emergence of colistin resistance with colistin and rifampin combinations against MDR A. baumannii. Studies were conducted over 72 h in an in vitro pharmacokinetic (PK)/pharmacodynamic (PD) model at inocula of ~10(6) and ~10(8) CFU/ml using two MDR clinical isolates of A. baumannii, FADDI-AB030 (colistin susceptible) and FADDI-AB156 (colistin resistant). Three combination regimens achieving clinically relevant concentrations (constant colistin concentration of 0.5, 2, or 5 mg/liter and a rifampin maximum concentration [C(max)] of 5 mg/liter every 24 hours; half-life, 3 h) were investigated. Microbiological response was measured by serial bacterial counts. Population analysis profiles assessed emergence of colistin resistance. Against both isolates, combinations resulted in substantially greater killing at the low inoculum; combinations containing 2 and 5 mg/liter colistin increased killing at the high inoculum. Combinations were additive or synergistic at 6, 24, 48, and 72 h with all colistin concentrations against FADDI-AB030 and FADDI-AB156 in, respectively, 8 and 11 of 12 cases (i.e., all 3 combinations) at the 10(6)-CFU/ml inoculum and 8 and 7 of 8 cases with the 2- and 5-mg/liter colistin regimens at the 10(8)-CFU/ml inoculum. For FADDI-AB156, killing by the combination was ~2.5 to 7.5 and ~2.5 to 5 log(10) CFU/ml greater at the low inoculum (all colistin concentrations) and high inoculum (2 and 5 mg/liter colistin), respectively. Emergence of colistin-resistant subpopulations was completely suppressed in the colistin-susceptible isolate with all combinations at both inocula. Our study provides important information for optimizing colistin-rifampin combinations against colistin-susceptible and -resistant MDR A. baumannii.

Pharmacokinetics and pharmacodynamics of 'old' polymyxins: what is new?

'Old' colistin and polymyxin B are increasingly used as last-line therapy against multidrug-resistant Gram-negative bacteria Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. For intravenous administration, colistin is dosed as its inactive prodrug colistin methanesulfonate (sodium), while polymyxin B is used as its sulfate (active antibacterial). Over the last decade, significant progress has been made in understanding their chemistry, pharmacokinetics (PK), and pharmacodynamics (PD). The first scientifically based dosing suggestions are now available for colistin methanesulfonate to generate a desired target steady-state plasma concentration of formed colistin in various categories of critically ill patients. As simply increasing polymyxin dosage regimens is not an option for optimizing their PK/PD due to nephrotoxicity, combination therapy with other antibiotics has great potential to maximize the efficacy of polymyxins while minimizing emergence of resistance. We must pursue rational approaches to the use of polymyxins and other existing antibiotics through the application of PK/PD principles.

Escherichia coli O25b-ST131: a pandemic, multiresistant, community-associated strain

Escherichia coli sequence type 131 (ST131) is a worldwide pandemic clone, causing predominantly community-onset antimicrobial-resistant infection. Its pandemic spread was identified in 2008 by utilizing multilocus sequence typing (MLST) of CTX-M-15 extended-spectrum β-lactamase-producing E. coli from three continents. Subsequent research has confirmed the worldwide prevalence of ST131 harbouring a broad range of virulence and resistance genes on a transferable plasmid. A high prevalence of the clone (∼30%-60%) has been identified amongst fluoroquinolone-resistant E. coli. In addition, it potentially harbours a variety of β-lactamase genes; most often, these include CTX-M family β-lactamases, and, less frequently, TEM, SHV and CMY β-lactamases. Our knowledge of ST131's geographical distribution is incomplete. A broad distribution has been demonstrated amongst antimicrobial-resistant E. coli from human infection in Europe (particularly the UK), North America, Canada, Japan and Korea. High rates are suggested from limited data in Asia, the Middle East and Africa. The clone has also been detected in companion animals, non-companion animals and foods. The clinical spectrum of disease described is similar to that for other E. coli, with urinary tract infection predominant. This can range from cystitis to life-threatening sepsis. Infection occurs in humans of all ages. Therapy must be tailored to the antimicrobial resistance phenotype of the infecting isolate and the site of infection. Phenotypic detection of the ST131 clone is not possible and DNA-based techniques, including MLST and PCR, are described.