The role of vancomycin in addition with colistin and meropenem against colistin-sensitive multidrug resistant Acinetobacter baumannii causing severe infections in a Paediatric Intensive Care Unit

Acinetobacter baumannii in the critically ill: complex infections get complicated

Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.

Potentiation of Vancomycin: Creating Cooperative Membrane Lysis through a "Derivatization-for-Sensitization" Approach

Gram-negative bacteria, especially the ones with multidrug resistance, post dire challenges to antibiotic treatments due to the presence of the outer membrane (OM), which blocks the entry of many antibiotics. Current solutions for such permeability issues, namely lipophilic-cationic derivatization of antibiotics and sensitization with membrane-active agents, cannot effectively potentiate the large, globular, and hydrophilic antibiotics such as vancomycin, due to ineffective disruption of the OM. Here, we present our solution for high-degree OM binding of vancomycin via a hybrid "derivatization-for-sensitization" approach, which features a combination of LPS-targeting lipo-cationic modifications on vancomycin and OM disruption activity from a sensitizing adjuvant. 10⁶- to 10⁷-fold potentiation of vancomycin and 20-fold increase of the sensitizer's effectiveness were achieved with a combination of a vancomycin derivative and its sensitizer. Such potentiation is the result of direct membrane lysis through cooperative membrane binding for the sensitizer-antibiotic complex, which strongly promotes the uptake of vancomycin and adds to the extensive antiresistance effectiveness. The potential of such derivatization-for-sensitization approach was also supported by the combination's potent in vivo antimicrobial efficacy in mouse model studies, and the expanded application of such strategy on other antibiotics and sensitizer structures.

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

Despite the recent development of antibacterials that are active against multidrug-resistant pathogens, drug combinations are often necessary to optimize the killing of difficult-to-treat organisms. Antimicrobial combinations typically are composed of multiple agents that are active against the target organism; however, many studies have investigated the potential utility of combinations that consist of one or more antibacterials that individually are incapable of killing the relevant pathogen. The current review summarizes in vitro, in vivo, and clinical studies that evaluate combinations that include at least one drug that is not active individually against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, or Staphylococcus aureus. Polymyxins were often included in combinations against all three of the Gram-negative pathogens, and carbapenems were commonly incorporated into combinations against K. pneumoniae and A. baumannii. Minocycline, sulbactam, and rifampin were also frequently investigated in combinations against A. baumannii, whereas the addition of ceftaroline or another β-lactam to vancomycin or daptomycin showed promise against S. aureus with reduced susceptibility to vancomycin or daptomycin. Although additional clinical studies are needed to define the optimal combination against specific drug-resistant pathogens, the large amount of in vitro and in vivo studies available in the literature may provide some guidance on the rational design of antibacterial combinations.

Clinical Efficacy and Nephrotoxicity of Colistin Alone versus Colistin Plus Vancomycin in Critically Ill Patients Infected with Carbapenem-Resistant Acinetobacter baumannii: A Propensity Score-Matched Analysis

Acinetobacter baumannii has emerged as a significant concern worldwide. The mortality rate of carbapenem-resistant A. baumannii (CRAB) is increasing, especially in the intensive care unit (ICU). Thus, the objective of this study is to compare the efficacy and safety of colistin plus vancomycin for the treatment of critically ill patients with CRAB in Chiang Mai University Hospital. We conducted a retrospective cohort study of critically ill patients in the ICU with CRAB infection who received colistin alone or colistin-vancomycin combination therapy at Chiang Mai University Hospital. A total of 365 critically ill patients met the inclusion criteria. The results in this study showed that after propensity score matching, colistin plus vancomycin showed no significant differences in the 30-day mortality compared to colistin alone. Likewise, for colistin plus vancomycin, compared with colistin therapy alone, there were no significant differences in the clinical response, microbiological response and nephrotoxicity. In conclusion, colistin plus vancomycin was no significant differences in 30-day mortality, clinical response, microbiological response compared to colistin alone for infections due to CRAB. The nephrotoxicity rates were similar for both groups, so colistin combination with vancomycin was not necessary for the management of infection caused by CRAB.

Cathelicidin-Derived Synthetic Peptide Improves Therapeutic Potential of Vancomycin Against Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) is the leading cause of corneal blindness worldwide. A constant increase in multi-drug resistant PA strains have heightened the challenge of effectively managing corneal infections with conventional antibiotics. Antimicrobial peptides are promising antibiotic analogs with a unique mode of action. Cathelicidin-derived shorter peptides (FK13 and FK16) have previously been shown to kill a range of pathogens in both in vitro and in vivo systems. Here, our aim was to exploit the potential of FK13 or FK16 to enhance the anti-Pseudomonas activity of vancomycin, which normally has low clinical efficacy against PA. Our results have demonstrated that FK16 is more potent than FK13 against different PA strains including a clinical isolate from a patient's ocular surface. FK16 was shown to enhance the membrane permeability of PAO1 at sub-inhibitory concentrations. Moreover, FK16 at lower concentrations was shown to increase the antibacterial susceptibility of vancomycin against PA strains up to eightfold. The bactericidal synergism between FK16 and vancomycin was shown to be stable in the presence of physiological tear salt concentration and did not cause toxic effects on the human corneal epithelial cells and human red blood cells. Our results have revealed that sub-inhibitory concentration of FK16 could augment the antimicrobial effects of vancomycin against PA. It is anticipated that the future exploitation of the peptide design approach may enhance the effectiveness of FK16 and its application as an adjuvant to antibiotic therapy for the treatment of multi-drug resistant infections.

Colistin-glycopeptide combinations against multidrug-resistant Acinetobacter baumannii in a mouse model of pneumonia

Aim: To assess the effect of colistin-glycopeptide combination against a multidrug-resistant strain of Acinetobacter baumannii. Materials & methods: We used in vitro procedures (Etest method, checkerboard test and kill-time assays) and a mouse model of a carbapenem-resistant A. baumannii pneumonia. Results: The colistin-teicoplanin combination allowed a 74% increase of the survival in the mouse model within the 4 days following bacterial inoculation as compared with saline or colistin alone (p = 0.06). Concurrently, the colistin-vancomycin combination presented a similar efficacy as compared with saline or colistin alone in the mouse model. Conclusion: According to those preliminary results, using the colistin-teicoplanin combination in therapeutic deadlocks encountered in certain multiresistant A. baumannii pneumonia could be envisaged if the results are confirmed.

In-Vitro Evaluation of Different Antimicrobial Combinations with and without Colistin Against Carbapenem-Resistant Acinetobacter Baumannii

Carbapenem-resistant Acinetobacter baumannii (CR-Ab) infections are associated with high morbidity and mortality. The aim of the study was to evaluate the in-vitro activity of different antimicrobial combinations (with and without colistin, COL) against clinical isolates of CR-Ab collected from patients with CR-Ab infection, including unconventional combinations such as COL + VANcomycin (VAN) and COL + rifampin (RIF). CR-Ab strains were collected from hospitalized patients at Sapienza University of Rome. Antimicrobial susceptibility patterns were determined throughout MIC50/90s whereas the synergistic activity was evaluated by qualitative (i.e., checkerboard) and quantitative (i.e., killing studies) methods. All the strains were found oxacillinase (OXA) producers and tigecycline (TIG) sensitive whereas 2 strains were resistant to COL. Application of the checkerboard method indicated complete synergism in COL combinations at different extension: 21.4%, 57.1%, 42.8%, 35.7% for COL + meropenem (MEM), COL + RIF, COL + VAN and COL + TIG, respectively, with the non-conventional combinations COL + VAN and COL + RIF exhibiting the highest rate of synergism. Regarding COL-free combination, complete synergism was observed in 35.7% of the strains for MEM + TIG. Killing studies showed that the combinations COL + MEM, COL + TIG and MEM + TIG were bactericidal and synergistic against both colistin-sensitive and low colistin-resistant strains whereas only the combinations COL + VAN and COL + RIF showed an early and durable bactericidal activity against all the tested strains, with absence of growth at 24 h. This study demonstrated that COL-based combinations lead to a high level of synergic and bactericidal activity, especially COL + VAN and COL + RIF, even in the presence of high level of COL resistance.

Clinical relevance of in vitro synergistic activity of antibiotics for multidrug-resistant Gram-negative infections: A systematic review

OBJECTIVES

The aim of this review was to investigate the outcomes of patients infected with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria following synergy-guided antibiotic combination therapy (SGACT).

METHODS

A systematic review of PubMed and Scopus databases was performed. Published studies of any design reporting outcomes of patients with MDR Gram-negative bacteria treated with SGACT were included. Two reviewers independently assessed the relevancy and quality of the retrieved articles and extracted the available data.

RESULTS

Nineteen reports (530 patients) were included. Eleven case reports/series described 26 cases of systemic infection due to MDR Gram-negative bacteria treated with SGACT. Five deaths were reported, two of which were attributed to the infection. Six studies (including one randomised controlled trial) provided comparative data for patients treated with SGACT and those treated with unguided combination therapy (UCT) or active monotherapy. In the pooled analysis of unadjusted data from these studies (504 patients), there was no difference between SGACT and UCT or monotherapy (OR=0.47, 95% CI 0.21-1.04; I²=52%). Analysis of adjusted data showed that SGACT was significantly associated with survival (OR=0.44, 95% CI 0.20-0.98; I²=54%).

CONCLUSION

These limited but promising findings warrant further investigation of SGACT in the outcome of patients with MDR Gram-negative infections in well-designed trials.

Comparison of Septic Shock Due to Multidrug-Resistant Acinetobacter baumannii or Klebsiella pneumoniae Carbapenemase-Producing K. pneumoniae in Intensive Care Unit Patients

A significant cause of mortality in the intensive care unit (ICU) is multidrug-resistant (MDR) Gram-negative bacteria, such as MDR Acinetobacter baumannii (MDR-AB) and Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp). The aim of the present study was to compare the clinical features, therapy, and outcome of patients who developed septic shock due to either MDR-AB or KPC-Kp. We retrospectively analyzed patients admitted to the ICU of a teaching hospital from November 2010 to December 2015 who developed septic shock due to MDR-AB or KPC-Kp infection. Data from 220 patients were analyzed: 128 patients (58.2%) were diagnosed with septic shock due to KPC-Kp, and 92 patients (41.8%) were diagnosed with septic shock due to MDR-AB. The 30-day mortality rate was significantly higher for the MDR-AB group than the KPC-Kp group (84.8% versus 44.5%, respectively; P < 0.001). Steroid exposure and pneumonia were associated with MDR-AB infection, whereas hospitalization in the previous 90 days, primary bacteremia, and KPC-Kp colonization were associated with KPC-Kp infection. For patients with KPC-Kp infections, the use of ≥2 in vitro-active antibiotics as empirical or definitive therapy was associated with higher 30-day survival, while isolation of colistin-resistant strains was linked to mortality. Patients with MDR-AB infections, age >60 years, and a simplified acute physiology score II (SAPS II) of >45 points were associated with increased mortality rates. We concluded that septic shock due to MDR-AB infection is associated with very high mortality rates compared to those with septic shock due to KPC-Kp. Analysis of the clinical features of these critically ill patients might help physicians in choosing appropriate empirical antimicrobial therapy.

Intravenous polymyxins: Revival with puzzle

With the increasing incidence of multi-drug resistant strains, especially carbapenem resistant strains, polymyxsins (mainly colistin and polymyxin B) based regimens seem to be a revival as an effective treatment of last resort in these infections. Evidence from 47 clinical trials or case series we reviewed showed that polymyxins based regimens are effective and have less toxicity compared with previous trials. When used alone, the mortality of intravenous polymyxsins ranged from 0% to 74.3%, clinical response (cure and improvement) rate was 7-82.1%, and microbiological eradication was 27.3-73.9%. The main reasons for the combination therapy are to get potential synergistic effects and to prevent the selection of heteroresistant strains. Several studies showed combination therapy seemed to be more effective than monotherapy, though a few doubts remain. Clinically, polymyxsins can be used in combination with several antibiotics, such as carberpenem, sulbactam, tigecycline, fosfomycin, glycopeptide, rifampicin and so on, but the optimal combination regimen is yet to be confirmed. The optimal dose of polymyxins is also controversial. With the limited clinical evidence, it's suggested loading dose regimens may be more effective, but more attention should be paid to adverse effects. Although recommended in some studies, high dose polymxins regimens with inconsistent clinical evidence need more trials to confirm. It is important to note that concerning dosing regimens, colistin and polymyxin B are not quite the same. In renal impaired patients polymyxin B should be prescribed without dosing adjustment. Risk of renal failure may increase in the following situations, such as the combination of intravenous colistin plus intravenous vancomycin, higher doses-colistin, and intravenous colistin combined with inhalational colistin. In conclusion, there're still controversies in combination regimens, dosing strategies and so on. Prospective trials of lager sample size are needed.

Risk factors and predictors of carbapenem-resistant Pseudomonas aeruginosa and Acinetobacter baumannii mortality in critically ill bacteraemic patients over a 6-year period (2010-15): antibiotics do matter

Purpose. Acinetobacter baumannii and Pseudomonas aeruginosa provoke serious infections, especially in intensive care unit (ICU) patients.Methodology. The risk factors and predictors of mortality for P. aeruginosa (n=84; 46 carbapenem-resistant) and A. baumannii (n=129; all carbapenem-resistant) bloodstream infections (BSIs) in an ICU were evaluated. Antibiotic susceptibility testing was performed using the agar disk diffusion method according to EUCAST guidelines. The minimum inhibitory concentration was determined by a gradient method (Etest). Multilocus sequence typing (MLST) was performed for P. aeruginosa during the carbapenem-resistant outbreak in 2014. Epidemiological data were collected from the patients' chart reviews.Results/Key findings. Hospitalization during the summer months, prior KPC-producing Klebsiella pneumoniae (KPC-Kp) BSI, and the administration of tigecycline, aminoglycosides and cortisone were independently associated with P. aeruginosa BSIs. MLST revealed the dissemination of clone ST227, including carbapenem-resistant P. aeruginosa strains. Hospitalization during the summer months, prior KPC-Kp BSI, and the administration of antibiotics, carbapenem and cortisone were independently associated with A. baumannii BSIs. The 30-day mortality rate for P. aeruginosa and A. baumannii BSI was 45.2 and 39.5 %, respectively. Sequential organ failure assessment (SOFA) score at onset, septic shock, age, and prior KPC-Kp BSI were significantly associated with P. aeruginosa BSI mortality. The administration of at least one active antibiotic was identified as a predictor of a good prognosis. Septic shock and simplified acute physiology score (SAPS) II at onset were independently associated with A. baumannii BSI mortality. The administration of at least one active antibiotic and colistin-vancomycin co-administration were identified as predictors of a good prognosis.Conclusion. KPC-Kp infection predisposes ICU patients to BSI by either A. baumannii or P. aeruginosa. The administration of at least one active antibiotic leads to better survival rates.

Disruption of Membrane by Colistin Kills Uropathogenic Escherichia coli Persisters and Enhances Killing of Other Antibiotics

Persisters are small populations of quiescent bacterial cells that survive exposure to bactericidal antibiotics and are responsible for many persistent infections and posttreatment relapses. However, little is known about how to effectively kill persister bacteria. In the work presented here, we found that colistin, a membrane-active antibiotic, was highly active against Escherichia coli persisters at high concentrations (25 or 50 μg/ml). At a clinically relevant lower concentration (10 μg/ml), colistin alone had no apparent effect on E. coli persisters. In combination with other drugs, this concentration of colistin enhanced the antipersister activity of gentamicin and ofloxacin but not that of ampicillin, nitrofurans, and sulfa drugs in vitro The colistin enhancement effect was most likely due to increased uptake of the other antibiotics, as demonstrated by increased accumulation of fluorescence-labeled gentamicin. Interestingly, colistin significantly enhanced the activity of ofloxacin and nitrofurantoin but not that of gentamicin or sulfa drugs in the murine model of urinary tract infection. Our findings suggest that targeting bacterial membranes is a valuable approach to eradicating persisters and should have implications for more effective treatment of persistent bacterial infections.

Multidrug resistance Acinetobacter species at the intensive care unit, Aseer Central Hospital, Saudi Arabia: A one year analysis

OBJECTIVE

To identify and to determine the antimicrobial susceptibility of Acinetobacter baumannii (A. baumannii) clinical isolates from ICU at Aseer Central Hospital.

METHODS

The study was conducted in the Intensive Care Unit, Aseer Central Hospital, Saudi Arabia over 13 months period (2014-2015). Acinetobacter species (n = 105) were isolated from various clinical samples. Isolates were identified using selected phenotypic criteria and confirmed using the Vitek 2 automated system. This system was used to determine the susceptibilities of 21 antimicrobial agents. Patients, isolates and drug data were analyzed using the SPSS statistical software package to determine some epidemiological and microbiological patterns.

RESULTS

Of the 105 stains, A. baumannii accounted for 49 (46.67%), A. baumannii complex, 19 (18.09%), A. baumannii/haemolyticus 32 (30.47), Acinetobacter haemolyticus 4 (3.81%), Acinetobater lwoffii 1 (0.95%) and unidentified Acinetobater species 2 (1.3%). Of the 105 Acinetobacter strains, 103 (98.1%) were found multidrug resistant (MDR). A. baumannii strain were 100% sensitive to colistin and 74.5% to trimethoprim + sulfamethoxazole. The remaining 19 antimicrobial agents revealed low or no sensitivities: amikacin 16.3%; ampicillin 7.7%; ceftazidime, 7.3%. Distribution of similar sensitivities was shown by other Acinetobacter species. Mean number of isolates from males and females indicates no statistical variation (P = 0.867) whereas age groups showed significant differences (P = 0.008) as it is clear from the high percentage of infected individuals more than 60 years followed by those aged 20-29 years old (19.05%). Upper respiratory tract (30.48%), lower respiratory tract (47.65%) and subcutaneous tissue (9.5%) were the main sources of Acinetobacter spp. but mean numbers of isolates from these specimens indicate no discrepancy between specimens (P = 0.731).

CONCLUSIONS

Acinetobacter species including A. baumannii were found MDR (98.1%) according to the current Acinetobacter spp. antimicrobial categorization. Approximately half of these strains were A. baumannii. All Acinetobacter species were 100% sensitive to colistin and to some extent to trimethoprim + sulfamethoxazole (74.5%). ICU-acquired pneumonia among patients over 60 years of age who spend prolong times at artificial ventilations made up the majority of the cases.