Difference in imipenem, meropenem, sulbactam, and colistin nonsusceptibility trends among three phenotypically undifferentiated Acinetobacter baumannii complex in a medical center in Taiwan, 1997-2007

Isolation and characterization of bacteriophages with activities against multi-drug-resistant Acinetobacter nosocomialis causing bloodstream infection in vivo

BACKGROUND

Acinetobacter nosocomialis (A. nosocomialis) is a glucose non-fermentative, gram-negative bacillus that belongs to the Acinetobacter calcoaceticus-baumannii complex. In recent years, studies have found an increased clinical prevalence of A. nosocomialis. However, given the increasing trend of antibiotic resistance, developing new antibacterial agents is vital. Currently, research regarding bacteriophage therapy against A. nosocomialis is only limited.

METHODS

Two A. nosocomialis bacteriophages, TCUAN1 and TCUAN2, were isolated from sewage. Experiments such as transmission electron microscopy (TEM), host-range analysis, and sequencing were performed to determine their biological and genomic characteristics. TCUAN2 were further subjected to in vivo experiments and their derived-endolysin were cloned and tested against their bacteria host.

RESULTS

Transmission electron microscopy revealed that TCUAN1 and TCUAN2 belong to Myoviridae and Podoviridae, respectively. Both phages show a broad host spectrum and rapid adsorption efficiency. Further biological analysis showed that TCUAN2 possesses a shorter latent period and larger burst size compared to TCUAN1. Because TCUAN2 showed a better antibacterial activity, it was injected into A. nosocomialis-infected mice which resulted in a significant decrease in bacterial load levels in the blood and increased the mice's survival. Finally, genomic analysis revealed that the complete nucleotide sequence of TCUAN1 is 49, 691 bps (containing 75 open reading frames) with a G + C content of 39.3%; whereas the complete nucleotide sequence of TCUAN2 is 41, 815 bps (containing 68 open reading frames) with a G + C content of 39.1%. The endolysin gene cloned and purified from TCUAN2 also showed antibacterial activity when used with a chelator EDTA.

The prediction values of carbapenemase detection methods and carbapenem susceptibility testing for clinical outcomes of patients with Acinetobacter bacteremia under carbapenem treatment

BACKGROUND

Carbapenem-resistant Acinetobacter species have emerged as notorious pathogens causing nosocomial infections. Several phenotypic methods have been developed for detecting carbapenemase production in Enterobacteriaceae. The accuracy of these methods in the prediction of carbapenemase production in Acinetobacter species has not been studied well.

METHODS

This retrospective study enrolled adult patients with Acinetobacter bacteremia from four medical centers in Taiwan between 2012 and 2016. Their demographics and clinical outcomes were recorded. The carbapenem susceptibility of the Acinetobacter species was determined using the agar diffusion method. The carbapenemase genes were detected by PCR. Four phenotypic methods, including the modified Hodge test (MHT), modified carbapenem inactivation method (mCIM), Carba NP test, and CarbAcineto NP test were carried out to determine the production of carbapenemase.

RESULTS

We analyzed 257 adults who received initial carbapenem monotherapy for the treatment of Acinetobacter bacteremia. Shock within three days of bacteremia and acquisition of carbapenem non-susceptible isolates were independently associated with a higher 14-day and 30-day mortality in patients with Acinetobacter bacteremia. Among the four phenotypic tests for carbapenemase detection, MHT using the imipenem disc displayed the greatest sensitivity (94%; 95% confidence interval [CI], 89-97%) and specificity (81%; 95% CI, 73-88%) for predicting imipenem non-susceptibility.

CONCLUSION

Carbapenem non-susceptibility and shock were independent risk factors for mortality in patients with Acinetobacter bacteremia. The MHT could predict the carbapenem susceptibility of Acinetobacter isolates. It is a cheap and quick assay, which could be applied in clinical practice.

A multicenter study on clinical characteristics of Acinetobacter bacteremia in patients with liver cirrhosis

BACKGROUND

Clinical characteristics and risk factors for mortality of Acinetobacter bacteremia in cirrhotic patients have not been investigated.

METHODS

Acinetobacter bacteremia cases from four medical centers were collected from 2009 to 2014, to compare between patients with and without liver cirrhosis. Risk factors for mortality of Acinetobacter bacteremia among cirrhotic patients were identified using multivariate logistic regression.

RESULTS

Among the patients with Acinetobacter bacteremia, 72 had liver cirrhosis and 816 had not. Patients with cirrhosis were younger (57.5 [50-71] vs. 72 [50.25-71], p < 0.001), had more solid tumor (51.4% vs. 31.4%, p = 0.001), lower Acute Physiology and Chronic Health Evaluation II (APACHE II) scores (17 [12-24] vs. 20 [13-28], p = 0.012), less sourced from pneumonia (19.4% vs. 35.8%, p = 0.008), and less caused by Acinetobacterbaumannii (33.3% vs. 50.6%, p = 0.007) than those without. After matching for age, sex, and causative pathogens, the 30-day mortality (34.7% vs. 29.2%, p = 0.592) and APACHE II scores (17 vs. 17, p = 0.769) were not significant. APACHE II score (odds ratio [OR], 1.146; 95% confidence interval [CI], 1.035-1.268; p = 0.009), bacteremia caused by A. baumannii (OR, 20.501; 95% CI, 2.301-182.649; p = 0.007), and solid tumor (OR, 18.073; 95% CI, 1.938-168.504; p = 0.011) were independent risk factors for 30-day mortality of cirrhotic patients with Acinetobacter bacteremia.

CONCLUSION

Even though cirrhotic patients with Acinetobacter bacteremia were younger and had lower APACHE II scores than non-cirrhotic patients, the mortality rates were insignificantly different between the two groups.

Multicenter Study of Clinical Features of Breakthrough Acinetobacter Bacteremia during Carbapenem Therapy

Breakthrough Acinetobacter bacteremia during carbapenem therapy is not uncommon, and it creates therapeutic dilemmas for clinicians. This study was conducted to evaluate the clinical and microbiological characteristics of breakthrough Acinetobacter bacteremia during carbapenem therapy and to assess the efficacy of various antimicrobial therapies. We analyzed 100 adults who developed breakthrough Acinetobacter bacteremia during carbapenem therapy at 4 medical centers over a 6-year period. Their 30-day mortality rate was 57.0%, and the carbapenem resistance rate of their isolates was 87.0%. Among patients with carbapenem-resistant Acinetobacter bacteremia, breakthrough bacteremia during carbapenem therapy was associated with a significantly higher 14-day mortality (51.7% versus 37.4%, respectively; P = 0.025 by bivariate analysis) and a higher 30-day mortality (P = 0.037 by log rank test of survival analysis) than in the nonbreakthrough group. For the treatment of breakthrough Acinetobacter bacteremia during carbapenem therapy, tigecycline-based therapy was associated with a significantly higher 30-day mortality (80.0%) than those with continued carbapenem therapy (52.5%) and colistin-based therapy (57.9%) by survival analysis (P = 0.047 and 0.045 by log rank test, respectively). Cox regression controlling for confounders, including severity of illness indices, demonstrated that treatment with tigecycline-based therapy for breakthrough Acinetobacter bacteremia was an independent predictor of 30-day mortality (hazard ratio, 3.659; 95% confidence interval, 1.794 to 7.465; P < 0.001). Patients with breakthrough Acinetobacter bacteremia during carbapenem therapy posed a high mortality rate. Tigecycline should be used cautiously for the treatment of breakthrough Acinetobacter bacteremia that develops during carbapenem therapy.

Carbapenem Breakpoints for Acinetobacter baumannii Group: Supporting Clinical Outcome Data from Patients with Bacteremia

The carbapenem breakpoints set by different organizations for Acinetobacter are discordant, but supporting clinical data are lacking. This study aimed to provide the first clinical outcome data to support the carbapenem breakpoints for Acinetobacter baumannii (Ab) group in patients with bacteremia. This study included 117 adults who received carbapenems for treatment of Ab group bacteremia in Taipei Veterans General Hospital over an 8-year period. We analyzed 30-day mortality rates among patient groups acquiring isolates with different carbapenem minimal inhibitory concentrations (MICs). The carbapenem MIC breakpoint derived from classification and regression tree (CART) analysis to delineate the risk of 30-day mortality was between MICs of ≤ 4 mg/L and ≥ 8 mg/L. Mortality rate was higher in patients acquiring isolates with carbapenem MIC ≥ 8 mg/L than ≤ 4 mg/L, by bivariate (54.9% [28/51] vs 25.8% [17/66]; P = 0.003) and survival analysis (P = 0.001 by log-rank test). Multivariate analysis using logistic regression and Cox regression models including severity of illness indices demonstrated that treating patients with Ab group bacteremia caused by isolates with a carbapenem MIC ≥ 8 mg/L with carbapenem was an independent predictor of 30-day mortality (odds ratio, 5.125; 95% confidence interval [CI], 1.946-13.498; P = 0.001, and hazard ratio, 2.630; 95% CI, 1.431-4.834; P = 0.002, respectively). The clinical outcome data confirmed that isolates with MIC ≤ 4 mg/L were susceptible to carbapenem, and those with MIC ≥ 8 mg/L were resistant in patients with Ab group bacteremia.

Investigating the in vitro synergistic activities of several antibiotic combinationsagainst carbapenem-resistant Acinetobacter baumannii isolates

BACKGROUND/AIM

Acinetobacter baumannii (A. baumannii) is one of the most common healthcare-associated infectious agents worldwide. The aim of this study was to investigate the in vitro synergistic activities of several antibiotic combinations against carbapenem-resistant (CR) A. baumannii isolates.

MATERIALS AND METHODS

Eighteen CR A. baumannii strains were isolated from the patients who were hospitalized in the intensive care unit between June 2012 and August 2012. The in vitro effects of single and binary combinations of meropenem (MEM), colistin (CST), tigecycline (TGC), and sulbactam (SUL) on these isolates were determined using the Epsilometer test (E-test) method.

RESULTS

All 18 isolates were resistant to MEM and SUL and susceptible to CST. TGC was detected as susceptible in two of the isolates and intermediate susceptibility results were observed in the remaining isolates. With MEM-CST and MEM-TGC combinations, synergism was determined against all isolates. The synergistic and/or additive effect ratios were detected in MEM-SUL, CST-SUL, TGC-SUL, and CST-TGC combinations as 16.7%, 38.9%, 16.7%, and 5.6%, respectively.

CONCLUSION

Among the tested antimicrobial combinations, the in vitro combination of MEM with TGC or CST was most effective against the CR A. baumannii strains.

Comparative Phosphoproteomics Reveals the Role of AmpC β-lactamase Phosphorylation in the Clinical Imipenem-resistant Strain Acinetobacter baumannii SK17

Nosocomial infectious outbreaks caused by multidrug-resistant Acinetobacter baumannii have emerged as a serious threat to human health. Phosphoproteomics of pathogenic bacteria has been used to identify the mechanisms of bacterial virulence and antimicrobial resistance. In this study, we used a shotgun strategy combined with high-accuracy mass spectrometry to analyze the phosphoproteomics of the imipenem-susceptible strain SK17-S and -resistant strain SK17-R. We identified 410 phosphosites on 248 unique phosphoproteins in SK17-S and 285 phosphosites on 211 unique phosphoproteins in SK17-R. The distributions of the Ser/Thr/Tyr/Asp/His phosphosites in SK17-S and SK17-R were 47.0%/27.6%/12.4%/8.0%/4.9% versus 41.4%/29.5%/17.5%/6.7%/4.9%, respectively. The Ser-90 phosphosite, located on the catalytic motif S(88)VS(90)K of the AmpC β-lactamase, was first identified in SK17-S. Based on site-directed mutagenesis, the nonphosphorylatable mutant S90A was found to be more resistant to imipenem, whereas the phosphorylation-simulated mutant S90D was sensitive to imipenem. Additionally, the S90A mutant protein exhibited higher β-lactamase activity and conferred greater bacterial protection against imipenem in SK17-S compared with the wild-type. In sum, our results revealed that in A. baumannii, Ser-90 phosphorylation of AmpC negatively regulates both β-lactamase activity and the ability to counteract the antibiotic effects of imipenem. These findings highlight the impact of phosphorylation-mediated regulation in antibiotic-resistant bacteria on future drug design and new therapies.

Molecular epidemiology of carbapenem non-susceptible Acinetobacter nosocomialis in a medical center in Taiwan

The mechanism by which carbapenem non-susceptible Acinetobacter nosocomialis (CNSAN) is disseminated is rarely described in the literature. In this study, we delineated the molecular epidemiology of CNSAN isolated from patients in a medical center in Taiwan. Fifty-four non-duplicate bloodstream isolates of CNSAN were collected at the Taipei Veterans General Hospital between 2001 and 2007. Pulsed-field gel electrophoresis (PFGE) was performed to determine their clonal relationship. Carbapenem-resistance genes and associated genetic structures were detected by polymerase chain reaction (PCR) mapping. Southern hybridization was performed to determine the plasmid location of carbapenem-resistance genes. Transmissibility of these genes to Acinetobacterbaumannii was demonstrated by conjugation tests. The overall carbapenem non-susceptibility rate among A. nosocomialis isolates during the study period was 21.6% (54/250). PFGE revealed three major pulsotypes: H (n=23), I (n=10), and K (n=8). The most common carbapenem-resistance gene was blaOXA-58 (43/54, 79.6%), containing an upstream insertion sequence IS1006 and a truncated ISAba3 (IS1006-ΔISAba3-like-blaOXA-58). All isolates belonging to the pulsotypes H, I, and K carried plasmid located IS1006-ΔISAba3-like-blaOXA-58. A common plasmid carrying ISAba1-blaOXA-82 was found in six isolates, which belonged to five pulsotypes. A type 1 integron that carried blaIMP-1 was detected in different plasmids of seven isolates, which belonged to five pulsotypes. Plasmids carrying these carbapenem-resistant determinants were transmissible from A. nosocomialis to A. baumannii via conjugation. In this medical center, CNSAN mainly emerged through clonal dissemination; propagation of plasmids and integrons carrying carbapenem-resistant determinants played a minor role. This study showed that plasmids carrying carbapenem-resistant determinants are transmissible from A. nosocomialis to A. baumannii.

The Acinetobacter baumannii group: a systemic review

BACKGROUND

The Acinetobacter baumannii group, including Acinetobacter baumannii, Acinetobacter genomospecies 3 and 13TU, is phenotypically indistinguishable and uniformly identified as Acinetobacter baumannii by laboratories of clinical microbiology. This review aimed to demonstrate the differences among them.

METHODS

Literatures associated with the Acinetobacter baumannii group were identified and selected from PubMed databases and relevant journals.

RESULTS

Acinetobacter genospecies 3 and 13TU possess a certain proportion in clinical isolates. There were considerable differences in epidemiologic features, clinical manifestations, antimicrobial resistances and therapeutic options among the Acinetobacter baumannii group. Compared with Acinetobacter genomospecies 3 and 13TU, Acinetobacter baumannii with a higher resistance to antimicrobial agents are easier to be treated inappropriately, and present a worse outcome in patients.

CONCLUSION

The Acinetobacter baumannii group comprises three distinct clinical entities, and their clinical value are not equal.

Risk factors and clinical outcome of sulbactam nonsusceptibility in monomicrobial Acinetobacter nosocomialis bacteremia

BACKGROUND

Sulbactam is an effective antimicrobial agent against multidrug-resistant Acinetobacter spp. This retrospective study evaluated the risk factors of sulbactam nonsusceptibility (SNS) in monomicrobial Acinetobacter nosocomialis bacteremia and its related outcome.

METHODS

This 9-year retrospective study included 267 patients who were admitted to a large teaching hospital in Taiwan with monomicrobial A. nosocomialis bacteremia. A. nosocomialis was identified to the species level using molecular methods. Antimicrobial susceptibilities were determined by the agar dilution method. To identify the risk factors of acquiring resistant strains, significant clinical variables derived from univariate analysis were entered into multivariate analysis. Polymerase chain reaction was used to identify blaTEM. Clonality was determined by pulsed-field gel electrophoresis.

RESULTS

A total of 41 of the 267 patients (15.4%) had SNS A. nosocomialis bacteremia. Compared to those with susceptible strains, these patients had higher 14-day mortality (17.1% vs. 7.5%, p = 0.049), were more likely to have higher Acute Physiology and Chronic Health Evaluation (APACHE) II score, were more frequently admitted to the intensive care unit, and had previously received broad-spectrum antibiotics and underwent invasive procedures. In multivariate analysis, the independent risk factors were high APACHE II score and prior use of arterial line [odds ratio (OR), 1.048; 95% confidence interval (CI), 1.007-1.091; p = 0.022 and OR, 2.936; 95% CI, 1.339-6.441; p = 0.007, respectively]. No outbreak was identified and SNS isolates did not harbor blaTEM.

CONCLUSION

For monomicrobial A. nosocomialis bacteremia, the mortality of patients with SNS strains was higher. The SNS strains are more commonly recovered from patients with higher APACHE score and receiving more invasive procedures, especially arterial line.

Comparison between bacteremia caused by carbapenem resistant Acinetobacter baumannii and Acinetobacter nosocomialis

Background

It is unknown whether there are differences between bacteremia caused by carbapenem resistant Acinetobacter baumannii (CRAB) and carbapenem resistant Acinetobacter nosocomialis (CRAN). This study aims to investigate the differences, especially in clinical outcomes, between patients with bacteremia caused by CRAB or CRAN.

Methods

This is a 9-year retrospective study comparing the clinical manifestations, antimicrobial susceptibilities, and clinical outcomes of 71 patients with CRAB bacteremia and 64 patients with CRAN bacteremia.

Results

Patients with CRAB were more likely to have hematologic malignancies and presented with more shock episodes than those with CRAN. CRAB isolates were more resistant to various classes of antimicrobials except colistin, and therefore the patients with CRAB bacteremia were more likely to receive inappropriate antimicrobial therapies. The 14-day mortality was significantly higher in patients with CRAB (40.8% vs. 14.1%; p = 0.001), and in this study, acquisition of CRAB was identified as an independent risk factor for mortality (odds ratio = 4.003; 95% confidence interval = 1.566-10.231; p = 0.004).

Conclusions

CRAB and CRAN bacteremia are different in clinical characteristics, antimicrobial susceptibilities, and mortality rates. Genomic species identification should be performed in the study of carbapenem resistant Acinetobacters to better delineate the role of different species.

Clinical characteristics and prognostic factors of Acinetobacter nosocomialis bacteraemia in patients with solid tumours

The clinical characteristics and risk factors for 28-day mortality in 120 patients with solid tumours with Acinetobacter nosocomialis bacteraemia were retrospectively analysed. Eighty-one patients (67.5%) had advanced-stage cancer. Most of the bacteraemia (37.5%) did not have an identified source. The bacteraemia episodes developed at a median of 15 days after hospitalization, and most during a non-neutropenic period (97.5%). Although only half of the patients received appropriate antimicrobial therapy, the mortality was relatively low (11.7%). High Pitt bacteraemia score and receipt of chemotherapy within the month before bacteraemia onset were independently associated with 28-day mortality.

Clinical characteristics and outcomes of bacteremia due to different genomic species of Acinetobacter baumannii complex in patients with solid tumors

PURPOSE

Acinetobacter baumannii, Acinetobacter genomic species 3 (AGS 3), and Acinetobacter genomic species sensu Tjernberg and Ursing (AGS 13TU) are phenotypically indistinguishable and are often reported together as the A. baumannii complex (ABC). Few studies have investigated the difference in outcome caused by these different species, and all involved heterogeneous groups of patients. This study aimed to delineate whether there are differences in the clinical characteristics and outcome among patients with solid tumors and bacteremia caused by A. baumannii or two other non-baumannii ABC species (AGS 3 plus AGS 13TU).

METHODS

Patients with solid tumors and ABC bacteremia over a period of 5 years in a medical center were identified. The patient data were retrospectively reviewed and analyzed.

RESULTS

We identified 103 patients with ABC bacteremia during the study period. Bacteremia was due to A. baumannii in 30 patients, AGS 3 in 24 patients, and AGS 13TU in 49 patients. Among the 103 patients with ABC bacteremia, recent stay in the intensive care unit (ICU) (p = 0.008) was independently associated with the acquisition of A. baumannii bacteremia. Multivariate analysis revealed that bacteremia caused by A. baumannii (hazard ratio [HR] 2.990, 95% confidence interval [CI], 1.021-8.752, p = 0.046) and Acute Physiology and Chronic Health Evaluation (APACHE) II score ≥21 (HR 4.623, 95% CI 1.348-15.859, p = 0.015) were independent factors associated with 14-day mortality.

CONCLUSIONS

Infection with A. baumannii and a high APACHE II score (≥21) might be associated with poor outcome in patients with solid tumors and ABC bacteremia.