Molecular characterisation of multiple drug-resistant Acinetobacter baumannii isolates in southern Taiwan

Collateral Changes in Cell Physiology Associated with ADC-7 β-Lactamase Expression in Acinetobacter baumannii

The ADC (AmpC) β-lactamase is universally present in the Acinetobacter baumannii chromosome, suggesting it may have a yet-to-be-identified cellular function. Using peptidoglycan composition analysis, we show that overexpressing the ADC-7 β-lactamase in A. baumannii drives changes consistent with altered l,d-transpeptidase activity. Based on this, we tested whether cells overexpressing ADC-7 would exhibit new vulnerabilities. As proof of principle, a screen of transposon insertions revealed that an insertion in the distal 3' end of canB, encoding carbonic anhydrase, resulted in a significant loss of viability when the adc-7 gene was overexpressed. A canB deletion mutant exhibited a more pronounced loss of viability than the transposon insertion, and this became amplified when cells overexpressed ADC-7. Interestingly, overexpression of the OXA-23 or TEM-1 β-lactamases also led to a pronounced loss of viability in cells with reduced carbonic anhydrase activity. In addition, we demonstrate that reduced CanB activity led to increased sensitivity to peptidoglycan synthesis inhibitors and to the carbonic anhydrase inhibitor ethoxzolamide. Furthermore, this strain exhibited a synergistic interaction with the peptidoglycan inhibitor fosfomycin and ethoxzolamide. Our results highlight the impact of ADC-7 overexpression on cell physiology and reveal that the essential carbonic anhydrase CanB may represent a novel target for antimicrobial agents that would exhibit increased potency against β-lactamase-overexpressing A. baumannii. IMPORTANCE Acinetobacter baumannii has become resistant to all classes of antibiotics, with β-lactam resistance responsible for the majority of treatment failures. New classes of antimicrobials are needed to treat this high-priority pathogen. This study had uncovered a new genetic vulnerability in β-lactamase-expressing A. baumannii, where reduced carbonic anhydrase activity becomes lethal. Inhibitors of carbonic anhydrase could represent a new method for treating A. baumannii infections.

Clinical and Pathophysiological Overview of Acinetobacter Infections: a Century of Challenges

Acinetobacter is a complex genus, and historically, there has been confusion about the existence of multiple species. The species commonly cause nosocomial infections, predominantly aspiration pneumonia and catheter-associated bacteremia, but can also cause soft tissue and urinary tract infections. Community-acquired infections by Acinetobacter spp. are increasingly reported. Transmission of Acinetobacter and subsequent disease is facilitated by the organism's environmental tenacity, resistance to desiccation, and evasion of host immunity. The virulence properties demonstrated by Acinetobacter spp. primarily stem from evasion of rapid clearance by the innate immune system, effectively enabling high bacterial density that triggers lipopolysaccharide (LPS)-Toll-like receptor 4 (TLR4)-mediated sepsis. Capsular polysaccharide is a critical virulence factor that enables immune evasion, while LPS triggers septic shock. However, the primary driver of clinical outcome is antibiotic resistance. Administration of initially effective therapy is key to improving survival, reducing 30-day mortality threefold. Regrettably, due to the high frequency of this organism having an extreme drug resistance (XDR) phenotype, early initiation of effective therapy is a major clinical challenge. Given its high rate of antibiotic resistance and abysmal outcomes (up to 70% mortality rate from infections caused by XDR strains in some case series), new preventative and therapeutic options for Acinetobacter spp. are desperately needed.

Carbapenem Resistance in Acinetobacter baumannii and Other Acinetobacter spp. Causing Neonatal Sepsis: Focus on NDM-1 and Its Linkage to ISAba125

Carbapenem-resistant determinants and their surrounding genetic structure were studied in Acinetobacter spp. from neonatal sepsis cases collected over 7 years at a tertiary care hospital. Acinetobacter spp. (n = 68) were identified by ARDRA followed by susceptibility tests. Oxacillinases, metallo-β-lactamases (MBLs), extended-spectrum β-lactamases and AmpCs, were detected phenotypically and/or by PCR followed by DNA sequencing. Transconjugants possessing the bla NDM-1(New Delhi metallo-β-lactamase) underwent further analysis for plasmids, integrons and associated genes. Genetic environment of the carbapenemases were studied by PCR mapping and DNA sequencing. Multivariate logistic regression was used to identify risk factors for sepsis caused by NDM-1-harboring organisms. A. baumannii (72%) was the predominant species followed by A. calcoaceticus (10%), A. lwoffii (6%), A. nosocomialis (3%), A. junni (3%), A. variabilis (3%), A. haemolyticus (2%), and 14TU (2%). Fifty six percent of the isolates were meropenem-resistant. Oxacillinases present were OXA-23-like, OXA-58-like and OXA-51-like, predominately in A. baumannii. NDM-1 was the dominant MBL (22%) across different Acinetobacter spp. Isolates harboring NDM-1 also possessed bla (VIM-2, PER-1, VEB-2, CTX-M-15), armA, aac(6')Ib, aac(6')Ib-cr genes. bla NDM-1was organized in a composite transposon between two copies of ISAba125 in the isolates irrespective of the species. Further, OXA-23-like gene and OXA-58-like genes were linked with ISAba1 and ISAba3 respectively. Isolates were clonally diverse. Integrons were variable in sequence but not associated with carbapenem resistance. Most commonly found genes in the 5' and 3'conserved segment were aminoglycoside resistance genes (aadB, aadA2, aac4'), non-enzymatic chloramphenicol resistance gene (cmlA1g) and ADP-ribosylation genes (arr2, arr3). Outborn neonates had a significantly higher incidence of sepsis due to NDM-1 harboring isolates than their inborn counterparts. This study demonstrates the significance of both A. baumannii and other species of Acinetobacter in cases of neonatal sepsis over an extended period. Oxacillinases and bla NDM-1 are the major contributors to carbapenem resistance. The dissemination of the bla NDM-1 is likely linked to Tn125 in diverse clones of the isolates.

Emergence of Multidrug Resistance and Metallo-beta-lactamase Producing Acinetobacter baumannii Isolated from Patients in Shiraz, Iran

BACKGROUND

Metallo-beta-lactamase (MβL) enzymes production is one of the most important resistance mechanisms against carbapenems in some bacteria including Acinetobacter baumannii.

AIMS

This study was aimed to determine the antimicrobial susceptibility and the prevalence of MβL among carbapenem-resistant isolates of A. baumannii.

MATERIALS AND METHODS

In this cross-sectional study from October 2012 to April 2013, 98 isolates were identified as A. baumannii using Microgen™ kits and confirmed by molecular method. These isolates were tested for antimicrobial susceptibilities by disk diffusion method according to the Clinical and Laboratory Standards Institute guidelines. Carbapenem-resistant isolates were further detected phenotypically by MβL minimal inhibitory concentration (MIC)-test strips, and subsequently positive MβL isolates were confirmed by polymerase chain reaction (PCR).

RESULTS

Overall, 98% (96/98) of A. baumannii isolates were detected as carbapenem-resistant by MIC test. Highest sensitivity to the tested antibiotic with 42.9% (42/98) was observed to colistin. Of 96 carbapenem-resistant isolates, 43 were phenotypically positive for MβL; out of 43 isolates, 37 were confirmed for the presence of MβL genes by PCR.

CONCLUSION

The frequency of drug resistance among the clinical samples of A. baumannii isolated in our study against most of the antibiotics was very high. Moreover, all MβL producing isolates were multidrug resistance. Therefore, systematic surveillance to detect MβL producing bacteria and rational prescription and use of carbapenems could be helpful to prevent the spread of carbapenem resistance.

Characterization of Oxacillinase and Metallo-β-Lactamas Genes and Molecular Typing of Clinical Isolates of Acinetobacter baumannii in Ahvaz, South-West of Iran

Background:

Carbapenem resistant Acinetobacter baumannii is an important nosocomial pathogen associated with a variety of infections.

Objectives:

The current study aimed to characterize the antimicrobial susceptibility, analyze the prevalence of oxacillinase and metallo-β-lactamase (MBL) genes and molecular typing of clinical isolates of A. baumannii.

Materials and Methods:

A total of 124 non-repetitive isolates of A. baumannii were collected from various clinical specimens in two teaching hospitals in Ahvaz, south-west of Iran. Antimicrobial susceptibility test was carried out by disk diffusion method. The minimum inhibitory concentrations (MICs) of imipenem, meropenem, colistin and tigecycline were determined using E-test. To screen for MBL production, double disk synergy (DDs) test and MBL E-test were performed. The presence of bla_OXA-23-like, bla_OXA-24-like, bla_OXA-51-like, bla_OXA-58-like, bla_VIM, bla_IMP and bla_SPM genes was assessed by polymerase chain reaction (PCR). To identify clonal relatedness, all isolates were subjected to repetitive sequence-based PCR (rep-PCR)

Results:

Based on disk diffusion results, the highest rate of resistance was observed in rifampin (96.8%). Colistin and polymyxin-B were the most effective agents in vitro. According to the MIC results, the rate of resistance to imipenem, meropenem, colistin and tigecycline were 78.2%, 73.4%, 0.8% and 0, respectively. Metallo-β-lactamase production was positive in 42.3% and 79.4% of the isolates by DDs test and E-test, respectively. All isolates (100%) carried bla_OXA-51-like gene. According to the results of multiplex PCR, bla_OXA-23-like and bla_OXA-24-like genes were detected in 85.6% and 6.2% of carbapenem resistant isolates, respectively. No bla_{OXA-58- like}, bla_VIM, bla_IMP and bla_SPM were detected. By rep-PCR, carbapenem resistant isolates were separated into six genotypes (A to F). Genotype A (30.9%) was the most prevalent (P value < 0.001). Genotypes B and C were found in 28.9% and 26.8% of the isolates, respectively.

Conclusions:

The rate of carbapenem resistant A. baumannii isolates were high in this study. Since, bla_OXA-58-like or MBL genes were not detected, it seems that resistance to carbapenems is related to bla_OXA-23-like and bla_OXA-24-like. Moreover, bla_OXA-23-like was the most prevalent oxacillinase (OXA) gene. Most of the isolates belonged to one of the four dominant genotypes indicating clonal dissemination in the hospitals under study. In order to control the spread of carbapenem-resistant A. baumannii, infection- control strategies are needed.

Molecular characterization of oxacillinases among carbapenem-resistant Acinetobacter baumannii nosocomial isolates in a Saudi hospital

BACKGROUND

Acinetobacter baumannii has successfully become a significant nosocomial pathogen because of its remarkable ability to acquire antibiotic resistance and to survive in nosocomial environments. This study aimed to determine the drug susceptibility patterns and the distribution of four subgroups of carbapenem-hydrolyzing class D β-lactamases (OXA-carbapenemases), as well as their insertion sequences (ISAba1), among A. baumannii nosocomial isolates from a Saudi tertiary care hospital.

METHODS

A total of 108 non-duplicate A. baumannii isolates were identified, and their susceptibilities to different antibiotics were determined using the breakpoint method. Isolates were then subjected to multiplex-PCR targeting blaOXA genes.

RESULTS

More than 75% of the isolates showed resistance to different antibiotics. The rates of susceptibility to colistin, meropenem, imipenem and trimethoprim-sulfamethoxazole were 95.6, 50, 48.1 and 34.3%, respectively. All isolates possessed a blaOXA-51-like gene. Of the 56 carbapenem-resistant isolates, 48 isolates (85.7%) carried blaOXA-23-like, 3 isolates (5.4%) carried blaOXA-40-like and two isolates (3.6%) had blaOXA-58-like genes. The ISAba1 element was found upstream of the blaOXA-23 and blaOXA-24 genes in 40 (71.4%) and 3 (5.4%) isolates, respectively, while it was detected upstream of blaOXA-51 in only one (1.8%) isolate.

CONCLUSION

Our findings further illustrate the challenge of increasing carbapenem-resistance in A. baumannii isolates in Saudi Arabia. The high distribution of class D carbapenemase-encoding genes, mainly ISAba1/OXA-23 and ISAba1/OXA-24 carbapenemases, is worrisome and presents an emerging threat in our hospital. Local molecular surveillance is essential to help control carbapenem-resistant A. baumannii nosocomial infections and to prevent DNA exchange among endemic nosocomial pathogens.

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.

Co-occurrence of carbapenem and aminoglycoside resistance genes among multidrug-resistant clinical isolates of Acinetobacter baumannii from Cracow, Poland

Background

Acinetobacter baumannii is a significant hospital pathogen, possessing a considerable degree of antimicrobial resistance. A. baumannii resistance to carbapenems and aminoglycosides is mostly conferred by class D OXA carbapenemases and aminoglycoside-modifying enzymes, respectively. The aim of this study was to determine the prevalence of selected genes encoding OXA carbapenemases and aminoglycoside-modifying enzymes in multidrug-resistant strains of A. baumannii.

Material/Methods

The study included 61 carbapenem-resistant and aminoglycoside-nonsusceptible A. baumannii isolates, collected between 2009 and 2011 in Cracow, Poland. Selected resistance genes, including: bla_OXA-51-like, bla_OXA-23-like, bla_OXA-40-like, bla_OXA-58-like, aac(6′)-Ih, aac(3)-Ia, aac(3)-IIa, aac(6′)-Ib, aph(3′)-Ia and aph(3′)-VI, were detected by PCR method.

Results

The bla_OXA-51-like genes were detected in all isolates, while acquired carbapenemase encoding genes were found in 96.7% of tested strains. Presence of bla_OXA-40-like and bla_OXA-23-like genes was observed among 65.6% and 27.9% of isolates, respectively. Assayed aminoglycoside resistance genes were found to harbor 98.4% of isolates. Among tested strains, we observed the following percentages of resistance determinants: aac(3)-Ia – 78.7%, aph(3′)-VI – 78.7% and aph(3′)-Ia – 27.9%. Analysis of co-occurrence of carbapenem and aminoglycoside resistance genes revealed the highest percentage of strains possessing bla_OXA-40-like, aac(3)-Ia, and aph(3′)-VI genes (44.3%).

Conclusions

The bla_OXA-40-like and aac(3)-Ia/aph(3′)-VI were the most prevalent genes encoding acquired OXA carbapenemases and aminoglycoside-modifying enzymes, respectively, among A. baumannii strains in Cracow, Poland. Genes conferring resistance to carbapenems and aminoglycosides coexisted in the clinical strains of A. baumannii. The phenomenon of A. baumannii resistance indicates the necessity of monitoring for the presence of the resistance genes.

Risk factors for healthcare-associated extensively drug-resistant Acinetobacter baumannii infections: a case-control study

The emergence of extensively drug-resistant Acinetobacter baumannii (XDRAB) is a serious threat to hospitalized patients. From 2008 to 2010, surveillance detected 25 hospital-acquired infection (HAI) cases caused by XDRAB at a medical center in Taipei. The site of XDRAB infection was bloodstream (n = 8), urinary tract (n = 12), lower respiratory tract (n = 3), surgical site (n = 1), and cardiovascular (n = 1). The isolates were resistant to all currently available antibiotics except for colistin. The XDRAB isolates are genetically diverse, shown by pulsed-field gel electrophoresis, but 23 of 25 harbored class 1 integron with a 2.3-kb gene cassette. Most of these isolates carry OXA-23 (n = 21) and OXA-51-like carbapenemase genes (n = 25). To identify the risk factors, a case-control study was conducted. The 25 cases were compared with 100 controls randomly selected from hospitalized patients without XDRAB-HAIs, matched by the onset date, ward, and age, at a ratio of 1∶4. Prior use of imipenem, meropenem, piperacillin/tazobactam or fourth-generation cephalosporins (adjusted OR: 3.2, 95% CI: 1.03–10.2, P = 0.04) and >30 days bed-ridden (adjusted OR: 6.0, 95% CI: 1.3–27.6, P = 0.02) were found to be the independent risk factors for XDRAB-HAIs. These findings highlight that, even in the absence of clonal dissemination, XDRAB can emerge under the selective pressure of broad-spectrum antibiotics and causes subsequent HAIs in compromised hosts. An appropriate response to the XDRAB threat therefore should include a component of prudent use of broad-spectrum antibiotics active against gram-negative bacteria.

TEM-1 β-lactamase as a source of resistance to sulbactam in clinical strains of Acinetobacter baumannii

OBJECTIVES

Sulbactam is well known to have clinically relevant intrinsic activity against Acinetobacter baumannii. Although secondary resistance to this drug has long been reported in acinetobacters, virtually nothing is known about its molecular basis. The aim of this study was to test the hypothesis that β-lactamase TEM-1 is responsible for sulbactam resistance in A. baumannii.

METHODS

Seventeen clinical strains of A. baumannii were selected to represent different combinations of quantitative susceptibilities to sulbactam and molecular typing characteristics. The strains were screened by PCR for the presence of the blaTEM-1 gene and its variants. Amplicons encompassing the blaTEM genes, including their promoters, were sequenced. The expression and copy number of the blaTEM genes were assessed using semi-quantitative real-time PCR. Transfer of the blaTEM-1 gene into a susceptible A. baumannii strain was achieved by electroporation.

RESULTS

Six strains were negative for the blaTEM gene and had sulbactam MICs of 0.5-1.0 mg/L, 10 strains harboured blaTEM-1 and showed MICs ≥ 8.0 mg/L, except for one strain with an MIC of 2 mg/L, while the remaining strain carried blaTEM-19 and had an MIC of 1 mg/L. The level of blaTEM-1 expression positively correlated with the MICs of sulbactam (r = 0.92). Promoter P4 was linked to the blaTEM gene in all strains except for a P3-carrying strain (an MIC of 2 mg/L). Transformation of the susceptible A. baumannii strain with blaTEM-1 resulted in a 64-fold increase in sulbactam MIC and in resistance to ticarcillin and piperacillin, but no change in susceptibility to broad-spectrum generation cephalosporins, aztreonam or carbapenems.

CONCLUSIONS

The results presented suggest that TEM-1 represents a clinically relevant mechanism of sulbactam resistance in A. baumannii.

Practices to prevent multidrug-resistant Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus in Thailand: a national survey

BACKGROUND

Multidrug-resistant organisms (MDRO) are increasing challenges for health care institutions worldwide, and there are many factors associated with their distribution.

OBJECTIVES

We conducted a national survey of Thai hospitals with 1 or more intensive care units and ≥250 hospital beds to evaluate hospital characteristics and current practices to minimize the endemic burden of multidrug-resistant (MDR) Acinetobacter baumannii (AB) and methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Research nurses collected survey data from participating hospitals between January 1 and April 30, 2011. Data collection focused on hospital characteristics and practices to prevent endemic MDR-AB and MRSA; logistic regression analyses were used to assess associations between hospital characteristics and infection prevention control (IPC) interventions.

RESULTS

There was an 80% survey response (N = 204) from 256 eligible hospitals. Endemic MDR-AB and MRSA were reported in 184 (90%) and 100 (40%) hospitals, respectively. The most frequently reported IPC interventions were contact isolation, hand hygiene campaigns, and antimicrobial stewardship; active surveillance, chlorhexidine gluconate bathing, and multifaceted interventions were uncommon. By multivariate analysis, having a physician as the lead infection control professional and participation in a collaborative effort to prevent MDR organisms were associated with multifaceted interventions to reduce MDR-AB, and medical school affiliation and participating in a collaborative effort to prevent MDR organisms were associated with multifaceted interventions to reduce MRSA.

CONCLUSION

Multifaceted interventions to reduce, if not prevent, MDR-AB and MRSA were infrequently reported from Thai hospitals. Our survey findings provide baseline data for IPC interventions for MDR-AB and MRSA. Future efforts that correlate IPC interventions and MDRO trends will help develop evidence-based practices in these resource-limited settings.