Multicity outbreak of carbapenem-resistant Acinetobacter baumannii isolates producing the carbapenemase OXA-40

Emerging broad-spectrum resistance in Pseudomonas aeruginosa and Acinetobacter baumannii: Mechanisms and epidemiology

Multidrug resistance is quite common among non-fermenting Gram-negative rods, in particular among clinically relevant species including Pseudomonas aeruginosa and Acinetobacter baumannii. These bacterial species, which are mainly nosocomial pathogens, possess a diversity of resistance mechanisms that may lead to multidrug or even pandrug resistance. Extended-spectrum β-lactamases (ESBLs) conferring resistance to broad-spectrum cephalosporins, carbapenemases conferring resistance to carbapenems, and 16S rRNA methylases conferring resistance to all clinically relevant aminoglycosides are the most important causes of concern. Concomitant resistance to fluoroquinolones, polymyxins (colistin) and tigecycline may lead to pandrug resistance. The most important mechanisms of resistance in P. aeruginosa and A. baumannii and their most recent dissemination worldwide are detailed here.

Carbapenemase-producing Gram-negative bacteria: current epidemics, antimicrobial susceptibility and treatment options

ABSTRACT 

Carbapenemases, with versatile hydrolytic capacity against β-lactams, are now an important cause of resistance of Gram-negative bacteria. The genes encoding for the acquired carbapenemases are associated with a high potential for dissemination. In addition, infections due to Gram-negative bacteria with acquired carbapenemase production would lead to high clinical mortality rates. Of the acquired carbapenemases, Klebsiella pneumoniae carbapenemase (Ambler class A), Verona integron-encoded metallo-β-lactamase (Ambler class B), New Delhi metallo-β-lactamase (Ambler class B) and many OXA enzymes (OXA-23-like, OXA-24-like, OXA-48-like, OXA-58-like, class D) are considered to be responsible for the worldwide resistance epidemics. As compared with monotherapy with colistin or tigecycline, combination therapy has been shown to effectively lower case-fatality rates. However, development of new antibiotics is crucial in the present pandrug-resistant era.

In vitro pharmacodynamics of various antibiotics in combination against extensively drug-resistant Klebsiella pneumoniae

Extensively drug-resistant (XDR) Klebsiella pneumoniae is an emerging pathogen in Singapore. With limited therapeutic options available, combination antibiotics may be the only viable option. In this study, we aimed to elucidate effective antibiotic combinations against XDR K. pneumoniae isolates. Six NDM-1-producing and two OXA-181-producing K. pneumoniae strains were exposed to 12 antibiotics alone and in combination via time-kill studies. A hollow-fiber infection model (HFIM) with pharmacokinetic validation was used to simulate clinically relevant tigecycline-plus-meropenem dosing regimens against 2 XDR K. pneumoniae isolates over 240 h. The emergence of resistance against tigecycline was quantified using drug-free and selective (tigecycline at 3× the MIC) media. The in vitro growth rates were determined and serial passages on drug-free and selective media were carried out on resistant isolates obtained at 240 h. Both the polymyxin B and tigecycline MICs ranged from 1 to 4 mg/liter. In single time-kill studies, all antibiotics alone demonstrated regrowth at 24 h, except for polymyxin B against 2 isolates. Tigecycline plus meropenem was found to be bactericidal in 50% of the isolates. For the isolates that produced OXA-181-like carbapenemases, none of the 55 tested antibiotic combinations was bactericidal. Against 2 isolates in the HFIM, tigecycline plus meropenem achieved a >90% reduction in bacterial burden for 96 h before regrowth was observed until 10(9) CFU/ml at 240 h. Phenotypically stable and resistant isolates, which were recovered from tigecycline-supplemented plates post-HFIM studies, had lower growth rates than those of their respective parent isolates, possibly implying a substantial biofitness deficit in this population. We found that tigecycline plus meropenem may be a potential antibiotic combination for XDR K. pneumoniae infections, but its efficacy was strain specific.

Clinical Outcomes of Carbapenem-Resistant Acinetobacter baumannii Bloodstream Infections: Study of a 2-State Monoclonal Outbreak

Objective.

To characterize the clinical outcomes of patients with bloodstream infection caused by carbapenem-resistant Acinetobacter baumannii during a 2-state monoclonal outbreak.

Design.

Multicenter observational study.

Setting.

Four tertiary care hospitals and 1 long-term acute care hospital.

Methods.

A retrospective medical chart review was conducted for all consecutive patients during the period January 1, 2005, through April 30, 2006, for whom 1 or more blood cultures yielded carbapenem-resistant A. baumannii.

Results.

We identified 86 patients from the 16-month study period. Their mortality rate was 41%; of the 35 patients who died, one-third (13) had positive blood culture results for carbapenem-resistant A. baumannii at the time of death. Risk factors associated with mortality were intensive care unit stay, malignancy, and presence of fever and/or hypotension at the time blood sample for culture was obtained. Only 5 patients received adequate empirical antibiotic treatment, but the choice of treatment did not affect mortality.

Fifty-seven patients (66.2%) had a single positive blood culture result for carbapenem-resistant A. baumannii; the only factor associated with a single positive blood culture result was the presence of decubitus ulcers. Interestingly, during the study period, a transition from single to multiple positive blood culture results was observed. Four patients, 3 of whom were in a burn intensive care unit, were bacteremic for more than 30 days (range, 36–86 days).

Conclusions.

To our knowledge, this is the first time a study has described 2 patterns of bloodstream infection with A. baumannii: single versus multiple positive blood culture results, as well as a subset of patients with prolonged bacteremia.

Multidrug Resistance among Gram-Negative Pathogens That Caused Healthcare-Associated Infections Reported to the National Healthcare Safety Network, 2006–2008

We evaluated isolates of Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii that were reported to the National Healthcare Safety Network from January 2006 through December 2008 to determine the proportion that represented multidrug-resistant phenotypes. The pooled mean percentage of resistance varied by the definition used; however, multidrug resistance was relatively common and widespread.

Four Years of Surveillance Cultures at a Long-Term Acute Care Hospital

Objective.

To characterize the degree of colonization with multidrug-resistant organisms (MDROs) among patients admitted to a long-term acute care hospital.

Design.

Ecologie Study.

Setting.

A 70-bed long-term acute care hospital (a hospital within a hospital) in the greater Chicago area.

Methods.

As part of an infection control initiative, specimens were collected from all consecutively admitted patients for culture of MDROs within 72 hours of admission. Cultures from July 28, 2005, through November 1, 2008, were analyzed on the basis of the bodily site from which the isolate was recovered and the organisms identified. If MDROs were yielded by culture of specimens that were obtained from 24 hours to 30 days after collection of the patient's original set of specimens, these MDROs were removed from the analysis. In addition, repeat rectal swab samples were collected for culture at 2 weeks after admission for all consecutive patients admitted from January 1 through March 31, 2007.

Results.

A total of 1,739 patients with a total of 5,198 specimens met entry criteria. Of the corresponding 5,198 surveillance cultures, 1,580 (30%) were positive for MDROs. Of the 1,739 patients, 947 (54%) had a culture-positive specimen recovered from any site. Vancomycin-resistant Enterococcus was the organism most commonly isolated in cultures of rectal swab samples (in 38% of such cultures) and wounds (in 18% of such cultures). The rate of rectal carriage of vancomycin-resistant Enterococcus increased from 29% in 2005 to 44% in 2008.

Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside

Acinetobacter baumannii (A. baumannii) is undoubtedly one of the most successful pathogens in the modern healthcare system. With invasive procedures, antibiotic use and immunocompromised hosts increasing in recent years, A. baumannii has become endemic in hospitals due to its versatile genetic machinery, which allows it to quickly evolve resistance factors, and to its remarkable ability to tolerate harsh environments. Infections and outbreaks caused by multidrug-resistant A. baumannii (MDRAB) are prevalent and have been reported worldwide over the past twenty or more years. To address this problem effectively, knowledge of species identification, typing methods, clinical manifestations, risk factors, and virulence factors is essential. The global epidemiology of MDRAB is monitored by persistent surveillance programs. Because few effective antibiotics are available, clinicians often face serious challenges when treating patients with MDRAB. Therefore, a deep understanding of the resistance mechanisms used by MDRAB can shed light on two possible strategies to combat the dissemination of antimicrobial resistance: stringent infection control and antibiotic treatments, of which colistin-based combination therapy is the mainstream strategy. However, due to the current unsatisfying therapeutic outcomes, there is a great need to develop and evaluate the efficacy of new antibiotics and to understand the role of other potential alternatives, such as antimicrobial peptides, in the treatment of MDRAB infections.

Assessment of Antimicrobial Stewardship Activities in a Large Metropolitan Area

PURPOSE

To describe antimicrobial stewardship programs (ASPs) of acute and long-term acute care (LTAC) hospitals in Houston, Texas.

METHODS

Two-part survey to clinical pharmacists and pharmacy directors. All acute care and LTAC facilities from the Harris County Medical Society database were invited to participate.

RESULTS

In part 1 of the telephone survey, 82 facilities within Houston, Harris county, were contacted by telephone of which 51 responded (response rate: 62%). Of respondents, 55% (n = 28) reported having an active ASP and 8% (n = 4) planned implementation within 12 months. Acute care and LTAC hospitals reported ASPs in 57% and 67% of facilities, respectively. Physician champions were involved in 71% (n = 20) of active ASPs; clinical pharmacists were involved in 75% (n = 21) of programs. In part II, 22 (43%) facilities completed the online survey; postprescription review with feedback was used in facilities with an ASP and medical training program (5 of 5) while formulary restriction was in facilities without stewardship or medical training (6 of 8).

CONCLUSION

This is the first major survey of ASP in a major metropolitan area. The stewardship effort in the city of Houston is encouraging; we expect the number of stewardship programs in all facilities will continue to rise as focus on antimicrobial resistance grows.

Acquired Class D β-Lactamases

The Class D β-lactamases have emerged as a prominent resistance mechanism against β-lactam antibiotics that previously had efficacy against infections caused by pathogenic bacteria, especially by Acinetobacter baumannii and the Enterobacteriaceae. The phenotypic and structural characteristics of these enzymes correlate to activities that are classified either as a narrow spectrum, an extended spectrum, or a carbapenemase spectrum. We focus on Class D β-lactamases that are carried on plasmids and, thus, present particular clinical concern. Following a historical perspective, the susceptibility and kinetics patterns of the important plasmid-encoded Class D β-lactamases and the mechanisms for mobilization of the chromosomal Class D β-lactamases are discussed.

In vitro synergistic activity of colistin with tigecycline or β-lactam antibiotic/β-lactamase inhibitor combinations against carbapenem-resistant Acinetobacter baumannii

OBJECTIVE

Nosocomial infection caused by carbapenem-resistant Acinetobacter baumannii is a worldwide problem and treatment options remain controversial. This study investigated the in vitro effect of various antibiotic combinations against carbapenem-resistant A. baumannii strains.

METHODS

Antibiotic susceptibility of A. baumannii strains was analysed. In vitro synergistic efficacy of colistin combined with tigecycline, cefoperazone/sulbactam or piperacillin/tazobactam was tested against carbapenem-resistant A. baumannii strains. Synergy studies were performed using an eplisometer test-strip method.

RESULTS

Of the 50 carbapenem-resistant A. baumannii strains tested, 96% were susceptible to colistin and 64% were susceptible to tigecycline. Colistin-tigecycline, colistin-cefoperazone/sulbactam and colistin-piperacillin/tazobactam combinations were found to have synergistic effects against six (12%), two (4%), and one (2%), respectively, of the strains tested.

CONCLUSIONS

Colistin combined with tigecycline, cefoperazone/sulbactam or piperacillin/tazobactam revealed synergistic effects in some carbapenem-resistant A. baumannii strains. These results, together with the shortage of treatment options and the risk of developing resistance to colistin, suggest that clinicians should use colistin combined with other antibiotics or β-lactamase inhibitors when treating carbapenem-resistant A. baumannii infection.

Epidemiology and prevention of carbapenem-resistant Enterobacteriaceae in the United States

Carbapenem-resistant Enterobacteriaceae (CRE) are multidrug-resistant organisms with few treatment options that cause infections associated with substantial morbidity and mortality. CRE outbreaks have been increasingly reported worldwide and are mainly due to the emergence and spread of strains that produce carbapenemases. In the United States, transmission of CRE is primarily driven by the spread of organisms carrying the Klebsiella pneumoniae carbapenemase enzyme, but other carbapenemase enzymes, such as the New-Delhi metallo-β-lactamase, have also emerged. Currently recommended control strategies for healthcare facilities include the detection of patients infected or colonized with CRE and implementation of measures to prevent further spread. In addition to efforts in individual facilities, effective CRE control requires coordination across all healthcare facilities in a region. This review describes the current epidemiology and surveillance of CRE in the United States and the recommended approach to prevention.

Prevalence of carbapenem-hydrolyzing class D β-lactamase genes in Acinetobacter spp. isolates in China

In order to assess the prevalence of carbapenem-hydrolyzing class D β-lactamase genes in Acinetobacter spp. isolates in China, we conducted a polymerase chain reaction (PCR)-based surveillance of OXA-type β-lactamase gene clusters for a total of 2,880 Acinetobacter spp. isolates collected from 23 Chinese provinces. All isolates were tested for susceptibility to 12 antimicrobial agents and showed high rates of resistance to all these agents except minocycline. We also found that the vast majority of carbapenem-resistant Acinetobacter spp. were OXA-23-like-producing isolates, predominantly Acinetobacter baumannii isolates. Besides, bla OXA-58-like and bla OXA-24-like genes were detected in 32 and 11 isolates, respectively, involving many provinces throughout China. Furthermore, these two carbapenem-resistance determinants were located on transferable plasmids in most cases, indicating an emerging threat for both OXA-58-like- and OXA-24-like-producing Acinetobacter spp. isolates in China. Interestingly, a novel homologue of the bla OXA-143 gene was identified in a susceptible Acinetobacter pittii isolate. Overall, these observations suggest that the bla OXA-23-harboring A. baumannii isolates are the most frequent carbapenem-resistant Acinetobacter spp. in China, and the bla OXA-24-like and bla OXA-58-like genes have emerged as potential threats of hospital outbreaks of multidrug-resistant Acinetobacter spp.

Acinetobacter baumannii producing OXA-23 detected in the Czech Republic

BACKGROUND

Acinetobacter baumannii is an opportunistic pathogen posing an increased risk to hospitalized persons, causing nosocomial pneumonias, urinary tract infections and postoperative infections.

METHODS

Between 1 December 2011 and 30 September 2012, strains of Acinetobacter spp. were isolated from clinical samples obtained from hospitalized patients. Susceptibility to antibiotics was determined by the standard microdilution method and phenotypic testing was used to detect the presence of serine carbapenemases and metallo-beta-lactamases. The polymerase chain reaction was used to detect the genes encoding carbapenemases. Pulsed field gel electrophoresis was used to investigate the genetic relationship among the carbapenem resistant isolates of Acinetobacter baumannii.

RESULTS

In three strains of Acinetobacter baumannii enzyme OXA-23 was detected. This positive result was confirmed by restriction analysis and sequencing. The study reported an OXA-23-producing strains of Acinetobacter baumannii in the Czech Republic. All three strains isolated from Military Hospital patients had a completely identical restriction profile, indicating clonal spread of a strain carrying serine carbapenemase OXA-23 in this health care facility. Moreover this was the first time the strain was detected in the country in patients who had not stayed abroad.

Impact of multidrug-resistant organisms on patients considered for lung transplantation

Infections with multidrug-resistant organisms are a growing problem in lung transplant recipients. Carriage of drug-resistant bacteria and fungi before transplantation is an important risk factor for such infections. In that regard Pseudomonas aeruginosa and species of Burkholderia, Acinetobacter, non-tuberculous mycobacteria and Scedosporium are particularly important. An understanding of the impact of these organisms is essential to the evaluation of lung transplant candidates. The microbiology, epidemiology, clinical manifestations, and approach to these pathogens before transplant are reviewed in this article.

Modified CHROMagar Acinetobacter medium for direct detection of multidrug-resistant Acinetobacter strains in nasal and rectal swab samples

This study aimed to investigate whether CHROMagar Acinetobacter medium (CHROMagar, France) in combination with an antimicrobial supplement (modified CHROMagar Acinetobacter; CHROMagar, France) can be used for detecting and isolating multidrug-resistant Acinetobacter species (MRA) in nasal and rectal surveillance cultures. Nasal and rectal swab samples were collected from patients in an intensive care unit at a teaching hospital. The samples were used to inoculate modified CHROMagar Acinetobacter plates, which were examined after 24 and 48 hr of incubation at 37℃. Their susceptibility against the antimicrobial agents meropenem, imipenem, ciprofloxacin, and amikacin was analyzed using the Etest (bioMerieux, France). A total of 406 paired samples (406 nasal swabs and 406 rectal swabs) were obtained from 226 patients, and 120 samples (28 nasal and 28 rectal cultures, 47 nasal cultures only, and 17 rectal cultures only) yielded MRA. Seventy-five MRA isolates (18.5%) were recovered from the 406 nasal samples, and 45 MRA isolates (11.1%) were recovered from the 406 rectal samples. Of the 120 MRA isolates, 3 (2.5%) were detected only after 48 hr of incubation. The use of modified CHROMagar Acinetobacter together with nasal and rectal swabs and 1-day incubation is an effective surveillance tool for detecting MRA colonization.

"Stormy waters ahead": global emergence of carbapenemases

Carbapenems, once considered the last line of defense against of serious infections with Enterobacteriaceae, are threatened with extinction. The increasing isolation of carbapenem-resistant Gram-negative pathogens is forcing practitioners to rely on uncertain alternatives. As little as 5 years ago, reports of carbapenem resistance in Enterobacteriaceae, common causes of both community and healthcare-associated infections, were sporadic and primarily limited to case reports, tertiary care centers, intensive care units, and outbreak settings. Carbapenem resistance mediated by β-lactamases, or carbapenemases, has become widespread and with the paucity of reliable antimicrobials available or in development, international focus has shifted to early detection and infection control. However, as reports of Klebsiella pneumoniae carbapenemases, New Delhi metallo-β-lactamase-1, and more recently OXA-48 (oxacillinase-48) become more common and with the conveniences of travel, the assumption that infections with highly resistant Gram-negative pathogens are limited to the infirmed and the heavily antibiotic and healthcare exposed are quickly being dispelled. Herein, we provide a status report describing the increasing challenges clinicians are facing and forecast the “stormy waters” ahead.

Evolution of a pathogen: a comparative genomics analysis identifies a genetic pathway to pathogenesis in Acinetobacter

Acinetobacter baumannii is an emergent and global nosocomial pathogen. In addition to A. baumannii, other Acinetobacter species, especially those in the Acinetobacter calcoaceticus-baumannii (Acb) complex, have also been associated with serious human infection. Although mechanisms of attachment, persistence on abiotic surfaces, and pathogenesis in A. baumannii have been identified, the genetic mechanisms that explain the emergence of A. baumannii as the most widespread and virulent Acinetobacter species are not fully understood. Recent whole genome sequencing has provided insight into the phylogenetic structure of the genus Acinetobacter. However, a global comparison of genomic features between Acinetobacter spp. has not been described in the literature. In this study, 136 Acinetobacter genomes, including 67 sequenced in this study, were compared to identify the acquisition and loss of genes in the expansion of the Acinetobacter genus. A whole genome phylogeny confirmed that A. baumannii is a monophyletic clade and that the larger Acb complex is also a well-supported monophyletic group. The whole genome phylogeny provided the framework for a global genomic comparison based on a blast score ratio (BSR) analysis. The BSR analysis demonstrated that specific genes have been both lost and acquired in the evolution of A. baumannii. In addition, several genes associated with A. baumannii pathogenesis were found to be more conserved in the Acb complex, and especially in A. baumannii, than in other Acinetobacter genomes; until recently, a global analysis of the distribution and conservation of virulence factors across the genus was not possible. The results demonstrate that the acquisition of specific virulence factors has likely contributed to the widespread persistence and virulence of A. baumannii. The identification of novel features associated with transcriptional regulation and acquired by clades in the Acb complex presents targets for better understanding the evolution of pathogenesis and virulence in the expansion of the genus.

Cationic amphiphilic alpha-helical peptides for the treatment of carbapenem-resistant Acinetobacter baumannii infection

The emergence of multidrug-resistant Gram-negative bacteria, in particular Acinetobacter baumannii and Pseudomonas aeruginosa, is a critical clinical problem worldwide. Antimicrobial peptides (AMPs) have received increasing attention due to their ability to overcome multidrug-resistant microbes. We recently reported that cysteine-functionalized alpha-helical peptides LLKKLLKKC and CLLKKLLKKC effectively eradicated Gram-negative bacteria in vitro. In this study, the antibacterial properties of these peptides against carbapenem-resistant clinical isolates of A. baumannii were studied both in vitro and in vivo. The minimum inhibitory concentrations (MICs) of the peptides against 20 clinical isolates of carbapenem-resistant A. baumannii were determined in comparison with imipenem. The results showed that the A. baumannii isolates were more susceptible to (LLKK)(2)C than to C(LLKK)(2)C in vitro, and 90% of the 20 tested strains had an MIC of lower than or equal to 36.8 and 63.1 μmol/L, respectively. However, the bactericidal effect of C(LLKK)(2)C was much faster than that of (LLKK)(2)C. Furthermore, these peptides also showed excellent potency in mouse models of peritonitis and pneumonia infections caused by carbapenem-resistant A. baumannii. Importantly, both peptides had a high therapeutic index (>25), but caused no significant adverse effects on the liver and kidney functions and the balance of electrolytes in the blood. These peptides can be a promising alternative treatment modality to traditional antibiotics for nosocomial bacterial infections caused by multidrug-resistant Gram-negative bacteria, especially carbapenem-resistant A. baumannii.

Impact of inappropriate empiric antimicrobial therapy on mortality of septic patients with bacteremia: a retrospective study

Background. Inappropriate empiric antimicrobials could be a major cause of unfavorable mortality rates in co-morbid patients. This study aimed to assess the prevalence and impact of first-dose and 24-hour inappropriate antimicrobials on mortality rates of bacteremic septic patients. Methods. A retrospective cohort study was employed. Case record forms of patients diagnosed as sepsis, severe sepsis, or septic shock with positive hemoculture during 2009 were retrieved from the medical wards, Siriraj Hospital. Demographic data, antimicrobial use, types of bacteria isolated from blood and susceptibilities, patients' comorbidities, 28-day and overall mortality rates were collected and analyzed. Results. There were 229 cases, mean age (SD) of 63.5 (17.2) years and mean (SD) APACHE II score of 24.7 (6.8). The prevalence of first-dose and 24-hour inappropriate antimicrobials was 29.7% and 25.3%, respectively. The 28-day and overall mortality rates between first-dose inappropriate and appropriate antimicrobial were 67.6% versus 60.2% (P = 0.301) and 75.0% versus 68.3% (P = 0.345), consequently. Patients with septic shock and inappropriate first-dose antimicrobials significantly had higher 28-day mortality rate (61.6% versus 41.9%; P = 0.017). Conclusion. Higher mortality rates in bacteremic septic patients were substantially associated with inappropriate first-dose antimicrobials and 3-hour delayed antimicrobial administration after sepsis diagnosis.

Investigation of Acinetobacter baumannii resistance to carbapenems in Marseille hospitals, south of France: a transition from an epidemic to an endemic situation

Carbapenem-resistant Acinetobacter baumannii infections are a worldwide endemic nosocomial threat. Between December 2010 and April 2011, an increase of carbapenem-resistant A. baumannii infections occurred in several Marseille University Hospitals. The aim of this study was to investigate the increase of carbapenem-resistant A. baumannii infections and to characterize the mechanisms of carbapenem resistance. The increase was detected by a homemade computer surveillance program, known as EPIMIC, that monitors antibiotic resistance profiles on a weekly basis. During this period, positive samples of carbapenem-resistant A. baumannii were retrieved from patients hospitalized in different units. Genotyping of the isolates was performed using pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST), and carbapenemase gene analyses were performed to detect the presence of carbapenemases and to determine the relationships of the isolates. Carbapenem-resistant A. baumannii were isolated in a total of 11 patients who were hospitalized in different hospitals units. We identified the presence of the bla(OXA23-like) carbapenemase-encoding gene in all of the isolates and found four major PFGE groups and different MLST groups. These results demonstrate a current evolution in the A. baumannii epidemiology in Marseille with a switch from an epidemic situation to an endemic situation and with several circulating clones.

Role of common blaOXA-24/OXA-40-carrying platforms and plasmids in the spread of OXA-24/OXA-40 among Acinetobacter species clinical isolates

The spread of OXA-24/OXA-40 (OXA-24/40)-producing Acinetobacter spp. in the Iberian Peninsula has been strongly influenced by clonal expansion, but the role of horizontal gene transfer has scarcely been explored. bla(OXA-24/40)-carrying plasmids and genetic environments were characterized in representative (n = 15) Acinetobacter species clinical isolates (obtained between 2001 and 2007) by Acinetobacter baumannii PCR-based replicon typing, sequencing, hybridization, and restriction fragment length polymorphism. Besides the identification of bla(OXA-24/40) within the chromosomes of some isolates, the circulation of common bla(OXA-24/40)-carrying plasmids (30-kb repA_AB; 10-kb aci2) and genetic backbones among Acinetobacter spp. was demonstrated.

The Acinetobacter baumannii Oxymoron: Commensal Hospital Dweller Turned Pan-Drug-Resistant Menace

During the past few decades Acinetobacter baumannii has evolved from being a commensal dweller of health-care facilities to constitute one of the most annoying pathogens responsible for hospitalary outbreaks and it is currently considered one of the most important nosocomial pathogens. In a prevalence study of infections in intensive care units conducted among 75 countries of the five continents, this microorganism was found to be the fifth most common pathogen. Two main features contribute to the success of A. baumannii: (i) A. baumannii exhibits an outstanding ability to accumulate a great variety of resistance mechanisms acquired by different mechanisms, either mutations or acquisition of genetic elements such as plasmids, integrons, transposons, or resistant islands, making this microorganism multi- or pan-drug-resistant and (ii) The ability to survive in the environment during prolonged periods of time which, combined with its innate resistance to desiccation and disinfectants, makes A. baumannii almost impossible to eradicate from the clinical setting. In addition, its ability to produce biofilm greatly contributes to both persistence and resistance. In this review, the pathogenesis of the infections caused by this microorganism as well as the molecular bases of antibacterial resistance and clinical aspects such as treatment and potential future therapeutic strategies are discussed in depth.

Acinetobacter infections in a tertiary level intensive care unit in northern India: epidemiology, clinical profiles and outcomes

BACKGROUND

Nosocomial Acinetobacter infections are an increasing concern in intensive care units (ICU).

OBJECTIVES

To study the demographic and clinical characteristics and the outcomes of ICU patients with Acinetobacter infections.

METHODS

A retrospective, 1-year audit of all Acinetobacter infections diagnosed in ICU patients between January 1 and December 31, 2009.

RESULTS

Acinetobacter infection occurred in 94 patients (108 episodes). The most common site of infection was the respiratory tract (83 patients, 76.85%), with medical patients being more susceptible than surgical patients to Acinetobacter lung infections (P=0.04), particularly late-onset ventilator-associated pneumonia (VAP) (P=0.04). The majority (63.8%) of infections were acquired in the ICU, and patients with ICU acquired infections were intubated significantly longer than the other patients (P=0.02). Seventy percent of the infections were caused by multidrug-resistant (MDR) strains, and the overall crude mortality rate was over 70%. The most important factors affecting mortality were the duration of intubation (P=0.001) and the inappropriate use of antibiotics (P=0.021) after diagnosis of the infection.

CONCLUSIONS

Acinetobacter infections are highly prevalent in the ICU, with medical patients being more susceptible to lung infections, particularly late-onset VAP. The early and appropriate selection of antibiotics is the most important determinant of survival among these patients.

Comparison of culture media for detection of Acinetobacter baumannii in surveillance cultures of critically-ill patients

The objective of this study was to evaluate the performance of CHROMagar Acinetobacter when compared to sheep blood agar, MacConkey agar and MacConkey agar with 6 μg/ml of imipenem for the detection of A. baumannii in surveillance cultures of hospitalized patients. We utilized peri-anal swabs and sputum samples from patients admitted to the University of Maryland Medical Center ICUs from December 7 through December 21, 2009. Samples were plated onto four media in the following order: (1) 5% sheep blood agar (SBA), (2) MacConkey agar, (3) MacConkey agar with 6 μg/ml of imipenem, and (4) CHROMagar Acinetobacter (CHROMagar). SBA was the gold standard to which all media was compared. There were 165 samples collected during the study period. SBA and CHROMagar detected 18 of 18 (100%) Acinetobacter and 11 of 11 (100%) MDR-A. baumannii. MacConkey agar detected 16 of 18 (89%) Acinetobacter and 10 of 11 (91%) MDR- A. baumannii while MacConkey agar with 6 μg/ml imipenem detected 9 of 11 (82%) MDR-A. baumannii. CHROMagar did not differentiate MDR- A. baumannii from non-MDR-A. baumannii. CHROMagar may be useful for rapid detection of patients with MDR-A. baumannii if improved upon to better select for MDR-A. baumannii.

Acinetobacter: a potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

Status report on carbapenemases: challenges and prospects

Antimicrobial resistance in hospital and community-onset bacterial infections is a significant source of patient morbidity and mortality. In the past decade, we have witnessed the increasing recovery of carbapenem-resistant Gram-negative bacteria. For many isolates, carbapenem resistance is due to the production of carbapenemases, β-lactamases that can inactivate carbapenems and frequently other β-lactam antibiotics. Currently, these enzymes are mainly found in three different β-lactamase classes (class A, B and D). Regardless of the molecular classification, there are few antimicrobials available to treat infections with these organisms and data regarding agents in development are limited to in vitro studies. This article focuses on the epidemiology of carbapenemase-producing Gram-negative bacteria. We also review available agents and those in development with potential activity against this evolving threat.

Genetic diversity of carbapenem-hydrolysing β-lactamases in Acinetobacter baumannii from Romanian hospitals

Thirteen carbapenem-resistant Acinetobacter baumannii isolates, collected in Romania during 2009-2010, were investigated to identify the mechanism(s) responsible for carbapenem resistance. Genotyping was performed by pulsed-field gel electrophoresis, multiplex PCR sequence typing and multilocus sequence typing. Eleven non-clonally related isolates harboured the bla(OXA-23) gene on their chromosome within a Tn2008 transposon structure. The two remaining isolates harboured a bla(OXA-58) gene that was either plasmid or chromosome borne. Two isolates co-expressed OXA-23 together with the extended-spectrum β-lactamase PER-1. This study constitutes the first report of OXA-58 and OXA-23-producing A. baumannii isolates in Romania.

Emergence of tigecycline and colistin resistance in Acinetobacter species isolated from patients in Kuwait hospitals

The development of resistance is a compelling reason for reviewing administration of antibiotics. Recently, most Acinetobacter infections are caused by multidrug-resistant (MDR) strains which have necessitated the use of tigecycline or colistin. This study was undertaken to determine the susceptibility of Acinetobacter spp. to these and other drugs. A total of 250 Acinetobacter isolates were collected from the 8 government hospitals over a period of 6 months. Susceptibility to 18 antibiotics, including tigecycline and colistin, was investigated by determining their minimum inhibitory concentrations using E test. Of the 250 isolates, 13.6% and 12% were resistant to tigecycline and colistin. A total of 25.2% and 37.2% were resistant to imipenem and meropenem, respectively. Of the 250 isolates 88.4% were MDR. This relatively high prevalence of tigecycline and colistin-resistant isolates indicates an emerging therapeutic problem which may severely compromise the treatment of MDR Acinetobacter spp. infections in Kuwait.

Impact of carbapenem resistance and receipt of active antimicrobial therapy on clinical outcomes of Acinetobacter baumannii bloodstream infections

Nosocomial Acinetobacter baumannii bloodstream infections occur with significant prevalence and mortality. The relationship between carbapenem resistance in A. baumannii and patient outcomes remains unclear. A retrospective cohort study was conducted on patients with A. baumannii bacteremia. Outcomes, controlling for confounders, were compared for carbapenem-nonresistant A. baumannii (CNRAB) and carbapenem-resistant A. baumannii (CRAB). The primary outcome studied was all-cause hospital mortality, and the secondary endpoints evaluated were time to mortality, time to negative cultures, and length of stay postinfection for survivors. A total of 79 patients, 37 infected with CRAB and 42 with CNRAB, were studied. Hospital mortality was greater in the CRAB group as determined based on bivariate analysis (P < 0.01); however, this effect was nullified when controlling for relevant confounders with logistic regression and a Cox proportional-hazards model (P = 0.71 and 0.75, respectively). Values for time to mortality and time to negative cultures did not differ between the groups. The median number of days of stay postinfection for survivors was greater for the CRAB group than the CNRAB group (14 versus 6.5; P < 0.01). Patients who received active antimicrobial therapy were less likely to die (93.5% versus 74.2%; P = 0.02), regardless of carbapenem susceptibility classifications, and this result was robust in the multivariate model (P = 0.02). Trends existed for improved outcomes in patients receiving an active beta-lactam, and patients fared worse if they had received a polymyxin as an active agent. Patients with CRAB bloodstream infections were more chronically ill and had more comorbidities. Inactive therapy was more important than carbapenem susceptibility with respect to outcomes, was a strong predictor of death, and is potentially modifiable.

In-vitro activity of polymyxin B, rifampicin, tigecycline alone and in combination against carbapenem-resistant Acinetobacter baumannii in Singapore

OBJECTIVE

Carbapenem-resistant Acinetobacter baumannii (CR-AB) is an emerging cause of nosocomial infections worldwide. Combination therapy may be the only viable option until new antibiotics become available. The objective of this study is to identify potential antimicrobial combinations against CR-AB isolated from our local hospitals.

METHODS

AB isolates from all public hospitals in Singapore were systematically collected between 2006 and 2007. MICs were determined according to CLSI guidelines. All CR-AB isolates were genotyped using a PCR-based method. Clonal relationship was elucidated. Time-kill studies (TKS) were conducted with polymyxin B, rifampicin and tigecycline alone and in combination using clinically relevant (achievable) unbound concentrations.

RESULTS

31 CR AB isolates were identified. They are multidrug-resistant, but are susceptible to polymyxin B. From clonal typing, 8 clonal groups were identified and 11 isolates exhibited clonal diversity. In single TKS, polymyxin B, rifampicin and tigecycline alone did not exhibit bactericidal activity at 24 hours. In combination TKS, polymyxin plus rifampicin, polymyxin B plus tigecycline and tigecycline plus rifampicin exhibited bactericidal killing in 13/31, 9/31 and 7/31 isolates respectively at 24 hours. Within a clonal group, there may be no consensus with the types of antibiotics combinations that could still kill effectively.

CONCLUSION

Monotherapy with polymyxin B may not be adequate against polymyxin B susceptible AB isolates. These findings demonstrate that in-vitro synergy of antibiotic combinations in CR AB may be strain dependant. It may guide us in choosing a pre-emptive therapy for CR AB infections and warrants further investigations.

Imipenem heteroresistance induced by imipenem in multidrug-resistant Acinetobacter baumannii: mechanism and clinical implications

Acinetobacter baumannii has emerged as a major pathogen causing nosocomial infections, particularly in critical patients admitted to the Intensive Care Unit. Increasing resistance to carbapenems in A. baumannii has been observed worldwide. Here we report the clinical impact and mechanism of imipenem heteroresistance (imipenem minimum inhibitory concentration of 6-32 μg/mL with the presence of resistant cells inside the inhibition zone of Etest strips or disks) in multidrug-resistant A. baumannii (MDR-AB). To identify risk factors associated with the emergence of imipenem heteroresistance, a retrospective case-control study was undertaken involving cases with subsequent clinical isolates of the same genotype showing loss of imipenem susceptibility and matched controls with isolates belonging to imipenem-susceptible MDR-AB. The molecular mechanism of heteroresistance was examined. From April 2006 to March 2007, 126 consecutive isolates of MDR-AB were identified from 29 patients. Switch from imipenem susceptibility to heteroresistance was more likely to occur in successive MDR-AB derived from patients who had been exposed to imipenem (length of use 10.9 ± 6.5 days for cases vs. 5.3 ± 4.8 days for controls; P=0.02). An insertion sequence (ISAba1) was found in the promoter region of a class C β-lactamase gene (bla(ADC-29)) in most imipenem-heteroresistant MDR-AB isolates. In vitro experiments indicated that imipenem heteroresistance, which was associated with overexpression of bla(ADC-29), could be induced by imipenem. Carbapenem use was the only risk factor identified for the emergence of carbapenem-heteroresistant MDR-AB. Physicians should weigh the benefits and risks of each carbapenem-based treatment in managing carbapenem-susceptible MDR-AB infection.

High mortality rates among solid organ transplant recipients infected with extensively drug-resistant Acinetobacter baumannii: using in vitro antibiotic combination testing to identify the combination of a carbapenem and colistin as an effective treatment regimen

Extensively drug-resistant (XDR) Acinetobacter baumannii infections caused 91% (10/11) mortality in transplant recipients. Isolates were colistin-susceptible initially, but susceptibility decreased during therapy in 40% (4/10). We tested antibiotic combinations against XDR Acinetobacter in vitro and demonstrated positive interactions for carbapenem-colistin. Subsequently, 80% (4/5) of transplant patients were treated successfully with carbepenem-colistin regimens.

Clinical experience with tigecycline as treatment for serious infections in elderly and critically ill patients

BACKGROUND

Tigecycline was approved for the treatment of complicated intra-abdominal and complicated skin/skin structure infections. Because of its in vitro effectiveness for multidrug-resistant (MDR) isolates, tigecycline has been prescribed more broadly. This study evaluated tigecycline use after its first introduction in Taiwan and experience with tigecycline for the treatment of MDR Acinetobacter baumannii (MDRAB) infection, especially for ventilator-associated pneumonia.

METHODS

Patients treated with tigecycline were collected retrospectively from February 2008 to July 2008 in Taipei Veterans General Hospital, a 2,900-bed tertiary care medical center in Taiwan. Patients were divided into three groups according to the indications: Group 1, Food and Drug Administration-approved indications; Group 2, health care-associated pneumonia (HAP); and Group 3, urinary tract infection, osteomyelitis, bacteremia, etc. Cases of MDRAB were also identified.

RESULTS

Among 66 cases, indications for the administration of tigecycline included Food and Drug Administration-approved indications (12, 18.2%), HAP (38, 57.6%), bacteremia (3, 4.5%), catheter-related infections (3, 4.5%), urinary tract infection (4, 6.1%), osteomyelitis (4, 6.1%), and others (2, 3%). Clinical outcome was positive in 20 cases, with higher clinical success rate for Group 1 than Group 2, which may correlate with higher Sequential Organ Failure Assessment score, older age, and more frequent intensive care admission in Group 2. Of the microbiologically evaluable cases, MDRAB predominated (33/51, 64.7%). Among infections with MDRAB (excluding pneumonia without ventilator), the clinical success rate was 12% (3/25).

CONCLUSIONS

The most common indication for the prescription of tigecycline was HAP. Success rate for MDRAB infection was lower than that previously reported, possibly because of serious underlying conditions and comorbidities in our patients. Because of limited choices, physicians should weigh the risk and benefit for prescribing tigecycline.

Structures of the class D carbapenemase OXA-24 from Acinetobacter baumannii in complex with doripenem

The emergence of class D β-lactamases with carbapenemase activity presents an enormous challenge to health practitioners, particularly with regard to the treatment of infections caused by Gram-negative pathogens such as Acinetobacter baumannii. Unfortunately, class D β-lactamases with carbapenemase activity are resistant to β-lactamase inhibitors. To better understand the details of the how these enzymes bind and hydrolyze carbapenems, we have determined the structures of two deacylation-deficient variants (K84D and V130D) of the class D carbapenemase OXA-24 with doripenem bound as a covalent acyl-enzyme intermediate. Doripenem adopts essentially the same configuration in both OXA-24 variant structures, but varies significantly when compared to the non-carbapenemase class D member OXA-1/doripenem complex. The alcohol of the 6α hydroxyethyl moiety is directed away from the general base carboxy-K84, with implications for activation of the deacylating water. The tunnel formed by the Y112/M223 bridge in the apo form of OXA-24 is largely unchanged by the binding of doripenem. The presence of this bridge, however, causes the distal pyrrolidine/sulfonamide group to bind in a drastically different conformation compared to doripenem bound to OXA-1. The resulting difference in the position of the side-chain bridge sulfur of doripenem is consistent with the hypothesis that the tautomeric state of the pyrroline ring contributes to the different carbapenem hydrolysis rates of OXA-1 and OXA-24. These findings represent a snapshot of a key step in the catalytic mechanism of an important class D enzyme, and might be useful for the design of novel inhibitors.

Hospital epidemiology and infection control in acute-care settings

Health care-associated infections (HAIs) have become more common as medical care has grown more complex and patients have become more complicated. HAIs are associated with significant morbidity, mortality, and cost. Growing rates of HAIs alongside evidence suggesting that active surveillance and infection control practices can prevent HAIs led to the development of hospital epidemiology and infection control programs. The role for infection control programs has grown and continues to grow as rates of antimicrobial resistance rise and HAIs lead to increasing risks to patients and expanding health care costs. In this review, we summarize the history of the development of hospital epidemiology and infection control, common HAIs and the pathogens causing them, and the structure and role of a hospital epidemiology and infection control program.

Bactericidal oncocin derivatives with superior serum stabilities

The proline-rich antimicrobial peptide oncocin is remarkably active in vitro against a number of important Gram-negative bacteria of concern to humans owing to their increasing resistance to antibiotics, i.e. Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae) and non-fermenting species (Acinetobacter baumannii and Pseudomonas aeruginosa). Degradation of oncocin in mouse serum was investigated in this study. Several approaches to stabilise the main cleavage sites (C-terminal to Arg-15 and N-terminal to Arg-19) by substituting either or both arginine (Arg) residues with non-proteinogenic amino acids, i.e. α-amino-3-guanidino-propionic acid, homoarginine, nitro-arginine, N-methyl-arginine, β-homoarginine, D-arginine (D-Arg) or ornithine (Orn), were tested. These modifications were found to increase the half-life of oncocin in full mouse serum. For oncocin with two Orn residues in positions 15 and 19, the half-life in full serum increased from 25 min to 3 h. An increase of >8 h was observed for oncocin with two D-Arg residues at these same positions. The antibacterial activities of these modified sequences were slightly better than the original oncocin sequence. Moreover, the three most stable analogues were found to be bactericidal against E. coli and were not toxic to HeLa cells or haemolytic to human erythrocytes.

Identification of diverse OXA-40 group carbapenemases, including a novel variant, OXA-160, from Acinetobacter baumannii in Pennsylvania

Three Acinetobacter baumannii isolates that possess OXA-40 group carbapenemase genes were identified. They belonged to novel sequence types (ST122, ST123, and ST124) and harbored bla(OXA-160), bla(OXA-72), and bla(OXA-40), respectively. OXA-160 is a novel variant of OXA-40 with a P227S substitution. An isogenic Escherichia coli clone producing OXA-160 was more susceptible to carbapenems than a clone producing OXA-40. The genetic environment of bla(OXA-160) and bla(OXA-40) beyond the putative XerC/XerD recombination sites was distinct from the scaffold reported previously.

Use of vaporized hydrogen peroxide decontamination during an outbreak of multidrug-resistant Acinetobacter baumannii infection at a long-term acute care hospital

OBJECTIVES

To describe vaporized hydrogen peroxide (VHP) as an adjuvant in the control of multidrug-resistant (MDR) Acinetobacter baumannii infection in a long-term acute care hospital (LTACH) and to describe the risk factors for acquisition of MDR A. baumannii infection in the LTACH population.

DESIGN

Outbreak investigation, case-control study, and before-after intervention trial.

SETTING

A 54-bed LTACH affiliated with a tertiary care center in northeastern Ohio.

METHODS

Investigation of outbreak with clinical and environmental cultures, antimicrobial susceptibility testing, polymerase chain reaction assay of repetitive chromosomal elements to type strains, and case-control study; and intervention consisting of comprehensive infection control measures and VHP environmental decontamination.

RESULTS

Thirteen patients infected or colonized with MDR A. baumannii were identified from January 2008 through June 2008. By susceptibility testing, 10 (77%) of the 13 isolates were carbapenem-resistant. MDR A. baumannii was found in wound samples, blood, sputum, and urine. Wounds were identified as a risk factor for MDR A. baumannii colonization. Ventilator-associated pneumonia was the most common clinical syndrome caused by the pathogen, and the associated mortality was 14% (2 of the 13 case patients died). MDR A. baumannii was found in 8 of 93 environmental samples, including patient rooms and a wound care cart; environmental and clinical cultures were genetically related. Environmental cultures were negative immediately after VHP decontamination and both 24 hours and 1 week after VHP decontamination. Nosocomial acquisition of the pathogen in the LTACH ceased after VHP intervention. When patients colonized with MDR A. baumannii reoccupied rooms, environmental contamination recurred.

CONCLUSION

Environmental decontamination using VHP combined with comprehensive infection control measures interrupted nosocomial transmission of MDR A. baumannii in an LTACH. The application of this novel approach to halt the transmission of MDR A. baumannii warrants further investigation.

Acinetobacter baumannii: An Emerging and Important Pathogen

OBJECTIVE

To review the clinical significance, management, and control of Acinetobacter infections.

METHODS

Literature review.

RESULTS

Acinetobacter infections have become a major cause of hospital-acquired infections worldwide. Acinetobacter is noted for its ability to survive for long periods on hospital surfaces and equipment, its predilection to develop resistance to multiple antibiotics, its affinity to cause serious infections in critically ill patients, and many well described outbreaks attributable to contamination of a common source. The crude ICU mortality is approximately 40%. Rigorous antibiotic stewardship and infection control measures are critical to prevent the spread of multidrug-resistant Acinetobacter infections. There is also a pressing need for new therapeutic options.

CONCLUSION

Acinetobacter is an emerging pathogen of increasing significance.