Investigation of a nosocomial outbreak of extended-spectrum beta-lactamase VEB-1-producing isolates of Acinetobacter baumannii in a hospital setting

Impact of antibiotic exposure on antibiotic-resistant Acinetobacter baumannii isolation in intensive care unit patients: a systematic review and meta-analysis

BACKGROUND

Acinetobacter baumannii (AB) poses a significant threat to critically ill patients in intensive care units (ICUs). Although an association between antibiotic exposure and resistant AB is reported in the literature, a synthesis of evidence in ICU patients is still lacking.

AIM

To summarize the evidence on the association between prior antibiotic exposure and the occurrence of resistant AB in ICU patients.

METHODS

Online databases were searched for cohort and case-control studies providing data on the association of interest. Carbapenem/multidrug-resistant AB isolation was compared with non-isolation; carbapenem/multidrug-resistant AB was compared with carbapenem/antibiotic-susceptible AB; and extensively drug-resistant AB isolation was compared with non-isolation. Each comparison was subjected to a restricted maximum likelihood random-effects meta-analysis per antibiotic class, estimating pooled ORs. Stratified meta-analyses were performed by study design, outcome type and association-measure adjustment.

FINDINGS

Overall, 25 high-quality studies were retrieved. Meta-analyses showed that carbapenem/multidrug-resistant AB isolation was associated with previous exposure to aminoglycosides, carbapenems, third-generation cephalosporines, glycylcyclines, and nitroimidazoles. Increased risk of isolation of carbapenem/multidrug-resistant AB isolation vs carbapenem/antibiotic-susceptible AB was shown for prior exposure to aminoglycosides, antipseudomonal penicillins, carbapenems, fluoroquinolones, glycopeptides, and penicillins. Third-generation cephalosporin exposure increased the risk of extensively drug-resistant AB isolation vs non-isolation.

CONCLUSION

This systematic review clarifies the role of antibiotic use in antibiotic-resistant AB spread in ICUs, although for some antibiotic classes the evidence is still uncertain due to the small number of adjusted analyses, methodological and reporting issues, and limited number of studies. Future studies need to be carried out with standardized methods and appropriate reporting of multivariable models.

Importance of control groups when delineating antibiotic use as a risk factor for carbapenem resistance, extreme-drug resistance, and pan-drug resistance in Acinetobacter baumannii and Pseudomonas aeruginosa: A systematic review and meta-analysis

BACKGROUND

Carbapenem-resistant (CR), extremely drug-resistant (XDR), and pan-drug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa pose a huge clinical threat. This study reviews the impact of control groups on the association of antecedent antibiotic use and the acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa.

METHODS

Studies investigating the role of antibiotics as a risk factor for CR/XDR/PDR A. baumannii and P. aeruginosa acquisition in adult hospitalized patients from 1950 to 2016 were identified in the databases. These were divided into two groups: antibiotic-resistant versus antibiotic-sensitive pathogens (group I); antibiotic-resistant versus no infection (group II). A random-effects model was performed.

RESULTS

Eighty-five studies (46 A. baumannii, 38 P. aeruginosa, and one of both) involving 22 396 patients were included. CR was investigated in 60 studies, XDR in 20 studies, and PDR in two studies. Prior antibiotic exposure was associated with significant acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa in both groups I and II (p<0.05). Antibiotic classes implicated in both groups included aminoglycosides, carbapenems, glycopeptides, and penicillins. Cephalosporin use was not associated with resistance in either group. Fluoroquinolone exposure was only associated with resistance in group I but not group II.

CONCLUSIONS

Control groups play an important role in determining the magnitudes of risk estimates for risk factor studies, hence careful selection is necessary. Antibiotic exposure increases the acquisition of highly resistant A. baumannii and P. aeruginosa, thus appropriate antibiotic use is imperative.

The role of systemic antibiotics in acquiring respiratory tract colonization with gram-negative bacteria in intensive care patients: a nested cohort study

OBJECTIVE

Colonization of the respiratory tract with Gram-negative bacteria in intensive care patients increases the risk of subsequent infections. Application of systemic antibiotics may prevent colonization with Gram-negative bacteria, but this effect has never been quantified. The objective of this study was to determine associations between systemic antibiotic use and acquisition of respiratory tract colonization with Gram-negative bacteria in ICUs.

DESIGN

A nested cohort study.

SETTING

A university hospital and a teaching hospital.

PATIENTS

Patients with ICU stay of more than 48 hours and absence of respiratory tract colonization with Gram-negative bacteria on ICU admission.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Acquisition was determined through protocolized surveillance. Associations were investigated with Cox regression models with antibiotics as a time-dependent covariate. In all, 250 of 481 patients (52%) acquired respiratory tract colonization with Gram-negative bacteria after a median of 5 days (interquartile range, 3-8 d) (acquisition rate, 77.1/1,000 patient-days at risk). Antibiotic exposure during ICU admission was present in 78% and 72% of the patients with and without acquired Gram-negative bacteria colonization, respectively. In Kaplan-Meier curve analysis, the median times to acquisition of Gram-negative bacteria were 9 days (95% CI, 7.9-10.1) and 6 days (95% CI, 4.8-7.2) in patients receiving and not receiving antibiotics, respectively. In time varying Cox regression analysis, however, the association between acquired colonization and systemic antibiotics was not statistically significant (hazard ratio, 0.90; 95% CI, 0.70-1.16).

CONCLUSIONS

Among patients not colonized with Gram-negative bacteria in the respiratory tract at admission to ICU, systemic antibiotics during ICU stay were not associated with a reduction in acquisition of Gram-negative bacteria carriage in the respiratory tract during the ICU stay.

Update on the Epidemiology, Treatment, and Outcomes of Carbapenem-resistant Acinetobacter infections

Carbapenem-resistant Acinetobacter species are increasingly recognized as major nosocomial pathogens, especially in patients with critical illnesses or in intensive care. The ability of these organisms to accumulate diverse mechanisms of resistance limits the available therapeutic agents, makes the infection difficult to treat, and is associated with a greater risk of death. In this review, we provide an update on the epidemiology, resistance mechanisms, infection control measures, treatment, and outcomes of carbapenem-resistant Acinetobacter infections.

Acinetobacter baumannii: An emerging pathogenic threat to public health

Over the last three decades, Acinetobacter has gained importance as a leading nosocomial pathogen, partly due to its impressive genetic capabilities to acquire resistance and partly due to high selective pressure, especially in critical care units. This low-virulence organism has turned into a multidrug resistant pathogen and now alarming healthcare providers worldwide. Acinetobacter baumannii (A. baumannii) is a major species, contributing about 80% of all Acinetobacter hospital-acquired infections. It disseminates antibiotic resistance by virtue of its extraordinary ability to accept or donate resistance plasmids. The procedures for breaking the route of transmission are still proper hand washing and personal hygiene (both the patient and the healthcare professional), reducing patient’s biofilm burden from skin, and judicious use of antimicrobial agents. The increasing incidence of extended-spectrum beta-lactamases and carbapenemases in A. baumannii leaves almost no cure for these “bad bugs”. To control hospital outbreaks of multidrug resistant-Acinetobacter infection, we need to contain their dissemination or require new drugs or a rational combination therapy. The optimal treatment for multidrug-resistant A. baumannii infection has not been clearly established, and empirical therapy continues to require knowledge of susceptibility patterns of isolates from one’s own institution. This review mainly focused on general features and introduction to A. baumannii and its epidemiological status, potential sources of infection, risk factors, and strategies to control infection to minimize spread.

Risk factors and outcomes in patients with carbapenem-resistant Acinetobacter infection

INTRODUCTION

Acinetobacter spp. are important pathogens increasingly reported as the cause of outbreaks of nosocomial infections. The aim of our study was to identify the risk factors and assess their influence on outcomes in patients with infections caused by carbapenem-resistant Acinetobacter spp.

METHODS

A retrospective data analysis was performed to evaluate risk factors and mortality in patients with Acinetobacter spp. infections. Methods used for the statistical analysis were the Student's t-test, Chi-square test, and multivariate analysis; p < 0.05 was considered statistically significant.

RESULTS

A total of 99 patients with an Acinetobacter spp. infection were identified. Comparing patients with carbapenem-sensitive and carbapenem-resistant Acinetobacter spp. infection, significant differences were found in the mean length of intensive care unit stay (4.17 ± 3.61 vs 7.92 ± 6.74 days, p = 0.038) and mechanical ventilation (3.25 ± 2.61 and 7.07 ± 5.79 days, p = 0.009). The previous use of carbapenems (odds ratio (OR) 10.1, 95% confidence interval (CI) 1.16-87.20) and fluoroquinolones (OR 3.6, 95% CI 1.13-11.51) was independently associated with resistance to carbapenems. Of the Acinetobacter spp. strains, 94.9% (n = 94) were resistant to piperacillin-tazobactam, 88.9% (n = 88) to ceftazidime, 85.9% (n = 85) to ciprofloxacin, 83.8% (n = 83) to gentamicin, 79.8 (n = 79) to amikacin, and 48.5% (n = 48) to cefepime.

CONCLUSIONS

Intensive care unit stay before infection and source of infection in the respiratory tract were independently associated with patient mortality. Resistance to carbapenems had no impact on mortality rates. Carbapenem-resistant Acinetobacter spp. isolates had high resistance rates to other antimicrobial drugs.

Multi-drug-resistant gram-negative bacterial infection in surgical patients hospitalized in the ICU: a cohort study

We sought to identify risk factors for postoperative infections, caused by multi-drug-resistant gram-negative bacteria (MDR-GNB) in surgical patients. This was a retrospective cohort study among patients hospitalized in the intensive care unit (ICU) for more than 5 days, following general surgical operations. Comparison of patients who developed infection caused by MDR-GNB with the remainder of the cohort showed that every minute of operative time, use of special treatments during hospitalization (antineoplastic, immunosuppressive or immunomodulating therapies), every day of metronidazole, and every day of carbapenems use, increased patients' odds to acquire an infection caused by MDR-GNB by 0.7%, 8.9 times, 9%, and 9%, respectively [OR (95% CI): 1.007 (1.003-1.011), p = 0.001; 8.9 (1.8-17.3), p = 0.004; 1.09 (1.04-1.18), p = 0.039; 1.09 (1.01-1.18), p = 0.023, respectively]. The above were adjusted in the multivariable analysis for the confounder of time distribution of infections caused by MDR-GNB. Finally, the secondary comparison, with patients that did not develop any infection, showed that patients who had received antibiotics, within 3 months prior to admission, had 3.8 times higher odds to acquire an infection caused by MDR-GNB [OR (95% CI): 3.8 (1.07-13.2), p = 0.002]. This study depicts certain, potentially modifiable, risk factors for postoperative infections in patients hospitalized in the ICU for more than 5 days.

Multi-drug resistant Acinetobacter ventilator-associated pneumonia

Background:

Ventilator-associated pneumonia (VAP) due to a multi-drug resistant (MDR) Acinetobacter is one of the most dreadful complications, which occurs in the critical care setting.

Aims and objectives:

To find out the incidence of Acinetobacter infection in VAP cases, to determine various risk factors responsible for acquisition of Acinetobacter infection and to determine the antimicrobial susceptibility pattern of Acinetobacter.

Materials and Methods:

A total of 60 endotracheal aspirate specimens from intubated patients diagnosed clinically and microscopically as VAP were studied bacteriologically. All clinical details and prior exposure to antibiotics were recorded.

Results:

An incidence of 11.6% of Acinetobacter VAP cases was recorded. Various underlying conditions like head injury, cerebral hemorrhage and chronic obstructive pulmonary disease (COPD) were found to be associated with Acinetobacter VAP. Acinetobacter strains exhibited MDR pattern.

Conclusion:

Strict infection control measures, judicious prescribing of antibiotics, antibiotic resistance surveillance programs and antibiotic cycling should be adopted to control infections due to these bacteria in patients admitted to intensive care units.

Epidemiology and impact of imipenem resistance in Acinetobacter baumannii

BACKGROUND

Acinetobacter baumannii is an emerging gram-negative pathogen that can cause healthcare-acquired infections among patients. Treatment is complicated for cases of healthcare-acquired infection with A. baumannii resistant to imipenem.

OBJECTIVE

To elucidate the risk factors for imipenem-resistant A. baumannii (IRAB) infection or colonization and to identify the effect of resistance on clinical and economic outcomes.

METHODS

We analyzed data from 2 medical centers of the University of Pennsylvania. Longitudinal trends in the prevalence of IRAB clinical isolates were characterized during the period from 1989 through 2004. For A. baumannii isolates obtained from 2001 through 2006, a case-control study was conducted to investigate the association between prior carbapenem use and IRAB infection or colonization, and a cohort study was performed to identify the effect of IRAB infection or colonization on mortality, length of stay after culture, and hospital cost after culture.

RESULTS

From 1989 through 2004, the annual prevalence of IRAB isolates ranged from 0% to 21%. During the period from 2001 through 2006, there were 386 unique patients with A. baumannii isolates, and 89 (23.1%) had IRAB isolates. Prior carbapenem use was independently associated with IRAB infection or colonization (adjusted odds ratio, 3.04 [95% confidence interval, 1.07-8.65]). There was a borderline significant association between IRAB infection or colonization and mortality, although this association was limited to isolates recovered from blood samples (adjusted odds ratio, 5.30 [95% confidence interval, 0.81-34.59]). Compared with patients with imipenem-susceptible A. baumannii infection or colonization, patients with IRAB infection or colonization had a longer hospital stay after culture (median, 21 vs 16 days; P = .07) and greater hospital charges after culture (mean, $334,516 vs $276,059; P = .03). After controlling for patient location in an intensive care unit, transfer from another facility, and length of hospital stay before culture, there was no longer an independent association between IRAB infection or colonization and higher cost after culture and length of stay after positive culture result.

CONCLUSIONS

Many A. baumannii isolates exhibit imipenem resistance, which is strongly associated with prior use of carbapenems. Given the high mortality rate associated with A. baumannii infection or colonization, interventions to curb further emergence of cases of IRAB infection and strategies to optimize therapy are needed.

Multidrug-resistant Acinetobacter baumannii: mechanisms of virulence and resistance

Infection due to Acinetobacter baumannii has become a significant challenge to modern healthcare systems. The organism shows a formidable capacity to develop antimicrobial resistance, yet the clinical impact of A. baumannii infection remains unclear. Much is known about the processes involved in multidrug resistance, but those underlying the pathogenicity and virulence potential of the organism are only beginning to be elucidated. In this article, we provide an overview of current knowledge, focusing on mechanisms of pathogenesis, the molecular basis of resistance and options for treatment in the absence of novel therapeutic agents.

Acinetobacter: an old friend, but a new enemy

Acinetobacter emerged as a significant nosocomial pathogen during the late 1970s, probably as a consequence, at least in part, of increasing use of broad-spectrum antibiotics in hospitals. Most clinically significant isolates belong to the species Acinetobacter baumannii or its close relatives, with many infections concentrated in intensive care, burns or high dependency units treating severely ill or debilitated patients. Large outbreaks can occur in such units, involving the infection or colonisation of numerous patients by specific epidemic strains of A. baumannii. Recently, a particular problem has concerned cross-infection of injured military patients repatriated from combat regions of the world (e.g. Iraq and Afghanistan). Carbapenems have previously been the treatment of choice for infected patients, but increasing reports worldwide now describe A. baumannii isolates resistant to all conventional antimicrobial regimens. Data to support therapeutic use of the limited number of new antimicrobial agents (e.g. tigecycline) with in-vitro activity against these pathogens are still very limited. Detailed advice concerning prevention and control of outbreaks caused by multidrug-resistant strains of acinetobacter is available from the UK Health Protection Agency. In addition to antibiotic prescribing policies and audit, these measures focus on reinforcing standard infection control procedures and precautions, with particular attention to thorough cleaning of patient areas to take account of the long-term survival of acinetobacter after drying and inadequate disinfection. Despite these measures, the problem continues to escalate, with many hospitals worldwide now reporting outbreaks caused by multidrug-resistant strains of acinetobacter.

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Acinetobacter baumannii: an emerging multidrug-resistant threat

Amid the recent attention focused on the growing impact of methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa infections, the pathogen Acinetobacter baumannii has been stealthily gaining ground as an agent of serious nosocomial and community-acquired infection. Historically, Acinetobacter spp. have been associated with opportunistic infections that were rare and of modest severity; the last two decades have seen an increase in both the incidence and seriousness of A. baumannii infection, with the main targets being patients in intensive-care units. Although this organism appears to have a predilection for the most vulnerable patients, community-acquired A. baumannii infection is an increasing cause for concern. The increase in A. baumannii infections has paralleled the alarming development of resistance it has demonstrated. The persistence of this organism in healthcare facilities, its inherent hardiness and its resistance to antibiotics results in it being a formidable emerging pathogen. This review aims to put into perspective the threat posed by this organism in hospital and community settings, describes new information that is changing our view of Acinetobacter virulence and resistance, and calls for greater understanding of how this multifaceted organism came to be a major pathogen.

Acinetobacter baumannii: a universal threat to public health?

Acinetobacter spp. are non-fermentative, strictly aerobic, Gram-negative microorganisms with a confusing taxonomic history. The Acinetobacter baumannii-Acinetobacter calcoaceticus complex is the species most commonly isolated from clinical specimens. It is ubiquitous in nature and has been found as part of the normal skin, throat and rectal flora as well as in food and body lice. It colonises patients in Intensive Care Units and contaminates inanimate hospital surfaces and devices as well as wounds, including war injuries. Although a frequent coloniser, Acinetobacter can be the cause of severe and sometimes lethal infections, mostly of nosocomial origin, predominantly ventilator-associated pneumonia. Bacteraemic infections are rare but may evolve to septic shock. Acinetobacter also emerges as a cause of nosocomial outbreaks and is characterised by increasing antimicrobial multiresistance. Antibiotic use, especially carbapenems and third-generation cephalosporins, is recognised as the most important risk factor for multiresistance. Described resistance mechanisms include hydrolysis by beta-lactamases, alterations in outer membrane proteins and penicillin-binding proteins, and increased activity of efflux pumps. Today, Acinetobacter resistant to carbapenems, aminoglycosides and fluoroquinolones presents a challenge to the clinician. However, sulbactam, tigecycline and colistin represent the current therapeutic approaches, which are associated with satisfactory efficacy.

[Characterization of the resistance mechanism to beta-lactams in Acinetobacter baumannii strains isolated in the university hospital Sahloul in Tunisia (2005)]

OBJECTIVE

The bacterial multiresistance to beta-lactams and imipenem is an emergent feature in the university hospital Sahloul in Tunisia. This study was conducted to elucidate natural and acquired mechanism of resistance to beta-lactams in strains of Acinetobacter baumannii isolated in different wards of the hospital.

MATERIALS AND METHODS

A specimen of 26 clinical strains of Acinetobacter baumannii was studied. beta-lactamases characterization was done by isoelectric focusing on gel of crude enzymatic extract, phenotypic tests for detection of extended spectrum beta-lactamases (ESBL) and metallo-beta-lactamases (MBL) and finally by amplification (PCR) and sequencing of genes encoding naturally occurring AmpC, the insertion sequence ISAbaI and oxacillinase with carbapenemase activity. Study of clonality of strains was performed by analysis of genomic DNA digested by the restriction enzyme ApaI and separated by pulsed field gel electrophoresis (PFGE).

RESULTS

The isoelectric focusing on gel revealed two bands of beta-lactamase activity with a pI upper than 8. None ESBL or MBL was detected. PCR for AmpC, ISAbaI and OXA-69 were positive for all studied strains. The sequencing of PCR products show high identity (99-100%) with genes described previously. PFGE analysis has demonstrated clonality of studied strains.

CONCLUSION

Resistance to beta-lactams including imipenem is associated to the hyper production of the AmpC enzyme and expression of OXA-69. Those enzymatic mechanisms are associated with the natural low permeability to beta-lactams which characterize Acinetobacter baumannii strains. High clonal relationship of studied strains proved by PFGE analysis has shown the necessity of implementation of strict hygienic rules and rational antibiotic usage.

Spread in an Italian hospital of a clonal Acinetobacter baumannii strain producing the TEM-92 extended-spectrum beta-lactamase

Clinical isolates of Acinetobacter baumannii (n = 470) were collected during a 7-year period and investigated for the genetic determinants of resistance to expanded-spectrum beta-lactams. Thirty-one isolates produced the TEM-92 extended-spectrum beta-lactamase (ESBL) and were clonally related. This is the first report of A. baumannii producing a TEM-type ESBL.

The Epidemiological Profile of Infections with Multidrug-Resistant Pseudomonas aeruginosa and Acinetobacter Species

Isolates of Pseudomonas aeruginosa or Acinetobacter species that are resistant to all, or almost all, commercially available antibiotics are now prevalent worldwide. Typically, these strains are recovered from patients in intensive care units who have ventilator-associated pneumonia. "Panresistant" strains can be defined as strains that are resistant to all beta -lactam and quinolone antibiotics recommended as empirical therapy for ventilator-associated pneumonia. These strains are well adapted to the hospital environment--molecular epidemiological studies have frequently revealed that only 1 or 2 clones caused outbreaks in intensive care units. However, panresistant strains may also be selected by antibiotic use. Given the lack of antibiotic options to treat infection with panresistant strains, enhanced surveillance for these organisms is necessary at unit-specific, institutional, and national levels.

Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa

Acinetobacter species and Pseudomonas aeruginosa are noted for their intrinsic resistance to antibiotics and for their ability to acquire genes encoding resistance determinants. Foremost among the mechanisms of resistance in both of these pathogens is the production of beta -lactamases and aminoglycoside-modifying enzymes. Additionally, diminished expression of outer membrane proteins, mutations in topoisomerases, and up-regulation of efflux pumps play an important part in antibiotic resistance. Unfortunately, the accumulation of multiple mechanisms of resistance leads to the development of multiply resistant or even "panresistant" strains.

The beta-lactamase threat in Enterobacteriaceae, Pseudomonas and Acinetobacter

Over the past 60 years, the use of successive generations of beta-lactam antibiotics has selected successive generations of beta-lactamase enzymes, each more potent than the last. Currently, rising problems include CTX-M extended-spectrum beta-lactamases (ESBLs), plasmid-mediated AmpC beta-lactamases and KPC carbapenemases in Enterobacteriaceae, while OXA- and metallo- carbapenemases are of growing importance in Acinetobacter spp. and (less so) in other non-fermenters. Escherichia coli isolates with CTX-M ESBLs are spreading multiresistance in the community and in hospitals, while carbapenemase-producing Acinetobacter spp., mostly from intensive care, are among the most multiresistant nosocomial bacteria known and are often susceptible only to polymyxins and, potentially, tigecycline. This review discusses the epidemiology and microbiology of these resistance problems, along with possible solutions.

Risk factors for the isolation of multi-drug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa: a systematic review of the literature

An understanding of the epidemiology of multi-drug-resistant (MDR) Acinetobacter baumannii and Pseudomonas aeruginosa infections is necessary in order to develop strategies to curtail their spread. For this purpose, the evidence linking the isolation of MDR A. baumannii and P. aeruginosa with specific risk factors was evaluated. PubMed was searched for the 20-year period from September 1985 to September 2005, and eligible studies were considered to be those that: (1) linked the isolation of A. baumannii and P. aeruginosa with specific risk factors; (2) described the characteristics of the affected patients in detail; and (3) provided data on the antibiotic resistance profile of the isolated micro-organisms. Fifty-five studies were found referring to A. baumannii (28 with case-control methodology and 27 outbreak investigations without case-control methodology), and 42 studies were found referring to P. aeruginosa (25 with case-control methodology and 17 outbreak investigations without case-control methodology). Although heterogeneous study designs and investigated risk factors limited this analysis, it was concluded that acquisition and spread of these micro-organisms appear to be related to a large number of variables. Among the most important were deficiencies in the implementation of infection control guidelines and the use of broad-spectrum antibiotics. Use of carbapenems and third-generation cephalosporins appear to be related to the development of an MDR phenotype by A. baumannii, while carbapenems and fluoroquinolones are implicated in MDR P. aeruginosa. The diversity of risk factors associated with the development of MDR A. baumannii and P. aeruginosa suggests that a separate outbreak investigation should be performed in each hospital setting. The development of innovative control strategies is needed in order to limit the spread of these pathogens.

Complex genetic structures with repeated elements, a sul-type class 1 integron, and the blaVEB extended-spectrum beta-lactamase gene

Two clinical isolates of Pseudomonas aeruginosa, TL-1 and TL-2, were isolated from a patient transferred from Bangladesh and hospitalized for osteomyelitis in Paris, France. P. aeruginosa TL-1 expressed the extended-spectrum beta-lactamase VEB-1a and was susceptible only to imipenem and colistin, while P. aeruginosa TL-2 expressed only the naturally occurring bla(AmpC) gene at a basal level and exhibited a wild-type beta-lactam resistance phenotype. In TL-1, the typical 5'-end conserved sequence (5'-CS) region of class 1 integrons usually present upstream of the bla(VEB-1a) gene was replaced by a truncated 3'-CS and a 135-bp repeated element (Re). Downstream of the bla(VEB-1a) gene, an insertion sequence, ISPa31 disrupted by ISPa30, and an orf513 sequence, belonging to a common region (conserved region 1 [CR1]) immediately upstream of the aphA-6 gene, were present. Further downstream, a second truncated 3'-CS region in direct repeat belonged to In51, an integron containing two gene cassettes (aadA6 and the OrfD cassette). Thus, the overall structure corresponded to a sul-type class 1 integron termed In121. Genetic analyses revealed that both isolates were clonally related and differed by a ca. 100-kb fragment that contained In121. Both isolates contained another integron, In122, that carried three gene cassettes: aadB, dfrA1, and the OrfX cassette. This work identifies for the first time the spread of Re-associated bla(VEB) genes located on a sul-type integron. It also reports for the first time a CR1 element in P. aeruginosa that is associated with an aminoglycoside resistance aphA-6 gene that is expressed from a composite promoter.