High prevalence of carbapenem-hydrolysing oxacillinases in epidemiologically related and unrelated Acinetobacter baumannii clinical isolates in Spain

Carbapenem-hydrolysing oxacillinases are reported increasingly in Acinetobacter baumannii. This study investigated the role of these beta-lactamases in causing resistance to carbapenems in 83 epidemiologically related and unrelated imipenem-resistant A. baumannii clinical isolates. The isolates were also analysed for the presence of ISAba1 in the promoter region of the bla(OXA-51)-like gene in order to investigate the role of ISAba1 in OXA-51 expression. All clinical isolates contained a bla(OXA-51)-like gene, 20% contained a bla(OXA-58)-like gene, and 42% contained a bla(OXA-40)-like gene; bla(OXA-23)-like, bla(IMP) and bla(VIM) genes were not detected in any of the isolates investigated. ISAba1 was found in 24 (82.7%) of 28 pulsetypes, and was located in the promoter region of the bla(OXA-51)-like gene in five (20.8%) of these pulsetypes. Expression of bla(OXA-51) was detected in the five isolates with ISAba1 located in the promoter region, but was not detected in an isogenic imipenem-susceptible A. baumannii isolate that did not have ISAba1 located in the promoter region. It was concluded that there is a high prevalence of oxacillinases with activity against carbapenems among genetically unrelated A. baumannii clinical isolates from Spain, and that concomitant expression of two carbapenemases (OXA-51-like and either OXA-40-like or OXA-58-like) may take place. Insertion of an ISAba1-like element in the promoter of the bla(OXA-51)-like gene promotes the expression of this gene, although this did not seem to play a major role in carbapenem resistance.

Risk factors and outcomes of bloodstream infections with metallo-beta-lactamase-producing Acinetobacter

The spread of Gram-negative bacilli with acquired metallo-beta-lactamase (MBL) threatens the successful treatment of major nosocomial infections. The objective of this study was to evaluate the differences in the clinical characteristics of bacteremia caused by MBL-producing Acinetobacter species and MBL non-producing isolates. Two retrospective case-control studies were conducted using data on patients with Acinetobacter bacteremia, who were admitted between January 2001 and December 2005 at a 1500-bed, tertiary-care teaching hospital. Case group 1 (n=27) included patients from whom imipenem-resistant Acinetobacter was isolated in blood culture, and case group 2 (n=7) consisted of those patients from group 1 who yielded MBL-producing isolates. The control group (n=41) included patients from whom carbapenem-susceptible Acinetobacter isolates were isolated in blood culture. Multivariate analysis revealed that the independent risk factors for imipenem-resistant Acinetobacter bacteremia were neutropenia and prolonged use of carbapenem. The independent risk factors for MBL-producing Acinetobacter bacteremia were neutropenia and prolonged use of cephalosporins. The results of this study suggest that a prolonged use of cephalosporins may be associated with MBL-producing Acinetobacter bacteremia.

Use of sequence-based typing and multiplex PCR to identify clonal lineages of outbreak strains of Acinetobacter baumannii

Representatives (n = 31) of outbreak strains of Acinetobacter baumannii from five countries fell into three clear groups, designated Groups 1-3, based on their ompA (outer-membrane protein A), csuE (part of a pilus assembly system required for biofilm formation) and bla(OXA-51-like) (the intrinsic carbapenemase gene in A. baumannii) gene sequences. With the exception of the closely related alleles within the Group 1 clonal complex, alleles at each locus were highly distinct from each other, with a minimum of 14 nucleotide differences between any two alleles. Isolates within a group shared the same combination of alleles at the three loci, providing compelling evidence that the outbreak strains investigated belonged to three clonal lineages. These corresponded to the previously identified European clones I-III. Sequence differences among the alleles were used to design multiplex PCRs to rapidly assign isolates belonging to particular genotypes to sequence groups. In the UK, genotypes belonging to the Group 1 clonal complex have been particularly successful, accounting for the vast majority of isolates referred from hospitals experiencing problems with Acinetobacter.

Genotypic diversity of imipenem resistant isolates of Acinetobacter baumannii in Spain

OBJECTIVES

To investigate relevant clinical and microbiological features of Acinetobacter baumannii in Spanish hospitals and to establish the genotypic diversity of imipenem resistant isolates.

MATERIAL AND METHODS

Seven Spanish hospitals collected 354 consecutive isolates that were subjected to antimicrobial susceptibility testing by standard methods. Further genetic analysis was determined by PFGE in a subset of 135 isolates from three hospitals selected because each of them presented high-, medium-, and low imipenem resistance rates.

RESULTS

Most isolates were from males (61.9%), age >65 years (52.3%), admitted to ICU (35.6%), and isolated from the respiratory tract (31.1%). Rates of carbapenem- and sulbactam resistance were 44.9% and 39.9%, respectively. Colistin was active against multiresistant isolates. Rates of imipenem resistance varied according to individual hospital (average: 43.8%; range: 13.5%-85.0%), medical department (more prevalent in ICU), and clinical sample (higher in isolates from the respiratory tract). Of the 135 isolates studied by PFGE (64 of them imipenem-resistant), 115 (85.1%) were distributed among 14 clusters and 20 were unrelated. Of the imipenem-resistant isolates, 45 (70.3%) belonged to six clusters that also had imipenem- susceptible isolates; 14 constituted four exclusive clusters, and five were unrelated.

CONCLUSIONS

Acquisition of imipenem resistance in A. baumannii is likely due to both clonal and non-clonal dissemination; resistance rates strongly vary between different hospitals and even between different hospital departments.

Prevalence of ISAba1in epidemiologically unrelatedAcinetobacter baumanniiclinical isolates

Seventy-five Acinetobacter baumannii strains belonging to different pulsetypes, plus one ceftazidime-susceptible strain, from a pulsetype in which all strains were resistant, were included in this study. The minimum inhibitory concentration of ceftazidime was determined by the microdilution method. The bla(ADC)-like gene, the IS(Aba1) element and the IS(Aba1) located in the bla(ADC)-like promoter were detected by PCR. The objective of the study was to determine the prevalence of IS(Aba1) in a collection of epidemiologically unrelated A. baumannii clinical isolates. The bla(ADC)-like gene was detected in 74 (97.3%) out of the 76 strains analysed. In these 74 strains, 51 (69%) were positive for the IS element and it was not detected in 23 (31%) strains. Among the A. baumannii strains containing the IS element, 40 (78.4%) had the IS element located in the promoter region of the bla(ADC)-like gene. In a high percentage of A. baumannii clinical isolates carrying the IS(Aba1), this is inserted into the promoter region of the bla(ADC)-like gene. In addition, two clinical isolates belonging to the same pulsetype, one with and one without the IS(Aba1), can be found in the clinical setting, suggesting the potential acquisition or loss of this genetic element in the hospital environment.

Community-acquired Acinetobacter infections

Acinetobacter infections have been attracting increasing attention during recent years because they have become common in hospitalized patients, especially in the intensive care unit (ICU) setting. However, the available literature suggests that the pathogen has another fearful potential; it can cause community-acquired infections. We searched PubMed and the reference lists of the initially identified articles and identified six case series regarding a total of 80 patients with community-acquired Acinetobacter baumannii infections; from these, 51 had pneumonia and 29 had bacteremia. Of these 80 patients, 45 (56%) died of the infection. In addition, we identified 26 case reports regarding 43 patients with community-acquired Acinetobacter infections; from these, 38 had pneumonia, two had meningitis, one had soft-tissue infection, one had ocular infection, and one had native valve endocarditis. Comorbidity was commonly present in patients reported in the case series as well as the case reports, mainly, chronic obstructive pulmonary disease, renal disease, and diabetes mellitus; heavy smoking and excess alcohol consumption were also common. Most of the studies originated from China, Taiwan, and tropical Australia. We also identified 12 retrospective or prospective studies (seven from the Far East, two from Oceania, one from N. Guinea, one from Palestine, and one from USA/Canada) that reported the frequency of community-acquired Acinetobacter infections; the range of isolation of Acinetobacter from patients with community-acquired pneumonia in these studies was 1.3%-25.9%. In conclusion, most community-acquired Acinetobacter infections have been reported from countries with tropical or subtropical climate, and mainly affect patients with some form of comorbidity or are associated with heavy smoking and excess alcohol consumption.

Multi-drug resistant Acinetobacter infections in critically injured Canadian forces soldiers

Background

Military members, injured in Afghanistan or Iraq, have returned home with multi-drug resistant Acinetobacter baumannii infections. The source of these infections is unknown.

Methods

Retrospective study of all Canadian soldiers who were injured in Afghanistan and who required mechanical ventilation from January 1 2006 to September 1 2006. Patients who developed A. baumannii ventilator associated pneumonia (VAP) were identified. All A. baumannii isolates were retrieved for study patients and compared with A. baumannii isolates from environmental sources from the Kandahar military hospital using pulsed-field gel electrophoresis (PFGE).

Results

During the study period, six Canadian Forces (CF) soldiers were injured in Afghanistan, required mechanical ventilation and were repatriated to Canadian hospitals. Four of these patients developed A. baumannii VAP. A. baumannii was also isolated from one environmental source in Kandahar – a ventilator air intake filter. Patient isolates were genetically indistinguishable from each other and from the isolates cultured from the ventilator filter. These isolates were resistant to numerous classes of antimicrobials including the carbapenems.

Conclusion

These results suggest that the source of A. baumannii infection for these four patients was an environmental source in the military field hospital in Kandahar. A causal linkage, however, was not established with the ventilator. This study suggests that infection control efforts and further research should be focused on the military field hospital environment to prevent further multi-drug resistant A. baumannii infections in injured soldiers.

Outbreak of Acinetobacter baumannii bacteremia related to contaminated morphine used for patient-controlled analgesia

We investigated a cluster of postoperative febrile episodes and episodes of Acinetobacter baumannii bacteremia in obstetrics and gynecology wards after an electrical blackout and loss of the water supply. The use of patient-controlled analgesia was the only independent risk factor associated with postoperative fever, and A. baumannii isolates recovered from the blood of patients who had received patient-controlled analgesia were genetically related to an isolate recovered from the diluted morphine solution used for this procedure. After inappropriate preparation of the morphine solution was identified and stopped, the outbreak ended.

Dissemination of imipenem-resistant Acinetobacter baumannii strains carrying the ISAba1–bla OXA-23 genes in a Chinese hospital

An outbreak of 95 clinical infections with imipenem-resistant Acinetobacter baumannii in a Chinese hospital was investigated and the carbapenemase-encoding genes and their relationship with ISAba1 of these and a further 16 isolates recovered from the intensive care unit (ICU) environment were analysed. Almost all isolates were resistant to a wide range of antimicrobials; the lowest resistance rates were found for polymyxin E (17.1 %), cefoperazone/sulbactam (30.6 %) and ampicillin/sulbactam (67.6 %). Six pattern types defined by DNA macrorestriction patterns were distinguished among the clinical isolates with dissemination of pattern A (50 isolates) to patients in seven hospital units and pattern B (35 isolates) to eight units; the environmental isolates from ICUs were also of pattern A. All isolates were positive for the bla OXA-66 and bla OXA-23 genes. The OXA-23-encoding gene was located 34 bp downstream of ISAba1. No plasmids were detected and conjugal transfer of resistance was not demonstrated. The bla OXA-23 probe hybridized with 200 and 220 kb ApaI chromosomal fragments for type patterns A and B, respectively.

Acinetobacter pneumonia: a review

Acinetobacter species are becoming a major cause of nosocomial infections, including hospital-acquired and ventilator-associated pneumonia. Acinetobacter species have become increasingly resistant to antibiotics over the past several years and currently present a significant challenge in treating these infections. Physicians now rely on older agents, such as polymyxins (colistin), for treatment. This paper reviews the epidemiology, treatment, and prevention of this emerging pathogen.

Molecular and epidemiologic study of polyclonal outbreaks of multidrug-resistant Acinetobacter baumannii infection in an Israeli hospital

OBJECTIVES

To perform a molecular and epidemiologic investigation of multidrug-resistant (MDR) Acinetobacter baumannii in an institution were polyclonal outbreaks have been observed and determine whether these polyclonal outbreaks had an endogenous origin or were caused by in-hospital patient-to-patient transmission.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

An epidemiologic and genotypic investigation of incident cases of MDR A. baumannii infection in an Israeli university tertiary care center.

PATIENTS

Hospitalized patients with MDR A. baumannii isolated from clinical samples during a 13-week period, from April 15, 2003, through July 15, 2003.

INTERVENTION

All patients with new MDR A. baumannii infections were recruited, and isolates were typed using pulsed-field gel electrophoresis. Data on in-hospital movements and consultations were extracted from computerized databases. Quantification of transmission opportunities (TOPs), defined as encounters between an established carrier and a future carrier of MDR A. baumannii, and analysis of ward clusters were performed.

RESULTS

We studied 96 MDR A. baumannii isolates, which belonged to 18 different pulsed-field gel electrophoresis clones. In 65% of cases, TOPs involving patients with the same clone were demonstrated, which is significantly greater than the number of TOPs involving patients with different clones (P=.01).

CONCLUSION

Although outbreaks of MDR A. baumannii infection may be polyclonal, we believe that patient-to-patient transmission explains most cases of transmission. Polyclonal local outbreaks reflect several clonal outbreaks occurring simultaneously. The cause of polyclonal outbreaks of A. baumannii infections clustered by ward and time remains to be explained.

Molecular typing of imipenem-resistant Acinetobacter baumannii-calcoaceticus complex in a Singapore hospital where carbapenem resistance is endemic

OBJECTIVE

To investigate the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex isolates in a tertiary care hospital where the prevalence of carbapenem resistance among these organisms is high.

DESIGN

The study was a prospective, observational study performed during an 8-month period (May 1 through December 31, 2004). A. baumannii isolates recovered from all clinical samples during the study period were included in the study. Antibiotic susceptibility testing was performed using the disk diffusion method, and all carbapenem-resistant strains were typed by a polymerase chain reaction-based typing method.Setting. An 800-bed hospital in Singapore.

RESULTS

More than half of recovered isolates were clonally unrelated, with the remaining isolates grouped into 4 genotypes.

CONCLUSIONS

The results of the study suggest that the high prevalence of carbapenem resistance among Acinetobacter organisms in this institution is not caused by the spread of a predominant clone and that other factors may need to be investigated.

Resistance to disinfectants in epidemiologically defined clinical isolates of Acinetobacter baumannii

Decreased susceptibility to biocides may contribute to epidemic spread of Acinetobacter baumannii in the hospital. This study was conducted to evaluate the susceptibility of different clinical A. baumannii strains to disinfectants. Twenty A. baumannii strains were examined, ten of which were outbreak-related and ten that were sporadic. Clinical isolates were selected on the basis of demonstrating a unique pulsed-field gel electrophoresis pattern. The in-vitro activities of propanol, combination of 1-propanol, 2-propanol and mecetronium ethylsulphate, polyvinylpyrrolidone (PVP)-iodine, triclosan and chlorhexidine were determined using a broth macrodilution method. Exposure times to the disinfectant ranged from 15 s to 2 min and concentrations ranged from undiluted to a 1:4000 dilution in order to investigate the impact of inadvertent dilution that might occur in clinical practice. Five American Type Culture Collection (ATCC) type strains (A. baumannii, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus aureus) were used as controls. All disinfectants inhibited growth of all isolates at concentrations and contact times recommended by the respective manufacturer. With most of the disinfectants tested, a relevant number of viable bacteria remained if contact times < 30s or diluted agents were used. No significant differences in susceptibility between outbreak-related and sporadic strains were detected, but larger studies would be required to confirm this. Resistance to currently used disinfectants is probably not a major factor in the epidemic spread of A. baumannii. However, even minor deviations from the recommended procedures leading to decreased concentrations or exposure times may play a role in nosocomial cross-transmission.

Dissemination of Acinetobacter baumannii clones with OXA-23 Carbapenemase in Colombian hospitals

During 2005, 66 carbapenem-resistant isolates of Acinetobacter baumannii were collected from seven tertiary-care hospitals participating in a nationwide surveillance network in Colombia. The isolates were multidrug resistant and produced the carbapenemases OXA-23 and OXA-51. Forty-five belonged to four clones while 21 were unique pulsotypes. One clone was present in two hospitals within one city, while another had spread between two hospitals in different cities. Blood, secretions, and abdominal fluids were the most frequent sites of isolation. This is the first description of widespread dissemination of OXA-23 in South America.

Prevalence of antimicrobial resistance in Acinetobacter calcoaceticus-baumannii complex in a Saudi Arabian hospital

During the period from 1998 through 2004, a total of 476 isolates of Acinetobacter calcoaceticus-baumannii complex were recovered. The organism showed high rates of resistance to ampicillin (86% of isolates), cefoxitin (89%), and nitrofurantoin (89%). The rate of resistance to imipenem was 3%; to ticarcillin-clavulanic acid, 16.5%; to gentamicin, 26%; and to ceftazidime, 38%. Multidrug resistance was observed in 14%-35.8% of Acinetobacter species isolates.

Importation of Acinetobacter baumannii into a burn unit: a recurrent outbreak of infection associated with widespread environmental contamination

A burn patient was infected with Acinetobacter baumannii on transfer to the hospital after a terrorist attack. Two patients experienced cross-infection. Environmental swab samples were negative for A. baumannii. Six months later, the bacteria reemerged in 6 patients. Environmental swab samples obtained at this time were inoculated into a minimal mineral broth, and culture results showed widespread contamination. No case of infection occurred after closure of the unit for disinfection.

Management of antimicrobial-resistant Acinetobacter in hospitals

This article examines the management of outbreaks of multi-drug resistant (MDR) Acinetobocter in hospitals. It briefly describes the organism and its properties and then discusses its role in disease and the risk to hospital patients, routes of transmission and patient reservoirs, mechanisms of drug resistance and susceptibility to antimicrobial agents, and measures for controlling outbreaks in hospitals. The success of these measures is illustrated by a detailed review of the control of an outbreak of MDR Acinetobacter boumannii infection in an intensive care unit in a London teaching hospital without closure of the ward or isolation of the patients.

An outbreak of multidrug-resistant Acinetobacter baumannii-calcoaceticus complex infection in the US military health care system associated with military operations in Iraq

BACKGROUND

We investigated an outbreak of multidrug-resistant Acinetobacter baumannii-calcoaceticus complex infection among US service members injured in Iraq.

METHODS

The investigation was conducted in Iraq and Kuwait, in the 2 military hospitals where the majority of injured service members were initially treated. After initially characterizing the outbreak, we evaluated 3 potential sources of infection for the period March 2003 to December 2004. The evaluation included screening samples that were obtained from the skin of patients for the presence of colonization and assessing the soil and health care environments for the presence of A. baumanii-calcoaceticus complex organisms. Isolates obtained from samples from patients in US Military treatment facilities, as well as environmental isolates, were genotypically characterized and compared using pulsed-field gel electrophoresis.

RESULTS

A. baumanii-calcoaceticus complex organisms were present on the skin in only 1 (0.6%) of 160 patients who were screened and in 1 (2%) of 49 soil samples. A. baumanii-calcoaceticus complex isolates were recovered from treatment areas in 7 of the 7 field hospitals sampled. Using pulsed-field gel electrophoresis, we identified 5 cluster groups in which isolates from patients were related to environmental isolates. One cluster included hospitalized patients who had not been deployed to Iraq. Among the clinical isolates, only imipenem, polymyxin B, and colistin demonstrated reliable in vitro antimicrobial activity. Generally, the environmental isolates were more drug susceptible than were the clinical isolates.

CONCLUSIONS

Our findings suggest that environmental contamination of field hospitals and infection transmission within health care facilities played a major role in this outbreak. On the basis of these findings, maintaining infection control throughout the military health care system is essential. Novel strategies may be required to prevent the transmission of pathogens in combat field hospitals.

Emergence and spread of carbapenem-resistant strains of Acinetobacter baumannii in a tertiary-care hospital in Poland

This study analysed the occurrence of carbapenem resistance among Acinetobacter baumannii isolates from a tertiary-care hospital in Poland, together with the molecular epidemiology of these isolates and the risk-factors for their acquisition and possible nosocomial spread. The medical charts of 21 patients with Acinetobacter infection or colonisation revealed that A. baumannii isolates were obtained most frequently from intensive care unit and surgical patients (particularly those receiving transplantation surgery). First isolation occurred, on average, on day 21 following admission (range 5-45 days). Infection with Acinetobacter contributed directly to the death of seven patients. Several patients were infected with more than one strain, and molecular typing revealed the co-circulation of three predominant clones, of which two belonged to the Acinetobacter lineages designated as European clones I and II. All three clones encoded an OXA-51-type carbapenemase, but were negative for carbapenemases belonging to the OXA-23, OXA-24 and OXA-58 families. The OXA-51 gene was found in both resistant and susceptible isolates, and was not associated directly with carbapenem resistance. Etests with imipenem and imipenem plus EDTA indicated production of a metallo-beta-lactamase (MBL) in carbapenem-resistant isolates. PCRs for IMP-type MBLs were negative, but PCR using consensus primers for VIM-type MBLs were positive for carbapenem-resistant isolates belonging to the European clone II lineage. The occurrence of a VIM-type MBL in association with one of the epidemic lineages of A. baumannii is a cause for concern. Further studies are needed to evaluate possible inter-hospital spread of resistant A. baumannii strains in Poland.

Emergence of resistant Acinetobacter baumannii in critically ill patients within an acute care teaching hospital and a long-term acute care hospital

BACKGROUND

Acinetobacter baumannii is a gram-negative, coccobacillus found in water and is a significant nosocomial pathogen in hospitals. This report chronicles the appearance in June 2003 of a multidrug-resistant A baumannii (MDR-AB) strain, its dissemination, and interventions used to control it in an acute care hospital (ACH) and long-term acute care facility (LTAC).

METHODS

Molecular typing using pulsed-field gel electrophoresis (PFGE) showed that 88 of 99 strains (89%) gave an identical banding designated as clone A. Eight additional isolates were variants of clone A, and 3 isolates were unrelated.

RESULTS

A baumannii was isolated from 229 patients between January 2003 and December 2004. Of these patients, 151 (66%) were colonized/infected with MDR-AB. Most isolates were resistant to antibiotics except for imipenem and ampicillin/sulbactam. Isolates included 108 (72%) in the respiratory tract, 32 (21%) in wounds, 6 (4%) in blood, and 5 (3%) in urine. Most isolates were found in the LTAC (70 isolates), ICU step-down (27 isolates), and ICU (26 isolates).

CONCLUSION

This epidemiologic history illustrates (1) epidemic clonal spread, (2) target populations, (3) variable monthly prevalence, and (4) intervention outcomes. With intervention, the number of new isolates in the ACH decreased by dedicating an infection control professional to critical care, daily surveillance, isolation of positive MDR-AB patients, universal gloving, and routinely reporting results.

Molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii in a university hospital in Italy

This study investigated the molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii that occurred between June 2003 and June 2004 in a tertiary-care hospital in Naples, Italy. A. baumannii was isolated from 74 patients, of whom 38 were infected and 36 were colonised. Thirty-three patients had ventilator-associated pneumonia, three had hospital-acquired pneumonia, and two had sepsis. Genotypic analysis of 45 available A. baumannii isolates revealed two distinct pulsed-field gel electrophoresis (PFGE) patterns. Of these, PFGE pattern 1 was represented by isolates from 44 patients and was identical to that of an epidemic A. baumannii clone isolated in another hospital of Naples during 2002. All A. baumannii isolates of PFGE type 1 showed identical multiresistant antibiotypes, characterised by resistance to all antimicrobial agents tested, including carbapenems, with the exception of colistin. In these isolates, inhibition of OXA enzymes by 200 mM NaCl reduced the imipenem MIC by up to four-fold. Molecular analysis of antimicrobial resistance genes showed that all A. baumannii isolates of PFGE type 1 harboured a class 1 integron containing the aacA4, orfX and bla(OXA-20) gene cassettes, an ampC gene and a bla(OXA-51)-like allele. Moreover, a bla(OXA-58)-like gene surrounded by the regulatory elements ISAba2 and ISAba3 was identified in a 30-kb plasmid from A. baumannii isolates of PFGE type 1, but not PFGE type 2. Thus, selection of a single A. baumannii clone producing an OXA-58-type carbapenem-hydrolysing oxacillinase was responsible for the increase in the number of A. baumannii infections that occurred in this hospital.