Two distinct clones of carbapenem-resistant Acinetobacter baumannii isolates from Korean hospitals

The Changes in Epidemiology of Imipenem-Resistant Acinetobacter baumannii Bacteremia in a Pediatric Intensive Care Unit for 17 Years

BACKGROUND

Acinetobacter baumannii infections cause high morbidity and mortality in intensive care unit (ICU) patients. However, there are limited data on the changes of long-term epidemiology of imipenem resistance in A. baumannii bacteremia among pediatric ICU (PICU) patients.

METHODS

A retrospective review was performed on patients with A. baumannii bacteremia in PICU of a tertiary teaching hospital from 2000 to 2016. Antimicrobial susceptibility tests, multilocus sequence typing (MLST), and polymerase chain reaction for antimicrobial resistance genes were performed for available isolates.

RESULTS

A. baumannii bacteremia occurred in 27 patients; imipenem-sensitive A. baumannii (ISAB, n = 10, 37%) and imipenem-resistant A. baumannii (IRAB, n = 17, 63%). There was a clear shift in the antibiogram of A. baumannii during the study period. From 2000 to 2003, all isolates were ISAB (n = 6). From 2005 to 2008, both IRAB (n = 5) and ISAB (n = 4) were isolated. However, from 2009, all isolates were IRAB (n = 12). Ten isolates were available for additional test and confirmed as IRAB. MLST analysis showed that among 10 isolates, sequence type 138 was predominant (n = 7). All 10 isolates were positive for OXA-23-like and OXA-51-like carbapenemase. Of 27 bacteremia patients, 11 were male (41%), the median age at bacteremia onset was 5.2 years (range, 0-18.6 years). In 33% (9/27) of patients, A. baumannii was isolated from tracheal aspirate prior to development of bacteremia (median, 8 days; range, 5-124 days). The overall case-fatality rate was 63% (17/27) within 28 days. There was no statistical difference in the case fatality rate between ISAB and IRAB groups (50% vs. 71%; P = 0.422).

CONCLUSION

IRAB bacteremia causes serious threat in patients in PICU. Proactive infection control measures and antimicrobial stewardship are crucial for managing IRAB infection in PICU.

Colistin resistance in Acinetobacter baumannii isolated from critically ill patients: clinical characteristics, antimicrobial susceptibility and outcome

Background

Acinetobacter baumannii (AB) is increasingly becoming a clinically relevant organism due to the rising number of associated nosocomial infections. The therapeutic options are extremely minimal because of its ability to develop resistance to all available antimicrobials, including colistin (CST). Data on the clinical and microbiological characteristics of colistin-resistant A. baumannii infections remain scarce to date.

Methods

In this prospective study, clinical isolates of colistin resistance among Acinetobacter strain was evaluated from the database of Microbiology Laboratory of King Khalid University Hospital, Saudi Arabia.

Results

In a total of 142 patients with 136 Acinetobacter isolates, Acintobacter baumannii was the predominant serotype 73% of the isolates and Acinetobacter lwoffii constituted 27% of the isolate . There was 8.5% colistin resistant isolates with colistin E-test MIC >4. The clinical characteristics were determined for colistin resistant Acinetobacter baumannii. All patients were critically ill and 64% of them were hositalized in the Intensive Care Unit (ICU). All patients have been previously given antibiotics. Other associated clinical characteristics included; morbid obesity and sleeve gastrectomy (21 %), mechanical ventilation and central venous catheter (50%). High mortality rate was found(28%).

Conclusion

There is an increase of colistin resistance among clinical isolates of Acinetobacter baumannii causing serious infections especially in critically ill patients.

In vitro activities of ceftazidime/avibactam alone or in combination with antibiotics against multidrug-resistant Acinetobacter baumannii isolates

OBJECTIVES

Infections caused by multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) are a growing problem because of the limited options for treatment. The number of antimicrobials that are currently being developed is still insufficient to control this global threat. Combination therapies of antibiotics with different antimicrobial mechanisms have been proposed as the best options for treating MDR A. baumannii infections. The objective of this study was to investigate the in-vitro effectiveness of ceftazidime/avibactam alone or in combination with antibiotics against MDR A. baumannii isolates using time-kill assays.

METHODS

Forty clinical MDR strains were screened, and minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of ceftazidime/avibactam, colistin, levofloxacin, meropenem, tigecycline, and tobramycin were determined by microbroth dilution method. The in-vitro synergistic activities of ceftazidime/avibactam with antibiotic combinations were determined by time-kill assays at 1× MIC and 4× MIC against five MDR A. baumannii isolates.

RESULTS

Based on MIC results, all isolates of A. baumannii were resistant to ceftazidime/avibactam, except for AB-5. All isolates were found to be resistant to meropenem and levofloxacin. At 4× MIC, all of the tested antibiotics showed bactericidal effect (≥3log₁₀killing). The synergistic activities of ceftazidime/avibactam+colistin, ceftazidime/avibactam+tobramycin and ceftazidime/avibactam+tigecycline combinations at 1× MIC were observed against studied 5/5, 4/5 and 4/5 strains, respectively. Furthermore, all of the tested combinations at 4× MIC were additive at 24h. No antagonism was observed.

CONCLUSIONS

The findings of this study suggest that a significant bactericidal effect was seen with all tested combinations. These findings present significant implications for antibiotic choice for the treatment of infections caused by MDR A. baumannii.

Antibiotic-resistant clones in Gram-negative pathogens: presence of global clones in Korea

Antibiotic resistance is a global concern in public health. Antibiotic-resistant clones can spread nationally, internationally, and globally. This review considers representative antibiotic-resistant Gram-negative bacterial clones-CTX-M- 15-producing ST131 in Escherichia coli, extended-spectrum ß-lactamase-producing ST11 and KPC-producing ST258 in Klebsiella pneumoniae, IMP-6-producing, carbapenem-resistant ST235 in Pseudomonas aeruginosa, and OXA-23-producing global clone 2 in Acinetobacter baumannii-that have disseminated worldwide, including in Korea. The findings highlight the urgency for systematic monitoring and international cooperation to suppress the emergence and propagation of antibiotic resistance.

Detection of ISAba1 in association with a novel allelic variant of the β-lactamase ADC-82 and class D β-lactamase genes mediating carbapenem resistance among the clinical isolates of MDR A. baumannii

PURPOSE

The objective of the present study is to investigate the diverse resistance determinants, their association with insertion sequence mobile elements and predilection of a particular clone for such associations in Acinetobacter baumannii.

METHODOLOGY

Fifty-four consecutive isolates collected during 2011-2012 from a tertiary care hospital were subjected to susceptibility testing followed by PCR screening of commonly reported β-lactamases and 16S rRNA methyltransferase encoding genes. The integrity of resistance-nodulation-cell division efflux pump-related genes in their respective operons was also investigated.

RESULTS

β-Lactamase genes such as blaADC (100 %), blaOXA-23 (81 %), blaPER-1 (81 %), blaIMP-1 (31 %) and blaNDM-1 (15 %) were found to be present more frequently while blaVIM-2 and blaOXA-24 were not observed in our study population. ISAba1 was associated only with blaOXA-51-like like (30 %), blaOXA-23-like (55 %) and blaADC-like (33 %). armA was found in 87 % of isolates and ISAba1 linked with one novel variant of ADC, namely blaADC-82, which was identified to have 15 nucleotide differences with blaADC-79, and this finding is of much significance. In many isolates, efflux pump genes were not intact, resulting in severely altered effluxing functions. For the first time, we have identified ISAba1-mediated disruption of adeN among the isolates of ST 195B, which would have led to overexpression of AdeIJK efflux pump causing elevated resistance. Multilocus sequence typing revealed the predominance of CC 92B (IC-IIB) and CC 447B clonal complexes.

CONCLUSION

High incidence of IC-II clones, novel resistance determinants (ADC-82) and elevated resistance mediated by ISAba1 reported here will be of enormous importance while assessing the emergence of extremely resistant A. baumannii in India.

Resistance to polymyxins in Gram-negative organisms

Polymyxins have recently been re-introduced into the therapeutic arsenal to combat infections caused by multidrug-resistant Gram-negative bacteria. However, the emergence of strains resistant to these last-resort drugs is becoming a critical issue in a growing number of countries. Both intrinsic and transferable mechanisms of polymyxin resistance have been characterised. These mechanisms as well as the epidemiological data regarding four relevant bacterial pathogens (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa) are considered in this review. A special focus is made on plasmid-mediated resistance and the spread of mcr genes.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Rapid dissemination of colistin and carbapenem resistant Acinetobacter baumannii in Central Greece: mechanisms of resistance, molecular identification and epidemiological data

Background

Colistin-resistant/carbapenem-resistant Acinetobacter baumannii is a significant challenge for antibiotic treatment and infection control policies. Since 2012, in Central Greece an increase of colistin/pan- resistant A. baumannii has occurred, indicating the need for further analysis.

Methods

A total of 86 colistin-resistant/carbapenem-resistant out of 1228 A. baumannii clinical isolates, consecutively collected between 2012 and 2014 in a tertiary Greek hospital of Central Greece, as well as one environmental isolate from surveillance cultures were studied. Molecular typing and mechanisms of resistance to colistin and to carbapenems were assessed, whereas, epidemiological and clinical data of the patients were reviewed.

Results

During the study period, the rate of colistin resistance gradually increased and reached 21.1 % in 2014. All colistin-resistant/carbapenem-resistant A. baumannii belonged to 3LST ST101 clone that corresponds to the international clonal lineage II. Carbapenem resistance was associated with the presence of bla_oxa-23-like, while resistance to colistin probably correlated with G54E and R109H amino acid substitutions in PmrA and PmrC, respectively.

Conclusions

Epidemiological data of the patients indicated that the first detection of colistin-resistant/carbapenem-resistant ST101 clone in the University Hospital of Larissa (UHL) was associated with a patient who previously had received colistin, while, the movement of the infected patients into the hospital probably resulted to its spread.

In vitro synergism of combinations of colistin with selected antibiotics against colistin-resistant Acinetobacter baumannii

Aim: The in vitro activity of colistin in combination with sulbactam, netilmicin, and vancomycin against colistin-resistant A. baumannii strains was investigated. Furthermore, the clonal relationship of the strains was analyzed.

Methods: Clonal relationship was investigated using rep-PCR. To screen for synergysm, the fractional inhibitory concentration index (FICI) was calculated using checkerboard assay. The killing kinetics of the combination of colistin with vancomycin was assessed using time-kill assay.

Results: Three different clones were found among 10 clinical isolates of colistin-resistant A. baumannii strains. Thereof, 8 strains were susceptible to netilmicin. Synergistic interaction was detected in 1 strain with the combination of colistin-netilmicin, in 5 strains with colistin-sulbactam, and in 9 strains with colistin-vancomycin. None of combinations had antagonistic activity. Colistin-vancomycin combination resulted in rapid bactericidal activity.

Conclusion: These results show a distinct in vitro synergism between colistin and vancomycin, which might be useful to treat infection with multiple-resistant strains, prevent emergence of resistant strains, and to lower doses for both antibiotics to be used.

Structure of the extended-spectrum class C β-lactamase ADC-1 from Acinetobacter baumannii

ADC-type class C β-lactamases comprise a large group of enzymes that are encoded by genes located on the chromosome of Acinetobacter baumannii, a causative agent of serious bacterial infections. Overexpression of these enzymes renders A. baumannii resistant to various β-lactam antibiotics and thus severely compromises the ability to treat infections caused by this deadly pathogen. Here, the high-resolution crystal structure of ADC-1, the first member of this clinically important family of antibiotic-resistant enzymes, is reported. Unlike the narrow-spectrum class C β-lactamases, ADC-1 is capable of producing resistance to the expanded-spectrum cephalosporins, rendering them inactive against A. baumannii. The extension of the substrate profile of the enzyme is likely to be the result of structural differences in the R2-loop, primarily the deletion of three residues and subsequent rearrangement of the A10a and A10b helices. These structural rearrangements result in the enlargement of the R2 pocket of ADC-1, allowing it to accommodate the bulky R2 substituents of the third-generation cephalosporins, thus enhancing the catalytic efficiency of the enzyme against these clinically important antibiotics.

Spread of carbapenem-resistant Acinetobacter baumannii global clone 2 in Asia and AbaR-type resistance islands

In this surveillance study, we identified the genotypes, carbapenem resistance determinants, and structural variations of AbaR-type resistance islands among carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from nine Asian locales. Clonal complex 92 (CC92), corresponding to global clone 2 (GC2), was the most prevalent in most Asian locales (83/108 isolates; 76.9%). CC108, or GC1, was a predominant clone in India. OXA-23 oxacillinase was detected in CRAB isolates from most Asian locales except Taiwan. blaOXA-24 was found in CRAB isolates from Taiwan. AbaR4-type resistance islands, which were divided into six subtypes, were identified in most CRAB isolates investigated. Five isolates from India, Malaysia, Singapore, and Hong Kong contained AbaR3-type resistance islands. Of these, three isolates harbored both AbaR3- and AbaR4-type resistance islands simultaneously. In this study, GC2 was revealed as a prevalent clone in most Asian locales, with the AbaR4-type resistance island predominant, with diverse variants. The significance of this study lies in identifying the spread of global clones of carbapenem-resistant A. baumannii in Asia.

Co-existence of blaOXA-23 and armA in multidrug-resistant Acinetobacter baumannii isolated from a hospital in South Korea

The co-existence of carbapenemase, 16S rRNA methylase and mutated quinolone resistance-determining regions (QRDRs) can cause serious difficulty in treating infections with multidrug-resistant Acinetobacter baumannii. In this study, we aimed to determine the mechanisms of imipenem, amikacin and ciprofloxacin resistance in A. baumannii isolates with resistance to these antibiotics. A total of 31 non-duplicate isolates of amikacin- and ciprofloxacin-resistant Acinetobacter isolates were identified from April to August 2010 from a single hospital in South Korea. To assess the clonal relatedness of the 31 Acinetobacter isolates, multilocus sequence typing, network phylogenetic analysis and enterobacterial repetitive intergenic consensus-PCR were utilized. Detection of OXA-type carbapenemase and 16S rRNA methylase was conducted using a multiplex PCR assay. The QRDRs of the gyrA and parC genes were amplified and sequenced. The result showed that 30/31 isolates harboured the blaOXA-23-like carbapenemase, which made them resistant to imipenem (MICs ≥16 µg ml(-1)). Twenty-eight of the 31 isolates were found to possess armA, a 16S rRNA methylase gene, and showed resistance to amikacin, arbekacin, gentamicin and tobramycin (MICs >256 µg ml(-1)). All of the isolates were determined to carry QRDR mutations in both gyrA and parC: a Ser83Leu substitution in gyrA and a Ser80Leu substitution in parC, causing a ciprofloxacin MIC ≥64 µg ml(-1). In conclusion, A. baumannii with co-existence of carbapenemase, 16S rRNA methylase and mutated QRDRs are extremely prevalent in South Korea, which may cause serious problems in the treatment of A. baumannii infections using carbapenem, amikacin and ciprofloxacin.

Molecular and epidemiological characterization of carbapenem-resistant Acinetobacter baumannii in non-tertiary Korean hospitals

PURPOSE

The increasing prevalence and global spread of carbapenem-resistant Acinetobacter baumannii (A. baumannii) has become a serious problem. The aim of this study was to investigate molecular and epidemiological characteristics of carbapenem-resistant A. baumannii isolates collected from Korean non-tertiary hospitals.

MATERIALS AND METHODS

Thirty six non-duplicated carbapenem-resistant A. baumannii isolates were collected from 17 non-tertiary hospitals in Korea between 2004 and 2006. Isolates were typed by multilocus sequence typing and repetitive-sequence-based PCR (rep-PCR). Detection of genes encoding OXA carbapenemase and their relationship with ISAba1 was performed by PCR.

RESULTS

Two clones were prevalent among 36 isolates: ST69 (17 isolates, 47.2%) and ST92 (19 isolates, 52.8%). Rep-PCR patterns were diverse and revealed that all isolates were clustered into eight band patterns. The ISAba1-activated blaOXA-23-like and ISAba1-activated blaOXA-51-like genes were prevalent among the carbapenem- resistant A. baumannii isolates.

CONCLUSION

The class D β-lactamase genes of A. baumannii were distributed nationwide in non-tertiary Korean hospitals.

Lipopolysaccharide-deficient Acinetobacter baumannii shows altered signaling through host Toll-like receptors and increased susceptibility to the host antimicrobial peptide LL-37

Infections caused by multidrug-resistant Acinetobacter baumannii have emerged as a serious global health problem. We have shown previously that A. baumannii can become resistant to the last-line antibiotic colistin via the loss of lipopolysaccharide (LPS), including the lipid A anchor, from the outer membrane (J. H. Moffatt, M. Harper, P. Harrison, J. D. Hale, E. Vinogradov, T. Seemann, R. Henry, B. Crane, F. St. Michael, A. D. Cox, B. Adler, R. L. Nation, J. Li, and J. D. Boyce, Antimicrob. Agents Chemother. 54:4971-4977, 2010). Here, we show how these LPS-deficient bacteria interact with components of the host innate immune system. LPS-deficient A. baumannii stimulated 2- to 4-fold lower levels of NF-κB activation and tumor necrosis factor alpha (TNF-α) secretion from immortalized murine macrophages, but it still elicited low levels of TNF-α secretion via a Toll-like receptor 2-dependent mechanism. Furthermore, we show that while LPS-deficient A. baumannii was not altered in its resistance to human serum, it showed increased susceptibility to the human antimicrobial peptide LL-37. Thus, LPS-deficient, colistin-resistant A. baumannii shows significantly altered activation of the host innate immune inflammatory response.

Insights into the global molecular epidemiology of carbapenem non-susceptible clones of Acinetobacter baumannii

The global emergence of multidrug resistance (MDR) among Gram-negative bacteria has dramatically limited the therapeutic options. During the last two decades, Acinetobacter baumannii has become a pathogen of increased clinical importance due to its remarkable ability to cause outbreaks of infections and to acquire resistance to almost all currently used antibiotics, including the carbapenems. This review considers the literature on A. baumannii and data from multilocus sequence typing studies to explore the global population structure of A. baumannii and detect the occurrence of clonality, with the focus on the presence of specific resistance mechanisms such as the OXA-carbapenemases. The worldwide dissemination of MDR and carbapenem non-susceptible A. baumannii is associated with diverse genetic backgrounds, but predominated by a number of extensively distributed clones, such as CC92(B)/CC2(P) and CC109(B)/CC1(P), which have frequently been supplemented by acquired OXA-type carbapenemase genes.

Current epidemiology and growing resistance of gram-negative pathogens

In the 1980s, gram-negative pathogens appeared to have been beaten by oxyimino-cephalosporins, carbapenems, and fluoroquinolones. Yet these pathogens have fought back, aided by their membrane organization, which promotes the exclusion and efflux of antibiotics, and by a remarkable propensity to recruit, transfer, and modify the expression of resistance genes, including those for extended-spectrum β-lactamases (ESBLs), carbapenemases, aminoglycoside-blocking 16S rRNA methylases, and even a quinolone-modifying variant of an aminoglycoside-modifying enzyme. Gram-negative isolates--both fermenters and non-fermenters--susceptible only to colistin and, more variably, fosfomycin and tigecycline, are encountered with increasing frequency, including in Korea. Some ESBLs and carbapenemases have become associated with strains that have great epidemic potential, spreading across countries and continents; examples include Escherichia coli sequence type (ST)131 with CTX-M-15 ESBL and Klebsiella pneumoniae ST258 with KPC carbapenemases. Both of these high-risk lineages have reached Korea. In other cases, notably New Delhi Metallo carbapenemase, the relevant gene is carried by promiscuous plasmids that readily transfer among strains and species. Unless antibiotic stewardship is reinforced, microbiological diagnosis accelerated, and antibiotic development reinvigorated, there is a real prospect that the antibiotic revolution of the 20th century will crumble.

Molecular characterization of carbapenem-non-susceptible Acinetobacter spp. in Japan: predominance of multidrug-resistant Acinetobacter baumannii clonal complex 92 and IMP-type metallo-β-lactamase-producing non-baumannii Acinetobacter species

We conducted an epidemiological study concerning carbapenem-non-susceptible clinical isolates of Acinetobacter spp. in Japan by molecular procedures including carbapenemase gene identification and amplified ribosomal DNA restriction analysis. Among 598 clinically isolated Acinetobacter spp. in 2007, 27 (4.5%) were non-susceptible to carbapenems. Most carbapenem-non-susceptible Acinetobacter baumannii (13/14) belonged to clonal complex (CC) 92, harbored bla (OXA-51-like) genes, including novel bla (OXA-206), downstream of ISAba1, and were recovered mainly from the Kanto region. Carbapenem-non-susceptible A. baumannii CC92 isolates were further divided by pulsed-field gel electrophoresis into two groups, one of which was characterized by the presence of bla (OXA-23). One A. baumannii CC276 isolate carried bla (IMP-1) and bla (OXA-58). Almost all non-baumannii Acinetobacter isolates (12/13), including Acinetobacter pittii (formerly Acinetobacter genomic species 3) and Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU), produced IMP-type metallo-β-lactamases, and were recovered from various regions in Japan. This is the first report describing the nationwide molecular epidemiology of carbapenem-non-susceptible Acinetobacter spp. with genomic species-level identification in Japan.

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.

Changes in antimicrobial susceptibility and major clones of Acinetobacter calcoaceticus-baumannii complex isolates from a single hospital in Korea over 7 years

Acinetobacter species have emerged as opportunistic nosocomial pathogens in intensive care units. Epidemic spread and outbreaks of multidrug-resistant or carbapenem-resistant Acinetobacter baumannii infections have been described worldwide. Species distribution, antimicrobial resistance and genotypes were investigated for Acinetobacter species isolates collected from a single institution in Korea over 7 years. Two hundred and eighty-seven Acinetobacter species isolates were collected from patients with bloodstream infections in one Korean hospital from 2003 to 2010. Most of them belonged to the Acinetobacter calcoaceticus-baumannii complex (94.4 %). The most frequently isolated species was A. baumannii (44.2 %), followed by Acinetobacter nosocomialis (formerly Acinetobacter genomic species 13TU) (34.1 %). The proportion of A. baumannii increased significantly from 2008 to 2010 (40.4 to 50.0 %). From 2008, imipenem and meropenem resistance rates increased significantly compared with 2003-2007 (12.9 % and 20.5 %, respectively, to 41.4 % and 41.5 %, respectively). An increased carbapenem resistance rate between the two periods was identified more clearly amongst A. baumannii isolates. Polymyxin-resistant A. baumannii isolates emerged in 2008-2010, despite the availability of few isolates. The increase of carbapenem resistance in A. baumannii might be due to the substitution of main clones. Although ST92 and ST69 were the most prevalent clones amongst A. baumannii in 2003-2007 (47.8 % and 15.9 %, respectively), ST75 and ST138 had increased in 2008-2010 (39.7 % and 25.9 %, respectively). Although ST92 showed moderate resistance to carbapenems, most ST75 and ST138 isolates were resistant to carbapenems. All ST75 and ST138 isolates, but only one ST92 isolate, contained the bla(OXA-23-like) gene. Increased carbapenem resistance in Acinetobacter species and A. baumannii isolates might be due to the expansion of specific carbapenem-resistant clones.

Quantification and analysis of airborne bacterial characteristics in a nursing care institution

Indoor air quality has become a critical issue because people spend most of their time in the indoor environment. The factors that influence indoor air quality are very important to environmental sanitation and air quality improvement. This study focuses on monitoring air quality, colony counts, and bacteria species of the indoor air of a nursing care institution. The regular colony counts in two different wards range from 55 to 600 cfu m(-3) Regression analysis results indicate that the bacterial colony counts have close correlation with relative humidity or carbon dioxide (CO2) but not with carbon monoxide (CO) or ozone (O3). Real-time PCR was used to quantify the bacterial pathogens of nosocomial infection, including Acinetobacter baumannii, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae, and methicillin-sensitive Staphylococcus aureus. The most abundant bacteria species in the air of the nursing care institution is E. coli.

PER-7, an extended-spectrum beta-lactamase with increased activity toward broad-spectrum cephalosporins in Acinetobacter baumannii

Acinetobacter baumannii isolate AP2 was recovered from a bronchial lavage sample of a patient hospitalized in Paris, France. A. baumannii AP2 was resistant to all β-lactams, including carbapenems, and expressed the extended-spectrum β-lactamase (ESBL) PER-7, which differs from PER-1 by 4 amino acid substitutions. Compared to PER-1, PER-7 possessed higher-level hydrolytic activities against cephalosporins and aztreonam. The blaPER-7 gene was chromosomally located and associated with a mosaic class 1 integron structure. Additionally, isolate AP2 expressed the carbapenem-hydrolyzing oxacillinase OXA-23 and the 16S RNA methylase ArmA, conferring high-level resistance to aminoglycosides.

Emergence of OXA-carbapenemase- and 16S rRNA methylase-producing international clones of Acinetobacter baumannii in Norway

This study was designed to investigate the molecular epidemiology and antibiotic-resistance characteristics of 11 carbapenem-resistant clinical isolates of Acinetobacter baumannii obtained in Norway between 2004 and 2009. Interestingly, all the isolates were linked with recent hospitalization outside Norway. The epidemiological status was investigated by multilocus sequence typing (MLST), multiplex PCR assays for major international clones, typing of blaOXA-51-like variants and PFGE. The genotypic-resistance characteristics, including the occurrence of OXA-carbapenemase-encoding and 16S rRNA methylase-encoding genes and class 1 integrons, were investigated by PCR assays and sequencing. Seven isolates were found to harbour blaOXA-66 and belong to MLST clonal complexes (CCs) CC2P (Pasteur Institute scheme) and CC92B (Bartual scheme), and international clone II. One isolate harboured blaOXA-69, and belonged to CC1P, CC109B and international clone I. Two isolates belonged to sequence group 9, probably a subgroup of international clone I, and one isolate belonged to sequence group 4, a proposed novel international clone. All isolates contained an acquired OXA-carbapenemase-encoding gene: blaOXA-23-like (n=9), blaOXA-24-like (n=1) and blaOXA-58-like (n=1). Four isolates with high-level aminoglycoside-resistance contained the 16S rRNA methylase-encoding armA gene. Class 1 integrons with six different variable regions were detected. Sequence analysis of gene cassettes identified four aminoglycoside (aacA4, aac(6')-Im, aadA1 and aacC1), two chloramphenicol (catB8 and cm1A5), one β-lactamase (blaOXA-20) and one rifampicin (arr-2) resistance gene in various combinations. In conclusion, the occurrence of A. baumannii isolates producing OXA carbapenemase and 16S rRNA methylase in Norway was related to the worldwide distribution of international clones I and II, and the emergence of novel international clones.

A single clone of Acinetobacter baumannii, ST22, is responsible for high antimicrobial resistance rates of Acinetobacter spp. isolates that cause bacteremia and urinary tract infections in Korea

We investigated the characteristics of a total of 96 Acinetobacter spp. isolates that were shown to cause bacteremia and urinary tract infections (UTIs) from 10 university hospitals located in various regions of Korea from November 2006 to August 2007. The antimicrobial susceptibilities of these isolates were determined using a broth microdilution method, and the species were identified using molecular identification. In addition, we performed multilocus sequence typing for Acinetobacter baumannii subgroup A isolates. A. baumannii subgroup A was the most prevalent in patients with both bacteremia (32 isolates, 53.3%) and UTIs (20 isolates, 55.6%), followed by Acinetobacter genomic species 13TU (15.0% and 27.8% in bacteremia and UTIs, respectively). A. baumannii subgroup B and Acinetobacter junii were found exclusively in isolates causing bacteremia (seven and five isolates, respectively). Among 96 Acinetobacter spp. isolates, 19.8% were resistant to imipenem and 25.0% were resistant to meropenem. Most carbapenem-resistant A. baumannii isolates contained PER or oxacillinase-23-like enzymes (65.2% and 78.3%, respectively). In addition, 13.5% were resistant to polymyxin B and 17.7% were resistant to colistin. A. baumannii subgroup A isolates (52 isolates, 54.2%) showed higher resistance rates to most antimicrobial agents than other species, but not to colistin. Among A. baumannii subgroup A isolates, ST22 was the most prevalent genotype (33 isolates, 63.5%) and showed higher resistance rates to all antimicrobial agents than the other genotypes. In addition, four out of five polymyxin-resistant A. baumannii group A isolates belonged to ST22. Thus, dissemination of the main clone of A. baumannii, ST22, may contribute to the high resistance rates of Acinetobacter isolates to antimicrobials, including carbapenems, in Korea.

Colistin resistance in Acinetobacter baumannii is mediated by complete loss of lipopolysaccharide production

Infections caused by multidrug-resistant (MDR) Gram-negative bacteria represent a major global health problem. Polymyxin antibiotics such as colistin have resurfaced as effective last-resort antimicrobials for use against MDR Gram-negative pathogens, including Acinetobacter baumannii. Here we show that A. baumannii can rapidly develop resistance to polymyxin antibiotics by complete loss of the initial binding target, the lipid A component of lipopolysaccharide (LPS), which has long been considered to be essential for the viability of Gram-negative bacteria. We characterized 13 independent colistin-resistant derivatives of A. baumannii type strain ATCC 19606 and showed that all contained mutations within one of the first three genes of the lipid A biosynthesis pathway: lpxA, lpxC, and lpxD. All of these mutations resulted in the complete loss of LPS production. Furthermore, we showed that loss of LPS occurs in a colistin-resistant clinical isolate of A. baumannii. This is the first report of a spontaneously occurring, lipopolysaccharide-deficient, Gram-negative bacterium.

Molecular epidemiology of multidrug-resistant Acinetobacter baumannii in a single institution over a 10-year period

Multidrug-resistant Acinetobacter baumannii is a worldwide nosocomial menace. We sought to better understand its behavior through studying the molecular epidemiology of this organism at the Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia, over a 10-year period. Multilocus sequence typing (MLST), semiautomated repetitive sequence-based PCR (rep-PCR), and pulsed-field gel electrophoresis (PFGE) were performed on a selection of 31 A. baumannii isolates collected over the 10-year period to determine their relationships to one another. MLST also allowed us to put this information in a global context. The presence or absence of bla(OXA-23) was also established. The presence of bla(OXA-23) closely correlated with carbapenem resistance in our collection. Sequence type 92 (ST92) was the dominant sequence type and was present in the hospital for 9 years. There was also evidence of the spread of ST69, ST73, and ST125 (novel) within the hospital, but this was not sustained over long periods. There were only single examples of the novel sequence types ST126 and ST127. The different typing methods clustered the isolates similarly; however, PFGE and rep-PCR were more discriminatory than MLST. Worldwide, ST92 and the associated clonal complex 92 represent the most sampled and widespread sequence type(s) and are also known as European clone 2 and worldwide clonal lineage 2. Antibiotic susceptibility within ST92 is variable, suggesting a role for mechanisms other than antibiotic resistance in its success.

Wide dissemination of OXA-23-producing carbapenem-resistant Acinetobacter baumannii clonal complex 22 in multiple cities of China

OBJECTIVES

In this study, multilocus sequence typing (MLST) was used to describe the genetic backgrounds of carbapenem-resistant Acinetobacter baumannii (CRAB) and carbapenem-susceptible A. baumannii (CSAB) from multiple cities of China.

METHODS

One hundred and fifty-two CRAB and 74 CSAB isolates obtained from 16 cities of China were selected for molecular characterization by MLST. eBURST was used to cluster sequence types (STs) into clonal complex (CCs) and infer evolutionary descent. PCR was used to detect carbapenemase-encoding genes and bla(AmpC) with the upstream element ISAba1.

RESULTS

CSAB showed more diverse genetic backgrounds than CRAB since 36 distinct STs were identified in CSAB while only 8 STs were identified in CRAB. ST22 and its three single-locus variants, all clustered into CC22, were the most prominent STs, accounting for 86.8% of CRAB and 45.9% of CSAB, distributed in all 16 cities and possessing more noticeable antibiotic resistance than other STs. PCR amplification was positive for bla(OXA-23) in most CRAB isolates but negative in CSAB isolates. The presence of ISAba1 upstream of bla(AmpC) was variable in distinct STs of CRAB. eBURST reveals that CC22 is the largest group in the Pubmlst database, which also contains ST6 previously identified in a European clone II isolate as a member of a subgroup of CC22.

CONCLUSIONS

We describe the wide dissemination of CRAB CC22 in China. The close relatedness between CC22 and European clone II implies the probable global spread of CC22. It is inferred that ST22-CSAB evolves to ST22-CRAB through acquiring bla(OXA-23) as a determinative factor.

Worldwide dissemination of the blaOXA-23 carbapenemase gene of Acinetobacter baumannii

To assess dissemination of OXA-23-producing strains of Acinetobacter baumannii, we obtained 20 carbapenem-resistant, OXA-23-producing isolates from different regions. Their clonal relationship was assessed by pulsed-field gel electrophoresis and multilocus sequence typing. We identified 8 sequence types, including 4 novel types. All except 2 strains belonged to 2 main European clonal lineages. The blaOXA-23 gene was either located on the chromosome or on plasmids and associated with 4 genetic structures.