The Distribution of Carbapenem-Resistant Acinetobacter Species and High Prevalence of CC92 OXA-23-Producing Acinetobacter Baumannii in Community Hospitals in South Korea.

Background: Clinical isolates of Acinetobacter species in South Korea are continuously exhibiting high rates of antimicrobial resistance to carbapenems, indicating that there are public health concerns among both healthcare-associated infections and community-associated infections. The aim of this study was to describe the prevalence and characteristics of carbapenem-resistant Acinetobacter isolates originating from community hospitals. Materials and Methods: A total of 817 non-duplicated Acinetobacter species were isolated from December 2022 to July 2023 at long-term care facilities and general hospitals in 16 regions geographically distributed throughout South Korea. Bacterial identification and antimicrobial susceptibility testing were performed using the VITEK-2 system. The bacteria were identified as Acinetobacter baumannii by blaOXA-51 PCR and as non-baumannii Acinetobacter species by rpoB sequence analysis. The carbapenem resistance genes (OXA-23, OXA-48, OXA-58, IMP, VIM, NDM, GES, and KPC) were identified via PCR and sequencing. The genetic relatedness of carbapenem-resistant A. baumannii (CRAB) isolates was assessed by multilocus sequence typing. Results: A total of 659 A. baumannii and 158 non-baumannii Acinetobacter isolates, comprising 19 different species, were identified in all 16 regions. The carbapenem resistance rate was 87.4% (n=576) for the A. baumannii isolates, and all the strains produced blaOXA-23. For non-baumannii Acinetobacter, the rate of carbapenem resistance was 8.9% (n=14); this resistance was primarily caused by blaOXA-23 (n=9), followed by blaNDM-1 (n=3) and blaVIM-2 (n=2). Of the 576 CRAB isolates, clonal complex 92 (CC92) was the predominant genotypes, followed by sequence type 229 (ST229), ST373, ST397, ST447, and ST620. Conclusion: Our results showed the distribution of Acinetobacter species and showed that CC92 CRAB clinical isolates with widespread production of blaOXA-23 were predominant in community hospitals. Our findings suggest that there is a need for urgent and effective methods to reduce carbapenem resistance in A. baumannii in South Korea.

Antibacterial effect of singlet oxygen depending on bacteria surface charge.

Here, we investigated the bactericidal effects of two types of photoinduced reactive oxygen species (ROS), superoxide anion and singlet oxygen, on bacteria with distinct surface charges. We fabricated photofunctional polymer films (PFPFs) capable of generating both types of ROS, and they were subjected to photodynamic inactivation tests for 12 various strains of Acinetobacter baumannii. The results showed that the type I ROS (superoxide anion) was significantly dependent on the surface charge of the bacteria owing to charge-charge repulsion, while the type II ROS (singlet oxygen) was independent of the surface charge of the bacteria. These results could be significant in enhancing treatment efficiency in the clinical field.

Evaluation of Modified Sequential Multiplex PCR for Streptococcus pneumoniae Serotyping.

The aims of this study were to develop modified sequential multiplex PCR (SM-PCR) primer sets and to evaluate their ability and efficiency for serotype determination. We selected target serotypes for SM-PCR testing according to serotype prevalence as reported in Asian publications. The modified SM-PCR consisted of 6 groups of PCR reactions, and each reaction was performed using 5 primer pairs. We evaluated the efficiency and performance of this modified multiplex PCR using 378 pneumococcal strains by comparing the findings with the results of the Quellung reaction. A total of 30 primer pairs were used in a consecutive set of 6 reactions. All results were concordant with those of the Quellung reaction and there was no cross-reactivity to unintended serotypes. We could identify the final serotypes of 370 isolates (97.9%). The coverage rates of modified SM-PCR were 42.6%, 65.9%, and 79.4% in reactions1, 2, and 3, respectively. The modified SM-PCR showed acceptable performance for detecting pneumococcal serotypes and can serve as useful alternative to the Quellung reaction.

Emergence of IMP-4-Producing Enterobacter aerogenes Clinical Isolate.

BACKGROUND: IMP-4 class B metallo-ß-lactamase-producing Enterobacteriaceae are resistant to carbapenems. The aim of this study was to characterize of IMP-4 metallo-ß-lactamase (MBL)-producing Enterobacter aerogenes clinical isolate. METHODS: IMP-4 MBL-producing E. aerogenes clinical isolate was collected from a Korean Hospital in 2017. Antimicrobial susceptibility was determined by disk diffusion methods. Further, minimum inhibitory concentrations of ß-lactams were determined by Etest. Detection of bla genes was performed by PCR. The genetic organization of class 1 integron carrying the MBL gene cassette was investigated by PCR mapping and sequencing. RESULTS: E. aerogenes strain YN170501 exhibited resistance to penicillins, cephalosporins, and carbapenems and was susceptible to monobactam, aminoglycosides, fluoroquinolone, tigecycline, and trimethoprim-sulfamethoxazole. The blaIMP-4 gene was located in class 1 integron. CONCLUSIONS: The blaIMP-4 gene has never been reported in Enterobacter aerogenes clinical isolate from Korea.

Extensively Drug-Resistant Escherichia coli Sequence Type 1642 Carrying an IncX3 Plasmid Containing the blaKPC-2 Gene Associated with Transposon Tn4401a.

BACKGROUND: Extensively drug-resistant (XDR) Enterobacteriaceae carrying the bla(KPC) gene have emerged as a major global therapeutic concern. The purpose of this study was to analyze the complete sequences of plasmids from KPC-2 carbapenemase-producing XDR Escherichia coli sequence type (ST) 1642 isolates. METHODS: We performed antimicrobial susceptibility testing, PCR, multilocus sequence typing (MLST), and whole-genome sequencing to characterize the plasmid-mediated KPC-2-producing E. coli clinical isolates. RESULTS: The isolates were resistant to most available antibiotics, including meropenem, ampicillin, ceftriaxone, gentamicin, and ciprofloxacin, but susceptible to tigecycline and colistin. The isolates were identified as the rare ST1642 by MLST. The isolates carried four plasmids: the first 69-kb conjugative IncX3 plasmid harbors bla(KPC-2) within a truncated Tn4401a transposon and bla(SHV-11) with duplicated conjugative elements. The second 142-kb plasmid with a multireplicon consisting of IncQ, IncFIA, and IncIB carries bla(TEM-1b) and two class 1 integrons. This plasmid also harbors a wide variety of additional antimicrobial resistance genes including aadA5, dfrA17, mph(A), sul1, tet(B), aac(3')-IId, strA, strB, and sul2. CONCLUSIONS: The complete sequence analysis of plasmids from an XDR E. coli strain related to persistent infection showed the coexistence of a bla(KPC-2)-carrying IncX3-type plasmid and a class 1 integron-harboring multireplicon, suggesting its potential to cause outbreaks. Of additional clinical significance, the rare ST1642, identified in a cat, could constitute the source of human infection.

Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options.

Acinetobacter baumannii is undoubtedly one of the most successful pathogens responsible for hospital-acquired nosocomial infections in the modern healthcare system. Due to the prevalence of infections and outbreaks caused by multi-drug resistant A. baumannii, few antibiotics are effective for treating infections caused by this pathogen. To overcome this problem, knowledge of the pathogenesis and antibiotic resistance mechanisms of A. baumannii is important. In this review, we summarize current studies on the virulence factors that contribute to A. baumannii pathogenesis, including porins, capsular polysaccharides, lipopolysaccharides, phospholipases, outer membrane vesicles, metal acquisition systems, and protein secretion systems. Mechanisms of antibiotic resistance of this organism, including acquirement of ß-lactamases, up-regulation of multidrug efflux pumps, modification of aminoglycosides, permeability defects, and alteration of target sites, are also discussed. Lastly, novel prospective treatment options for infections caused by multi-drug resistant A. baumannii are summarized.

Molecular Characteristics of First IMP-4-Producing Enterobacter cloacae Sequence Type 74 and 194 in Korea.

The worldwide dissemination of carbapenemase-producing Enterobacteriaceae (CPE) has become a major therapeutic concern in clinical settings. Enterobacter cloacae is a major pathogen that causes serious hospital-acquired infections. We investigated the clinical characteristics and molecular mechanisms of the first IMP-4-producing E. cloacae clinical isolates in Korea. Five carbapenemase-producing E. cloacae strains out of 792 E. cloacae clinical isolates, which have been identified at a university hospital in Korea between March 2014 and February 2016, were included in this study. Antimicrobial susceptibilities to imipenem, meropenem, and ertapenem were tested using E-test. Carbapenemase determinant screening, genetic environment, and multilocus sequence typing were conducted using PCR and sequencing analysis. All isolates were not susceptible to at least one of the tested carbapenems and presented highly similar pulsed-field gel electrophoresis (PFGE) patterns, evidencing hospital-wide clonal dissemination. Among all isolates harboring the blaIMP-4 carbapenemase gene, four isolates identified as predominant ST74, also contained blaCMY-2. One strain, designated as rare ST194, carried blaCMY-1. The E. cloacae strain, harboring both blaIMP-4 and blaCMY-1, was resistant to all three tested carbapenems. The blaIMP-4 gene was located on a highly mobile class 1 integron, showing a new form of the blaIMP-4-qacG-aacA4 array. This is the first description of IMP-4-producing E. cloacae strains in Korea. This observation implicates the widespread of blaIMP-4 in Enterobacteriaceae clinical isolates and provides insights into the epidemic potential and clinical therapeutic importance of IMP-4-producing E. cloacae for healthcare-associated infections.

Serotype Distribution and Antimicrobial Resistance of Streptococcus pneumoniae Isolates Causing Invasive and Noninvasive Pneumococcal Diseases in Korea from 2008 to 2014.

Introduction. Streptococcus pneumoniae is an important pathogen with high morbidity and mortality rates. The aim of this study was to evaluate the distribution of common serotypes and antimicrobial susceptibility of S. pneumoniae in Korea. Methods. A total of 378 pneumococcal isolates were collected from 2008 through 2014. We analyzed the serotype and antimicrobial susceptibility for both invasive and noninvasive isolates. Results. Over the 7 years, 3 (13.5%), 35 (10.8%), 19A (9.0%), 19F (6.6%), 6A (6.1%), and 34 (5.6%) were common serotypes/serogroups. The vaccine coverage rates of PCV7, PCV10, PCV13, and PPSV23 were 21.4%, 23.3%, 51.9%, and 62.4% in all periods. The proportions of serotypes 19A and 19F decreased and nonvaccine serotypes increased between 2008 and 2010 and 2011 and 2014. Of 378 S. pneumoniae isolates, 131 (34.7%) were multidrug resistant (MDR) and serotypes 19A and 19F were predominant. The resistance rate to levofloxacin was significantly increased (7.2%). Conclusion. We found changes of pneumococcal serotype and antimicrobial susceptibility during the 7 years after introduction of the first pneumococcal vaccine. It is important to continuously monitor pneumococcal serotypes and their susceptibilities.

Identification of Acinetobacter Species Using Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry.

BACKGROUND: Acinetobacter baumannii has a greater clinical impact and exhibits higher antimicrobial resistance rates than the non-baumannii Acinetobacter species. Therefore, the correct identification of Acinetobacter species is clinically important. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has recently become the method of choice for identifying bacterial species. The purpose of this study was to evaluate the ability of MALDI-TOF MS (Bruker Daltonics GmbH, Germany) in combination with an improved database to identify various Acinetobacter species. METHODS: A total of 729 Acinetobacter clinical isolates were investigated, including 447 A. baumannii, 146 A. nosocomialis, 78 A. pittii, 18 A. ursingii, 9 A. bereziniae, 9 A. soli, 4 A. johnsonii, 4 A. radioresistens, 3 A. gyllenbergii, 3 A. haemolyticus, 2 A. lwoffii, 2 A. junii, 2 A. venetianus, and 2 A. genomospecies 14TU. After 212 isolates were tested with the default Bruker database, the profiles of 63 additional Acinetobacter strains were added to the default database, and 517 isolates from 32 hospitals were assayed for validation. All strains in this study were confirmed by rpoB sequencing. RESULTS: The addition of the 63 Acinetobacter strains' profiles to the default Bruker database increased the overall concordance rate between MALDI-TOF MS and rpoB sequencing from 69.8% (148/212) to 100.0% (517/517). Moreover, after library modification, all previously mismatched 64 Acinetobacter strains were correctly identified. CONCLUSIONS: MALDI-TOF MS enables the prompt and accurate identification of clinically significant Acinetobacter species when used with the improved database.

Detection of Carbapenemases in Clinical Enterobacteriaceae Isolates Using the VITEK AST-N202 Card.

BACKGROUND: The rapid and accurate detection of carbapenemase-producing Enterobacteriaceae (CPE) in clinical microbiology laboratories is essential for the treatment and control of infections caused by these microorganisms. This study was performed to evaluate the ability of the VITEK AST-N202 card to detect CPE isolates. MATERIALS AND METHODS: A total of 43 (Klebsiella pneumoniae, n = 37; Escherichia coli, n = 3; and Enterobacter cloacae, n = 3) CPE isolates and 79 carbapenemase-non-producing Enterobacteriaceae (CNE) isolates were included in this study. The CPE isolates harbored KPC-2 (n = 11), KPC-3 (n = 20), GES-5 (n = 5), VIM-2 (n = 2), IMP-1 (n = 1), NDM-1 (n = 2), or OXA-232 (n = 2). Of the 79 CNE isolates, eight K. pneumoniae isolates were resistant to ertapenem, imipenem, and meropenem, while the remaining 71 isolates were susceptible to the carbapenems. Antimicrobial susceptibilities were tested using the VITEK AST-N202 card, and the results were interpreted as positive when the isolates showed resistant or intermediate results. Modified-Hodge tests (MHTs) were performed using ertapenem or meropenem disks for the screening of carbapenemase production. Polymerase chain reaction (PCR) and direct sequencing were used to identify ß-lactamase genes. RESULTS: Sensitivity of MHT with ertapenem and meropenem disks for the detection of carbapenemase was 81.4% (35/43) and 81.4% (35/43), respectively, and a combination with both antibiotic disks increased the sensitivity to 88.4% (38/43). Specificity of the MHT was 100% (79/79) for the CNE isolates. Sensitivity of ertapenem, imipenem, and meropenem as assessed by the VITEK AST-N202 card was 100% (43/43), 93% (40/43), and 95.3% (41/43), respectively. Specificity (89.8%, 71/79) of the test with each carbapenem was improved to 100% (71/71) when eight carbapenem-resistant CNE isolates were excluded from the testing. CONCLUSION: The VITEK AST-N202 card showed high sensitivity for the detection of carbapenemases in Enterobacteriaceae strains. PCR and sequencing experiments for the detection of carbapenemases are recommended when clinical Enterobacteriaceae isolates show non-susceptibility to carbapenems.

Epidemiology and Characteristics of Metallo-ß-Lactamase-Producing Pseudomonas aeruginosa.

Metallo-ß-lactamase-producing Pseudomonas aeruginosa (MPPA) is an important nosocomial pathogen that shows resistance to all ß-lactam antibiotics except monobactams. There are various types of metallo-ß-lactamases (MBLs) in carbapenem-resistant P. aeruginosa including Imipenemase (IMP), Verona integron-encoded metallo-ß-lactamase (VIM), Sao Paulo metallo-ß-lactamase (SPM), Germany imipenemase (GIM), New Delhi metallo-ß-lactamase (NDM), Florence imipenemase (FIM). Each MBL gene is located on specific genetic elements including integrons, transposons, plasmids, or on the chromosome, in which they carry genes encoding determinants of resistance to carbapenems and other antibiotics, conferring multidrug resistance to P. aeruginosa. In addition, these genetic elements are transferable to other Gram-negative species, increasing the antimicrobial resistance rate and complicating the treatment of infected patients. Therefore, it is essential to understand the epidemiology, resistance mechanism, and molecular characteristics of MPPA for infection control and prevention of a possible global health crisis. Here, we highlight the characteristics of MPPA.

In Vivo Selection of Pan-Drug Resistant Acinetobacter baumannii during Antibiotic Treatment.

PURPOSE: Colistin resistance in Acinetobacter baumannii (A. baumannii) is mediated by a complete loss of lipopolysaccharide production via mutations in lpxA, lpxC, and lpxD gene or lipid A modifications via mutations in the pmrA and pmrB genes. However, the exact mechanism of therapy-induced colistin resistance in A. baumannii is not well understood. MATERIALS AND METHODS: We investigated the genotypic and phenotypic changes that underlie pan-drug resistance mechanisms by determining differences between the alterations in extensively drug-resistant (XDR) A. baumannii (AB001 and AB002) isolates and a pan-drug resistant (PDR) counterpart (AB003) recovered from one patient before and after antibiotic treatment, respectively. RESULTS: All three clinical isolates shared an identical sequence type (ST138), belonging to the global epidemic clone, clonal complex 92, and all produced OXA-23 carbapenemase. The PDR AB003 showed two genetic differences, acquisition of armA gene and an amino acid substitution (Glu229Asp) in pmrB gene, relative to XDR isolates. No mutations were detected in the pmrA, pmrC, lpxA, lpxC, or lpxD genes in all three isolates. In matrix-assisted laser desorption ionization-time of flight analysis, the three isolates commonly showed two major peaks at 1728 m/z and 1912 m/z, but peaks at 2034 m/z, 2157 m/z, 2261 m/z, and 2384 m/z were detected only in the PDR A. baumannii AB003 isolate. CONCLUSION: Our results show that changes in lipid A structure via a mutation in the pmrB gene and acquisition of armA gene might confer resistance to colistin and aminoglycosides to XDR A. baumannii strains, resulting in appearance of a PDR A. baumannii strain of ST138.

Characteristics of Metallo-ß-Lactamase-Producing Pseudomonas aeruginosa in Korea.

BACKGROUND: The aim of this study was to investigate the molecular epidemiological characteristics of metallo-ß-lactamase (MBL)-producing Pseudomonas aeruginosa clinical isolates in Korea. MATERIALS AND METHODS: Three hundred and twenty nine P. aeruginosa clinical isolates were collected from 23 general hospitals in Korea from March to June 2014. Species were identified by matrix-assited laser desorption/ionization-time of flight and 16S rRNA sequencing. Antimicrobial susceptibility was determined by disk diffusion methods. Further, minimum inhibitory concentrations of carbapenems were determined by Etest. Polymerase chain reaction and sequencing were performed to identify genes encoding MBLs. Multi-locus sequence typing and pulsed-field gel electrophoresis were performed to determine epidemiological characteristics of MBL-producing P. aeruginosa isolates. RESULTS: Of the 329 isolates, 229 (69.6%) were susceptible to the carbapenems tested, including imipenem and meropenem; while 100 (30.4%) were non-susceptible to more than one of the carbapenems. Genes encoding imipenemase-6 (IMP-6) and Verona imipenemase-2 (VIM-2) MBLs were identified in 21 (6.4%) isolates (n = 17 and 4, respectively). All MBL-producing isolates showed multi-drug resistant phenotype, and a majority (n = 19) of the isolates were identified as sequence type 235 (ST235). The remaining isolates (n = 2) were identified as ST309 and ST463. CONCLUSION: P. aeruginosa ST235 might play an important role in dissemination of MBL genes in Korea.

Evaluation of peptide nucleic acid-mediated multiplex real-time PCR kits for rapid detection of carbapenemase genes in gram-negative clinical isolates.

The emergence of clinical isolates of carbapenemase-producing microbes confers multidrug-resistance to these bacteria and renders them difficult to treat. This study was performed to evaluate peptide nucleic acid (PNA) probe-based multiplex real-time PCR kits used to detect carbapenemase genes. In total, 324 carbapenemase genes, collected from 318 gram-negative clinical isolates in 36 different hospital laboratories, were assayed to evaluate multiplex real-time PCR kits (PANAGENE; Daejeon, Korea). The nine most prevalent carbapenemase genes (KPC, OXA-48, GES, IMP, VIM, NDM, ISAba1-OXA-51, OXA-23, and OXA-58) were included in this study. The sensitivity and specificity of the multiplex real-time PCR assay to all of the carbapenemase genes were above 99.0%, except for ISAba1-OXA-51. The detection limit of the assay was 100 target copies per 25 µL of reaction volume for all of the nine genetic types of carbapenemases, and the genes were all detected in a single three-hour PCR. The assay also showed considerable efficiency (above 80.0%), stable reproducibility (coefficient of variation, below 5.0%) and a long shelf-life (more than eight months) with no cross reactivity. The developed PNA-mediated multiplex real-time PCR assay was useful for the rapid, accurate and simultaneous identification of nine carbapenemase genes in gram-negative clinical isolates, suggesting its potential to help choose the appropriate antibiotics and aid the control of carbapenemase genes.

Combined use of the modified Hodge test and carbapenemase inhibition test for detection of carbapenemase-producing Enterobacteriaceae and metallo-ß-lactamase-producing Pseudomonas spp.

BACKGROUND: We evaluated the combined use of the modified Hodge test (MHT) and carbapenemase inhibition test (CIT) using phenylboronic acid (PBA) and EDTA to detect carbapenemase-producing Enterobacteriaceae (CPE) and metallo-ß-lactamase (MBL)-producing Pseudomonas spp. METHODS: A total of 49 isolates of CPE (15 Klebsiella pneumoniae carbapenemase [KPC], 5 Guiana extended-spectrum ß-lactamase [GES]-5, 9 New Delhi metallo-ß-lactamase [NDM]-1, 5 Verona integron-encoded metallo-ß-lactamase [VIM]-2, 3 imipenem-hydrolyzing ß-lactamase [IMP], and 12 oxacillinase [OXA]-48-like), 25 isolates of MBL-producing Pseudomonas spp. (14 VIM-2 and 11 IMP), and 35 carbapenemase-negative controls were included. The MHT was performed for all isolates as recommended by the Clinical and Laboratory Standards Institute. Enhanced growth of the indicator strain was measured in mm with a ruler. The CIT was performed by directly dripping PBA and EDTA solutions onto carbapenem disks that were placed on Mueller-Hinton agar plates seeded with the test strain. RESULTS: Considering the results of the MHT with the ertapenem disk in Enterobacteriaceae and Pseudomonas spp., the CIT with the meropenem disk in Enterobacteriaceae, and the imipenem disk in Pseudomonas spp., three combined disk tests, namely MHT-positive plus PBA-positive, EDTA-positive, and MHT-positive plus PBA-negative plus EDTA-negative, had excellent sensitivity and specificity for the detection of KPC- (100% sensitivity and 100% specificity), MBL- (94% sensitivity and 100% specificity), and OXA-48-like-producing isolates (100% sensitivity and 100% specificity), respectively. CONCLUSIONS: Combined use of the MHT and CIT with PBA and EDTA, for the detection of CPE and MBL-producing Pseudomonas spp., is effective in detecting and characterizing carbapenemases in routine laboratories.

Clonal and horizontal spread of the blaOXA-232 gene among Enterobacteriaceae in a Korean hospital.

All 16 Klebsiella pneumoniae isolates and both Escherichia coli isolates harbored the bla(OXA-232) and bla(CTX-M-15) genes. Furthermore, all 16 K. pneumoniae isolates belonged to a unique pulsed-field gel electrophoresis clone and were assigned to an identical sequence type (ST14). The 2 E. coli isolates were identified as ST131 and ST457. The bla(OXA-232) gene underwent horizontal transfer to E. coli isolates via a conjugative ColE-type plasmid. The introduction of this K. pneumoniae ST14 strain to the Korean hospital was attributed to an index patient who was likely colonized during a prior hospitalization in India.

The drug susceptibility profile and inducible resistance to macrolides of Mycobacterium abscessus and Mycobacterium massiliense in Korea.

We conducted drug susceptibility testing (DST) against various antimicrobial agents, including new candidate drugs, and investigated the relationship between inducible resistance (IR) to macrolides and erm(41) gene in Mycobacterium abscessus complex. Sixty-two isolates of M. abscessus complex from 2 tertiary care hospitals in South Korea were tested against 10 antimicrobial agents. Thirty-five isolates were M. abscessus, and 27 were Mycobacterium massiliense. Amikacin, moxifloxacin, linezolid, clofazimine, and tigecycline were active against most isolates and cefoxitin and ciprofloxacin against moderate number of isolates. M. massiliense remained susceptible to macrolides; in contrast, M. abscessus became highly resistant on day 14 after incubation. DST pattern did not differ between clarithromycin and azithromycin. IR to clarithromycin was correlated with erm(41) genotype in M. abscessus. Variations in susceptibility to antimicrobial agents within species and the difference in DST patterns between M. abscessus and M. massiliense suggest that DST and identification of M. abscessus complex are significant before treatment.

Risk factors for mortality in patients with bloodstream infections caused by carbapenem-resistant Pseudomonas aeruginosa: clinical impact of bacterial virulence and strains on outcome.

The incidence of carbapenem-resistant Pseudomonas aeruginosa (CRPA) bacteremia has increased in recent years, and infections caused by CRPA result in higher mortality than those caused by susceptible strains. This study was performed to evaluate the risk factors for mortality and to study the impact of virulence factors and bacterial strains on clinical outcomes in patients with CRPA bacteremia. Data on 63 episodes of CRPA bacteremia that have occurred between January 1, 2007, and December 31, 2009, in a teaching hospital (2000 beds) in Seoul, Korea, were analyzed. The Acute Physiology and Chronic Health Evaluation II (APACHE II) score at the time of CRPA bacteremia and the capacity of CRPA to form biofilm were independent predictive factors for mortality in patients with CRPA bacteremia. In addition, the biofilm-forming ability and elastase activity of strains were correlated with APACHE II scores to measure the severity of disease and estimate predicted mortality in the patients.

Misidentification of Candida guilliermondii as C. famata among strains isolated from blood cultures by the VITEK 2 system.

Introduction. The aim of this study was to differentiate between Candida famata and Candida guilliermondii correctly by using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and gene sequencing. Methods. Twenty-eight Candida strains from blood cultures that had been identified as C. famata (N = 25), C. famata/C. guilliermondii (N = 2), and C. guilliermondii (N = 1) by the VITEK 2 system using the YST ID card were included. We identified these strains by MALDI-TOF MS and gene sequencing using the 28S rRNA and ITS genes and compared the results with those obtained by the VITEK 2 system. Results. All 28 isolates were finally identified as C. guilliermondii. Sequencing analysis of the 28S rRNA gene showed 99.80%-100% similarity with C. guilliermondii for all 28 strains. The ITS gene sequencing of the strains showed 98.34%-100% homology with C. guilliermondii. By MALDI-TOF, we could correctly identify 21 (75%) of 28 C. guilliermondii isolates. Conclusion. We should suspect misidentification when C. famata is reported by the VITEK 2 system, and we always should keep in mind the possibility of misidentification of any organism when an uncommon species is reported.

In vivo emergence of colistin resistance in Acinetobacter baumannii clinical isolates of sequence type 357 during colistin treatment.

This study was performed to investigate the mechanisms of in vivo acquisition of colistin resistance in A. baumannii during colistin treatment. Three colistin-susceptible/resistant pairs of A. baumannii were recovered from patients who underwent colistin treatment. All of the 6 isolates included in this study shared an identical sequence type (ST), ST375, and they showed identical SmaI-macrorestriction patterns by pulsed-field gel electrophoresis. The individual colistin-resistant isolates harbored distinct mutations in the pmrB gene. Mutations detected in the pmrB gene were Ala227Val, Pro233Ser, and frame shift from Phe26. In matrix-assisted laser desorption ionization-time of flight analysis, colistin-resistant isolates were different from their colistin-susceptible counterparts, and they showed additional distinct peaks at 1852 m/z, 1937 m/z, 1954 m/z, 1975 m/z, 2034 m/z, and 2157 m/z. In vivo selection of colistin-resistant A. baumannii occurred independently in strains of ST357 during colistin treatment, and the strains acquired colistin resistance via mutations in the pmrB gene resulting in modification of lipid A components.