Acclimatization ; Acinetobacter ; metabolism ; Cold Temperature ; Transcriptome

OBJECTIVEGas chromatography (GC) was used to investigate the cellular fatty acid (CFA) composition of 141 Acinetobacter baumannii and 32 A. calcoaceticus isolates from different locations in China and to find chemical markers to differentiate these two closely related bacteria.

METHODSWhole cell fatty acid methyl esters (FAMEs) were obtained by saponification, methylation, and extraction for GC analysis, followed by a standardized Microbial Identification System (MIS) analysis.

RESULTSAll A. baumannii and A. calcoaceticus strains contained some major fatty acids, namely, 18:1 ω9c, 16:0, Sum In Feature 3, 12:0, 17:1ω8c, 3-OH-12:0, 17:0, Sum In Feature 2, 2-OH-12:0, and 18:0 compounds. Although most of the total CFAs are similar between A. baumannii and A. calcoaceticus strains, the ratios of two pairs of CFAs, i.e., Sum In Feature 3/18:1 ω9c versus 16:0/18:1 ω9c and Sum In Feature 3/18:1 ω9c versus unknown 12.484/18:1 ω9c fatty acids, could differentiate these two closely related bacteria. A. baumannii could be easily classified into two subgroups by plotting some ratios such as Sum In Feature 3/16:0 versus 17:0 and Sum In Feature 3/2-OH-12:0 versus 17:0 fatty acids.

CONCLUSIONThe ratios of some CFAs could be used as chemical markers to distinguish A. baumannii from A. calcoaceticus.

Acinetobacter baumannii ; classification ; cytology ; metabolism ; Acinetobacter calcoaceticus ; classification ; cytology ; metabolism ; Biomarkers ; metabolism ; Fatty Acids ; metabolism ; Species Specificity

Acinetobacter baumannii has emerged as one of the leading bacteria for nosocomial infections, especially in burn wards and ICUs. The bacteria can easily form biofilm and readily attach to abiotic and biotic surfaces, resulting in persistent biofilm-mediated infections. Being surrounded by self-produced extracellular polymeric substance (EPS), the microorganisms in biofilm can acquire protective property against detrimental environment and their tolerance toward antibiotics is increased. Poly-β-1-6-N-acetylglucosamine (PNAG), the common constituent of EPS in Acinetobacter baumannii, acts as the key virulence factor and plays a crucial role in biofilm formation process. This review describes the properties and functions of the PNAG and its influence on biofilm formation and drug resistance of Acinetobacter baumannii.
Acinetobacter Infections ; drug therapy ; Acinetobacter baumannii ; drug effects ; Anti-Bacterial Agents ; therapeutic use ; Biofilms ; drug effects ; growth & development ; Burns ; Cross Infection ; Drug Resistance, Multiple, Bacterial ; beta-Glucans ; metabolism

Acinetobacter has been the major pathogen of nosocomial infection. With the wide use of carbapenems, the emergence of multi-resistant isolates especially those resistant to carbapenem, brings a great problem to clinical treatment. The production of inactive enzymes is the main mechanism for antibiotic resistance, particularly the production of carbapenemases mediated by chromosome or plasmid. Combinations of β-lactam antibiotics and sulbactam may show synergism or partial synergism for acinetobacter isolates.
Acinetobacter ; drug effects ; enzymology ; Acinetobacter Infections ; drug therapy ; Anti-Bacterial Agents ; pharmacology ; therapeutic use ; Bacterial Proteins ; metabolism ; Carbapenems ; pharmacology ; therapeutic use ; Drug Resistance, Bacterial ; Microbial Sensitivity Tests ; beta-Lactamases ; metabolism

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.
Acinetobacter Infections/*microbiology/pathology ; Acinetobacter baumannii/*chemistry/classification/isolation & purification ; Bacterial Proteins/chemistry/genetics/metabolism ; Databases, Factual ; Humans ; Phylogeny ; RNA, Ribosomal, 16S/chemistry/genetics/metabolism ; *Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

BACKGROUND: Multidrug-resistant (MDR) Acinetobacter spp. acquire antimicrobial agent-resistance genes via class 1 integrons. In this study, integrons were characterized to investigate the antimicrobial resistance mechanisms of MDR Acinetobacter isolates. In addition, the relationship between the integron type and integron-harboring bacterial species was analyzed by using epidemiological typing methods. METHODS: Fifty-six MDR Acinetobacter spp.-A. baumannii (N=30), A. bereziniae (N=4), A. nosocomialis (N=5), and A. pittii (N=17)-were isolated. The minimum inhibitory concentrations (MICs) were determined on the basis of the results of the Epsilometer test (Etest). PCR and DNA sequencing was performed to characterize the gene cassette arrays of class 1 integrons. Multilocus sequence typing (MLST) and repetitive extragenic palindromic sequence (REP)-PCR were performed for epidemiological typing. RESULTS: Class 1 integrons were detected in 50 (89.3%) of the 56 isolates, but no class 2 or 3 integron was found within the cohorts. The class 1 integrons were classified into 4 types: 2.3-kb type A (aacA4-catB8-aadA1), 3.0-kb type B (aacA4-blaI(MP-1)-bla(OXA-2)), 3.0-kb type C (bla(VIM-2)-aacA7-aadA1), and 1.8-kb type D (aac3-1-bla(OXA-2)-orfD). Type A was most prevalent and was detected only in A. baumannii isolates, except for one A. bereziniae isolate; however, type B was amplified in all Acinetobacter isolates except for A. baumannii isolates, regardless of clone and separation time of the bacteria. CONCLUSIONS: Although class 1 integron can be transferred horizontally between unrelated isolates belonging to different species, certain types of class 1 integrons tend to transfer horizontally and vertically among A. baumannii or non-baumannii Acinetobacter isolates.
Acinetobacter/drug effects/isolation & purification/*metabolism ; Acinetobacter Infections/epidemiology/microbiology ; Acinetobacter baumannii/drug effects/isolation & purification/metabolism ; Anti-Bacterial Agents/pharmacology ; DNA, Bacterial/chemistry/metabolism ; Drug Resistance, Multiple, Bacterial ; Humans ; Integrons/*genetics ; Microbial Sensitivity Tests ; Multilocus Sequence Typing ; Polymerase Chain Reaction ; Republic of Korea

Pathogenic bacteria have increasingly been resisting to antimicrobial therapy. Recently, resistance problem has been relatively much worsened in Gram-negative bacilli. Acinetobacter spp. are typical nosocomial pathogens causing infections and high mortality, almost exclusively in compromised hospital patients. Acinetobacter spp. are intrinsically less susceptible to antibiotics than Enterobacteriaceae, and have propensity to acquire resistance. A surveillance study in Korea in 2009 showed that resistance rates of Acinetobacter spp. were very high: to fluoroquinolone 67%, to amikacin 48%, to ceftazidime 66% and to imipenem 51%. Carbapenem resistance was mostly due to OXA type carbapenemase production in A. baumannii isolates, whereas it was due to metallo-beta-lactamase production in non-baumannii Acinetobacter isolates. Colistin-resistant isolates were rare but started to be isolated in Korea. Currently, the infection caused by multidrug-resistant A. baumannii is among the most difficult ones to treat. Analysis at tertiary care hospital in 2010 showed that among the 1,085 isolates of Acinetobacter spp., 14.9% and 41.8% were resistant to seven, and to all eight antimicrobial agents tested, respectively. It is known to be difficult to prevent Acinetobacter spp. infection in hospitalized patients, because the organisms are ubiquitous in hospital environment. Efforts to control resistant bacteria in Korea by hospitals, relevant scientific societies and government agencies have only partially been successful. We need concerted multidisciplinary efforts to preserve the efficacy of currently available antimicrobial agents, by following the principles of antimicrobial stewardship.
Acinetobacter/classification/*drug effects/genetics/metabolism ; Anti-Bacterial Agents/pharmacology ; Bacterial Proteins/metabolism ; Drug Resistance, Multiple, Bacterial/genetics ; beta-Lactamases/metabolism

BACKGROUND: Despite increasing importance of Acinetobacter baumannii in nosocomial infections and rapid development of multi-antimicrobial resistance in this strain, the resistance mechanisms of beta-lactam antimicrobials in A. baumannii were not clearly defined. In order to observe the resistance mechanisms against beta-lactams and carbapenem, we characterized the production of beta-lactamases and outermembrane protein (OMP) profiles for the 44 clinical isolates of A. baumannii. METHODS: The MICs of antimicrobials were determined by agar dilution test. The secondary beta-lactamases were characterized by isoelectric focusing, polymerase chain reactions and nucleotide sequencing, and the production of chromosomal beta-lactamases was quantitated by spectrophotometric method. For two strains with an elevated MIC of carbapenem, outermembrane protein (OMP) profile was analyzed by ultracentrifugation of the sonicated bacteral cells and SDS-PAGE. RESULTS AND CONCLUSION: Twenty two or 4 of 44 strains produced TEM-1-like beta-lactamase or PER-1 extended-spectrum beta-lactamase, respectively. However, when we analyzed the MICs of several beta-lactams with the beta-lactamase production, the resistance level of beta-lactam was mainly determined by the production of chromosomal beta-lactamase, not by the secondary beta-lactamases in the clinical isolates of A. baumannii. In two strains with an elevated MIC of imipenem, a decrease or loss of about 35 kDa and 22 kDa proteins in OMP was observed, which suggested that the change of OMP played a role in carbapenem resistance.
Acinetobacter/*drug effects/isolation & purification/metabolism ; Acinetobacter Infections/drug therapy/microbiology ; Antibiotics, Lactam/*pharmacology ; Bacterial Outer Membrane Proteins/biosynthesis ; Carbapenems/pharmacology ; Cross Infection/drug therapy/microbiology ; Drug Resistance, Bacterial ; Human ; beta-Lactamases/biosynthesis

BACKGROUNDAcinetobacter baumanii (A. baumanii ) remains an important microbial pathogen resulting in nosocomial acquired infections with significant morbidity and mortality. The mechanism by which nosocomial bacteria, like A. baumanii, attain multidrug resistance to antibiotics is of considerable interest. The aim in this study was to investigate the spread status of antibiotic resistance genes, such as multiple β-lactamase genes and aminoglycoside-modifying enzyme genes, from A. baumanii strains isolated from patients with lower respiratory tract infections (LRTIs).

METHODSTwo thousand six hundred and ninety-eight sputum or the bronchoalveolar lavage samples from inpatients with LRTIs were collected in 21 hospitals in the mainland of China from November 2007 to February 2009. All samples were routinely inoculated. The isolated bacterial strains and their susceptibility were analyzed via VITEK-2 expert system. Several kinds of antibiotic resistant genes were further differentiated via polymerase chain reaction and sequencing methods.

RESULTSTotally, 39 A. baumanii strains were isolated from 2698 sputum or bronchoalveolar lavage samples. There was not only a high resistant rate of the isolated A. baumanii strains to ampicillin and first- and second-generation cephalosporins (94.87%, 100% and 97.44%, respectively), but also to the third-generation cephalosporins (ceftriaxone at 92.31%, ceftazidine at 51.28%) and imipenem (43.59%) as well. The lowest antibiotic resistance rate of 20.51% was found to amikacin. The OXA-23 gene was identified in 17 strains of A. baumanii, and the AmpC gene in 23 strains. The TEM-1 gene was carried in 15 strains. PER-1 and SHV-2 genes were detected in two different strains. Aminoglycoside-modifying enzyme gene aac-3-Ia was found in 23 strains, and the aac-6'-Ib gene in 19 strains. aac-3-Ia and aac-6'-Ib genes hibernated in three A. baumanii strains that showed no drug-resistant phenotype.

CONCLUSIONSA. baumanii can carry multiple drug-resistant genes at the same time and result in multi-drug resistance. Aminoglycoside-modifying enzyme genes could be hibernating in aminoglycoside sensitive strains without expressing their phenotype.

Acinetobacter ; genetics ; metabolism ; pathogenicity ; Acinetobacter Infections ; microbiology ; Bacterial Proteins ; genetics ; Bronchoalveolar Lavage Fluid ; microbiology ; Drug Resistance, Multiple, Bacterial ; genetics ; Humans ; Microbial Sensitivity Tests ; Polymerase Chain Reaction ; Respiratory Tract Infections ; microbiology ; Sputum ; microbiology

BACKGROUND: Acinetobacter baumannii is an aerobic, gram-negative, glucose-nonfermenting bacterium, which has emerged as a serious opportunistic pathogen. In recent years, the increasing instance of carbapenem-resistant A. baumannii producing metallo-beta-lactamases (MBLs) or OXAtype beta-lactamases is causing a serious clinical problem. In this study, we investigated the prevalence of Ambler class A, B, and D beta-lactamases and their extended-spectrum derivatives in carbapenem-resistant A. baumannii isolates. METHODS: A total of 31 consecutive, non-duplicate, carbapenem-resistant A. baumannii were isolated from three university hospitals in the Chungcheong province of Korea. The modified Hodge and inhibitor-potentiated disk diffusion tests were conducted for the screening of carbapenemase and MBL production, respectively. PCR and DNA sequencing were performed for the detection of beta-lactamase genes. We also employed the enterobacterial repetitive intergenic consensus (ERIC)-PCR method for the epidemiologic study. RESULTS: Twenty-three of 31 isolates harbored bla(OXA-2) (51.6%), bla(OXA-23) (22.6%), bla(IMP-1) (48.4%),and bla(VIM-2) (3.2%). All of the OXA-2-producing strains also evidenced MBLs. The strains that harbored bla(OXA-23) were isolated only in hospital C, and only in a limited fashion. The ERIC-PCR pattern of the five OXA-23 strains indicated that the isolates were closely related in terms of clonality. The six strains producing IMP-1 isolated from hospital A were confirmed to be identical strains. CONCLUSIONS: A. baumannii strains harboring IMP-1 or OXA-type beta-lactamases are currently widely distributed throughout the Chungcheong province of Korea. The most notable finding in this study was that a bla(OXA-2)-producing A. baumannii harboring MBL, which has not been previously reported, can also lead to outbreaks.
Acinetobacter Infections/microbiology ; Acinetobacter baumannii/drug effects/*enzymology/genetics ; Anti-Bacterial Agents/*pharmacology ; Carbapenems/*pharmacology ; Disk Diffusion Antimicrobial Tests ; Drug Resistance, Multiple, Bacterial ; Humans ; Polymerase Chain Reaction ; beta-Lactamases/biosynthesis/genetics/*metabolism