Molecular epidemiology of Acinetobacter species in a medical center in central Taiwan : comparison of genospecies and antimicrobial-resistant profiles from various clinical specimens and in non-adult population

• Main Authors: Ni Tien, 田霓
• Other Authors: Chao-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/r7gdhu

博士 === 國立中興大學 === 獸醫學系暨研究所 === 101 === Acinetobacter is a gram-negative and immobile coccobacillus, with no ability of fermentation of glucose and many carbohydrates. It exists on the human skin and in the environment. The bacteria form biofilms easily. It is one of the common antibiotic-resistant bacteria in nosocomial infection in hospitals. Acinetobacter genus contains many species. Among them, Acinetobacter calcoaceticus-Acinetobacter baumanii complex (Ac-Ab complex) is the most common one, but the clinical importance of A. lwoffii has increased significantly. Most of Acinetobacter organisms are frequently isolated from specimens of blood, wounds, sputum, urine and patients with catheter-related infections. The aim of this research attempts to conduct a retrospective analysis using past records from the clinical microbiology laboratory of a medical center in central Taiwan and to use molecular typing of the collected bacterial isolates, for studying molecular epidemiology of Acinetobacter from clinical aspects. Research topics include: (I) to compare genospecies and antimicrobial resistance profiles of isolates in the Acinetobacter calcoaceticus-Acinetobacter baumannii complex from various clinical specimens; (II) to study molecular epidemiology of Acinetobacter infection in non-adult population in central Taiwan. In part I of the study, the antimicrobial susceptibility profiles tested by 12 different antibiotics were compared using 1381 isolates in the Ac-Ab complex collected from different clinical specimens. A total of 205 clinical isolates were further analyzed by ARDRA of intergenic spacer (ITS) region of the 16S-23S rRNA gene. In the 1381 isolates, except for colistin, it was found that the overall percentage of the isolates from the non-sterile sites that were resistant to 11 antibiotics tested was significantly higher than that of the isolates from sterile sites (46 % vs. 22 %; p<0.05). After further ARDRA analysis for the 205 isolates, 97% of the 62 isolates resistant to all antibiotics tested were A.baumannii genospecies. However, among the 143 isolates susceptible to all 11 antibiotics tested, only 31% of them were A. baumannii. Other genospecies were 13 TU (34%), genospecies 3 (29%) and A. calcoaceticus genospecies (5%). In part II of the study, the historical records of a total of 177 cases from 2008 to 2011 were used for analysis to understand Acinetobacter infection in the population less than 18 years old. A total of 99 clinical Acinetobacter isolates were further analyzed by ARDRA method. It was found that most of the isolates belong to the Ac-Ab complex (79.7%), following by A. lwoffii (13%). In patients aged less than 1 year-old, isolates were mainly Ac-Ab complex (87.7%), followed by A. lwoffii (6.2%). On the contrary, in patients aged more than 1 year-old, higher proportion (18.8 %) was due to A. lwoffii. Except for the patients from emergency room, patients from other ward sources were mainly infected with Ac-Ab complex. Patients from emergency room were mostly infected with A. lwoffii (44.4%), followed by Ac-Ab complex (33.3%). The profiles of antimicrobial resistance of Ac-Ab complex and A. lwoffii were further compared. Except for colistin, the increasing trend of antimicrobial resistance from 2008 to 2011 was identified in Ac-Ab complex isolates, including aminoglycosides, fluoroquinolones, sulfonamides, beta-lactams and carbapenems. It was not until 2011 that the first isolate of Ac-Ab complex resistant to colistin was identified. However, there was no consistently increasing/or decreasing trend of antimicrobial resistance in A. lwoffii. The genotyping results of 99 isolates showed that the major one is A. baumannii genospecies (70%). This study indicated current emergence of carbapenem, fluoroquinolone, aminoglycoside, cephalosporin-resistant Ac-Ab complex isolates in central Taiwan. Clinicians need to aware that not only the so-called “A. baumanii” has clinical importance, but also other genospecies may carry different characteristics of antimicrobial resistance and virulence potential. The results of this study also offer the epidemiological characteristics and profiles of various antimicrobial resistance of the infection due to different Acinetobacter species. in the non-adult population. Higher isolation rate of A. lwoffii in patients from emergency room raised the concern whether the infection could be from community source. The substantially increasing trend of resistance to multiple antimicrobials in Ac-Ab complex since 2010 needs further investigation.