The multidrug resistance of microorganisms has become the critical problem in nosocomial infections, especially P. aeruginosa and Acinetobacter spp. Both pathogens have been listed in six famous ESKAPE pathogens (Enterococcus faecium Staphylococcus aureus Klebsiella pneumoniae Acinetobacter species, Pseudomonas aeruginosa, and Enterobacter species) and identified as the most emerging threats in this century . Antimicrobial resistance surveillance, has been performed in almost every countries to identify the major problem in nosocomial infections. This study provides the first update data on the genetic relatedness of CR-MDR P. aeruginosa clinical isolates from tertiary hospitals across Thailand.
Antimicrobial resistance surveillance studies have been observed in many countries throughout the world. Most of these studies also determined carbapenem resistance rates which described higher resistance rate for imipenem than for meropenem [15, 22–24]. However, the Thailand national surveillance during 2000–2005 by Dejsirilert et al. was described in a different manner and showed a slightly greater resistance rate for meropenem than for imipenem . Moreover, a recent study which was conducted by Piyakul et al. in a tertiary hospital in Thailand indicated that P. aeruginosa clinical isolates exhibited a greater meropenem resistance rate than a rate for imipenem . In agreement with the study of Piyakul et al., our data which analyzed MDR isolates of P. aeruginosa, showed a greater difference of resistance rates between meropenem and imipenem compared to Piyakul et al.. This difference might be caused by the variety of the participated hospitals in the studies. These studies indicated that carbapenem usage in Thailand should be considered when drug susceptibility profile was unavailable.
Although the carbapenem resistance rate in P. aeruginosa or the MDR rate in P. aeruginosa is increasing, the carbepenem resistance rate among MDR strains has seldom been observed. The criteria for MDR P. aeruginosa in the study of Sekiguchi et al. which was resistant to imipenem, amikacin and ciprofloxacin was demonstrated 100% resistance rate to imipenem and meropenem and more than 90% resistance to arbekacin, doripenem, and aztreonam. Only resistances to polymyxin B and gentamicin were found to be significantly lower, at about 28% and 57.5%, respectively . According to MDR criteria in this study which was less stringent, antibiotic resistance rates of MDR P. aeruginosa were higher than 50% for most antibiotics. Only doripenem susceptibility was found to be more than 60%. This lower resistance rate might be because doripenem was recently approved for use in Thailand. Interestingly, the overall resistance rate of MDR P. aeruginosa in Thailand was found quite high. These situations could urge an awareness of limit antibiotic usage. Only recent launched antibiotic, doripenem, was showed the resistance rate less than 40%. Thus, highly concern should be recommended especially in the strategy to prevent drug resistance emerging and to preserve sensitivity of present antibiotics.
MDR P. aeruginosa is a life-threatening problem that limits the use of critical antibiotics for treatment. The ratio of CR-MDR among MDR isolated was very high in hospitals, especially the university hospitals. The results of the present study indicated that those hospitals, which handled more complicated cases and thus employed more complicated antibiotic treatments, could develop more complicated drug resistance problems. Moreover, inappropiate consumption of antibiotics has been a concern in tertiary care hospitals and especially university hospitals in Thailand . High amounts of drug consumption in a hospital can cause a selective pressure on microorganisms resulting in increased drug resistance . This study reported significantly higher rate of CR-MDR P. aeruginosa in university hospitals than regional hospitals. Correlated with the study of Danchaivijitr et al., the data showed that university hospitals had greater consumption of carbapenem than regional hospitals .
It was noteworthy that a single resistance of doripenem in CR-MDR P. aeruginosa was not detected in this study. This finding was correlated to lower MIC of doripenem compared to other carbapenem . The doripenem single resistance could be explained by the fact that this drug was newly introduced to Thailand. This data implied that resistance mechanisms for doripenem have not yet been fully acquired by multidrug resistant strains. Moreover, double resistance of imipenem and doripenem was found in only one strain as compared to double resistance of meropenem and doripenem which could be detected in twenty-five strains. The well-known resistance mechanisms of carbapenem such as loss of porins, increasing of efflux systems and enzyme degradation, were also reported to affect doripenem . Metallo-beta-lactamases were reported to affect all carbapenem, but imipenem and meropenem had different response to loss of oprD and efflux pump overexpression . Increasing the efflux pumps could mainly affect both meropenem and doripenem, but not imipenem [29, 30]. However, some doripenem-resistant P. aeruginosa clinical isolates have been found to lack functional OprD . The multiple resistances of CR-MDR P. aeruginosa suggested the possible use of polymyxin for treatment. Although polymyxin remains active on the CD-MDR strains, polymyxin is a drug with high nephrotoxic side effect . Our data suggested that treatment with doripenem might be an optional treatment instead of polymyxin to avoid side effect.
The PFGE results demonstrated a multiple DNA patterns among the resistant strains . One hundred and seven clones were identified from 218 clinical isolates indicating remarkable clonal diversity. Only 4 from 107 different clones were found to be inter-hospital transmission. Two from four clones were detected in the same region and only two clones were found in different regions. Because of the difficulty in accessing patient histories, the method of transmission between hospitals could not be determined. There was a possibility that infected patients were transferred between the hospitals. The clonal dissemination ratio showed limited of inter-hospital transmission. The ratio of higher than 2.0 was found in two hospitals indicating that one clone was infected in more than two patients. Additionally, these hospitals were found dominant clones at about 9 isolates per clone as showed in the Table 2. For other six hospitals, the clonal dissemination showed that each patient was infected by different clones indicating high variation of CR-MDR P. aeruginosa. It was possible that high consumption of antibiotic usage could provide high pressure condition inducing mutation in bacteria.
The available results indicated that the high resistance rate of MDR P. aeruginosa was localized and was due to the antibiotic selection pressure. Antibiotic usage should be carefully evaluated for its effect on the development of bacterial resistance. Infectious Diseases Society of America (IDSA) has presented guidelines for developing an institutional program to enhance antibiotic stewardship . The aim of the guidelines is to optimize antibiotic selection and usage while maximize the clinical outcomes. Since our results indicated that Thailand might have some patterns of resistance different from that of other countries. Therapeutic options in Thailand should be considered and adapted to minimize our resistance problems. An appropriate adjustment of antibiotic usage should reduce the emergence of antibiotic resistance microorganisms and also can preserve the existing and future antimicrobial agents [33, 34].
Because CR-MDR P. aeruginosa infections are frequently life-threatening, strategies to control the spreading of antibiotic resistance phenomenon are necessary. Our results showed that the spreading of CR-MDR in Thailand was local, but the resistance rate of these strains was high. The high consumption of antibiotics might be a major problem. Therefore, antibiotic stewardship is one of the strategies that might help resolve the problems. The effective strategies to control the mutation of bacterial resistance are required to prevent the spreading and also antibiotic strategy for treatment.