الفهرس 
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Abstract
K. pneumoniae is a common opportunistic pathogen that is associated with urinary tract infection, pneumonia, septicemia, as well as bacterial meningitis and biliary tract infection. The over use of antibiotic and/or inappropriate antibiotic therapy are the major causes of the emergence of antibiotic resistant K. pneumoniae. In the recent years, the problem of increasing resistance to antibiotics has threatened the entire world. Production of β-lactamases, including ESBL, AmpC enzymes and carbapenemases, has been one of the most important resistance mechanisms of many bacterial species, mainly in the Enterobacteriaceae family.
The aim of the present study was to determine the phenotypic resistance pattern to β-lactam antibiotics among Klebsiella clinical isolates and to identify the genetic determinants responsible for β-lactam antibiotic resistance.
Fifty Klebsiella isolates were included in this study. The isolates were primarily identified using colonial appearance, growth on MacConkey agar and Gram stain. Biochemical reactions, including TSI, IMVC and urease, were used to confirm the identity of the isolates as K. pneumoniae.
Using MALDI-TOF MS, all isolates were identified to the subspieces level as K. pneumoniae subsp. penumoniae. The score values for the 50 isolates were more than 2 indicating a reliable genus and probable species identification. The results revealed an excellent performance of MALDI-TOF MS in comparison with time-consuming biochemical methods in identifying Klebsiella isolates to the subspecies level.
Concerning the antibiotic resistance among the clinical isolates, the highest rate of resistance was against cefaclor and cephradine (n=48, 96%), followed by amoxicillin-clavulanic acid (n=47, 94%) and ampicillin-sulbactam (n=46, 92%). High rate of resistance was also detected against third-generation cephalosporins (n=41, 82%). The resistance to carbapenems, cefoxitin and aztreonam was detected among 12 (24%), 19 (38%) and 37 (74%) isolates, respectively. Regarding fluoroquinolones, tetracyclines, aminoglycosides and co-trimoxazole, the resistance was observed in 30 (60%), 34 (68%), 23 (46%) and 41 (82%) isolates, respectively. The most effective antibiotics were colistin and tigecycline which were active against 50 (100%) and 48 (96%) isolates, respectively.
The MIC values of ceftazidime, cefotaxime and cefepime were determined and it was shown that they were in concordance with the results of the antimicrobial susceptibility testing using disk diffusion method.
A total of 37 (74%) isolates were resistant to agents in more than 2 classes of antimicrobial agents and were defined as MDR. Furthermore, 8 (16%) isolates showed resistance to at least one agent in all classes with the exception of one or two classes and were defined as XDR.