Infectious diseases due to Gram-negative bacteria are a leading cause of morbidity and mortality worldwide. Antimicrobial agents represent one major therapeutic tools implicated to treat these infections. The misuse of antimicrobial agents has resulted in the emergence of resistant strains of Gram-negatives in particular Enterobacteriaceae and non-fermenters; they have an effect not only on a human but on the public health when bacteria use the resistance mechanisms to spread in the hospital environment and to the community outside the hospitals by means of mobile genetic elements. Gram-negative bacteria have become increasingly resistant to antimicrobial agents. They have developed several mechanisms by which they can withstand to antimicrobials, these mechanisms include the production of Extended-spectrum β-lactamases (ESBLs) and carbapenemases, furthermore, Gram-negative bacteria are now capable of spreading such resistance between members of the family Enterobacteriaceae and non-fermenters using mobile genetic elements as vehicles for such resistance mechanisms rendering antibiotics useless. Therefore, addressing the issue of mechanisms of antimicrobial resistance is considered one of most urgent priorities. This review will help to illustrate different resistance mechanisms; ESBLs, carbapenemases encoded by genes carried by mobile genetic elements, which are used by Gram-negative bacteria to escape antimicrobial effect.
An Achromobacter xylosoxidans strain from the Tripoli central hospital produced a unique metallo--lactamase, designated TMB-1, which is related to DIM-1 (62%) and GIM-1 (51%). bla TMB-1 was embedded in a class 1 integron and located on the chromosome. The TMB-1 -lactamase has lower k cat values than both DIM-1 and GIM-1 with cephalosporins and carbapenems. The K m values were more similar to those of GIM-1 than those of DIM-1, with the overall k cat /K m values being lower than those for GIM-1 and DIM-1.
ᰔIn 1997, the first SPM-1-positive Pseudomonas aeruginosa isolate (48-1997A) from a 4-year-old leukemic girl in San Paulo, Brazil, was characterized. bla SPM-1 was flanked by two ISCR elements, designated ISCR4, and probably transposes via a mechanism called rolling-circle replication (8). Reports of ISCR elements are continually being linked with antibiotic resistance, particularly -lactamases in Gram-negative bacteria (http://www .cardiff.ac.uk/medic/aboutus/departments/medicalmicrobiology /genetics/iscr_elements.html) (3,4,8).In 2007, a single isolate of P. aeruginosa, designated BH121, was recovered from a soft-wound infection of a 34-year-old Swiss male. The patient received primary care at the Regional General Hospital in Recife, Brazil, before being transported to the University Hospital Basel. P. aeruginosa BH121 gave a positive result with the MBL Etest (AB BioMérieux, Solna, Sweden). MICs were determined by agar dilution in accordance with CLSI guidelines (2). BH121 was resistant to all antibiotics (piperacillin-tazobactum, ceftazidime, cefotaxime, cefepime, meropenem, imipenem, all aminoglycosides, and all fluoroquinolones) except aztreonam and colistin. Imipenem hydrolysis by crude cell extracts from BH121 suggested the presence of an active metallo--lactamase (MBL) (7).PCR analysis detected bla SPM-1 and was thus extended to determine flanking sequences, which showed that the MBL gene is flanked by two copies of ISCR4-like elements. Sequence analysis confirmed that BH121 carries bla SPM-1 and that it possesses two copies of ISCR4 identical to that reported by Poirel et al., indicating perfect preservation of this DNA region for Ͼ10 years (5, 7, 10).DNA macroanalysis using pulsed-field gel electrophoresis (PFGE) after restriction with SpeI was undertaken to ascertain the relatedness of BH121 to 15 other SPM-1-positive P. aeruginosa isolates from Brazil between 1997 and 2007 (6). This analysis showed that BH121 had a DNA restriction pattern almost identical to that of the other Brazilian strains, differing by only three or four bands, thus indicating that all isolates of P. aeruginosa are distantly related.Genomic DNAs from P. aeruginosa BH121 and the 15 retrospective Brazilian isolates were digested with SpeI and probed with bla SPM-1 . Probing of SpeI genomic DNA digests of the clinical P. aeruginosa isolates with bla SPM-1 shows two copies of the MBL gene in three strains, including P. aeruginosa BH121 and the index case strain, 48-1997. The duplication of bla SPM-1 is likely to have arisen from ISCR4 transposition proceeded by homologous recombination.To determine the genetic location of the MBL gene, genomic DNA from all isolates was digested separately with nucleases S1 and I-Ceu-1, separated by PFGE, and subsequently probed with bla SPM-1 (1). Data showed that the bla SPM-1 probe hybridized only to chromosomal DNA and not the separated plasmid bands, indicating that the MBL gene is chromosomally mediated. DNA digestion with I-Ceu-1 and probing with bla SPM-1 also confirmed that the gene is ch...
Introduction: The aim of the study was to investigate the prevalence of extended-spectrum β-lactamase (ESBL) and carbapenemase production among clinical isolates of Enterobacteriaceae recovered from Tunisian and Libyan hospitals. Methodology: Bacterial isolates were recovered from patients in intensive care units and identified by biochemical tests and MALDI-TOF. Antibiotic susceptibility testing was performed by disk diffusion and the E-test method. ESBL and carbapenemase activities were detected using standard microbiological tests. Antibiotic resistance-encoding genes were screened by PCR and sequencing. Clonal relationships between Klebsiella pneumoniae strains were carried out using multi-locus sequence typing (MLST). Results: A total of 87 isolates were characterized, with 51 and 36, respectively, identified as E. coli and K. pneumoniae. Overall the resistance prevalence was high for aminoglycosides (> 60%), fluoroquinolones (> 80%), and extended-spectrum cephalosporins (> 94%), and was low for imipenem (11.4%). Among this collection, 58 strains (66.6%) were ESBL producers and 10 K. pneumoniae strains (11.4%) were carbapenemase producers. The antibiotic resistance-encoding genes detected were blaCTX-M-15 (51.7%), blaTEM-1 (35.6%), several variants of blaSHV (21.8%), and blaOXA-48 (11.4%). The MLST typing of K. pneumoniae isolates revealed the presence of multiple clones and three novel sequence types. Also, close relationships between the OXA-48-producing strains from Tunisia and Libya were demonstrated. Conclusions: This study is the first paper describing the emergence of carbapenemase-and ESBL-producing Enterobacteriaceae, sensitive to colistin, isolated in Tunisia and Libya. Active surveillance and testing for susceptibility to colistin should be implementing because resistance to colistin, mainly in Klebsiella, has been recently reported worldwide.
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