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.

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.

Background: Antibiotic-resistant bacteria have been surveyed widely in water bodies, but few studies have determined the diversity of antibiotic-resistant bacteria in river waters. This study was undertaken to investigate the origin of resistance among polluted river bacterial isolates in Tunisia. Methods: In this study 128 isolates resistant to β-lactam antibiotics were obtained from 2 polluted rivers in the north of Tunisia. Isolates were identified using Phoenix phenotyping criteria. The occurrence of bla_TEM, bla_SHV, bla_CTX-M, bla_CMY, bla_VIM, and bla_IMP was studied by polymerase chain reaction (PCR) amplification and sequencing, and the genetic relatedness of the 16 IMP-producing Klebsiella pneumoniae isolates was analyzed by comparison of XbaI pulsed-field gel electrophoresis (PFGE) profiles. Results: Using Phoenix phenotyping criteria, diverse genera of bacteria were identified with different rates of prevalence and with different minimum inhibitory concentrations against different antibiotics. The occurrence of bla_TEM, bla_SHV, bla_CTXM, bla_CMY, bla_VIM, and bla_IMP genes was confirmed. The DNA sequences upstream and downstream of bla_IMP genes were determined, revealing that all IMP-encoding genes constituted the first cassette of class 1 integrons, followed by aacA gene cassettes encoding aminoglycoside resistance. Comparison of PFGE profiles showed that only 2 of the isolates were clonal, the other 14 displaying unique profiles. The bla_CTX-M gene was the most dominant of the extended-spectrum β-lactamase (ESBL) genes, while the bla_TEM gene was the second-most dominant. Conclusion: The discovery of highly diverse ESBL-producing bacteria and metallo-β-lactamases, particularly bla_IMP, in polluted river water raises alarms with regard to the potential dissemination of antibiotic-resistant bacteria in communities through river environments.

The wide spread of multidrug-resistant bacteria, particularly carbapenem-resistant Gram-negative bacteria (CR-GNB), constitutes a major public health threat worldwide, owing to the limited therapeutic options. This review will describe and uncover the Tunisian experience in the challenge against carbapenem resistance. Indeed, we illuminate on the dissemination of CR-GNB in different hospitals, animals, and other natural environments in this country. We resumed the different carbapenemase variants detected from various bacterial species and mapped their regional distribution, basing on Tunisian published data during a period extended from 2006, the date of its first description in Tunisia, to February 2019. We also resumed the different mobile genetic elements implicated in their dissemination. This review shows that the majority of the research reports focused in the north and the coastal cities in spite of the fact that KPC and IMP carbapenemases were uncommonly detected in our country. However, VIM, NDM-1, and OXA-48 enzymes were usually reported with the predominance of OXA-48 among Enterobacteriaceae. Furthermore, OXA-23, OXA-51, and OXA-58 carbapenemases constituted the main mechanism conferring carbapenem resistance among Acinetobacter baumannii in Tunisia. Collaborative efforts and raising awareness of the threat of antibiotic resistance are required in order to minimize the spread of multidrug-resistant bacteria.