Background: Actually, no data on the prevalence of plasmid colistin resistance in Tunisia are available among clinical bacteria. Objectives: This study aimed to investigate the current epidemiology of colistin resistance and the spread of the mcr gene in clinical Gram-negative bacteria (GNB) isolated from six Tunisian university hospitals. Methods: A total of 836 GNB strains were inoculated on COL-R agar plates with selective screening agar for the isolation of GNB resistant to colistin. For the selected isolates, mcr genes, beta-lactamases associated-resistance genes and molecular characterisation were screened by PCRs and sequencing. Results: Colistin-resistance was detected in 5.02% (42/836) of the isolates and colistin-resistant isolates harboured an ESBL (bla_CTX-M-15) and/or a carbapenemase (bla_OXA-48, bla_VIM) encoding gene in 45.2% of the cases. The mcr-1 gene was detected in four E. coli isolates (0.59%) causing urinary tract infections and all these isolates also contained the bla_TEM-1 gene. The bla_CTX-M-15 gene was detected in three isolates that also carried the IncY and IncFIB replicons. The genetic environment surrounding the mcr-carrying plasmid indicated the presence of pap-2 gene upstream mcr-1 resistance marker with unusual missing of ISApl1 insertion sequence. The Conclusions: This study reports the first description of the mcr-1 gene among clinical E. coli isolates in Tunisia and provides an incentive to conduct routine colistin susceptibility testing in GNB clinical isolates.

Background: Since 2012, few reports on the molecular epidemiology of Pseudomonas aeruginosa were reported in Tunisia. Objectives: This study aimed to evaluate carbapenem-resistance determinants and molecular epidemiology and to compare the carbapenemase-phenotypic detection methods of multidrug-resistant P. aeruginosa isolates. Methods: During a period of four years (2014 to 2017), all imipenem-ceftazidime-resistant P. aeruginosa isolates were retrospectively selected at the microbial laboratory of Charles Nicolle hospital of Tunis. These isolates were examined by the modified Hodge test, modified carbapenem inactivation method (mCIM), and another mCIM, called CIMTris, and their performance was evaluated using PCR analysis as the gold standard. Results: A total of 35 isolates were recovered among patients hospitalized in different units. All strains were colistin-susceptible.All carbapenem-resistant isolates showed a high-level resistance to carbapenems. CIMTris and mCIM showed 96.15% and 46.15% sensitivity and 44.44% and 100% specificity, respectively, for detecting carbapenemase production.Conclusions: CIMTris is a promising approach for detecting carbapenemase activity in P. aeruginosa and merits further testing. Moreover, this study described the first detection of GES-5- and GES-9-producing P. aeruginosa in Tunisia as well as the co-occurrence of the bla_GES-5 and bla_VIM-11 carbapenemase genes in one isolate. These findings are of great concern because the rapid dissemination of MDR strains represents a major therapeutic and epidemiological threat.

Background/Objectives: Streptococcus pneumoniae is a leading respiratory pathogen responsible for significant morbidity and mortality, particularly among vulnerable populations. Understanding its antimicrobial resistance patterns and serotype distribution is crucial for guiding treatment and prevention strategies. This study aims to examine these trends in S. pneumoniae isolates from Tunisia over a two-decade period (2000–2019). Methods: A retrospective time series analysis was conducted on data (n = 4284) gathered from eight university hospital centers across Tunisia. Antimicrobial susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Pneumococcal serotypes were determined for a subset of samples from 2012 to 2019 (n = 903) using multiplex PCR and latex agglutination. Results: Penicillin G resistance decreased from 9–13.7% during 2000–2002 to 4.3% by 2019, while amoxicillin resistance increased until reaching 10% in 2019. Erythromycin resistance initially increased before stabilizing between 61.9% and 66.3% during 2014–2019, whereas tetracycline resistance declined from 2000 to 2008 and fluctuated around 40% during 2009–2019. Levofloxacin resistance did not exceed 1.2% throughout the study period. The most prevalent serotypes were 14, 19F, 19A, 23F, 3, 6B, 6A, and 9V. Among them, serotype 3 was the most susceptible overall. Serotypes 23F, 14, 9V, and 6B displayed the highest levels of multi-drug resistance. Conclusions: Penicillin G (high-dosage), cefotaxime, and levofloxacin are still effective against most S. pneumoniae strains in Tunisia, while erythromycin and tetracycline are not reliable options for treating pneumococcal infections. Alarming resistance rates among prevalent serotypes, except serotype 3, underscore the need for preventive measures, rational antibiotic use, and ongoing surveillance.