Ghassan Tayh

Shiga toxin–producing Escherichia coli produce Shiga toxins, the primary virulence factors responsible for severe gastroenteritis and, in some cases, hemolytic uremic syndrome. The objective of this study was to investigate host- and strain-associated factors influencing the distribution of stx genes by analyzing data from Shiga toxin–producing Escherichia coli strains isolated from fecal samples of healthy livestock and poultry in Tunisia. A total of 116 Shiga toxin–producing Escherichia coli isolates from cattle, camels, and chickens in Tunisia were analyzed for the distribution of stx genes in relation to serogroups, host species, phylogroups, and integron carriage. This analysis was carried out to identify the factors influencing stx gene frequency and to explore potential mechanisms involved in their dissemination among diverse Shiga toxin–producing Escherichia coli serotypes. Shiga toxin genes were detected in all 116 isolates, with stx1 and stx2 identified in 75% (87/116) and 32.8% (38/116) of isolates, respectively. Across the seven tested serogroups (O26, O45, O91, O103, O121, O145, and O157), stx1 was detected in all groups, whereas stx2 was most frequent in serogroup O145 and absent in O121 and O91. The prevalence of stx1 varied significantly by host (p = .002), with the highest proportion in chickens, followed by cattle, while stx2 was most prevalent in camels and secondarily in cattle (p = .001). A significantly higher prevalence of stx2 was observed in phylogroups E and Clade I compared to other phylogroups (p = .005). Furthermore, stx1 was significantly more common in integron-positive isolates than in integron-negative isolates (p = .003). Shiga toxin genes were frequently detected in high-risk serogroups (O103, O145, and O157), predominantly within pathogenic phylogroups B2 and E, indicating an increased zoonotic risk. The significant association between integrons and stx genes (p = .003) suggests the co-selection of virulence and antimicrobial resistance traits, which represents a potential public health risk in Tunisian food animals. Cite this article as: Tayh, G., & Messadi, L. (2026). Distribution of shiga toxin genes in shiga toxin–producing Escherichia coli from healthy livestock and poultry in Tunisia: zoonotic risk and association with integrons. Acta Veterinaria Eurasia, 52, 0260, doi:10.5152/actavet.2026.25260.

Klebsiella pneumoniae is a leading cause of hospital‐acquired infections, particularly in intensive care units (ICUs), where multidrug‐resistant (MDR) and hypervirulent strains represent major therapeutic challenges. This study investigated the phenotypic and molecular features of isolates recovered from ICU patients and the hospital environment in Benghazi, Libya. Antimicrobial susceptibility was determined using disk diffusion and the colistin broth disk elution method. Extended‐spectrum‐ β ‐lactamase (ESBL) and carbapenemase production were assessed phenotypically and confirmed by PCR and sequencing, whereas clonal relatedness was analyzed through OmpK36 typing. Hypervirulence was evaluated using the string test, PCR detection of virulence genes, and biofilm formation assays. A total of 56 isolates (46 clinical and 10 environmental) were included. All isolates were resistant to ceftriaxone, with high resistance rates to ceftazidime, cefotaxime, carbapenems, ciprofloxacin, and gentamicin. ESBL production was observed in 76% of clinical and 80% of environmental isolates, and 95% of all isolates were classified as MDR. A significant proportion of K. pneumoniae isolates ( n = 15) exhibited resistance to colistin in the absence of detectable mcr genes. Strong and moderate biofilm production was detected in 30.4% and 17.9% of isolates, respectively. The bla _NDM-5 was prevalent among clinical (45/46; 97.8%) and environmental (9/10; 90%) isolates. Similarly, bla _CTX-M-15 was detected in 35/46 (76%) clinical isolates and 8/10 (80%) environmental isolates, whereas bla _OXA-48 was detected in 26/46 (56.5%) clinical and 10/10 (100%) environmental isolates. A potentially hypervirulent phenotype was observed in 17.8% of the isolates, associated with the virulence genes iuc A, iut A, and peg ‐344. OmpK36 Groups C and D predominated. These results highlight the alarming spread of MDR and hypervirulent strains in ICUs and underscore the need for reinforced infection control strategies.

The aim of this study was to investigate the frequency of antimicrobial resistance and the rate of extended-spectrum β-lactamase (ESBL) in Escherichia coli isolated from caecum content collected in slaughterhouses located in three regions of Tunisia. E. coli isolates from chicken caecal samples, obtained using media supplemented with cefotaxime, were screened for antimicrobial susceptibility by the disk diffusion method. ESBL production was assessed by the double-disk synergy test, and the presence of β‑lactamase encoding resistance genes was evaluated by PCR. Out of 111 faecal samples, 108 samples were positive for E. coli isolated from media supplemented with cefotaxime with 70% of ESBL-producing isolates. Alarming proportions of resistance against most of the 21 tested antibiotics were observed with 90% of multidrug resistant strains. Most strains exhibited resistance to amoxicillin, cefepime, tetracycline, cephalothin, piperacillin, cefotaxime, aztreonam, streptomycin, ceftazidime, cefuroxime, chloramphenicol, and florfenicol. The same resistance patterns were found in comparison between the three chicken slaughterhouses. A high prevalence of β‑lactamase genes was observed, with bla _CTX-M-G1 -ESBL in 79.6% of strains, bla _TEM in 45.4%, and bla _SHV in 33.3%. The bla _CTX-M-G1 and bla _TEM genes were significantly more frequent in strains from slaughterhouses A and C. Additionally, carbapenem resistance genes, bla _OXA-48 and bla _IMP , were demonstrated in 13% and 6.5% of strains, respectively. The study showed high frequency of ESBL-producing E. coli and high antibiotic resistance in broilers. Poultry farms could represent a significant reservoir of ESBL-producing bacteria, suggesting the dissemination of these pathogens to humans and environment. These findings indicate the need for achievement of control and surveillance system.

This study investigated the molecular and phenotypic characteristics of antimicrobial resistance in Escherichia coli isolates recovered from the ceca of healthy broilers in Tunisia. A total of 111 E. coli isolates were obtained from chicken samples collected at slaughterhouses and cultured on cefotaxime-supplemented MacConkey agar. All isolates exhibited a multidrug-resistant (MDR) phenotype, and 72.1% were confirmed as extended-spectrum β-lactamase (ESBL) producers. The most frequent β-lactamase gene was bla_CTX-M-G1, followed by bla_TEM and bla_SHV. Carbapenem resistance genes (bla_OXA-48 and bla_IMP) were detected in 12.6% and 6.3% of isolates, respectively, while six isolates harbored the colistin resistance gene mcr-1. Among the tested virulence genes, fimH, traT, and iutA were the most prevalent, detected in over 70% of isolates. Class 1 integrons were present in 83% of isolates, and class 2 integrons in 39.6%, with gene cassettes encoding resistance to trimethoprim (dfrA) and streptomycin (aadA). These findings highlight the widespread presence of MDR and ESBL-producing E. coli strains with virulence traits and integrons in poultry, underscoring the risk of transmission to humans. This study provides essential data supporting the implementation of integrated surveillance strategies in line with the One Health approach.

The use of treated wastewater (TWW) for crop irrigation has increased worldwide as an alternative to preserving freshwater resources. However, choosing this alternative still requires more data about its impact on the environment, crop quality, and human health. In this regard, the present study aimed to assess the irrigation impact with TWW for a long time (35 years) on soil properties and on cereal and bean yield. To evaluate this effect, two sites were studied: the first one irrigated with TWW (S1) and the second irrigated with tap water (S2). Soil analysis from S1 revealed higher salinity and high levels of inorganic and organic pollutants compared to FAO standards (3.39 ± 0.45 µg/g MS for Cd and 68 ± 1.9 µg/g MS for Cu, respectively). In TWW, the concentrations were 1.15 ± 0.05 µg/L for Cd, 0.32 ± 0.18 µg/L for Ni, and 1.11 ± 0.01 µg/L for Pb, respectively. Additionally, high concentrations of organochlorine compounds were detected with chromatography coupled with mass spectrometry (GC–MS) in TWW, such as Aldrin (0.01 µg/mL) and γ-HCH (0.016 µg/mL), as well as in soil (0.883 µg/g). These compounds exceeded the Tunisian standards (NT: 106.03) and the FAO guidelines for irrigation. Also, irrigation with TWW over 35 years increased the aerial biomass of Triticum turgidum and Hordeum vulgare but negatively affected the plant growth of Medicago sativa L. Organic contaminants, such as pesticides, reduced soil fertility and biodiversity. Furthermore, mineral pollutants accumulated in soil, such as heavy metals, affect plant growth, which poses a risk directly for the food chain and indirectly for human health. Continuous irrigation with wastewater alters the physicochemical properties of the soil and leads to the accumulation of inorganic pollutants in food crops. This alteration depends not only on the soil’s physical and chemical properties but also on the duration of irrigation. Based on this study, long-term irrigation with TWW poses significant risks to both human health and ecosystems. Therefore, continuous monitoring and proper management of TWW irrigation are crucial to mitigate these potential risks and ensure the long-term sustainability of agricultural practices.

Antibiotics are frequently used in the poultry industry, which has led to the emergence of bacterial strains that are resistant to antimicrobial treatments. The main objectives of this research were to conduct a multimodal risk assessment, to determine the extent of contamination of chicken meat with Escherichia coli, assess the prevalence of strains resistant to extended-spectrum cephalosporins (ESC), and characterise the genes associated with resistance and virulence. A standardised procedure involving enrichment in buffered peptone water and isolation of E. coli on MacConkey agar was carried out on 100 chicken carcasses. Subsequently, the sensitivity of the strains was tested against 21 antibiotic discs. Additionally, ESBL production was detected using a double synergy test. Specific PCRs were employed to identify resistance to critical antibiotics in human medicine (such as cephalosporins, carbapenems, fluoroquinolones, and colistin), as well as the presence of virulence genes. The contamination rate of chicken meat with E. coli was 82%. The prevalence of ESC-resistant isolates was 91.2%. Furthermore, 76.5% of the isolates exhibited ESBL production, with the different beta-lactamase genes (bla_CTXM, bla_TEM, and bla_SHV). The mcr-1 gene, associated with colistin resistance, was detected in four strains (5.9%). Some isolates also carried resistance genes such as sul1, sul2, sul3, tetA, tetB, qnrB, and qnrS. In addition, several virulence genes were detected. In our study, we were able to link the expression of AMR to the iron metabolic regulatory elements using a multimodal machine learning approach; this mechanism could be targeted to mitigate the bacteria virulence and resistance. The high prevalence of ESBL-producing and multi-resistant E. coli strains in poultry presents significant human health risks, with the focus on antibiotic-resistant uropathogenic strains since poultry meat could be an important source of uropathogenic strains, underscoring the danger of hard-to-treat urinary tract infections, stressing the need for controlled antibiotic use and thorough monitoring.

Houseflies (Musca domestica) live in close contact with humans. They are carriers of human pathogenic bacteria in the digestive tract and on their body. This study aimed to assess the prevalence of antibiotic-resistant Gram-negative bacteria in flies.Sixty-one isolates were collected from 100 houseflies at three different locations: a laying hen farm, a market, and three houses, comprising 23 Escherichia coli, 31 Klebsiella pneumoniae and 7 Pseudomonas aeruginosa. Antimicrobial sensitivity was determined by the disk diffusion method, and the ESBL-producing isolates were screened by the double-disc synergy test. β-lactamase genes, associated resistance genes, and integrons were studied by PCR.The ESBL-producing isolates comprised14.8% (9/61) of the isolates, seven K. pneumoniae isolates, and two E. coli isolates. The highest rate of ESBL-producing strains was observed in houses (7/22; 31.8%), followed by the market (2/43; 4.7%). Multi-drug-resistant bacteria were detected in 19/61 (31.2%) insects. Third-generation cephalosporin-resistant isolates (n= 30) were used to identify the resistance genes. The following resistance genes were identified in the isolates; blaCTX-M-G-1 (76.7%, 23/30), blaSHV-1 (43.3%, 13/30), blaTEM-1 (36.7%, 11/30), blaIMP (16.7%, 5/30), blaOXA-48 (10%, 3/30) and blaNDM (3.3%, 1/30). The quinolone resistance genes qnrs, aac(6′)-Ib-cr, qnrB and qnrA were found in 11, 11, 7 and 5 isolates, respectively. Integron 1 (intI1) was detected in 15 (50%) isolates, qacEΔ1+sul1 was identified in ten intI1-positive isolates. Class 2 integron was detected in three isolates. Houseflies collected from houses and markets may be implicated in the spread of multi-drug resistant bacteria which constitute a considerable threat to human public health. The ESBLs in flies reflect the contamination status of the environment and can be used as indicators of contamination.

Background Gram-negative bacteria with quinolone resistance and extended-spectrum beta-lactamases (ESBLs) present significant treatment challenges. This study evaluated the prevalence and characteristics of quinolone resistance in Gram-negative strains, investigating the relationship between plasmid-mediated quinolone resistance (PMQR), ESBLs, and integrons. Methods and results We collected 146 Gram-negative isolates from patients in three Palestinian hospitals. For quinolone resistance isolates, the presence and characterization of PMQR, β-lactamase genes and integrons were studied by PCR and sequencing. Out of 146 clinical isolates, 64 (43.8%) were resistant to quinolones, with 62 (97%) being multidrug-resistant (MDR) and 33 (51.5%) ESBL-producers. PMQR-encoding genes were present in 45 (70.3%) isolates, including aac(6′)-Ib-cr (26.6%), qnrA (18.8%), qnrS1 (20.8%), and qnrB (6.4%). Bla_CTX−M genes were detected in 50% (32/64) of isolates, with bla_CTX−M−15 being the most common. Bla_TEM−1, bla_SHV−1 and bla_VIM genes were found in 13, 6, and 4 isolates, respectively. Class I integrons were found in 31/64 (48%) of isolates, with 14 containing gene cassettes conferring resistance to trimethoprim (dhfr17, dfrA12, dfrA1) and aminoglycosides resistance genes (aadA1, aadA2, aadA5, and aadA6). Conclusions This study found a high rate of quinolone resistance, ESBL and integrons in clinical Gram-negative isolates from our hospitals. Urgent measures are crucial, including implementing an antimicrobial resistance surveillance system, to control and continuously monitor the development of antimicrobial resistance.