3. Discussion
The data showed that the majority of isolated bacterial strains (71.1%) come from infections contracted in the community. This reflects the high prevalence of community-acquired infections, particularly urinary infections, which account for almost all (95.8%) of the analyses in this group. The predominance of urinary infections is consistent with the trends observed at the national level, where
E. coli is often responsible for these infections, especially in young or elderly females. This trend is confirmed by a recent Tunisian pediatric study, which showed a majority of female cases among patients with
E. coli urinary infections, with a high frequency in young children and marked resistance to common antibiotics [
10].
On the other hand, hospital-acquired infections (28.9%) are much less frequent than community-acquired infections. The analyses mainly come from pus (43.6%), which suggests frequent wound or surgical site infections in the hospital setting. Nosocomial urinary infections (28.2%) remain common as well, often linked to the use of urinary catheters, a well-known risk factor. A Moroccan study showed that urinary catheterization is responsible for 43% of nosocomial infections in Africa. The identified risk factors include advanced age, poor hygiene, medical history (such as diabetes or past urinary infections), as well as the lack of training of healthcare personnel [
11].
The presence of analyses from invasive medical devices (such as femoral, central catheters, or thoracic drains) indicates a significant problem in the hospital setting. Infections related to medical devices represent a significant portion of healthcare-associated infections, particularly in intensive care units, where they are feared for their severity and the high risk of sepsis [
12]. Infections associated with invasive medical devices, such as venous catheters, urinary catheters, and mechanical ventilation systems, are primarily caused by the formation of bacterial biofilms. These biofilms, which form on the devices, confer increased resistance to antimicrobial treatments to the bacteria [
13].
The results of this study showed that most of the samples were taken from female patients; these results align with those of other studies, where, out of 214 recorded cases, 99 (46.3%) were males and 115 (53.7%) were females [
14]. This trend may also be related to the fact that females seek healthcare more often than males and are three times more likely to have reported undergoing a health check-up [
15]. A higher prevalence of
E. coli urinary infections was observed in females (66.33%, n = 52) compared to males (30.67%, n = 23), across all age groups, by Jamil et al. (2018), confirming the observation of a higher proportion of samples from females in this study [
16].
In terms of age distribution, adults (18–64 years) represented 68.1% of bacterial isolates, followed by the elderly and children. This distribution is significant (
p = 0.001), confirming that middle-aged adults are the population most affected by bacterial infections. These results are consistent with those of Zhan et al. (2024), who found an increased prevalence among individuals in the younger age groups, particularly in the 50–69 age range, showing the highest proportion (57.3%) [
17]. Moreover, 76.3% of the samples were urinary, indicating a high frequency of urinary infections in this population, especially among adults, as also reported by Jamil et al. (2018), who observed a high prevalence of
E. coli urinary infections in females [
16], and Zhan et al. (2024), who highlighted an increased frequency of these infections in middle-aged individuals [
17].
The higher frequency of infections in females may be due to anatomical and physiological factors, such as the shortness of the urethra, its proximity to the anus, and changes during pregnancy, which increase the risk of urinary infections [
14], and the predominance of
E. coli in females is explained by the colonization of the area around the urethra by bacteria of intestinal origin, with
E. coli being a normal component of the intestinal flora. The anatomical characteristics of females favor the ascent of these bacteria to the bladder [
18].
Enterobacteriaceae represented 68.8% of the isolated bacteria in our study. A study conducted at the military hospital in Meknes showed that Enterobacteriaceae constitute approximately 68% of positive urine isolates in urinary tract infections [
19]. Overall, Gram-negative bacilli were predominant (84.4%), particularly
E. coli (40.7%), the main cause of urinary infections which is consistent with the results presented by Almutawif and Eid (2023), where Gram-negative bacteria were also the most frequently isolated group (76.14%), while Gram-positive bacteria accounted for 22.7% of the cases [
20]. The predominance of Enterobacterales family especially
E. coli bacteria due to its proximity to the urethra and its ability to adhere to the cells of the urinary epithelium, thus facilitating its migration to the bladder [
21]. Other bacilli such as
Pseudomonas spp. and
Enterobacter spp. were also common, especially in hospital settings, where they often exhibit antibiotic resistance [
22]. Gram-positive cocci, which are less numerous (15.6%), were mainly represented by
Staphylococcus spp., often involved in infections related to medical devices [
23].
The antibiogram results showed a high prevalence of bacterial resistance to the tested antibiotics, particularly to amoxicillin with 83% of resistant strains, confirming a concerning trend already observed. In the study by Kara et al. (2024) [
24]. Piperacillin also showed high resistance, reaching 73.25% in the same study, which confirms the 72.6% obtained in our results [
24]. Furthermore, in a study conducted in Mali by Goita et al. (2025) [
25],
E. coli strains exhibited a resistance rate of 57.14% to ticarcillin–clavulanic acid, which is concerning, but is slightly lower than the 89.54% observed for ticarcillin alone [
25]. Our results showed limited resistance to piperacillin–tazobactam (20%), making it one of the most effective antibiotics against the tested strains. This observation aligns with that of Kara et al. (2024) [
24], who showed that the combination of tazobactam with piperacillin significantly reduced bacterial resistance from 73% to 19%; tazobactam inactivates the bacterial β-lactamase enzymes, allowing piperacillin to remain effective against otherwise resistant bacteria [
26].
The evaluation of the sensitivity of the 135 isolated strains to cephalosporins revealed very high resistance rates. These results are in agreement with those reported by Angho et al. (2024) [
27], where more than 80% of the
Enterobacteriaceae isolates exhibited resistance to cephalosporins. This high resistance is mainly due to the production of extended-spectrum β-lactamases (ESBL), detected in 68.3% of the strains isolated in this study, which showed a marked alteration in the effectiveness of these antibiotics [
27]. On the other hand, lower resistance rates were observed for cefotaxime and cefepime (48.9%), these data correspond to those of a study conducted in Nigeria on
P. aeruginosa, where the resistance rate to cefepimes was 28% [
28].
The results showed varying levels of resistance depending on the tested fluoroquinolones. Ofloxacin, ciprofloxacin, and nalidixic acid, which showed resistance rates of 69.6%, 61.5%, and 51.9%, respectively. These results were consistent with those of Deku et al. (2022) in Ghana, who reported a resistance of 51.1% to ciprofloxacin, 51% to nalidixic acid in
E. coli isolated from various infections [
29]. Similarly, in the Ethiopian study by Hailemariam et al. (2021), resistance to ciprofloxacin reached 63.6% in
E. coli and 80.9% in
K. pneumoniae [
30].
Regarding imipenem, a 40% rate of resistant strains has been noted. This data should be interpreted with caution, as it varies according to bacterial species and geographical contexts. In
E. coli, Kara et al. (2024) [
24] specifically studied 86 strains already resistant to imipenem. For
P. aeruginosa, variable rates have been reported: Ugwuanyi et al. (2021) [
28] noted imipenem resistance in 25.6% of strains isolated in Nigeria, while Vaez et al. (2015) observed a higher resistance, reaching 55.6% of hospital isolates in Iran [
31].
The analysis of the 135 bacterial strains showed a worrying prevalence of antibiotic multi-resistance profile, with all strains (100%) being resistant to at least one antibiotic from three different families, these results correspond to a recent meta-analysis conducted in West Africa, which estimated the overall prevalence of multidrug-resistant bacteria at 59%, with significant variations between countries and sample types [
32]. A significant portion of the bacterial strains studied exhibited resistance to six–eight antibiotics, reflecting a worrying trend towards multidrug resistance. These data confirm the global trends reported by WHO which highlight an increase in multidrug-resistant infections in healthcare facilities [
33]. A recent review in West Africa also confirms this trend [
34]. In the study by Ahmed et al. (2023) on 89
K. pneumoniae, 57.3% exhibit an MDR phenotype during COVID-19 [
35]. According to Saeli et al. (2024), the prevalence of aminoglycoside-resistant
P. aeruginosa isolates was 48%, of which 94.7% exhibited multidrug resistance (MDR) [
36].
The analysis of correlations between aminoglycosides and other antibiotics showed significant cross-resistance, especially between gentamicin and several β-lactams such as cephalexin and cefixime. This co-resistance is often linked to common genetic mechanisms, such as ESBLs or enzymes modifying aminoglycosides [
37]. Correlations between carbapenems (imipenem) and aminoglycosides also suggest an increase in multidrug-resistant strains, a phenomenon confirmed by a recent meta-analysis on infections caused by Gram-negative bacilli [
38]. Finally, the observed links between quinolones and aminoglycosides indicate cross-resistance mechanisms such as efflux pumps, supported by recent research on the effect of cross-exposure to antibiotics [
39].
The distribution of resistance determinants among the studied isolates revealed a significantly higher prevalence of β-lactamase genes compared with quinolone resistance determinants (
p < 0.001 for both), with
blaTEM being the most frequent (35.6%), consistent with reports from Switzerland [
40] where aminoglycosides-resistant strains presented both ESBL and AmpC phenotypes, where
blaTEM was the predominant β-lactams resistance machine followed by
blaCTX-M. Strong association was found between the co-carriage of
blaOXA-1 β-lactamase type and
aac(60)-Ib-cr, which compromises amikacin and tobramycin resistance [
41].
Gram-negative bacteria dominated the analyzed samples, with a high proportion of strains capable of producing a biofilm. This observation is consistent with the data reported by Maione et al. (2023), which showed that among 1039 community samples, 96.2% of the isolates were Gram-negative compared to only 3.8% being Gram-positive [
42]. Similarly, Dumaru et al. (2019) reported that, out of 314
E. coli isolates, 38% represented the most common strain [
43].
Consistent to our results, Joshi et al. (2021) reported that 47.44% of the strains isolated from urine samples produced a biofilm [
44]. Similarly, Belbase et al. (2017) observed that 46.1% of
S. aureus isolates from pus or wound samples had this capability [
45]. Most of our strains were weak biofilm producers, particularly
E. coli,
P. aeruginosa, and
Enterobacter spp., while
Staphylococcus spp. showed a higher proportion of strongly producing strains. These results were supported by several studies. Dumaru et al. (2019) showed that 62.73% of the tested isolates were positive for biofilm production, with a strong involvement of
Klebsiella spp. and
Pseudomonas spp. [
43]. Karigoudar et al. (2019) also reported that, out of 100 urinary
E. coli isolates, 69% were capable of producing a biofilm [
46]. Macias-Valcayo et al. (2022) observed that 97% of Gram-positive studied strains formed biofilm [
47], Murthy et al. (2024) reported 22% of biofilm producers in
S. aureus strains [
48]. Biofilms exhibit strong antibiotic resistance by limiting drug penetration, inactivating antibiotics, harboring dormant cells, and upregulating efflux pumps and resistance genes [
49].
The production of extracellular enzymes is a key factor in bacterial pathogenicity. In this study, proteases were the most frequently produced (49.6%), a result consistent with those of Bertelloni et al. (2021) who reported (46.0%) [
50]. Lecithinase activity was observed in 24.4% of the isolates, the same rate recorded for
Clostridium perfrengens [
51]. The production of lipases remained rarer (10.4%), although it can reach 52.0% according to Bertelloni et al. (2021), which reflects variability related to strains or conditions. Regarding hemolysis, Bertelloni et al. (2021) also indicate a dominance of the mixed α/β profile, followed by the β type and the α type [
50]. Finally, Rahman et al. (2024) showed that lipase and protease-producing strains were more resistant to antibiotics, suggesting a link between enzymatic virulence and antibiotic resistance [
52].
4. Materials and Methods
This study was conducted in several geographical locations around Setif province in the northeastern of Algeria; the collection was distributed on seven medical diagnostic laboratories, and three government hospitals. The study was approved by the Ethics and Deontology Committee in University Ferhat Abbas of Setif-1 under the study registered with the number of the paper, UFAS1/09/03/2023/ETH-Deon-A-301, and informed written consent was obtained from each participant.
4.1. Samples Collection and Bacteria Identification
During a three-year period from 2021 to 2023, 135 samples were selected for this study. All clinical samples: urine, pus, vaginal swab, catheters (central, femoral, bladder), blood, thoracic drainage, and tracheal tube, were collected under aseptic precautions. The samples were taken from patients of different ages and of both sexes. Patient information (age, sex, nature of sample, date of collection, patient type) was recorded in samples register at the microbiology laboratory, a positive culture without contamination respecting sterility criteria and showing decreasing sensitivity to one aminoglycoside agent were included in this study. The following samples were excluded from this study: samples with incomplete clinical or laboratory data; samples that did not meet the quality control or sterility criteria; samples which were not maintained at the required temperature or for the required duration of conservation before analysis; multiple samples from the same patient. All samples were cultured on non-selective and selective media such as nutrient agar, Hektoen agar, MacConkey agar, or Chapman agar and incubated at 37 °C for 24 h.
Identification of isolates was done by microscopic examination, colony morphology, Gram staining, motility and biochemical tests: indole production, mannitol, citrate utilization, glucose, sucrose, lactose fermentation in TSI agar, catalase, oxidase, urease and gas production. Then, the identified strains were preserved in a nutrient broth containing 30% sterile glycerol.
4.2. Antimicrobial Susceptibility Testing
Antimicrobial susceptibility tests were performed on Mueller–Hinton agar using the Kirby-Bauer disk diffusion method. A total of 24 antimicrobial agents were tested, including penicillins: amoxicillin (AX, 25 µg), ticarcillin (TC, 75 µg), and piperacillin (PRL, 100 µg). β-lactam/inhibitor combinations were tested: amoxicillin–clavulanic acid (AMC, 30 µg), ticarcillin–clavulanic acid (TTC, 85 µg), and piperacillin–tazobactam (TPZ, 110 µg). Cephalosporins were tested, including cefalexin (CL, 30 µg) as a first-generation agent, cefoxitin (FOX, 30 µg) as a second-generation agent, cefixime (CFM, 5 µg), ceftazidime (CAZ, 30 µg), and cefotaxime (CTX, 30 µg) as third-generation agents, and cefepime (FEP, 30 µg) as a fourth-generation agent. Carbapenems included imipenem (IMP, 10 µg); aminoglycosides included gentamicin (CN, 10 µg), amikacin (AK, 30 µg), tobramycin (TOB, 10 µg), and kanamycin (K, 30 µg); quinolones and fluoroquinolones included nalidixic acid (NA, 30 µg), ciprofloxacin (CIP, 5 µg), ofloxacin (OFX, 5 µg), and levofloxacin (LEV, 5 µg); phenicols included chloramphenicol (C, 30 µg), monobactam aztreonam (ATM, 30 µg), and the sulfonamide combination trimethoprim–sulfamethoxazole (SXT, 25 µg).
For this test, a bacterial inoculum was prepared from young culture for 20 ± 4 h in a non-selective culture medium and placed in a saline solution containing 0.9% sodium chloride. The surface of Mueller–Hinton agar plates (TM-Media, Delhi, India) was inoculated with the bacterial inoculum by swabbing within 15 min of the inoculum preparation. The swab was moved three times over the entire surface of the agar plate. The plate was then rotated 60° after each stroke to distribute the inoculum. Antibiotic disks were selected according to each species’ appropriate applicability; they were then placed on the agar surface. The antibiotics were selected according to the species’ appropriate applicability, with the plates applied using sterile forceps, pressing each disk down. The plates were then incubated at 35 ± 2 °C for 20 ± 4 h. Finally, after measuring the different inhibition zones with a ruler after the incubation period and comparing them with the critical diameter, the strain resistance data were interpreted according to the European Committee for Antimicrobial Susceptibility Testing (EUCAST) guidelines for 2022 [
53]. They were categorized as follows: resistance (R), susceptible (S), or intermediate (I). This study included isolates with decreased sensitivity to at least one agent in an aminoglycoside family (resistant or intermediate phenotypes). Using the definition of multidrug-resistant bacteria (MDR) [
8], our strains were classified as MDR strains.
4.3. Molecular Assays for Resistance Gene Screening by Multiplex PCR
Antimicrobial resistance genes (ARGs) were analyzed in isolates classified as resistant or intermediate to at least one antimicrobial agent (β-lactams and quinolones) by Kirby–Bauer testing. Genomic DNA was released from colonies using a heat–lysis method adapted from Woodman et al. (2016) [
54] for each isolate. One–two colonies grown overnight on nutrient agar (Oxoid, Milan, Italy) were suspended in sterile water (100 µL), heated at 99 °C for 15 min, and centrifuged at 10,000×
g for 10 min. The resulting supernatant was used as a DNA template. DNA integrity was checked by agarose gel electrophoresis, DNA samples showing a single, intact high-molecular-weight band without visible smearing were considered acceptable for further analyses. Concentration and purity were measured with a NanoDrop 2000c (Thermo Fisher Scientific, Waltham, MA, USA). Successful extraction was confirmed by PCR amplification of the 16S rRNA gene using primers F1 and R12 [
55].
The presence of β-lactamase genes was assessed by two multiplex PCR assays: set 1 targeting
blaCTX-M IV,
blaTEM,
blaOXA, and
blaSHV; set 2 targeting
blaCMY II,
blaCTX-M I,
blaCTX-M II, and
blaDHA, as described by Kim et al. (2009) [
56]. Plasmid-mediated quinolone resistance determinants (
qnrA,
qnrB,
qnrC,
qnrD,
qnrS) were analyzed by singleplex PCR (
Table 8). Each PCR was performed in 25 µL containing DreamTaq Buffer, dNTPs, primers (adjusted depending on singleplex or multiplex design), DreamTaq DNA Polymerase (Thermo Fisher Scientific), and 2 µL of template DNA. The amplification program included an initial denaturation, 35 cycles of denaturation, annealing at the primer-specific temperature and extension, followed by a final elongation step.
4.4. Biofilm Production
Biofilm formation is an important factor in the virulence of some bacteria and plays a significant role in increasing antibiotic resistance and host immune defense. To detect biofilm-forming capacity, a 96-well microtiter plate (TrustBio Corporation Ltd, Shanghai, China) was used, as described by Stepanović and et al. (2007) and Türkel et al. (2018) [
58,
59]. After growing bacterial strains in non-selective agar at 37 °C for 24 h, and after verifying the purity of the strains, a 0.5% McFarland solution in Brain Heart Infusion broth BHIB (Liofilchem, Abruzzo, Italy) supplemented with 2% glucose was prepared. A measure of 200 µL of each culture was then placed in microtiter plates with polystyrene wells (three wells for each bacterial isolate) and incubated at 37 °C for 24 h. Three wells were filled with sterile BHIB and designated as the negative control. All biofilm assays were performed in triplicate and repeated in at least three independent experiments to ensure reliability.
The medium was discarded after incubation, and the wells were washed three times with distilled water. To stabilize the adherent cells, 150 µL of methanol was added for 20 min. At room temperature, the biofilms were stained with a 0.2% (w/v) crystal violet solution for 15 min. The crystal violet was then removed, the wells were rinsed with sterile distilled water, and the plates were left to air-dry. The biofilms were then dissolved in 150 µL of 95% ethanol, and the absorbance was measured at 570 nm using an ELISA reader (BioTek, El Dorado Hills, CA, USA). The results were divided into four categories by comparing the measured OD with the negative control (ODc). Based on optical density (OD), four levels of biofilm production were distinguished. Strains with an OD equal to or lower than that of the ODc were classified as non-biofilm producers. Those with an OD higher than the ODc but less than twice (2 ODc) were considered as low biofilm producers. Moderate biofilm production was defined when the OD was between two and four times that of the ODc. Finally, strains with an OD greater than four times the control (4 ODc) were categorized as high-output biofilm producers.
4.5. Hemolysin Production
The tested isolates were cultured on blood human agar base (BHIB), which was prepared by adding 5% human blood to a blood agar base at a temperature of 45–50 °C. These isolates were incubated at 37 °C for 18–24 h. Hemolytic activity was determined by colony appearance and the presence of halos surrounding the colonies on blood agar [
60,
61]. Three phenotypes were observed: complete lysis of red blood cells, characterized by a clear zone around the colonies (β-hemolysis); partial lysis, forming a greenish halo due to the reduction of hemoglobin to methemoglobin (α-hemolysis); no visible change around the colonies, indicating the absence of lysis (γ-hemolysis).
4.6. Protease, Lecithinase and Lipase Production
The ability of the studied strains to produce proteases was determined on skimmed milk agar plates, which consist of peptone, yeast extract, and agar. After sterilization, 100 mL/L of ultra-high-temperature (UHT) sterilized milk was added to the base at a temperature ranging from 45 to 50 °C. The tested strains were then cultured and incubated at 37 °C for 24 h. The presence of a clear zone around the bacterial colonies indicates protease activity.
E. coli ATCC 25922 was used as a negative control, while
P. aeruginosa ATCC 27853 served as a positive control [
62]. And to determine the lecithinase and lipase production capacity of the studied strains, they were cultured on egg yolk agar (EYA) plates (TM-Media, Delhi, India). A non-selective agar was used, to which egg yolk emulsion (egg yolk + sterile saline) was added at 45–50 °C. The cultures were then incubated at 37 °C for 24 h. The appearance of halos around the colonies indicates lecithinase activity.
Bacillus cereus and
E. coli ATCC 25922 were used as positive and negative control, respectively, while the appearance of an iridescent sheen on the surface of the colony indicates lipase activity.
P. aeruginosa ATCC 27853 and
S. aureus ATCC 29213 were used as the positive and negative control [
63].
4.7. Statistical Analysis
Statistical analysis of resistance was performed using SPSS version 27 to calculate frequencies of qualitative variables. Pearson’s and chi-square tests were used when necessary to compare percentages in bivariate analysis. A p-value less than or equal to 0.05 was considered statistically significant.