Presence of Antibiotic-Resistant Aeromonas caviae in Bush Meat from the Mulundu Department in Ogooué-Lolo, Gabon

Bekale Obame Aimé Lionel Loïc¹, Mbehang Nguema Pierre Philippe^1*, Zinga Koumba Christophe Roland¹, Lendamba Romeo Wenceslas², Pambou Yvon-Bert¹, Apinda Legnouo Emelie Arlette¹, Makanga Boris Kevin¹, Akomo Okoue Etienne François¹, Mbeang Jean Constant¹, Etoughe Pascale Stéphanie¹, Mavoungou Jacques François¹

¹Institute for Research in Tropical Ecology (IRET) / National Center for Scientific and Technological Research (CENAREST), Gabon
²Lambaréné Medical Research Center (CERMEL), Gabon

*Correspondence author: Mbehang Nguema Pierre Philippe, Institute for Research in Tropical Ecology (IRET) / National Center for Scientific and Technological Research (CENAREST), Gabon; Email: mbehangphilippe@gmail.com

Citation: Loïc BOAL, et al. Presence of Antibiotic-Resistant Aeromonas caviae in Bush Meat from the Mulundu Department in Ogooué-Lolo, Gabon. Jour Clin Med Res. 2025;6(3):1-13.

Copyright^© 2025 by Loïc BOAL, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Table 1: Species of animals collected.

Antibiotic susceptibility testing

Antimicrobial susceptibility was evaluated using the disc diffusion method on Mueller-Hinton agar (BioMérieux, France), (Bauer, et al., 1966), following the Clinical and Laboratory Standards Institute (CLSI) 2023 guidelines for interpretive thresholds. The tested antibiotics included: ticarcillin + clavulanic acid (85 µg), piperacillin + tazobactam (100/10 µg), imipenem (10 µg), ceftazidime (30 µg), tobramycin (30 µg), ciprofloxacin (5 µg), chloramphenicol (30 µg), gentamicin (10 µg), tetracycline (30 µg), vancomycin (30 µg), rifampicin (5 µg), amoxicillin + clavulanic acid (20/10 µg), penicillin (10 µg), oxacillin (5 µg), cephalexin (30 µg) and cefepime (30 µg).

Statistical Analysis

Data analyses were conducted using R statistical software. Differences in antibiotic resistance proportions across animal species were assessed using chi-square tests. Data visualization was performed through graphical representations to effectively communicate the results.

Results

Species Composition and Abundance

The 147 bushmeats belonged to 20 species, including Blue duiker (Philantomba monticola), Peter’s Duiker (Cephalophus callipygus), Brush-tailed porcupine (Atherurus africanus), Moustached monkey (Cercopithecus cephus) and Long-tailed Pangolin (Uromanis tetradactyla) were the most abundant in this sampling (Table 1).

Bacterial Identification

Identification of all colonies with the API 20 gallery NE gave the following biochemical characteristics (Table 2).

Table 2: Biochemical test results for bacterial identification.

The analysis revealed that ten different bushmeat species tested positive for the presence of Aeromonas caviae (A. caviae), with an overall positivity rate of 36.05% (53 out of 147 animals sampled). The distribution of A. caviae-positive cases varied among species, as detailed in Table 3. The blue duiker had the highest number of positive samples, representing 26.42% of the 53 positive cases and 9.52% of the total 147 animals. This was followed by Peters’s duiker at 22.64% of positives (8.16% total) and the brush-tailed porcupine at 18.87% of positives (6.80% total). Other species with positive detections included the long-tailed pangolin (7.55% of positives), the water chevrotain and moustached monkey (each 5.66%) and the African civet, putty-nosed monkey, red river hog and sitatunga with lower proportions ranging from approximately 1.89% to 3.77% among positive samples. This variation highlights species-specific differences in the prevalence of A. caviae within the bushmeat sample population.

Table 3: Species tested positive for the presence of A. caviae.

Antibiotic Susceptibility Tests

Resistance and Overall Sensitivity

The overall mean antibiotic resistance among the 53 isolates was approximately 49.06%, while the average sensitivity was 50.94%. This near-equal distribution indicates a balanced situation between resistant and susceptible strains at the global level. Table 4 summarizes these findings, showing 416 instances of resistance (49.06%) and 432 instances of sensitivity (50.94%). Fig. 2 visually represents the overall susceptibility pattern to antibiotics across the isolates, reinforcing the evidence of a roughly equal proportion of resistant and sensitive strains.

Table 4: Overall sensitivity.

Figure 2: Overall susceptibility to antibiotics.

Resistance and Sensitivity by Species

The proportions of antibiotic resistance and sensitivity vary by species, as shown in Table 5. Species such as the African Civet, Red river hog and Sitatunga exhibit higher resistance levels, with resistance rates of 65.63%, 59.38% and 56.25%, respectively. Conversely, various duiker species, including Peters’s Duiker and Blue Duiker, have lower resistance levels, indicating higher susceptibility to antibiotics.

Table 3 details these differences, highlighting that for some species like the Long-tailed Pangolin, Putty-nosed Monkey and several duikers, resistance and sensitivity are nearly balanced, each hovering between 45% and 55%. In these cases, represented by Fig. 3, the lengths of the turquoise bars (sensitivity) and salmon bars (resistance) are nearly equal, reflecting this equilibrium.

Table 5: Contingency by species between resistance R and sensitivity S.

However, Fig. 3 also reveals notable imbalances where resistance exceeds 60% or sensitivity falls below 40%, specifically in the Sitatunga, Red river hog, Moustached monkey, Water Chevrotain and especially the African Civet, which shows the highest resistance rate. This pattern underscores species-specific differences in antibiotic susceptibility within the bushmeat sample population.

Table 6 and Fig. 4 summarize the antibiotic resistance profiles of A. caviae isolates. Remarkably, all isolates were resistant to at least five different antibiotics and universally resistant to penicillin, oxacillin and vancomycin, with 100% resistance and no sensitivity detected for these three antibiotics. Resistance to β-lactams showed variability: combinations such as Ticarcillin + Clavulanic Acid (TCC) exhibited very high resistance (98.11%), whereas piperacillin + Tazobactam (TZP) showed lower resistance (32.08%), with only one isolate from a blue duiker sensitive to TCC.

Figure 3: Antibiotic susceptibility by species.

Figure 4: Proportions of resistant sensitive by species.

Cephalosporins also had high resistance rates: ceftazidime (94.34%), cephalexin (50.94%) and cefepime (66.04%). Imipenem (IMI) stood out as the only β-lactam with predominantly high sensitivity, showing just 5.66% resistance. Several other antibiotics showed high sensitivity levels, including ciprofloxacin (84.91%), gentamicin (96.23%), tobramycin (71.70%), chloramphenicol (98.11%) and amoxicillin + clavulanic acid (73.59%). Notably, tetracycline was fully effective against all isolates, with 100% sensitivity.

Statistical analysis based on the resistance/sensitivity contingency table yielded a chi-square value of 6.15 and a p-value of 0.72, indicating no significant difference in antibiotic resistance distribution between species. This suggests that resistance proportions are generally consistent across the different bushmeat species sampled (Fig. 5).

Table 6: Frequency of resistance to antibiotics tested on A. caviae.

Figure 5: Antibiotic susceptibility of A. caviae.

Discussion

This study is one of several investigations to identify pathogens in bush meat consumed by people in the Mulundu district, in order to protect their health. Analyses of feces from purchased bushmeats animals showed the detection of Aeromonas caviae (A. caviae). The genus Aeromonas is a bacterium commonly found in fish and marine animals, but also isolates infections in humans [9]. The diagnosis of this bacterium is somewhat rare in clinical routine, which makes it a bacterium less identified in human pathologies. Nevertheless, in humans it is responsible for various infections ranging from acute gastroenteritis to soft tissue infections and even severe septicemia [9,12]. The interest of studying A. caviae in the wildlife of the department of Mulundu lies essentially in its capacity for zoonotic transmission between bushmeat and the populations that consume it. In this study, the number of wild mammal species (10/20 species, 1/2 of the animals) being positive for the presence of this bacterium and the overall antibiotic resistance rate estimated at 49.06% seem to be important and alarming on the potential for transmission of antibacterial resistance found in this bacterium. The identical frequencies of overall resistance (49.06%) and overall sensitivity (50.94%) in the tested animals indicate a balanced situation between resistant and sensitive strains on a global scale. The prevalence rate of A. caviae in the stools of this study was estimated at 36.05%. In Spain, a study carried out from January 2015 to December 2017 at the Galdakao-Usansolo Hospital revealed the presence of A. caviae from the stools of 85 out of 98 patients, i.e. 86.73% [21]. This result is significantly higher than the prevalence in our study. In Kenya, out of 188 human fecal samples that were analyzed to determine the etiological agents of diarrhea, only three cases were positive for A. caviae [9]. A. caviae and other Aeromonas (A. hydrophila and A. veronii) were identified in another study of 109 clinical isolates isolated from individuals with gastroenteritis in Spain and Mexico [22].

Overall antibiotic susceptibility shows a heterogeneous distribution by species. Some species have higher prevalences of antibiotic resistance than others (the African Civet, the red river hog and the sitatunga); while others have the highest rates of antibiotic susceptibility (the blue duiker, the Peters’ duiker, the Brush-tailed porcupine, the Moustached monkey and the water chevrotain). This distribution could be explained by the fact that A. caviae is a heterogeneous bacterium found on a variety of hosts and whose antibacterial resistance varies greatly [23]. These results also seem to show that wild mammals with the highest resistance rates most frequently frequent forest areas most frequented by humans [24, 25]. It should also be emphasized that the overall resistance is influenced by the natural resistance of’ Aeromonas with respect to rifampicin, there penicillin and oxacillin [10-12]. However, the estimated p-value of 0.7247259 confirms that the overall proportions of susceptibility (S) and resistance R, although S slightly exceeds R in this dataset, the resistance proportions are broadly similar between species; and the chi-square test shows no significant difference in the R/S distribution between species (p > 0.05).

Regarding the antibiotics tested, only one antibiotic, tetracycline, was sensitive to all isolates. However, all aminoglycosides tested, tetracycline (100%), gentamicin (96.23%) and tobramycin (71.70%), showed high sensitivities. Other studies on A. caviae have also shown it to be sensitive to tetracycline and aminoglycosides, including the studies by Monika Nowrotek, et al., and Yiling Dai, et al., and the study by Arun Sharma, et al., also noted the sensitivity of A. caviae to gentamicin and tetracycline [26,27]. On the other hand, the study by Xue, et al., presented A. caviae resistant to tetracyclines and doxycycline [28]. In our study, penicillin and oxacillin were 100% resistant, ceftazidime 94.34%, cephalexin 50.94% and cefepime 33.96%. In general, Aeromonas carry intrinsic resistance to beta-lactams [12,29]. On the other hand, other studies have also revealed A. caviae to be 100% resistant to penicillin. Herawati, et al., high resistance to penicillin and other beta-lactams, including oxacillin, ampicillin and first-generation cephalosporins [9,26,27]. In addition, ceftazidime and cefepime, third and fourth generation cephalosporins respectively, have a very high prevalence of resistance for ceftazidime (94.34%) and a fairly high prevalence for cefepime (33.96%). These resistance rates are quite worrying, as these antibiotics are used clinically to combat severe bacterial resistance as a last resort. Other antibiotics have also shown high prevalence of resistance, namely the combination of ticarcillin + clavulanic acid (98.11%), piperacillin + tazobactam (32.08%) and amoxicillin + clavulanic acid (26.41%). Cases of A. caviae resistant to beta-lactam/beta-lactam inhibitor combinations have already been reported [30]. Resistance to rifampicin (94.34%) and vancomycin (100%) is also significant, even though these antibiotics are used in cases of Mycobacterium infections and infections with Gram-positive bacteria such as Enterococci, respectively. However, the use of these two antibiotics confirms the natural resistance of the Aeromonas genus to them [9]. One study did show Aeromonas hydrophila isolates with resistance rates above 70% [31]. Which suggests that this bacteria appears to have a natural resistance to glycopeptides.

Several isolates were multiresistant to at least five antibiotics of different classes [32] and on several different host species. Most of the Brush-tailed porcupine (Atherurus africanus) were resistant to penicillin, oxacillin, ticarcillin + clavulanic acid, ceftazidime, vancomycin and rifampicin (MDR isolate). Except for these antibiotics, one Atherurus africanus was resistant to these antibiotics but also to tobramycin, chloramphenicol, vancomycin and all beta-lactams (MDR isolate). One blue duiker was resistant to all beta-lactams except imipenem, but also to ciprofloxacin, vancomycin and rifampicin. All Peters’ duikers were resistant to the combination of ticarcillin + clavulanic acid, ceftazidime, vancomycin, rifampicin, penicillin and oxacillin (MDR isolate). One Peters’ duiker was resistant not only to the above antibiotics, but also to imipenem, tobramycin and ciprofloxacin (MDR isolate). One tawny cat showed resistance to twelve out of fourteen antibiotics, only four antibiotics were sensitive (chloramphenicol, gentamicin, tetracycline and cephalexin). Aeromonas are generally resistant to beta-lactams. However, the cases of multidrug resistance recorded in bushmeat, isolated from several different species is not a negligible fact and requires monitoring. In addition, several bushmeat species showed a quite high sensitivity to imipenem (94.34%), tobramycin (71.70%), ciprofloxacin (84.91%), chloramphenicol (98.11%), gentamicin (96.23%) and tetracycline (100%). Resistance to chloramphenicol is not common, it is an antibiotic of restricted use [33]. Other studies have also mentioned the sensitivity of A. caviae to these antibiotics, at fluoroquinolones (ciprofloxacin), tetracycline and aminoglycosides and carbapenems [9,28].

Strength and Limitations of Study

Strength

This study was conducted as part of a collaboration between the Institute for Research in Tropical Ecology (IRET) and the Center for International Cooperation in Agricultural Research for Development (CIRAD). CIRAD covered the cost of samples bushmeat and laboratory reagents for all field missions. In Mulundu, bushmeat was easily purchased from hunters grouped into three Sustainable Management Units (SMUs) by CIRAD researchers who had informed them about our study.

Limitations

The amount of money we had to buy the game wasn’t enough to get a really big sample. Some species of wild mammals are fully protected in Gabon. This explains the low diversity of species in our sampling. In Gabon, it rains almost all the time. Hunting could only take place when it wasn’t raining. This made it impossible for us to access certain areas to purchase bushmeat, thereby reducing the diversity of species.

Conclusion

This study highlighted the presence of resistant and multi-resistant A. caviae in bushmeat consumed by local populations in the Mulundu department of Gabon, a resistance to clinically important antibiotics such as several beta-lactams, rifampicin, vancomycin. Overall, the resistance rate and the sensitivity rate were approximately equal. This indicates a balanced situation between resistant and sensitive strains on a global scale. This study also explores the risks associated with bushmeat consumption and the emergence of a pathogen often ignored in our clinical diagnoses, but with the potential to be a causative agent of acute gastroenteritis, soft tissue infections, septicemia and uremic syndrome. Finally, our research highlights the importance of monitoring the emergence of antibiotic-resistant bacteria in bushmeat consumed by local populations.

Conflict of Interest

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Financial Disclosure

This research did not receive any grant from funding agencies in the public, commercial or not-for-profit sectors.      

Consent To Participate

The authors certify that they have obtained all appropriate patient consent.

Data Availability and Consent of Patient

Data is available for the journal. Informed consents were not necessary for this paper.

Author’s Contribution

All authors contributed equally for this paper.

Acknowledgment

Financial support for fieldwork and laboratory analyses was provided by the Sustainable Wildlife Management (SWM) Program from French Agricultural Research Centre for International Development (CIRAD). The study was facilitated by the Gabonese authorities, particularly the National Center for Scientific and Technological Research (CENAREST), through the issuance of research permits. Valuable scientific and logistical assistance was received from researchers at the Institute for Research in Tropical Ecology (IRET), including Dr. Patrice Makouloutou Nzassi, Dr. Lilian Brice Mangama Koumba, Ms. Ngolo Moukangni, Mr. Bernie Bouchedi and Mr. Guy Landry Mamboundou Kouima. Appreciation is also extended to the Mulundu Department of Water and Forestry in Lastoursville and to the communities of the SWM Program villages for their cooperation and hospitality during field activities.

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