Out of 1649 canine clinical samples submitted between January 2015 and December 2022, ninety-one clinical isolates (collected from clinical cases of otitis, UTIs, abscesses and wound infections) were found to be positive for
P. aeruginosa. These ninety-one isolates were further studied for their antimicrobial susceptibility pattern using the Kirby-Bauer disc diffusion method. From the reports of these clinical isolates of
P. aeruginosa, high susceptibility was recorded for gentamicin (95.6%), ceftazidime (96.7%), imipenem (97.7%) and ciprofloxacin (97.8%). One isolate showed an intermediate susceptibility to the ceftazidime and imipenem drug. This intermediate susceptibility could be categorized as an emerging resistant strain (Table 1).
Table 1 tabulates only the antimicrobials recommended for treating
Pseudomonas sp. infections. Other antimicrobials such as amoxicillin+clavulanic acid, clindamycin, cephalexin, ceftriaxone, novobiocin, oxytetracycline and chloramphenicol used for the antimicrobial susceptibility test were not shown under this tabulation as these antimicrobials were not treatment choices for
P. aeruginosa infections because of their inherent resistance.
During this study period, only seven
P. aeruginosa isolates have been evaluated against amikacin (30 µg) antimicrobial drug. Out of this, only one isolate showed resistance to amikacin in 2021. Also, effective antibacterial drugs such as gentamicin, ceftazidime, imipenem and ciprofloxacin exhibited resistance patterns progressively since 2021 (Fig 1). This indicates that antimicrobial resistance has been triggered in a few
P. aeruginosa isolates.
However, multidrug resistance was not documented in this study. This is a positive indication that the resistance development among
P. aeruginosa is very minimal and could be well prevented by proper antibiotic use measures in Grenada.
P. aeruginosa is the most resistant bacteria and contributes major to nosocomial infections
(Kollef et al., 2014). This bacterial pathogen exhibits multiple resistance mechanisms and is known for its high antimicrobial resistance pattern
(Todar, 2020; Poole, 2011). The antimicrobial resistance mechanisms have gradually progressed over a period due to chronic/injudicious use of antimicrobials. The primary mechanisms to counter antibiotic efficacy in
P. aeruginosa could be either intrinsic or acquired mechanisms. Intrinsic mechanisms include the expression of non-specific porin molecule (OprF) which limits the permeation of antibiotics, reduced expression of outer cell membrane porin channels and expression of efflux pumps that expel antibiotics out of the cell. Furthermore,
P. aeruginosa could produce biofilm encapsulation, which prevents the antibacterial drug permeation
(Breidenstein et al., 2011). The acquired resistance relates to the resistant gene development acquired through horizontal gene transfer mechanisms such as transformation, transduction and conjugation. The resistant bacterium could synthesize antibiotic-inactivating enzymes to inactivate the antibiotic
(Breidenstein et al., 2011; Okazaki et al., 2002; Mulcahy et al., 2010). The emergence of resistant
P. aeruginosa strains is gradually increasing the challenge of treating resistant microbial infections
(Giamarellou, 2002).
In this study, the antimicrobial susceptibility pattern of
P. aeruginosa isolated from clinical samples of dogs in Grenada were evaluated. Under this retrospective study conducted from January 2015 to December 2022, ninety-one (91) isolates of
P. aeruginosa were isolated from the clinical conditions of otitis, abscess, wound infections and UTI infections in dogs. This is in confirmation with the other research studies indicating
P. aeruginosa as the cause of these clinical conditions. The results of this study report revealed that
P. aeruginosa isolates of dogs in Grenada are susceptible to gentamicin, amikacin, ciprofloxacin, ceftazidime and imipenem. On comparing this retrospective study report to a similar study done for the period between 2005 through 2009 at St. George’s University in Grenada
(Hariharan et al., 2009), we found that
P. aeruginosa isolates in Grenada have maintained a similar susceptibility pattern to aminoglycoside drugs, gentamicin and amikacin. The AST pattern of
P. aeruginosa documented that the susceptibility of the bacterial isolates has been consistent over the last eleven years in Grenada. This is considered remarkable in the context of stabilized susceptibility patterns and emphasizes the importance of minimizing the possibilities of antimicrobial resistance development in the future.
The present study data from Grenada were compared with the global antimicrobial susceptibility pattern of
P. aeruginosa, from South American, European and Asian continents. In Columbia, out of 89 Gram-negative bacterial isolates from canine patients collected between June 2013 and May 2014, at various clinics, 10 isolates were found to be
P. aeruginosa. The antimicrobial susceptibility pattern of these isolates had documented susceptible responses to ceftazidime (70%), amikacin (70%), gentamicin (70%), ciprofloxacin (80%) and imipenem (90%)
(Bernal-Rosas et al., 2015). Comparing this report with that of the present study data, the susceptibility pattern of canine
P. aeruginosa isolates of Grenada revealed a higher sensitivity with gentamicin (95.6%), ceftazidime (96.7%), imipenem (97.7%) and ciprofloxacin (97.8%). The differences in antimicrobial susceptibility response rates between these two studies are of considerable significance and have demonstrated the sustained susceptibility pattern of
P. aeruginosa in Grenada.
Multidrug resistance of
P. aeruginosa has been demonstrated in France in canine patients, attributed to the high use of antimicrobials for otitis conditions in dogs. The antimicrobial susceptibility study conducted in France with 46 canine clinical isolates of
P. aeruginosa that were collected between 2008 and 2011 showed a resistant response to gentamicin and ciprofloxacin of 56.5 % and 63% respectively
(Haenni et al., 2015). On the contrary, this study revealed that there is no prevalence of multidrug-resistant strains of
P. aeruginosa. In comparison with this study report, it became evident that a greater number of antimicrobials provides an effective susceptibility pattern against
P. aeruginosa in canine species of Grenada.
In the present study analysis, out of eighty-seven (87) isolates of
P. aeruginosa tested for imipenem, one isolate had shown intermediate resistance (1.15%) and one isolate exhibited complete resistance (1.15%). This is following the 6% imipenem resistance pattern reported for
P. aeruginosa isolated from a veterinary academic hospital in South Africa
(Eliasi et al., 2020). These reports are indicative of the progressive development of imipenem resistance among the
P. aeruginosa bacterial strains. Carbapenem resistance has been reported for
P. aeruginosa (Haenni et al., 2017) associated with increased expression of genes encoding efflux pumps to extrude the antimicrobial drug out of the bacterial organism
(Poole, 2000). As imipenem is a broad-spectrum drug with effective action against
P. aeruginosa, it became imperative to prevent the further development of antimicrobial resistance.
This study report documented a lower proportion of antimicrobial resistance recorded for
P. aeruginosa against aminoglycoside antibiotic, gentamicin (4.4%) in Grenada. This is following a similar study conducted in Japan with 200 clinical samples of
P. aeruginosa isolated from dogs around seven major regions from September 2014 through February 2015. These isolates exhibited resistant responses to gentamicin and amikacin, occurring at 4.5% and 2.5% respectively
(Yukawa et al., 2017). In this retrospective study, only seven isolates of
P. aeruginosa are tested for amikacin antibacterial drug and this could be correlated to the reduced use of amikacin in Grenada.
P. aeruginosa demonstrated higher multidrug-resistant strains and was categorized as the main pathogen by WHO
(Langendonk et al., 2021). Antimicrobial stewardship has been a challenge in recent years, as antibiotics use has increased to control common infections without any proper antimicrobial sensitivity test. This increased usage, along with the high level of prophylactic antibiotic use, the addition of antibiotics as a feed additive in animal feed and increased exposure to antiseptics and disinfectants globally, may further accelerate the development and spread of multidrug cross-resistance to antibiotics.
A recent study conducted in a veterinary teaching hospital testing the surface and liquid samples including sinks, rubber tubes and anesthesia breathing circuit had shown that the isolated
P. aeruginosa isolates were highly resistant to gentamicin (47.4%), piperacillin/tazobactam (36.8%), levofloxacin (36.8%) and ciprofloxacin (36.8%). This study is authenticated proof of confirming the prevalence of
P. aeruginosa strains in the animal clinic surroundings and is associated with the possible transfer of resistant organisms to the human population
(Soonthornsit et al., 2023). Hence, continued antimicrobial surveillance in Veterinary hospitals is required to prevent the spread of resistant microorganisms.
In contradiction to the global reports, this study has demonstrated that
P. aeruginosa isolates of Grenada are susceptible to antipseudomonal drugs used in Grenada. However, the smaller percentage of resistance level dictates that the resistance is emerging for the recommended antimicrobials. The probable reason for documented AMR could be correlated to the high level of antibiotic use in clinical conditions. Hence, it becomes mandatory to follow the essential surveillance pattern.
Furthermore, the antimicrobial susceptibility pattern exhibited by canine isolates of
P. aeruginosa in Grenada revealed an effective susceptibility pattern compared to the global susceptibility pattern
(Bourley et al., 2019). This is a significant update on the antimicrobial susceptibility pattern of
P. aeruginosa isolates of canines in Grenada, West Indies.
