Out of the 27 studies reviewed, 17 (63%) conducted an antimicrobial susceptibility test on the isolates. Among these, 12 (71%) studies reported isolates resistant to more than one antimicrobial. Bacteria resistant to multiple drugs identified included MRSA (20, 34, 40, 45), MRSP (42), A. baumannii (28, 39), E. coli (31, 48), Salmonella Typhimurium (46, 47), E. faecalis and E. faecium (43).

Methicillin-resistant Staphylococcus aureus isolates showed resistance toward ampicillin, amoxicillin, oxacillin, clindamycin, gentamycin, ciprofloxacin, cephalexin, enrofloxacin, cefuroxime, chloramphenicol, erythromycin, and kanamycin while MRSP isolates showed resistance toward azithromycin, oxacillin, penicillin, clindamycin, gentamycin, tetracycline, and ciprofloxacin. Clostridioides difficile showed resistance toward rifampin, moxifloxacin, and chloramphenicol. Enterococcus faecalis and E. faecium showed resistance toward ampicillin, tetracycline, ciprofloxacin, enrofloxacin, erythromycin, and rifampicin (43). Enterococcus faecium was also reported to be resistant to amoxicillin and vancomycin (42).

Acinetobacter baumannii exhibited resistance to amoxicillin, tetracycline (39), ciprofloxacin (28) and imipenem (28). While E. coli showed resistance to ampicillin, cefoxitin, oxacillin, and penicillin (31, 48) and Salmonella was resistant to ampicillin, amoxicillin, cefoxitin, gentamycin, tetracycline, chloramphenicol, rifampicin, and streptomycin (47) (Table 5).

Among Staphylococcus species, mecA was reported in five MRSA studies (20, 35, 36, 40, 49) and two MRSP studies (9, 42). β-lactamase gene (bla_{CMY − 2} gene) was reported in Salmonella spp. (47) and E. coli isolates (17, 31, 48). While the vancomycin-resistant gene (vanA gene) was reported by one E. faecium study (42). The flo gene was identified in one E. coli study (31) (Table 6).

Identification of sources of organisms associated with HAIs in veterinary settings is critical to reducing the risk of transmission to patients and humans. Therefore, it is not surprising that most studies have largely focused on the hospital environment and commonly used instruments as potential reservoirs for organisms associated with HAIs (29, 32, 39, 41, 44). Furthermore, there are ongoing epidemiological studies to understand the relationship between environmental cleanliness and the risk of transmission of HAIs in veterinary settings (4).

The intensive care unit (ICU), surgical ward, in-house laboratory, and consultation rooms were the most important environmental sources of bacteria associated with HAIs in veterinary hospitals (17, 20, 30, 36, 42). Furthermore, environmental surfaces with human contact tend to have higher contamination levels compared to those without human contact (17, 20, 40, 42), suggesting that humans may play a major role in the transmission of these organisms within the hospital environment. This is further emphasized by studies that have isolated similar pathogens strains from the environment and hands of HCWs (28, 47, 53). Therefore, HCWs in veterinary hospitals must be trained on hand hygiene compliance to reduce the risk of transmission of HAI organisms.

Fomites served as sources of HAI organisms and facilitated transmission between animal patients, the hospital environment, and humans (32). Fomites such as clippers, personnel clothing (32, 39), cell phones (41), stethoscopes (39), and weighing scales (39) were reported to be contaminated with bacteria associated with HAIs. Therefore, the development and implementation of cleaning and disinfection protocols to prevent transmission is needed (2). In addition, all surgical materials, instruments, and other fomites which increase the possibility of transmission of these organisms must be sterilized before use (36).

Methicillin-resistant Staphylococcus aureus was among the most common organism associated with HAIs in this study (30, 37). The organisms were reported in wound infection (19, 35), invasive procedures (19, 35), skin infections (34), asymptomatic animals (45), septic arthritis, pneumonia, incisional site infection, and rhinitis (19). Studies done in veterinary medicine also reported Staphylococcus strains similar to those reported in humans were reported in this study (19, 27, 45). For example, Loeffler et al. (27) in the UK identified MRSA clones (CC22 and CC30) among humans working with or in close proximity to animals suggesting transmission between animals and humans is precise (37).

Unhygienic environmental conditions are a major source of MRSA (20, 40, 44). Therefore, implementing effective infection prevention and control (9, 30, 36, 37, 40, 52) and screening animals before hospitalization will reduce the spread of MRSA in veterinary hospitals. This is likely to reduce costs associated with increased length of hospital stay (19, 20, 27, 36, 45).

Most MRSA isolates in this study were resistant to β-lactam, 2nd generation cephalosporins, lincosamides, and aminoglycosides. While one study reported intermediate susceptibility to vancomycin among MRSA isolates (36). The presence of vancomycin resistance is concerning as it is the last resort for the treatment of MRSA in humans. Similarly, the presence of β-lactam resistance among staphylococci facilitated by the mecA gene (20, 35–37, 40, 49) is likely to contribute to resistance to other antimicrobials with a β-lactam ring (9, 40, 42, 45). Therefore, the implementation and constant review of infection control protocols are needed to help reduce the risk of the transfer of resistance genes to other organisms (9, 55–57). Without these interventions, patient care and treatment will likely be negatively impacted (36, 40).

Methicillin-resistant Staphylococcus pseudintermedius like MRSA has emerged as a leading cause of opportunistic infections in companion animals (32, 42). The organism has been reported in asymptomatic animals, implant-associated surgical sites (41), fomites (9, 32, 41), and in the environment within the veterinary hospital (44). Therefore, colonized, and contaminated areas remain potential sources of hospital-acquired infections (32).

Areas in the veterinary facilities have been shown to harbor MRSP. These include surfaces such as tables, chairs, floors, and surgical environments (58–60). Moreover, some MRSP organisms are able to survive cleaning and disinfection (58, 59). In view of the potential resistance to disinfectants coupled with ineffective cleaning, these areas can become a source of infection for susceptible animals. Notwithstanding, some disinfectants if used at the correct concentrations are effective against MRSP (61, 62).

Of concern is that MRSP is highly resistant to antimicrobials commonly used for the treatment of S. pseudintermedius infections (63–65). These organisms have been isolated from the environment and hands of HCWs (42), which is concerning as it limits treatment options. Similar to MRSA, MRSP can acquire the mecA gene (42). Shoen et al. (9) showed coagulase positive S. pseudintermedius commonly isolated from the skin of dogs can acquire the mecA gene from a coagulase-negative S. epidermidis commonly found in humans.

The zoonotic cases associated with MRSP are not common (32). However, an MRSA spa type 18/t338 from animal-related fomites has been reported in humans (41). The rise in the number of MRSP cases between dogs, pet owners, and veterinary staff is concerning, therefore, effective hand hygiene should be performed before and after contact with the patient, as well as after contact with potentially contaminated environmental sites within veterinary hospitals.

Enterococcus species are commensal of the gut flora of cats and dogs (3, 43). However, they are also opportunistic pathogens (3). In recent years, Enterococcus species have emerged as causes of HAIs in veterinary medicine associated with urinary tract infections (UTIs) (66). The transmission is mainly due to fecal contaminated fomites or environmental surfaces (29). These organisms can survive in a hospital environment for a long period. Furthermore, they can survive high temperatures and disinfectants such as chlorine and alcohol (42).

Enterococcus faecium and E. faecalis are the most predominant species reported in dogs (30, 43), hospital environments and in hands of HCWs (42). Of the two species, E. faecalis is the predominant enterococci. Multidrug-resistant enterococci have also been reported as a commensal and pathogenic organism (3, 42, 43). The presence of MDR among Enterococcus species has largely been attributed to overuse and misuse of antimicrobials (42, 43). It is also possible that some may have acquired resistance through other mechanisms including genetic transfer or mutation (43). For example, resistance to erythromycin has been associated with the methylation of the ribosomal target site of these antibiotics (42, 67). Nonetheless, the presence of MDR enterococci is likely to impact patient care in veterinary hospitals (42).

Of concern is the emergence of vancomycin-resistant E. faecium (42) which is an important antimicrobial in the treatment of enterococci infections (43, 67) and is mediated by the presence of vanA genes. These genes are important as they confer multidrug resistance and may be transmitted to other bacterial species such as Staphylococcus and create even bigger problems in the treatment of HAIs (42). Furthermore, these genes can also be transferred from animals to humans (3, 43).

Clostridioides difficile is found in the hospital environmental and it is difficult to eradicate (17). Both humans and animals are asymptomatically carriers of the organism. In humans, its presence has been attributed to the overuse of antimicrobials. However, in veterinary medicine there is limited information about the organism. Therefore, future studies should look at whether the overuse of antimicrobials could be a driver of C. difficile in veterinary settings (17). The ability of the pathogen to survive harsh environmental conditions and resistance to most disinfectants makes it a suitable indicator of the effective IPC measures (17). Therefore, it is possible that this organism can also be used as an indicator of effective infection prevention and control in veterinary hospitals.

Acinetobacter baumannii causes life-threatening infections in both humans and animals. This organism has been reported in UTIs, pyothorax, upper airway obstruction, bloodstream infection, and wound infections in animals (39). In infected animals, it is associated with increased morbidity and prolonged length of hospital stay (68). Acinetobacter baumannii survives on dry surfaces (29, 39, 69). Therefore, commonly used fomites, bed rails, cages, and examination tables could serve as reservoirs for A. baumannii.

The organism can survive stressful environmental conditions and remains viable on different surfaces (70). However, if used at correct concentrations, sodium hypochlorite (bleach) and 70% ethanol are effective against A. baumannii (70, 71). Lanjri et al. (71) observed that chlorhexidine digluconate was effective against A. baumannii. La Forgia et al. (72) also reported that sodium hypochlorite was effective in reducing the incidence rate of A. baumannii in hospital settings. In light of this findings, choosing the correct disinfectant is important in reducing cases of A. baumannii in hospital settings.

Most A. baumannii are multiple drug resistant with a high prevalence of resistance toward cephalexin, enrofloxacin, amoxicillin-clavulanic acid, sulphamethoxazole-trimethoprim, and tetracycline (39). Resistance to the above antimicrobials is concerning as these antimicrobials are commonly used for the treatment of bacterial infections in small animal medicine (68). In addition, the blaOXA-51 gene reported in an A. baumannii isolate from pigs has also been reported in humans (67).

Escherichia coli is commonly reported in UTIs and bloodstream infections (17, 31, 39, 73). The bacterium spreads from patient to patient via fecal contaminated hands of HCWs and shared equipment (31). Given, that environmental surfaces could potentially be a reservoir of E. coli, measures to minimize fecal contamination in companion animal hospitals including cleaning and disinfection of the hospital environment should be implemented. Moreover, Sanchez et al. (31) shows the transfer of E. coli isolates with similar antimicrobial resistance patterns between two different animals admitted to the same ICU.

In this study, E. coli isolates exhibited resistance toward cephalosporins and β-lactams including amoxycillin-clavulanic acid. This broad-spectrum antimicrobial resistance among E. coli is attributed to the presence of ampC like gene, bla_CMY2 (17, 31), which has been identified to be of public health concern (17). Another study reported resistance among E. coli isolates to chloramphenicol mainly due to the presence of cmlA homologue flo among gram-negative bacteria (31). The presence of these genes has also been linked to the development of resistance to other commonly used antibiotics such as gentamycin, spectinomycin, and sulfadimethoxine (31, 39, 50). Considering this resistance, strict guidelines should be implemented on the prudent use of antimicrobials in veterinary medicine.

Although most animals are asymptomatic carriers of Salmonella spp., they shed the bacterium in high quantities through their feces resulting in Salmonella outbreaks in equine veterinary hospitals (46, 47). Furthermore, infections associated with Salmonella species have also been reported in bovine with diarrhea, fever, dehydration (38) and colic in horses (47). In affected animals, the disease is characterized by high morbidity and mortality. There is a potential spread of organisms and the occurrence of zoonotic infection that may result in the closure of facilities and a loss of income for the hospital (38, 46). Therefore, personnel working in close contact with infected animals are at an increased risk of infection (46).

Managing transmission in the veterinary settings remains a challenge as Salmonella can persist in the environment for a long time. Rodents and contaminated feed could also be a source (46, 47). Therefore, biosecurity measures must be intensified in veterinary hospitals to reduce the risk of transmission. Additionally, education programs can also be developed targeting specific aspects of hygiene, movement control, and cleanliness of equipment.

Salmonella isolates were resistant to ceftiofur, gentamycin, amoxicillin, ampicillin, streptomycin, and trimethoprim/ sulfadiazine (46, 47). One study reported the presence of the cephalomycinase gene, bla_cmy2 (47) which has been associated with cephalosporin resistance among Salmonella species. This gene has also been reported to mediate resistance to amoxicillin, amoxicillin-clavulanic acid, cephalothin, cefoxitin, ceftiofur, and ceftriaxone (47).