1. Introduction
In recent years, the number of pets in the European countries has gradually increased with dogs and cats being the two most prevalent types of companion animals in households [
1]. The social role of companion animals has changed and attention to their health and welfare has significantly increased, too [
2]. Skin wounds are very common in small animals. Such wounds are frequently colonized by bacteria or show signs of bacterial infection. Both, colonization and infection often result in healing delay and difficulties, thus increasing cost of treatment [
3]. Currently, the treatment of wounds in veterinary medicine is based on the administration of broad –spectrum antibiotics, the continuous administration of which contributes to the increasing antimicrobial resistance among both pathogenic bacteria and even commensal skin microbiota [
4].
In this context, the threat of wound infection, especially by antimicrobial resistant bacteria (ARB), becomes even more serious problem. This is due to the risk of acquiring the ARB or the relative antibiotic resistance genes (ARGs) by the pet owners via contact with their companion animals [
2]. The risk of interspecies transmission of bacteria, including antibiotic resistant or multidrug resistant bacteria is very high, because the majority of bacterial pathogens of companion animals are the bacterial species that can commonly occur in humans, too. These pathogens and opportunistic pathogens are:
Staphylococcus (including
S. aureus),
Pseudomonas (including
P. aeruginosa), beta-haemolytic
Streptococcus,
E. coli or
Enterococcus (including
E. faecalis or
E. faecium) [
1,
2,
3,
4,
5,
6].
With respect to the high risk of interspecies transmission of pathogenic ARB, the risk of infection treatment failure is high not only among companion animals, but also among their owners. There is surprisingly small number of studies concerning the scope of AMR in companion animals, while research of animal wound infections is limited to a only a few texts [
3,
4]. For this reason, understanding the prevalence of antimicrobial resistant bacterial infections in wounds of companion animals, that can easily be transmitted to their owners is among the most important gaps to be filled. With this in mind, the aim of this study was to identify the most common pathogens infecting wounds of companion animals treated in veterinary clinics, to assess their resistance to antibacterial agents used in their treatment in both veterinary and human medicine and to determine the genes determining the resistance mechanisms. The combination of culture-based, molecular biology and proteomic methods was used in order to obtain the most reliable results.
2. Results
A total of 136 bacterial isolates were obtained from the collected swabs, including: 52 (38.24%) from cats, 80 (58.82%) from dogs and 4 (2.94%) from rabbits. There were 71 (52.21%) Gram-positive and 65 (47.79%) Gram-negative isolates. The dominant genera were
Staphylococcus spp. (n=37, 27.21%), followed by
Enterococcus spp. (n=17, 12.50%),
Escherichia (n=11, 8.09%) and
Acinetobacter (n=10, 7.35%), with the following dominant species:
S. pseudintermedius (n=13, 9.56%),
E. coli and
E. faecalis (both n=11, 8.09%). The dominant bacterial species differed between the examined groups of animals (
Table 1).
Antimicrobial resistance of 120 bacterial isolates was tested using 16 antimicrobial agents in five combinations, based on the target organism (
Table 1). Among the group of
Enterobacterales, the resistance to amoxicillin/clavulanic acid was the most prevalent (detected in 68.3% of strains), followed by ampicillin (52.6%) and tylosin (44.7%). The ESBL mechanism of resistance was detected in 13.16% of strains (
Figure 4A,
Figure 5A;
Table 4). None of the examined antimicrobials were effective against all strains. All strains of
Pseudomonas spp. (n=7) were resistant to ceftazidime, piperacillin/tazobactam, imipenem and tylosin. Out of the tested antibiotics, only amikacin proved effective against all tested strains (
Figure 4B). Finally,
Acinetobacter (n=9) showed the highest percentage of resistance to tylosin (55.5% of strains), followed by enrofloxacin and gentamicin (both 44.4%,
Figure 5C). In the case of Gram-positive bacteria, all
Enterococcus spp. strains (n=15) were resistant to imipenem, 66.7% were resistant to tigecycline and 46.7% to enrofloxacin (
Figure 6A). In
Staphylococcus spp., the resistance to clindamycin was the most frequently observed (i.e. in 39.2% of strains). Methicillin resistance, shown by the resistance to cefoxitin was the second most prevalent, and was observed in 33.3% of strains (
Table 4,
Figure 4B), along with the resistance to erythromycin (also detected in 33.3% of strains). Both MSb and MLSb constitutive type of resistance mechanism was observed in 13.7%, while inducible MLSb mechanism was observed in 3.9% of strains (
Figure 4C and D;
Figure 6B,
Table 4).
Figure 1.
The resistance mechanisms observed in the examined groups of bacteria. A – Extended Spectrum Beta Lactamases (ESBL) in Enterobacterales; B – methicillin resistance in Staphylococcus pasteuri; C – inducible resistance to macrolides, lincosamids and streptogramins b (MLSb) in Staphylococcus pseudintermedius; D – constitutive MLSb in S. pseudintermedius.
Figure 1.
The resistance mechanisms observed in the examined groups of bacteria. A – Extended Spectrum Beta Lactamases (ESBL) in Enterobacterales; B – methicillin resistance in Staphylococcus pasteuri; C – inducible resistance to macrolides, lincosamids and streptogramins b (MLSb) in Staphylococcus pseudintermedius; D – constitutive MLSb in S. pseudintermedius.
One
Enterobacterales strain (canine
Proteus mirabilis), out of all examined, was resistant (or insusceptible) to eight out of nine antimicrobial agents tested. Two other Gram-negative strains (
K. pneumoniae and
Aeromonas media) were resistant to 7 antimicrobials (
Table 4). Among Gram-positives, three
Staphylococci were resistant to seven out of eight antimicrobials tested (
Table 4; feline
S. pseudintermedius and
S. aureus, and canine
S. pseudintermedius).
Figure 2.
Share (%) of resistant (R) and susceptible (S) Gram-negative bacterial strains (A – Enterobacterales; B – Pseudomonas; C – Acinetobacter) isolated from wounds of companion animals. CN – gentamycin; SXT – trimethoprim/sulfamethoxazole; CTX – cefotaxime; AK – amikacin; AMC – amoxicillin/clavulanic acid; CAZ – ceftazidime; ENR – enrofloxacin; AMP – ampicillin; IMP – imipenem; TY – tylosin; TZP – piperacillin/tazobactam; ESBL – extended-spectrum-beta-lactamase-producing strains of Enterobacterales.
Figure 2.
Share (%) of resistant (R) and susceptible (S) Gram-negative bacterial strains (A – Enterobacterales; B – Pseudomonas; C – Acinetobacter) isolated from wounds of companion animals. CN – gentamycin; SXT – trimethoprim/sulfamethoxazole; CTX – cefotaxime; AK – amikacin; AMC – amoxicillin/clavulanic acid; CAZ – ceftazidime; ENR – enrofloxacin; AMP – ampicillin; IMP – imipenem; TY – tylosin; TZP – piperacillin/tazobactam; ESBL – extended-spectrum-beta-lactamase-producing strains of Enterobacterales.
Figure 3.
Share (%) of resistant (R) and susceptible (S) Gram-positive bacterial strains (A –Enterococcus; B – Staphylococcus) isolated from wounds of companion animals. AMP – ampicillin; CN – gentamycin; DA – clindamycin; E – erythromycin; IMP – imipenem; ENR – enrofloxacin; FOX – cefoxitin; SXT – trimethoprim/sulfamethoxazole; TGC – tigecycline; TE – tetracycline; TY – tylosin; MSb – resistance mechanisms to macrolides and streptogramins b; MLSb ind – inducible mechanisms of resistance to macrolides, lincosamids and streptogramins b; MLSb const – constitutive mechanisms of resistance to macrolides, lincosamids and streptogramins b.
Figure 3.
Share (%) of resistant (R) and susceptible (S) Gram-positive bacterial strains (A –Enterococcus; B – Staphylococcus) isolated from wounds of companion animals. AMP – ampicillin; CN – gentamycin; DA – clindamycin; E – erythromycin; IMP – imipenem; ENR – enrofloxacin; FOX – cefoxitin; SXT – trimethoprim/sulfamethoxazole; TGC – tigecycline; TE – tetracycline; TY – tylosin; MSb – resistance mechanisms to macrolides and streptogramins b; MLSb ind – inducible mechanisms of resistance to macrolides, lincosamids and streptogramins b; MLSb const – constitutive mechanisms of resistance to macrolides, lincosamids and streptogramins b.
Table 2.
Prevalence of resistance profile in groups of bacteria isolated from wounds of companion animals.
Table 2.
Prevalence of resistance profile in groups of bacteria isolated from wounds of companion animals.
|
number of antibiotics bacteria are resistant to (%) |
resistance mechanism |
Group of bacteria |
R0 |
R1 |
R2 |
R3 |
R4 |
R5 |
R6 |
R7 |
R8 |
MDR |
ESBL |
MRS |
MSb |
MLSb-i |
MLSb-c |
Enterobacterales (n=38) |
3 (7.9) |
2 (5.3) |
12 (31.6) |
7 (18.4) |
6 (15.8) |
3 (7.9) |
2 (5.3) |
2 (5.3) |
1 (2.6) |
16 (42.1) |
5 (13.2) |
- |
- |
- |
- |
Pseudomonas (n=7) |
0 |
0 |
0 |
1 |
0 |
3 (42.9) |
3 (42.9) |
0 |
0 |
7 (100) |
0 |
- |
- |
- |
- |
Acinetobacter (n=9) |
0 |
5 (55.6) |
1 (11.1) |
1 (11.1) |
1 (11.1) |
1 (11.1) |
0 |
- |
- |
3 (33.3) |
- |
- |
- |
- |
- |
Enterococcus (n=15) |
0 |
3 (20.0) |
3 (20.0) |
2 (13.3) |
7 (46.7) |
0 |
- |
- |
- |
9 (60) |
- |
- |
- |
- |
- |
Staphylococcus (n=51) |
14 (27.5) |
15 (29.4) |
8 (15.7) |
3 (5.9) |
5 (9.8) |
0 |
3 (5.9) |
3 (5.9) |
0 |
14 (27.5) |
- |
17 (33.3) |
7 (13.7) |
2 (3.9) |
7 (13.7) |
Finally, PCR tests were carried out to search for 12 genetic determinants of antibiotic resistance to all antimicrobial classes used in the treatment of Gram-positive and Gram-negative bacteria. Due to the fact that various resistance mechanisms may be characteristic of Gram-positive and Gram-negative bacteria, some genes examined in these two groups of bacteria varied (such as methicillin and MLSb resistance determinants in Gram-positives and ESBL determinants in Gram-negatives), while others (such as strA determining the aminoglycoside resistance and sul3 that determines the resistance to sulfonamides) were common for both these groups.
Figure 4.
Positive results of PCR test for the few exemplary bacterial isolates. Lanes marked as M – DNA Marker 3 (A&A Biotechnology, Poland); lanes 1-18 (A) and 1-24 (B) – bacterial DNA isolates; lanes 5-7 and 13-18 (A) and 10,17, 19, 20 (B) – DNA bands of searched length, confirming the presence of (A) blaTEM and (b) lnuA genes.
Figure 4.
Positive results of PCR test for the few exemplary bacterial isolates. Lanes marked as M – DNA Marker 3 (A&A Biotechnology, Poland); lanes 1-18 (A) and 1-24 (B) – bacterial DNA isolates; lanes 5-7 and 13-18 (A) and 10,17, 19, 20 (B) – DNA bands of searched length, confirming the presence of (A) blaTEM and (b) lnuA genes.
Ten out of the tested 12 genetic determinants of antimicrobial resistance were detected in the DNA extracted from bacterial isolates from cats, dogs and rabbit (
Table 5,
Table 6,
Figure 7 A and B). Genes
ereA (erythromycin esterase),
qnrA and
qnrD (plasmid-mediated quinolone resistance genes) were not detected in any of the examined samples. On the other hand, the streptomycin resistance gene,
strA, was detected in 29 samples, in all groups thereof, in both Gram-positive and Gram-negative bacteria. In terms of the detection frequency, it was followed by
sul3, a sulfonamide resistance gene (14 positive samples, in Gram-positive and Gram-negative isolates of both cats and dogs) and
blaTEM, an ESBL determinant, characteristic of Gram-negative bacteria (13 positive samples in cats and dogs,
Table 6,
Figure 7A).
Table 3.
Positive results in Gram-positive (n =59) bacteria isolated from cats (n=25) and dogs (n=34).
Table 3.
Positive results in Gram-positive (n =59) bacteria isolated from cats (n=25) and dogs (n=34).
Animal |
n (%) |
mecA |
msrA |
lnuA |
strA |
tetK |
sul3 |
ereA |
Cat |
0 |
3 (12) |
0 |
7 (28) |
6 (21.4) |
6 (21.4) |
0 |
Dog |
4 (11.8) |
1 (2.9) |
4 (11.8) |
10 (29.4) |
3 (8.8) |
3 (8.8) |
0 |
Table 4.
Positive results in Gram-negative (n= 49) bacteria isolated from cats (n=12), dogs (n=33) and rabbit (n=4).
Table 4.
Positive results in Gram-negative (n= 49) bacteria isolated from cats (n=12), dogs (n=33) and rabbit (n=4).
Animal |
n (%) |
blaTEM |
blaSHV |
blaCTX-M |
blaOXA-1 |
sul3 |
qnrD |
strA |
Cat |
3 (25) |
0 |
1 (8.3) |
0 |
3 (25) |
0 |
1 (8.3) |
Dog |
10 (30.3) |
3 (9.1) |
1 (3) |
1 (3) |
2 (6.1) |
0 |
10 (30.3) |
Rabbit |
0 |
1 (25) |
0 |
0 |
0 |
0 |
1 (25) |
Interestingly, there have been six canine and one feline bacterial isolates with phenotypic and molecular resistance profiles (
Table 5) that could make them alarming, as they were resistant to all or nearly all examined antimicrobial agents and their DNA contained three or four different ARGs.
Table 5.
Selected phenotypic and molecular resistance profiles of canine and feline bacteria isolated from wounds.
Table 5.
Selected phenotypic and molecular resistance profiles of canine and feline bacteria isolated from wounds.
Origin |
Species |
phenotype of resistance (antibiotic class) |
resistance genes (type of resistance) |
feline |
Enterococcus faecalis |
IMP (β-lactam -carbapeneme) ENR (fluoroquinolone) TGC (tetracycline) TY (macrolide) |
mecA (methicillin) msrA (macrolides) lnuA (lincosamides) tetK (tetracyclines) |
canine |
Enterococcus faecalis |
IMP (β-lactam -carbapeneme) ENR(fluoroquinolone) TGC (tetracycline) TY (macrolide) |
msrA (macrolides) strA (aminoglycosides) tetK (tetracyclines) sul3 (sulfonamides) |
canine |
Staphylococcus sciuri |
- |
lnuA (lincosamides) strA (aminoglycosides) tetK (tetracyclines) |
canine |
Staphylococus pseudintermedius |
TE (tetracycline) DA (lincosamide) E (macrolide) SXT (diaminopyrimidines/sulfonamide) ENR (fluoroquinolone) CN (aminoglycoside) TY (macrolide) |
lnuA (lincosamides) strA (aminoglycosides) tetK (tetracyclines) |
canine |
Escherichia coli |
CN (aminoglycoside) AMC (β-lactam/ β-lactamase inhibitor) AMP (β-lactam - aminopenicillin) IMP (β-lactam -carbapeneme) |
blaTEM (ESBL) blaSHV (ESBL) strA (aminoglycosides) |
canine |
Escherichia coli |
CTX (β-lactam – 3rd gen. cephalosporin) AMC (β-lactam/ β-lactamase inhibitor) CAZ (β-lactam – 3rd gen. cephalosporin) AMP (β-lactam - aminopenicillin) TY (macrolide) |
blaTEM (ESBL) blaSHV (ESBL) strA (aminoglycosides) |
canine |
Proteus mirabilis |
CN (aminoglycoside) SXT (diaminopyrimidines/sulfonamide) CTX (β-lactam – 3rd gen. cephalosporin) AMC (β-lactam/ β-lactamase inhibitor) CAZ (β-lactam – 3rd gen. cephalosporin) ENR (fluoroquinolone) AMP (β-lactam - aminopenicillin) IMP (β-lactam/carbapeneme) |
blaTEM (ESBL) blaOXA-1 (ESBL-carbapenemes) strA (aminoglycosides) |
3. Discussion
There is growing evidence that resistant bacteria (including multidrug resistant individuals) occur in companion animals and that many species among them are shared between animals and humans ([
2]). With this in mind, the inappropriate use of antimicrobials in animals may result in the selection and spread of antimicrobial resistance, thus constituting a potential risk to public health [
2]. This study provides data on bacteria colonizing wounds of companion animals, their antimicrobial resistance profiles and genetic determinants of resistance to all classes of antimicrobial agents among Gram-negative and Gram-positive bacteria. The distribution of bacterial taxa shows that
Staphylococcus spp. (with S
. pseudintermedius and
S. aureus),
Enterococcus spp. (with
E. faecalis),
E. coli,
Acinetobacter spp. (with
A. ursingii) and
Pseudomonas (with
P. aeruginosa) were the most frequently isolated from all samples. High prevalence of
Staphylococcus spp. with higher numbers of
S. pseudintermedius than of
S. aureus was reported by [
6,
7]. [
3] also observed that
Staphylococcus (including
S. intermedius, later reclassified to
S. pseudintermedius) was the most frequent among wound-infecting Gram-positive bacteria, while
E. coli was most frequently identified Gram-negative.
Staphylococcus pseudintermedius is the most common canine bacterial pathogen, but it is, indeed, accompanied by a variety of other – both Gram-positive and Gram-negative bacteria.
In recent years, increased attention is being paid to the welfare of small, companion animals, which results in e.g. increased expenses on veterinary care. This involves frequent use of antimicrobial agents in pets, and many of these antimicrobials are commonly used in both human and veterinary medicine. However, identification of causal agents and their antimicrobial susceptibility is often neglected, leading to inappropriate empirical treatment [
8]. In both cats and dogs, the most frequent causes of antimicrobial use are wound infections [
8]. The most frequently used classes of antibiotics in animals are fluoroquinolones, β-lactams, cephalosporins, sulfonamides, macrolides and glycopeptides [
9]. Among the consequences of antimicrobial use in companion animals is that the amounts and patterns of antibiotic administration reflect in the rate at which the resistance develops and spreads in the exposed bacterial population [
8].
In our study, high percentage of
Enterobacterales were resistant to β-lactam antibiotics (amoxicillin/clavulanic acid and ampicillin – 68.3% and 52.6%, respectively), while 100% of
Pseudomonas isolates were insusceptible to ceftazidime (cephalosporin), piperacillin/tazobactam (β-lactam), imipeneme (carbapaneme) and tylosin (macrolide). However, the resistance to enrofloxacin (fluoroquinolone) ranged from 11.8% in
Staphylococci to 46.7% in
Enterococci and it was never the highest - only in
Acinetobacter spp. it was the third highest (44.4%) among the observed resistance rates. Generally, enrofloxacin is commonly used systemically in infection treatment of small animals and although it is still efficient, there have been cases of treatment failure [
8]. With respect to the fact that inappropriate use (e.g. pulse-dose, low dose) is very common in treatment of small animals, this might favor the development of resistant strains, particularly when long-term treatment is required [
10]. As far as the antibiotic administration effect is concerned, it has been reported that enrofloxacin treatment promotes MDR
E. coli colonization and that the proportion of dogs carrying resistant
E. coli increased with the duration of hospital stay and with the antimicrobial treatment [
2].
Even though the antimicrobial resistance is spread among environmental microorganisms, human and animal pathogens, of special concern seems the situation when the resistance against last-resort antimicrobial agents for human medicine is detected, particularly in microorganisms that can be easily transmitted between animals and humans [
2,
8]. Insusceptibility to imipeneme (carbapeneme antimicrobial) has been detected quite frequently in our study. All
Enterococcus spp. and all
Pseudomonas spp. isolates were resistant to this antimicrobial. Importantly, both canine
E. faecalis MDR strains, positive for four genetic determinants of resistance and resistant to four antibiotics, mentioned in
Table 7, were also resistant to imipeneme. In the case of Gram-negative isolates mentioned in the special concern group (
Table 7), one canine
E. coli and
P. mirabilis were also imipeneme-resistant. All these species are listed as human pathogens, too. They cause, among many others, urinary tract infections [
8,
11]. Close interaction between pets and humans favors the transmission of bacteria by both direct contact and through the domestic environment and children are at greater risk than adults. This is due to their more common and closer physical contact with pets and with household environment [
8]. The most important hazard for human health is therefore related to the transmission of antimicrobial resistant bacteria from pets to humans and the related zoonotic infections [
2].
Notably, antimicrobial resistance can be transmitted by low bacterial numbers or even in the absence thereof, if only the genetic determinants are present in the environment. The resistance gene transfer frequently occurs horizontally. Most classes of antibiotics have long been used in both human and veterinary medicine, thus the same resistance genes are being identified in bacteria isolated from humans and animals [
8]. In our study, ten genetic determinants of antimicrobial resistance have been identified in bacterial isolates of cats, dogs and rabbit. Streptomycin resistance (
strA) was most frequently identified, followed by sulfonamide resistance (
sul3) and one of the ESBL determinants (
blaTEM). Studies on the genetic determinants in bacteria isolated from companion animals are scarce, however the listed genes have also been mentioned by other authors to occur in bacteria isolated from companion animals [
8,
12,
13]. All four examined ESBL determinants were detected in this study in the following frequency:
blaTEM >
blaSHV >
blaCTX-M >
blaOXA. [
12] on the other hand, detected
blaTEM,
blaCTX-M and
blaSHV in similar proportions in
E. coli isolates obtained from dogs and their owners. [
13] examined the presence of nine genes determining the resistance to tetracyclines, quinolones, aminoglycosides, sulfonamides and trimethoprim in
E. coli isolates from pet cats. Similarly as in our study,
qnr genes (determining the quinolone resistance) were very rare or absent. In this study, the resistance to enrofloxacin, which is most frequently applied fluoroquinolone veterinary antibiotic varied and ranged from 11.7% in staphylococci to 46.7% in enterococci. In an earlier study focused on antimicrobial resistance and the molecular resistance mechanisms in chicken feces-derived
E. coli, [
14] observed that the fluoroquinolone resistance would reach even 93.3% of isolates. At the same time, the resistance to β-lactams was also very frequent, in some experimental groups reaching 100% of bacterial isolates. Consequently,
qnrB and
qnrS genes were very frequent (detected in more than 81% and 86% of isolates of some experimental groups, respectively). However, the selection pressure put on bacteria present in farm poultry is much higher than bacteria derived from pet animals, despite the restrictions resulting from the European Union regulations.
Author Contributions
Conceptualization, A.L-B. and K.S.; methodology, A.L-B., K.S. and M.T; software, A.L-B and K.D.; validation, K.S. and K.D.; formal analysis, A.L-B and K.S.; investigation, N.C., A.R., K.B., M.H., D.S., I.S. and D.C.; resources, A.L-B., K.S., K.D., I.S. and M.T; data curation, K.S.; writing—original draft preparation, A.L.-B.; writing—review and editing, K.S. and K.D.; visualization, A.L.-B. and K.S.; supervision, A.L.-B.; project administration, A.L-B.; funding acquisition, A.L-B. and M.T. All authors have read and agreed to the published version of the manuscript.