Carbapenems are β-lactam antibiotics with broad antimicrobial spectrum. With the emergence of Extended Spectrum β-lactamases (ESBLs), carbapenems became the antibiotics of last resort for treatment of human patients with ESBL-producing Enterobacterales infections
[1]. Although carbapenems are not hydrolysed by most β-lactamases, their effectiveness was seriously compromised by the emergency of carbapenem-hydrolysing enzymes, the carbapenemases
[1][2]. The most important carbapenemases belong to three different Amber classes
[2]: (i) class A, including the KPC, IMI/NMC, SFC, GES type enzymes
[1][2]; (ii) class B, including VIM, IMP, and NDM metallo-β-lactamases (MBL)
[3]; and (iii) class D, including OXA-48-like type enzymes
[4].
Regulation on the use of carbapenems in animals varies worldwide and they do not belong to the OIE List of Antimicrobial Agents of Veterinary Importance
[5]. According to the European Medicine Agency categorization of antibiotics for animal use, carbapenems are included in category A (“Avoid”), meaning they are not authorized for use in veterinary medicine in the European Union (EU), except in exceptional clinical cases in companion animals, under the cascade according to Article 112 of the veterinary medicinal products Regulation 2019 of the European Union Legislation
[6]. Reports of carbapenemase-producing (CP) and carbapenem-resistant Enterobacterales (CRE) detection among companion animals are emerging worldwide (
Table 1). The identification of CP bacteria in companion animals, which have significant direct contact with humans, has raised public health concern as animals may constitute an important reservoir of carbapenems resistance genes and contribute to its dissemination
[7]. Very recently, the building of an European Antimicrobial Resistance Surveillance network in veterinary medicine (EARS-Vet) has been reported
[8]. However, carbapenem resistance epidemiology remains quite unknow, as, unlike in human medicine, no global surveillance protocol is currently in place for companion animal veterinary medicine. Furthermore, the detection of CP bacteria relying on antimicrobial susceptibility testing alone (AST) presents several pitfalls leading to its possible miss detection in veterinary medicine. Appropriate monitoring and detection of antimicrobial resistance against these critically important antimicrobials in veterinary medicine is of the utmost importance to avoid treatment failure and prevent its dissemination to humans and the environment. However, there is a lack of recommendations directed specifically to the veterinary medicine needs in the published literature.
2. Carbapenemase-Producing Bacteria in Companion Animals
To researchers' best knowledge, more than 25 reports of CP bacteria in dogs and cats have been published worldwide. These include, both infection and colonization CP isolates harbouring KPC, VIM, IMP, NDM, or OXA β-lactamases (Table 1).
Briefly, three studies detected KPC-producing
Escherichia coli and
Klebsiella pneumoniae from dogs in Brazil and in
Enterobacter xiangfangensis from a dog in the United States
[9][10][11]. A IMP-4-enzyme in
Salmonella isolates was recovered from a cat’s faecal samples in Australia
[12], VIM-2 in
Pseudomonas aeruginosa from dogs with pyoderma and otitis in South Korea
[13] and VIM-1 in
K. pneumoniae from dogs in Spain
[14]. A number of NDM-5-producing
E. coli have been found in dogs and cats
[15][16][17][18][19][20][21][22], one NDM-1-producing
Acinetobacter radioresistens was detected in a dog, six NDM-1-producing
E. coli from dogs and cats in the United States, two NDM-1-producing
E. coli from a dog in China, and finally one NDM-9 from a farm dog in China
[23][24][25]. Several OXA-48-like carbapenemase-producing
E. coli,
K. pneumoniae, Klebsiella oxytoca, and
Enterobacter cloacae isolates were recovered from dogs, cats, and horses, representing one of the most frequent carbapenemases detected in companion animals alongside with NDM-5 (
Table 1)
[17][26][27][28][29][30][31][32]. In addition, OXA-23- and OXA-66-producing
Acinetobacter baumannii were isolated from clinical samples from dogs and cats
[23][33][34].
Interestingly, although the detection of CP bacteria in companion animals dates to at least 2009, detection methods vary widely between studies, with the use of selective culture media being the most frequent for the detection of commensal CP isolates, while antimicrobial susceptibility testing alone (AST) is the main method used for the detection of CP isolates in infection cases (
Table 1). Another important finding is that most CP bacterial species isolated from companion animals belong to the priority 1 (“critical”) category within the WHO priority pathogens list
[35], thus highlighting the importance of properly monitoring and effectively detecting these carbapenem resistance mechanisms in companion animals.
Table 1. Carbapenemases found in companion animals across the world.
Enzyme |
Year |
Country |
Host |
Source |
Bacterial Species |
Detection Methods |
Refs. |
IMP-4 |
2016 |
Australia |
Cats |
Commensal |
Salmonella enterica serovar Typhimurium |
AST |
[12] |
KPC-2 |
2018 |
Brazil |
Dog |
Infection (UTI) |
Escherichia coli |
Imipenem synergy test, modified Hodge testing, PCR |
[9] |
KPC-2 |
2021 |
Brazil |
Dog |
Infection (UTI) |
Klebsiella pneumoniae |
Imipenem synergy test, AST |
[10] |
KPC-4 |
2018 |
USA |
Dog |
Infection (UTI, SSTI) |
Enterobacter xiangfangensis |
Biochemical Tests |
[11] |
NDM-1 |
2013 |
United States |
Dogs, Cats |
Infection (SSTI, UTI) |
Escherichia coli |
AST |
[24] |
NDM-1 |
2017 |
China |
Dogs |
Commensal |
Escherichia coli |
Selective culture media |
[16][25] |
NDM−1 |
2018 |
Italy |
Dog |
Commensal |
Acinetobacter radioresistens |
Selective culture media |
[23] |
NDM-5 |
2016 |
Algeria |
Dogs |
Commensal |
Escherichia coli |
PCR |
[17] |
NDM-5 |
2017 |
China |
Dogs |
Commensal |
Escherichia coli |
Selective culture media |
[16] |
NDM-5 |
2019 |
United Kingdom |
Dog |
Infection (SSTI) |
Escherichia coli |
AST |
[19] |
NDM-5 |
2018 |
Finland |
Dogs |
Infection (Otitis externa) |
Escherichia coli |
AST followed by modified Hodge testing, UV spectrometric detection of imipenem hydrolysis |
[18] |
NDM-5 |
2021 |
Italy |
Dog |
Infection (UTI) |
Escherichia coli |
Meropenem synergy test |
[15] |
NDM-5 |
2018 |
United States |
Dog |
Infection (URTI) |
Escherichia coli |
AST |
[20] |
NDM-5 |
2018 |
United States |
Dogs, Cats |
Infection (UTI, URTI) |
Escherichia coli |
AST |
[22] |
NDM-5 |
2018 |
South Korea |
Dog, Cat |
Commensal |
Escherichia coli |
AST, PCR |
[21] |
NDM-9 |
2017 |
China |
Dog |
Commensal |
Escherichia coli |
Selective culture media |
[16] |
OXA-48 |
2009–2010 |
Germany |
Dogs, Cats, Horses |
Infection |
Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae |
Selective culture media for cephalosporin resistance, PCR |
[36] |
OXA-48 |
2013 |
Germany |
Dog |
Commensal, Infection (UTI, SSTI, URTI, CRBSI) |
Klebsiella pneumoniae, Escherichia coli |
AST |
[29] |
OXA-48 |
2016 |
United States |
Dogs, Cats |
Infection (UTI, SSTI, Genital tract) |
Escherichia coli |
AST |
[31] |
OXA-48 |
2016 |
Algeria |
Dogs |
Commensal |
Escherichia coli |
PCR |
[17] |
OXA-48 |
2017 |
Algeria |
Dogs, Cat, Horses, Pet birds |
Commensal |
Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae |
Selective culture media |
[32] |
OXA-48 |
2017 |
France |
Dog |
Commensal |
Escherichia coli |
Selective culture media |
[30] |
OXA-48 |
2018 |
Germany |
Dogs, Cats, Horses |
Infection (UTI, SSTI, genital tract, otitis, URTI) |
Klebsiella pneumoniae, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca |
Selective culture media |
[28] |
OXA-181 |
2018 |
Switzerland |
Dogs, Cats |
Commensal |
Escherichia coli |
Selective culture media |
[26] |
OXA-181 |
2020 |
Portugal |
Dog |
Commensal |
Escherichia coli |
Selective culture media and AST |
[27] |
OXA-181 |
2021 |
Portugal |
Cat |
Infection (SSTI) |
Klebsiella pneumoniae |
Selective culture media and AST |
[37] |
OXA-23 |
2014 |
Portugal |
Cat |
Infection (UTI) |
Acinetobacter baumannii |
AST |
[33] |
OXA-23 |
2017 |
Germany |
Dogs, Cats |
Infection (UTI, suppurate inflammation) |
Acinetobacter baumannii |
Selective culture media |
[34] |
OXA−23 |
2018 |
Italy |
Dogs, Cats |
Commensal |
Acinetobacter baumanni |
Selective culture media |
[23] |
OXA-66 |
2017 |
Germany |
Dogs, Cats |
Infection (UTI, SSTI, URTI, CRBSI, suppurate inflammation) |
Acinetobacter baumannii |
Selective culture media |
[34] |
VIM-1 |
2016 |
Spain |
Dog |
Commensal |
Klebsiella pneumoniae |
Selective culture media, Meropenem synergy test |
[14] |
VIM-2 |
2018 |
South Korea |
Dog |
Infection (SSTI) |
Pseudomonas aeruginosa |
AST |
[13] |
3. Phenotypic Characteristics of Carbapenemases and Their Genetic Background in Isolates from Companion Animals
The β-lactam resistance phenotype of CP isolates can vary depending on the type of carbapenemase and its hydrolysing activity (Table 2).
Table 2. Common β-lactam hydrolysis profile of carbapenemases.
Amber Class |
Representative Carbapenemase Type |
Hydrolysis Profile |
Refs. |
Narrow Spectrum Cephalosporins |
Extended Spectrum Cephalosporins |
Imipenem * |
Meropenem * |
Class A |
KPC |
+ |
+ |
+ |
+ |
[2][9] |
Class B |
IMP, VIM, NDM, |
+ |
+ |
+ |
+ |
[3] |
Class D |
OXA-48-like |
+ |
- |
Variable 1 |
- |
[4][38][39] |
OXA-23-like |
+ |
+ |
+ |
+ |
[4] |
3.1. Serine Carbapenemases
Serine carbapenemases of molecular (Ambler) class A corresponds to the KPC, IMI/NMC, SFC, and GES enzymes that have a hydrolytic mechanism involving an active site serine at position 70 (Ambler numbering of class A β-lactamases), conferring resistance to first-, second-, and third-generation cephalosporins, imipenem, and meropenem
[2].
Class A carbapenemases have been rarely detected in companion animals, the KPC enzyme being the only one reported until now from dogs with UTI and SSTI (
Table 1). In
K. pneumoniae and
E. coli from dogs, the
blaKPC-2 gene was found in Tn
4401 transposons contained in IncN plasmids
[9][10] and the
blaKPC-4 gene was detected in an IncHI2 plasmid in the context of Tn
4401b transposon in
E. xiangfangensis isolated from a dog’s clinical samples
[11].
3.2. Metallo-β-Lactamases
Class B carbapenemases have a critical clinical significance due to their ability to hydrolyse all β-lactams (
Table 2)
[3][40]. So far, more than 50 allelic β-lactamase-conferring imipenem resistance (IMP) variants are listed at GenBank DNA sequence database. However, only IMP-4 has been reported among companion animals, namely, cats, in
Salmonella enterica serovar Typhimurium (
Table 1)
[12]. The IMP-4 coding gene was located on a gene cassette (
blaIMP-4-
qacG-aacA4-catB3) in a class 1 integron, associated with a conjugative plasmid IncHI2, also carrying other resistance genes, such as
tetA (mediating resistance to tetracycline),
aac (resistance to aminoglycosides),
cat (chloramphenicol resistance),
sul (sulphonamide resistance),
blaOXA (different serine oxacillinases), and
blaTEM-1 (narrow-spectrum β-lactamases)
[12].
Verona Integron-encoded Metallo-β-Lactamase (VIM) enzymes are the second most common Class B carbapenemase detected in companion animals (
Table 1). VIM-1 and VIM-2 were described in
K. pneumoniae and
P. aeruginosa isolates from dogs, respectively; both located in class 1 integrons incorporated on untyped plasmids
[13][14].
The
blaNDM genes pose a serious public health concern, since most common plasmids associated with its spread often have various antibiotic resistance genes resulting in multidrug resistance phenotypes
[18][19][41]. Until now, 28 variants have been described, with resistance against all β-lactams expect monobactams
[42]. In companion animals only NDM-1 and NDM-5 have been described so far (
Table 1), the latter being more frequent. For one metallo-β-lactamase NDM-1, the encoding gene was located in a transposon Tn
125 (composed of
blaNDM-1-
bleMBL-
trpF-
TAT-
cutA1-
groES-
groEL-
insE-
Δpac genes between a pair of IS
Aba125), integrated in the chromosome of an
A. radioresistens isolated from a dog in Italy
[23]. This Tn
125 transposon usually encompasses
blaNDM genes with two flanking IS
Aba125 elements, and in companion animals it was also found in
blaNDM-5 carrying strains
[16][23]. A NDM-1-producing
E. coli isolate harboured
blaNDM-1 in another genetic region, which was not flanked by IS
Aba125 elements downstream of the resistance gene
[25]. NDM-5 metallo-β-lactamase differs from NDM-1 by four amino acids and has been found in the chromosome of an integrated IncF plasmid, from an
E .coli isolate causing skin and soft tissue infection on a dog in the United Kingdom
[19]. In the United States, the
blaNDM-5-encoding gene has been found on IncFII-type plasmids
[20][22], whereas in South Korea it was described in an IncX3-type plasmid
[21] with the surrounding genetic environment of IS
Aba125-blaNDM-5-
bleMBL-
trpF-
TAT-IS
CR26.
3.3. Oxacillinases
The class D, carbapenem-hydrolysing OXA-48 and its variants, namely, OXA-181, are one of the most common in veterinary settings (
Table 1). The OXA-181 variant weakly hydrolyses both carbapenem and extended-spectrum cephalosporins and differs from OXA-48 at four amino acid substitution, yet its kinetic properties appear broadly similar to OXA-48
[43][44][45]. These enzymes can be associated more with different β-lactam hydrolysis profiles than the other serine-metallo-β-lactamases, making its accurate detection difficult. By possibly being susceptible in vitro to meropenem and imipenem (
Table 2), two widely used surrogates to identify carbapenem resistance in clinical microbiology, carbapenem-resistant bacteria harbouring OXA-48-like carbapenemases may easily be misdiagnosed as ESBL-producers, which may lead to treatment failure. OXA-48-coding genes in CP isolates have been associated with no other resistance genes; or with extended-spectrum β-lactamases coding genes, thus conferring either low or high MIC against carbapenems
[46]. High-level resistance to carbapenems has also been observed
[31] that may be associated with the combination of these carbapenemases with outer membrane lack of permeability
[47]. Importantly, regardless of the carbapenem susceptibility profile detected in vitro, carbapenem therapy is not reliable against OXA-48-like-producing bacteria
[45].
In companion animals, the
blaOXA-48 gene has been commonly observed on pOXA-48a plasmid, a self-conjugative IncL/M plasmid
[28][29][30]. This plasmid has a high conjugation rate, therefore, it can be transferred at a very high frequency across Gram-negative bacteria
[41][48]. Flanking the
blaOXA-48 gene is the Tn
1999 composite transposon, which cooperates in mobilizing pOXA-48a or closely related plasmids
[44][48].
The
blaOXA-181 gene was found to be part of the transposon Tn
2013, inserted at the downstream region of IS
Ecp1, which is a very efficient genetic vehicle for spreading ESBL genes, namely, the
blaCTX-M-15 gene
[49]. The
blaOXA-181 gene has been frequently identified in IncX3 plasmids
[26][27].
The frequency of OXA-48-like-producing bacteria in companion animals (Table 1) and its frequent association with mobile genetic determinants that facilitate its dissemination, highlight the importance of monitoring this resistance mechanism in companion animals. Furthermore, the possible misdiagnosis of OXA-48-like-producing bacteria when using meropenem and imipenem as surrogates may lead to underestimating its frequency and the epidemiological role of companion animals as reservoirs.
The
blaOXA-23 gene has been reported coming from
A. baumannii isolates (
Table 1). This gene is often located on transposon Tn
2006, but has also been identified in transposon Tn
2008 in animals isolates
[23][34]. The
blaOXA-23 is usually flanked between IS
Aba1 insertion sequences, known to promote the expression of
blaOXA-23 and
blaOXA-51-like genes in
A.
baumannii for an elevated level sufficient to display carbapenem resistance
[23][50]. In addition to carbapenems, the OXA-23 enzymes can hydrolyse cephalosporins, aminopenicillins, piperacillin, oxacillin, and aztreonam (
Table 2)
[4].