Fecal shedding of extended-spectrum beta-lactamase-producing Enterobacterales in cats admitted to an animal shelter

Abstract

Objectives

The objective of this study was to evaluate shedding of extended-spectrum beta-lactamase (ESBL)-producing bacteria in cats admitted to an animal shelter.

Methods

Fecal samples were collected from cats admitted to an animal shelter between 12 June and 23 August 2018. Selective enrichment culture for ESBL-producing bacteria was performed and isolates were speciated and tested for selected ESBL genes using PCR.

Results

ESBL-producing Enterobacterales were identified in fecal samples from 2/87 (2.3%; 95% confidence interval 0.6–8.0) cats. One isolate was an Escherichia coli that possessed bla_CTX-M-1, bla_CMY-2 and bla_TEM genes. The other was Enterobacter cloacae possessing bla_CTX-M-1 and bla_CMY-2.

Conclusions and relevance

While the study sample size and prevalence rate for ESBL-producing bacteria were low, these data document that cats admitted to similar shelters could harbor these agents. The risk posed by ESBL-producing bacterium shedding in cats, both to cats and other species, is currently unclear. However, these findings support the need for more investigation of interspecies transmission of ESBL-producing bacteria and ESBL genes, as well as the importance of antimicrobial stewardship and routine infection control measures.

Keywords

Antimicrobial resistance gastrointestinal microbiota surveillance

Introduction

Antimicrobial resistance is an increasing and widespread concern in humans, animals and the environment. Of particular concern across that ‘One Health’ spectrum is the emergence and spread of extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales. The production of ESBLs confers resistance to extended spectrum cephalosporins, an important class of beta-lactam antimicrobials in veterinary and human medicine, and ESBL-producing bacteria are also often resistant to other antimicrobials, further limiting treatment options. ESBL-producing Enterobacterales such as Escherichia coli, Klebsiella and Enterobacter species are important causes of disease in humans and are increasingly identified in infections of domestic animals.^1–4

Numerous Enterobacterales species can carry and transfer ESBL genes, and ESBL-producing bacteria can be found in healthy individuals, predominantly within the gastrointestinal microbiota. Reported shedding rates in cats have been highly variable (0–74%), likely reflecting geographic, methodological and individual study population factors.^5–11 However, a prevalence of <2% may be more reflective of the healthy, non-antibiotic-treated pet cat population.^6,7,9,11 The implications of gastrointestinal carriage of ESBL Enterobacterales in cats have not been elucidated, but, presumably, carriers pose some degree of risk to themselves (developing of opportunistic infections) or others. Further, there may be the potential for horizontal transfer of ESBL genes from commensal to pathogenic bacterial species within the gut. Zoonotic concerns are also present given the presence of the same ESBL-producing bacteria in humans and animals.^12,13

Better understanding of the epidemiology of ESBL-producing Enterobacterales is important for control measures and risk assessment. The objective of this study was to evaluate fecal shedding of ESBL-producing bacteria in cats admitted to an animal shelter.

Materials and methods

Fecal samples were collected from cats within 24 h of admission to an animal shelter. First, fecal samples collected after admission were used and all cats were individually housed. Samples were collected from litter boxes as soon as possible after defecation and stored at 4°C until processing. All cats admitted between 12 June and 23 August 2018 were eligible for inclusion if a fecal sample was available within 24 h of admission, unless they were being treated with antimicrobials at the time of sampling. Sample size was dependent on the number of feline admissions during the time period when sampling was possible.

Approximately 200 mg of feces was inoculated in 9 ml of Miller LB broth and incubated at 37°C for 24 h. Ten microlitres were then inoculated onto ChromID ESBL agar (BioMerieux Canada) and incubated at 37°C for 24 h. Isolates that grew on the selective agar were sub-cultured onto Mueller Hinton agar and ESBL production was confirmed by double-disk diffusion using both ceftazidime and ceftazidime/clavulanic acid disks, as well as cefotaxime and cefotaxime/clavulanic acid disks.¹⁴ ESBL-producing isolates were identified using matrix-associated laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) and tested for bla_CTX-M, bla_SHV and bla_TEM genes by PCR.^15,16

Results from routine admission testing for feline immunodeficiency virus (FIV) antibody and feline leukemia virus (FeLV) antigen (SNAP FIV/FeLV Combo Test; IDEXX Laboratories) were collected.

Results

A total of 87 cats were sampled within 24 h of shelter admission. Age was known or estimated for 70 (80%) cats, with a median age of 2 years (range 2 months to 11 years). Sixty-one (70%) were domestic shorthairs, nine (10%) were domestic longhairs, one (1.1%) was a domestic mediumhair and one (1.1%) was a Maine Coon. Breed was not reported for 15 (17%) cats. Forty (56%) were male, 32 (44%) were female and sex was not reported for 15 (17%). One cat was FIV positive (1.4%), while test results were not available for 17 (20%). None of the 59 tested cats were positive for FeLV. Forty-four cats (61%) were strays, 28 (39%) were surrendered and the origin of 15 (17%) was not reported.

ESBL-producing Enterobacterales were identified in fecal samples from 2/87 (2.3%; 95% confidence interval 0.6–8.0) cats. Both were FIV and FeLV negative and clinically normal. One isolate was an E coli isolate that possessed bla_CTX-M Group 1 and bla_TEM genes. This was isolated from a 3-year-old domestic shorthair spayed female that was surrendered with no reported medical abnormalities and normal clinical examination. Enterobacter cloacae possessing bla_CTX-M-1 was isolated from an approximately 8-month-old male stray. Risk factor analysis was not performed because of the low prevalence.

Discussion

Shedding of ESBL-producing bacteria was uncommon but present in cats at the time of shelter admission, in the absence of any known antimicrobial exposure or other identified risk factors. This is similar to previous studies of healthy owned cats,^6,7,11 while somewhat lower than the 7.7% prevalence reported in cats admitted to a shelter in Japan.¹⁰ It highlights the potential for antimicrobial-resistant pathogens to be shed by any individual, regardless of health status or history, and supports the importance of routine infection control and hygiene practices.

A variety of ESBL genes were identified among the two isolates, consistent with previous studies of fecal and clinical isolates in dogs and cats.^2,10,13,17 bla_CTX-M Group 1 was found in both isolates. Being encoded on conjugative plasmids, bla_CTX-M genes are widespread internationally in various bacterial species, and bacteria harboring bla_CTX-M Group 1 have been isolated from numerous animal species, including dogs and cats.^18–21 This gene is also commonly found in clinical ESBL isolates in humans,^22,23 as well as those found in livestock.^20,24,25 bla_TEM was also identified in one isolate. There are >200 variants of this gene and many (but not all) are ESBLs. The degree of resistance depends on amino acid changes conferred by the different gene variations. Sequence analysis of this gene can determine whether it confers narrow-spectrum resistance (eg, bla_TEM-1) or is an ESBL, but that was beyond the scope of this study.

The presence of ESBL-producing bacteria in dogs and cats raises concerns about the potential for zoonotic transmission, as some bacterial species that harbor these genes can be zoonotic pathogens. Finding the same gene in isolates present in humans and animals does not confirm zoonotic transmission risks, particularly as ESBL genes can be found in a range of bacterial species and because cats and people can plausibly be exposed from the same sources. However, the presence of important ESBL genes in bacterial species that cause opportunistic infections in humans certainly raises concern about the potential for interspecies, bidirectional transmission of ESBL-producing bacteria. Additionally, finding ESBL genes that are of importance in human pathogens also raises concern about the potential for cats to be reservoirs of genes that could be transferred to human pathogens.

As there are many possible sources of human exposure, including other people, various animal species and food, care must be taken not to dismiss the potential role of companion animals but also not to over-react and over-interpret the data. ESBL-producing Enterobacterales probably pose some degree of zoonotic risk, highlighting the need for good general infection control and hygiene practices in shelters and households, rather than more active measures such as screening. However, it is reasonable to assume that all cats shed one or more zoonotic pathogens at any time, and the presence of ESBL-producing Enterobacterales is unlikely to constitute a serious increase in risk or be a reason to avoid adoption. In shelters, transmission of ESBL-producing Enterobacterales is of potential concern, but is just one of many infection control and zoonotic disease issues, further highlighting the need for general infection control and hygiene practices to reduce the risk of opportunistic infection, as well as exposure to opportunistic pathogens from animals or their environment.

As is typical for studies of animal shelter populations, limited animal information was available. While there was no history of potential risk factors such as antimicrobial exposure, historical data are limited in shelter admissions and prior antimicrobial treatment cannot be ruled out, particularly for stray cats that might have been owned. The study also only involved one shelter and one time period, and there may be temporal and geographical variation. The study size was limited to cats that were presented to the shelter for the period during which samples could be collected. A larger sample size would provide a more precise prevalence estimate and a greater ability to assess risk factors.

Conclusions

These data show that two cats in this shelter were harboring ESBL-producing organisms and suggest that similar findings could be recognized in other similar shelters. The risk posed by ESBL-producing bacterium shedding in cats, both to cats and other species, is currently unclear. However, these findings support the need for more investigation of interspecies transmission of ESBL-producing bacteria and ESBL genes, as well as the importance of antimicrobial stewardship and routine infection control measures.

Footnotes

Acknowledgements

The authors thank the Guelph Humane Society for assistance with sample collection and data access.

Accepted: 5 January 2022

Conflict of interest

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

funding

This study was supported by the Ontario Veterinary College Pet Trust.

Ethical approval

The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS.

Informed consent

Informed consent was obtained from the owner or legal custodian of all animals described in this work for all procedures undertaken. No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required

ORCID iD

J Scott Weese

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