Findings About Dog Antimicrobial Resistance in Growth Medium
Antimicrobial resistance poses a major threat to public health globally. While resistance emerging in bacteria from food animals grabs headlines, the role of dogs as mediators of resistance merits dedicated focus. The close bond shared between humans and dogs creates a conduit for exchange of resistant microbes. Understanding the public health risks stemming from antimicrobial usage in canines is pivotal, given their intimate status as human companions.
What is the link between resistant bacteria in dogs and human health?
Dogs live in very close contact with humans, sharing spaces in homes and public areas. This intimacy creates many opportunities for transfer of resistant bacteria between dogs and humans. Dogs can readily transmit microbes to humans through direct contact, fecal contamination of shared environments, and handling of dog feces. At the same time, dogs can pick up resistant bugs shed by human hosts into the home and outdoor spaces. Dogs essentially serve as reservoirs of resistant bacteria that can move between species through multiple routes. This zoonotic transmission is facilitated by the affinity between dogs and humans. Studies have clearly shown bidirectional transfer of resistant organisms like methicillin-resistant Staphylococcus aureus (MRSA) between humans and their canine companions. This inter-species movement of resistant bacteria is a significant public health concern.
What growth media were used to culture bacteria in this study?
In this study, the lower respiratory tract samples collected from dogs and cats were cultured using MacConkey agar to isolate Gram-negative bacteria like E. coli and Pseudomonas species. MacConkey agar is a selective and differential growth medium containing bile salts and crystal violet dye, which inhibits growth of Gram-positive bacteria while allowing growth and color-based differentiation of lactose fermenting and non-fermenting Gram-negative bacilli. The inclusion of antibiotics like cefotaxime and ciprofloxacin in some of the MacConkey agar plates enabled selection and isolation of resistant E. coli strains from the clinical samples. The choice of MacConkey agar facilitated isolation of major Gram-negative respiratory pathogens in dogs and cats. However, use of this selective medium means fastidious organisms would be missed. Broader media like blood agar or chocolate agar could recover a wider range of organisms including Gram-positives. Still, MacConkey agar was an appropriate choice given the study's aims centered on tracking resistance in recognized Gram-negative respiratory pathogens. The incorporation of antimicrobials into the agar allowed efficient screening for resistant isolates.
What types of resistant bacteria are commonly found in dogs?
Several studies have uncovered alarming levels of resistance in common bacteria found in dogs, including strains highly relevant to human medicine. For example, genes making Escherichia coli resistant to critically important antibiotics like tetracyclines, ampicillin, and streptomycin are widespread in dogs. Another major issue is the global spread of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in dog populations. ESBLs confer resistance to penicillins, cephalosporins like cefotaxime, and aztreonam. But carbapenem antibiotics remain effective against ESBL-producers. Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is another multidrug-resistant pathogen with zoonotic potential that is increasingly being isolated from dogs.
How do resistance levels compare between owned dogs versus strays?
Some studies have found that stray or free-roaming dogs show higher levels of antibiotic resistance compared to home dogs with owners. For instance, a study in Argentina detected E. coli resistance rates to tetracycline of 70% in strays versus 27.7% in home dogs. Stray dog isolates also had markedly higher prevalence of ESBL producers (36% vs 8% in home dogs) and multidrug resistance. Possible reasons for the discrepancy include frequent antibiotic administration by non-professionals to strays, uncontrolled access to antibiotics, and exposure of strays to garbage containing resistant bacteria and antibiotic residues. Home dogs likely benefit from more responsible antibiotic use and regular preventative healthcare. However, resistance remains problematic even in owned dogs.
What are the main public health risks from resistance in dogs?
The public health impacts of rising resistance rates in bacteria from dogs are multidimensional. At the individual level, humans infected with organisms like MRSA, ESBL-producing E. coli, or multidrug-resistant Pseudomonas aeruginosa risk delays in effective treatment and heightened morbidity/mortality when empiric antibiotic regimens fail. From a broader perspective, dogs serve as amplifiers and disseminators of resistance genes within microbial communities shared with humans. This facilitates wider propagation and persistence of resistance, compromising antibiotic effectiveness. Dogs may also contribute significant antibiotic-selective pressure through vectors like fecal waste contaminating environments. Altogether, the close functional linkage between dogs and humans underscores why canine resistance is very much a public health priority.
What strategies can mitigate the public health risks associated with canine resistance?
A collaborative One Health approach is required to reign in resistance in bacteria of canine origin and protect human health. Key elements include establishing prudent antibiotic use guidelines for dogs, restricting over-the-counter access in favor of prescription-only policies, educating veterinarians about judicious prescribing, enhancing owner awareness, improving preventative care for dogs, instituting active surveillance programs, and elucidating transmission pathways between dogs, humans, and shared environments. While curbing agricultural usage is important, the focus cannot fall solely on food animals. Pets like dogs which live so intimately with people likely contribute significant antibiotic selective pressure and require dedicated stewardship efforts.
What are the priority knowledge gaps regarding transmission of resistant bacteria between dogs and humans?
Major gaps persist in our understanding of how resistant bacteria, especially emerging threats like ESBL-producers, disseminate between dogs and humans and migrate through interconnected environments. Concrete data quantifying the relative contributions of canine vs human antibiotic use to burgeoning resistance in zoonotic bacteria are sparse. Elucidating directions of transmission is also critical - are particular resistant strains predominantly dog to human, versus human to dog? Active surveillance studies targeting key interfaces between dogs, humans, and their shared surroundings can help provide tangible evidence guiding risk management policies. Overall, recognizing dogs as potential vectors of antimicrobial resistance between humans and environments merits expanded research attention.
In conclusion, the intricate bonds between humans and dogs facilitate bidirectional transfer of resistant bacteria between species. Dogs may serve as amplifiers and disseminators of resistance genes in microbial communities shared with human hosts. A One Health approach that engages both medical and veterinary professionals is imperative to curb canine resistance and safeguard antibiotic efficacy for the future. Understanding this phenomenon remains critical to effective risk mitigation, given the intimate place dogs hold in human lives and societies around the globe.
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1. Marchetti L, Buldain D, Gortari Castillo L, Buchamer A, Chirino-Trejo M, Mestorino N. Pet and Stray Dogs as Reservoirs of Antimicrobial-Resistant Escherichia coli. Int J Microbiol. 2021 Jan 25;2021:6664557. doi: 10.1155/2021/6664557. PMID: 33564312; PMCID: PMC7850822.
2. Mavrides DE, Morgan AL, Na JG, Graham PA, McHugh TD. Antimicrobial resistance profiles of bacteria associated with lower respiratory tract infections in cats and dogs in England. Vet Rec. 2022 Feb;190(4):e779. doi: 10.1002/vetr.779. Epub 2021 Aug 11. PMID: 34379795.
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