- WSU Paul G. Allen School for Global Animal Health
- Veterinary Clinical Sciences
- Veterinary Teaching Hospital
- American Society for Microbiology
- Washington Veterinary Medical Association
- Veterinary Infection Control Group
- National Association of State Public Health Veterinarians
- Association for Veterinary Epidemiology and Preventive Medicine
Phone: 509-335- 3831
Dr. Davis graduated from the WSU College of Veterinary Medicine in 1985 and practiced small animal medicine for 3 years She obtained a Master’s of Public Health (MPH) in Epidemiology (1992) at UW and worked as an epidemiologist for the Seattle-King County Department of Public Health from 1990-1996. She returned to WSU to pursue a PhD in molecular epidemiology (2002). Her research interests include molecular epidemiology and transmission dynamics of the major zoonotic enteropathogens Campylobacter, E. coli O157:H7 and Salmonella. Public health impacts of these pathogens are often complicated by antibiotic resistance and her research area includes the epidemiology of resistance genes and their associated mobile genetic elements. She is currently PI of a Morris Animal Foundation-funded project titled “Evaluation of genotyping methods for Staphylococcus pseudintermedius at local, regional and global scales.” which involves whole genome sequencing of an international set of methicillin-resistant Staphylococcus pseudintermedius isolates. Dr. Davis is currently serving as the Washington State University’s Veterinary Teaching Hospital Infection Control epidemiologist and instructs seminar classes on infectious disease epidemiology for graduate students, as well as the elective International Veterinary Medicine for veterinary students.
One of the most important experiences in my life was the large outbreak of E. coli O157:H7 infections associated with Jack in the Box restaurants in 1992-1993 in Washington State. (Subsequently, previously undetected cases were found in other states like California and Nevada.) Because people died in that outbreak, many of them young children, I became emotionally connected to infection prevention and wanted to learn more about the molecular epidemiological techniques that could be used to track sources of infection in an outbreak. After my PhD at WSU I learned that these techniques could be used to answer much broader questions than food sources in an outbreak – such as sources and transmission routes on a wider geographic and temporal scale. In the meantime I have watched the molecular epidemiological capabilities develop from simple restriction enzyme-based techniques like PFGE to whole genome sequencing, which is becoming the standard now. This is both exciting and daunting as molecular and analytic methods become more sophisticated; it’s gratifying to see a younger generation of scientists being educated and trained to use newer tools.
Outside of work I enjoying hiking, dog sitting, playing the piano and reading fiction.
Education and Training
I was trained at Washington State University (Pullman, WA) for my DVM and my PhD, and at the University of Washington (Seattle, WA) for my MPH in epidemiology.
General Research / Expertise
I study the molecular epidemiology of antibiotic resistance in bacteria. Right now, there are four major areas:
- Beta-lactam resistance in commensal E. coli in dairy cattle and their environments.
- Antibiotic resistance in E. coli that colonize or infect companion animals (dogs) and how related they are to pathogenic E. coli from humans.
- Antibiotic resistance infections in companion animals, particularly in veterinary hospitals.
- Infection control in veterinary hospitals
Some types of bacteria may infect and cause disease in humans and animals and I am interested in ways that these bacteria move (or are transmitted) between different individuals and populations of humans and animals. One way to study this is to genetically fingerprint the bacteria and “track” them using the genetic fingerprint to determine where they came from. Disease-causing bacteria can also become resistant to certain antibiotics, meaning that doctors can no longer use those antibiotics to treat that bacterial infection. I also try to find out how bacteria in animals become resistant to antibiotics. This often happens as a result of treatment with antibiotics, but other forces can also favor the growth of the resistant strains. Antibiotic resistance is very complex and doctors and veterinarians are worried that too many infections are becoming resistant to many of the antibiotics they use to treat their patients.
My work has and can be used to understand the epidemiology of zoonotic infections, particularly infections with antibiotic-resistant E. coli, Salmonella and Campylobacter. These are all gram-negative bacteria that are often transmitted from food-producing animals to people by the foodborne route. They may become resistant to antibiotics if the animals are treated with antibiotics, making some people think that to solve the problem of antibiotic resistance, all we need to do is to stop using antibiotics in animal populations. My work and others’ indicates that the answer to that problem is not so simple. For example, in one study we found that people are more likely to get resistant Salmonella infections by having direct contact with animals rather than eating meat. Another study found that E. coli with a particular resistance gene were likely transmitted from humans to cattle rather than the other way around. One possibility for that would be transmission via wastewater which comes from human waste and may enter rivers and canals and find its way to crops that are used to feed animals. This is speculative but fits the data better than a simple animal > food > human direction of transmission. In fact, we are finding that the big picture of antibiotic resistance include many inputs, pathways and host species.
I have also been working on resistant infections in companion animals (mainly dogs). Dogs are treated medically more similarly to humans than farm animals such as cattle, pigs and chickens. In my work as an infection control officer, I see many infections in our veterinary teaching hospital that are the same type of bacteria as the ones that cause infections in human hospitals. They have the same types of antibiotic resistance, too. We are studying these infections with our genetic fingerprinting tools to determine how they are spread in the hospital or even outside of the hospital in the community. Someday I hope to be able to assess whether pet dogs and/or their owners may be risk factors for acquiring multi-drug resistant, hospital-associated infections.
My lab is currently conducting a project to sequence the genomes of at least 100 methicillin-resistant Staphylococcus pseudintermedius (MRSP), a pathogen of dogs that has an epidemiology in that host species that is very similar to the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in human beings. This is an emerging pathogen since about the mid-2000s in North America. Like other health-care associated infections, the resistance spectrum beyond that of the expected beta-lactam resistance is variable and is extremely extensive in some cases, so that the therapeutic options are becoming narrower all the time. We have assembled an international set of MRSP isolates, and are now analyzing sequence data for approximately 50 isolates. We recently submitted a Genome Announcement and data for 12 MRSP isolates to GenBank. Ultimately we will evaluate some of the currently used typing methods such as pulsed-field gel electrophoresis (PFGE), spa-typing, Mec-typing, dru-typing and multilocus sequence typing (MLST). We will also develop a technique that will be cheaper and faster than whole genome sequencing, or multilocus variable number of tandem repeats analysis (MLVA). We hope to evaluate this method prospectively in our hospital.
In 2015 we published evidence that commensal E. coli that carry blaCTX-M had become significantly prevalent in dairy cattle across Washington State within the past decade. However, the use of ceftiofur in cattle had become common in the early 2000s, and the dominant third-generation cephalosporin resistance gene in the field was blaCMY-2. CTX-M enzymes show stronger resistance to ceftiofur as measured by zones of inhibition in disk diffusion tests, but the reason for the recent emergence of these plasmids in dairy cattle can’t be completely explained by that advantage. There is evidence that human medical centers across the country and including Washington State were detecting blaCTX-M –carrying Enterobacteriaceae in the early 2000s, preceding their detection in cattle by at least 8 years. One hypothesis that could explain the flow of resistance traits from human to cattle populations was that phage transduction played an important role in transmission of either plasmids or genes, and bacteriophages can be carried by waterways, and are not affected by wastewater treatments. This had been demonstrated in Europe, Africa and Asia but had yet to be explored in the United States. We carried out a project sampling water from wastewater effluents, river and canals at different sites throughout the Yakima Valley in Washington State and found a very high sample prevalence of blaCTX-M and significant sample prevalences of other beta-lactamase genes including carbapenemases such as blaKPC , blaOXA-48 and blaNDM-1 . A even more recently we have published the molecular epidemiology of the commensal E. coli from cattle, which suggested a surprising lack of association between CXT-M plasmid types and their bacterial host sequence types. This suggests an “epidemic plasmid” scenario that we hope to explore in future projects.
- Afema JA, Ahmed S, Besser TE, Jones LP, Sischo WM, Davis MA. (2018) Molecular Epidemiology of Dairy Cattle-Associated Escherichia coli Carrying blaCTX-M Genes in Washington State. Appl Environ Microbiol. 84(6). pii: e02430-17. doi: 10.1128/AEM.02430-17. PMID: 29305512 PMCID: PMC5835732
- Ahmed S, Besser TE, Call DR, Weissman SJ, Jones LP, Davis MA (2016) Evaluation of two multi-locus sequence typing schemes for commensal Escherichia coli from dairy cattle in Washington State. J Microbiol Methods. 124, 57-61 PMID: 27001705 PMCID:
- Davis MA, Sischo WM, Jones LP, Moore DA, Ahmed S, Short DM, Besser TE (2015) Recent Emergence of Escherichia coli with Cephalosporin Resistance Conferred by blaCTX-M on Washington State Dairy Farms. Appl Environ Microbiol 81(13), 4403-10 PMID: 25911480 PMCID: PMC4475894
- Suthar N, Roy S, Call DR, Besser TE, Davis MA (2014) An individual-based model of transmission of resistant bacteria in a veterinary teaching hospital. PLoS One. 9(6), e98589 PMID: 24893006 PMCID: PMC4043964
- Davis MA, Moore DL, Baker KN, French NP, Patnode M, Hensley J, Macdonald K, Besser TE (2013) Risk factors for campylobacteriosis in two washington state counties with high numbers of dairy farms. J Clin Microbiol 51(12), 3921-7 PMID: 24025908 PMCID: PMC3838072
- 2012, ADVANCEing EXCELinSE External Mentor Program. Mentor: Dr. Paul Morley, Colorado State University, to advance infection control surveillance strategies.
- 2014, ADVANCEing EXCELinSE External Mentor Program Follow Up for return visit by Dr. Morley.