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Multidrug-resistant Salmonella Typhimurium, Pacific Northwest, United States.

We compared human and bovine isolates of Salmonella enterica Salmonella enterica is a rod shaped, flagellated, Gram-negative bacterium, and a member of the genus Salmonella.[1] Serovars
S. enterica has an extraordinarily large number of serovars
 using antimicrobial-drug resistance profiles and pulsed-field gel electrophoresis gel electrophoresis
Electrophoresis performed in a gel composed of agarose, polyacrylamide, or starch.
. From 2000 through 2006, we observed an increase in a novel multidrug-resistant clone of S. Typhimurium with no recognized phage phage: see bacteriophage.

phage - A program that modifies other programs or databases in unauthorised ways; especially one that propagates a virus or Trojan horse. See also worm, mockingbird. The analogy, of course, is with phage viruses in biology.
 type. This clone may represent an emerging epidemic strain in the Pacific Northwest.


Nontyphoidal salmonellosis salmonellosis (săl'mənĕlō`sĭs), any of a group of infectious diseases caused by intestinal bacteria of the genus Salmonella,  has been characterized by a pattern of dissemination of clonal Salmonella enterica. The most well-known example of this was S. enterica serovar Typhimurium definitive phage type 104 (DT104), a clone that emerged and disseminated globally in the 1990s (1). Other examples of epidemic clones include Salmonella serovar Wien, which spread from North Africa through Europe in the 1970s; S. Typhimurium phage type 10 (DT10), which disseminated across Canada Across Canada was an afternoon program that formerly aired on The Weather Network. The segment ran from early 1999 until mid 2002. The show ran from 3:00PM ET until 7:00 PM ET.  in the 1970s, and other phage types of S. Typhimurium associated with cattle that disseminated widely in Europe during the 1980s (2). More recently, multidrug-resistant (MDR MDR,
n See multidrug resistance.

n the abbreviation for minimum daily requirement, specifically the Minimum Daily Requirements for Specific Nutrients compiled by the United States Food and Drug Administration.
) S. Agona was disseminated in poultry in Belgium; MDR S. Paratyphi B dT+ in Germany, Belgium, and the Netherlands; and MDR S. Newport that harbors the plasmid-mediated AmpC resistance in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area.  (3). Epidemic clones may remain largely restricted to the animal reservoir for years before their incidence rises among human infections: S. Typhimurium phage type 204c disseminated throughout the United Kingdom in cattle from 1980 through 1984, but its proportion among human S. Typhimurium infections was not high during that period (4). Some epidemic clones, for example DT10 and DT104, expanded in the absence of a specific resistance advantage (1). The mechanisms underlying emergence, dissemination, and subsequent decline of novel Salmonella clones are unknown, although some researchers have hypothesized that fitness-associated genetic factors may allow more efficient dissemination in specific hosts and environments (5) and that acquisition of these fitness genes may be phage mediated (6).

One approach to understanding clonal replacement events is to conduct prospective surveillance of Salmonella infections in animal and human hosts. We initiated such a study to compare human- and animal-origin Salmonella strains by serovar, antimicrobial drug resistance pattern, and pulsed-field gel electrophoresis (PFGE PFGE Pulsed-Field Gel Electrophoresis ).

The Study

In Washington, all clinical laboratories and healthcare providers are required to submit Salmonella isolates to the Washington State Department of Health Public Health Laboratory (PHL) for serotyping and surveillance (Washington Administrative Code 246-101-201). The PHL is a participant in PulseNet, a national surveillance system established in 1996 that allows state and local public health epidemiologists to compare PFGE profiles of Salmonella strains from all US regions (7). All human isolates are compared at the PHL by using a standard PFGE PulseNet protocol (8). Beginning in January 2004, all human-origin isolates were obtained from the PHL by the Washington State University Washington State University, at Pullman; land-grant and state supported; chartered 1890, opened 1892 as an agriculture college. From 1905 to 1959 it was the State College of Washington.  Zoonosis Zoonosis Definition

Zoonosis, also called zoonotic disease refers to diseases that can be passed from animals, whether wild or domesticated, to humans.
 Research Unit in Pullman. Animal-origin isolates were obtained from the Washington Animal Disease Diagnostic Laboratory in Pullman, the Washington Avian Health Laboratory in Puyallup, and a private veterinary diagnostic laboratory. In addition to isolates originating from clinical veterinary submissions, we obtained isolates from a research study targeting Salmonella occurrence on dairy farms in Washington (D. Hancock et al., unpub, data). All isolates were tested for resistance to a panel of antimicrobial drugs with a standard disk-diffusion method (9) according to Clinical and Laboratory Standards Institute guidelines (10) (Table 1). Isolates collected from January 1, 2000, through April 2005 were tested for susceptibility to a panel of antimicrobial drugs (Table 1). Animal-origin isolates that matched human-origin isolates by serotype serotype /se·ro·type/ (ser´o-tip) the type of a microorganism determined by its constituent antigens; a taxonomic subdivision based thereon.

See serovar.

 and resistance pattern were further compared by using a standard PFGE protocol (8). Cluster analysis Cluster analysis

A statistical technique that identifies clusters of stocks whose returns are highly correlated within each cluster and relatively uncorrelated across clusters. Cluster analysis has identified groupings such as growth, cyclical, stable, and energy stocks.
 using the unweighted pair group method with arithmetic mean (mathematics) arithmetic mean - The mean of a list of N numbers calculated by dividing their sum by N. The arithmetic mean is appropriate for sets of numbers that are added together or that form an arithmetic series.  analysis (UPGMA UPGMA Unweighted Pair Group Method, Arithmetic Mean ) of Dice similarity coefficients based on PFGE banding patterns was computed in Bionumerics (Applied Maths, Sint-Martens-Latem, Belgium). To limit the effect of nonindependence among isolates, only the first in each serotype and resistance pattern group within each herd and calendar year was included in the analysis. Statistical significance testing of the change in proportions was conducted in Epi-Info version 6.0 with [chi square chi square (kī),
n a nonparametric statistic used with discrete data in the form of frequency count (nominal data) or percentages or proportions that can be reduced to frequencies.
] for linear trend (11).

We observed an increase in bovine-origin S. Typhimurium isolates that were represented by 2 highly similar PFGE patterns, identified as Washington State PulseNet types TYP TYP Typical
TYP Type
TYP Typist
TYP Tribal Youth Program
TYP Take Your Pick
TYP Transitional Year Program (higher education)
TYP Ten Year Plan
TYP Taiwan Yellow Pages
TYP Thank You, Partner
035 and TYP187 (Table 2). They were clearly distinguishable from phage type DT104 strains isolated during the same time frame (online Appendix Figure, available from htm). To determine whether these XbaI PFGE types were clonal, we characterized 60 S. Typhimurium isolates, including 32 TYP035-TYP187 isolates from bovines and 19 TYP035-TYP187 isolates from humans, by PFGE following digestion of DNA DNA: see nucleic acid.
 or deoxyribonucleic acid

One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes.
 by SpeI. SpeI patterns within each XbaI type showed only minor banding variations. Thirteen isolates that were XbaI-TYP035 had SpeI patterns indistinguishable from those of XbaI-YYP187 isolates. In the cluster analysis of SpeI patterns, the TYP035 and TYP 187 isolates' XbaI patterns were at least 90.1% similar compared to an overall 83.7% similarity for all S. Typhimurium isolates in the analysis. Characterization of isolates within the XbaI PFGE type TYP035 also included plasmid profiles of 38 isolates with published plasmid-profiling methods (12). Isolates were selected for plasmid profiling to maximize the diversity of resistance patterns, geographic origin, and year of isolation. Plasmid sizes were estimated relative to a BAC-Tracker Supercoiled DNA ladder (EPICENTRE epicentre

Point on the surface of the Earth that is directly above the source (or focus) of an earthquake. There the effects of the earthquake usually are most severe. See also seismology.
 Biotechnologies, Madison, WI, USA). Fifteen of the 38 tested isolates harbored a single [approximately equal to] 120-kb plasmid. The remainder had variable plasmid profiles, but the plasmid profiling data did not correlate with resistance phenotype or SpeI-banding variations (data not shown). Similar results were obtained with phage typing of a convenience sample of 31 isolates by Rafiq Ahmed at the National Microbiology Laboratory The National Microbiology Laboratory (NML) is located in the Canadian Science Centre for Human and Animal Health in Winnipeg, Manitoba. This modern state-of-the-art facility houses the NML's Biological Safety Level 4 (BSL-4) containment laboratory, currently Canada's only BSL-4 , Winnipeg, Manitoba, Canada. All 31 TYP35 isolates were phage-type untypable with the standard Colindale panel of phages, although an additional set of phages were able to discriminate among some of them (R. Ahmed, pers. commun.). The resulting categories of untypable phages (UT2, UT5, UT7, and UT8) were also not consistent with either plasmid profile or resistance phenotypes (data not shown).

The proportion of all bovine independent S. Typhimurium isolates in the TYP035-TYP187 clade clade Cladus, subtype Genetics A branch of biological taxa or species that share features inherited from a common ancestor; a single phylogenetic group or line. See Inheritance, Species.  increased significantly from 2000 to 2006 in Washington ([chi square] for linear trend, p<0.01). The proportion also increased significantly among human S. Typhimurium isolates during the same period ([chi square] for linear trend, p<0.01) (Table 2). Expansion of TYP035 apparently occurred in the bovine population of the Pacific Northwest before its increase among human isolates because in 2000 it represented over one quarter of all bovine S. Typhimurium, but it was uncommon among human-source S. Typhimurium before 2002 to 2003 (Table 1). Similarly, TYP187 was detected in bovine isolates 2 years before its detection in human isolates. Resistance characteristics varied among TYP035 and TYP187 isolates. Before 2003, the predominant resistance pattern among TYP035 isolates was the AKSSuT phenotype; after 2002, isolates were distributed more widely among several resistance patterns (Table 1). The predominant resistance pattern among isolates of TYP 187 was AKSSuTCaz (Table 1).


The strain type reported here may be an emerging epidemic clone of MDR Salmonella with the potential to expand further. Since 2001, TYP035 has been infrequently reported in the National PulseNet Database, and most sporadic cases were from Washington. The TYP 187 profile has never been reported outside of Washington. Comparison of PFGE patterns between Northwest and New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of
 State S. Typhimurium isolates at the Cornell University Zoonosis Research Unit showed no occurrences of TYP035 or TYP187 among 23 bovine and 29 human S. Typhimurium isolates from the same period. These comparisons with isolates from other parts of the United States suggest that the emergence of the TYP035/TYP187 clade is currently focused in the Pacific Northwest region but has the potential to become more widespread. In 2006, the Massachusetts Department of Public Health The Massachusetts Department of Public Health is a governmental agency of the Commonwealth of Massachusetts with various responsibilities related to public health within that state.  investigated an outbreak of salmonellosis associated with owl pellets among elementary school students (46 primary cases, 12 secondary cases) (13). This outbreak was caused by TYP035 S. Typhimuriurn, and the supplier of the owl pellets was located in a rural county in south-central Washington. This outbreak illustrates that epidemic clones may disseminate widely by means of unpredictable vehicles and that nonfoodborne transmission can have a major public health impact.

The TYP035/TYP187 clade first increased in the animal reservoir, followed by spillover spill·o·ver  
1. The act or an instance of spilling over.

2. An amount or quantity spilled over.

3. A side effect arising from or as if from an unpredicted source:
 into the human population, consistent with its being an emergent clone. Whether or not this strain will continue to expand, further characterization of this PFGE type and continued surveillance will be important steps for improving our understanding of epidemic Salmonella clones (3,5).


We thank Carol Fraczak, Rafiq Ahmed, Jean Whichard, Yubei Zhang, and Min-Su Kang.

This project was funded by the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services Noun 1. Department of Health and Human Services - the United States federal department that administers all federal programs dealing with health and welfare; created in 1979
Health and Human Services, HHS
, under contract no. N01-AI30055.


(1.) Hancock D, Besser T, Gay JM, Rice D, Davis M, Gay C. The global epidemiology of multiresistant Salmonella enterica serovar Typhimurium DTI Diffusion tensor imaging (DTI)
A refinement of magnetic resonance imaging that allows the doctor to measure the flow of water and track the pathways of white matter in the brain.
04. In: Brown C, Bolin CA, editors. Emerging diseases of animals. Washington: ASM (1) (Association for Systems Management) An international membership organization based in Cleveland, Ohio. Founded in 1947 and disbanded in 1996, it sponsored conferences in all phases of administrative systems and management.  Press; 2000. p. 217-43.

(2.) Davis MA, Hancock DD, Besser TE. Multiresistant clones of Salmonella enterica: the importance of dissemination. J Lab Clin Med. 2002;140:135-41.

(3.) Butaye P, Michael GB, Schwarz S, Barrett T J, Brisabois A, White DG. The clonal spread of multidrug-resistant non-typhi Salmonella serotypes. Microbes Infect. 2006;8:1891-7.

(4.) Threlfall EJ, Rowe B, Ferguson JL, Ward LR. Increasing incidence of resistance to gentamicin gentamicin /gen·ta·mi·cin/ (jen?tah-mi´sin) an aminoglycoside antibiotic complex isolated from bacteria of the genus Micromonospora,  and related aminoglycosides in Salmonella typhimurium Salmonella ty·phi·mu·ri·um
A bacterium that causes food poisoning.
 phage type 204c in England, Wales Wales, Welsh Cymru, western peninsula and political division (principality) of Great Britain (1991 pop. 2,798,200), 8,016 sq mi (20,761 sq km), west of England; politically united with England since 1536. The capital is Cardiff.  and Scotland. Vet Rec. 1985;117:355-7.

(5.) Kang MS, Besser TE, Hancock DD, Porwollik S, McClelland M, Call DR. Identification of specific gene sequences conserved in contemporary epidemic strains of Salmonella enterica. Appl Environ Microbiol. 2006;72:6938-47.

(6.) Brussow H, Canchaya C, Hardt WD. Phages and the evolution of bacterial pathogens: from genomic rearrangements to lysogenic lysogenic /ly·so·gen·ic/ (li-so-jen´ik)
1. producing lysins or causing lysis.

2. pertaining to lysogeny.

 conversion. Microbiol Mol Biol Rev. 2004;68:560-602.

(7.) Swaminathan B, Barrett TJ, Fields R Surveillance for human Salmonella infections in the United States. J AOAC AOAC Association of Official Analytical Chemists (now AOAC International)
AOAC Association of Analytical Communities
AOAC Association of Analytical Chemists
AOAC Always On/Always Connected
AOAC Aero-Optic Evaluation Center
 Int. 2006;89:553-9.

(8.) Hunter SB, Vauterin P, Lambert-Fair MA, van Duyne MS, Kubota K, Graves L, et al. Establishment of a universal size standard strain for use with the PulseNet standardized pulsed-field gel electrophoresis protocols: converting the national databases to the new size standard. J Clin Microbiol. 2005;43:1045-50.

(9.) Bauer AW, Kirby MMW MMW Millimeter Wave
MMW Medeski, Martin, and Wood
MMW Magne Magler Wiggen (Norwegian architects)
MMW Mark My Words
MMW Making of the Modern World
, Sherris JC, Turck M. Antibiotic susceptibility testing by a standard single disk method. Am J Clin Pathol. 1966;45:493-6.

(10.) National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing, 13th informational supplement, 13th ed. Approved standard M100-S13. Wayne (PA): The Committee; 2003.

(11.) Dean AG, Dean JA, Coulombier D, Brendel KA, Smith DC, Burton AH, et al. EpiInfo, Version 6: a word processing, database, and statistics programs for epidemiology on microcomputers. Atlanta: Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. ; 1994.

(12.) Kado CI, Liu ST. Rapid procedure for detection and isolation of large and small plasmids. J Bacteriol. 1981;145:1365-73.

(13.) Bureau of Communicable Disease communicable disease
A disease that is transmitted through direct contact with an infected individual or indirectly through a vector. Also called contagious disease.
 Control Massachusetts Department of Public Health. Salmonella outbreak related to owl pellets. Communicable Disease Update. 2006; 14:2. [cited 2007 Jun 11]. Available from

Margaret A. Davis, * Thomas E. Besser, * Kaye Eckmann, ([dagger]) J. Kathryn MacDonald, ([dagger]) Donna Green, ([dagger]) Dale D. Hancock, * Katherine N.K. Baker, * Lorin D. Warnick, ([double dagger]) Yesim Soyer, ([double dagger]) Martin Wiedmann, ([double dagger]) and Douglas R. Call *

* Washington State University, Pullman, Washington, USA; ([dagger]) Washington State Department of Health Public Health Laboratories, Shoreline, Washington, USA; and ([double dagger]) Cornell University, Ithaca, New York
This article is about the City of Ithaca and the region. For the legally distinct town which itself is a part of the Ithaca metropolitan area, see Ithaca (town), New York.

For other places or objects named Ithaca, see Ithaca (disambiguation).

Address for correspondence: Margaret A. Davis, Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164, USA; email:

All material published in Emerging Infectious Diseases is in the public domain and may be used and reprinted without special permission; proper citation, however, is required.

Dr Davis works at the Washington State University Department of Veterinary Microbiology and Pathology. Her main research interests are the molecular epidemiology molecular epidemiology Molecular medicine An evolving field that combines the tools of standard epidemiology–case studies, questionnaires and monitoring of exposure to external factors with the tools of molecular biology–eg, restriction endonucleases,  of enteric enteric /en·ter·ic/ (en-ter´ik) within or pertaining to the small intestine.

1. Of, relating to, or within the intestine.

 pathogens and antimicrobial resistance.
Table 1. Trends in resistance of bovine-origin
Salmonella Typhimurium PFGE types TYP035 and TYP187 *

characteristics ([dagger])   2001   2002   2003   2004   2005   2006

  ASu                                         1      1      1
  ACaz                                                             1
  AKSuT                                1                    1
  AKSSuT                        7      7      1      4      1      4
  ACKSSuT                       1      1
  AKSSuTCaz                                          3
  AKSxtSSuT                                          1
  ACKSSuTCaz                                  2      2
  ACKSxtSSuT                                                1
  AKSuTCaz                                                  1
  AKSSuTCaz                                                 1      1
  ACKSSuTCaz                                                2      1
  ACKSxtSSuTCaz                        1      1      6      4
  AGKSxtSSuTCaz                                                    1
Total                           8     10      5     17     12      8

  ACSSuTCaz                                          1
  AKSSuTCaz                                                 1     12
  AKSuTCaz                                                  1
Total                                                1      2     12

* PFGE, pulsed-field gel electrophoresis.

([dagger]) A, ampicillin; Su, triple-sulfa, Caz, ceflazidime,
K, kanamycin, T, tetracycline, S, streptomycin, C, chloramphenicol;
Sxt, trimethoprim-sulfamethoxazole; G. gentamicin. In April 2005
nitrofurantoin, trimethoprim, and ciprofloxacin were dropped from
the panel, and amoxicillin-clavulanic acid, nalidixic acid, and
ceftazidime-clavulanic acid were added.

Table 2. Human- and bovine-source Salmonella Typhimurium
isolates from Washington that were XbaI-PFGE type TYP035
or TYP187 *

                         Total no. ([dagger])
Year   TYP035   TYP187   (%) ([double dagger])

2000     1        0            222 (0.5)
2001     1        0            174 (0.6)
2002     8        0            143 (5.6)
2003     13       0            153 (8.5)
2004     7        0            143 (4.9)
2005     18       0            124 (8.9)
2006     3        7            118 (8.5)

                         Total no. ([dagger])
Year   TYP035   TYP187   (%) ([double dagger])

2000     16       0            61 (26.2)
2001     18       0            47 (38.3)
2002     10       0            31 (32.3)
2003     5        0            13 (38.5)
2004     10       1            26 (42.3)
2005     12       2            29 (48.3)
2006     8        12           39 (51.3)

* For human isolates only a single isolate per individual was
included, and for bovine isolates only independent isolates
were included. PFGE, pulsed-field gel electrophoresis.

([dagger]) Total number of unique S. Typhimurium isolates.

([double dagger]) Percentage of the total that were part
of the TYP035-TYP187 clade.
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Title Annotation:DISPATCHES
Author:Davis, Margaret A.; Besser, Thomas E.; Eckmann, Kaye; MacDonald, J. Kathryn; Green, Donna; Hancock,
Publication:Emerging Infectious Diseases
Date:Oct 1, 2007
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