Molecular epidemiology of Salmonella Heidelberg in an equine hospital

Ciprofloxacin-resistant ST198 Salmonella Kentucky in a hospitalized American black bear (Ursus americanus), with evidence of subsequent nosocomial transmission

Global emergence of ciprofloxacin-resistant ST198 Salmonella Kentucky poses an important public health threat. While conducting Salmonella surveillance among wildlife patients admitted to our veterinary medical teaching hospital in central New York, we isolated multidrug-resistant (MDR) ST198 Salmonella Kentucky from an American black bear (Ursus americanus) in September 2020. The isolate was phenotypically resistant to numerous antimicrobial agents, including ceftriaxone and ciprofloxacin, and several antimicrobial resistance genes and mutational resistance determinants were detected. Between April and July 2021, the same strain of MDR ST198 Salmonella Kentucky was also isolated from seven other wildlife patients and multiple hospital environmental locations, suggesting nosocomial transmission. Ciprofloxacin resistance is conferred by triple point mutations in the quinolone resistance-determining regions (QRDRs), a genotypic profile indicative of Clade ST198.2. To our knowledge, this is the first report of this ciprofloxacin-resistant clade being identified in animals or animal products in the United States. Timely resolution of the outbreak was achieved following efforts to further enhance environmental disinfection protocols and biosecurity measures at the hospital, with no known cases or positive environmental samples after July 2021.

Willingness to adopt personal biosecurity strategies on thoroughbred breeding farms: Findings from a multi-site pilot study in Australia's Hunter Valley

There are almost 9,500 full-time employees in Australia's thoroughbred horse breeding industry. During foaling, they can be exposed to bodily fluids and mucous membranes which may present risks for zoonotic disease. These risks can be mitigated through personal biosecurity strategies. The aim of this study was to identify which personal biosecurity strategies were more or less likely to be adopted by workers. Seventeen participants representing 14 thoroughbred breeding farms and three equine veterinary practices in Australia's largest thoroughbred breeding region trialed up to 16 stakeholder-nominated personal biosecurity strategies over the 2021 foaling season. The strategies encompassed personal protective equipment (PPE), zoonotic disease awareness, policies and protocols, supportive environments, and leadership. Strategy adoption was monitored through three repeated self-audit surveys designed around the Transtheoretical Model of change (TTM) and findings were reviewed in exit interviews. For all survey waves in aggregate, 13 strategies were practiced by at least 50.0% of participants. Participants were most likely to use a ready-made foaling box (98.0%), communicate the message that PPE usage is a personal responsibility (94.1%) and use ready-made PPE kits (88.2%). However, 31.4% had no intention of doing practice sessions and/or dummy runs for PPE use and 27.5% had no intention of using a buddy system on farm/practice to check use of PPE. Whilst these rates indicate workers' willingness to adopt and maintain personal biosecurity strategies, they also indicate capacity for more practices to be implemented more often. Overall, the findings highlight the need for personal biosecurity interventions to be sensitive to the demands of the annual thoroughbred breeding calendar, the size of the breeding operation and the availability of skilled staff.

Widespread Environmental Presence of Multidrug-Resistant Salmonella in an Equine Veterinary Hospital That Received Local and International Horses

Salmonella enterica is a highly infectious microorganism responsible for many outbreaks reported in equine hospitals. Outbreaks are characterized by high morbidity and mortality rates, nosocomial transmission to other patients, zoonotic transmission to hospital personnel, and even closure of facilities. In this study, 545 samples (environmental and hospitalized patients) were collected monthly during a 1-year period from human and animal contact surfaces in an equine hospital that received local and international horses. A total of 22 Salmonella isolates were obtained from human contact surfaces (e.g., offices and pharmacy) and animal contact surfaces (e.g., stalls, surgery room, and waterers), and one isolate from a horse. Molecular serotyping revealed 18 isolates as Salmonella Typhimurium and three as Salmonella Infantis. Nineteen isolates were resistant to at least one antimicrobial class, and only two isolates were susceptible to all antimicrobials tested. In addition, we identified nine multidrug-resistant (MDR) isolates in S. Typhimurium, which displayed resistance to up to eight antimicrobials (i.e., amoxicillin/clavulanate, ampicillin, ciprofloxacin, chloramphenicol, streptomycin, gentamicin, trimethoprim/sulfamethoxazole, and tetracycline). Pulsed-field gel electrophoresis (PFGE) revealed the presence of three PFGE patterns permanently present in the environment of the hospital during our study. The persistent environmental presence of MDR Salmonella isolates, along with the fact that local and international horses are attended in this hospital, highlights the importance of improving biosecurity programs to prevent disease in horses and the hospital personnel and also for the global dissemination and acquisition of MDR Salmonella.

Detection of Salmonella from animal sources in South Africa between 2007 and 2014

Retrospective laboratory-based surveillance was conducted on Salmonella serotypes isolated from various animal species from 2007 to 2014 at the Agricultural Research Council, Onderstepoort Veterinary Research Institute, South Africa. During the surveillance period, 1229 salmonellae isolations were recorded. Around 108 different serotypes were recovered from nine different food and non-food animal host species. The three most common serotypes were Salmonella enterica subspecies enterica serotype Heidelberg (n = 200), Salmonella enterica subspecies enterica serotype Enteritidis (n = 170) and Salmonella enterica subspecies enterica serotype Typhimurium (n = 146). These were followed by Salmonella enterica subspecies enterica serotype Anatum (n = 62) and Salmonella enterica subspecies enterica serotype Infantis (n = 57). Salmonella enterica subspecies enterica serotype Schwarzengrund and Salmonella enterica subspecies enterica serotype Muenchen were recovered in 50 and 48 cases, respectively. Of the total number of isolations recorded during the period under review, 871 (70.8%) occurred in poultry and other birds, 162 (13.2%) in horses, 116 (9.4%) in cattle, 26 (2.1%) in sheep and goats, 22 (1.8%) in rhinoceroses, 16 (1.3%) in pigs, 8 (0.6%) in crocodiles, 6 (0.5%) in cats and 6 (0.5%) in leopards. Food animals accounted for 83.5% of the total isolations, with cattle and poultry representing approximately 72.7%. Forty-two (3.4 %) isolates were found from non-food animals that include rhinoceroses (n = 22), crocodiles (n = 8), leopards (n = 6) and cats (n = 6). Salmonella Heidelberg was the most frequently isolated serotype, whereas S. Typhimurium had the widest zoological distribution. Clinical laboratory isolation of different Salmonella serotypes from various hosts may aid in recognising the threat to livestock, public and environmental health. Moreover, it may also highlight the potential zoonotic and food safety risk implications of the detected Salmonella serotypes.

Salmonella enterica serovar Oranienburg outbreak in a veterinary medical teaching hospital with evidence of nosocomial and on-farm transmission

Nosocomial salmonellosis continues to pose an important threat to veterinary medical teaching hospitals. The objectives of this study were to describe an outbreak of salmonellosis caused by Salmonella enterica serovar Oranienburg within our hospital and to highlight its unique features, which can be used to help mitigate or prevent nosocomial outbreaks in the future. We retrospectively analyzed data from patients that were fecal culture-positive for Salmonella Oranienburg between January 1, 2006, and June 1, 2011, including historical, clinical, and pulsed-field gel electrophoresis (PFGE) data. Salmonella Oranienburg was identified in 20 horses, five alpacas, and three cows during this time frame, with dates of admission spanning the period from August, 2006, through January, 2008. We consider most of these patients to have become infected through either nosocomial or on-farm transmission, as evidenced by molecular subtyping results and supportive epidemiologic data. Interpretation of PFGE results in this outbreak was challenging because of the identification of several closely related Salmonella Oranienburg subtypes. Furthermore, a high percentage of cases were fecal culture-positive for Salmonella Oranienburg within 24 h of admission. These patients initially appeared to represent new introductions of Salmonella into the hospital, but closer inspection of their medical records revealed epidemiologic links to the hospital following the index case. Cessation of this outbreak was observed following efforts to further heighten biosecurity efforts, with no known cases or positive environmental samples after January, 2008. This study demonstrates that a Salmonella-positive culture result within 24 h of admission does not exclude the hospital as the source of infection, and it underscores the important role played by veterinary medical teaching hospitals as nodes of Salmonella infection that can promote transmission outside of the hospital setting.

Identification of predictors of Salmonella shedding in adult horses presented for acute colic

BACKGROUND

Colic has been associated with shedding of Salmonella. Horses with salmonellosis typically develop diarrhea, fever, and leukopenia. Overlooking additional predictors may result in failure to detect shedding horses and increase environmental contamination.

OBJECTIVES

Evaluate associations between signalment and clinicopathologic data during early hospitalization and Salmonella shedding in horses treated for acute colic.

ANIMALS

Horses with acute colic admitted to a referral hospital. A total of 59 horses shedding Salmonella compared to 108 Salmonella-negative horses.

METHODS

Retrospective case-control study evaluating patient and Salmonella culture data. Associations between variables and Salmonella shedding were identified using logistic regression. Two multivariable models were developed pertaining to (1) information available within 24 hours of admission and (2) clinical findings that developed later during hospitalization.

RESULTS

Variables retained for multivariable model 1 indicated that Warmbloods and Arabians had increased odds for shedding Salmonella, as did horses requiring surgery (OR, 2.52; 95% CI, 1.10-5.75) or having more severe gastrointestinal disease (OR, 2.59; 95% CI, 1.08-6.20). Retained variables for model 2 demonstrated that horses that were treated surgically (OR, 1.60; 95% CI, 0.70-3.62), developed fever >103°F (OR, 2.70; 95% CI, 0.92-7.87), had abnormal leukocyte count (OR, 1.38; 95% CI, 0.61-3.09), or became inappetent and lethargic (OR, 16.69; 95% CI, 4.08-68.24) had increased odds for shedding Salmonella.

CONCLUSIONS AND CLINICAL IMPORTANCE

In horses with acute colic that present without signs of diarrhea, fever, or leukopenia, additional predictors associated with shedding Salmonella could be used to more promptly identify horses likely to shed organisms.

Salmonella enterica shedding in hospitalized horses and associations with diarrhea occurrence among their stablemates and gastrointestinal-related illness or death following discharge

OBJECTIVE

To evaluate the potential association between Salmonella enterica shedding in hospitalized horses and the risk of diarrhea among stablemates, and to characterize gastrointestinal-related illness and death following discharge among horses that shed S. enterica while hospitalized.

DESIGN

Retrospective cohort study [corrected].

ANIMALS

221 horses (59 that shed S. enterica during hospitalization and 162 that tested negative for S. enterica shedding ≥ 3 times during hospitalization).

PROCEDURES

Information from medical records (signalment, results of microbial culture of fecal samples, clinical status at the time of culture, and treatment history) was combined with data collected through interviews with horse owners regarding formerly hospitalized horses and their stablemates. Data were analyzed to investigate risk factors for death and diarrhea.

RESULTS

Occurrence of diarrhea among stablemates of formerly hospitalized horses was not associated with S. enterica shedding in hospitalized horses but was associated with oral treatment with antimicrobials during hospitalization. Salmonella enterica shedding during hospitalization was not associated with risk of death or gastrointestinal-related illness in study horses ≤ 6 months after discharge, but shedding status and history of gastrointestinal illness were associated with increased risk of death during the preinterview period.

CONCLUSIONS AND CLINICAL RELEVANCE

Stablemates of horses that shed S. enterica during hospitalization did not appear to have an increased risk for diarrhea, but comingling with horses that receive orally administered antimicrobials may affect this risk. Salmonella enterica shedding during hospitalization may be a marker of increased long-term risk of death after discharge. Risks are likely influenced by the S enterica strain involved and biosecurity procedures used.

Outbreak of equine endometritis caused by a genotypically identical strain of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that has been recognized as a cause of endometritis in mares. Pulsed field gel electrophoresis was used to characterize and compare isolates of P. aeruginosa from an outbreak of endometritis and unrelated isolates collected at the same time as the outbreak. The restriction endonuclease digestion patterns and antimicrobial resistance profiles of all outbreak isolates were identical. Therefore, a single strain of P. aeruginosa was responsible for the cases of endometritis. The unrelated isolates could be distinguished from the outbreak strain using the techniques outlined in the present study. The results establish that this pathogen was not venereally transmitted between all the horses from which it was isolated, but rather must have been disseminated, at least initially, from a contaminated water source. Once the water used to clean the mares and stallions was replaced, there were no further reports of endometritis caused by this organism on the affected stud. Furthermore, the fertility of the stallions was not affected, in spite of persistent carriage for 1 to 2 months. The current study has shown that the use of pulsed field gel electrophoresis has considerable value in epidemiological investigations of equine urogenital tract infections with P. aeruginosa.

Simultaneous analysis of multiple enzymes increases accuracy of pulsed-field gel electrophoresis in assigning genetic relationships among homogeneous Salmonella strains

Due to a highly homogeneous genetic composition, the subtyping of Salmonella enterica serovar Enteritidis strains to an epidemiologically relevant level remains intangible for pulsed-field gel electrophoresis (PFGE). We reported previously on a highly discriminatory PFGE-based subtyping scheme for S. enterica serovar Enteritidis that relies on a single combined cluster analysis of multiple restriction enzymes. However, the ability of a subtyping method to correctly infer genetic relatedness among outbreak strains is also essential for effective molecular epidemiological traceback. In this study, genetic and phylogenetic analyses were performed to assess whether concatenated enzyme methods can cluster closely related salmonellae into epidemiologically relevant hierarchies. PFGE profiles were generated by use of six restriction enzymes (XbaI, BlnI, SpeI, SfiI, PacI, and NotI) for 74 strains each of S. enterica serovar Enteritidis and S. enterica serovar Typhimurium. Correlation analysis of Dice similarity coefficients for all pairwise strain comparisons underscored the importance of combining multiple enzymes for the accurate assignment of genetic relatedness among Salmonella strains. The mean correlation increased from 81% and 41% for single-enzyme PFGE up to 99% and 96% for five-enzyme combined PFGE for S. enterica serovar Enteritidis and S. enterica serovar Typhimurium strains, respectively. Data regressions approached 100% correlation among Dice similarities for S. enterica serovar Enteritidis and S. enterica serovar Typhimurium strains when a minimum of six enzymes were concatenated. Phylogenetic congruence measures singled out XbaI, BlnI, SfiI, and PacI as most concordant for S. enterica serovar Enteritidis, while XbaI, BlnI, and SpeI were most concordant among S. enterica serovar Typhimurium strains. Together, these data indicate that PFGE coupled with sufficient enzyme numbers and combinations is capable of discerning accurate genetic relationships among Salmonella serovars comprising highly homogeneous strain complexes.

Temporal clusters of bovine Salmonella cases at a veterinary medical teaching hospital, 1996-2007

The objectives of this study were to identify and characterize temporal clusters of bovine Salmonella cases at a veterinary medical teaching hospital and to determine which clusters were likely to have involved nosocomial transmission. Data on fecal Salmonella shedding status, serotype, and antimicrobial resistance were collected retrospectively for all cattle admitted to the Cornell University Equine and Farm Animal Hospital between January 1, 1996, and June 1, 2007. Pulsed-field gel electrophoresis (PFGE) was performed on all available isolates. Cluster analysis was used to identify temporal clusters of cases. A total of 5398 cattle were admitted during the study period; the prevalence of fecal Salmonella shedding among clinical suspects was 6.5%, whereas that among nonsuspects tested through routine surveillance was 2.5%. Eight temporal clusters (including 57 cattle) were investigated as possible outbreaks involving nosocomial transmission, ranging in size from 4 to 10 cases. All but one cluster were centered over the month of August or September. A total of 15 Salmonella serotypes were represented, with the most common being Typhimurium (33%), Newport (23%), and Agona (12%). Among the isolates available for PFGE analysis, there were 19 PFGE types represented. The majority of temporal clusters during the study period were not nosocomial in origin. However, two of the clusters were outbreaks directly resulting from nosocomial Salmonella transmission, based on case histories, serotype data, antimicrobial resistance patterns, and PFGE analysis. The clear seasonal pattern exhibited by these clusters underscores the need for heightened Salmonella vigilance during the late summer and early fall. The combination of statistical methods, routine bacteriologic data, and PFGE analysis is an effective means of conducting surveillance and outbreak investigations in a hospital setting.

Detection and control of a nosocomial outbreak caused by Salmonella newport at a large animal hospital

BACKGROUND

Nosocomial salmonellosis is often assumed to occur because infection control and surveillance practices are inadequate, but published evidence is lacking to support the related contention that rigorous application of these practices can impact the severity of outbreaks.

OBJECTIVE

Describe active surveillance, early recognition, and intensive mitigation efforts used in an effort to control an outbreak of nosocomial Salmonella enterica serotype Newport infections without hospital closure.

ANIMALS

Large animals hospitalized at a referral hospital.

METHODS

This prospective outbreak investigation was initiated when Salmonella Newport infections were detected among hospitalized animals by active surveillance. Data were analyzed to identify temporal and spatial patterns for epidemic spread of Salmonella in the hospital. Mitigation efforts were aggressively adjusted in response to surveillance data. Genetic relatedness of isolates was investigated by pulsed-field gel electrophoresis.

RESULTS

Of 145 large animals sampled, 8 (5.6%) were infected with the Salmonella strain associated with this outbreak, and all but 1 shed Salmonella in the absence of or before the onset of disease. This strain was recovered from 14.2% (42/295) of environmental samples (ENV samples), indicating that widespread environmental contamination had occurred. Isolates of Salmonella Newport obtained from infected animals and the environment were genetically indistinguishable, confirming clonal dissemination.

CONCLUSIONS AND CLINICAL IMPORTANCE

Active surveillance allowed early detection of nosocomial Salmonella transmission and hospital contamination. Use of aggressive interventions was followed by cessation of transmission. Active surveillance can allow earlier recognition and mitigation compared with programs by only sampling of clinically affected animals.

Acute diarrhea in hospitalized horses

The development of diarrhea among hospitalized horses is a major concern for equine veterinary hospitals and referral centers. It is a potential complication of hospitalization for surgical or medical procedures and can contribute to the morbidity and mortality of horses with gastrointestinal and non-gastrointestinal diseases. Unfortunately, it can be difficult to pinpoint the exact cause of acute diarrhea or colitis, and in most cases, the specific etiologic agent is presumptive or undetermined. This article discusses the major etiologic agents of diarrhea in hospitalized horses, considers factors that place hospitalized horses at special risk for diarrhea, and examines several infectious colitis outbreaks that have occurred at veterinary referral centers.

Inoculation of newly hatched broiler chicks with two Brazilian isolates of Salmonella Heidelberg strains with different virulence gene profiles, antimicrobial resistance, and pulsed field gel electrophoresis patterns to intestinal changes evaluation

Salmonella Heidelberg is one of the 3 most frequently isolated serovars from human Salmonella cases in Canada, and the fourth most commonly reported Salmonella serovar in human foodborne disease cases in the United States. Since 1962, Salmonella Heidelberg has been isolated and reported in poultry and poultry products in Brazil. The poultry industry has focused efforts on reducing salmonellae incidence in live production in an effort to reduce Salmonella in the processing plant. A better understanding of the initial infection in chicks could provide approaches to control Salmonella contamination. The objective of the present study was to evaluate 2 Salmonella Heidelberg strains that differed in the presence of virulence genes invA, agfA, and lpfA; antimicrobial resistance profiles; and epidemiologic profiles on aspects of pathogenicity and intestinal morphology. Newly hatched broiler chicks were inoculated with 2 strains (SH23 and SH35) of Salmonella Heidelberg and cecal morphometry, histopathology, electron microscopy, and bacterial counts in the liver and cecum were assessed. The SH23 and SH35 strains resulted in different changes in villi height and crypt depth and inflammatory cell infiltration in the cecum. The SH35 group had higher liver and cecum bacterial cell counts when compared with SH23 strains.

Antimicrobial resistance in companion animals

Antimicrobial resistance (AMR) is an emerging problem in companion animals, because of difficult-to-treat infections, possible pressure to use antimicrobials that are important in human medicine, and potential zoonotic transmission. The extent and importance of AMR in companion animals are poorly understood, in part because of limited surveillance; however, it is clear that resistance is problematic in many pathogens and commensals, including staphylococci, enterococci, Escherichia coli and Salmonella.

An enhanced discriminatory pulsed-field gel electrophoresis scheme for subtyping Salmonella serotypes Heidelberg, Kentucky, SaintPaul, and Hadar

Conventional pulsed-field gel electrophoresis (PFGE) protocols, used extensively as a successful approach for subtyping many salmonellae, may be inadequate for discriminating strains sharing levels of homogeneity within the same serotype. Four additional restriction enzymes (SpeI, PacI, SfiI, and NotI), in addition to XbaI and BlnI, were used in PFGE typing of 33 Salmonella Heidelberg, 27 Salmonella Kentucky, 27 Salmonella SaintPaul, and 27 Salmonella Hadar isolates that were recovered from poultry and porcine retail meats from different states of the United States. A dendrogram derived from the combined analysis of six enzymes was highly discriminatory with a Simpson index of diversity value of over 0.950. The ratio of nodes to isolates was more than 0.75 with an average of fewer than three isolates in each polytomy for all four serotypes. Two three-enzyme combinations, SpeI/NotI/SfiI for Salmonella Heidelberg and Salmonella Hadar, and SpeI/BlnI/SfiI for Salmonella Kentucky and Salmonella SaintPaul, were found to have comparable discriminatory abilities of differentiating isolates of these Salmonella serotypes with the six-enzyme combination. The enhanced discriminatory PFGE-based subtyping scheme can be used effectively for the differentiation of strains of the four Salmonella serotypes. The findings also highlight PFGE analysis as a continued essential and informative subtyping method for source tracking and outbreak investigations of these and other Salmonella pathogens.

Characteristics of biosecurity and infection control programs at veterinary teaching hospitals

OBJECTIVE

To characterize biosecurity and infection control practices at veterinary teaching hospitals located at institutions accredited by the AVMA.

DESIGN

Cross-sectional survey.

POPULATION

50 biosecurity experts at 38 veterinary teaching hospitals.

PROCEDURES

Telephone interviews were conducted between July 2006 and July 2007, and questions were asked regarding policies for hygiene, surveillance, patient contact, education, and awareness. Respondents were also asked their opinion regarding the rigor of their programs.

RESULTS

31 of 38 (82%) hospitals reported outbreaks of nosocomial infection during the 5 years prior to the interview, 17 (45%) reported > 1 outbreak, 22 (58%) had restricted patient admissions to aid mitigation, and 12 (32%) had completely closed sections of the facility to control disease spread. Nineteen (50%) hospitals reported that zoonotic infections had occurred during the 2 years prior to the interview. Only 16 (42%) hospitals required personnel to complete a biosecurity training program, but 20 of the 50 (40%) respondents indicated that they believed their hospitals ranked among the top 10% in regard to rigor of infection control efforts.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that differences existed among infection control programs at these institutions. Perceptions of experts regarding program rigor appeared to be skewed, possibly because of a lack of published data characterizing programs at other institutions. Results may provide a stimulus for hospital administrators to better optimize biosecurity and infection control programs at their hospitals and thereby optimize patient care.

Comparison of molecular typing methods for the differentiation of Salmonella foodborne pathogens

Bacteria belonging to the genus Salmonella are among the leading causes of foodborne disease of bacterial etiology. These bacteria are also widely disseminated throughout the animal kingdom. The ability to identify the food source from which a human pathogen originated would be of great value in reducing the incidence of foodborne disease and the extent of disease outbreaks due to Salmonella. To date, efforts to identify the origin of these pathogens have centered on phenotypic and genotypic characterization of Salmonella isolates. This review focuses molecular or genotypic techniques that are currently being used for typing, and examines their strengths and weaknesses for determining the source of Salmonella foodborne infections.

Principles of antimicrobial therapy: what should we be using?

Although the use of antimicrobials has had an insurmountable impact on preventing patient morbidity and mortality, problems with antimicrobial resistance and antimicrobial-induced diarrhea are becoming more apparent in human and veterinary medicine. The mortality associated with nosocomial infection with antimicrobial-resistant bacteria in human patients is alarming. Similarly, in veterinary medicine, the morbidity and high cost of treatment of patients with postoperative infection, for example, are concerns. Specifically in equine medicine, the high morbidity and mortality associated with antimicrobial-induced diarrhea have been devastating in many equine practices. Misuse of antimicrobials is extremely common in human and veterinary medicine. All clinicians have the responsibility to consider the appropriateness of their antimicrobial use carefully and, whenever possible, to minimize antimicrobial administration to patients.

Comparison of Salmonella enterica serotype Infantis isolates from a veterinary teaching hospital

AIMS

To compare Salmonella enterica serotype Infantis isolates obtained from patients or the environment of a veterinary teaching hospital over a period of 9 years following a nosocomial outbreak to determine whether isolates were epidemiologically related or represented unrelated introductions into the hospital environment.

METHODS AND RESULTS

Fifty-six S. Infantis isolates were compared based on their phenotypic (antimicrobial drug [AMD] susceptibility pattern) and genotypic (pulsed-field gel electrophoresis [PFGE] pattern and presence of integrons) characteristics. Epidemiologically unrelated S. Infantis isolates clustered separately from all but two of the hospital isolates, and several isolates from different years and various sources were indistinguishable from each other in cluster analysis of two-enzyme PFGE results. A high percentage of isolates (80.3%) were resistant to at least one AMD, with 67.8% showing resistance to >5 AMD. The majority (74.1%) of isolates tested contained type 1 integrons.

CONCLUSION

Results strongly suggest that there was nosocomial transmission of S. Infantis during the initial outbreak, and that contamination arising from this outbreak persisted across years despite rigorous hygiene and biosecurity precautions and may have led to subsequent nosocomial infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

Evidence of persistence and transmission of Salmonella clones across years, even in the face of rigorous preventive measures, has important implications for other facilities that have experienced outbreaks of Salmonella infections.

The genomic island SGI1, containing the multiple antibiotic resistance region of Salmonella enterica serovar Typhimurium DT104 or variants of it, is widely distributed in other S. enterica serovars

The global dissemination of the multiply-antibiotic-resistant Salmonella enterica serovar Typhimurium DT104 clone with the resistance genes located in a class 1 integron, here designated In104, within genomic island SGI1 is a significant public health issue. Here, we have shown that SGI1 and variants of it carrying different combinations of resistance genes are found in several Salmonella enterica serovars. These are serovars Cerro, Derby, Dusseldorf, Infantis, Kiambu, and Paratyphi B dT(+) isolated from human infections and serovar Emek from sewage effluent. Two new variants, SGI1-I and SGI1-J, both of which include the dfrA1-orfC cassette array, were identified.

Efficacy of directed misting application of a peroxygen disinfectant for environmental decontamination of a veterinary hospital

OBJECTIVE

To evaluate effectiveness of 4% peroxymonosulfate disinfectant applied as a mist to surfaces in a large animal hospital as measured by recovery of Staphylococcus aureus and Salmonella enterica serovar Typhimurium.

DESIGN

Field trial.

SAMPLE POPULATION

Polyester transparencies inoculated with bacteria.

PROCEDURE

Polyester transparencies were inoculated with S aureus or S Typhimurium and placed in various locations in the hospital. After mist application of the peroxygen disinfectant, viable bacterial numbers were quantified and compared with growth from control transparencies to assess reduction in bacterial count.

RESULTS

When applied as a mist directed at environmental surfaces contaminated with a geometric mean of 4.03 x 10(7) CFUs of S aureus (95% confidence interval [CI], 3.95 x 10(7) to 4.11 x 10(7)) or 6.17 x 10(6) CFUs of S Typhimurium (95% Cl, 5.55 x 10(6) to 6.86 x 10(6)), 4% peroxymonosulfate reduced the geometric mean number of viable S aureus by 3.04 x 10(7) CFUs (95% Cl, 8.6 x 10(5) to 1.7 x 10(6)) and S Typhimurium by 3.97 x 10(6) CFUs (95% Cl, 8.6 x 10(5) to 3.5 x 10(6)).

CONCLUSIONS AND CLINICAL RELEVANCE

Environmental disinfection with directed mist application of a 4% peroxymonosulfate solution was successful in reducing counts of bacterial CFUs by > 99.9999%. Directed mist application with this peroxygen disinfectant as evaluated in this study appeared to be an effective and efficient means of environmental disinfection in a large animal veterinary hospital and would be less disruptive than more traditional approaches to intensive environmental cleaning and disinfection.

New integron-associated gene cassette encoding a 3-N-aminoglycoside acetyltransferase

A fifth gene cassette containing an aacC gene, aacCA5, was found in an aacCA5-aadA7 cassette array in a class 1 integron isolated from a multiply drug resistant Salmonella enterica serovar Kentucky strain. The AacC-A5 or AAC(3)-Ie acetyltransferase encoded by aacCA5 is related to other AAC(3)-I enzymes and confers resistance to gentamicin.

Investigation and control of an outbreak of salmonellosis caused by multidrug-resistant Salmonella typhimurium in a population of hospitalized horses

An outbreak of salmonellosis in a population of hospitalized horses resulted in the closure of a teaching hospital for a period of 10 weeks. Fecal samples were collected from suspected cases and cultured for Salmonella. Salmonella isolates were characterized using antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and phage typing. Thirty-three cases of infection by a multidrug-resistant strain of S. typhimurium were detected. The index case was admitted on 26 August 1999. Fifteen (45%) cases occurred between April and June 2000. PFGE results suggested that this strain of S. typhimurium might have been introduced into the hospital environment by a foal presenting with diarrhea. The hospital was closed on June 13, and intensive environmental cleaning and disinfection were completed. Enforcement of infectious disease control protocols in hospitals and environmental and patient surveillance is needed to prevent outbreaks of salmonellosis.

The effect of Virkon S fogging on survival of Salmonella enterica and Staphylococcus aureus on surfaces in a veterinary teaching hospital

The objective of the study was to determine the disinfection efficacy of aerosolizing (cold fogging) Virkon S on survival of Stahpylococcus aureus and Salmonella enterica on different surfaces. Two experiments were conducted in different locations. Salmonella enterica and S. aureus were grown in broth culture and then seeded into pre-marked areas in each location and allowed to dry. Virkon S (1%) was aerosolized into the rooms (approximately 1L of per 30 m(3)). Samples were collected pre- and post-fogging for quantitative cultures to evaluate the efficacy of aerial disinfection. The reduction of S. enterica or S. aureus counts ranged from 3.40 to 0.95 log(10) (Salmonella) or 4.92 to 0.02 log(10) (Staphylococcus). The greatest reduction was evident in samples collected from non-porous horizontal surfaces, which were not obstructed from the air flow. These results indicate that fogging with Virkon S could be beneficial in routine disinfection of pre-cleaned surfaces. The benefits of routine use of cold fogging with Virkon S in veterinary hospital settings would include its wide-range antimicrobial action and minimal working-men power required to disinfect large areas. Also, fogging would potentially minimize microbial contamination in the hard to reach areas.

Surveillance for nosocomial infections in veterinary hospitals

Surveillance for nosocomial infection and disease is a critical component in an integrated and highly effective infection control program. Surveillance activities provide a sensory role to guide ongoing control practices so that they are focused and efficient. Without input from surveillance results, infection control practices are likely to be guided more by emotion and opinion than by data and evidence. This article discusses issues to be considered when developing effective nosocomial infection surveillance programs as well as the historical perspective of surveillance efforts for nosocomial infection in human health care settings.

Multidrug-resistant Salmonella and nosocomial infections

Nosocomial infections are a serious threat to optimum patient care. In addition, nosocomial infections can have far-reaching consequences for the hospital personnel and the financial aspects of the hospital. Nosocomial infections with Salmonella spp have been described among hospitalized equine populations more frequently than any other agent. Salmonella spp associated with hospitalized equids often possess more antimicrobial resistance determinants than do Salmonella spp isolated from healthy horses in the general population. There is little evidence to suggest that resistant salmonellae are more virulent than nonresistant forms. MDR forms of Salmonella complicate the selection of appropriate antimicrobials when they are indicated, however. Furthermore, the use of some antimicrobials may apply selection pressure toward enhanced ability of MDR Salmonella to colonize equine patients. Further research should help to elucidate the risky uses of antimicrobials in the hospital setting and define the role of disinfectants and treatments such as NSAIDs in the ecology of MDR forms of nosocomial infections, including Salmonella. In the meantime, thoughtful selection of when and how to use antimicrobials in equine patients, together with deliberate selection of which antimicrobials to use based on monitoring data and other factors, such as safety and spectrum, is advised.

Phage-based typing scheme for Salmonella enterica serovar Heidelberg, a causative agent of food poisonings in Canada

Salmonella enterica serovar Heidelberg is perhaps the second most frequent Salmonella serovar isolated from humans and the most common isolated from animals in Canada. This pathogen has shown increasing resistance to antimicrobial agents and mimics the multidrug resistance observed in S. enterica serovar Typhimurium strain DT 104. However, unlike for serovar Typhimurium, a rapid and inexpensive subtyping method has not been available for large-scale surveillance efforts. We developed a phage typing scheme and subtyped 2,523 strains of serovar Heidelberg from outbreaks, sporadic infections, and environmental sources in Canada between January 1991 and December 2000. All strains were sensitive to one or more phages and could be subdivided into 49 phage types. A total of 196 isolates from 13 major outbreaks could be subtyped into six phage types, while 86 strains from family outbreaks were assigned to seven phage types. All strains were typeable, and epidemiologically related strains isolated from patients and implicated foods had identical phage types, antibiograms, and pulsed-field gel electrophoresis (PFGE) patterns. Combining PFGE with phage typing increased the discriminatory power of the analysis beyond that of either method alone. We concluded that this phage typing scheme, in conjunction with PFGE, enhances subtyping of serovar Heidelberg strains. Furthermore, this phage typing scheme is a rapid, economical, stable, and reliable epidemiologic tool for tracing the origin of food-borne disease and for the surveillance of sporadic infections.

Evaluation of pulsed-field gel electrophoresis as a tool for determining the degree of genetic relatedness between strains of Escherichia coli O157:H7

Pulsed-field gel electrophoresis (PFGE) has been used extensively to investigate the epidemiology of Escherichia coli O157:H7, although it has not been evaluated as a tool for establishing genetic relationships. This is a critical issue when molecular genetic data are used to make inferences about pathogen dissemination. To evaluate this further, genomic DNAs from 62 isolates of E. coli O157:H7 from different cattle herds were digested with XbaI and BlnI and subjected to PFGE. The correlation between the similarity coefficients for these two enzymes was only 0.53. Four additional restriction enzymes (NheI, PacI, SfiI, and SpeI) were used with DNAs from a subset of 14 isolates. The average correlations between similarity coefficients using sets of one, two, and three enzymes were 0.405, 0.568, and 0.648, respectively. Probing with lambda DNA demonstrated that some DNA fragments migrated equal distances in the gel but were composed of nonhomologous genetic material. Genome sequence data from EDL933 indicated that 40 PFGE fragments would be expected from complete XbaI digestion, yet only 19 distinguishable fragments were visible. Two reasons that similarity coefficients from single-enzyme PFGE are poor measures of relatedness (and hence are poorly correlated with other enzymes) are evident from this study: (i) matching bands do not always represent homologous genetic material and (ii) there are limitations to the power of PFGE to resolve bands of nearly identical size. The findings of the present study indicate that if genetic relationships must be inferred in the absence of epidemiologic data, six or more restriction enzymes would be needed to provide a reasonable estimate using PFGE.