Table of Contents Author Guidelines Submit a Manuscript
Veterinary Medicine International
Volume 2011, Article ID 686923, 7 pages
http://dx.doi.org/10.4061/2011/686923
Research Article

Frequency of Detection of Escherichia coli, Salmonella spp., and Campylobacter spp. in the Faeces of Wild Rats (Rattus spp.) in Trinidad and Tobago

School of Veterinary Medicine, Faculty of Medical Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago

Received 31 October 2010; Revised 29 January 2011; Accepted 4 February 2011

Academic Editor: Giuliano Bettini

Copyright © 2011 Comfort Nkogwe et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The study was conducted to determine the frequency of isolation of Salmonella, Campylobacter and E. coli O157 in the faecal samples of rats trapped across the regional corporations in Trinidad and to assess their resistance to antimicrobial agents. A total of 204 rats were trapped for the detection of selected bacteria. Standard methods were used to isolate Salmonella, Campylobacter and E. coli O157. Characterization of E. coli was done on sorbitol MacConkey agar to determine non-sorbitol fermentation, blood agar to determine haemolytic and mucoid colonies and by using E. coli O157 antiserum to determine O157 strain. The disc diffusion method was used to determine resistance to nine antimicrobial agents. Of the 204 rats, 4 (2.0%), 7 (3.4%) and 171 (83.8%) were positive for Salmonella spp., Campylobacter spp. and E. coli, respectively. Of the 171 isolates of E. coli tested 0 (0.0%), 25 (14.6%) and 19 (11.1%) were haemolytic, mucoid and non-sorbitol fermenters, respectively. All isolates were negative for the O157 strain. The frequency of resistance to the 9 antimicrobial agents tested was 75% (3 of 4) for Salmonella, 85.7% (6 of 7) of Campylobacter spp. and 36.3% (62 of 171) for E. coli ( 𝑃 < . 0 5 ; χ2).

1. Introduction

Zoonoses which could be caused by bacterial pathogens have represented a burden to human health throughout times [1, 2]. Rats (Rattus spp.) contaminate food and transmit diseases to other animals and humans [3]. Their activities therefore pose both economic and public health implications, particularly with the zoonotic agents they transmit [47].

Escherichia coli (E. coli) has been reportedly isolated from several wildlife species including free-roaming rodents in domestic and rural areas, bats, farmed and wildlife in zoological gardens [810]. A number of phenotypic and other characteristics of E. coli isolated from various wildlife have been described. Some of these characteristics include mucoid and haemolytic properties which have been suggested to be virulence markers [11, 12]. A majority of E. coli O157:H7 serotypes are also known to be nonsorbitol fermenters [13]. In recent years, E. coli O157:H7 has emerged as a major food-borne, zoonotic pathogen in humans, responsible for the haemorrhagic colitis and haemolytic uraemic syndrome [14].

Rodents have been reported to be reservoirs of different serotypes of Salmonella spp. and have been implicated in contaminating foods with the pathogen and transmitting the pathogen in livestock farms [15, 16]. Rodent-borne salmonellosis has also been reported in humans [17, 18]. Failure to control rodent populations in some geographical locations has continued to pose health problems to humans with particular reference to salmonellosis and other pathogens [19, 20].

Campylobacter spp. have been isolated from various animal species, but avian species, particularly poultry are important reservoirs of Campylobacter spp. [21, 22]. Meerburg et al. [23] reported on the isolation of Campylobacter spp. from house rats and wild brown rats in the Netherlands on organic farms. Wild rats therefore could act as reservoir or sources of Campylobacter spp. for livestock and humans.

Resistance of pathogens associated with wildlife including rodents has been documented, and it has been suggested that they may acquire or spread resistant strains to humans and livestock [24]. The chemotherapeutic implication for humans, livestock and pet animals can therefore not be ignored.

In Trinidad and Tobago and the Caribbean region, pathogens including E. coli, Salmonella, Campylobacter spp., leptospires, and hantavirus have been documented in rodents and other wildlife [2528].

Considering the potential public health risk posed by rodents to livestock, pet animals, and humans because of their presence in rural and urban populations and closeness to humans, the current study was, therefore, conducted to determine the prevalence of selected pathogens (E. coli including the O157 serotype, Salmonella spp., and Campylobacter spp.) in free-roaming rats in Trinidad and to determine the frequency of resistance to antimicrobial agents amongst the isolates of the pathogens.

2. Materials and Methods

2.1. Sample Size Determination

The sample size of rats to be sampled was determined using the prevalence of 10% for Salmonella spp. infection for urban rats (Rattus norvegicus) as described by Hilton et al. [29] and a precision rate of 4%. The following formula [30] was used: N o = 𝑡 2 ( 𝑝 ) ( 1 𝑝 ) / 𝑑 2 , where 𝑡 = 1 . 9 6 , 𝑑 = desired level of precision, 004, and 𝑝 = p r e v a l e n c e . An estimated sample size of 216 was determined.

2.2. Source of Wild Rats

The investigation was conducted between January 2006 and August 2006 when rats were randomly trapped at various locations across Trinidad as shown in Figure 1.

686923.fig.001
Figure 1: Location in Trinidad where rats were trapped for the study.
2.3. Trapping of Rats

The study was part of a larger study designed to determine the serovars of Leptospira serologically and by culture in rats [28]. The rodent control units of each of the Regional Heath Authority covering 7 counties in the country assisted in trapping rats using metal live catch traps with baits of cheese, fish, and other food items. The trappings took place in rat-infested areas such as surroundings of fast food restaurants and other eating establishments, food markets, and residential areas following complaints by members of the population. All rats caught during the day were transported to the laboratory, covered with ventilated bags to reduce the excitement of trapped rats, and transported to the laboratory within approximately 2 h after which the animals were trapped. Rats caught overnight were transported to the laboratory soonest possible in the morning. The age (adult or juveniles) and sex of each caught rat were noted as well as the geographical location of which it was trapped.

2.4. Collection of Samples from Rats

In the laboratory, the caged rats were covered with a black bag and rendered unconscious by the introduction of carbon dioxide from a pressurized tank into the sealed bag. Unconsciousness was determined by the evidence of lateral recumbency and the loss of pedal reflex. This was immediately followed by anaesthesia which was achieved by the use of a combination of a 10% ketamine solution (Dutch Farm Veterinary Pharmaceutical Company, Loosdrecht, Holland) and xylazine marketed as Bromazine 2% solution (Bomac Laboratories, Wiri Station Road, Manukau City, Auckland, New Zealand). For most rats, approximately the minimal dosage administered intramuscularly was 85 mg ketamine mixed with 15 mg xylazine per kg of rat [31], but more of the solution was administered, to affect rats until no response to pain and the loss of reflex were observed. The abdominal cavity was exposed using a surgical blade and a pair of forceps and the gastrointestinal tracts were removed and put in sterile Plastic Petri dishes as recommended by the Guidelines of the Canadian Council of Animal Care.

2.5. Bacteriological Culture of Faecal Samples

The gastrointestinal tract was cut open to remove all the content from the small intestine to the caeca of the rats. For the detection of E. coli, swabs of the intestinal contents were plated onto MacConkey agar (MAC), (Oxoid Ltd., Detroit, Michigan, USA) and eosin methylene blue (EMB) agar (Oxoid Ltd., Detroit, Michigan, USA) and incubated aerobically for 24 h at 37°C. Sterile loopful of characteristic colonies on EMB agar (metallic green sheen) and reddish/pinkish colonies on MAC agar was subjected to biochemical tests for identification of E. coli using standard methods [32]. All isolates identified as E. coli were inoculated and plated on blood agar and sorbitol MacConkey (SMAC) agar plates, which were again incubated aerobically at 37°C overnight. Phenotypic characteristics of E. coli, specifically mucoid appearance and haemolysis on blood agar plates and the ability to ferment sorbitol on SMAC agar as earlier described, [13] were observed. The O157 serotype was detected amongst 3 to 5 E. coli isolates per agar plate, with characteristic appearance on SMAC agar by the use of E. coli O157 antisera (Oxoid Ltd., Michigan, Ohio, USA) using the slide agglutination test.

To isolate Campylobacter spp., swabs of gastrointestinal contents were inoculated onto Campylobacter blood-free agar containing CCDA (charcoal cefoperazone deoxycholate agar) supplement (Oxoid Ltd., Basingstoke, Hampshire, England) and incubated for 48 h at 42°C in an atmosphere of 8% CO2 in an incubator (Formo Scientific Marietta, Ohio, USA) to detect thermophilic Campylobacter. Colonies (3 to 5) showing typical appearance of Campylobacter on blood-free agar plates, specifically grayish with running appearance and nontranslucent, were gram-stained. Isolates that were gram-negative with sea gull or comma-shaped appearance were presumptively classified as Campylobacter spp. The procedure of Lior [33] was used to identify Campylobacter spp. and to classify the isolates as either C. jejuni or C. coli.

To isolate Salmonella spp., approximately 1 g of intestinal contents of rats was added to 9 ml of selective enrichment broths: selenite cystein (SC) and tetrathionate (TT) broths, thoroughly agitated in a vortex mixer and incubated overnight at 42°C and 37°C, respectively. Enriched broths were then subcultured onto xylose lysine desoxycholate, XLD agar (Oxoid), and brilliant green agar (BGA) (Oxoid Limited, Detroit, Mich., USA) and incubated aerobically at 37°C and examined after 24 h. Suspect isolates (3 to 5) of Salmonella spp., which were pink colonies with black centers on XLD agar and pink colonies on BGA were subjected to biochemical tests using standard methods [32]. Biochemically identified Salmonella isolates were, thereafter, tested by slide agglutination using commercially available Salmonella polyvalent antiserum (Ai & Vi) (Difco Ltd., Detroit, Mich., USA). All isolates positive by the slide test were sent to the Caribbean Epidemiology Centre (CAREC), Port of Spain, Trinidad and Tobago, for confirmation and serotyping.

2.6. Determination of Resistance to Antimicrobial Agents

The resistance of isolates of E. coli, Salmonella spp. and Campylobacter spp. to the nine antimicrobial agents was determined using the disc diffusion method. The antimicrobial agents and the concentrations used were as follows: gentamicin (CN, 10 μg), ampicillin (AMP, 10 μg), cephalothin (KF, 30 μg), tetracycline (TE, 30 μg), streptomycin (S,10 μg), nalidixic acid (NA, 30 μg), kanamycin (K, 30 μg), chloramphenicol (C, 30 μg), and trimethoprim/sulpharmethoxazole (SXT, 23.25 μg, 1.75 μg). The breakpoints of the National Committee for Clinical Laboratory Standards [34] were used to determine susceptibility or resistance of isolates. For the study, all isolates that displayed resistance, based on their zone sizes, were classified as resistant isolates.

2.7. Statistical Analyses

The frequency of isolation of the three bacteria tested as well as the prevalence of resistance to the nine antimicrobial agents tested was compared and subjected to the chi-squared test (χ2). The level of significance was determined at an alpha level of 5%.

2.8. Ethics Committee Approval

Prior to the commencement of the study, the research proposal was approved by the Ethics Committee of the Faculty of Medial Sciences, University of the West Indies.

3. Results

3.1. Geographical Locations of Trapped Rats

Figure 1 displays the geographical locations across the country where rodents used in the study were trapped. Rats were trapped from a total of 44 geographical sites across 7 counties in the island. A majority of the rats sampled originated from the western part of the island, reflective of the fact that it was convenience sampling.

3.2. Frequency of Isolation of Selected Bacteria

Of a total of 204 trapped rats, intestinal contents were positive for E. coli (83.8%), Campylobacter spp. (3.4%), and Salmonella spp. (2.0%). The difference in the frequency of isolation was significant ( 𝑃 < . 0 5 ; χ2) as shown in Table 1. Amongst the 7 isolates of Campylobacter spp., 3 were C. jejuni while 4 were C. coli. Of the 4 isolates of Salmonella spp. recovered, only 3 were typable and their serovars were as follows: Schwarzzund 4, 12: d: 1, 7, Senftenberg 1, 3, 19: g, (s), t, and Rubislaw 11: r: e, n, x.

tab1
Table 1: Frequency of isolation of Escherichia coli, Campylobacter spp., and Salmonella spp. from the faecal sample of rats.
3.3. Characteristics of Bacterial Isolates

Table 2 shows the characteristics of E. coli isolates of which amongst the 171 isolates tested, 25 (14.6%) were mucoid and 19 (11.1%) were nonsorbitol fermenters (NSF) while all were negative for haemolytic or O157 strain of E. coli.

tab2
Table 2: Characteristics of isolates of Escherichia coli from rats.
3.4. Prevalence of Resistance of Bacteria to Antimicrobial Agents

Overall, of 182 isolates of E. coli, Campylobacter spp., and Salmonella spp. tested, 71 (39.0%) exhibited resistance to one or more of the antimicrobial agents tested (Table 3). The prevalence of resistance was 36.3% (62 of 171), 75.0% (3 of 4), and 85.7% (6 of 7) for E. coli, Salmonella spp. and Campylobacter spp., respectively. The difference was statistically significant ( 𝑃 < . 0 5 ; χ2). Amongst E. coli isolates, resistance to tetracycline (18.1%), ampicillin (15.8%), and chloramphenicol (8.2%) was higher compared with what was exhibited to cephalothin (0.0%), streptomycin (0.0%), and gentamicin (3.5%). Of the four Salmonella isolates, only one isolate was resistant to ampicillin, nalidixic acid, tetracycline, and chloramphenicol, and they were all susceptible to the five remaining antimicrobial agents tested. For the seven Campylobacter isolates, five exhibited resistance to cephalothin, sulphamethoxazole/Trimethoprim (SXT), streptomycin, and nalidixic acid while only one isolate was resistant to chloramphenicol and ampicillin.

tab3
Table 3: Frequency of resistance to antimicrobial agents amongst zoonotic bacteria tested.

4. Discussion

Rats are important as carriers and transmitters of a number of pathogens to humans and livestock as well as pet animals thereby posing public health hazards to humans [5, 16, 35, 36]. It was therefore of epidemiological relevance that the rats trapped in the current study which were from as many as 44 locations across the island of Trinidad were positive for E. coli, Salmonella spp., and Campylobacter spp. which have the potential to be bacterial pathogens. Equally important is the fact that a majority of the rats were trapped in areas close to human habitation and market areas making contamination of human foods and environment a possibility.

It was no surprise that E. coli strains were isolated from the gastrointestinal tracts of the rats studied as they constitute a major group of the family Enterobacteriaceae in animals [37]. The prevalence of 83.8% found in rats in the current study is slightly higher than the 61.8% reported for rodents at the local zoo in the country [9]. It is, however, known that a majority of E. coli strains are commensals, but pathogenic or enterotoxigenic strains are known to exist [14, 37]. In mammalian wildlife that are free-ranging, 58% were positive for E. coli [8], for wildlife kept on private farms and at the zoo, the prevalence of E. coli in faecal materials was 88.2% [8] and 88.1% [9], respectively.

Of importance are the characteristics of the E. coli strains although most are commensals in the gastrointestinal tracts of animals [38]. Mucoid colonies and production of haemolysins have been considered as virulence markers for E. coli strains [12]. In the current study, 14.2% of the isolates were mucoid, a frequency considerably higher than the 2% found in bats [10] and the 4.6% reported for mammalian wildlife at the local zoo [9]. None of the E. coli isolates produced haemolysin, a finding at variance with the report on isolates from other wildlife in the country where 10.2% were from bats [10], and 3.6% for mammalian wildlife at the local zoo were found to be haemolysin producers [9].

E. coli O157 serotype has become a very important food-borne pathogen globally because of the verocytotoxins they produce [14]. It has been demonstrated that most E. coli O157 serotypes are nonsorbitol fermenters [13] although some sorbitol-fermenting E. coli O157 strains have been reported [39]. In the current study, as many as 11.1% of the isolates were nonsorbitol fermenters, a finding higher than that found in E. coli isolates from free-ranging mammalian wildlife in the country where the frequency of nonsorbitol fermenting strains was 0.4% [8], wildlife on private farms 3.1% [8], and at a local zoo 3.0% [9]. All E. coli isolates (sorbitol and nonsorbitol fermenters) were, however, non-O157 serotype as earlier reported for E. coli strains recovered from wildlife sampled from various sources in the country [9]. This is a further evidence that wildlife in the country are not important reservoir for E. coli O157 or verocytotoxigenic E. coli (VTEC). It is, however, pertinent to mention that non-O157 Shiga toxin-producing E. coli has been documented in the literature [14]. Studies in other countries have, however, reported the isolation of E. coli O157 strain from rats and other wildlife, with the obvious potential that they could transmit this important pathogen to other animals and contaminate foods and the environment [4042].

The prevalence of resistance (36.3%) exhibited by E. coli isolates from rats is considerably higher than the 20% found in rats in Kenya [43] but much lower than the 61.8% reported in Trinidad and Tobago [9]. Similarly, the prevalence of resistance, which by comparison to other antimicrobial agents, was high to tetracycline (18.1%), ampicillin (15.8%), and chloramphenicol (8.2%) but lower than the rates reported for in Trinidad. For example, E. coli isolates from free-ranging wildlife in the country had a prevalence of resistance of 37.2% to ampicillin but 1.3% to chloramphenicol [44] while for confined wildlife, the corresponding prevalence was 21.7% and 11.3% [9]. The observed low prevalence of resistance to gentamicin (3.5%), cephalothin (0.0%), and streptomycin (0.0%) is however in agreement with published reports on mammalian wildlife in the country by others [9, 44].

The frequency of 2.0% for Salmonella spp. in the current study is considerably lower than that found in other countries: 6.0% in France [45], 10.0% in the UK [29], 16.2% in the USA [46], and 32% in Nigeria [47]. Gopee et al. [26] had earlier reported 0% prevalence for Salmonella spp. in rats sampled at a zoo in the country.

The serotypes of Salmonella spp. isolated from rodents have been reported to be epidemiologically significant based on the fact that molecular studies established their association with human salmonellosis [17, 18, 36]. Although only three of the four isolates were typable, it is relevant to mention that these serotypes have been recovered from human gastroenteritis [48, 49], confined birds [26], pet dogs [50], and from captured bats [10] in the country.

The four isolates of Salmonella spp. in the current study exhibited resistance to ampicillin, nalidixic acid, tetracycline, and chloramphenicol. Although the number of isolates recovered was low, it has been reported that rodents served as sources of multiresistant Salmonella spp. in cases and epidemics of human salmonellosis [17, 18]. Resistance to antimicrobial agents has been reported by others [51] to reflect the use of antimicrobial agents in human and animal populations.

The frequency of isolation of 3.4% for Campylobacter spp. found in the 204 rats sampled in the country is low compared to the 18% prevalence reported for rats trapped in France [46] and 57.4% for black rats in Portugal [52]. A survey of other mammalian wildlife (free-ranging on land, confined or farmed, and in free-flying bats) in the country reported similarly low prevalence that ranged from 0% to 7.4% [10, 44, 53]. It, therefore, appears that the carriage rate for campylobacters in rats and wildlife is generally low in the country.

The resistance of isolates of Campylobacter spp. from rats in the current study was rather high, that is, five of seven resistant to cephalothin, SXT, streptomycin, and nalidixic acid but also low with one of seven isolates resistant to chloramphenicol and ampicillin. In a study on Campylobacter spp. isolated from wildlife including rats in Portugal, a frequency of resistance of 5.5% to ampicillin and tetracycline was reported [52]. It is, however, pertinent to mention that factors such as selected antimicrobial concentrations, methods, and the breakpoints used, affect the antibiograms obtained and should be considered in comparing antimicrobial resistance of bacteria in different studies.

It was concluded that because the rats sampled originated from locations across the country and were shown to be carriers of enteric pathogens (Salmonella spp. Campylobacter spp.), albeit at a low frequency, might have posed potential health risk to livestock, pet animals, and humans in the geographical location from where they were trapped. The possibility of them being carriers of other uncultured pathogens also cannot be ignored. It is therefore imperative that regular rodent control measures should be practiced to reduce this risk.

Acknowledgments

The authors are grateful to the members of the rodent gangs in the Regional Health Authority and members of the School of Veterinary Medicine who assisted in the trapping of rats. The laboratory assistance of Elliot Neptune and Shenelle Sudan is appreciated.

References

  1. R. E. Khan, D. F. Clouser, and J. A. Richt, “Emerging infections: a tribute to the one medicine, one health concept,” Zoonoses and Public Health. In press.
  2. J. A. Richt and H. Feldmann, “Emerging zoonoses: recent advances and future challenges,” Zoonoses and Public Health, vol. 56, no. 6-7, p. 257, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  3. B. G. Meerburg, G. R. Singleton, and A. Kijlstra, “Rodent-borne diseases and their risks for public health Rodent-borne diseases and their risks for public health,” Critical Reviews in Microbiology, vol. 35, no. 3, pp. 221–270, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  4. J. D. Easterbrook, J. B. Kaplan, N. B. Vanasco et al., “A survey of zoonotic pathogens carried by Norway rats in Baltimore, Maryland, USA,” Epidemiology and Infection, vol. 135, no. 7, pp. 1192–1199, 2007. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  5. C. M. Gaudie, C. A. Featherstone, W. S. Phillips et al., “Human Leptospira interrogans serogroup icterohaemorrhagiae infection (Weil's disease) acquired from pet rats,” Veterinary Record, vol. 163, no. 20, pp. 599–601, 2008. View at Google Scholar · View at Scopus
  6. J. M. Lieberman, “North American zoonoses,” Pediatric Annals, vol. 38, no. 4, pp. 193–198, 2009. View at Publisher · View at Google Scholar · View at Scopus
  7. K. Inoue, S. Maruyama, H. Kabeya et al., “Prevalence and genetic diversity of Bartonella species isolated from wild rodents in Japan,” Applied and Environmental Microbiology, vol. 74, no. 16, pp. 5086–5092, 2008. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  8. A. A. Adesiyun, “Absence of Escherichia coli O157 in a survey of wildlife from Trinidad and Tobago,” Journal of Wildlife Diseases, vol. 35, no. 1, pp. 115–120, 1999. View at Google Scholar · View at Scopus
  9. N. V. Gopee, A. A. Adesiyun, and K. Caesar, “A longitudinal study of Escherichia coli strains isolated from captive mammals, birds, and reptiles in Trinidad,” Journal of Zoo and Wildlife Medicine, vol. 31, no. 3, pp. 353–360, 2000. View at Google Scholar · View at Scopus
  10. A. A. Adesiyun, A. Stewart-Johnson, and N. N. Thompson, “Isolation of enteric pathogens from bats in Trinidad,” Journal of Wildlife Diseases, vol. 45, no. 4, pp. 952–961, 2009. View at Google Scholar · View at Scopus
  11. J. Prada, G. Baljer, J. Derycle et al., “Characteristics of alpha-haemoytic strains of Escherichia coli isolates from dogs with gastroenteritis,” Veterinary Microbiology, vol. 29, pp. 59–73, 1991. View at Google Scholar
  12. L. R. M. Marques, C. M. Abe, P. M. Griffin, and T. A. T. Gomes, “Association between alpha-hemolysin production and HeLa cell-detaching activity in fecal isolates of Escherichia coli,” Journal of Clinical Microbiology, vol. 33, no. 10, pp. 2707–2709, 1995. View at Google Scholar · View at Scopus
  13. S. B. March and S. Ratnam, “Sorbitol-MacConkey medium for detection of Escherichia coli O157:H7 associated with hemorrhagic colitis,” Journal of Clinical Microbiology, vol. 23, no. 5, pp. 869–872, 1986. View at Google Scholar · View at Scopus
  14. M. A. Karmali, V. Gannon, and J. M. Sargeant, “Verocytotoxin-producing Escherichia coli (VTEC),” Veterinary Microbiology, vol. 140, no. 3-4, pp. 360–370, 2010. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  15. R. Lapuz, H. Tani, K. Sasai, K. Shirota, H. Katoh, and E. Baba, “An epidemiological analysis of Salmonella enteritidis contamination in a rat-infested chicken layer farm, an egg processing facility, and liquid egg samples by pulsed-field gel electrophoresis,” Journal of Veterinary Medical Science, vol. 69, no. 6, pp. 649–652, 2007. View at Publisher · View at Google Scholar · View at Scopus
  16. R. Lapuz, H. Tani, K. Sasai, K. Shirota, H. Katoh, and E. Baba, “The role of roof rats (Rattus rattus) in the spread of Salmonella enteritidis and S. Infantis contamination in layer farms in eastern Japan,” Epidemiology and Infection, vol. 136, no. 9, pp. 1235–1243, 2008. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  17. Centers for Disease Control Prevention (CDC), “Outbreak of multi-resistant Salmonella typhimurium associated with rodents purchased at retail pet stores-United States, December 2003-October 2004,” Morbidity and Mortality Weekly Reports, vol. 54, pp. 429–433, 2005. View at Google Scholar
  18. S. J. Swanson, C. Snider, C. R. Braden et al., “Multidrug-resistant Salmonella enterica serotype Typhimurium associated with pet rodents,” The New England Journal of Medicine, vol. 356, no. 1, pp. 21–28, 2007. View at Google Scholar · View at Scopus
  19. R. K. Hoop, “The Swiss control programme for Salmonella enteritidis in laying hens: experiences and problems,” Revue Scientifique et Technique of International Office of Epizootics, vol. 16, pp. 885–890, 1997. View at Google Scholar
  20. J. D. Easterbrook, J. B. Kaplan, G. E. Glass, J. Watson, and S. L. Klein, “A survey of rodent-borne pathogens carried by wild-caught Norway rats: a potential threat to laboratory rodent colonies,” Laboratory Animals, vol. 42, no. 1, pp. 92–98, 2008. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  21. D. J. Wilson, E. Gabriel, A. J. H. Leatherbarrow et al., “Tracing the source of campylobacteriosis,” PLoS Genetics, vol. 4, no. 9, Article ID e1000203, 2008. View at Publisher · View at Google Scholar · View at PubMed
  22. B. Wysok and J. Uradziński, “Campylobacter spp.—a significant microbiological hazard in food. I. Characteristics of Campylobacter species, infection source, epidemiology,” Polish Journal of Veterinary Sciences, vol. 12, no. 1, pp. 141–148, 2009. View at Google Scholar · View at Scopus
  23. B. G. Meerburg, W. F. Jacobs-Reitsma, J. A. Wagenaar, and A. Kijlstra, “Presence of Salmonella and Campylobacter spp. in wild small mammals on organic farms,” Applied and Environmental Microbiology, vol. 72, no. 1, pp. 960–962, 2006. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  24. T. Kassa, S. Gebre-Selassie, and D. Asrat, “Antimicrobial susceptibility patterns of thermotolerant Campylobacter strains isolated from food animals in Ethiopia,” Veterinary Microbiology, vol. 119, no. 1, pp. 82–87, 2007. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  25. A. A. Adesiyun, N. Seepersadsingh, L. Inder, and K. Caesar, “Some bacterial enteropathogens in wildlife and racing pigeons from Trinidad,” Journal of Wildlife Diseases, vol. 34, no. 1, pp. 73–80, 1998. View at Google Scholar · View at Scopus
  26. N. V. Gopee, A. A. Adesiyun, and K. Caesar, “Retrospective and longitudinal study of salmonellosis in captive wildlife in Trinidad,” Journal of Wildlife Diseases, vol. 36, no. 2, pp. 284–293, 2000. View at Google Scholar · View at Scopus
  27. L. M. Keenan, A. Chikweto, R. N. Sharma et al., “Seroprevalence of Hantavirus in Rattus norvegicus in Grenada, West Indies,” West Indian Veterinary Journal, vol. 8, pp. 67–71, 2008. View at Google Scholar
  28. S. M. Suepaul, C. V. F. Carrington, M. Campbell, G. Borde, and A. A. Adesiyun, “Serovars of Leptospira isolated from dogs and rodents,” Epidemiology and Infection, vol. 138, no. 7, pp. 1059–1070, 2010. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  29. A. C. Hilton, R. J. Willis, and S. J. Hickie, “Isolation of Salmonella from urban wild brown rats (Rattus norvegicus) in the West Midlands, UK,” International Journal of Environmental Health Research, vol. 12, no. 2, pp. 163–168, 2002. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  30. I. D. Glenn, “Determination of sample size,” Fact Sheet PEOD-6, a series of the Program Evaluation and Organization Development, Florida Cooperative Extension Service, Institute, 2002.
  31. S. K. Wixson, W. J. White, H. C. Hughes Jr., C. M. Lang, and W. K. Marshall, “The effects of pentobarbital, fentanyl-droperidol, ketamine-xylazine and ketamine-diazepam on arterial blood pH, blood gases, mean arterial blood pressure and heart rate in adult male rats,” Laboratory Animal Science, vol. 37, no. 6, pp. 736–742, 1987. View at Google Scholar · View at Scopus
  32. J. F. Mcfadden, Biochemical Tests for Identification of Medical Bacteria, Lippicott Williams and Wilkins, Philadelphia, Pa, USA, 3rd edition, 2000.
  33. H. Lior, “New, extended biotyping scheme for Campylobacter jejuni, Campylobacter coli, and ‘Campylobacter laridis’,” Journal of Clinical Microbiology, vol. 20, no. 4, pp. 636–640, 1984. View at Google Scholar · View at Scopus
  34. National Committee for Clinical Laboratory Standards (NCCLS), “Performance standards for antimicrobial discs and dilution susceptibility for bacteria isolated from animals,” Approved Standards-Second Edition, vol. 22, pp. 1–52, 2002. View at Google Scholar
  35. R. G. Bengis, F. A. Leighton, J. R. Fisher et al., “The role of wildlife in emerging and re-emerging zoonoses,” Revue Scientifique et Technique of International Office of Epizootics, vol. 23, pp. 497–511, 2004. View at Google Scholar
  36. C. C. Fuller, S. L. Jawahir, F. T. Leano et al., “A multi-state Salmonella Typhimurium outbreak associated with frozen vacuum-packed rodents used to feed snakes,” Zoonoses and Public Health, vol. 55, no. 8-10, pp. 481–487, 2008. View at Publisher · View at Google Scholar · View at Scopus
  37. C. L. Gyles, “Escherichia coli,” in Pathogenesis of Bacterial Infections in Animals, pp. 164–189, Iowa University Press, Ames, Iowa, USA, 1993. View at Google Scholar
  38. K. Baldy-Chudzik and M. Stosik, “Prevalence of antibiotic resistance profile in relation to phylogenetic background among commensal Escherichia coli derived from various mammals,” Polish Journal of Microbiology, vol. 56, no. 3, pp. 175–183, 2007. View at Google Scholar · View at Scopus
  39. D. Orth, K. Grif, L. B. Zimmerhackl, and R. Würzner, “Sorbitol-fermenting Shiga toxin-producing Escherichia coli O157 in Austria,” Wiener Klinische Wochenschrift, vol. 121, no. 3-4, pp. 108–112, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  40. H. Asakura, S. I. Makino, T. Shirahata et al., “Detection and genetical characterization of shiga toxin-producing Escherichia coli from wild deer,” Microbiology and Immunology, vol. 42, no. 12, pp. 815–822, 1998. View at Google Scholar · View at Scopus
  41. D. H. Rice, D. D. Hancock, and T. E. Besser, “Faecal culture of wild animals for Escherichia coli O157:H7,” Veterinary Record, vol. 152, no. 3, pp. 82–83, 2003. View at Google Scholar · View at Scopus
  42. E. M. Nielsen, M. N. Skov, J. J. Madsen, J. Lodal, J. B. Jespersen, and D. L. Baggesen, “Verocytotoxin-producing Escherichia coli in wild birds and rodents in close proximity to farms,” Applied and Environmental Microbiology, vol. 70, no. 11, pp. 6944–6947, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  43. P. M. Gakuya, M. N. Kyule, P. B. Gathura, and S. Kariuki, “Antimicrobial susceptibility and plasmids from Escherichia coli isolated from rats,” East African Medical Journal, vol. 78, no. 10, pp. 518–522, 2001. View at Google Scholar · View at Scopus
  44. A. A. Adesiyun and M. Downes, “Characteristics of Escherichia coli strains isolated from free-ranging and confined wildlife in Trinidad,” Veterinarski Archiv, vol. 69, pp. 335–347, 1999. View at Google Scholar
  45. B. Seguin, Y. Boucaud-Maître, P. Quenin, and G. Lorgue, “Epidemiologic evaluation of a sample of 91 rats (Rattus norvegicus) captured in the sewers of Lyon,” Zentralblatt für Bakteriologie, Mikrobiologie, und Hygiene. Series A, vol. 261, no. 4, pp. 539–546, 1986. View at Google Scholar · View at Scopus
  46. D. J. Henzler and H. M. Opitz, “The role of mice in the epizootiology of Salmonella enteritidis infection on chicken layer farms,” Avian Diseases, vol. 36, no. 3, pp. 625–631, 1992. View at Google Scholar · View at Scopus
  47. S. I. Oboegbulem and I. Okoronkwo, “Salmonellae in the African great cane rat (Thryonomys swinderianus),” Journal of Wildlife Diseases, vol. 26, no. 1, pp. 119–121, 1990. View at Google Scholar · View at Scopus
  48. Caribbean Epidemiology Center (CAREC), “Surveillance Report,” CAREC, Port of Spain, Trinidad, 2007.
  49. Caribbean Epidemiology Center (CAREC), “Surveillance Report,” CAREC, Port of Spain, Trinidad, 2008.
  50. A. A. Adesiyun, M. Campbell, and J. S. Kaminjolo, “Prevalence of bacterial enteropathogens in pet dogs in Trinidad,” Journal of Veterinary Medicine, Series B, vol. 44, no. 1, pp. 19–27, 1997. View at Google Scholar · View at Scopus
  51. M. Sherley, D. M. Gordon, and P. J. Collignon, “Variations in antibiotic resistance profile in Enterobacteriaceae isolated from wild Australian mammals,” Environmental Microbiology, vol. 2, no. 6, pp. 620–631, 2000. View at Publisher · View at Google Scholar · View at Scopus
  52. J. Cabrita, J. Rodrigues, F. Braganca, C. Morgado, I. Pires, and A. P. Goncalves, “Prevalence, biotypes, plasmid profile and antimicrobial resistance of Campylobacter isolated from wild and domestic animals from northeast Portugal,” Journal of Applied Bacteriology, vol. 73, no. 4, pp. 279–285, 1992. View at Google Scholar · View at Scopus
  53. A. A. Adesiyun, K. Caesar, and L. Inder, “Prevalence of Salmonella and Campylobacter species in animals at Emperor Valley Zoo, Trinidad,” Journal of Zoo and Wildlife Medicine, vol. 29, no. 2, pp. 237–239, 1998. View at Google Scholar · View at Scopus