Multidrug-resistant Shiga toxin-producing Escherichia coli in dogs with diarrhea
Escherichia coli Shiga toxigênica resistente a múltiplas drogas isoladas de cães com diarreia
C.J.S. PaulaI; J.M. MarinII, * * Autor para correspondência ( corresponding author) E.mail: firstname.lastname@example.org
IAluno de pós-graduação - FCAV-UNESP Jaboticabal, SP
IIDepartamento de Morfologia, Estomatologia e Fisiologia - FORP-USP Avenida do Café s/n 14040-904 Ribeirão Preto, SP
Keywords:Escherichia coli, diarrheic dogs, STEC, multidrug-resistance
Noventa e duas amostras de Escherichia coli, isoladas de 25 cães diarreicos, em Ituverava, SP, foram examinadas para a detecção dos genes codificadores de Shiga toxinas (stx 1 e stx 2). Por meio da reação em cadeia da polimerase, foram identificadas sete amostras positivas para o gene stx 1 e cinco para o gene stx 2, não foi detectada nenhuma amostra com os dois genes. As 12 amostras que apresentavam genes codificadores de Shiga toxinas (stx 1 e stx), foram testadas frente a 11 agentes antimicrobianos, sendo que sete delas (58,0%) apresentaram resistência a múltiplas drogas, o que representa um motivo de preocupação.
Palavras-chave: Escherichia coli, cão diarreico, STEC, resistência a múltiplas drogas
Increased prevalence of antimicrobials resistance of pathogenic bacteria is a growing world wide concern. Its major risk factor has been generally considered as a consequence of the wide use of antimicrobials leading to the emergence and dissemination of resistant bacteria and resistance genes (van den Bogaard and Stobberingh, 2000). Pet animals, especially dogs, represent potential sources for the spreading of antimicrobial resistance resulting from the extensive use of antimicrobial agents in these animals and their close contact with humans (Guardabassi et al., 2004). Reports of extra-intestinal infections in dogs due to multidrug-resistant Escherichia coli (MDREC) strains, resistant to third-generation cephalosporins and fluoroquinolones, have aroused special concern (Warren et al., 2001; Sanchez et al., 2002). Canine MDREC have been shown to harbor class 1 integron-associated resistance genes that had been identified in bacteria isolated from human clinical infections suggesting the spread of resistance mechanisms from canine to human bacteria, possibly via co-selection and transfer of multidrug resistance plasmids (Kang et al., 2005). Although the transfer of integrons between human and animal bacterial strains has not been fully explained, it is known that resistance to antimicrobial agent can spread from animals to humans via transferable plasmids (Winokur et al., 2001).
An emerging pathogen, Shiga toxin-producing E. coli (STEC) of the O157:H7 serotype, has been considered to be responsible for many outbreaks of hemorrhagic colitis and the hemolytic uremia syndrome in humans (Caprioli et al., 2005). However, other E. coli serogroups, known to be non-O157, are also important and prevalent in animals, suggesting that humans may also be exposed to them (Blanco et al., 2004). Two types of Shiga toxins, known as stx 1 and stx 2, constitute the main virulence factor in STEC strains (Law, 2000), commonly isolated from the feces of ruminants, like cattle and sheep (Kudva et al., 1997; Rigobelo et al., 2006), and occasionally from pigs (Macedo et al., 2007). Dogs have also been found to carry STEC strains, but their role as bacterial reservoirs has not been totally elucidated (Bentancor et al., 2007). The prevalence of STEC strains among intestinal bacterial strains has been shown to be of highly variable occurrence (Bentancor et al., 2007).
The use of antimicrobial drugs for diarrhea treatment remains questionable, in special when STEC strains are involved; nevertheless, intensive use of antimicrobial drugs in pets has been well documented (Guardabassi et al., 2004). Dogs that carry MDREC in their feces may readily contaminate the environment and are potential sources for the transmission of these bacteria to other animals and to humans (Warren et al., 2001). Thus, it was the aim of the present work, to study the occurrence of STEC strains in diarrheic dogs, and to examine their susceptibility to 11 antimicrobial agents, to verify their multidrug resistance patterns, and to assess their significance as sources of infection.
From January to December of 2006, 25 diarrheic dogs were examined after their arrival for consultation at a private clinic in the city of Ituverava, SP, Brazil. Samples collected by rectal swabbing, under the supervision of a veterinarian, were placed in a Stuart transport medium and taken to a laboratory for immediate processing. They were transferred to MacConkey agar1 1 Mac-Difco- Difco - USA. , and incubated for 24h at 37ºC. At least five randomly chosen colonies from each plate were selected for analysis. Biochemical confirmation of the strains as E. coli was performed according to Koneman et al. (1997). Bacteria overnight grown in nutrient broth2 2 Sigma Chemical Co - St Louis, USA. at 37ºC were tested for the presence of stx genes (stx 1 and stx 2), using the polymerase chain reaction (PCR) protocol of Orden et al. (1998). DNA templates were prepared from bacterial cells, resuspended in sterile distilled water, and boiled at 100ºC for 10min. Reference E. coli strains used as controls were EDL 933 (O157:H7, stx1, stx 2,and eae); DH5α was used as the negative control. STEC samples were typed for the serotype O157 using the O157 latex agglutination test kit3 3 Oxoid, Basingstoke - Hampshire, UK. . Negative strains on agglutination were considered non-O157 strains.
Antimicrobial disk susceptibility tests were performed using the disk diffusion method, recommended by the NCCLS (Performance , 2002). Drug-impregnated disks4 4 CEFAR - São Paulo, Brazil. were placed on the surface of the agar using a disk dispenser.
The following 11 antimicrobial agents were tested for bacterial resistance: ampicillin, amoxicillin, amoxicillin/clavulanic acid, amikacin, cephalothin, gentamicin, tetracycline, streptomycin, nalidixic acid, cotrimoxazole, and ciprofloxacin.
A total of 92 E. coli strains were isolated from the 25 diarrheic dogs, and all of them were investigated by PCR for the presence of Shiga toxin-producing genes (stx 1 and stx 2). Table 1 shows that 12 (13.0%) of the strains carried the stx gene; seven (7.6%) carried only the stx 1 gene, five (5.4%) the stx 2 gene, and none carried both genes. All STEC isolated strains were tested by the O157 latex agglutination test kit; no O157 was detected in the isolated strains. The occurrence of stx genes (40.0%) among E. coli samples from diarrheic animals in the present study agrees with the results on the same subject reported by Hammermuler et al. (1995), i.e 44.4%, as well as the presence of stx 1 or stx 2 genes among STEC strains, but not of both of them together. However, it is noteworthy that Nakazato et al. (2004), in Brazil, did not find STEC strains carrying stx 1 or stx 2 genes among 146 diarrheic and 36 healthy dogs examined.
The existence of multidrug-resistant phenotypes among bacteria housed by animals has been a cause of concern to veterinarians. Sanchez et al. (2002) reported the isolation of E. coli resistant to 12 antimicrobial drugs from two dogs; and Warren et al. (2001), the isolation of 18 multidrug-resistant E. coli strains from 10 dogs in Australia; all showed an extended spectrum of β lactamase activity. Normand et al. (2000) reported that 30% of the E. coli samples isolated from dogs that they examined in England were multidrug-resistant; however, all of them did not work with STEC strains.
In the present work, among the 12 STEC isolated samples examined, seven (58%) presented a MDREC phenotype resistant to four or more antimicrobial drugs, although it is not common for STEC strains to exhibit resistance to several antimicrobial drugs (Bettelheim et al., 2003). However, Cergole-Novella et al. (2006) also reported the isolation of STEC strains from humans and from bovine species in Brazil showing resistance to five or six antimicrobial drugs.
The carrying of MDREC organisms by dogs represents a potential hazard for people having contact with such animals, running the risk of spreading resistance genes. In the present study, results showing a high percentage of STEC strains isolated from diarrheic dogs, presenting a multidrug-resistance phenotype, give rise to considerable concern and suggest that monitoring of the extent of this problem is an advisable measure.
The authors thank FAPESP for financial support.
Recebido em 28 de maio de 2008
Aceito em 4 de fevereiro de 2009
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Autor para correspondência (corresponding author)E.mail:
Mac-Difco- Difco - USA.
Sigma Chemical Co - St Louis, USA.
Oxoid, Basingstoke - Hampshire, UK.
CEFAR - São Paulo, Brazil.
Publication in this collection
06 July 2009
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