In vitro antimicrobial susceptibility of staphylococci isolated from canine pyoderma in Rio de Janeiro, Brazil

Susceptibilidade in vitro a antimicrobianos de staphylococci isolados de cães com piodermatite no estado do Rio de Janeiro, Brasil

VETERINARY MICROBIOLOGY

In vitro antimicrobial susceptibility of staphylococci isolated from canine pyoderma in Rio de Janeiro, Brazil

Susceptibilidade in vitro a antimicrobianos de staphylococci isolados de cães com piodermatite no estado do Rio de Janeiro, Brasil

Penna, B.; Varges, R.; Medeiros, L.; Martins, G.M.; Martins, R.R.; Lilenbaum, W^*

Laboratório de Bacteriologia Veterinária, Instituto Biomédico, Universidade Federal Fluminense, Niterói, RJ, Brasil

ABSTRACT

The study aimed to determine the etiology and antimicrobial resistance of staphylococci isolated from canine pyoderma. Samples were obtained from dogs with pyoderma and isolates were identified by biochemical reactions and tested for susceptibility to 15 antimicrobials. Thirty nine staphylococci isolates were obtained, and S. pseudintermedius was the most frequent (47.4%). All isolates showed resistance to at least one drug and 77.1% were multiresistant. The most effective drug was oxacillin. The study reports the alarming antimicrobial resistance of Staphylococcus isolated from canine pyoderma samples.

Key words: Staphylococci, resistance, antimicrobial agents, dog, pyoderma

RESUMO

O estudo se propõe a avaliar a etiologia e a susceptibilidade de estafilococos isolados de cães com dermatite. Os isolados foram identificados por provas bioquímicas e testados quanto a sua susceptibilidade a 15 antimicrobianos. Trinta e nove isolados de Staphylococci foram obtidos, e S. pseudintermedius foi mais freqüente (47,4%). Todos isolados apresentaram resistência a pelo menos uma droga e 77,1% foram multirresistentes. A oxacilina foi a droga mais eficaz. O estudo demonstra níveis alarmantes de resistência antimicrobiana nos Staphylococcus de pioderma canino.

Palavras-chave: Staphylococci, resistência, agentes antimicrobianos, cães, pioderma

Pyoderma is a common disease in dogs and its treatment usually involves antimicrobial therapy (3). Many studies have demonstrated that members of the Staphylococcus genus are commonly isolated from skin of healthy and diseased dogs (6), and that the coagulasepositive species Staphylococcus pseudintermedius (previously referred as S. intermedius), a common inhabitant of the skin of dogs, is the principal bacterial species responsible for canine pyodermas (3). The S. intermedius species entity was useful because it separated these staphylococci from S. aureus, avoiding in this way, an epidemiologically important source of confusion. Since this new species has been reported, strains from dogs identified by traditional means are to be reported as S. pseudintermedius, unless shown by genomic investigation to belong to other related species (2). Nevertheless, other staphylococcal species inhabiting skin may be involved, as S. aureus, S. epidermidis, S. haemolyticus, S. simulans, S. saprophyticus and S. schleiferi (6,8).

Knowledge about the resistance patterns of bacteria to antimicrobial drugs requires constant actualization. Although the impact of veterinary usage of the drugs is unknown, empiric treatments carried out by practitioners without assistance of bacteriological culture and antimicrobial susceptibility test (ATS) has contributed for the selection of multiresistant strains (6). The purpose of the present study was to determine the species distribution and antimicrobial resistance of Staphylococcus sp. isolates obtained from dogs with pyoderma in Rio de Janeiro, Brazil.

Specimens were obtained from samples of 39 adult dogs of both sexes submitted to the Bacteriology Laboratory of Universidade Federal Fluminense from veterinary clinics in Rio de Janeiro for identi?cation and susceptibility testing between march of 2007 and march 2008. Although detailed historic of clinical cases were not provided, specimens were collected before treatment of the dogs. Animals presented lesions that indicated bacterial skin infections such as pustules, local pain, pruritus, erythema and desquamation of the epithelium. Samples were obtained using sterile swabs, which were immediately inoculated in Brain Heart Infusion broth (Merck, Rio de Janeiro, RJ - Brazil) and incubated at 37ºC. If growth occurred after 24 or 48h, smears were made, Gramstained and examined microscopically. Samples with morphologies compatible with Staphylococcus sp. were transferred to tryptic soy agar (Merck, Rio de Janeiro, RJ - Brazil), 5% sheep blood agar (Newprov, Curitiba, PR - Brazil) and mannitol salt agar (Merck, Rio de Janeiro, RJ - Brazil). One sample of each dog was studied.

After growth, staphylococcal isolates were identi?ed according to Bergey's Manual of Determinative Bacteriology (5) and tested for susceptibility to antibiotics by disc agar diffusion (1) for gentamicin, neomycin, amikacin, ciprofloxacin, enrofloxacin, amoxicillin-clavulanic acid combination - AMC, amoxicillin, oxacillin, cephalexin, cephadroxil, nitrofurantoin, erythromycin, mupirocin, bacitracin and chloramphenicol. After measuring the antimicrobial zone diameters and following the manufacturer's instructions (Oxoid, Hampshire, UK), the isolates were categorised as sensitive or resistant to the drug.

Thirty nine staphylococci isolates obtained from canine pyoderma were recovered. Among those 39 isolates of Staphylococcus genus, the coagulasepositive staphylococci (CoPS) were the most frequently isolated and were obtained from 25/39 (64.1%) samples, what agrees with other studies (3,4,9). Among the CoPS, S. pseudintermedius (19/39 - 48.7%) was the most common species, followed by S. aureus (5/39 - 12.8%) and S. schleiferi coagulans (1/39 - 2.6%). The predominance of S. pseudintermedius over S. aureus and S.schleiferi coagulans was not unexpected, since this species, previously referred as S. intermedius, is known as the major staphylococcal species involved in canine infections (3).

Coagulase negative staphylococci (CoNS) were isolated from 14 samples (35.9%), distributed among S. schleiferi schleiferi (7/39 - 17.9%), S. epidermidis (3/39 - 7.7%), S. simulans (3/39 - 7.7%), and S. haemolyticus (1/39 - 2.6%) (Table 1).CoNS constitutes a major component of the skin microflora of human beings, dogs and cats and can determine opportunistic infections (7,8). The species distribution of staphylococci isolates from pyoderma is depicted in table 1.

Regarding to the susceptibility pattern (table 1), all the isolates were resistant to at least one drug, and 94.9% of the isolates were multiresistant - here defined as resistance to three or more antimicrobial classes - what is a much higher proportion than that reported on older studies (3,9). One isolate of S. pseudintermedius was resistant to all the tested antimicrobial agents.

Some years ago it has been stated that this genus was presenting a rapid development and spread of antimicrobial resistance (3). Similar findings were observed in the present study, when compared to a previous study conducted by our group in a similar dog population in Rio de Janeiro, Brazil (6).

Resistance to the penicillin class was verified on 71.8% (28/39) of the isolates; although amoxicillin was the less effective penicillin (resistance of 71.8%), when combined to clavulanic acid the resistance dropped to 20.5%. This was not surprising, since it has been recently demonstrated that up to 62% the isolates of the S.pseudintermedius (S.intermedius) strains of canine origin could be β-lactamase producers (3). When compared to a previous study conducted by our group (6), when resistance to that drug class in a similar population was 38.6% (17/44), a substantially grown in this resistance could be observed. Despite oxacillin was the most effective drug of the study, 17.9% (7/39) of the isolates were resistant to this drug, what is an alarming finding, since in 2000 our group reported such resistance on 4.6% of the isolates (2/44) (6).

Resistance to aminoglycosides was observed in 38 (97.4%) isolates; neomycin and gentamicin were the less effective drugs of this class, with 97.4% and 76.9% of the isolates being resistant, respectively; also amikacin did not present good efficiency rates, since 61.5% of the isolates were resistant to this drug. Gentamicin was reported as a very efficient drug for the treatment of canine otitis externa in 2000 (6), when resistance was 15.9% (7/44), what clearly contrasts to the 76.9% (30/39) frequency of resistant isolates observed in the present study. This fact is probably a consequence of the overusage of this drug in several topic phormulae indicated for the treatment of canine pyoderma, that became more common in the last decade. Similar findings were observed to other classes of drugs (Table 1) that, when compared to previous studies (3,7,8,9), constantly indicate an increasing resistance rate among the isolates.

In conclusion, antimicrobial resistance of staphylococci from canine pyoderma is a serious and increasing problem worldwide. The present study emphasizes the need for bacterial culture with species identification and antimicrobial susceptibility tests in order to choose the appropriate antimicrobial agent for each case.

ACKNOWLEDGEMENTS

This study was founded by CNPq, CAPES, FLAP and FAPERJ. WL is a research fellow of CNPq.

Submitted: January 09, 2009;

Returned to authors for corrections: February 11, 2009;

Approved: May 04, 2009.

• ¹
  Clinical and Laboratory Standards Institute/NCCLS. (2008). Performance Standards for Antimicrobial Disk and Dilution Susceptibility Tests for Bacteria Isolated From Animals; Approved Standard. 3rd ed. Document M31-A3, vol 28 No. 8. NCCLS, Villanova, PA.
• 2. Devriese, L.A.; Hermans. K.; Baele, M.; Haesebrouck, F. (2009). Staphylococcus pseudintermedius versus Staphylococcus intermedius. Vet. Microbiol. 133, 206-207
• 3. Ganiere, J.P.; Medaille, C.; Mangion, C. (2005). Antimicrobial drug susceptibility of Staphylococcus intermedius clinical isolates from canine pyoderma. J. Vet. Med. B. 52, 25-31.
• 4. Hoekstra, K.A.; Paulton, R.J.L. (2002). Clinical prevalence and antimicrobial susceptibility of Staphylococcus aureus and Staph. intermedius in dogs. J. Appl. Microbiol. 93, 406-413.
• 5. Holt, J.G.; Krieg, N.R.; Sneath, P.H.A.; Stalley, J.T.; Willians, S.T. (1994). Staphylococcus spp. In: Bergey's Manual of Determinative Bacteriology 9th edn. Williams and Wilkins Baltimore, MD., 544-51.
• 6. Lilenbaum, W.; Veras, M.; Blum, E.; Souza, G.N. (2000). Antimicrobial susceptibility of staphylococci isolated from otitis externa in dogs. Lett. Appl. Microbiol 31, 42-45.
• 9. Prescott, J.F.; Hanna, W.J.B.; Smith, R.R.; Drost, K. (2002). Antimicrobial drug use and resistance in dogs. Can. Vet. J 43,107-116.

Publication Dates

• Publication in this collection
  19 Aug 2009
• Date of issue
  Sept 2009

History

• Accepted
  04 May 2009
• Reviewed
  11 Feb 2009
• Received
  09 Jan 2009