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Antibiotic resistance in staphylococci associated with cats and dogs

2005; Oxford University Press; Volume: 99; Issue: 6 Linguagem: Inglês

10.1111/j.1365-2672.2005.02699.x

1365-2672

Shaukat Iqbal Malik, Haihong Peng, Mary Barton,

Antimicrobial Peptides and Activities

Dogs and cats have become an integral part of modern society in the developed world and as such attention is given to their care and welfare. At some stage of their lives many cats and dogs suffer from skin and other superficial staphylococcal infections such as pyoderma and otitis externa and are therefore treated with antibiotics. This practice has led to the emergence of resistant staphylococci in these animals. Antimicrobial susceptibility studies in companion animals have revealed that staphylococci isolated from cats and dogs exhibit similar resistance patterns to human staphylococci and that resistance development is influenced by the frequency of use of certain antibiotics. This review examines the antibiotic resistance patterns of the most frequently isolated staphylococci from cats and dogs and the mechanisms underlying resistance. The possible transfer of methicillin-resistant staphylococci from cats and dogs to humans has been identified as a potential public health issue. Typing tools used for epidemiological differentiation of pathogenic and nonpathogenic staphylococci and for species identification studies may help to elucidate the importance or otherwise of this problem. Staphylococci are Gram-positive cocci, which are nonmotile, nonspore forming and facultative anaerobes that are commonly found on the skin of mammals. Thirty-seven species have been identified (Euzeby 1997) and all species are part of the normal microflora of the skin and mucosal surfaces of the upper respiratory tract of man and animals. In dogs Staphylococcus intermedius causes infections such as pyoderma and otitis externa, however, Staphylococcus aureus and Staphylococcus schleiferi are emerging as common pathogenic species in small animals (Igimi et al. 1990; Bes et al. 2002a; Frank et al. 2003; Yamashita et al. 2005). Staphylococci do not generally appear to cause any major specific diseases in cats (Igimi et al. 1994) but cases of superficial dermatitis, bacterial folliculitis and superficial pyoderma caused by Staph. intermedius have been reported (Austin 1978; Scott 1980). Intimate association between potential hosts can enhance staphylococcal dispersal as they are easily spread by skin-to-skin contact, aerosols from sneezing and coughing and also through saliva. Upon gaining entry into deeper tissues of the body, staphylococci especially Staph. aureus can cause a wide variety of diseases in man (exfoliative skin diseases, toxic shock syndrome and food poisoning) and animals (mastitis, pyoderma and otitis externa). A wide range of antibiotics has been used to treat infections in dogs and cats caused by staphylococci and have led to the emergence of resistant strains. Antibiotics frequently used in cat and dog therapy are: penicillins, cephalosporins, macrolides, lincosamides, fusidic acid, tetracyclines, chloramphenicol, potentiated sulphonamides, aminoglycosides and fluoroquinolones (Watson and Rosin 2000). Kunkle (1987) and Reedy et al. (1997) concluded that dogs, which had not received prior antibiotic therapy were much more likely to have staphylococci isolates that were susceptible to a wide spectrum of drugs compared with those that had received prior antimicrobial drugs. Cats and dogs could also acquire resistance determinants from their surroundings via food and contaminated bedding and faeces (Patel et al. 1999). Resistance to antibiotics seen in staphylococci of animal origin shows both similarities and differences to that in human strains. On one hand, use of specific antibiotic compounds in both humans and animals is followed by an increase of the prevalence of resistant strains to that antibiotic. On the other hand, the most common resistance seen in cat and dog isolates is to the penicillins, tetracyclines and erythromycin (Noble 1996; Prescott et al. 2002) whereas there is often much more extensive resistance seen in many human isolates (Jones et al. 2004). The pattern of antibiotic resistance observed in cats and dogs correlate with the amount and frequency of use of certain antibiotics. Studies conducted in late 1950s when antibiotics had just been introduced into clinical use in cats shows that most of the Staph. aureus isolated from the nostrils were susceptible to penicillin (Mann 1959). Various studies in recent years have shown that staphylococci isolated from cats have become resistant to at least one class of antibiotics (Love et al. 1981). Medleau and Blue (1988) observed that Staph. aureus, Staph. intermedius and Staphylococcus epidermidis isolated from cats were frequently resistant to penicillin G, ampicillin and tetracyclines. Studies conducted in Brazil found that isolates from healthy cats were frequently resistant to penicillin G, oxacillin, tetracyclines and enrofloxacin and that coagulase-positive staphylococci from cats were much more resistant when compared to coagulase-negative species (Lilenbaum et al. 1998,1999). This is probably due to the fact that, the major pathogenic staphylococci Staph. aureus and Staph. intermedius are not indigenous to cats and rarely cause disease in them (Igimi et al. 1994). An increase in resistance in coagulase-negative staphylococci to cotrimoxazole, lincomycin, enrofloxacin or oxytetracycline has been reported in England (Patel et al. 1999). It is apparent therefore that it is not only coagulase-positive species from cats that have developed resistance mechanisms to various antibiotics but coagulase-negative species which constitute the normal bacteria flora in cats can also acquire resistance to at least one antibiotic. In contrast, other studies have found that staphylococci from both healthy and diseased cats are susceptible to gentamicin, clavulanic acid-amoxycillin, chloramphenicol, cephalexin and bacitracin (Medleau and Blue 1988; Lilenbaum et al. 1998,1999; Patel et al. 1999). Studies of antimicrobial sensitivity of dog isolates of staphylococci were first reported in the 1960s (Shimizu and Shibata 1967). Rohrich et al. (1983) reported Staph. aureus and Staph. intermedius isolated from urinary tract infections in dogs in the US were highly susceptible to ampicillin, chloramphenicol, trimethoprim–sulfamethoxazole, nitrofurantoin, cephalexin, kanamycin and gentamicin. Moderate resistance was observed for nalidixic acid and oxytetracycline. Further studies by Cox et al. (1984) and Medleau et al. (1986) in the US on dogs with clinical infections including urinary tract infection and dogs suffering from pyoderma respectively have shown that Staph. intermedius was more resistant to ampicillin, penicillin and tetracycline. Several other studies in recent years on different infections in dogs have shown that resistance in Staph. intermedius is most common to ampicillin, penicillin and tetracycline (Greene and Lammler 1993; Pedersen and Wegener 1995; Pellerin et al. 1998) in agreement with earlier studies. Hoekstra and Paulton (2002) in a Canadian study observed that resistance to antibiotics in dog isolates is dependent on the species, site of isolation, sex and age of the animal. That is, Staph. aureus were significantly more resistant to cloxacillin and erythromycin compared with Staph. intermedius and that ear isolates, irrespective of species were more resistant to cephalothin compared with isolates from other body sites. Data collected over a 15-year period on Staph. aureus and Staph. intermedius of canine origin in another Canadian study depicts a picture of increased resistance to some antimicrobials but decreased resistance to others, reflecting the patterns of use of specific antibiotics in veterinary hospitals (Prescott et al. 2002). Penicillin and ampicillin resistance was observed in this study but there was a slight decrease in resistance to trimethoprim–sulfonamides. Erythromycin and clindamycin resistance however remained constant as a result of on-going use of these antibiotics and there was an increase in resistance to cephalothin, enrofloxacin and gentamicin. Antibiotic susceptibility studies in isolates from dogs have largely concentrated on Staph. aureus and Staph. intermedius with very little investigation of coagulase-negative species. Recently a study of canine ear isolates from Japan found resistance to a range of antibiotics in a small number of coagulase-negative isolates (Yamashita et al. 2005). Resistance reported included penicillin, ampicillin, fluoroquinolones, kanamycin and erythromycin. More studies are therefore needed on coagulase-negative species from dogs, which form the bulk of resident staphylococci on dogs to assess the potential to transfer of resistance genes to the coagulase-positive species. Since the commercial introduction of antibiotics into clinical use staphylococci have shown rapid acquisition of resistance to almost all the major classes of antibiotics, particularly in those strains associated with nosocomial infections in humans. Very little is known about the development and spread of antimicrobial resistance in staphylococci in cats and dogs. However, plasmids are likely to play a very important role in the spread of antimicrobial resistance in these organisms. Plasmids can act directly as carriers of resistance genes or as vectors for transposon-borne resistance genes. Horizontal gene transfer has been reported to occur between Staph. aureus and Staph. intermedius and Staph. aureus and coagulase-negative staphylococci (Schwarz and Noble 1999). Staphylococci share an ecological habitat with a wide range of Gram-positive and negative species on the skin, mucosal surfaces and respiratory tract of mammals and therefore are exposed to a wide gene pool. Resistance genes are easily acquired in such a polymicrobial environment. Their habitat on mammals makes staphylococci very amenable to spread from one animal to another and in some situations to humans by cat and dog bites (Talan et al. 1989). Staphylococci are largely species specific and most of the times strains from one species do not cause infections in another species and there are few reports in the literature of spread of staphylococci between species. However, human Staph. aureus and possibly Staph. epidermidis strains can cause infection in other animals such as cattle and cats (Hummel and Meene 1979; Cox et al. 1985). Mechanisms of resistance of the various classes of antibiotics used in cats and dogs therapy are discussed below. 3.2.1 Penicillins. Penicillins are one of the earliest classes of antimicrobial agents to be used in human medicine and also used to treat large and small animals for a variety of disease conditions (Harvey and Hunter 1999). Penicillin is use to treat pyoderma in dogs and cats. Intrinsic resistant to penicillins caused by the production of β-lactamases is very wide spread among canine staphylococci (Medleau et al. 1986; Kruse et al. 1996). In human medicine, there is increasing prevalence of methicillin or oxacillin-resistant staphylococci especially in Staph. aureus and of late, there have been reported cases of isolation of methicillin-resistant staphylococci (MRS) in cats and dogs (Lilenbaum et al. 1998,1999; Gortel et al. 1999; Pak et al. 1999; Tomlin et al. 1999; van Duijkeren et al. 2003; Kania et al. 2004). The isolation rate from animals is very low (Gortel et al. 1999) when compared to the isolation rate from humans, but this methicillin-resistant Staph. aureus and Staph. intermedius strains have the potential to cause zoonotic infections in humans (Tanner et al. 2000; Manian 2003). Coagulase-negative MRS such as Staph. epidermidis, Staphylococcus hominis, Staphylococcus haemolyticus, Staphylococcus xylosus, Staphylococcus felis and Staphylococcus simulans have also been isolated from cats and dogs (Lilenbaum et al. 1998; Gortel et al. 1999) and there are recent reports of detection of the mecA gene in Staph. schleiferi and Staphylococcus warneri isolated from the ear canals and skin pyodermas of dogs (Kania et al. 2004; Yamashita et al. 2005). Methicillin resistance is related to the production of a modified penicillin-binding protein, referred to as PBP2A or PBP2 (Georgopapadakou et al. 1982; Hartman and Tomasz 1984). PBP2A is a low-affinity binding protein encoded by mecA gene. Resistance is associated with the acquisition of a large DNA element that ranges from 20 to more than 100 kb termed the staphylococcal cassette chromosome mec (SSCmec) (Katayama et al. 2000), which is integrated into the chromosome of Staph. aureus. In human medicine, MRSA infections are very difficult to treat but the clinical significance in cats and dogs has not been investigated. 3.2.2 Tetracyclines. Tetracyclines have been used widely for therapy and prevention of bacterial infections in humans, animals and plants (Roberts 1996). Four different tetracycline resistance (tet) genes assigned to classes K, L, M and O have been detected in staphylococci of animal origin (Schwarz et al. 1998b; Kim et al. 2005). These genes encode resistance mechanisms such as active efflux and ribosome protection (Roberts 1996). Tetracycline influx proteins K and L consist of 14 transmembrane regions (Paulsen et al. 1996; Roberts 1996) and the corresponding genes, tetK and tetL, are most often plasmid borne (Schwarz and Noble 1999). tetM and tetO that code for ribosome protective proteins have been identified in staphylococci and they appear to be inducible by tetracycline. The tetM gene is part of conjugative transposons and exhibits a broad host range (Roberts 1996; Taylor and Chau 1996). 3.2.3 Macrolides. Macrolides are widely used in veterinary medicine for the treatment of infections caused by Staph. intermedius resistant to penicillins (Prescott et al. 2000) and resistance to spiramycin in Staph. intermedius has been reported (Pedersen and Wegener 1995; Pellerin et al. 1998). Staphylococcal resistance to macrolides is mainly due to erythromycin-resistance methylases, which cause target-site modification. Active efflux and enzymatic inactivation has also been reported (Schwarz and Noble 1999). Target modification is the most common mechanism and it involves the demethylation of adenine residues in the 23S rRNA (Werckenthin et al. 2001). Four rRNA methylase (erm) genes namely, erm(A), erm(B), erm(C) and erm(F) have been identified in staphylococci of animal origin (Schwarz and Blobel 1990; Schwarz et al. 1990,1998a; Eady et al. 1993; Lodder et al. 1996,1997; Werckenthin et al. 1996,1999; Chung et al. 1999; Jensen et al. 1999; Werckenthin and Schwarz 2000). The distribution of these genes among staphylococci of animal origin is highly specific, with ermB being the most dominate genes in canine Staph. intermedius isolates (Eady et al. 1993; Boerlin et al. 2001). 3.2.4 Mupirocin. Mupirocin shows activity mainly against Gram-positive bacteria such as staphylococci and streptococci. It is occasionally used in veterinary medicine to treat canine pyoderma caused by multi-resistant Staph. intermedius (Werckenthin et al. 2001). It acts by competitively inhibiting isoleucyl tRNA synthase, thereby preventing incorporation of the amino acid isoleucine into growing polypeptide chains during polypeptide synthesis (Hughes and Mellows 1978a,b,1980) and finally results in breakdown of protein biosynthesis. Mupirocin resistance could be high or moderate depending on whether the resistance gene is plasmid or chromosomally located. Resistant staphylococci harbour plasmids that carry the mupA gene (Needham et al. 1994). 3.2.5 Fluoroquinolones. Fluoroquinolones are a group of antibiotics with a wide spectrum of activity amongst Gram-positive and negative bacteria where they act by inhibiting the DNA gyrase, an enzyme responsible for packaging DNA within the cell (Lloyd et al. 1999). Enrofloxacin and marbofloxacin have been used extensively in the treatment of pyoderma caused by Staph. intermedius in dogs (Paradis et al. 1990; Ihrke 1996; Koch and Peters 1996; Ihrke et al. 1999). Resistance to fluoroquinolones may be due to the result of stepwise mutations in DNA gyrase. Although fluoroquinolone resistance has been well studied in human medicine there has been little investigation in animal isolates especially those from companion animals. Lloyd et al. (1999) reported a prevalence level of 0.9% fluoroquinolone resistance amongst 858 Staph. intermedius isolates from dogs examined between 1996 and 1998. A much higher rate (8–12%) in Staph. intermedius isolated from dogs in Sweden has been reported (SVARM 2002). 3.2.6 Sulfonamides and trimethoprim. These have a broad spectrum of activity and are very effective in treating pyoderma. Resistance to sulfonamide is believed to emanate from the overproduction of p-amino benzoic acid probably due to chromosomal DNA mutation (Werckenthin et al. 2001). Trimethoprim resistance is due to dihydrofolate reductases that have a low affinity for trimethoprim. The mechanisms of resistance of sulfonamides and trimethoprim have not been specifically investigated in cats and dogs but in humans, genes encoding for dihydrofolate reductase (dfr) A and B have been identified (Rouch et al. 1987). 3.2.7 Chloramphenicol. Chloramphenicol is occasionally used in dogs and cats. Resistance to chloramphenicol is thought to be due to enzymatic inactivation (Schwarz and Noble 1999) by plasmid-borne chloramphenicol acetyltransferases encoded by cat genes. Expression of cat genes found in staphylococci is inducible by chloramphenicol via translational attenuation (Lovett 1990). Schwarz et al. (1995) investigated chloramphenicol resistance in seven canine Staph. intermedius. Four of the isolates had cat genes that were located on a plasmid and the remaining three isolates had cat genes that were located in the chromosomal DNA. 3.2.8 Aminoglycosides. Aminoglycosides have wide veterinary applications and resistance to streptomycin, neomycin and kanamycin is a common phenomenon in animal pathogens (Prescott et al. 2000). A large variety of genes encoding for aminoglycosides resistance by acetyltransferases, nucleotidyltransferases and phosphotransferases have been described in staphylococci (Shaw et al. 1993). Aminoglycosides resistance genes aaDE, sat4 and aphA-3 have been identified in canine Staph. intermedius (Boerlin et al. 2001). These genes mediate resistance to streptomycin, streptothricin and neomycin. The first report of the isolation of MRSA from animals appeared in 1975 when it was reported that MRSA had been isolated from the milk of mastitic cows (Devriese and Hommez 1975). At that time the MRSA isolates were suspected of being transferred from the dairymen to the cows on the basis of phenotypic characteristics and because at that time occurrence of MRSA in animals was considered a rare event. Recent studies have reported the isolation of MRSA from several species of animals (Hartman et al. 1997; Shimizu et al. 1997; van Duijkeren et al. 2004a) and methicillin-resistant coagulase-negative staphylococci have even been isolated from chickens and horses (Kawano et al. 1996; Yasuda et al. 2000). Although MRSA and methicillin-resistant coagulase-negative staphylococci are not clinically important in cats and dogs, a few reports in the past have suggested the transfer of Staph. intermedius from dogs to humans (Harvey et al. 1994; Tanner et al. 2000) and there is somewhat anecdotal evidence that MRSA has been transferred indirectly from a dog to a patient in an intensive care unit (Cefai et al. 1994) and a patient and his wife in a household setting (Manian 2003). Studies based on pulse-field gel electrophoresis and SCCmec typing of Staph. aureus strains isolated from a dog and its owner show possible transmission of MRSA between a human and a dog (van Duijkeren et al. 2004b). On circumstantial grounds a cat has been implicated in the passive transfer of MRSA among hospital patients in a ward (Scott et al. 1988). Several reports in the past have indicated that antimicrobial resistant staphylococci isolated from cats were acquired from their owners and in those studies Staph. aureus were the predominant species (Hearst 1967; Krogh and Kristensen 1976; Devriese et al. 1984). The determination of epidemiological relationships of staphylococci isolated from cats and dogs is of particular importance for the differentiation between clonal spread and the horizontal spread of resistance genes. Typing methods used in studying staphylococci of cats and dogs origin can be grouped into two broad categories: phenotypic and genotypic methods. Phenotypic methods are techniques based on outward expression of a gene for differentiation and they include techniques such as biotyping, antimicrobial susceptibility patterns, bacteriophage typing and ribotyping (Tenover et al. 1997). Genotypic methods on the other hand, are those based on the genetic constituent analysis of an organism and they include restriction endonucleases, polymerase chain reaction (PCR) and pulse field gel electrophoresis (PFGE) (Tenover et al. 1997). We will briefly describe each of these methods in respect of their application to canine and feline staphylococci differentiation. 5.1.1 Antibiotic susceptibility patterns. Antibiotic susceptibility patterns have been used extensively and will continue to be used to type staphylococci of canine and feline origin because of their low cost, lack of requirement for expensive equipment and straightforward interpretation of results. However, it can be a time consuming and laborious technique when screening large collections of isolates using standard dilution methods. With the introduction of commercially available high throughput screening systems such as VITEK 2 and Combas Micro System, antibiotic susceptibility testing with large collection of samples is more straightforward (Simoons-Smit and Maclaren 1994; Ling et al. 2003). The main drawback to the use of antibiotic susceptibility patterns is their poor discriminatory power because antimicrobial resistance is under constant selection pressure from continued used of antimicrobial agents (Tenover and McGowan 1996) and it is often associated with mobile genetic elements such as transposons and plasmid (Davies 1994). 5.1.2 Phage typing. Phage typing of Staph. aureus of human origin was standardized by the World Health Organization (WHO) about 30 years ago (Bannerman et al. 1995) and has since been used to type staphylococci of human and animal origin. Different panels of phage are used for typing isolates from each animal species. Various phage sets are capable of typing 64–74% of canine isolates (Greene and Lammler 1993). The traditional human and bovine phage sets are capable of typing less than 10% of canine staphylococci (Wang 1978). Phage typing has been employed to investigate possible transmission of staphylococci from cats and dogs to human and the results indicated that the dog strains were nontypable with human strain phages but two of the cat strains had similar phage types to some human types (Mann 1959; Mann et al. 1965). The most recent report of phage typing of canine staphylococci appears to be the work done by Overturf et al. (1991). Phages isolated in this study appeared to be highly specific for Staph. intermedius but limited lytic patterns were observed so it was difficult to distinguish between isolates from healthy and sick animals. Despite this, phage typing may be a useful tool in distinguishing epidemiologically related strains of Staph. intermedius and Staph. aureus of canine and feline origin. The draw backs of phage typing are; it characterizes isolates on the basis of a phenotypic marker that has poor reproducibility, it does not type all isolates and it requires maintenance of a large number of phage stocks and propagating stocks, which confines its use to small number of reference laboratories (Bannerman et al. 1995). In recent years, molecular techniques ranging from restriction endonuclease analysis of chromosomal DNA to the PCR–DNA sequencing have been used for epidemiological studies of canine staphylococci. 5.2.1 Ribotyping (ribosomal RNA gene restriction analysis). Ribotyping (Grimont and Grimont 1986; Stull et al. 1988) is a method based on the detection of genetic differences in the genomic sequences within or flanking the 16S, 5·8S and 23S ribosomal RNA genes. This technique has dual applications; that is molecular epidemiological studies (Bingen et al. 1996) and the identification of species (Brisse et al. 2000). Pedersen and Wegener (1995) observed notable differences in ribotype patterns between isolates from otitis externa, pyoderma cases and healthy dogs but Hesselbarth and Schwarz (1995) did not find any differences between Staph. intermedius from canine pyoderma or from healthy carriers despite the fact that both studies used the same restriction enzyme, EcoRI. This technique has found little recent application in canine Staph. intermedius and there are no reported studies of feline staphylococci. Therefore it is difficult to speculate on its usefulness in epidemiological and identification studies but in human medicine, it is now less frequently used because of its poor discriminatory power (Gordillo et al. 1993). 5.2.2 Pulse-field gel electrophoresis (PFGE). PFGE involves the digestion of a bacteria genome with a restriction enzyme that has relatively a few recognition sites and thus may generate approx. 10–30 fragments ranging from 10 to 80 kb (Tenover et al. 1997). It has been applied extensively to distinguish different strains of Staph. aureus of human origin including methicillin-resistant Staph. aureus (MRSA) (Udo and Grubb 1993; Bannerman et al. 1995; Manian 2003). Shimizu et al. (1996) reported a successful typing of canine strains of Staph. intermedius by PFGE. Other applications of PFGE in canine staphylococci include typing of MRS (Pak et al. 1999; Yamashita et al. 2005). The discriminatory ability of PFGE is very high and has been shown to be superior to bacteriophage typing, antibiogram and ribotyping (Tenover et al. 1994; Bannerman et al. 1995). Results from PFGE are more reliable and very reproducible. PFGE has thus been proposed as a ‘gold standard’ for MRSA typing (Bannerman et al. 1995). The draw backs of PFGE are; the inability to compare inter-centre results with each other, the technical demands of the procedure and the initial cost of the equipment. 5.2.3 Pyrolysis-mass spectrometry (Py-MS). Py-MS is a spectroscopic method that analyses the total biochemical makeup (phenotype) of an organism (Magee 1993). Goodacre et al. (1997) applied this technique to Staph. intermedius of canine and human origin. They concluded that, man and dogs carry the same strains of Staph. intermedius and that dogs probably act as a reservoir. The effectiveness of Py-MS as an epidemiological typing tool has been assessed in a wide variety of pathogenic bacteria (Freeman et al. 1990,1991; Gould et al. 1991; Magee et al. 1991,1993). In all these reports, Py-MS rated as a successful alternative technique to conventional typing methods such as antibiogram, biotype and plasmid profile. The speed, reproducibility versatility and relative low cost could suggest that Py-MS may be a valuable technique for the epidemiological typing of feline and canine staphylococci. However, it demands technical expertize to conduct and analyse the results. 5.2.4 Multilocus enzyme electrophoresis (MLEE). The first reported case of application of MLEE to Staph. intermedius of canine origin came from Barrs et al. (2000). The genetic structure of Staph. intermedius from normal skin and variety of disease conditions in dogs was examined. The authors observed limited genetic diversity between isolates of Staph. intermedius from healthy and diseased dogs, compared to ribotyping results (Hesselbarth and Schwarz 1995). MLEE has been applied to many bacterial species including Staph. aureus (Selander et al. 1986) but the discriminatory ability depends to a large extent on the number of enzymes used (Tenover et al. 1994). 5.2.5 Polymerase chain reaction (PCR). This is a method of creating copies of specific fragments of DNA. This technique has the ability to produce millions of copies of a particular DNA segment with high fidelity within 3–4 h. PCR techniques have many useful applications such as detection of resistance genes and for epidemiological studies. In the study of MRS, PCR has been used to detect the mecA gene in Staph. aureus, Staph. intermedius, Staph. epidermidis, Staph. hominis, Staph. haemolyticus and Staph. xylosus, Staph. schleiferi, Staph. warneri of canine origin (Gortel et al. 1999; Pak et al. 1999, Kania et al. 2004; Yamashita et al. 2005). Typing techniques involving PCR can be divided into four main groups: PCR-restriction fragment length polymorphism (PCR-RFLP), PCR-ribotyping, arbitrarily primed PCR or random amplified polymorphic DNA (AP-PCR/RAPD) and repetitive palindromic extragenic elements PCR (Rep-PCR) (Power 1996). Of these, PCR-ribotyping is the most frequently used method and it has had some limited application in assessing the zoonotic transmission of canine Staph. intermedius (Tanner et al. 2000), identification of Staph. schleiferi (Yamashita et al. 2005) and population diversity studies (Bes et al. 2002b). In human medicine, strain typing with molecular methods has been helpful for investigating outbreaks caused by a wide range of bacterial pathogens such as MRSA, vancomycin-resistant enterococci (VRE), Pseudomonas aeruginosa, Klebsiella pneumonia and Salmonella (Podschun and Ullmann 1998; Campbell et al. 2000; Enright et al. 2000; Tassios et al. 2000; Turabelidze et al. 2000). However, there has been little application of molecular typing to staphylococci of canine and feline origin. In this review we have highlighted staphylococcal susceptibility and resistance to various classes of antibiotics used for cat and dog therapy, mechanisms of resistance and typing techniques commonly used in differentiation of feline and canine isolates. Antibiotic resistance in feline staphylococci is not well studied or documented. Canine staphylococci have received some attention but the techniques used in epidemiological studies have not been powerful enough to discriminate between disease causing staphylococci and nonpathogenic isolates. Methicillin resistant staphylococci especially MRSA remain a huge public health problem but there have only been limited studies of methicillin resistance in feline and canine staphylococci. Most of the reported cases of methicillin resistance in feline or canine staphylococci rely on antibiotic susceptibility patterns which can be influenced by environmental conditions such as temperature, pH and salt concentrations in the media (Brown 2001) and give no indication of the genetic basis of resistance. For instance, there are examples of human Staph. aureus strains resistant to methicillin in vitro which lack the mecA gene but which have been shown to overproduce β-lactamases or to carry modifications of the normal penicillin-binding proteins (McDougal and Thornsberry 1986; Tomasz et al. 1989; Petinaki et al. 2002). At this stage it is not know if these mechanisms also play a part in methicillin resistance in animal strains. The rapid emergence and spread of resistant staphylococci in cats and dogs is a worrying development. Resistant staphylococci in cats and dogs are similar to human staphylococci that is, highly resistant to penicillin, ampicillin and tetracycline. Effective molecular typing tools such as pulsed-field gel electrophoresis, multilocus sequence typing and the recently introduced DNA macro array technology must be applied to investigate antibiotic resistance in feline and canine staphylococci. Few studies have investigated the molecular epidemiology of resistant staphylococci of dogs and there are no published reports on cats. Such studies are required to improve treatment of animals and also to determine what if any role cats and dogs play in the epidemiology of antimicrobial resistance in human staphylococci. The hypothesis that dogs and cats could serve as a reservoir for MRSA infections in human may impact on people's attitudes to their pet. However, it is important to note that Staph. aureus is rarely recovered from cats and very few cases of methicillin-resistant Staph. intermedius have been reported so it may be that pets are at risk of acquiring MRSA from their owners rather than the other way round.