Methicillin resistance among staphylococci isolated from dogs

OBJECTIVE: To determine whether methicillin-resistant staphylococci from dogs expressed the mecA gene and to determine what proportion of canine staphylococcal isolates positive for the mecA gene were resistant to oxacillin and other antibiotics. SAMPLE POPULATION: 25 methicillin-resistant (10 coagulase-positive and 15 coagulase-negative) and 15 methicillin-susceptible (8 coagulase-positive and 7 coagulase-negative) staphylococci isolated from dogs. PROCEDURE: All strains were tested for methicillin resistance by use of oxacillin agar screening and identified by use of standard techniques. Minimum inhibitory concentrations of 16 antibiotics were determined for all 40 isolates. A polymerase chain reaction method targeting a 533-basepair fragment of the mecA gene was used to detect mecA gene expression. RESULTS: 23 of the 25 methicillin-resistant isolates and none of the methicillin-susceptible isolates possessed the mecA gene. For 10 of 16 antibiotics, the proportion of mecA-positive isolates that were resistant or of intermediate susceptibility was significantly higher than the proportion of mecA-negative isolates that were resistant or of intermediate susceptibility. Only 1 methicillin-resistant coagulase-positive isolate was identified as Staphylococcus intermedius; the other 9 were identified as S. aureus. CONCLUSIONS AND CLINICAL RELEVANCE: Results confirm that staphylococci isolated from dogs may have methicillin resistance mediated by the mecA gene. Isolates positive for the mecA gene were more likely to be resistant to various antibiotics than were isolates negative for the mecA gene. Results suggest that in dogs, infections caused by staphylococci that have the mecA gene may be difficult to treat because of resistance to antibiotics.     

牛源耐甲氧西林金黄色葡萄球菌的检测

本研究旨在了解甘肃地区奶牛乳房炎金黄色葡萄球菌的耐药性和耐甲氧西林金黄色葡萄球菌的感染情况,为奶牛乳房炎的防制提供理论依据。采用KB纸片扩散法,检测17株金黄色葡萄球菌对8种不同抗菌药物的敏感性;再用琼脂稀释法检测了苯唑西林、万古霉素对金黄色葡萄球菌的最小抑菌浓度(MICs);头孢西丁纸片扩散法和PCR扩增特异性mecA耐药基因对所有受试菌株进行全面的耐甲氧西林金黄色葡萄球菌检测。结果表明,菌株对青霉素、磺胺异恶唑具有较强抗性,而对环丙沙星、头孢唑啉、万古霉素和苯唑西林全敏感;头孢西丁纸片扩散法未能检测出表型为MRSA的阳性菌株,而PCR方法却检测出8株mecA基因阳性菌株,且这些菌株的苯唑西林MIC均小于2 μg/mL。菌株的耐药情况较严重,对甲氧西林敏感而携带mecA基因的菌株高频存在于被调查地区的奶牛场中。     

The prevalence of methicillin-resistant staphylococci in healthy horses in the Netherlands

Two hundred healthy horses housed at 23 different farms and one clinic and 42 persons in close contact with these horses were screened for the presence of methicillin resistant staphylococci. Samples were taken from the nose and the pastern of the horses and from the nose and throat of the humans and incubated in selective media. Isolates were identified by standard techniques and their susceptibilities were tested using an agar diffusion method. Methicillin-resistant strains were tested for the presence of the mecA gene by PCR. In 45 horses (22.5%) and 15 humans (35.7%) mecA positive staphylococci were found. All isolates were coagulase negative staphylococci, except for one methicillin-resistant Staphylococcus aureus isolated from a veterinarian. Staphylococcus sciuri was the predominant species found among the methicillin resistant staphylococci (MRS) in the horses, whereas S. epidermidis predominated in the humans. From the horses, often more than one species of MRS could be isolated, resulting in a total of 175 mecA positive equine isolates. The equine isolates were predominantly susceptible to most antimicrobials tested, whereas the human isolates showed more resistance. In conclusion, no methicillin-resistant Staphylococcus aureus was found in healthy horses in the Netherlands, but methicillin-resistant coagulase negative staphylococci were found frequently. Further studies are needed in order to investigate whether horses can be a reservoir for MRS or the mecA gene for humans.     

Methicillin-resistant staphylococci isolated from animals

Staphylococci isolated from animals (n=311) were screened for methicillin resistance by oxacillin agar screening. Oxacillin-resistant strains were tested for the presence of the mecA gene by PCR. Isolates were identified by standard techniques and 16S rDNA analysis, and their antimicrobial susceptibilities were tested using an agar diffusion method. MecA-positive strains were further analyzed using pulsed-field gel electrophoresis (PFGE). From 11 multidrug-resistant staphylococci, 6 were mecA-positive: 2 methicillin-resistant Staphylococcus aureus (MRSA) and 4 Staphylococcus haemolyticus. Screening of 300 staphylococci (100 S. aureus, 100 S. intermedius and 100 coagulase-negative staphylococci (CNS)) randomly chosen from the strain collection of the Veterinary Microbiological Diagnostic Center yielded five oxacillin-resistant coagulase-negative staphylococci, four of which were mecA-positive. PFGE showed that all mecA-positive staphylococci isolated from animals had distinct patterns. However, one MRSA isolated from a flank fistula of a dog showed homology to a human epidemic MRSA cluster, suggesting that transfer of MRSA between humans and dogs might occur.     

Prevalence of antibiotic resistance genes in staphylococci isolated from ready-to-eat meat products

Prevalence of mecA, blaZ, tetO/K/M, ermA/B/C, aph, and vanA/B/C/D genes conferring resistance to oxacillin, penicillin, tetracycline, erythromycin, gentamicin, and vancomycin was investigated in 65 staphylococcal isolates belonging to twelve species obtained from ready-to-eat porcine, bovine, and chicken products. All coagulase negative staphylococci (CNS) and S. aureus isolates harbored at least one antibiotic resistance gene. None of the S. aureus possessed more than three genes, while 25% of the CNS isolates harbored at least four genes encoding resistance to clinically used antibiotics. In 15 CNS isolates the mecA gene was detected, while all S. aureus isolates were mecA-negative. We demonstrate that in ready-to-eat food the frequency of CNS harboring multiple antibiotic resistance genes is higher than that of multiple resistant S. aureus, meaning that food can be considered a reservoir of bacteria containing genes potentially contributing to the evolution of antibiotic resistance in staphylococci.     

A real-time PCR assay to detect the Panton Valentine Leukocidin toxin in staphylococci: screening Staphylococcus schleiferi subspecies coagulans strains from companion animals

Recent reports suggest that methicillin-resistant strains of Staphylococcus schleiferi subspecies coagulans are now commonly isolated from dogs. Given the association of a potentially mobile SCCmec type IV element with lysogenic phage-encoded Panton Valentine Leukocidin (PVL) toxin genes in community-acquired methicillin-resistant Staphylococcus aureus strains we hypothesized that methicillin-resistant S. schleiferi ssp. coagulans strains may also encode PVL toxin genes. Forty S. schleiferi ssp. coagulans strains isolated from companion animals were studied. Susceptibility to oxacillin was determined by broth microdilution and all isolates were screened by PCR for the presence of the mecA gene. SCCmec typing was performed on 14 isolates. A real-time PCR assay was developed for the detection of the PVL genes using a SmartCycler. Pulsed-field gel electrophoresis (PFGE) was performed to determine whether S. schleiferi ssp. coagulans strains were homogeneous. Twenty-eight of the 40 isolates (70%) were resistant to oxacillin and 26/28 possessed the mecA gene by PCR. SCCmec IV was identified in seven strains; the other seven isolates were not typable by this technique. All 40 strains were negative for the PVL toxin gene. PFGE showed a heterogeneous population and 13 different profiles were determined. In conclusion, this study showed that PVL toxin genes were not detected in a heterogeneous population of methicillin-resistant S. schleiferi ssp. coagulans strains isolated from companion animals.     

Methicillin resistance of staphylococci isolated from the skin of dogs with pyoderma

OBJECTIVE: To determine the methicillin-resistant profile of staphylococcal isolates from the skin of dogs with pyoderma. ANIMALS: 90 dogs with pyoderma. PROCEDURE: Staphylococci isolated from dogs with pyoderma were tested for susceptibility to methicillin by use of a standard disk diffusion test with oxacillin disks. The DNA extracted from the isolates was tested for the mecA gene that encodes the penicillin-binding protein 2a (PBP2a) by use of a polymerase chain reaction (PCR) assay. The expression of PBP2a was determined with a commercial latex agglutination assay. Species of staphylococcal isolates were identified by use of morphologic, biochemical, and enzymatic tests. RESULTS: Most of the isolated staphylococci were methicillin-susceptible, coagulase-positive Staphylococcus intermedius isolates. Whereas only 2 of 57 S. intermedius isolates were resistant to methicillin, approximately half of the isolates had the mecA gene and produced PBP2a. Staphylococcus schleiferi was the second most common isolate. Widespread resistance to methicillin was found among S. schleiferi isolates. More coagulase-negative S. schleiferi isolates were identified with mecA gene-mediated resistance to methicillin, compared with coagulase-positive S. schleiferi isolates. CONCLUSIONS AND CLINICAL RELEVANCE: The latex agglutination assay for the detection of PBP2a expression coupled with the PCR assay for the mecA gene may provide new information about emerging antimicrobial resistance among staphylococcal isolates.     

Methicillin-resistant coagulase-negative staphylococci isolated from healthy horses in Japan

OBJECTIVE: To determine patterns of methicillin-resistant staphylococci isolated from apparently healthy horses. SAMPLE POPULATION: 44 horses from 8 riding clubs in Japan. PROCEDURE: Methicill in-resistant staphylococci were isolated from the skin or nares, using a selective medium containing a beta-(symboric) lactam antibiotic, ceftizoxime. Clonality of isolates was determined by use of pulsed-field gel electrophoresis. Detection of mecA, mecl, and mecR1 genes was accomplished by use of polymerase chain reactions. RESULT: Of the 44 horses, 13 (29.5%) yielded 15 isolates of methicillin-resistant staphylococci. The 15 isolates were identified as 6 species (Staphylococcus epidermidis, S lentus, S saprophyticus, S xylosus, S sciuri, and S haemolyticus). However, methicillin-resistant S aureus was seldom isolated. Each isolate contained the mecA gene and had a high resistance to beta-lactam antibiotics. Some isolates also were resistant to other antibiotics such as erythromycin and kanamycin. CONCLUSIONS AND CLINICAL RELEVANCE: Methicillin-resistant coagulase-negative staphylococci that were highly resistant to various antibiotics were isolated from apparently healthy horses in Japan. These organisms must be considered a potential threat to horses and veterinarians who care for them.     

Antimicrobial susceptibility of udder pathogens isolated from dairy herds in the west littoral region of Uruguay

A total of 522 strains belonging to streptococci, enterococci and staphylococci isolated from sub-clinical and clinical cases of bovine mastitis from the west littoral region of Uruguay were analysed for their susceptibility to several antimicrobial agents. The susceptibility patterns were studied by agar disk diffusion methods (ADDM) and broth micro-dilution to determine the minimum inhibitory concentration (MIC). The concentration that inhibits 90% (MIC90) of the analysed strains reported in micrograms per millilitre, for Staphylococcus aureus were > 8, 8, < or = 0.5, < or = 4, < or = 1, < or = 0.5, > 64, < or = 0.25, 0.5, < or = 1 and < or = 1 to penicillin, ampicillin, oxacillin, cephalotin, gentamicin, erythromycin, oxitetracycline, enrofloxacin, trimethoprim/sulfamethoxazole, neomycin, and clindamycin, respectively. Coagulase-negative staphylococci (CNS) had different values for penicillin (4) and ampicillin (2), while the other antimicrobial agents had the same MIC90 values as reported for S. aureus. The MIC90 values for streptococci were 0.12, 0.25, < or = 4, 16, < or = 0.25, 0.5, 0.25 for penicillin, ampicillin, cephalotin, gentamicin, erythromycin, oxytetracycline and trimethoprim-sulfamethoxazole, whereas MIC90 for enterococci were 4, 4, 4, < or = 0.5, 2, > 8 for penicillin, ampicillin, gentamicin, erythromycin, oxytetracycline and trimethoprim-sulfamethoxazole, respectively. Of 336 strains of S. aureus, 160 (47.6%) were resistant to penicillin. For 41 CNS strains, 10 (27%) presented penicillin-resistance. All the streptococcal strains were susceptible to penicillin, while 3 (7%) of the 43 enteroccocal strains were resistant. Non significant statistical differences were found between the results obtained by ADDM and broth micro-dilution for classifying bacterial isolates as susceptible or resistant according to the National Committee of Clinical Laboratory Standards.     

Phenotypic and genotypic characteristics of methicillin/oxacillin-resistant Staphylococcus intermedius isolated from clinical specimens during routine veterinary microbiological examinations

Methicillin/oxacillin resistance of 10 S. intermedius strains was investigated by conventional and molecular methods. The strains tested had been isolated in Germany during routine veterinary microbiological examinations of specimens from a small animal clinic between May and September 2005. Epidemiological relationships of the strains were studied by macrorestriction analysis of their chromosomal DNA using pulsed field gel electrophoresis (PFGE). Species identity of the 10 S. intermedius strains was confirmed by conventional methods and by PCR mediated amplification of S. intermedius specific segments of thermonuclease encoding gene nuc. As controls, four methicillin/oxacillin resistant S. intermedius (MRSI) strains obtained from specimens sent by four veterinarians and three selected methicillin/oxacillin sensitive S. intermedius (MSSI), also obtained from the small animal clinic, were tested. The 10 strains, representing approximately 6% of all S. intermedius isolated from the clinic throughout the time period mentioned above, and the four MRSI obtained from veterinarians, were methicillin/oxacillin and penicillin resistant using disk diffusion tests and could be cultivated on oxacillin resistant screening agar base (ORSAB). Both resistances could be confirmed by multiplex PCR detecting the resistance genes mecA and blaZ. The three MSSI were methicillin/oxacillin sensitive in all tests. Epidemiological investigation by macrorestriction analysis of the chromosomal DNA of the strains by pulsed field gel electrophoresis revealed that all 10 MRSI strains obtained from the clinic and the four MRSI strains obtained from veterinarians, in contrast to the three MSSI strains, represent identical or closely related bacterial clones possibly indicating a cross-infection of the animals in the clinic and the distribution of a single MRSI clone in the pet population.     

Antimicrobial resistance of Staphylococcus aureus and coagulase negative staphylococci isolated from mastitis milk samples from sheep and goats

Staphylococcus aureus and coagulase negative staphylococci (CNS) were isolated from ovine and caprine mastitis milk samples originating from more than 40 Swiss farms. CNS dominated as causal microorganisms of mastitis in small ruminants. By restriction fragment length polymorphism (RFLP) analysis of the groEL gene and sequencing of 16S rDNA, various CNS species were identified, albeit certain of them predominated. For susceptibility testing of mastitis pathogens to selected antibiotics, minimal inhibitory concentrations were determined. Of the 67 S. aureus and 208 CNS strains, 31.3 % and 8.2 % were resistant to penicillin, 29.9 % and 1.0 % to ampicillin, 1.5 % and 10.6 % to erythromycin, and 3.0 % and 7.7 % to tetracycline, respectively. Moreover, 10 CNS strains (4.8 %) were resistant to oxacillin and one CNS strain to sulfamethoxazole/trimethoprim. The results obtained describe for the first time the resistance situation of mastitis pathogens from sheep and goats in Switzerland. However, accompanying and preventing measures are also of importance in mastitis control of small ruminants.     

Screening of Staphylococcus aureus, Staphylococcus intermedius, and Staphylococcus schleiferi isolates obtained from small companion animals for antimicrobial resistance: a retrospective review of 749 isolates (2003-04)

Companion animal staphylococcal isolate antibiograms were screened retrospectively to determine the frequency of methicillin-resistant (MR) infection by Staphylococcus aureus, Staphylococcus intermedius, and Staphylococcus schleiferi. Rates of MR were: S. aureus 35%, S. intermedius 17%, and S. schleiferi 40%. Frequency of isolation of methicillin-resistant S. aureus (MRSA) from dogs and cats was similar, whereas methicillin-resistant S. intermedius (MRSI) and methicillin-resistant S. schleiferi (MRSS) were significantly more common in dogs. MRSS was more commonly associated with superficial (skin and ear canal) infections, whereas MRSA was more commonly associated with deep infections. The MR strain resistance pattern to other classes of antibiotics was also investigated. MRSA was resistant to the most classes of antibiotics, followed by MRSI, while MRSS maintained the most favourable susceptibility profile. MR staphylococci may pose a significant risk to animal and public health. Therefore, to avoid selecting for resistant strains in cases of suspected staphylococcal infection, clinicians should consider culture and susceptibility testing early in the course of treatment.     

乳房炎奶牛金黄色葡萄球菌毒素基因的检测及PFGE分型研究

作者针对临床及亚临床乳房炎奶牛乳汁中金黄色葡萄球菌分离株的毒素基因进行检测和脉冲场凝胶电泳(PFGE)基因分型,比较2种类型乳房炎金黄色葡萄球菌分离株的差异.无菌法采集奶样,采用国际标准方法从中分离金黄色葡萄球菌,用多重PCR方法扩增nuc基因和mecA基因以确证金黄色葡萄球菌(SA)和耐甲氧西林金黄色葡萄球菌(MRSA).进一步用PCR方法检测SA的各种毒素基因(SEs、ETs、TSST 1和PVL基因等).利用限制性内切酶Sma Ⅰ对SA基因组DNA进行酶切和PFGE分析,最后利用BioNumerics软件进行聚类分析.结果:19.3％(23/119)的临床乳房炎奶样和14.8％(26/176)的亚临床乳房炎奶样确定为金黄色葡萄球菌阳性样品,分别从中分离鉴定出43株和26株金黄色葡萄球菌,其中临床乳房炎分离株中有5株为mecA基因阳性.临床乳房炎奶牛奶样中检测到SA的SEA、SEB、SED、SEJ和PVL毒素基因,检出率分别为3.8％(1株)、11.5％(3株)、19.2％(5株)、7.7％(2株)和31.2％(10株);亚临床乳房炎奶牛乳样中仅检测到SA的SEA和PVL毒力基因,检出率分别为7.0％(3株)和84.1％(37株).表明临床与亚临床乳房炎奶牛乳汁中SA菌株携带的毒素基因不一样,SEs可能是临床乳房炎菌株的重要致病基因,PVL可能是亚临床乳房炎菌株的重要致病基因.69株SA使用Sma Ⅰ酶切分型后,可分为7个大簇、50个基因型,来源相同的SA分型后大部分位于同一簇内.临床乳房炎奶牛乳汁中检测到MRSA菌株,PVL基因在亚临床乳房炎中的检出率为临床乳房炎的2.7倍.PFGE方法能较好的区分临床乳房炎和亚临床乳房炎的SA分离菌株.     

Prevalence of and resistance to anti-microbial drugs in selected microbial species isolated from bulk milk samples

The prevalence of strains of Staphylococcus aureus, coagulase-negative (CN) staphylococci, Listeria monocytogenes, Escherichia coli, Enterococcus faecalis, E. faecium and Bacillus cereus, was investigated in 111 bulk milk samples. Staphylococcus aureus was isolated from 38 samples, CN staphylococci from 63 samples, E. coli from 49 samples, E. faecalis or E. faecium from 107 samples, and L. monocytogenes from two samples. Bacillus cereus was not found in any of the samples and three samples were free of any of the selected species. Sensitivity to the anti-microbial drugs amikacin, ampicillin, ampicillin + sulbactam, cephalothin (CLT), cephotaxime, clindamycin, chloramphenicol (CMP), co-trimoxazole, erythromycin (ERY), gentamicin, neomycin, norfloxacin, oxacillin, penicillin, streptomycin (STR), tetracycline (TTC) and vancomycin was tested using the standard dilution technique. Minimum inhibitory concentration (MIC) characteristics (MIC50, MIC90, MIC range) were determined for each microbial species. Resistance against one or more anti-microbial drugs was found in 93% of S. aureus, 40% of CN staphylococci, 73% of E. coli, 88% of E.faecalis, 55% of E.faecium, and one L. monocytogenes strain. Most of the strains, particularly enterococci, were resistant to STR, TTC, and ERY (MIC50 4 microg/ml). A high percentage of staphylococci were resistant to beta-lactam antibiotics. High resistance to CLT was found in 11 strains of E. coli (MIC 256 microg/ml) and strains resistant to CMP (MIC90 16 microg/ml) were detected. The highest numbers of resistance phenotypes were found in E. coil (16) and CN staphylococci (12). Eighteen identical resistance phenotypes were demonstrated in indicator bacteria (E. coli, E. faecalis, E. faecium) and pathogens (S. aureus, CN staphylococci) isolated from the same bulk milk sample. The obtained resistance data were matched against the herd owners' information on therapeutic use of the drugs. This confrontation could not explain the findings of strains resistant to ERY or CMP. Our findings are evidence of selection of resistant strains among not only pathogenic agents, but also among indicator bacteria which can become significant carriers of transmissible resistance genes.     

Antibiotic resistance of staphylococci from humans, food and different animal species according to data of the Hungarian resistance monitoring system in 2001

Based on data of the Hungarian resistance monitoring system the antibiotic resistance of Staphylococcus strains of human and animal origin was studied. No methicillin-resistant staphylococci harbouring mecA gene were isolated from animals in 2001. Penicillin resistance, mediated by penicillinase production, was the most frequent among Staphylococcus aureus strains isolated from humans (96%), from bovine mastitis (55%), from foods (45%) and from dogs. In staphylococci isolated from animals low resistance percentages to aminoglycosides (0-2%), fluoroquinolones (0.5-3%) and sulphonamides (0.5-4%) were found but in strains isolated humans these figures were higher (1-14%, 5-18% and 3-31%, respectively). The most frequent antibiotic resistance profiles of strains isolated from animals and food were penicillin/tetracycline, penicillin/lincomycin and penicillin/lincomycin/tetracycline. Penicillin/tetracycline resistance was exhibited by strains from mastitis (3), samples from the meat industry (31), poultry flocks (1), poultry industry (1), noodle (1) and horses (2). Penicillin/lincomycin resistance was found in 10 Staphylococcus strains from mastitis, 1 from the dairy industry, 1 from the meat industry and 6 from dogs. Isolates from mastitis (2), from the dairy industry (2), from pigs (1), from the meat industry (1) and from poultry (1) harboured penicillin/lincomycin/tetracycline resistance pattern. Multiresistant strains were usually isolated only from one and sometimes from two animal species; therefore, the spread of defined resistant strains (clones) among different animal species could not be demonstrated. These results also suggest that the transfer of antibiotic resistance of S. aureus from animals to humans probably occurs less frequently than is generally assumed.     

Antimicrobial resistance patterns to beta-lactams of gram-positive cocci isolated from bovine mastitis in Lithuania

The aim of the study was to isolate gram-positive cocci from cows with mastitis and to determine their resistance to beta-lactamic antibiotics. Eight hundred and nine strains were isolated and identified as staphylococci (n=516), streptococci (n=199) and enterococci (n=94) from sub-clinical and clinical cases of bovine mastitis in Lithuania. The most common causative agents of udder disease included: S. epidermidis (n=176), S. aureus (n=176), S. agalactiae (n=134), S. hyicus (136) and E. hirae (n=68). Isolates were analysed for antimicrobial resistance to penicillin, ampicillin, amoxicillin, cephalothin, cephalexin, amoxicillin + clavulanate. The susceptibility patterns were analysed using the agar disk diffusion method. S. aureus showed the highest level of resistance to amoxicillin (81.3%), penicillin (76.7%) and ampicillin (78.4%). The corresponding values for CNS strains were 59.7%, 59.7% and 50.6% against penicillin, ampicillin and amoxicillin respectively. Streptococci were the most frequently resistant to amoxicillin (29.3%), and enterococci to penicillin (27%), amoxicillin (27.5%) and amoxicillin/clavulanic acid (23.8%). The resistance of all tested mastitis pathogens to aminopenicillins and penicillin highly correlated (r=0.83). Compared with other antibiotics, amoxicillin and clavulanic acid combination tended to be more effective (p<0.05) against all tested bacteria in vitro. However, S. aureus, in 38.1% of cases, was resistant to this combination of antimicrobials. This study demonstrates that S. epidermidis, S. aureus, S. hyicus, S. agalactiae and E. hirae remain the most frequent mastitis causative agents on Lithuanian cattle farms. The highest resistance in vitro to penicillins was demonstrated by S. aureus, S. hyicus and S. intermedius. Resistance to cephalosporins remains low, irrespective of bacterial species of gram-positive cocci.     

Antimicrobial susceptibility and presence of resistance genes in staphylococci from poultry

The species distribution, susceptibility to 19 antimicrobial agents and presence of selected genes encoding resistance to macrolides, streptogramins and tetracyclines were examined among 118 staphylococcal isolates from infections of poultry in Denmark. Isolates were identified using a combination of conventional biochemical testing and 16S rDNA sequencing. The most common species were Staphylococcus aureus (83), Staphylococcus hyicus (11), Staphylococcus xylosus (9) and Staphylococcus cohnii (6). The isolates were susceptible to most antimicrobials tested. A high frequency of S. aureus (30%) was resistant to ciprofloxacin. Only six (7%) S. aureus isolates and one Staphylococcus saprophyticus were penicillin resistant. Resistance to sulphamethoxazole was observed among 16 (19%) of S. aureus isolates and two coagulase negative staphylococci (CNS). Twenty (24%) of the S. aureus isolates were resistant to erythromycin and 19 of these isolates contained the ermA gene, whereas the remaining isolate contained the ermC gene. Eleven (48%) of the novobiocin resistant CNS were resistant to erythromycin and all these isolates contained the ermA gene. Two isolates identified as S. xylosus, were found to be resistant to streptogramins and both contained the vatB- and the vgaB-genes. Thirty-nine (47%) of the S. aureus isolates, three of nine S. hyicus and eight of the 23 novobiocin resistant CNS were tetracycline resistant and all contained the tet(K) gene. A single S. aureus isolate also contained the tet(M) gene. The present study showed a frequent occurrence of resistance to fluoroquinolones, tetracycline and macrolides among staphylococci isolated from broilers in Denmark, whereas the occurrence of resistance to other antimicrobial agents remains low. Similar genes, encoding resistance to erythromycin, tetracycline and streptogramins to those previously observed, were detected.     

Antibiotic resistance of canine Staphylococcus intermedius group (SIG)--practical implications

A total of 221 SIG strains were isolated from clinical samples of canine origin submitted to the Diagnostic Laboratory of the Division of Bacteriology and Molecular Biology at the Warsaw University of Life Sciences in Warsaw during the period 2006-2010. The aim of the study was to investigate the frequency of prevalence of methicillin-resistant SIG strains and to determine the MIC values of cephalotin, amoxicillin/clavulanic acid, ciprofloxacin, clindamycin, gentamicin, chloramphenicol, mupirocin for a collection of randomly selected 79 strains belonging to Staphylococcus intermedius group (SIG), including 23 mecA-positive and 56 mecA-negative strains. All isolates were identified as belonging to SIG based on their phenotypic properties and PCR amplification of S. intermedius-specific fragment of the 16S rRNA gene. The mecA gene was detected in 26 (12%) of 221 SIG strains. All tested mecA-negative SIG strains were susceptible to amoxicillin/clavulanic acid and cephalotin. One of the 56 mecA-negative SIG strains was resistant to ciprofloxacin, six (11%) to gentamicin. It was found that sixteen (29%) of 56 mecA-negative SIG strains were resistant to clindamycin. Most of the mecA-positive SIG strains were resistant to ciprofloxacin (96%), clindamycin (96%), and gentamicin (96%). Only one MRSIG strain was resistant to chloramphenicol. All examined mecA-positive SIG strains were found to be susceptible to mupirocin. Our results imply that staphylococcal multidrug resistance has become more prevalent, which could lead to difficulties in effective treatment. With some resistant strains the only therapeutic possibility are antimicrobial agents important in human medicine. New regulations for veterinary medicine concerning appropriate therapy of infections caused by multidrug-resistat staphylococci are needed.     

Antimicrobial resistance studies in staphylococci and streptococci isolated from cows with mastitis in Argentina

Background Staphylococcus aureus and Streptococcus agalactiae are the main cause of clinical mastitis in dairy cattle in Argentina, whereas coagulase-negative staphylococci (CNS) and environmental streptococci are the main cause of subclinical mastitis. Bacteria isolated from infected animals show increasing antimicrobial resistance.ObjectivesThis study aims to determine the antimicrobial resistance of staphylococci and streptococci isolated from milk with mastitis, and to genotypically characterize the methicillin-resistant (MR) staphylococci.MethodsIsolation was performed on blood agar and identification was based on biochemical reactions. Antimicrobial susceptibility was according to the Clinical and Laboratory Standards Institute guidelines. The antimicrobial resistance genes, SCCmec type and spa type were detected by the polymerase chain reaction method.ResultsWe isolated a total of 185 staphylococci and 28 streptococci from 148 milk samples. Among the staphylococcal isolates, 154 were identified as CNS and 31 as S. aureus. Among the 154 CNS, 24.6% (n = 38) were resistant to penicillin, 14.9% (n = 23) to erythromycin, 17.5% (n = 27) to clindamycin, 6.5% (n = 10) to cefoxitin and oxacillin. Among the S. aureus isolates, 16.1% (n = 5) were resistant to penicillin, 3.2% (n = 1) to cefoxitin and oxacillin (MRSA). Six MR isolates (5 CNS and 1 MRSA) were positive to the mecA gene, and presented the SCCmec IVa. The MRSA strain presented the sequence type 83 and the spa type 002. Among the 28 streptococcal isolates, 14.3% (n = 4) were resistant to penicillin, 10.7% (n = 3) to erythromycin and 14.3% (n = 4) to clindamycin.ConclusionsThe present findings of this study indicate a development of antimicrobial resistance in main bacteria isolated from cows with mastitis in Argentina.