CPRMethicillin resistant coagulase-negative staphylococci isolated from South Korean ducks exhibiting tremor

Background

We describe coagulase-negative staphylococci (CoNS) isolates collected from ducklings exhibiting tremor in South Korea over the period of 2010 to 2011. Screening of antimicrobial susceptibility and analysis of SCCmec elements of CoNS were also investigated.

Results

Staphylococcus cohnii was the most frequent staphylococcus (9 isolates) and S. sciuri (4 isolates), S. lentus (3 isolate), S. simulans (1 isolate) and S. epidermidis (1 isolate) were also detected. Among the 15 antimicrobials tested in this study, resistance against oxacillin (15 isolates, 83.3%) was most frequently observed, but only one isolate (SNUDS-1) possessed mecA. This isolate was shown to possess SCCmec type III; the type 3 ccr complex and the class A mec complex.

Conclusions

Based on these results, isolate SNUDS-1 was shown to possess SCCmec type III; the type 3 ccr complex and the class A mec complex. Although the SCCmec type III is not predominant in human, MR-CoNS (Methicillin resistance Coagulase-negative staphylococci) in food animals should be monitored to prevent the dissemination of antimicrobial resistance genes and resistant pathogens to the community.     

Dissimilarity of ccrAB gene sequences between methicillin-resistant Staphylococcus epidermidis and methicillin-resistant Staphylococcus aureus among bovine isolates in Korea

The sequences of the ccrAB genes from bovine-, canine- and chicken-originating methicillin-resistant Staphylococcus (S.) epidermidis (MRSE) and bovine methicillin-resistant Staphylococcus (S.) aureus (MRSA) were compared to investigate the frequency of intra-species horizontal transfer of the staphylococcal cassette chromosome mec (SCCmec) complex. Nineteen MRSE strains were isolated from bovine milk, chickens, and dogs, and their genetic characteristics were investigated by multilocus sequence typing and SCCmec typing. Among the animal MRSE strains, the most frequent SCCmec type was type IV, which consisted of the type B mec complex and ccrAB type 2. The ccrA2 and ccrB2 genes were sequenced from the bovine, chicken and canine MRSE strains and compared with those of the bovine MRSA strains. The sequences generally clustered as MRSA and MRSE groups, regardless of the animal source. Additionally, no bovine MRSE sequence was associated with the bovine MRSA groups. Although most of the bovine MRSE and MRSA isolates possessed SCCmec type IV sequences, our results suggest that the intra-species gene transfer of the SCCmec complex between bovine S. aureus and bovine S. epidermidis strains is not a frequent event.     

Genetic basis of penicillin resistance of S. aureus isolated in bovine mastitis

Background

The blaZ gene encoding penicillin resistance can be located either chromosomally or on plasmids. The aim of this study was to investigate the genetic relationships and to determine the location of the blaZ gene in S. aureus isolated in bovine mastitis in Finland and Sweden.

Methods

Seventy-eight β-lactamase positive S. aureus isolates from bovine mastitis (34 from Finland and 44 from Sweden) were included in the study. The localization of blaZ gene was determined by Southern blotting. The blaZ genes of the isolates were sequenced and the sequences were translated to beta-lactamase proteins and further grouped as different protein signatures. The isolates and, as control, 33 Swedish and 36 Finnish beta-lactamase negative isolates were typed with pulsed-field gel electrophoresis (PFGE).

Results

In 26 out of 34 Finnish isolates (76.5%) and in 25 out of 44 Swedish isolates (56.8%) the blaZ gene was localized on a plasmid. Six different protein signatures were found. One signature was found only in four Swedish isolates, but all other signatures were found both in Finnish and Swedish isolates. The PFGE results revealed a diversity of S. aureus clones. The protein signatures were not clearly associated with certain pulsotypes.

Conclusions

The plasmid location of the blaZ gene was not statistically significantly more common in Finland than in Sweden, and hence does not explain the higher proportion of penicillin-resistant isolates of S. aureus causing bovine mastitis in Finland compared to Sweden.     

Prevalence,species distribution and antimicrobial resistance patterns of methicillin-resistant staphylococci in Lithuanian pet animals

Background

The bacterial genus Staphylococcus consists of many species that causes infections in pet animals. Antimicrobial resistant staphylococci cause infections that are difficult to treat and they are important from the point of one health perspective. The aim of this study was to determine the prevalence of methicillin-resistant Staphylococcus (MRS) species, including methicillin-resistant S. aureus (MRSA) in diseased pet animals (Group A) and kennel dogs (Group B) in Lithuania and to characterize the isolates according to their antimicrobial resistance.

Results

Twenty-one MRS isolates were obtained from 395 clinical samples (5.3 %; CI 95 % 3.5-8.0) of Group A animals. Sixteen, four and one isolates were from dogs, cats and a pet rabbit, respectively. The mecA gene was present in 20 isolates, whereas one isolate was positive for the mecC gene. Twenty-one MRS isolates (20.0 %; CI 95 % 13.5-28.6) were obtained from the vagina of female dogs (n = 105) (Group B). All isolates carried the mecA gene. Twelve MRS species were isolated of which S. pseudintermedius was the most common (18/42) followed by S. haemolyticus (8/42) and S. lentus (4/42). MRSA was not found. All MRS strains were susceptible to vancomycin, linezolid, daptomycin and quinupristin/dalfopristin. Resistance to tetracycline (16/21), clindamycin (15/21) and erythromycin (14/21) was the most common types of resistance in Group A animals. Three isolates also demonstrated resistance to rifampin. Resistance toward gentamicin (16/21), ciprofloxacin (15/21), macrolides (15/21) and tetracycline (12/21) was the most common in kennel dogs (Group B). The most common genes encoding resistance to antimicrobials (excluding beta-lactams) in isolates from Group A pets were tetK (21/42), aph(3′)-IIIa (11/42) and aac(6'')-Ie-aph(2'''')-Ia (9/42).

Conclusions

A wide range of MRS species were found in pet animals in Lithuania. MRSA was not found.     

Antimicrobial susceptibilities and population structure of Staphylococcus epidermidis associated with ovine mastitis

Intramammary infections are a serious problem for dairy sheep farms, and Staphylococcus epidermidis is one of the main etiological agents of ovine mastitis. In this work, 131 S. epidermidis isolates, collected from 2201 dairy Sarda sheep belonging to 14 flocks with high somatic cell count scores, were studied. The flocks were located in diverse geographical areas of Sardinia, Italy. The aim of study was to assess the susceptibility of isolates to 13 antimicrobial agents, many of which are frequently used in mastitis therapy. Oxacillin was used for detecting methicillin-resistant S. epidermidis (MRSE) by disk diffusion test. Thirty-eight percent of the isolates (n = 50) were resistant to penicillin, 7.6% (n = 10) were resistant to tetracycline, and 2.3% (n = 3) were resistant to both penicillin and tetracycline (PTRSE). Two isolates were resistant to five antimicrobials including methicillin. Analysis of staphylococcal cassette chromosome mec (SCCmec) elements showed that both MRSE isolates harbored SCCmec type IVa. Based on pulsed-field gel electrophoresis (PFGE) typing by SmaI macrorestriction, S. epidermidis isolates were grouped into four clusters at 75% similarity level. The two multi-drug resistant MRSE isolates displayed distinct PFGE patters. This study indicates that S. epidermidis isolates from sheep milk samples may accumulate resistance markers for different antimicrobial agents. Furthermore, the occurrence of PTRSE and MRSE suggests to adopt adequate hygienic measures when handling animals with intramammary infections, in order to prevent spreading PTRSE and MRSE strains to humans through direct contact and/or consumption of contaminated food.     

Characterization of coagulase negative staphylococci from cases of subclinical mastitis in dairy cattle in Kampala,Uganda

Background

Coagulase negative staphylococci (CNS) are the most common pathogens leading to subclinical mastitis (SCM) in dairy cattle in Uganda. Coagulase negative staphylococci can vary between bacterial species in how they cause disease. The aim of the study was to characterize CNS, from cows with SCM in Uganda, at the species level.

Findings

Quarter milk samples (n = 166) were collected from 78 animals with SCM. Bacteriological analyses were carried out at Makerere University, Kampala, Uganda and at the National Veterinary Institute (SVA), Uppsala, Sweden. The most common pathogens found in milk samples from cows with SCM were CNS (31.7%). Two species of CNS were found, S. epidermidis (85%) and S. haemolyticus (15%). Of the CNS isolates, 16/20 (80%) were positive for β-lactamase production (β+).

Conclusions

In milk samples from cows with SCM caused by CNS, S. epidermidis was most prevalent, followed by S. haemolyticus.     

Changes in blood and milk lymphocyte sub-populations during acute and chronic phases of Staphylococcus aureus induced bovine mastitis

Staphylococcus aureus (S. aureus) often causes long-lasting chronic sub-clinical udder infections in dairy cows. To investigate if this can be due to a negative impact of S. aureus on lymphocytes important for the immune defence, alterations in proportions and expression intensity of CD4+, CD8+, WC1+, B and IL-2R+ lymphocytes was studied in blood and milk, as S. aureus mastitis developed from acute clinical to chronic sub-clinical form. Six healthy dairy cows were inoculated with S. aureus in one udder quarter per cow, and one quarter per cow acted as an uninfected control. Blood samples, and milk samples from infected and non-infected quarters were collected before infection and for five weeks after infection. All infected quarters developed acute clinical mastitis, of which five turned into chronic sub-clinical mastitis. In infected quarters, the proportions of all lymphocyte sub-sets, except WC1+ cells, differed in acute phase compared to pre-infection, while the dominant finding in the chronic phase was increased expression intensities per cell. An impact on blood lymphocytes and milk lymphocytes in non-infected quarters also occurred, mainly during the chronic phase. The most prominent finding was the increased proportion and expression of B-lymphocytes in blood, infected and non-infected quarters during chronic sub-clinical mastitis. As S. aureus can invade and survive intracellularly, a preferential stimulation of B-cells, suggesting development of a humoral response, may not be sufficient to eliminate intracellular bacteria, which could explain the persistence of the infection.     

Phenotypic and genotypic characterization of Staphylococcus aureus isolated from raw camel milk samples

In the present study 320 milk samples collected from 160 apparently healthy camels of three different locations in Sudan were investigated for the presence of Staphylococcus aureus resulting in the isolation of this bacterial pathogen from 28 milk samples from 24 camels. Twenty-five S. aureus were identified phenotypically and by PCR mediated amplification of species-specific genes or gene segments. Investigation of the S. aureus for toxinogenic potential revealed that three S. aureus strains were positive for the enterotoxin encoding gene sec and the genes seg, sei, sem, sen and seo, representing the egc gene cluster. In addition all 25 S. aureus were positive for the superantigen-like encoding gene ssl7 (set1). Partial sequencing of gene sec of the three S. aureus strains yielded an almost complete sequence identity to the sequence of the sec variant sec2. However, all three sec2 genes of the present study showed a deletion of one base causing a frame shift and a corresponding earlier stop codon.According to the present results, the raw camel milk collected from three locations in Sudan seems to be, at least at this stage, of minor importance as vector causing staphylococcal food poisoning.     

spa typing and enterotoxin gene profile of Staphylococcus aureus isolated from bovine raw milk in Korea

Staphylococcus aureus is a major etiological pathogen of bovine mastitis, which triggers significant economic losses in dairy herds worldwide. In this study, S. aureus strains isolated from the milk of cows suffering from mastitis in Korea were investigated by spa typing and staphylococcal enterotoxin (SE) gene profiling. Forty-four S. aureus strains were isolated from 26 farms in five provinces. All isolates grouped into five clusters and two singletons based on 14 spa types. Cluster 1 and 2 isolates comprised 38.6% and 36.4% of total isolates, respectively, which were distributed in more than four provinces. SE and SE-like toxin genes were detected in 34 (77.3%) isolates and the most frequently detected SE gene profile was seg, sei, selm, seln, and selo genes (16 isolates, 36.3%), which was comparable to one of the genomic islands, Type I νSaβ. This is a first report of spa types and the prevalence of the recently described SE and SE-like toxin genes among S. aureus isolates from bovine raw milk in Korea. Two predominant spa groups were distributed widely and recently described SE and SE-like toxin genes were detected frequently.     

Characterization of Aerococcus viridans isolated from milk samples from cows with mastitis and manure samples

Thirty-eight Aerococcus viridans isolates were obtained from milk from 478 cows with clinical mastitis in a farm during the periods between November 2011 and February 2012, and between December 2012 and March 2013. Additional isolates were obtained from processed manure (a mixture of composted manure, straw and hydrated lime) and bedding materials. The processed manure was later used to cover the floor of the stalls in barns as bedding materials. The temperatures recorded in the composted and processed manure were not as high as those generally observed during satisfactory composting. To reveal the association of A. viridans in manure-related products with intramammary infection in cows, isolates were characterized by their DNA fragment patterns as determined by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing. Isolates obtained from milk, processed manure and bedding materials had identical DNA fragment patterns. Antimicrobial susceptibilities were determined for 29 isolates from milk, processed manure and bedding materials. Of these, 26 (89.7%) were resistant to clindamycin, whereas virtually all the isolates were susceptible to 12 other antimicrobials including cefalosporins that have been used to treat bovine mastitis in Japan. In vitro, three A. viridans isolates from milk and an isolate from processed manure survived for 3 hr in Good’s buffer (pH 9) at high temperature (50°C). The results suggest that the processed manure and bedding materials in this farm were possible sources of A. viridans that caused infection in the cows with mastitis.     

Phylogenetic distribution of virulence genes in Escherichia coli isolated from bovine mastitis in Iran

One hundred and twenty seven Escherichia coli isolates from bovine mastitis were examined to detect the phylogenetic group/subgroups and a selection of virulence associated genes. Forty nine (38.58%) isolates belonged to group B1 the remaining isolates fell into four phylogenetic subgroups: A₀ (18.11%), A₁ (26.77%), D₁ (6.29%) and D₂ (10.23%). None of the isolates belonged to B2 group. Forty seven (37.00%) isolates were positive for at least one virulence gene, among them f17A was the most common gene, found in 20.47% of the isolates. Among the E. coli isolates, 11.81% had iucD, 9.44% f17c-A, 9.44% cnf2, 7.87% f17b-A, 6.29% afaD-8 and afaE-8, 3.14% f17d-A, 0.78% cnf1 and 0.78% clpG genes. All of the detected virulence genes were present alone or in combination with each other except clpG and f17d-A genes that were only found alone. None of the isolates contained the genes for F17a-A, intimin, P or S fimbriae.     

In vitro algaecide effect of sodium hypochlorite and iodine based antiseptics on Prototheca zopfii strains isolated from bovine milk

Prototheca zopfii has been considered one of the most important causes of environmental mastitis in Brazil. These algae are refractory to conventional therapy and cause great damage to the mammary gland. The present study evaluated the in vitro algaecide effect of sodium hypochlorite and iodine based antiseptics on 27 P. zopfii strains isolated from the milk of cattle. Low concentrations of sodium hypochlorite (0.0390625-0.15625%) and iodine (0.15625-0.625%) were effective against the isolates. These antiseptics may be recommended for hygiene routines, pre and postdipping and cauterization of bovine mammary glands infected by P. zopfii.     

Genetic diversity and methicillin resistance of Staphylococcus aureus originating from buffaloes with mastitis in Iran

The aims of the present study were to investigate the genetic diversity and methicillin resistance in S. aureus isolates recovered from mastitis-affected buffaloes. Five hundred seventy-eight milk samples were obtained from buffaloes with mastitis in three provinces, Iran. Ninety-one of the 578 tested samples contained S. aureus (15.74%), in two cases were methicillin resistant S. aureus (MRSA). Isolates were typed by spa typing, followed by MLST on some representative isolates and SCCmec typing for MRSA strains. The presence of genes encoding Panton–Valentine leukocidin (PVL) was also tested by PCR. Eight spa types were identified, with t3576 (n = 18), t7311 (n = 18) and t937 (n = 17) were the most common, followed by t304 (n = 11), t7308 (n = 9), t521 (n = 7), t267 (n = 6), and t527 (n = 5). MLST revealed four different sequence types (STs) including ST97 (related to t521 and t527 spa types), ST352 (related to t267), ST291 (related to t304 and t937) and ST522 (related to t7338, t7311 and t3576). Two MRSA were identified as t304-ST291-SCCmecIV and t7311-ST522-SCCmecIV. No PVL-positive S. aureus were found. A significant difference in geographical distribution of genotypes was observed, with some types being prevalent in all studied provinces (P < 0.001). The results demonstrated genetic diversity among the S. aureus strains involved in mastitis in buffaloes. This study also provides evidence of the presence of MRSA belonging to genotypes which have been earlier reported in human infections, emphasizing the need for their epidemiological monitoring.     

Prevalence of thermophilic Campylobacter species in Swedish dogs and characterization of C. jejuni isolates

Background

The aims of this study were to investigate the prevalence of Campylobacter species in Swedish dogs, to identify the species of the Campylobacter isolates and to genotype the C. jejuni isolates. Young and healthy dogs were targeted and the sampling was performed at 11 veterinary clinics throughout Sweden from October 2011 to October 2012. Faecal swab samples were collected and sent to the laboratory at the National Veterinary Institute (SVA) for isolation of Campylobacter, speciation and genotyping.

Results

Campylobacter spp. were isolated from 67 of the 180 sampled dogs which yields an overall prevalence of 37%. The most prevalent species of Campylobacter among the participating dogs was C. upsaliensis with 52 of the 67 identified isolates. A lower prevalence was observed for C. jejuni with seven identified isolates and one isolate was identified as C. helveticus. Multi-locus sequence typing (MLST) was carried out on the seven C. jejuni isolates and all sequence types that were found are also commonly found in humans. The dogs were divided into three age groups; 1) under 12 months, 2) 12 to 23 months and 3) 24 months and older. The highest prevalence was found in the two younger age groups. Dogs shedding C. jejuni were between 3–12 months of age while dogs shedding C. upsaliensis were found in all ages.

Conclusions

The present investigation finds that Campylobacter spp. known to cause campylobacteriosis in humans are present in Swedish dogs. The results suggest an age predisposition where dogs under 2 years of age are more likely to shed Campylobacter spp. than older dogs. The most commonly isolated species was C. upsaliensis followed by C. jejuni, which was only detected in dogs up to 12 months of age. All C. jejuni isolates identified in the present study were of the same MLST types that have previously been described both in humans and in animals. The awareness of the Campylobacter risk of healthy young dogs may be an important way to reduce the transmission from dogs to infants, young children and immunocompromised adults.     

Expression of cytokines and respiratory burst activity of milk cells in response to Azadirachta indica during bovine mastitis

The immuno therapeutic potential of hydro-methanolic extract of Azadirachta indica (A. indica) was studied during bovine clinical mastitis (CM). The somatic cell count (SCC), total bacterial count (TBC), milk differential leukocyte count (DLC), hydrogen peroxide (H₂O₂), superoxide anion (O₂ ⁻) production and interleukin- 2 (IL-2) and gamma interferon (IFN-γ) cytokines expression were studied before and after intramammary infusion of A. indica extract in diseased cows. The results revealed that A. indica treatment significantly (P < 0.05) decreased the SCC, TBC, milk neutrophil percent and significantly (P < 0.05) enhanced milk lymphocyte percent, H₂O₂ and O₂ ⁻ production by milk cells. The IL-2 and IFN-γ were expressed in normal healthy cows and diseased cows after A. indica treatment, whereas both the cytokines could not be expressed in cows treated with antibiotic and in untreated diseased cows. The results of the present study indicated anti inflammatory, antibacterial and immunomodulatory potential of the herb, these activities could be due to the presence of bioactive principle in the extract. This is a preliminary trial indicated beneficial effect of the herb against bovine mastitis it can be developed as an alternative therapy where the use of antibiotics is normally restricted.     

Prevalence of bacterial genotypes and outcome of bovine clinical mastitis due to Streptococcus dysgalactiae and Streptococcus uberis

Background

Streptococcus dysgalactiae and Streptococcus uberis are common causes of clinical mastitis (CM) in dairy cows. In the present study genotype variation of S. dysgalactiae and S. uberis was investigated, as well as the influence of bacterial species, or genotype within species, on the outcome of veterinary-treated CM (VTCM). Isolates of S. dysgalactiae (n = 132) and S. uberis (n = 97) were genotyped using pulsed-field gel electrophoresis. Identical banding patterns were called pulsotypes. Outcome measurements used were cow composite SCC, milk yield, additional registered VTCMs and culling rate during a four-month follow-up period.

Results

In total, 71 S. dysgalactiae pulsotypes were identified. Nineteen of the pulsotypes were isolated from more than one herd; the remaining pulsotypes were only found once each in the material. All S. uberis isolates were of different pulsotypes. During the follow-up period, the SCC of S. dysgalactiae-cows was significantly lower than the SCC of S. uberis-cows (P <0.05). Median SCC of S. dysgalactiae-cows was 71 500 cells/ml and of S. uberis-cows 108 000 cells/ml. No other differences in outcome parameters could be identified between species or genotypes.

Conclusions

Identical S. dysgalactiae genotypes were isolated from more than one herd, suggesting some spread of this pathogen between Swedish dairy herds. The genetic variation among S. uberis isolates was substantial, and we found no evidence of spread of this pathogen between herds. The milk SCC was lower during the follow-up period if S. dysgalactiae rather than S. uberis was isolated from the case, indicating differences in treatment response between bacterial species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13028-014-0080-0) contains supplementary material, which is available to authorized users.     

PCR-based detection of genes encoding virulence determinants in Staphylococcus aureus from bovine subclinical mastitis cases

The present study was carried out to genotypically characterize Staphylococcus aureus (S. aureus) isolated from bovine mastitis cases. A total of 37 strains of S. aureus were isolated during processing of 552 milk samples from 140 cows. The S. aureus strains were characterized phenotypically, and were further characterized genotypically by polymerase chain reaction using oligonucleotide primers that amplified genes encoding coagulase (coa), clumping factor (clfA), thermonuclease (nuc), enterotoxin A (entA), and the gene segments encoding the immunoglobulin G binding region and the X region of protein A gene spa. All of the isolates yielded an amplicon with a size of approximately 1,042 bp of the clfA gene. The amplification of the polymorphic spa gene segment encoding the immunoglobulin G binding region was observed in 34 isolates and X-region binding was detected in 26 isolates. Amplification of the coa gene yielded three different products in 20, 10, and 7 isolates. The amplification of the thermonuclease gene, nuc, was observed in 36 out of 37 isolates. All of the samples were negative for the entA gene. The phenotypic and genotypic findings of the present strategies might provide an understanding of the distribution of the prevalent S. aureus clones among bovine mastitis isolates, and might aid in the development of steps to control S. aureus infections in dairy herds.     

ermB-mediated erythromycin resistance in Streptococcus uberis from bovine mastitis

The ermB gene was identified in 111 erythromycin resistant isolates of Streptococcus uberis from cases of bovine mastitis associated either with a constitutive (47/111) or an inducible (64/111) phenotype, as well as a phenotypic resistance to all macrolides tested. Resistance to lincosamides was identified in 14 other isolates of S. uberis from bovine mastitis cases and was mainly mediated by the linB gene; resistance conferred by a combination of two genes (linB–lnuD, ermB–linB) was also detected.     

Occurrence of methicillin-resistant Staphylococcus aureus in rats living on pig farms

In The Netherlands, MRSA ST398 has emerged in hospitals and human carriers have been associated with exposure to pigs and cattle. High prevalences of MRSA ST398 in pigs and pig farmers have been determined and the transmission routes of MRSA on pig farms need to be elucidated. In the south of the Netherlands, in recent years, the black rat (Rattus rattus) has emerged as a prominent rodent on livestock farms. From March till May 2008, a survey on MRSA in rats living on livestock farms in the south of The Netherlands and the north of Belgium was conducted. In total, 40 black rats (R. rattus) and 3 brown rats (Rattus norvegicus) were collected on 12 farms including five pig farms, five poultry farms, one mixed pig and veal farm and one goat farm. MRSA ST398 was detected in black rats captured at two of the five pig farms as well as in a black rat living on the mixed pig and veal farm. From one black rat captured at another pig farm MRSA ST 97 was isolated. Considering the behaviour of rats on livestock farms, it is concluded that rats might play a role in the spread and persistence of MRSA on pig farms.     

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.