Antimicrobial susceptibility of coagulase-positive staphylococci isolated from Louisiana dogs

Disk diffusion susceptibility tests were done on 1,178 clinical strains of coagulase-positive staphylococci (CPS) isolated from dogs during a 7-year period. Relative decreases of 7% to 33% were found in the percentages of CPS sensitive to 8 antimicrobics. Relative percentages of CPS sensitive to 9 other antimicrobics were increased or decreased less than 5%. Sensitivity to the beta-lactam antibiotics showed the least relative change. Regression analysis demonstrated that the greatest change in percentage sensitivity of CPS occurred to gentamicin and cephalothin and the least change occurred to penicillin and ampicillin. Recent canine clinical isolates of CPS, specifically identified as Staphylococcus intermedius (n = 109), were uniformly sensitive to novobiocin, amikacin, tobramycin, spectinomycin, and amoxicillin-clavulanic acid. Twenty-two isolates were also sensitive to 17 other antimicrobics. Eighty-seven isolates were resistant to 1 or more antimicrobics tested. Resistance was most common to sulfonamides, penicillin G, ampicillin, tetracycline, and streptomycin. Differences in susceptibility results between S intermedius and unspecified CPS were not statistically significant.     

Antimicrobial susceptibility of coagulase-negative staphylococci isolated from bovine milk samples

The aim of this study was to examine whether antimicrobial resistance profiles of coagulase-negative Staphylococcus (CNS) species isolated from milk of dairy cows differed between bacterial species, and to compare results obtained by phenotypic and genotypic profiling of resistance to penicillin, oxacillin and macrolide-lincosamide (ML) antibiotics. Of 170 CNS isolates, 83 (48.8%) were phenotypically susceptible to all antimicrobial agents tested in minimum inhibitory concentration (MIC) assays, 40.6% expressed resistance to a single compound or a single class of compounds, and 10.6% to multiple drug classes. Nine percent, 68%, 19%, 4% and 1% of isolates were negative for all resistance genes tested by PCR or positive for one, two, three or four resistance genes, respectively. Phenotypic resistance and detection of resistance genes other than blaZ were relatively rare in Staphylococcus chromogenes, which was the most common CNS species (36% of 170 genotypically identified isolates). In Staphylococcus epidermidis, which was the second most common CNS species (14% of isolates), phenotypic penicillin resistance was significantly more common than in other CNS species. Almost half of the S. epidermidis isolates carried multiple resistance genes and 30% carried the methicillin resistance gene mecA. Survival analysis using MIC values showed significant associations between phenotypic and genotypic resistance profiles. We conclude that CNS species from bovine milk differ significantly in phenotypic and genotypic antimicrobial resistance profiles, which has implications for treatment and management decisions.     

Coagulase negative staphylococci isolated from cow milk

The species composition was determined in the set of 52 randomly selected strains of coagulase-negative staphylococci, which were isolated from the milk of dairy cows in 1989. Of this set of strains, the following species were identified: Staphylococcus hyicus subsp. chromogenes (26.9% strains of the set), S. hyicus subsp. hyicus (10.3%), S. xylosus (19.3%), S. saprophyticus (11.5%), S. warneri (9.6%), S. haemolyticus (9.6%), S. hominis (3.8%). Attention is drawn to the increasing occurrence and significance of coagulase-negative staphylococci from the point of view of mastitis in dairy cows.     

Phage typing coagulase-positive staphylococci from rooks and gulls

Phage typing was performed on 86 strains of Staphylococcus aureus and 25 strains of Staphylococcus intermedius from rooks and gulls with human, bovine, chicken and canine phages. Eighty per cent of the S aureus strains and 64 per cent of the S intermedius strains were typable. The S aureus biotype D strains of rook origin were specifically lysed at routine test dilution (RTD) by chicken phages from groups I or I + IV, by human phages belonging to groups I and M, and partly by canine phage 58. The other rook and gull S aureus strains did not show characteristic phage patterns. The S intermedius strains isolated from both species of birds could be typed only with canine phages and this correlated with their classification into biotypes. All the biotype 1 strains tested but only two of 12 biotype 2 strains were lysed with canine phages at RTD.     

Identification and characterization of staphylococci isolated from cats

Staphylococcus simulans was found to be the most common staphylococcal species present on the healthy skin and in the nares of cats. S. aureus was the most frequent Staphylococcus species in lesions. Most of the S. aureus strains showed the characteristics of the human ecovar. Other strains isolated formed a heterogenic collection in which not less than 13 species were represented. One of these, S. epidermidis, was almost exclusively associated with lesions. It was concluded that coagulase-positive staphylococci are not endogenous to cats. Staphylococci from other sources, most frequently from man, are often associated with lesions in these animals.     

Identification of clumping-factor-negative staphylococci isolated from cows' udders

Identification to species level was attempted on a collection of 954 cultures of catalase-positive, clumping-factor- and beta-haemolysin-negative Gram-positive cocci isolated from teats and milk of cows. Eighty-seven per cent of the strains were identified as Staphylococcus xylosus, S epidermidis, S sciuri, S haemolyticus, S hyicus subsp hyicus and chromogenes, S simulans and S cohnii. Nine per cent of the collection belonged to another group which could not be identified with any of the known Staphylococcus species. Many of the strains of this group and also part of the S epidermidis and S hyicus subsp chromogenes strains examined showed various degrees of growth enhancement on certain media when fatty substances were added. Only nine strains were classified as Micrococcus. A scheme for the identification of coagulase-negative staphylococci from cows' milk is proposed.     

Classification of coagulase-negative staphylococci isolated from bovine clinical and subclinical mastitis

One hundred and forty eight strains of coagulase-negative staphylococci (CNS) from bovine clinical and subclinical mastitis were classified by conventional biochemical testing. Staphylococcus simulans was the most frequently isolated species. The distribution of CNS species in the two groups was similar regardless of whether the cow suffered from clinical or subclinical mastitis. There was no significant difference between the grades of severity of the clinical mastitis associated with the various CNS. The small difference in pathogenicity observed between species in this study, and the similarity of distribution in the various species of clinical and subclinical mastitis could indicate that the species per se is of minor importance in the development of mastitis.     

Biochemical properties and differentiation of coagulase-positive staphylococci from rooks and gulls

Coagulase-positive staphylococci were found in the throats of 46 rooks (69 per cent) and 47 gulls (21 per cent) out of totals of 67 and 229 birds, respectively. Of 111 strains isolated from throat swabs 86 (77.5 per cent) were classified as Staphylococcus aureus and 25 strains (22.5 per cent) as Staphylococcus intermedius. Of the S aureus strains 82 per cent from rooks and 50 per cent from gulls were biotyped. Most of them were identified as biotypes D and B, only a few as biotype A, and none as biotype C. Moreover, among the 24 S intermedius strains (96 per cent) biotypes 1 and 2 could be differentiated according to the type of growth on crystal violet agar and their ability to produce acetoin and acid from maltose, mannitol and trehalose.     

Occurrence and characterization of methicillin-resistant staphylococci from bovine mastitis milk samples in Finland

Background

Methicillin-resistant staphylococci (MRS) are increasingly being isolated in bovine mastitis. The aim of our study was to evaluate the occurrence of MRS in Finnish mastitis milk samples and characterize the MRS isolates using molecular methods.

Results

Methicillin-resistant S. aureus (MRSA) was a rare finding in bovine mastitis in Finland. Only two out of 135 (1.5%) S. aureus isolates were positive for mec genes. One of these carried mecA and was of spa type t172, SCCmec type IV and ST375, and the other harboured mecC, being spa type t3256, and ST130. MRSA ST375 is common among human MRSA isolates in Finland, but this is the first report in the country of bovine mecC MRSA. In coagulase-negative staphylococci (CoNS) originating from bovine mastitis, methicillin resistance was more common. In the two CoNS collections studied, 5.2% (17/324) and 1.8% (2/110) of the isolates were mecA positive. Eighteen of these were methicillin-resistant S. epidermidis (MRSE), which were divided into 6 separate PFGE clusters. One pulsotype was detected in different parts of the country, indicating clonal spread. Most MRSE (13/18) were of SCCmec type IV, one was of type V and four were non-typeable. Comparison with a human staphylococcal database indicated that bovine MRSE strains were not closely related to human MRSE isolates.

Conclusions

The occurrence of MRS, especially MRSA, in bovine mastitis in Finland was low. Most methicillin-resistant bovine CoNS are MRSE, and we found evidence of a bovine MRSE strain that may spread clonally. This is the first report of a Finnish bovine isolate of MRSA_mecC ST130. The study provides a baseline for further MRS monitoring.     

Antibiotic susceptibility of methicillin-resistant and methicillin-susceptible coagulase-negative staphylococci isolated from bovine mastitis

The aim of the present study was to evaluate the antibiotic susceptibility of methicillin-susceptible (MS) and methicillin-resistant (MR) coagulase-negative Staphylococcus (CNS) strains isolated from milk of cows with mastitis. The study was conducted on 100 CNS strains (20 MRCNS and 80 MSCNS) isolated from milk samples of 86 cows from the Lublin (Poland) region farms. Antibiotic susceptibility of microorganisms was evaluated using the disc-diffusion method on the Mueller-Hinton agar according to the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS). The highest efficacy against MSCNS was demonstrated for cephalosporin antibiotics, i.e. cefacetril (91.3%), ceftiofur (67.5%), cefoperazone (66.3%) and cephalexin (60.0% of susceptible MSCNS strains). Moreover, a high percentage of vancomycin-susceptible strains was demonstrated (83.8%). The activity of combination of amoxicillin with clavulanic acid and gentamicin was found weaker (63.8% and 61.3% of susceptible strains, respectively). About 50.0% of MSCNS were susceptible to erythromycin, enrofloxacine and amoxicillin. A large proportion of CNS was resistant to neomycin, penicillin, tetracycline, streptomycin, lincomycin and ampicillin (28.8%, 30.0%, 31.3%, 31.3%, 33.8% and 33.8% of susceptible strains, respectively). The highest percentage of MRCNS was susceptible to vancomycin (75.0%), erythromycin (65.0%) and streptomycin (50.0%). Their susceptibility to enrofloxacine (35.0%) as well as gentamicin and tetracycline (30.0%) was markedly lower. The lowest activity was found for lincomycin and neomycin (20.0% of susceptible MRCNS strains, each).     

Antimicrobial activity of marine sponges against coagulase-negative staphylococci isolated from bovine mastitis

Bovine mastitis remains worldwide a major challenge for the dairy industry despite the widespread implementation of control strategies. The increasing number of coagulase-negative staphylococci (CNS) causing mastitis and of bacteria resistant to conventional antibiotics has become a serious problem in recent years. Marine sponges are a rich source of bioactive compounds, and many species can be useful for the development of new antimicrobial drugs. In the present study, 49 CNS strains were isolated from bovine mastitis cases from 21 different dairy herds kept at farms in Southeast Brazil. Strains were analyzed for antimicrobial susceptibility and mecA gene detection. Fifty-nine percent of the CNS strains were resistant to at least one of the drugs tested and 12.2% were classified as multiresistant. Three strains carried the mecA gene, confering resistance to the beta-lactamic antibiotics. In addition, the CNS strains were submitted to in vitro screening for antimicrobial activities of extracts from marine sponges. Extracts from the sponge species Cinachyrella sp., Haliclona sp. and Petromica citrina showed antibacterial activity against 61% of the CNS strains, including strains resistant to conventional antibiotics. Extracts from P. citrina showed the largest spectrum of inhibitory activity. The aqueous extract inhibited 51% of the CNS strains and presented a bactericidal effect over susceptible and multiresistant-bacteria at a minimal inhibitory concentration of 1.024μg/ml. This study shows the potential of marine sponges as new sources of antibiotics and disinfectants for the control of CNS involved in bovine mastitis.     

Comparison of penicillin-G susceptibility testing methods of staphylococci isolated from bovine mastitis.

Penicillin-G susceptibility was analyzed on forty staphylococcal strains isolated from mastitic bovine quarters (29 coagulase positive and 11 coagulase negative) by the standard Kirby-Bauer agar diffusion method, the epsilon-Test, the Vetmic, turbidimetric MIC analysis in Iso-Sensitest Broth (ISB) and whey. Penicillinase production was tested. Parallel susceptibility tests were carried out in whole milk, whey and ISB using resazurin and triphenyltetrazolium as the indicators of bacterial activity. The traditional susceptibility testing methods (radial agar diffusion, MIC in broth culture) showed good agreement with each other and confirmed that the tests can be used interchangeably with the current breakpoint values (0.25 micrograms/ml and phi 26 mm). The tests carried out in whey showed good correlation with the traditional tests. However, the susceptibility testings in milk resulted in additional variation. Therefore, traditional susceptibility tests of Penicillin-G in artificial media are limited in estimation of bacterial susceptibility when they grow in whole milk. The relevance of this observation regarding mastitis therapy is discussed.