Temporal study of staphylococcal species on healthy dogs.

During a 1-year period, specimens were obtained monthly from 5 hair coat and 7 mucous membrane sites of 11 healthy dogs. Among 804 isolates of staphylococci, 13 species were identified. Staphylococcus intermedius was the most frequently isolated (40.2% of total isolates) coagulase-positive species, and S xylosus was the most frequently isolated (17.3%) coagulase-negative species. Moreover, S intermedius was the most frequently isolated species from the 12 sites evaluated and was isolated persistently from 8 of the 9 dogs that completed the 1-year study. On the basis of a commercial identification system, 14 profile numbers were identified for isolates of S intermedius. However, 2 profile numbers accounted for a majority (70.9%) of the isolates. Specific S intermedius biotypes identified on the basis of hemolysis, coagulase production, beta-lactamase activity, and antimicrobial susceptibility patterns were found repeatedly in 3 dogs. Seemingly, S intermedius was a resident of the normal bacterial microflora of these dogs; however, the inability to isolate S intermedius from 1 dog during the study year indicated that not all dogs harbor S intermedius as a resident microorganism.

Protein A in Staphylococcus intermedius isolates from dogs and cats.

The presence and quantity of extracellular and cell-bound protein A of Staphylococcus intermedius isolates from dogs and cats were determined, using an enzyme-linked immunoglobulin-binding assay. Horseradish peroxidase-conjugated rabbit anti-bovine immunoglobulin G purified by affinity chromatography was reacted with whole cell and supernatant fractions of S intermedius (n = 139), a protein A-producing strain of S aureus, and a protein A-deficient strain of S epidermidis. Extracellular protein A was found in 118 (84.9%) of 139 isolates of S intermedius. Most (69/118; 58.5%) of these isolates produced greater than 0.2 micrograms of extracellular protein A/ml. Cell-bound protein A was found in 6 (4.3%) of 139 isolates. Only 1 of these isolates contained cell-bound protein A exclusively. The other 5 isolates produced significantly greater amounts of extracellular protein A than cell-bound protein A. Additionally, greater than 96% of extracellular protein A could be removed from supernatants by adsorption with agarose gel containing immunoglobulin G.

Distribution of staphylococcal species on clinically healthy cats.

Among 827 isolates derived from 113 clinically healthy cats, 12 species of staphylococci were identified. Staphylococci were isolated from each cat and from 54.9% of the anatomic sites evaluated. A mode of 6 (range = 2 to 11) of the 11 anatomic sites evaluated per cat yielded staphylococci. A mode of 8 (range = 2 to 12) isolates were found per cat. Staphylococcus simulans was the most isolated (43.9% of total) coagulase-negative species. Moreover, S simulans was the most isolated species from each of the 11 sites evaluated and, except for the mouth and haircoat, comprised greater than 50% of the isolates from each site. Staphylococcus intermedius was the most isolated (13.5% of the total) coagulase-positive species. Three other species (S epidermidis, S xylosus, and S aureus) comprised 32.2% of the isolates, and 7 species (S haemolyticus, S hominis, S hyicus, S capitis, S warneri, and S saprophyticus) comprised 10.4% of the isolates. Six species (S intermedius [96 of 112 isolates], S haemolyticus [20 of 22], S sciuri [17 of 18], S warneri [10 of 13], S hyicus [10 of 10], and S capitis [7 of 8]) were isolated primarily from household cats. Only 1 species, S xylosus (75 of 87), was isolated primarily from cattery cats. Haircoat specimens (n = 452) yielded 508 isolates (61.4% of the total) distributed among all 12 staphylococcal species and included greater than 50% of the isolates of all species other than S simulans and S sciuri. A more heterogeneous population of staphylococci was isolated from household cats than was isolated from cattery cats.

Comparison of coagulase test methods for identification of Staphylococcus intermedius from dogs.

Staphylococcus intermedius isolates from dogs were tested for coagulase activity by 6 commercial methods and by conventional methods, using rabbit and dog plasma. When compared with the conventional tube method using rabbit plasma, none of the 6 commercial methods was suitable for identification of S intermedius, although the 6 tests performed well using strains of S aureus. Use of rabbit plasma identified more S intermedius isolates than did use of dog plasma.

Detection of beta-lactamase produced by Staphylococcus intermedius.

One iodometric, 2 chromogenic, and 3 acidometric methods were compared for the detection of beta-lactamase produced by Staphylococcus intermedius (n = 105) isolated from dogs. Of 575 tests performed, using the 6 methods evaluated, 316 (55.0%) were positive for beta-lactamase production. The iodometric method was the reference method. With the exception of a high correlation (r = 0.962) between 1 acidometric method and 1 chromogenic method, the 5 commercial methods had correlation coefficients less than 0.900 when comparisons were made among them. The 6 methods were in agreement for 69 (65.7%) of the isolates. Based on the findings of this study, an inexpensive, laboratory-prepared, paper strip iodometric method was as reliable as 5 commercial methods for beta-lactamase detection and is recommended for routine use in clinical laboratories.

Comparative evaluation of a commercial microdilution method and a conventional disk diffusion method for determination of antibiograms of gram-positive cocci.

A commercial broth microdilution system for testing the antimicrobial susceptibility of gram-positive cocci was compared with the standardized disk agar-diffusion method by testing 254 clinical strains of staphylococci and streptococci using both methods. A total of 2,794 parallel determinations were made with 92.3% complete agreement between the 2 methods; of the discrepancies encountered, 3.0% were minor, 2.5% were major, and 2.1% were very major. The results indicate that the commercial microdilution system may provide a reliable quantitative method for antimicrobial susceptibility testing of clinical isolates from animals.

Effect of beta-lactamase of Staphylococcus intermedius on disk agar diffusion susceptibility tests.

Clinical strains of canine Staphylococcus intermedius (n = 120) were tested for susceptibility to beta-lactam antimicrobics (n = 6) by the standardized disk agar diffusion method and for beta-lactamase (BL) production. Significant differences between susceptibilities for BL producing (n = 68) and non-producing (n = 52) strains were found for penicillin G and ampicillin. Zone sizes of BL producing strains were significantly smaller than those of non-producers for penicillin G, ampicillin, cephalothin, carbenicillin and amoxicillin-clavulanic acid but not for methicillin. However, all strains were sensitive to cephalothin and amoxicillin-clavulanic acid; only one strain was resistant to methicillin; and one strain was intermediate in susceptibility to carbenicillin. Although 62 (52%) strains were sensitive to penicillin G and ampicillin based on established zone size interpretive criteria, 15 (24%) of these strains produced BL. Zone size measurements obtained with beta-lactam antimicrobics that are highly susceptible to inactivation by BL are not reliable and should be disregarded for canine S. intermedius which produce BL.

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.

Species of Staphylococcus isolated from animal infections.

One hundred randomly selected clinical strains of staphylococci were identified by species using a commercial micromethod system. Eight species of staphylococci were identified. Staphylococcus intermedius was the most frequent (n = 74) species identified and accounted for 70/74 (94.6%) of the coagulase-positive strains and 70/79 (88.6%) of the total isolates from dogs. Other species identified, in order of their frequency, included S. epidermidis (8), S. aureus (7), S. simulans (4), S. sciuri (2), S. xylosus (2), S. hyicus (2) and S. saprophyticus (1). These results show that at least 8 different species of staphylococci can be recovered from animal infections and that coagulase-positive species such as S. intermedius may be more common than S. aureus. The relative significance of these other species in animal infections needs to be assessed.