Rapid and reliable identification of Staphylococcus aureus by a latex agglutination test

Comparative evaluation of a latex test for the identification of Staphylococcus aureus

A rapid latex agglutination test, Staphaurex, was tested for its ability to identify Staphylococcus aureus using 72 reference strains and 785 clinical isolates of the family Micrococcaceae. All reference strains of Staphylococcus aureus were Staphaurex-positive. Non-Staphylococcus aureus reference strains were negative. Using clinical strains, the results of the Staphaurex test were compared with the results of other tests commonly used to identify Staphylococcus aureus. A total of 393 clinical isolates were classified as Staphylococcus aureus. The Staphaurex, slide coagulase, tube coagulase/human plasma and tube coagulase/rabbit plasma tests correctly identified 98%, 93.6%, 93.6% and 97.5% of the Staphylococcus aureus strains, respectively. The performance of the Staphaurex test, in terms of sensitivity and specificity, was significantly better than the slide coagulase test. It was as sensitive and almost as specific as the tube coagulase rabbit test and more sensitive than the tube coagulase human test.

Late-onset neonatal sepsis due to multiply-resistant coagulase-negative staphylococci

A cluster of septic episodes that were caused by coagulase-negative staphylococci occurred in eight patients, over a six-month period from August 1, 1984 to January 31, 1985, in a Brisbane neonatal intensive-care unit where sepsis which was due to these organisms previously was uncommon. The organisms were universally-resistant to tobramycin (the aminoglycoside agent that was used at that time) and were variably-resistant to gentamicin, flucloxacillin and cephalothin. All organisms were sensitive to netilmicin, vancomycin, fusidic acid and rifampicin. The affected infants were all of 32 weeks' or less gestation and most of them weighed less than 1500 g at birth. All neonates had been ventilated artificially and had had long intravascular lines. Two infants had ventriculoperitoneal shunts that had been infected with coagulase-negative staphylococci--a potentially-important problem that has not been noted in premature infants in previous reports. Our experience demonstrates that it is important to consider the patterns of resistance to aminoglycoside as well as to beta-lactam antibiotic agents for the empirical therapy of septic episodes and for neurosurgical prophylaxis in nurseries where coagulase-negative staphylococci are emerging as common nosocomial pathogens.

Efficacies of rapid agglutination tests for identification of methicillin-resistant staphylococcal strains as Staphylococcus aureus

Four commercially available rapid agglutination tests for the identification of Staphylococcus aureus were compared with the tube coagulase test for the identification of 300 methicillin-resistant isolates of staphylococci. Isolates tested included 207 methicillin-resistant S. aureus and 93 coagulase-negative staphylococci, collected from five medical centers. Strain variability was documented by phage typing and antimicrobial susceptibility patterns. Results of rapid identification tests ranged between 82 and 86% sensitivity, significantly poorer than the 98% sensitivity which the tube coagulase test provided.

Particle agglutination assays for rapid detection of fibronectin, fibrinogen, and collagen receptors on Staphylococcus aureus

Latex beads (0.8-micron diameter; Difco Laboratories) were coated with fibronectin, fibrinogen, collagen type I, or denatured collagen (gelatin) and evaluated in a particle agglutination assay (PAA) for the rapid detection of fibronectin, fibrinogen, or collagen binding to Staphylococcus aureus. These assays were compared with a commercial test for detecting the binding of fibrinogen and immunoglobulin G (Staphaurex). Bacterial cells (approximately 10(10) cells per ml) suspended in 0.02 M potassium phosphate buffer (pH 6.8) caused the clumping of standard fibronectin, collagen, gelatin, and fibrinogen latex suspensions within 2 min on glass slides. The test results were scored semiquantitatively from strongly positive ( ) to weakly positive (+) and negative (-) reactions. The negative PAA reactions corresponded to a median value of 11.5% relative to the binding of 125I-labeled protein to strain Cowan 1, indicating the high sensitivity of the test. The reactions with fibronectin and fibrinogen latex suspensions and with Staphaurex were optimal for cells grown on tryptic soy and brain heart infusion broth media. Blood agar was optimal for reactions with collagen and gelatin latex suspensions. Media containing high salts (mannitol salt agar and staphylococcus medium 110) enhanced the tendency of cells to autoaggregate. These assays were also clinically evaluated on 187 S. aureus isolates. The PAA reagents were stable, and the assays were highly specific, sensitive, and reproducible, thus making PAA suitable for the rapid screening of the binding of various bacterial pathogens to serum and connective-tissue proteins.

Performance of four slide agglutination methods for identification of Staphylococcus aureus when testing methicillin-resistant staphylococci

Four commercially available slide agglutination systems for identifying Staphylococcus aureus were compared with the conventional slide (clumping factor) and tube coagulase tests. The systems evaluated included Bacto Staph Latex (Difco Laboratories, Detroit, Mich.), Staphyloslide (BBL Microbiology Systems, Cockeysville, Md.), Mini ID Accu-Staph (Carr-Scarborough Microbiologicals, Inc., Decatur, Ga.), and Staphaurex (Wellcome Diagnostics, Research Triangle Park, N.C.). A total of 338 clinical isolates, including methicillin-resistant S. aureus (n = 149), methicillin-susceptible S. aureus (n = 78), methicillin-resistant, coagulase-negative staphylococci (n = 45), and methicillin-susceptible, coagulase-negative staphylococci (n = 66), were tested by each method. The slide test for clumping factor, the 4-h tube coagulase test, Bacto Staph Latex, Staphyloslide, Mini ID Accu-Staph, and Staphaurex detected 212 (93.4%), 218 (96%), 223 (98.2%), 223 (98.2%), 221 (97.4%), and 224 (98.7%) of the S. aureus (44% methicillin-resistant) isolates, respectively. There were no false-positive results with any of the methods when the 111 strains of coagulase-negative staphylococci were tested. The results of this evaluation suggest that the four slide identification methods tested can provide rapid and accurate identification of methicillin-resistant S. aureus strains.

Reliability of latex agglutination tests for identification of Staphylococcus aureus resistant to oxacillin

Commercial latex agglutination tests (LATs) for the simultaneous detection of clumping factor and protein A are gaining increased acceptance as a means of identifying Staphylococcus aureus. We evaluated two LATs (Accu-Staph; Carr-Scarborough, Decatur, Ga.; Staphaurex; Wellcome, Dartford, England) with particular emphasis on their ability to correctly identify oxacillin-resistant S. aureus. We tested 59 oxacillin-resistant S. aureus, 136 oxacillin-susceptible S. aureus, and 92 coagulase-negative staphylococcal strains with the two LATs and with thermonuclease, slide clumping factor, tube coagulase, and protein A hemagglutination tests. Clumping factor and protein A were present in 96.9 and 82.1% of our S. aureus strains, respectively. Accu-Staph correctly identified 92.8% and Staphaurex correctly identified 91.3% of S. aureus strains. No significant difference in LAT positivity rates, presence of clumping factor, or presence of protein A was found between oxacillin-resistant and -susceptible S. aureus. Overall, there were 31 false-negative LATs for 20 S. aureus strains, 14 with Accu-Staph and 17 with Staphaurex. Ninety-five percent of these strains possessed either clumping factor or protein A or both when these factors were determined independently. There were five false-positive LATs for four strains of coagulase-negative staphylococci (three Staphylococcus epidermidis and one Staphylococcus warneri), four with Accu-Staph and one with Staphaurex. Clumping factor was present in one S. warneri strain. Thus, the specificities of Accu-Staph, Staphaurex, and the clumping factor test were 95.6, 98.9, and 98.9%, respectively. Our results indicated that LATs identify oxacillin-resistant and -susceptible S. aureus equally well; however, they offer no greater sensitivity or specificity than the clumping factor test for identification of S. aureus.

Failure of rapid agglutination methods to detect oxacillin-resistant Staphylococcus aureus

Although a latex agglutination test (StaphAurex) and a hemagglutination test (Staphyloslide) correctly identified all strains of Staphylococcus aureus that were susceptible or had intermediate susceptibility to oxacillin, 17 of 73 (23%) and 18 of 73 (25%) strains of oxacillin-resistant S. aureus were not identified by StaphAurex and Staphyloslide, respectively. All strains not detected were resistant to trimethoprim-sulfamethoxazole and rifampin.

Comparative evaluation of identification systems for testing methicillin-resistant strains of Staphylococcus aureus

Several commercial systems are available to distinguish between Staphylococcus aureus and the coagulase-negative species of the Micrococcaceae family. Four latex agglutination systems (Accu-Staph, SeroSTAT, Staphaurex, and Staphylatex) and two hemagglutination systems (Hemastaph and Staphyloslide) were compared for their performance in the rapid identification of 232 isolates of staphylococci, including 114 of methicillin-resistant S. aureus. Accu-Staph, Staphaurex, and Staphyloslide correctly identified 100% of the methicillin-resistant S. aureus isolates; Hemastaph and Staphylatex, 99.1%; and SeroSTAT, 94.7%. Most reactions were easy to interpret, although 15% of the SeroSTAT reactions were weak. Autoagglutination occurred only with isolates of coagulase-negative staphylococci. False-positive reactions were rare and occurred only with systems which did not detect autoagglutination. Five of these six systems appear to be adequate for the rapid identification of S. aureus, including methicillin-resistant isolates.

Comparison of a yellow latex reagent with other agglutination methods for the identification of Staphylococcus aureus

A new commercial yellow latex agglutination reagent (Bacto-Staph) was compared with the slide and tube coagulase tests and three other commercial reagents for the identification of 283 Staphylococcus aureus and 54 non-S. aureus staphylococcal strains. Test sensitivities for the identification of S. aureus were as follows: tube coagulase, 99.6%; slide coagulase, 98.6%; Bacto-Staph, 99.6%; Staphylatex, 98.6%; Sero STAT Staph, 98.2%; and Staphyloslide, 97.5%. No false-positive reactions were observed with any of the commercial reagents.

Evaluation of various rapid agglutination methods for the identification of Staphylococcus aureus

A latex agglutination test (SeroSTAT Staph; Scott Laboratories, Fiskeville, R.I.) and two hemagglutination tests (Staphyloslide; BBL Microbiology Systems, Cockeysville, Md.; and Hemastaph; Remel, Lenexa, Kans.) were compared with the slide coagulase (SC) and tube coagulase (TC) tests at room temperature (22 to 25 degrees C) and at 37 degrees C for the rapid identification of Staphylococcus aureus. A total of 380 clinical strains of staphylococci were tested. The TC test performed at room temperature yielded the largest number of TC-positive results (n = 239), and based on this observation 239 organisms were classified as S. aureus and 141 were classified as non-S. aureus. The SC, TC (37 degrees C), SeroSTAT Staph, Staphyloslide, and Hemastaph tests correctly identified 210 (87.9%), 221 (92.5%), 238 (99.6%), 239 (100%), and 236 (98.7%) of the S. aureus isolates, respectively. Of the S. aureus isolates that were TC positive at room temperature 68% required 24 h of incubation before coagulase production was detected. There was one false-negative SeroSTAT Staph result and one false-negative Hemastaph result. The Staphyloslide test yielded two noninterpretable results (both organisms were later confirmed as non-S. aureus), whereas there were six noninterpretable results recorded with the Hemastaph test (four organisms were classified as non-S. aureus, and two were classified as S. aureus). The SeroSTAT Staph, Staphyloslide, and Hemastaph tests were all more sensitive than the conventional SC and TC (37 degrees C) tests and were considerably more rapid than the TC test at either temperature.

Evaluation of three commercial agglutination tests for the identification of Staphylococcus aureus

Three commercially available rapid slide agglutination tests for the identification of Staphylococcus aureus were evaluated with 354 recent clinical isolates (165 strains of S. aureus). The test results of two latex agglutination products, SeroSTAT Staph (Scott Laboratories, Inc.) and Staphylatex (American Micro Scan), and one hemagglutination product, Staphyloslide (BBL Microbiology Systems), were compared with the results of the tube coagulase test, which was read at 4 h (4-h tube coagulase test) and, if negative, again after overnight incubation at room temperature (24-h tube coagulase test). Discrepancies between agglutination and tube coagulase identifications were resolved by use of the thermonuclease, mannitol fermentation, and slide coagulase tests. All sensitivities, specificities, predictive values of a positive result, and predictive values of a negative result for the three agglutination tests were at least 98.8% and comparable with the 4-h tube coagulase test. Best results were obtained with the 24-h tube coagulase test, which yielded one false-negative and no false-positive tests. Agglutination identifications may be performed on organisms taken directly from a primary plate when sufficient growth is present. Kit agglutination procedures yield rapid and reliable identifications and are easy to perform. This study also demonstrates the usefulness of the 24-h tube coagulase test.

Evaluation of latex agglutination and microtube coagulase tests for detection of Staphylococcus aureus

In a blind study, a latex agglutination test (Serostat Staphylococcus, Scott Laboratories) and a microtube coagulase test (Staphase, API) were evaluated for their ability to detect Staphylococcus aureus. Of 289 isolates of catalase-positive, gram-positive cocci, 122 were identified as S. aureus based on positive reactions in at least three of the following tests: tube coagulase, slide coagulase, DNase production, or anaerobic fermentation of mannitol. The latex agglutination test gave positive reactions for all S. aureus isolates and 10 (6%) non-S. aureus isolates. The slide coagulase test was positive for 121 S. aureus isolates and three (2%) non-S. aureus isolates. The microtube coagulase test detected 53, 90, and 98% of the S. aureus isolates after 2, 4, and 24 hr, respectively. In contrast, the conventional tube coagulase test detected 97% of the S. aureus isolates after 2 hr, and 98% after 4 and 24 hr. Two isolates of S. aureus gave negative tube coagulase reactions at 37 degrees C, but positive reactions at room temperature after 24 hr. The combination of tube and slide coagulase tests provided the most reliable results. The slide and tube coagulase tests gave more reliable results than the latex agglutination and microtube coagulase tests, respectively.

Comparison of rapid identification assays for Staphylococcus aureus

A total of 137 strains of Staphylococcus species were blindly tested by four rapid serological assays, and the results were compared with those of the tube coagulase assay. For the S. aureus isolates, the Sero-STAT Staph assay gave six false-negative results, four of which were for methicillin-resistant strains. The Accu -Staph, Staphylatex , and Staphyloslide assays identified all the coagulase-positive strains as Staphylococcus aureus. Among the coagulase-negative staphylococci, false-positive results were seen with strains of S. capitis. S. saprophyticus, and S. cohnii. The overall accuracy of the kits compared with the tube coagulase test ranged from 95.1 to 100%.

Evaluation of latex agglutination tests for establishing coagulase status of staphylococci from milk

A total number of 640 staphylococci isolated from cows' milk were tested by latex agglutination and coagulase tests. About 50% of coagulase positive and 5% of coagulase negative staphylococci were positive to the latex agglutination tests. Latex agglutination tests were found to be not satisfactory for determining the coagulase status of staphylococci isolated from cows' milk.

Comparison of two commercially available test methods with conventional coagulase tests for identification of Staphylococcus aureus

The API STAPHase (Analytab Products, Inc., Plainview, N.Y.) and SeroSTAT Staph (Scott Laboratories, Fiskville, R.I.) tests were compared to the conventional tube coagulase test and a slide coagulase test by using fresh isolates of members of the family Micrococcaceae. The 4-h, 24-h, and combined readings of the tube coagulase test detected 94.5, 99.5 and 100%, respectively, of 219 Staphylococcus aureus isolates. The API STAPHase, SeroSTAT Staph, and slide coagulase tests detected 95.9, 95.4 and 95.9% of the isolates of S. aureus, respectively. There were no false-positive results with any of the systems when tested with 103 strains of members of the family Micrococcaceae other than S. aureus. We concluded that the STAPHase and SeroSTAT Staph tests were equal in accuracy to the slide coagulase and 4-h tube coagulase tests and were suitable for use in the clinical microbiology laboratory. However, SeroSTAT Staph gave faster results than the API STAPHase, and the test was easier to perform. Also, the false-negative rate was high enough with the STAPHase, SeroSTAT Staph, and the slide coagulase tests that all negative reactions should be confirmed with a tube test.

Comparison of four methods for differentiation of Staphylococcus aureus from other Micrococcaceae in the routine laboratory

Four methods for the identification of Staphylococcus aureus (tube coagulase test, thermostable nuclease test, indirect agglutination of fibrinogen coated erythrocytes and a commercial latex kit: SeroSTAT Staphylococcus Test) have been compared. Clinical isolates (698) and 40 reference strains of Micrococcaceae were included in the study together with control organisms. The coagulase test gave no false positive results but 39/406 clinical isolates of S. aureus were negative at 2h and one half were only weakly positive. At 18 h, all but 2 of 406 isolates gave a positive reaction. The thermostable nuclease test was very specific; no clinical isolates of S. aureus gave negative results and no "coagulase-negative" clinical isolates gave a definite positive reaction. The indirect haemagglutination method was sometimes difficult to interpret and frequently gave negative or doubtful results for S. aureus. The SeroSTAT test was easy to use and interpret and was specific; the method is suitable for routine laboratory use, particularly when a rapid result is desirable.

Direct identification of Staphylococcus aureus in blood culture fluid with a commercial latex agglutination test

A commercial latex agglutination slide test (SeroSTAT Staph, Scott Laboratories, Inc., Fiskeville, R.I.) accurately identified Staphylococcus aureus when applied directly to blood culture fluid containing staphylococci. This latex agglutination test exhibited 100% accuracy when 30 seeded aerobic and anaerobic radiometric blood cultures (15 strains of S. aureus, 15 strains of other staphylococcal species) were tested blindly. In 36 actual clinical specimens yielding 16 isolates of S. aureus and 20 isolates of Staphylococcus epidermidis, 94.4% accuracy was achieved. The latex agglutination test provided positive test results before objective criteria of blood culture positivity such as radiometric growth indices and Gram stains became positive.

Speciation of coagulase-negative staphylococci in the clinical laboratory

The purpose of this study was to evaluate the efficacy of the API Staph System for the speciation of coagulase-negative staphylococci. Three hundred and seventy-one coagulase-negative clinical isolates were studied; 50% of these could be speciated using the code profiles of the API System. By reference to the Kloos and Schleifer schema, 93% of the isolates could be speciated. The distribution of the various staphylococcal species in clinical specimens was determined. It was concluded that the API Staph System would be a satisfactory method of speciation if the data base could be expanded. Such speciation may at times be helpful in interpreting the significance of coagulase-negative staphylococcal isolates in the clinical laboratory.

Evaluation of a commercial latex agglutination test for identification of Staphylococcus aureus

A new, commercially available latex agglutination test (SeroSTAT Staph; Scott Laboratories, Inc., Fiskeville, R.I.) was compared with the tube coagulase and slide coagulase tests as means for identifying Staphylococcus aureus. Of 160 clinical isolates of S. aureus, 159 (99.4%) yielded positive results with the latex agglutination test. Negative latex agglutination test results were obtained with 266 of 267 clinical isolates of Micrococcus spp. and staphylococcal species other than S. aureus (99.6%). The latex agglutination test was found to be a rapid, technically nondemanding method for identifying S. aureus. It was as accurate as the tube coagulase test and more accurate than the slide coagulase test.

Evaluation of the latex slide agglutination test for identification of Staphylococcus aureus

This study evaluated the reliability of the latex slide agglutination test for identifying Staphylococcus aureus. A total of 806 clinical isolates of staphylococci were tested for latex agglutination, clumping factor, and free coagulase. Positive latex tests occurred in 98.3% of coagulase-positive strains, whereas 99.6% of coagulase-negative strains gave negative latex tests. It is concluded that in most instances, the latex slide agglutination test is a reliable method for identifying S. aureus in the clinical laboratory.

Measurement of staphylococcal protein A and detection of protein A-carrying staphylococcus strains by a competitive ELISA method

A competitive ELISA for the estimation of staphylococcal protein A is described. Tetanus toxoid is insolubilized on polystyrene and incubated with human antitoxin, which renders the Fc-piece of this antibody freely accessible to protein A. The binding of the latter is demonstrated by its competition with protein A-phosphatase conjugate. The method has been shown to be sensitive and reproducible. It has been used for the detection of protein A in culture supernatants and on living pathogenic staphylococci. The test could therefore be of diagnostic value. Protein A is also present in extracts of food contaminated with enterotoxic staphylococci. It can be eliminated by a simple absorption with insoluble porcine IgG.