Evaluation of commercial latex agglutination reagents for grouping streptococci

Monolayers of Poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) Microparticles Formed by Controlled Self-Assembly with Potential Application as Protein-Repelling Substrates

The kinetics of the self-assembly of poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) microparticles on poly(allylamine hydrochloride)-derivatized silicon/silica substrate was determined by direct AFM imaging and streaming potential (SP) measurements. The kinetic runs acquired under diffusion-controlled transport were quantitatively interpreted in terms of the extended random sequential adsorption (RSA) model. This allowed confirmation of a core/shell morphology of the microparticles. The polyglycidol-rich shell of thickness equal to 25 nm exhibited a fuzzy structure that enabled penetration of particles into each other resulting in high coverage inaccessible for ordinary microparticles. The SP measurements interpreted by using the 3D electrokinetic model confirmed this microparticle structure. Additionally, the acid-base characteristics of the microparticle monolayers were determined for a broad pH range. By using the streaming potential measurements, human serum albumin (HSA) adsorption on the microparticle monolayers was investigated under in situ conditions. It was confirmed that the protein adsorption was considerably lower than for the reference case of bare silicon/silica substrate under the same physicochemical conditions. This effect was attributed to the presence of the shell diminishing the protein/microparticle physical interactions.

Streptococcus agalactiae mastitis: a review

Streptococcus agalactiae continues to be a major cause of subclinical mastitis in dairy cattle and a source of economic loss for the industry. Veterinarians are often asked to provide information on herd level control and eradication of S. agalactiae mastitis. This review collects and collates relevant publications on the subject. The literature search was conducted in 1993 on the Agricola database. Articles related to S. agalactiae epidemiology, pathogen identification techniques, milk quality consequences, and control, prevention, and therapy were included. Streptococcus agalactiae is an oblique parasite of the bovine mammary gland and is susceptible to treatment with a variety of antibiotics. Despite this fact, where state or provincial census data are available, herd prevalence levels range from 11% (Alberta, 1991) to 47% (Vermont, 1985). Infection with S. agalactiae is associated with elevated somatic cell count and total bacteria count and a decrease in the quantity and quality of milk products produced. Bulk tank milk culture has, using traditional milk culture techniques, had a low sensitivity for identifying S. agalactiae at the herd level. New culture methods, using selective media and large inocula, have substantially improved the sensitivity of bulk tank culture. Efficacy of therapy on individual cows remains high. Protocols for therapy of all infected animals in a herd are generally successful in eradicating the pathogen from the herd, especially if they are followed up with good udder hygiene techniques.

Evaluation of new streptococcal latex grouping kit

AIMS

To evaluate a new streptococcal latex grouping kit (Shield Diagnostics Ltd) and compare it against an established latex agglutination method (Streptex; Wellcome Diagnostics).

METHODS

Two hundred and forty seven strains of streptococci and enterococci were tested with each kit by one operator and according to the manufacturer's instructions. Strains failing to group or giving discordant results were identified to species level.

RESULTS

Two discrepant grouping results were observed and 13 non-beta haemolytic streptococci failed to group with either product. The Shield kit successfully identified 232 isolates at 15 minutes of enzyme extraction incubation compared with 224 and 233 on short (15 minutes) and long (1 hour) incubations, respectively, for Streptex (p > 0.23 for both comparisons). On short incubation only, the Shield kit detected significantly more strains of Enterococcus faecium (p = 0.007). The reaction strengths were similar for both kits (p > 0.16). No cross-reactions were observed but the Streptex kit produced significantly fewer tests with visible granularity (p < 0.003).

CONCLUSIONS

Although the Shield product appeared to detect group D antigen more readily, overall no important differences in performance were observed. Prospective users of the new method should first become familiar with its characteristics.

Liquid medium for rapid presumptive identification of group B streptococci

A suitable test was developed for distinguishing group B streptococci from other beta-hemolytic streptococci during growth in liquid medium. One hundred and sixty of 161 human group B strains tested yielded positive reactions within a 5 h incubation. The dye medium tested is a reliable substitute for more expensive serological procedures.

Streptococci from primary isolation plates grouped by reverse passive haemagglutination

Reverse passive haemagglutination, a novel microtitre based assay, was compared with the Streptex (Wellcome UK) latex slide agglutination kit for streptococcal grouping in a diagnostic microbiology laboratory. Three hundred and fifty two extracts from 349 consecutive primary isolation plates were assayed by both methods. Reverse passive haemagglutination gave identical grouping results for 98.0% of the 345 streptococci identified by Streptex, and the kappa coefficient of agreement between the methods for all 352 extracts tested was 0.973. Cross reactions with Listeria spp seen with Streptex were not found by reverse passive haemagglutination. In the reverse passive haemagglutination method 11 streptococci could be grouped on each 96-well plate and most reactions were stable for at least 30 minutes. Reverse passive haemagglutination is more rapid to perform than latex slide agglutination when many organisms are to be grouped, and the patterns of haemagglutination are easily recognised. If the method was taken into routine use in a diagnostic laboratory, the persistence of reverse passive haemagglutination reactions would enable grouping results to be checked for quality control purposes.

Classification and identification of the viridans streptococci

This review traces the history of the human, nonhemolytic, or viridans, streptococci and describes improvements in their taxonomy wrought by study of their biochemical profiles and analysis of their nucleic acids. The goal was to define species on the basis of genetic relationships and to describe these species by their phenotypic characteristics so that they can be easily identified. This method has resulted in the division of some species. Streptococcus mutans has been divided into four species, two of which are common in humans. Three more mutans group species are indigenous to animals. Conversely, S. constellatus, S. intermedius, and "S. milleri" have been combined under S. anginosus. S. mitis (or "S. mitior") can be well-defined and includes S. sanguis II. There is genetic heterogeneity within S. sanguis, but the species is usually easy to identify. There is also some heterogeneity in S. bovis, but most human isolates are genetically related. Discussions of the taxonomy of these species are accompanied by descriptions of the characteristics by which these streptococci can be identified. Among these species are potential pathogens which should be suspected in cases of endocarditis and purulent infections of liver, brain, and other tissues.

Evaluation of rapid, commercial latex techniques for serogrouping beta-hemolytic streptococci

The clinical need to rapidly and correctly differentiate beta-hemolytic streptococci into Lancefield groups has prompted the development of commercially available rapid agglutination techniques. A modified Streptex (Wellcome Diagnostics, Research Triangle Park, N.C.) technique and the PathoDx latex Strep Grouping Kit (Diagnostic Products Corporation, Los Angeles, Calif.) technique were applied to 220 strains of beta-hemolytic streptococci that were serologically grouped by standard techniques. Agreements between standard and modified Streptex and PathoDx techniques were 99.1 and 100%, respectively. Modified Streptex produced a false-negative for one group G isolate and a weak-positive reaction for a group G reagent with a nongroupable isolate. Sixty-five strains representative of bacteria that may be found in the posterior pharynx in concentrations high enough to cause potential reactions with antigen detection reagents were tested with Streptex and PathoDx reagents. No cross-reactions were observed with any reagent tested when challenged with these 65 strains. When combined with colonial morphology and hemolytic reaction, both modified Streptex and PathoDx were rapid, specific tests for identifying streptococci, with PathoDx being slightly faster.

Comparison of Meritec-Strep with Streptex for direct colony grouping of beta-hemolytic streptococci from primary isolation and subculture plates

Meritec-Strep (Meridian Diagnostics, Inc., Cincinnati, Ohio) a coagglutination method, was compared with Streptex (Wellcome Diagnostics, Research Triangle Park, N.C.), a latex agglutination method, for the identification of beta-hemolytic streptococcal groups A, B, C, F, and G by the direct colony method. A total of 124 beta-hemolytic streptococcal isolates were tested, which included 77 from group A, 15 from group B, 10 from group C, 1 from group F, and 21 from group G. All were tested from subculture, and 74 (60%) were also tested from primary isolation plates. For Meritec-Strep, usually one colony was directly applied to the reaction card for testing each grouping reagent, while for Streptex, five colonies were tested after a 1-h extraction process. Complete agreement was obtained for all isolates tested from subculture with the kits. From primary isolation plates, Meritec-Strep correctly identified 97.3% of the isolates compared with 94.6% correctly identified for Streptex. Meritec-Strep produced a false-negative for one group A isolate and positive reactions for group A and F reagents with another group A isolate. A diphtheroid contaminant caused the positive group F reaction. Streptex produced false-negative results for one group A and three group C isolates. Most positive reactions were strong and rapid (less than 30 s) for both kits. The negative test control provided in the individual group A and B kits was nonreactive for all isolates. Meritec-Strep accurately identified isolated colonies of beta-hemolytic streptococci on primary isolation and subculture plates. It provided faster results than Streptex by eliminating the time and manipulation of antigen extraction and needed fewer colonies when individual group A or B reagents were used.

Evaluation of TestPack Strep A for the detection of group A streptococci in throat swabs

The performance of TestPack Strep A (Abbott Laboratories), a rapid enzyme immunoassay, was compared with a culture-based method for the detection of group A streptococci in 648 throat swabs. The rapid test correctly detected 99 of the 128 positive and 511 of the 520 negative specimens, a sensitivity of 77% and a specificity of 98%. Although highly specific, TestPack Strep A is less sensitive than culture techniques for the detection of group A streptococci in throat swabs.

Enzyme release of antigen from Streptococcus faecalis and Listeria monocytogenes cross-reactive with Lancefield group G typing reagents

Enzyme extraction methods are commonly used to release antigen for Lancefield serogrouping of streptococci. Recently, up to 47% of enterococci have been found to possess antigens cross-reactive with both the group D and the group G grouping reagents. We investigated whether the organisms had recently emerged or whether changes in extraction methods (enzyme extraction) have resulted in our awareness of their existence. We found that approximately 20% of our enterococcal isolates released material cross-reactive with the group G reagents. These organisms have been present for at least 6 years, and probably for many more. In addition, we found that most strains of Listeria monocytogenes also released antigen cross-reactive with the group G reagent. The clinical significance of these findings is also discussed.

Streptococci with dual antigen specificity for Lancefield groups D and G

Streptococci have been isolated which may be identified in serological tests as belonging to Lancefield group G, but in fact belong to group D. Twenty-two cultures with this property were obtained from four countries; they included Streptococcus bovis and Streptococcus durans as well as Streptococcus faecalis. Selected strains were studied in serological tests and cross-absorption procedures, in which it was found that the group G reaction given by these isolates is due to an epitope with at least partial identity with reference group G antigen. Identification of an enterococcus as a group G streptococcus could lead to erroneous and ineffective chemotherapy. Antibiotic sensitivity testing of streptococcus group G isolates should be a routine procedure, and bile-aesculin and salt-tolerance testing of these isolates would be a wise precaution.

Comparison of latex agglutination and immunofluorescence for direct Lancefield grouping of streptococci from blood cultures

Simulated positive blood cultures with 84 known stock strains of streptococci were used to comparatively evaluate the direct identification of these organisms by fluorescein-tagged antibody staining (immunofluorescence [IF]) and latex agglutination (LA). IF was not evaluated for Lancefield group D strains (a total of 81 strains tested) and had 89% sensitivity and 91% specificity. IF was least sensitive for the identification of Lancefield group F, in which three of seven strains showed no fluorescence with the group F reagent. Since LA was more convenient and revealed comparable sensitivities and specificities on 84 simulated cultures, we tested this procedure using an additional 29 fresh positive clinical blood cultures, for a total of 113 cultures tested by this technique. Of 11 Streptococcus pneumoniae strains, 9 reacted with the LA group C reagent, a problem not observed with IF. However, all these strains were identified by a rapid modified bile solubility test. Of the 12 Streptococcus faecalis strains, 4 were falsely negative with the group D reagent, but all were correctly identified by a rapid litmus milk reduction test. Of 12 group A strains, 1 was not detected. Of all 113 strains tested by LA, eliminating S. faecalis and S. pneumoniae, the sensitivity and specificity were 97 and 98%, respectively. LA was simple and reliable in the rapid identification of streptococci from blood cultures and appeared to be preferable to IF. When LA is used, the group D reagent should not be used, and all samples reacting with the group C reagent should be tested by a modified rapid bile solubility test to exclude S. pneumoniae.

Identification of Streptococcus bovis and Streptococcus salivarius in clinical laboratories

Streptococci identified as Streptococcus bovis, S. bovis variant, and Streptococcus salivarius were examined with respect to physiological and serological characteristics and cellular fatty acid content. Similarities in physiological reactions and problems encountered in serological analysis were noted, suggesting that an expanded battery of physiological tests is needed to definitively identify these streptococci. Cellular fatty acid analysis provided an accurate method for distinguishing S. salivarius from S. bovis and S. bovis variant.

Clinical evaluation of the improved streptex method for grouping streptococci

The improved Streptex method for serogrouping streptococci incorporates a new extraction enzyme and a simplified procedure requiring no centrifugation. A total of 114 clinical isolates of beta-hemolytic streptococci were serogrouped from primary plates, isolation plates, and Todd-Hewitt broth cultures using this system. Results were compared to those of the heat extraction Lancefield precipitin method. An additional 33 stock culture isolates of related streptococcal species and 5 strains of Listeria were serogrouped to assess the specificity of the test. Agreement between the two methods was 82.5% with primary plates and 96.5% with both isolation plates and broth cultures. Four isolates from three different serogroups were nongroupable by the Lancefield method, but did agglutinate in specific Streptex antisera; therefore, the enzyme extraction procedure appeared more sensitive than the heat extraction method. Streptex accurately grouped five isolates of gamma-hemolytic group B streptococci, but failed to detect antigen in 33% of the group D streptococcal extracts tested. In addition, cross-reactions were observed with strains of alpha-hemolytic streptococci. Streptex produced fewer ambiguous results and required fewer repeat tests. When used with isolation plates or broth cultures, Streptex is both sensitive and specific for the grouping of beta-hemolytic streptococci of groups A, B, C, F, and G.

Evaluation of slide agglutination methods for identifying group D streptococci

Three commercial reagents for the rapid identification of group D streptococci by slide agglutination were evaluated. These included SeroSTAT (Scott Laboratories, Fiskeville, R.I.), Streptex (Wellcome Laboratories, Research Triangle Park, N.C.), and Phadebact (Pharmacia Diagnostics, Piscataway, N.J.). The methods included direct colony testing, enzyme extraction with pronase, and broth culture. A total of 72 strains of group D streptococci were tested. The SeroSTAT and Streptex reagents with pronase extraction each identified 65 (90%) of the strains. The SeroSTAT reagent was somewhat more specific since it did not cross-react with other streptococci of the viridans group. The Phadebact reagent was nonreactive. We conclude that the latex reagents can be very useful for the quick recognition of group D streptococci in the clinical laboratory.

Inhibition of nonspecific streptococcal coagglutination reactions

The reliability of latex coagglutination testing for the serological grouping of hemolytic streptococci is limited by the relatively high incidence of false-positive reactions. Pretreatment of streptococcal suspensions with antisera for the various groups that show clumping gives a specific inhibition of the latex agglutination with the true group, whereas the other groups continue to agglutinate aspecifically. The method is rapid and easy to perform, allows the exact grouping of those streptococci giving aspecific reactions, and is also a useful confirmatory test with monoreactive strains.

Serological grouping of streptococci: a collective evaluation in six laboratories of three rapid methods

Three serological methods for streptococci grouping: latex agglutination after pronase extraction (LAP), latex agglutination after nitrous acid extraction (LAN) and counterimmunoelectrophoresis after nitrous acid extraction (CIEN) were evaluated in six laboratories with 310 strains of streptococci. To reduce the possible influence of a particular laboratory, each serological procedure was performed in two different laboratories with identical protocols and strains. Between the three procedures, a total agreement of 81.3% with six identical results was obtained. Since only one discordant result was obtained in 12.2% (CIEN 4.8%-LAN 5.8%-LAP 1.6%) and two discordant results with two different serological methods in 2.6%, it could be concluded that agreement between the three procedures was 96%. For B (99 strains tested) and D(100 strains tested) groups, total agreements of respectively 95% and 92% were achieved. In conclusion, LAP, LAN, and CIEN gave equivalent results for streptococci grouping, but LAN was the most simple needing no heating, centrifugation, or electrophoresis equipment and lacking cross-reactivity of group C antibody.

Comparison of the API 20S Streptococcus identification system with an immunorheophoresis procedure and two commercial latex agglutination tests for identifying beta-hemolytic streptococci

The API 20S Streptococcus identification system and a new immunorheophoresis procedure were evaluated as means for determining the Lancefield serogroup of beta-hemolytic streptococci recovered from human clinical specimens. The serogroup of 96 strains was determined by these methods and by two commercially available latex agglutination tests. Streptex and SeroSTAT. The results of all four procedures were compared with the results of a classical precipitin test. The API 20S system correctly categorized 92.7% of the isolates; 94.8% were correctly identified by the immunorheophoresis procedure. The latex agglutination procedures were of comparable accuracy, yielding correct identifications with approximately 92% of the strains tested.

Evaluation of Phadebact and Streptex Kits for rapid grouping of streptococci directly from blood cultures

The Phadebact Streptococcus Test and the Streptex Test kits were evaluated for grouping streptococci directly from blood cultures. Pellets of bacteria obtained from centrifuged samples of positive blood cultures were inoculated into Todd-Hewitt broth for 2- and 4-h Phadebact tests and into pronase for Streptex tests. Hemolysis was determined after pipetting a portion of each pellet into cuts made in blood agar plates incubated anaerobically for 2 to 6 h. Serological groups were also determined from colonies of the 137 strains of streptococci used in the study by the Lancefield precipitin method. Of the 126 strains tested by the 4-h Phadebact method, 120 (95.2%) agreed with Lancefield groupings, and 133 (97.1%) of the 137 strains tested by Streptex were in agreement. In contrast, only 31 of 55 strains (56.4%) were correctly identified by the 2-h Phadebact method. Misidentifications were related to multiple agglutinations and weak agglutinations in homologous antisera. Group A isolates were most frequently misidentified by all of the test methods. Hemolysis was determined within 4 h for 92.7% of the isolates and within 6 h for the remaining strains. Although the 4-h Phadebact procedure and the Streptex procedure were comparable in overall accuracy, cost, and technologist time, Streptex was the method of choice for direct groups. Results were available within 75 min for the Streptex procedure compared with 4 h for the Phadebact method. Because few cross-reactions occurred, agglutination responses were clearer and easier to interpret. Results from 2-h Phadebact tests were not satisfactory, and this method is not recommended.

Identification of group D streptococci by SeroSTAT

Clinical isolates of group D streptococci presumptively identified by biochemical methods were grouped by latex agglutination using a commercially prepared reagent specifically sensitized with group D antiserum (SeroSTAT; Scott Laboratories, Inc., Fiskeville, R.I.). Streptococcus species tested included S. faecalis, S. faecium, S. durans, S. avium, S. bovis, and S. equinus. Colonies of the organism to be tested were picked from agar plates, emulsified in a drop of glycine-buffered saline on a slide, and mixed with a drop of the latex reagent. Macroscopic agglutination occurred within 60 s. A total of 115 isolates of group D streptococci were tested; 103 (89.6%) gave positive reactions with SeroSTAT. Twelve strains failed to react with the latex reagent; these 12 strains also gave negative results with group D antiserum when tested by the Lancefield method. Two of 14 group A streptococci also reacted with the SeroSTAT group D reagent; after trypsinization, the cross-reaction was eliminated. Group B streptococci, viridans group streptococci, anaerobic streptococci, and staphylococci all gave negative reactions with the SeroSTAT reagent. The SeroSTAT reagent is a useful diagnostic tool for the prompt identification of enterococcal and non-enterococcal group D streptococci.

The systems approach to diagnostic microbiology

"Classical" and "conventional" methods for microbial identification are still utilized in clinical microbiology laboratories; however, significant advances in methodology have taken place in the last two decades. In the transition from classical to contemporary methodologies, the reference point has changed from multistep procedures to unitary procedures with marked emphasis on standardization, speed, reproducibility, and most recently, mechanization and automation. The most evident expression of this transition is the adaptation or streamlining of classical methods in the form of "miniaturized identification systems" and their commercial availability. This review analyzes the development of the underlining principles that make the systems approach to diagnostic microbiology possible.

Serogrouping single colonies of beta-hemolytic streptococci from primary throat culture plates with nitrous acid extraction and Phadebact streptococcal reagents

The serogrouping of isolated beta-hemolytic streptococcal colonies from throat cultures by a micronitrous acid extraction method employing Phadebact Streptotoccus Test reagents was compared with results obtained with the direct-plate Phadebact procedure and the autoclave and Streptomyces albus enzyme-lysozyme extraction methods. These data were compared with those from the Lancefield grouping obtained with a capillary precipitin test. The micronitrous acid extraction method was modified to yield an uncomplicated method that provides specific coagglutination responses from one beta-hemolytic streptococcal colony that may be collected from a primary blood agar plate either on the end of an applicator stick or from a sweep of an inoculating loop from mixed growth.