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

Rapid, direct identification of Staphylococcus aureus and Streptococcus pneumoniae from blood cultures using commercial immunologic kits and modified conventional tests

To develop safe and rapid methods for identification of Staphylococcus aureus and Streptococcus pneumoniae directly from positive blood culture bottles (BCB) (BACTEC, Johnston Laboratories), several commercial biochemical and immunological tests as well as modified conventional tests were evaluated. Preliminary studies demonstrated that both S. aureus and St. pneumoniae could be identified directly using only a small aliquot (100 microliters) of the blood culture broth obtained via vent without need for centrifugation or other separation steps. A simple tube coagulase exhibited 98% sensitivity and 100% specificity for 32 S. aureus isolates and 157 blood cultures positive for coagulase-negative staphylococci when read at 2 hr. All systems employed for direct identification of St. pneumoniae exhibited excellent sensitivity and specificity using aliquots from blood culture broths, but Pneumoslide (BBL Microbiology Systems, Cockeysville, MD) was easiest to perform and interpret. The results of this study show that S. aureus and St. pneumoniae can be identified directly from blood culture broth aliquots using rapid methods that eliminate the need for centrifugation or use of needles and syringes.

Latex agglutination testing directly from throat swabs for rapid detection of beta-hemolytic streptococci from Lancefield serogroup C

A latex agglutination method for the rapid detection of beta-hemolytic streptococci from Lancefield serogroup C in throat swabs from 403 university students with symptomatic pharyngitis was evaluated. Compared with culture, the rapid test was poorly sensitive (34.4%) but very specific (98.4%) in detecting group C beta-hemolytic streptococci. The sensitivity of the rapid test improved with an increasing quantity of growth on culture.

Evaluation of several commercial biochemical and immunologic methods for rapid identification of gram-positive cocci directly from blood cultures

To develop laboratory methods for the rapid identification of gram-positive cocci from blood cultures, several commercial immunological and biochemical tests for identifying staphylococci and streptococci from two different blood culture systems (Thiol/TSB, Difco Laboratories; BACTEC, Johnston Laboratories, Inc.) were evaluated and compared with conventional identification methods. A total of 44 cultures contained Staphylococcus aureus as determined by conventional methods. Commercial immunological methods (six tested) ranged in overall sensitivity from 38.6 (Staphyloslide; BBL Microbiology Systems) to 77.3% (Staphaurex; Wellcome Diagnostics). All methods tested had 100% specificity. A total of 30 isolates of group D streptococci were tested with immunological and biochemical identification systems. The overall sensitivity ranged from 14.2% (Phadebact Group D; Pharmacia Diagnostics) to 100% with Streptex (Wellcome; immunological) and Identicult A-E (Scott Laboratories, Inc.; biochemical). The results of this study suggest that some reagents can be used to provide rapid identification of gram-positive cocci from blood cultures 24 h earlier than standard methods.

Direct detection of groups A, C and G streptococci in clinical specimens by a trivalent colour test

A simple trivalent colour test, developed for the rapid detection and identification of streptococci belonging to Lancefield groups A, C and G, was evaluated for sensitivity and specificity with cultures and when directly used with wound and throat swabs. In tests performed on cultures, all of 94 group A, 78 group C and 94 group G cultures were correctly identified. In direct tests on wound swabs, 49 of 52 group A, 17 of 19 group C and 48 of 51 group G streptococci were detected and correctly identified; no false positives were observed. With throat swabs from pharyngitis patients 34 of 36 group A, 3 of 6 group C and 5 of 8 group G streptococci gave positive results. Almost 10% of these swabs gave false positive reactions with the group C component of the test system. Samples taken from uninfected individuals indicated that the false positives were probably associated with blood group A. The test system gives rapid and reliable results with streptococcal cultures, but when directly applied to clinical samples the results must be interpreted with caution, particularly if the patient's blood group is not known.

Rapid presumptive identification of streptococci directly from blood cultures by serologic tests and the L-pyrrolidonyl-beta-naphthylamide reaction

The value of the Strepslide kit for the rapid presumptive identification of streptococci directly from blood cultures without prior determination of hemolysis patterns was assessed and compared with that of the Streptex and Phadebact streptococcus kits. Studies involved 94 simulated and 60 clinical isolates of 83 streptococci. The Streptex and Strepslide kits had excellent sensitivity and specificity for group A, B, F, and G organisms, and the Phadebact kit had excellent sensitivity and specificity for groups B and G. Group C reactions usually occurred with all of the streptococcus kits with pneumococci and occasionally with alpha-hemolytic streptococci. Although these kits were unacceptable for group C and D organisms, enterococci which were common clinical isolates could be directly identified in blood cultures by a supplementary rapid L-pyrrolidonyl-beta-naphthylamide biochemical test. Direct application of the Phadebact pneumococcus kit to blood cultures was also assessed with 29 isolates of 20 organisms. The specificity was good, but the sensitivity was only 65.5%.

Cross-reaction between Streptococcus pneumoniae and group C streptococcal latex reagent

The extent of cross-reactivity between Streptococcus pneumoniae and two commercial streptococcal latex grouping reagents was examined. Cross-reactivity with the group C latex reagent was demonstrated in 91% (20 of 22) of blood cultures tested directly and in 97% (73 of 75) of clinical isolates of various serotypes tested after enzymatic extraction. This is important in the clinical laboratory because it may lead to erroneous identification of organisms present in blood cultures.

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.