Direct Testing of Blood Cultures for Detection of Streptococcal Antigens

Abstract

A direct, rapid, and simple method for the detection of streptococcal antigens of Lancefield groups A, B, C, D, and G from blood cultures was developed by using a coagglutination test. Fifty-five clinical specimens and 117 simulated blood cultures containing gram-positive cocci were tested. Out of 6,261 clinical blood cultures screened, 55 cultures from 53 patients were positive, with organisms resembling streptococci, by Gram stain. Of these cultures, 78% (43 of 55) were pure cultures of streptococci, and 22% (12 of 55) were mixed with at least one other organism. Of the 43 pure cultures only, correct reactions were obtained (grouping correctly or giving no cross-reactions, or both) with 86% (37 of 43) of the isolates, 12% (5 of 43) exhibited cross-reactions, and 2% (1 of 43) gave false-negative reactions. All of the cross-reacting isolates were Streptococcus pneumoniae , which reacted with the group C reagent, and the false-negative reaction occurred with a Streptococcus bovis isolate. However, by using a direct modified bile solubility test, the correct identification of the S. pneumoniae isolates was obtained. Therefore, by using the modified bile solubility test in conjunction with the direct grouping method, 98% (42 of 43) of the isolates in pure culture could be identified accurately and rapidly after the detection of a positive Gram stain. Correct grouping reactions were obtained with 83% (10 of 12) of the mixed blood cultures, and false-negative results occurred with 17% (2 of 12) of them. Both cultures contained an enterococcus and a gram-negative rod. Of the 117 simulated blood cultures, there was only one incorrect grouping reaction; this occurred with an S. bovis isolate that cross-reacted with the group C reagent. The direct grouping reaction was positive when blood cultures contained a minimum of 1 × 10 8 to 8 × 10 8 colony-forming units per ml. In general, this procedure provided information on the identification of the organism 24 h earlier than by conventional identification methods.

Cross-reactions between pneumococci and other streptococci due to C polysaccharide and F antigen

“…In our routine diagnostic laboratory, pneumococci have regularly been observed to react with a co-A reagent prepared with antistreptococcal group C antiserum, and this cross-reaction has also been reported by others (5,20,30). Since both streptococcal group C polysaccharide and pneumococcal F antigen are Forssman antigens (6, 7), we investigated whether this common feature could explain these cross-reactions.…”

Evaluation of the Phadebact CSF test for detection of the four most common causes of bacterial meningitis

“…Some of the culture-positive, COA-negative results may have been due to the numbers of organisms present or the antigen concentration in the clinical specimens, which may have been below the detection limit for COA. Olcen (8) found that he could not detect concentrations below 105 CFU/ml, whereas Wetkowski et al (13) found that 107 to 108 CFU/ml were necessary for detection of streptococci in positive blood cultures. Colony counts were known for two of the N. meningitidis specimens; one specimen did not grow on solid media and the organism was recovered only in broth, the other produced 120 colonies or ca.…”

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

“…These procedures confirmed the false cross-reactions and were in complete agreement with the LA results obtained on the same cultures. Although all strains studied by Wellstood were tested by the Lancefield precipitin method (15), the reference procedure used is not clearly stated in the study by Wetkowski et al (16). b All false-positive reactions for S. pneumoniae were with the group C reagent.…”

“…The serological grouping of streptococci has become technically simple with the development of immunofluorescent (IF), coagglutination, and latex agglutination (LA) techniques (1, 3,5,6,13,15,16). Furthermore, rapid identification of bacteria from a variety of sources, especially blood and body fluids, has become a subject of intensive investigation in recent years (9, 9a, 14-16).…”

“…Furthermore, rapid identification of bacteria from a variety of sources, especially blood and body fluids, has become a subject of intensive investigation in recent years (9, 9a, 14-16). Few investigators have applied modern serological techniques to the identification of Lancefield-groupable streptococci in blood culture broths (15,16). With few exceptions, the techniques described in the literature for direct identification of strains from blood culture broths are still time consuming and require antigen extraction, incubation for 2 h or longer, multiple centrifugation steps, or a boiling step (14)(15)(16).…”