Streptococcus pyogenes streptolysin O as a cause of false-positive CAMP reactions

Reliable Detection of Group B Streptococcus in the Clinical Laboratory

Group B streptococcus (GBS) is a leading cause of invasive neonatal infections and a significant pathogen in immunocompromised adults. Screening to detect GBS colonization in pregnant women determines the need for antibiotic prophylaxis in that pregnancy. Efficient determination of the GBS colonization status of pregnant women is crucial. Methods that maximize the probability of GBS recovery are needed. The availability of technologies such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), molecular techniques, and chromogenic culture media, including Granada-type media, have changed the scenario for GBS detection and identification. This review presents and evaluates novel diagnostic tools, as well as classic identification techniques, for GBS species determination.

Cooperative, synergistic and antagonistic haemolytic interactions between haemolysin BL, phosphatidylcholine phospholipase C and sphingomyelinase from Bacillus cereus

Haemolysis of erythrocytes from different species (sheep, bovine, swine and human), caused by various combinations of phosphatidylcholine (PC)-preferring phospholipase C (PC-PLC), sphingomyelinase (SMase) and the three-component, pore-forming toxin haemolysin BL (HBL) from Bacillus cereus was analysed. The lytic potency of HBL did not correlate with phospholipid (PL) content, but lysis by the individual or combined enzymes did. SMase alone lysed ruminant erythrocytes, which contain 46-53% sphingomyelin (SM). The cooperative action of PC-PLC and SMase was needed to lyse swine and human erythrocytes (22-31% PC and 28-25% SM). SMase synergistically enhanced haemolysis caused by HBL for all erythrocytes tested, which all contained >25% SM. PC-PLC enhanced HBL haemolysis only in cells containing significant amounts of PC (swine, 22% PC; human, 31% PC). Unexpectedly, PC-PLC inhibited HBL lysis of sheep erythrocytes (<2% PC) and enhanced the discontinuous haemolysis pattern that is characteristic of HBL in sheep blood agar. Inhibition and pattern enhancement was abolished by washing PC-PLC-treated erythrocytes or by adding EDTA, suggesting that enzymic alteration of the membrane is not involved, but that zinc in the active site is required, perhaps to facilitate binding. These observations highlight the potential for cooperative and synergistic interactions among virulence factors in B. cereus infections and dependence of these effects on tissue composition.

Identification, cloning, and expression of the CAMP factor gene (cfa) of group A streptococci

The CAMP reaction is a synergistic lysis of erythrocytes by the interaction of an extracellular protein (CAMP factor) produced by some streptococcal species with the Staphylococcus aureus sphingomyelinase C (beta-toxin). Group A streptococci (GAS [Streptococcus pyogenes]) have been long considered CAMP negative, and this reaction commonly has been used to distinguish GAS from Streptococcus agalactiae. We here provide evidence that GAS possess this gene and produce an extracellular CAMP factor capable of participating in a positive CAMP reaction. The S. pyogenes CAMP factor is specified by a 774-bp open reading frame homologous to the CAMP factor genes from S. agalactiae and Streptococcus uberis. This gene, designated cfa, was isolated on a 1,256-bp fragment and cloned in Escherichia coli. Recombinant clones of E. coli expressing cfa secreted an active CAMP factor. The deduced 28.5-kDa protein encoded by cfa consists of 257 amino acids, with a predicted 28-amino-acid signal peptide. The cfa gene is widely spread among GAS: 82 of 100 clinical GAS isolates produced a positive CAMP reaction. Of the CAMP-negative strains, 17 of the 18 GAS strains contained the cfa gene. Additionally, CAMP activity was detected in streptococci from serogroups C, M, P, R, and U. The cfa gene was cloned and actively expressed in Escherichia coli and gene fusions were made, placing the beta-galactosidase gene (lacZ) under control of the cfa promoter. These cfa promoter-lacZ fusions were introduced into S. pyogenes via a bacteriophage-derived site-specific integration vector where they showed that the cfa gene has a strong promoter that may be subject to as-yet-unidentified regulatory factors. The results presented here, along with previous reports, indicate that the CAMP factor gene is fairly widespread among streptococci, being present at least in groups A, B, C, G, M, P, R, and U.

Identification, cloning, and expression of the CAMP factor gene (cfa) of group A streptococci

The CAMP reaction is a synergistic lysis of erythrocytes by the interaction of an extracellular protein (CAMP factor) produced by some streptococcal species with the Staphylococcus aureus sphingomyelinase C (beta-toxin). Group A streptococci (GAS [Streptococcus pyogenes]) have been long considered CAMP negative, and this reaction commonly has been used to distinguish GAS from Streptococcus agalactiae. We here provide evidence that GAS possess this gene and produce an extracellular CAMP factor capable of participating in a positive CAMP reaction. The S. pyogenes CAMP factor is specified by a 774-bp open reading frame homologous to the CAMP factor genes from S. agalactiae and Streptococcus uberis. This gene, designated cfa, was isolated on a 1,256-bp fragment and cloned in Escherichia coli. Recombinant clones of E. coli expressing cfa secreted an active CAMP factor. The deduced 28.5-kDa protein encoded by cfa consists of 257 amino acids, with a predicted 28-amino-acid signal peptide. The cfa gene is widely spread among GAS: 82 of 100 clinical GAS isolates produced a positive CAMP reaction. Of the CAMP-negative strains, 17 of the 18 GAS strains contained the cfa gene. Additionally, CAMP activity was detected in streptococci from serogroups C, M, P, R, and U. The cfa gene was cloned and actively expressed in Escherichia coli and gene fusions were made, placing the beta-galactosidase gene (lacZ) under control of the cfa promoter. These cfa promoter-lacZ fusions were introduced into S. pyogenes via a bacteriophage-derived site-specific integration vector where they showed that the cfa gene has a strong promoter that may be subject to as-yet-unidentified regulatory factors. The results presented here, along with previous reports, indicate that the CAMP factor gene is fairly widespread among streptococci, being present at least in groups A, B, C, G, M, P, R, and U.

Relatedness of Streptococcus canis from canine streptococcal toxic shock syndrome and necrotizing fasciitis

The emergence of streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis (NF) in dogs caused by Streptococcus canis has been reported by our laboratory. Since clonal expansion is thought to be partially responsible for the spread of invasive strains of Streptococcus pyogenes in humans, the relatedness of 15 isolates of S. canis from canine STSS and/or NF was examined using pulsed field gel electrophoresis and biotyping; production of proteases and of a CAMP-like reaction were also examined. Only 2 of the 15 STSS and/or NF isolates were clonally related, suggesting that the emergence of canine STSS/NF is not the result of clonal expansion of one or more highly virulent strains of S. canis. All of the isolates produced proteases and demonstrated a CAMP-like reaction, which appear to be additional characteristics of S. canis.

Presumptive identification of group B streptococci by rapid detection of CAMP factor and pigment production

Modified rapid versions of CAMP and pigment tests were developed for the identification of group B streptococci using the supernatant and cell deposit of organisms grown for 4 hr in a modified Todd-Hewitt broth. All but one of 203 group B streptococci were reliably differentiated from 148 nongroup B strains.

The influence of nutritional and cultural factors on CAMP factor production by group B streptococci

Twelve group B streptococci were examined for their capacity to produce CAMP factor in liquid culture media in which the carbohydrate type and concentration and/or the buffering capacity of the media were altered. The effects of these variations of media content on CAMP factor production were determined and related to effects on growth yield and pH changes during growth. For 9 of the 12 strains tested higher CAMP factor titres were obtained in maltose broth than in glucose broth, and accompanying changes in pH were greater and more rapid in glucose containing media. It is suggested that the lesser pH changes occurring during growth in maltose broth may be the mechanism whereby higher CAMP titres were obtained with these strains. The influence of carbohydrate type was not observed with the remaining 3 strains tested, but maximum CAMP factor yields were obtained in the presence of maltose and non-inhibitory concentrations of buffer. CAMP factor production for all strains of GBS may be increased by the addition of maltose and buffer to standard media.