Molecular characterization of phenotypically CAMP-negative Streptococcus agalactiae isolated from bovine mastitis

Group B streptococci (GBS) strains evading molecular diagnostics showed novel chromosomal deletions encompassing the CAMP-factor (cfb) encoding gene

A highly conserved fragment adjacent to the cfb gene encoding the CAMP factor is the target of PCR-based molecular diagnostic systems for the identification of S. agalactiae (group B streptococci (GBS)). Six PCR-negative, culture-positive GBS strains were whole genome sequenced to assess why they escaped molecular diagnostics. GBS strains did not constitute a clonal cluster and presented variably sized chromosomal deletions (from 7 to 33 kb) which always included the cfb gene, a finding never described before. GBS strains that escape molecular diagnostics are considered rare; however, they can cause false-negative results using molecular diagnostics alone, affecting medical decisions.

Analysis of molecular characteristics of CAMP-negative Streptococcus agalactiae strains

Background

Streptococcus agalactiae can produce CAMP factor, which can promote the β-hemolysin activity of Staphylococcus aureus, forming an arrow-shaped hemolysis enhancement zone at the intersection of the two bacterial species on a blood agar plate. This characteristic feature of Streptococcus agalactiae has led to the widespread use of the CAMP test as an identification method.

Methods

Vaginal/rectal swabs, collected from women at 35-37  weeks of pregnancy, were first inoculated into a selective enrichment broth media, then subcultured onto GBS chromogenic agar and 5% sheep blood agar sequentially. The VITEK-2 automatic identification system and MALDI-TOF MS were initially employed for identification, followed by the CAMP test. CAMP-negative strains underwent 16S rDNA and cfb gene sequence analysis, as well as bacterial multilocus sequence typing.

Results

A total of 190 strains were isolated, with 15 identified as CAMP-negative. Further 16S rDNA gene sequence analysis confirmed that all 15 strains were Streptococcus agalactiae. The MLST typing assay revealed that these 15 strains were of the ST862 type. The cfb gene was amplified and electrophoresed, but no specific fragments were found, indicating that these strains lack the CAMP factor due to cfb gene deletion. Antibiotic susceptibility tests demonstrated no resistance to penicillin, ampicillin, vancomycin and linezolid among the GBS strains. However, there are significant differences in resistance rates to tetracycline.

Conclusion

This study found that 7.9% of GBS strains isolated from the vagina/rectum of pregnant women were CAMP-negative, suggesting that the CAMP test method or primers targeting the cfb gene should not be used as the sole presumptive test for GBS identification.

Multicenter Evaluation of the Cepheid Xpert GBS LB XC Test

Early-onset neonatal sepsis due to Streptococcus agalactiae (group B Streptococcus [GBS]) infection is one of the leading causes of newborn mortality and morbidity. The latest guidelines published in 2019 recommended universal screening of GBS colonization among all pregnant women and intrapartum antibiotic prophylaxis for positive GBS. The updated procedures allow rapid molecular-based GBS screening using nutrient broth-enriched rectovaginal samples. Commercially available molecular assays for GBS diagnosis target mainly the cfb gene, which encodes a hemolysin protein responsible for producing the Christie-Atkins-Munch-Petersen (CAMP) factor. cfb is considered a conserved gene in essentially all GBS isolates. However, false-negative GBS results on Cepheid Xpert GBS and GBS LB tests due to deletions in or near the region that encodes cfb were reported recently. Therefore, the new Xpert GBS LB XC test was developed. This study is a multicenter evaluation of the new test for GBS identification from nutrient broth-enriched rectal/vaginal samples from antepartum women. A total of 621 samples were prospectively enrolled. The samples were tested with the Xpert GBS LB XC test, the composite comparator method, which included the Hologic Panther Fusion GBS test combined with bacterial culture, followed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) identification, and bacterial culture alone, followed by MALDI-TOF MS identification. The respective sensitivity and specificity of the Xpert GBS LB XC test were 99.3% and 98.7% compared to the composite comparator method and 99.1% and 91.8% compared to bacterial culture alone with MALDI-TOF MS identification. Overall, the Xpert GBS LB XC test performed comparatively to the composite comparator method and is equivalent to traditional bacterial culture followed by MALDI-TOF MS.

Vancomycin resistant Streptococcus equi subsp. equi isolated from equines suffering from respiratory manifestation in Egypt

Background and Aim:

Upper respiratory tract infections are common in horses and can be caused by a variety of pathogens, mainly Streptococcus equi subsp. equi, which are a significant equine pathogen causing major health issues as well as financial losses to the equine industry. This study aimed to determine the prevalence of Streptococcal bacteria in equines in Egypt, and characterize vancomycin-resistant S. equi subsp. equi phenotypically and genotypically.

Materials and Methods:

S. equi subsp. equi was isolated from internal nares of horses. All strains were confirmed by polymerase chain reaction-based detection of Streptococcus genus-specific 16S rRNA, sodA and seeI genes. Antibiotic susceptibility was determined phenotypically using the disk diffusion method. Genotypic detection of antibiotic resistance genes was performed by analyzing as b-lactamase resistance (blaZ), tetracycline resistance (tetK), vancomycin resistance (vanA), and chloramphenicol resistance (fexA).

Results:

Eight streptococcal isolates were confirmed as S. equi subsp. equi. The genotypic characterization of antibiotic resistance showed resistance to vanA and tetK, with a frequency of 87.5% and 12.5%, respectively, while the frequency of sensitivity was 100% for blaz gene and fexA gene.

Conclusion:

In this study, we assessed vancomycin-resistant S. equi subsp. equi from equines suffering from respiratory manifestation in Egypt.

Comparative study of Revogene GBS LB assay and GeneXpert GBS LB assay for the detection of group B Streptococcus in prenatal screening samples

Background

Group B Streptococcal (GBS) infections in the United States are a leading cause of meningitis and sepsis in newborns. The CDC therefore recommends GBS screening for all pregnant women at 35–37 weeks of gestation and administration of intrapartum prophylaxis (in those that tested positive) as an effective means of controlling disease transmission. Several FDA approved molecular diagnostic tests are available for rapid and accurate detection of GBS in antepartum women.

Method

In this study, we report a clinical comparison of the Xpert GBS LB assay and a novel FDA-cleared test, Revogene GBS LB assay. A total of 250 vaginal-rectal swabs from women undergoing prenatal screening were submitted to the University of Wisconsin’s clinical microbiology laboratory for GBS testing.

Results

We found 96.8% of samples were concordant between the two tests, while 3.2% were discordant with a positive percent agreement of 98.0% and a negative percent agreement of 96.5% between the Revogene GBS LB assay and the GeneXpert GBS LB assay.

Conclusion

Overall, we report that both assays perform well for the detection of GBS colonization in pregnant women.

Is a positive Christie-Atkinson-Munch-Peterson (CAMP) test sensitive enough for the identification of Streptococcus agalactiae?

Background

For a long time, the Christie-Atkinson-Munch-Peterson (CAMP) test has been a standard test for the identification of Streptococcus agalactiae, and a positive result for S.agalactiae has been considered sensitive enough.

Methods

To confirm whether a positive CAMP test is a requirement for the identification of S.agalactiae, five suspected CAMP-negative S.agalactiae isolates from two hospitals, confirmed as Gram-positive and catalase-negative streptococci, were verified by the CAMP test in three batches of plates from two manufacturers and identified by the Phoenix system, MALDI-TOF MS, the PCR assay and the 16S rDNA gene sequencing.

Results

All five suspected strains were S.agalactiae, four of which were CAMP-negative and one of which was not S.agalactiae by the PCR assay.

Conclusions

A positive CAMP test was lacking sensitivity for the identification of S.agalactiae, and the question of whether the cfb gene is worthy of targeting should be further studied.

Multiplex polymerase chain reaction for identification and differentiation of Streptococcus equi subsp. zooepidemicus and Streptococcus equi subsp. equi

The closely related streptococcal species Streptococcus equi subsp. zooepidemicus and S. equi subsp. equi were identified by polymerase chain reaction using oligonucleotide primers designed according to species-specific parts of the superoxide dismutase A encoding gene sodA. A further differentiation of both subspecies could be performed by amplification of the genes seeH and seeI encoding the exotoxins SeeH and SeeI, respectively, which could be detected for S. equi subsp. equi but not for S. equi subsp. zooepidemicus. A further simplification of the identification and differentiation of both subspecies was conducted by sodA-seeI multiplex polymerase chain reaction.