AUTHOR=Zhou Jie , Zhang Li , Zhang Yang , Liu Hui , Xu Kangli , Zhang Baohu , Feng Tianyuan , Yang Shucai 

TITLE=Analysis of molecular characteristics of CAMP-negative Streptococcus agalactiae strains

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1189093

DOI=10.3389/fmicb.2023.1189093

ISSN=1664-302X

ABSTRACT=<sec><title>Background</title><p><italic>Streptococcus agalactiae</italic> can produce CAMP factor, which can promote the β-hemolysin activity of <italic>Staphylococcus aureus</italic>, forming an arrow-shaped hemolysis enhancement zone at the intersection of the two bacterial species on a blood agar plate. This characteristic feature of <italic>Streptococcus agalactiae</italic> has led to the widespread use of the CAMP test as an identification method.</p></sec><sec><title>Methods</title><p>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 <italic>cfb</italic> gene sequence analysis, as well as bacterial multilocus sequence typing.</p></sec><sec><title>Results</title><p>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 <italic>Streptococcus agalactiae</italic>. The MLST typing assay revealed that these 15 strains were of the ST862 type. The <italic>cfb</italic> gene was amplified and electrophoresed, but no specific fragments were found, indicating that these strains lack the CAMP factor due to <italic>cfb</italic> 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.</p></sec><sec><title>Conclusion</title><p>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 <italic>cfb</italic> gene should not be used as the sole presumptive test for GBS identification.</p></sec>