Objective: To explore identification and resistance characteristics of CAMP-negativeStreptococcus agalactiae. Methods : Using matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF MS) and the CAMP assay, 33 presumptive strains ofStreptococcus agalactiaewere identified. The CAMP-negative strains were further validated through 16S rDNA, while the CAMP factor encoding gene(cfb) was detected using real-time fluorescence quantitative polymerase chain reaction(qPCR). Antimicrobial susceptibility testing was conducted using the microbroth dilution method, and the resistance rates of CAMP-negative and CAMP-positive strains were compared. Results : Based on MALDI-TOF MS identification, all 33 strains were classified asStreptococcus agalactiae. Among them, 7 strains tested negative for CAMP were subsequently confirmed asStreptococcus agalactiaethrough 16S rDNA. The qPCR results indicated that, only 1 strain showedcfbpresence. The CAMP-negative and CAMP-positive strains were sensitive to penicillin G, cefepime, cefotaxime, vancomycin, and linezolid. The resistance rates of the former to chloramphenicol and tetracycline(28.57%, 85.71%) were slightly higher than the latter(15.38%, 57.69%), while the resistance rates to moxifloxacin, levofloxacin, and erythromycin(14.29%, 14.29%, 42.86%) were slightly lower than the latter(34.62%, 34.62%, 57.69%), but was not significant. Conclusion Drug risistance of CAMP-negativeStreptococcus agalactiaeis the same as CAMP-positive strains, but traditional CAMP assay andcfb-targeted qPCR can result in missed detections. MALDI-TOF MS offers a quick, simple, and accurate identification method that merits wider adoption.

Objective : To investigate the antagonistic activity of Lactococcus garvieae SHAMU-LG6 against Staphy- lococcus . Methods : VITEK 2 GP identification card , Microflex LT MALDI-TOF mass spectrometer and 16S rDNA amplification sequencing were used to identify the strain species . The antagonistic activity of L. garvieae SHAMU- LG6 against different Staphylococcus was detected by Oxford cup method for bacterial inhibition ; the antimicrobial active components were preliminarily isolated and purified by adsorption on XAD16 nonionic macroporous resin , gradient ethanol elution and rotary evaporation drying. Results : L. garvieae SHAMU-LG6 exhibited potent antago- nistic effect against methicillin-resistant Staphylococcus aureus , methicillin-susceptible S. aureus , S. epidermidis , S. saprophyticus , S. lugdunensis , S. hominis , S. capitis and S. warneri , with inhibitory indices of 3 . 3 , 3 . 0 , 4. 3 , 2. 0 , 4. 0 , 3 . 5 , 3 . 8 , and 3 . 5 , respectively. The antimicrobial active components produced by L. garvieae SHAMU-LG6 were mainly present in 70% and 80% ethanol eluates . Conclusion L. garvieae SHAMU-LG6 ex- hibits a potent antagonistic effect on Staphylococcus , and the antimicrobial active components produced by it are ex- pected to be a lead compound for the development of novel antimicrobial agents .

Objective : To explore the molecular characteristics of four CAMP negativeStreptococcus agalactiae(S.agalactiae) in whole genome sequencing. Methods : The identification of suspicious bacterial strains was conducted using matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF MS). For the strains confirmed asS.agalactiaethrough identification, further CAMP experiments were conducted. For CAMP negative strains, whole genome sequencing was performed using MGI DNBSEQ-T7 and MinION Flow Cell sequencing platforms. Subsequently, multi-locus sequence typing(MLST), virulence genes and resistance genes of the strains were compared and analyzed using various databases. Phoenix M50 fully automatic drug sensitivity analyzer was employed to determine the sensitivity of the bacterial strains to commonly used antibiotics. Results: Four CAMP-negativeS.agalactiaestrains were included. Whole-genome sequencing analysis revealed that all four CAMP-negativeS.agalactiaestrains belonged to the ST862 type. These strains harbored 22 virulence genes associated with capsular polysaccharides, β-hemolysin, and hyaluronidase, as well as seven resistance genes linked to macrolides, lincosamides, polypeptides, and aminoglycosides. Antimicrobial susceptibility testing revealed that CAMP-negativeS.agalactiaewas susceptible to penicillin G, cefepime, cefotaxime, and vancomycin. However, three strains exhibited resistance to erythromycin, and one strain demonstrated resistance to clindamycin. Conclusion Four CAMP negativeS.agalactiaeof the ST862 type possess multiple virulence and drug resistance genes, showing high resistance to erythromycin, warranting clinical attention.

Objective To explore the microbiological characteristics of Staphylococcus aureus(S.aureus)with no-vel incomplete hemolytic phenotype(SIHP).Methods Hemolytic phenotypes were detected and categorized by u-sing the three-point inoculation method.A total of 11 novel SIHP and 33 randomly matched S.aureus with com-plete hemolytic phenotype(SCHP)were included.Antibiotic susceptibility test was performed using broth microdi-lution method.Coagulase test was performed with freeze-dried rabbit plasma.Catalase activity was detected by slide catalase test.Expression of hemolysin genes was detected by qRT-PCR.Toxicity to human red blood cells was as-sessed by microplate method.Microplate biofilm formation was measured using crystal violet staining method.Growth kinetic determination was performed through microcultivation assay.Results Compared with SCHP,the expression profiles of the four hemolysin genes(hla,hlb,hlc,and hld)in the new SIHP were different.The new SIHP had higher resistance rates to penicillin,oxacillin,gentamicin,quinolones,clindamycin,and trimethoprim-sulfamethoxazole.Furthermore,the new SIHP had stronger hemolytic toxicity,plasma coagulase activity,and bio-film formation ability.Additionally,the new SIHP grown faster in the logarithmic phase.Conclusion Taken to-gether,the microbiological characteristics of the new SIHP are different from those of SCHP,including stronger an-tibiotic resistance and pathogenicity,which should be paid more attention by clinicians.