OBJECTIVE To analyze the biological characteristics and genomic features of highly lytic bacteriopha-ges isolated from sewage in tropical hospitals and provide references for the hospital-associated infection prevention and control of multidrug-resistant Acinetobacter baumannii(MDR-Ab).METHODS With MDR-Ab as the host bacterium,bacteriophages were isolated from sewage.Transmission electron microscopy was employed to observe their morphology,and determine the optimal multiplicity of infection(MOI),one-step growth curve and environ-mental stability.Whole-genome sequencing and bioinformatics analysis were conducted to annotate functional genes and construct a phylogenetic tree.RESULTS A virulent bacteriophage,HN_Aba_01,was isolated.Elec-tron microscopy revealed that it belonged to the Myoviridae family,with a head diameter of 50 nm and a tail length of 90 nm.This bacteriophage exhibited strong lytic activity,with an optimal MOI of 0.000 000 1,a latent period of 5 minutes and a lysis yield of 15 PFU/cell.It remained stable at temperatures ranging from 4 ℃ to 60 ℃and pH values from 3 to 10.Genomic analysis identified 85 ORFs,including lyase,perforin and depolymerase genes.It shared 98.12％identity with the bacteriophage AbP2 genome(reference genome)and was classified into the Obolenskvirus genus.CONCLUSIONS The bacteriophage isolated from tropical hospital sewage,with high lyt-ic activity and good environmental adaptability,can be used for the hospital-associated infection prevention and control of MDR-Ab.

OBJECTIVE To analyze the biological characteristics and genomic features of highly lytic bacteriopha-ges isolated from sewage in tropical hospitals and provide references for the hospital-associated infection prevention and control of multidrug-resistant Acinetobacter baumannii(MDR-Ab).METHODS With MDR-Ab as the host bacterium,bacteriophages were isolated from sewage.Transmission electron microscopy was employed to observe their morphology,and determine the optimal multiplicity of infection(MOI),one-step growth curve and environ-mental stability.Whole-genome sequencing and bioinformatics analysis were conducted to annotate functional genes and construct a phylogenetic tree.RESULTS A virulent bacteriophage,HN_Aba_01,was isolated.Elec-tron microscopy revealed that it belonged to the Myoviridae family,with a head diameter of 50 nm and a tail length of 90 nm.This bacteriophage exhibited strong lytic activity,with an optimal MOI of 0.000 000 1,a latent period of 5 minutes and a lysis yield of 15 PFU/cell.It remained stable at temperatures ranging from 4 ℃ to 60 ℃and pH values from 3 to 10.Genomic analysis identified 85 ORFs,including lyase,perforin and depolymerase genes.It shared 98.12％identity with the bacteriophage AbP2 genome(reference genome)and was classified into the Obolenskvirus genus.CONCLUSIONS The bacteriophage isolated from tropical hospital sewage,with high lyt-ic activity and good environmental adaptability,can be used for the hospital-associated infection prevention and control of MDR-Ab.

OBJECTIVE To explore the molecular characteristics of small colony variants(SCVs)of Staphylococcus aureus isolates so as to provide theoretical bases for clinical control of the persistent and recurrent infections in-duced by the SCVs.METHODS The clinical blood specimens that were collected from the First Affiliated Hospital of Traditional Chinese Medicine University of Guangzhou were cultured to acquire 1 strain of SCV S.aureus S2.The colonial morphology,growth rate,catalase,plasma-coagulase,production capability of biofilm and antimi-crobial susceptibility of the strain SCVs were observed,the growth curve and autolysis curve were drawn,the whole genome sequencing was performed for the S2,the phylogenetic evolution of the genome and the single nu-cleotide polymorphism(SNP)were analyzed.RESULTS The S2 was identified as S.aureus,with the catalase and plasma-coagulase tested positive.The strain was resistant to various types of antibiotics,including macrolides like erythromycin and azithromycin,fluroquinolones such as levofloxacin and ciprofloxacin,and penicillin.The forma-tion of pigment was reduced,the formation of hemolytic rings was low;the growth rate of the strain was slower than that of ATCC 25923(quality control strain)and ZC1(the normal control strain),the autolytic activity of the strain was higher than that of the ATCC 25923 and ZC1,and the biofilm production of the strain was remarkably less than that of the ATCC 29213(P＜0.05).The whole genome sequencing demonstrated that the molecular typ-ing of the S2 was ST239-t030 clone,which harbored a variety of drug resistance genes and virulence genes,and the menB gene had missense mutation.CONCLUSION The formation of SCVs may be associated with the inhibited synthesis of menadione caused by the missense mutation of menB gene.

OBJECTIVE To explore the molecular characteristics of small colony variants(SCVs)of Staphylococcus aureus isolates so as to provide theoretical bases for clinical control of the persistent and recurrent infections in-duced by the SCVs.METHODS The clinical blood specimens that were collected from the First Affiliated Hospital of Traditional Chinese Medicine University of Guangzhou were cultured to acquire 1 strain of SCV S.aureus S2.The colonial morphology,growth rate,catalase,plasma-coagulase,production capability of biofilm and antimi-crobial susceptibility of the strain SCVs were observed,the growth curve and autolysis curve were drawn,the whole genome sequencing was performed for the S2,the phylogenetic evolution of the genome and the single nu-cleotide polymorphism(SNP)were analyzed.RESULTS The S2 was identified as S.aureus,with the catalase and plasma-coagulase tested positive.The strain was resistant to various types of antibiotics,including macrolides like erythromycin and azithromycin,fluroquinolones such as levofloxacin and ciprofloxacin,and penicillin.The forma-tion of pigment was reduced,the formation of hemolytic rings was low;the growth rate of the strain was slower than that of ATCC 25923(quality control strain)and ZC1(the normal control strain),the autolytic activity of the strain was higher than that of the ATCC 25923 and ZC1,and the biofilm production of the strain was remarkably less than that of the ATCC 29213(P＜0.05).The whole genome sequencing demonstrated that the molecular typ-ing of the S2 was ST239-t030 clone,which harbored a variety of drug resistance genes and virulence genes,and the menB gene had missense mutation.CONCLUSION The formation of SCVs may be associated with the inhibited synthesis of menadione caused by the missense mutation of menB gene.