Evaluation Of Antibiotic Resistance And Proteolytic Ability Of Lactobacillus Paracasei Strains

Lactobacillus paracasei is a desirable probiotic that can colonize human gastrointestinal tracts and exert its probiotic effect.Due to its significant probiotic benefits,L.paracasei can be used in fermented milk as a starter culture to promote human health.Therefore,research on the safety and technological properties of L.paracasei strains can provide an important basis for screening strains for the fermentation industry.L.paracasei strains that are resistant to antibiotics may transfer the antibiotic genes to pathogenic bacteria in human gastrointestinal tracts,thereby jeopardizing human health.In addition,strains that exhibit hemolysis may cause sepsis in the human body.Therefore,evaluation of antibiotic resistance and hemolysis is crucial when assessing the safety of L.paracasei strains.In this study,36 strains of L.paracasei previously isolated from the research laboratory were evaluated for their resistance to eighteen antibiotics in order to determine their antibiotic sensitivity.Moreover,hemolysis of these strains was also evaluated.The results showed that 31 strains are sensitive to more than 11 antibiotics.Only five strains(C11,E15,B7,C10,B3)have multiple resistance to more than 7 antibiotics.Among them,Y3-1,C3,C2,K5,C7,1482,C6,E14,and E17 are particularly safe and are sensitive to more than 14 antibiotics.In the hemolysis experiment,E15 and B6 produced ?-hemolysis on the hemolysis plate,B5,B7,and C10 produced ?-hemolysis,while the other strains did not produce hemolysis.Antibiotic resistance genes may be transmitted to pathogenic bacteria in human gastrointestinal tracts making them resistant to the antibiotics as well,thereby having a negative impact on human health.In addition,the virulence factors in bacteria may also cause health issues.In this study,bioinformatics analysis on antibiotic genes and virulence factors was performed on the C10 strain since it performed poorly in both the antibiotic resistance experiment and hemolytic evaluation.This was done with the aim of further exploring the antibiotic genes and potential virulence factors in the C10 genome.The C10 genome was predicted to contain mutant rpo B,resistance genes gyr A,gyr B,efm A,arl R,Imr D,pat A,Isa A,and vat F.The above genes are resistant to Rifampin(rpo B),Fluoroquinolone antibiotics(gyr A,gyr B,emf A,arl R),Macrolide antibiotics(emf A,Isa A),Lincosamide antibiotics(Imr D,pat A,Isa A),and Streptomycin(vat F,Isa A).In the analysis of the virulence factors of C10,it was found that the predicted virulence factors are homologous to various pathogenic bacteria,such as Listeria monocytogenes,Mycoplasma pyogenes,Streptococcus pneumoniae,Bacillus thuringiensis,and Listeria monocytogenes.Among them,there were as many as five predicted virulence factors that are homologous to L.monocytogenes.The real virulence factors in the C10 genome are cyl R2,hyl A and sag A.They are all related to the production of hemolysin,which is consistent with the results of the previously mentioned phenotypic hemolysis experiment.The proteolytic system plays an important role in the fermentation of lactic acid bacteria,and L.paracasei strains capable of converting methionine to cysteine can grow more easily in milk.In this study,the proteolytic ability of the 36 strains was determined,and the gene cluster cys K-ctl-cys E which is responsible for the conversion between methionine and cysteine was screened.It showed that eight strains including P4,C3,B5,B6,B7,C2,C8,and C7 showed low proteolytic ability,with the content of free amino acids in the system being less than 250 ?g / m L during the fermentation.By contrast,the strains K1,Y3-1,P4-2,C4,C8,C10,B1,B4,E2,E12,and E14 had high proteolytic ability,with a content of free amino acids of up to 450 ?g / m L,among which C4 and B4 were particularly good,with the production of free amino acids more than 500 ?g / m L.In the experiment of screening strains for the gene cluster cys K-ctl-cys E,it was found that E2,C3,C4,C7,B8,E2,E3,E7,E12,E13,E17,P1,P4,and Y3-1 all contained the gene cluster.This study analyzed antibiotic resistance and hemolysis of the L.paracasei strains previously isolated in the laboratory as well as evaluated the proteolytic ability of these strains,thereby providing an important basis for screening strains for the fermentation industry.