The novel surface-anchored protein SasX promotes aggregation and colonization of Staphylococcus aureus / 中华微生物学和免疫学杂志

Objective To determine whether the novel surface-anchored protein SasX promotes aggregation of S.aureus and adherence of S.aureus to human nasal epithelial cells.Methods MRSA ST-239 HS770 sasX gene mutant ( HS770 △sasX) and complement [ HS770 △sasX (pRBsasX) ] were gotten by gene knock-out and complement methods.The aggregation ability of S.aureus was observed through microscope.By adherence assay which was used for detection of the adherence ability of wild type and mutant to human nasal epithelial cells and blocking experiments which detected the ability of the purified recombinant SasX protein in blocking the adherence of S.aureus to human nasal epithelial cells,we investigated the influence SasX on colonization of S.aureus.Results Compared to wild type,HS770△sasX showed a reduction in cell aggregation,while the complement had no difference with wild type in aggregation. HS770 △sasX showed a significant reduction of adherence to human nasal epithelial cells compared to wild type ( P＜0.01 ),and the complement showed a very clear increasement of adherence to human nasal epithelial cells compared to wild type(P＜0.01 ).Preincubation of nasal epithelial cells with the purified recombinant SasX protein inhibited S.aureus binding significantly.Conclusion SasX had an influence in aggregation of S.aureus and its adherence to human nasal epithelial cells.By acquiring sasX,S.aureus colonized more easily to the susceptible sites of the host,and thus caused infection.

Distribution of the novel cell wall anchored protein-encoding gene sasX in Staphylococcus aureus strains / 中华检验医学杂志

ObjectiveTo investigate the distribution and effect on antibiotic resistance of the novel cell wall anchored protein-encoding gene sasX.MethodsA total of 300 S.aureus isolates were randomly collected from inpatients with S.aureusinfection in ShanghaiHuashanhospitalin 2004, 2007and 2010.Meanwhile,170 S.aureus isolates from the nasal swabs of healthy people were collected as part of a population-based community prevalence study.Typing of S.aureus isolates were identified by using multilocus sequence typing (MLST) and S.aureus-specific staphylococcal protein A typing (spa typing).Determination of oxacillin MICs was used to screen MRSA.PCR and sequencing were used to analyze sasX gene.The effect on antibiotic resistance of sasX gene was detect by disc agar diffusion drug sensitive test.ResultsThe major clonal types of the 300 S.aureus isolates collected from inpatients with S.aureus infection were ST239 ( 110,36.7％) and ST5 (122,40.7％).From 2004 to 2010,the percentage of isolates from inpatients with S.aureus infection was increased from 17％ to 39％,but sasX was only found in 0.59％ of the S.aureus isolates from the nasal swabs of healthy people.The percentage of sasX positive was increased from 47.2％ to 83.8％ in ST239.The percentage of sasX positive MRSA was increased from 26.4％ to 50.8％,but the percentage of sasX positive MSSA was about 10％.Antibiotic resistance of sasX positive strains were higher than that of sasX negative strains.Conclusions SasX gene is mainly detected in nosocomial pathogenic S.aureus and it is a possible virulence factor of S.aureus in hosptal setting.The presence of sasX gene is related to antibiotic resistance.For better understanding the real function of this novel gene,further studies such as expression of the encoded protein should be carried out.

Molecular characterization of Staphylococcus aureus collected from 2004 to 2010 in patients with blood stream infection / 中华检验医学杂志

Objective To investigate the clonal types of Staphylococcus aureus collected from 2004to 2010 in patients with blood stream infection from a Grade A tertiary care hospital in Shanghai as well as the dynamic changes and to detect the variation in antimicrobial resistance and virulence-gene content in different strain types.Methods A total of 103 nonduplicate S.aureus isolates were collected from 2004 to 2010 from inpatients with S.aureus blood stream infection from Shanghai Huashan hospital.Determination of oxacillin MICs and the type of SCCmec gene were used to screen MRSA.Typing of S.aureus isolates was identified by using multilocus sequence typing(MLST) and S.aureus-specific staphylococcal protein A typing(spa typing),PCR was used to detect the antimicrobial resistance and virulence-gene.Results Sixtysix isolates(64.1%) MRSA were detected in 103 nonduplicate S.aureus isolates,and 35 isolates were MRSA with SCCmec type Ⅱ ,Twenty-nine isolates were MRSA with SCCmec type Ⅱ,two isolates were MRSA with SCCmec type Ⅳ,Thirty-seven isolates(35.9%) were MSSA.Thirty-three MRSA isolates were ST5,Twenty-nine MRSA isolates were ST239,two MRSA isolates were ST59,one MRSA isolates was ST641 and one MRSA isolates was ST6.All of the other clones belonged to MSSA.The percentage of ST5 and ST239 were decreased significantly after 2009(ST5 was decreased from 52.9% to 15.4%; ST239 was decreased from 61.1% to 15.4%),and new clonal types MSSA increased significantly(in 2009,the percentage of ST7 was 41.7%; new clonal types such as ST188 and ST15 were detected in 2010).In 2010,it was shown that 84.6% of MSSA were isolated from S.aureus blood stream infection,nineteen isolates(18.4%) harbored mupA gene and 41 isolates(39.8%) harbored qacA/B gene in 103 nonduplicate S.aureus isolates.It was shown that 70.6% ST239 harbored qacA/B gene.Four isolates of ST398 and 1 isolates of ST9were detected which were originally from animal.There was no significant difference of the virulence gene presence in the same strain types except sasX、lukSF and arcA genes,but there were a lot of genes which were restricted to different genomic background.Conclusions The percentage of ST5 and ST239 were decreased and new clonal types of MSSA were increased significantly in S.aureus blood stream infection,antimicrobial resistance and virulence-gene were restricted to different clonal types.

Rapid identification and susceptibility testing of positive blood culture caused by gram negative bacteria / 中华微生物学和免疫学杂志

Objective To reduce the turnaround time for laboratory diagnosis of bacteremia, the feasibility of rapid identification and susceptibility testing using samples taken directly from positive blood culture bottles was evaluated. Methods The growth of microorganisms in blood culture bottles was screened by the BACTEC 9000 blood culture system. 65 positive blood culture bottles containing gram-negative bacteria were adopted to test. Culture fluid was injected into BD SST vacutainer and centrifuged to pellet blood cells. After collecting required McFarland units, they were cultured on Phoenix 100 NMIC/ID-4(identification-gram-negative bacteria and susceptibility testing) cards using 0.25 McF and 0.5 McF methods respectively. They were also evaluated by the standard method, involving subculture tests from positive blood culture bottles. Results 63 of 65 gram-negative bacteria (96. 9% ) were correctly identified with 0. 25 McF method. 59 of 65 gram-negative bacteria(90.8% ) were correctly identified with 0.5 McF method. For antimicrobial susceptibility testing, the 0.25 McF direct method had an agreement rate more than 94% , the 0.5 McF method was more than 85.7% and direct blood sample KB method was more than 93.8% compared to the standard method. But the overall minor error rate in susceptibility testing of direct blood sample KB method is higher than other methods. Conclusion Applying 0. 25 McF and 0. 5 McF rapid identification and susceptibility test was practical. During to possessing more prominent advantages, laboratory put the 0. 25 McF direct method into practice had a timely, remarkable significance.

Screening the factors which affect α-toxin expression of CA-MRSA / 中华检验医学杂志

Objective To screen the factors that can affect α-toxin expression of CA-MRSA except for quorum-sensing system and to investigate the regulative mechanism of the interesting genes. Methods S. aureus CA-MRSA transposon mutagenesis library was constructed by using mariner based transposon mutagenesis system. The clones with significantly changed level of hemolysis were selected, the location of erm insertion in a gene was confirmed by arbitrary primed (inverse) PCR and nucleotide sequence. Genetic complementation, mice bacteremia and skin abscess models and real time RT-PCR were used to study the function of the interesting gene. Results Twenty-five mutants with down-expression of α-toxin were selected by screening about 104 isolates of transposon mutagenesis library. The hemolytic diameter of CA-MRSA wild type was about 212 mm, no clear hemolysis was found in AraC-, The hemolytic diameter of AraC-pT181 araC was about 197 mm. Real time RT-PCR results showed that compared to the expression of the virulence factors in CA-MRSA wild type( PSMα 257. 30 ±37. 33 ;agr 115. 60 ±0. 81 and α-toxin 3.23 ±0. 21), in AraC-, α-toxin, PSMα and agr were significantly down regulated(α-toxin 1.09 ±0.01 :t = 10. 18, P <0.01 ;PSMα 34.85 ±2. 15:t=5.95,P<0.05;agr35. 19 ±1. 72:t =42. 33, P<0. 01). The result of mice bacteremia model showed that the virulence of wild type and AraC- ( (x) ± s ) were significantly different (x2 = 21. 34, P < 0.01). The expression of PSMα, agr and α-toxin in AraC-pT181araC ( PSMa 180.10 ± 15.29;agr 101. 50 ±8. 96;α-toxin 2.59 ±0.26) had no significant difference compared to the expression of the virulent factors in CA-MRSA wild type (PSMα: t =1.914, P>0.05;agr:t= 1.563, P>0.05;α-toxm: t = 1. 923, P > 0. 05 ). There were no significant difference of the expression of ClpP in AraC-(0. 21 ±0.01) and in AraC-pT181araC(0.17 ±0.03)compared to the expression of ClpP in CA-MRSA wild type (0. 20 ± 0.01) (t=0.555, P>0.05 and t=0. 851, P>0.05). The result of mice skin abscess model showed that the dermonecrosis area caused by CA-MRSA was (136. 5 ±21.45) mm2, the dermonecrosis area caused by AraC- was (55. 69 ± 13. 81) mm2, the different was significant (t = 3.169, P < 0. 05). Conclusion In CA-MRSA, AraC-type transcriptional regulator controlled the pathogenesis of CA-MRSA by regulating the expression of the most important virulence factors such as hla, PSMα and agr.

Analysis of cefoxitin-sensitive, penicillin-resistant Staphylococcus tested by disk diffusion method / 中华检验医学杂志

Objective To evalue the ability of detecting the resistance of cefoxitin-sensitive,penicillin-resistant Staphylococcus by different methods and analyze the antibiotic susceptibility spectrum of coagulase-negative Staphylococcus which are non-mecA-mediated oxacillin resistance. Methods All the isolates were collected from Huashan hospital between 2007 and 2009. The isolates were recovered from various clinical sources, including respiratory tract, urine, secretion and sterile fluids samples. The oxacillin susceptibility of Staphylococcus aureus was determined by cefoxitin disk diffusion test, cefoxitin MIC test,oxacillin disk diffusion test and oxacillin MIC test Likewise, the oxacillin susceptibility of coagulasenegative Staphylococcus was determined by cefoxitin disk diffusion test and oxacillin MIC test. All the isolates with sensitive to cefoxitin were screened for the mec A gene by PCR Finally, the MIC of non-mecA-mediated oxacillin-resistant Staphylococcus were determined. Results Among 255 cefoxitin disk diffusion test sensitive and penicillin-resistant Staphylococcus aureus, 6 isolates were intermediated to oxacillin and 4 were resistant by oxacillin disk diffusion test, but all the isolates were sensitive by the cefoxitin disk diffusion test,cefoxitin MIC test and oxacillin MIC test. Among 75 cefoxitin disk diffusion test sensitive and penicillin-resistant coagulase-negative Staphylococcus, 16 isolates were resistant to oxacillin by oxacillin MIC method and 4 carried mecA gene. Among 12 non-mecA-mediated oxacillin-resistant Staphylococcus, the susceptible isolates of gentamicin is 10, clindamycin is 8, ciprofloxacin is 11, erythrornycin is 6, trimethoprim/sulfamethoxazo]e is 11 ,and cephalosporins, teicoplaninl, vancomycin, piperacillin/tazobactam, tetracycline are all 12. Conclusions The cefoxitin disk diffusion test can reliably predict mecA-mediated oxacillin resistant Staphylococcus aureus. It would be best to combine cefoxitin disk diffusion test and oxacillin MIC test to improve accuracy of detection of mecA-mediated oxacillin resistant coagulase-negative Staphylococcus.Furthermore, infections due to the non-mecA-mediated oxacillin resistant coagulase-negative Staphylococcus can be treated by penicillinase-stable penicillins, β-lactam/β-lactam inhibitor combinations, relevant cephems and carbapenems.