Molecular characteristics and virulence genes of Staphylococcus aureus in bloodstream infection from children during 2016-2021 / 中华检验医学杂志

Objectives:To study the molecular characteristics, virulence gene and resistance profiles of Staphylococcus aureus ( S. aureus, SA) isolates from bloodstream infections (BSI), so as to further understand the molecular characteristics of S. aureus in pediatric patients. Methods:A total of 53 S. aureus strains in bloodstream infections from Shanghai Children′s Hospital between 2016 and 2021 were collected. Antimicrobial susceptibility test were adopted by instrumental and disk diffusion method. Thirty-two kinds of virulence genes were detected by PCR and underwent multi-locus sequence typing (MLST), Staphylococcus protein A (spa) typing and staphylococcal chromosome cassette (staphylococcal cassette chromosome mec, SCCmec) typing characterizing methicillin-resistant Staphylococcus aureus (MRSA). Statistical analysis was performed using χ 2 test or Fisher exact test. Results:MRSA isolates accounted for 50.94% of the total(27/53), with ST398-t034-SCCmecV (6/53, 11.32%) and ST59-t437-SCCmecIV (4/53, 7.55%) as the most common MRSA clones. Methicillin-sensitive Staphylococcus aureus (MSSA) isolates occupied 49.06% (26/53), among which typing ST22-t309 (3/53, 5.66%) and ST7-t091/t1685 (2/53, 3.77% each) were prevalent. Of the 53 strains, all carried ≥6 virulence genes, 33 strains (62.26%) carried ≥10 virulence genes, including 18 strains of MSSA (69.23%) and 15 strains of MRSA (55.56%). The carriage rate of pvl gene in MSSA was higher than that of MRSA isolates (12/26, 33.33% vs. 6/27, 22.22%), and sasX was only detected in MRSA isolates (4/53, 7.55%). The resistant rates of BSI-SA isolates to penicillin, erythromycin and clindamycin were 98.11%, 49.06% and 41.51%, respectively. MRSA were more resistant to clinical antimicrobial agents than MSSA. Conclusions:MRSA strains cover a high proportion in S. aureus bloodstream infection of children, with ST398-t034 and ST59-t437 being the most common clones. The virulence gene carrying rate for BSI-SA was high with a greater pvl gene carrying rate in MSSA isolates while sasX was only detected in MRSA isolates. More clinical attention should be paid to the high resistance status and virulence genes characteristics of BSI-SA.

Antimicrobial resistance surveillance in Shanghai Children's Hospital from 2011 to 2016 / 中国感染与化疗杂志

Objective To investigate the distribution and resistance profile of bacterial isolates in Shanghai Children's Hospital. Methods Antimicrobial susceptibility of all isolates was determined by Kirby-Bauer disk diffusion method according to 2016 CLSI standard. The data were analyzed by WHONET 5.6 software. Results A total of 23 259 non-duplicate strains were isolated from 2011 to 2016, including 10 885(46.8％)gram-postive cocci and 12 374(53.2％)gram-negative bacilli. The average prevalence of methicillin-resistant S. aureus(MRSA)and coagulase-negative Staphylococcus(MRCNS)was 35.8％ and 82.2％, respectively. The prevalence of MRSA rose from 27.4％ in 2011 to 42.9％ in 2016. The resistance rate of MRSA and MRCNS strains were significantly higher than methicillin sensitive strains. The resistance rate of Enterococcus faecium strains was significant higher than Enterococcus faecalis. The prevalence of non-susceptible Streptococcus pneumoniae was 31.2％(908). No gram-positive strain was resistant to vancomycin or linezolid. The prevalence of carbapenem resistance increased in gram-negative strains. The resistance rate of Klebsiella pneumoniae to imipenem and meropenem rose from 3.1％ and 4.8 ％ in 2011 to 28.7％ and 37.4％ in 2016, respectively.The rate of Pseudomonas aeruginosa resistance to imipenem and meropenem rose from 13.8％ and 16.5％ in 2011 to 18.8％ and 19.4％ in 2016, respectively, while Acinetobacter baumannii showed resistance rate of 38.3％ and 39.9 ％ in 2011 to 68.4％ and 69.7％ in 2016. Conclusions Increasing prevalence of MRSA, carbapenem-resistant K. pneumoniae, extensively drug-resistant A.baumannii has become a concern in clinical practice. Therefore, antimicrobial resistance surveillance should be highly strengthened in children's hospital.

Analysis of mutations detection in 23S rRNA gene locus of Mycoplasma pneumoniae among children / 国际检验医学杂志

Objective To understand the mutations of macrolide resistance gene locus (23S rRNA) of Mycoplasma pneumoniae (MP) and its correlation with clinical features .Methods A total of 354 respiratory tract samples were collected from children pa-tients with pneumonia .MP and its mutations in 23S rRNA gene locus were detected by real-time PCR .The children cases of MP positive were divided into the mutation group and non-mutation group .Then the clinical data were compared between the two groups .Results Among 354 respiratory tract samples ,166 cases(46 .9% ) were MP positive ,moreover the mutation of 23S rRNA gene locus existed in 135 MP positive samples with the positive detection rate of 81 .3% ,while no 23S rRNA gene locus mutations were detected in 31 samples .Analyzing the clinical data of the mutation group and non-mutation group found that there was no sta-tistical difference in the aspects of age and gender between the two groups .The occurrence rates of severe pneumonia and extrapul-monary complications in the mutation group were higher than those in the non-mutation group (P<0 .05) ,moreover the average hospitalization time and fever duration in the mutation group were longer than those in the non-mutation group (P<0 .05) .Conclu-sion 23S rRNA gene locus mutation has higher detection rate ,prompting that MP shows high resistant rate to macrolides ,which could provide a certain basis for treatment of M P infections .

Antimicrobial resistance profile and genotypes of Haemophilus influenzae isolates from respiratory tract in children / 中国感染与化疗杂志

Objective To investigate the antibiotic resistance profile and ftsⅠ genotypes of Haemophilus influenzae isolates from respiratory tract in children.Methods A total of 141 consecutive nonduplicate clinical strains of H.influenzae were collected from January to March 2016.Antimicrobial susceptibility was determined using Kirby-Bauer method.Beta-lactamase production was detected by nitrocefin disk test.PCR technique was employed for ftsⅠ genotyping.Antimicrobial resistance was compared between differentfisⅠ genotypes.Results The prevalence of β-lactamases was 40.4％ (57/141) in H.influenzae isolates.More than half (53.2％,75/141) of the strains were resistant to ampicillin.Mutation offtsI gene was positive in 72.3％ (102/141) of the isolates.The dominant genotype of genomic beta-lactamase-negative ampicillin-resistant (gBLNAR) strains was type Ⅲ (72/102,70.6％).The gBLNAR strains showed higher resistance rate to ampicillin and cefuroxime than the genomic beta-lactamase-negative ampicillin susceptible (gBLNAS) strains (P＜0.05).Conclusions High prevalence offisⅠgene mutation is found in the strains ofH.influenzae isolated from respiratory tract in children.The dominant genotype of gBLNAR strains was type Ⅲ.Mutation offtsⅠ gene in H.influenzae is associated with higher resistance rate to ampicillin and cefuroxime.

Resistant mechanism of β-lactam antibiotic of invasive Streptococcus pneumoniae / 中华检验医学杂志

Objective To understand the drug resistance and antibiotic resistance mechanism ofβ-lactam antibiotics of invasive Streptococcus pneumoniae isolated from Shanghai Children′s Hospital, provides the reference for the rational use of antimicrobial agents.Methods This study is based on the research of the mechanism of drug resistance.62 isolates of invasive Streptococcus pneumoniae were collected from Shanghai Children′s Hospital from January 2005 to December 2011.Minimum inhibitory concentrations ( MIC) of strains to 9 antimicrobial agents were determined by E-test method.The penicillin binding protein coding genes pbp2x, pbp2b, and pbp1a of Streptococcus pneumoniae were amplified by PCR.Then, the correlation between the gene mutation andβ-lactam antibiotics resistant level were analyzed.The murM gene of Streptococcus pneumoniae was amplified by PCR and the correlation of mutation and β-lactam antibiotics resistant level was analyzed.Results Out of 62 strains of invasive Streptococcus pneumoniae from children, the detection rate of penicillin resistant Streptococcus pneumoniae was 43.6% (27/62).Between penicillin intermediate Streptococcus pneumoniae ( PISP ) ( 100%, 25/25 ) and penicillin sensitive Streptococcus pneumoniae (PSSP) (3/10), the difference of gene mutation rate near the pbp2b conserved sequence was statistically significant (χ2 =21.875, P<0.01).The same situation occurred between penicillin resistant Streptococcus pneumoniae (PRSP)(100%, 27/27)and PSSP (3/10) (χ2 =23.310, P<0.01).Also the difference of gene mutation rate of PISP (84%, 21/25) vs PSSP (0) and PSSP (0) vs PRSP (85.2%, 23/27) near or in the pbp2x conserved sequence were statistically significant (χ2 =21.000, P <0.01;χ2 =22.513,P<0.01).The difference of gene mutation rate near the pbp1a conserved sequence and Insertion sequence, which were statistically significant, occurred between PISP and PSSP (χ2 =13.22,P<0.01), between PRSP and PSSP (χ2 =37.000,P<0.01), between PISP and PRSP (χ2 =10.211,P=0.001). MurM gene mutation rate was statistically significant different between the 2 group penicillin MIC≥8 mg/L or ceftriaxone MIC≥2 mg/L group (95.8%, 23/24) and penicillin MIC<8 mg/L or ceftriaxone MIC<2 mg/L group (0) (χ2 =56.2,P =0.002 6).Conclusions The resistance phenomenon of invasive Streptococcus pneumoniae in Shanghai Children′s Hospital is serious.The gene mutations of pbps and murM play a role in amide in the beta of antibiotic resistance, and there is a certain correlation with the antibiotic resistance level.

Analysis of distribution and antimicrobial resistance of enteric pathogens among children / 中国感染与化疗杂志

Objective To investigate the distribution,epidemiologic features and antibiotic resistance of the enteric pathogens i-solated from children with diarrhea.Methods Enteric pathogens were isolated from children’s stool samples.The children with diarrhea were treated in the outpatient and inpatient of Shanghai Children’s Hospital between 2008 and 2013.Antimicrobial susceptibility testing was conducted by disk diffusion method for Salmonella and Shigella with 6 antimicrobial agents.Results A total of 545 enteric pathogens were collected.Salmonella was the dominant pathogen,accounting for 67.2%,followed by Shigella (20.7%),S.aureus (4.6%),C.jejuni (3.7%),Aeromonas (2.4%),and enteropathogenic E.coli (0.9%).The main serotypes of Salmonella were S.typhimurium and S.enteritidis.Approximately 56.3% of the patients were boys.A-bout 72.7% of the patients were infants under 2 years.The prevalence of diarrhea peaked in summer and autumn (72.9%). The susceptibility of these isolates was only tested with seven antibiotics.Shigella showed higher level of resistance to ampicil-lin and trimethoprim-sulfamethoxazole than Salmonella (P<0.05).Significantly higher percentage of S.flexneri isolates were resistant to sulbactam-ampicillin,ceftriaxone,ciprofloxacin,and chloramphenicol than S.sonnei (P<0.001).Further-more,the prevalence of multidrug resistant strains in Shigella (68.3%)was much higher than that in Salmonella (44.7%,P<0.001).Conclusions A variety of diarrhea-causing enteric pathogens are isolated from the children in Shanghai Children’s Hospital.The isolates are predominantly Salmonella and Shigella species.The epidemiological features of Salmonella and Shigella species are different in terms of gender,age,season and geographical distribution.The resistance to antibiotics is a serious problem and varies with different types of pathogens. Intensive and ongoing surveillance of enteric pathogens and their changing resistant pattern is required to control diar-rhea in children.