Molecular characteristics and antimicrobial susceptibility of Staphylococcus aureus among children with respiratory tract infections in southwest China.

BACKGROUND: The molecular characteristics and antimicrobial susceptibility of Staphylococcus aureus (S. aureus) in general pediatric wards and county-level hospitals were rarely reported in China. METHODS: Staphylococcus aureus was isolated from children hospitalized with respiratory tract infection (RTI) in Zhongjiang and Youyang counties in 2015. All isolates were typed by multilocus sequence, staphylococcal protein A, accessory gene regulator (agr), and staphylococcal cassette chromosome mec [SCCmec, for methicillin-resistant S. aureus (MRSA) only]. Polymerase chain reaction was used to screen 21 super-antigen (SAg) genes and panton-valentine leukocidin (pvl). Antimicrobial susceptibility testing was performed by E test. RESULTS: A total of 2136 children were enrolled. Overall, 125 (5.9%) children carried S. aureus, among which MRSA accounted for 42.4%. ST59-SCCmec type IV-t437-agr group I (58.5%) was the most prevalent genotype in MRSA, and ST188-t189-agr group I (22.2%) was the top genotype in methicillin-sensitive S. aureus (MSSA). The pvl carriage rate in MRSA and MSSA was 15.1% and 9.7%, respectively (P = 0.4112). About 96.8% of S. aureus isolates were positive for at least one SAg gene. The most common SAg gene profile in the dominant ST59 clone was seb-sek-seq (42.8%). All S. aureus isolates were resistant to penicillin and erythromycin (minimum inhibitory concentration 90 was > 32 and 256 mg/L to penicillin and erythromycin, respectively), but usually susceptible to other tested non-ß-lactam antimicrobials. CONCLUSIONS: Staphylococcus aureus and MRSA were detected with a high frequency in children with RTI in county-level hospitals of China. ST59-SCCmec type IV-t437-agr group I was the dominant MRSA clone. The S. aureus isolates exhibited high resistance to penicillin and erythromycin.

Epidemiological study on the penicillin resistance of clinical Streptococcus pneumoniae isolates identified as the common sequence types.

There were some limitation in the current interpretation about the penicillin resistance mechanism of clinical Streptococcus pneumoniae isolates at the strain level. To explore the possibilities of studying the mechanism based on the sequence types (ST) of this bacteria, 488 isolates collected in Beijing from 1997-2014 and 88 isolates collected in Youyang County, Chongqing and Zhongjiang County, Sichuan in 2015 were analyzed by penicillin minimum inhibitory concentration (MIC) distribution and annual distribution. The results showed that the penicillin MICs of the all isolates covering by the given ST in Beijing have a defined range, either <0.25 mg/L or≥0.25 mg/L, except for the ST342. The isolates with penicillin MIC <0.25 mg/L were mainly collected before 2001, after which the isolates with MIC≥0.25 mg/L occurred and became the major population gradually. This law of year distribution, however, was not obvious for any specific ST. The isolates covering by any given ST could be determined with different penicillin MICs in the first few years after it was identified. The penicillin MIC of isolates identified as common STs and collected in Youyang County, Chongqing and Sichuan Zhongjiang County, including the ST271, ST320 and ST81, was around 0.25~2 mg/L (≥0.25 mg/L). Our study revealed the epidemiological distribution of penicillin MICs of the given STs determined in clinical S. pneumoniae isolates, suggesting that it is reasonable to research the penicillin resistance mechanism based on the STs of this bacteria.

[Prevalence of Moraxella catarrhalis in the nasopharyngeal specimen from 1 082 hospitalized children with respiratory infection and the drug resistance of the isolates].

OBJECTIVE: To investigate the prevalence of Moraxella catarrhalis in the nasopharyngeal region of children with respiratory infection and the sensitivity of Moraxella catarrhalis isolates to common antimicrobial drugs. METHODS: Nasopharyngeal swabs were collected from 1 082 children with respiratory infection, and Moraxella catarrhalis strains were isolated. The E-test method and disc diffusion test were used to determine the sensitivity of these strains to 11 common antimicrobial drugs. The test results were interpreted with reference to the standards of European Committee on Antimicrobial Susceptibility Testing (EUCAST), Clinical and Laboratory Standards Institute (CLSI), and British Society for Antimicrobial Chemotherapy (BSAC). The nitrocefin disc method was used to detect whether the isolated strains produced ß-lactamase. RESULTS: Among the 1 082 children with respiratory infection, 77 (77/1 082, 7.12%) carried Moraxella catarrhalis in the nasopharyngeal region. All the strains produced ß-lactamase. With reference to all the three standards, all the strains were sensitive to amoxycillin-clavulanate and had a susceptibility rate of >95% towards ciprofloxacin and tetracycline. According to the EUCAST and CLSI standards, the susceptibility rate of the strains towards sulfamethoxazole-trimethoprim was as high as 98.7%, and more than 80% of all strains were sensitive to the three cephalosporins detected; however, with reference to the BSAC standard, only 2.6% of the strains were sensitive to cefuroxime, with an intermediate rate of 44.2% and a drug resistance rate of 53.2%. The rate of resistance to ampicillin was 81.8%. According to the CLSI standard, the non-susceptibility rate of the strains to erythromycin was 79.2%, and according to the EUCAST or BSAC standards, their non-susceptibility rate reached 90.9%; more than one third of the strains (27/77, 35.1%) had a minimal inhibitory concentration of >256 mg/L. CONCLUSIONS: All of the Moraxella catarrhalis isolates in the nasopharyngeal region of children with respiratory infection produce ß-lactamase and are sensitive to amoxycillin-clavulanate. These isolates have high susceptibility rates to the third- and fourth-generation cephalosporins and sulfamethoxazole-trimethoprim, but most of the isolates are resistant to ampicillin, cefuroxime, and erythromycin.