Effect of Macrolides and β-lactams on Clearance of Bordetella pertussis in the Nasopharynx in Children With Whooping Cough

Alterations of Growth, Biofilm-Forming, and Gene Expression of Bordetella pertussis by Antibiotics at Sub-Minimal Inhibitory Concentrations

Bordetella pertussis is the primary agent of the acute respiratory disease pertussis. It has been reported that the disease has recently become more common, especially in adults and adolescents, and adaptation of the pathogen is thought to have an important influence on the recurrence of the disease. This study aims to determine the effect of erythromycin, azithromycin, and trimethoprim-sulfamethoxazole used in the treatment of pertussis on the virulence gene expressions (prn, ptxS1, fhaB), biofilm-forming and growth of B. pertussis. In this study, the minimal inhibitory concentration (MIC) values of azithromycin and erythromycin in B. pertussis local strain Saadet were determined to be 0.09 μg/mL and 0.3 μg/mL, respectively. However, the Tohama-I and Saadet strains were resistant to trimethoprim-sulfamethoxazole (MIC>32 μg/mL). The biofilm-forming of the Saadet strain decreased with the increase in antibiotic doses. It was observed that 1/32MIC erythromycin and 1/32MIC azithromycin upregulated the expression of fhaB in Tohama-I, whereas the expression of ptxS1 and prn significantly decreased in sub-MICs of erythromycin. In the Saadet strain, only ptxS1 was highly expressed at 1/16MIC azithromycin and erythromycin (p>0.05). This is the first study to investigate the effect of sub-MIC antibiotics on the expression of virulence genes and biofilm-forming of B. pertussis.

Genotyping and macrolide-resistant mutation of Bordetella pertussis in East and South-East Asia

OBJECTIVES

Macrolide-resistant Bordetella pertussis (MRBP) has been emerging and prevailing in mainland China since 2011. In this study, we aimed to investigate the genotype and macrolide resistance of circulating B. pertussis in East and Southeast Asia using genetic analyses.

METHODS

A total of 302 DNA extracts from clinical specimens and isolates from 2010 to 2020 were analyzed: 145 from Vietnam, 76 from Cambodia, 48 from Taiwan, and 33 from Japan. Genotypes were determined by multilocus variable-number tandem-repeat analysis (MLVA). Macrolide-resistant A2047G mutation in B. pertussis 23S rRNA was investigated using the duplex Cycleave real-time polymerase chain reaction (PCR) assay. Whole-genome sequencing was performed on two MRBP isolates that were identified for the first time in Taiwan.

RESULTS

Overall, 286 DNA extracts (95%) generated a complete MLVA genotype and 283 DNA extracts (94%) yielded a complete result for the A2047G mutation analysis. The A2047G mutation was detected in 18 DNA extracts: fourteen from Vietnam, one from Cambodia, two from Taiwan, and one from Japan. Most of them (78%) showed the genotypes MT104 and MT195, which have previously been reported in Chinese MRBP isolates. Further, the Taiwanese MRBP isolates were classified into the MT104 clade of Chinese MRBP isolates.

CONCLUSION

After MRBP emerged and spread in mainland China, it may have spread to East and Southeast Asia in the 2010s. Continued surveillance targeting the A2047G mutation of MRBP is needed to prevent further spread of this emerging pathogen.

Macrolide Resistance in Bordetella pertussis: Current Situation and Future Challenges

Pertussis is a highly contagious respiratory infection caused by Bordetella pertussis bacterium. The mainstay of treatment is macrolide antibiotics that reduce transmissibility, shorten the duration of symptoms and decrease mortality in infants. Recently, the macrolide resistance of B. pertussis has been reported globally but is especially widespread in mainland China. In this review, we aim to summarise the current understanding of the epidemiology, resistance mechanisms and clinical implications of B. pertussis macrolide resistance. Since the first appearance of macrolide-resistant B. pertussis in Arizona, USA, in 1994, only sporadic cases have been reported outside China. In certain parts of China, on the other hand, up to 70-100% of the recent clinical isolates have been found to be macrolide resistant. Reasons for macrolide resistance being centred upon China during the last decade can only be speculated on, but the dominant B. pertussis lineage is different between China and most of the high-income countries. It seems evident that efforts to increase awareness, guide molecular epidemiological surveillance and carry out systematic screening of B. pertussis positive samples for macrolide resistance should be implemented globally. In addition, practices to improve the clinical care of infants with pertussis caused by resistant strains should be studied vigorously.

[Clinical features and epidemiological significance of pertussis in infants]

Infantile pertussis is clear evidence for the persistent transmission of pertussis in communities. Infants are the most vulnerable population for pertussis infection and are also important nodes in pertussis transmission networks in communities, and therefore, the prevention of infantile pertussis is the core of prevention and control measures against pertussis including vaccine immunization. Although the cases of pertussis reported in China are mainly infants with pertussis, the actual number of infants with pertussis might be higher than the reported number. It is necessary in clinical practice to improve the awareness of this disease and promote related laboratory tests. On the basis of emphasizing the identification of pertussis in infants, timely diagnosis and treatment, follow-up visits, and standard management of the close contacts of infants with pertussis should be performed to reduce and block the community transmission of pertussis.

A Cross-Sectional Study Revealing the Emergence of Erythromycin-Resistant Bordetella pertussis Carrying ptxP3 Alleles in China

Background

Previous limited studies have identified that Bordetella pertussis (B. pertussis) isolates circulating in China possess distinct molecular features and high rates of erythromycin-resistance (ER). Their evolution and potential impact on the prevention and control of global pertussis are worthy of attention.

Methods

The present cross-sectional study involved 311 non-duplicate and unrelated B. pertussis strains isolated from Chinese children from 2017 to 2019. Their antimicrobial susceptibilities were assessed using both E-test strips and Kirby-Bauer (KB) disk diffusion methods. Seven virulence-related genes (ptxA, ptxC, ptxP, prn, fim2, fim3, and tcfA2) and the A2047G mutation in the 23S rRNA gene were detected by PCR. Based on the susceptibilities and genotypes, 50 isolates were selected for multi-locus variable-number tandem-repeat analysis (MLVA) typing and whole-genome sequencing.

Results

A total of 311 B. pertussis strains were isolated from children with a median age of 4 months (interquartile range: 2–9 months). Strains carrying the ptxP1 allele were more frequent (84.9%, 264/311), were always ER (except for one strain), and were mainly related to ptxA1/ptxC1/prn1 alleles (99.6%, 263/264). The remaining 47 (15.1%) strains carried the ptxP3 allele, mainly harboring the ptxA1/ptxC2/prn2 alleles (93.6%, 44/47), and were sensitive to erythromycin (except for two strains). The two ER-ptxP3 isolates were first identified in China, belonged to MT27 and MT28 according to MLVA, and were classified into sub-lineage IVd by phylogenetic analysis of their genome sequences. This sub-lineage also includes many strains carrying the ptxP3 allele spreading in developed countries. For each tested antimicrobial, the susceptibilities judged by KB disks were consistent with those determined by E-test strips.

Conclusion

The present results reveal that B. pertussis strains with the ptxP1-ER profile still dominate in China, and a few strains carrying the ptxP3 allele have acquired the A2047G mutation in the 23S rRNA gene and the ER phenotype. The surveillance of the drug susceptibility of B. pertussis is necessary for all countries, and the KB disk method can be adopted as a screening test.

Establishment of Epidemiological Resistance Cut-Off Values of Aquatic Aeromonas to Eight Antimicrobial Agents

The abuse of antibiotics in aquaculture has led to the increasing rate of antibiotic resistance of aquatic bacteria including Aeromonas, which is an increasing threat to environmental and human health. To date, no epidemiological cut-off values (COWT) for Aeromonas spp. have been established by the Clinical and Laboratory Standards Institute nor the European Commission on Antimicrobial Susceptibility Testing. In this study, commercially prepared minimum inhibitory concentration (MIC) test 96-well plates (dry-form plates) were used to determine the MIC of eight antimicrobial agents against 556 Aeromonas strains. The obtained MIC distributions were simulated and analyzed by NRI and ECOFFinder to obtain tentative COWT values for Aeromonas spp. The COWT values of eight kinds of representative antimicrobial agents including trimethoprim–sulfamethoxazole, erythromycin, doxycycline, neomycin, colistin, florfenicol, enrofloxacin, and ceftazidime for Aeromonas spp. were established and were 0.25, 64/32, 4/2, 8, 4, 1, 0.062/0.125, and 0.5 μg/mL, respectively. Results showed that Aeromonas spp. had a very high proportion of non-wild-type strains to enrofloxacin, florfenicol, and doxycycline, which are the most widely used antimicrobials in aquaculture. The COWT values for Aeromonas spp. obtained in this study can contribute to the final establishment of COWT for Aeromonas spp. internationally.