Molecular Analysis of PBP1A in Streptococcus pneumoniae Isolated from Clinical and Normal Flora Samples in Tehran, Iran: A Multicenter Study

Affinity of cefditoren for penicillin-binding proteins in bacteria and its relationship with antibiotic sensitivity

Penicillin-binding proteins (PBPs) are the targets of β-lactam antibiotics; however, changes in the affinity of PBPs for beta-lactam antibiotics often affect the susceptibility of bacteria to antibiotics. The purpose of this study was to elucidate the mechanism by which cefditoren, an oral third-generation cephalosporin, binds PBPs. The minimal inhibitory concentration (MIC), bactericidal curves, and inhibition zone comparisons were assessed to evaluate the antibacterial activity of cefditoren. PBP1A and PBP2X proteins from Streptococcus pneumoniae were purified, and their ability to bind to cefditoren was investigated via microscale thermophoresis. The Kd of cefditoren toward PBP1A was 0.005 ± 0.004 µM, which was lower than those of other cephalosporins (cefcapene, cefixime and cefdinir). In contrast, the Kd of cefditoren toward PBP2X of S. pneumoniae was 9.70 ± 8.24 µM, which was lower than that of cefixime but higher than those of cefcapene and cefdinir. Additionally, the biotinylated ampicillin (BIO-AMP) method was employed to evaluate the affinity of cefditoren toward PBPs of Haemophilus influenzae, and the results demonstrated that cefditoren and PBP3A/B had the lowest IC50 values (0.060 ± 0.002 µM). These findings indicate that cefditoren has a strong affinity for PBP1A of H. influenzae. Cefditoren has a high affinity toward the PBP1As of S. pneumoniae and PBP1A and PBP3A/B of H. influenzae, which may contribute to the effective antibacterial effects of cefditoren against clinical strains and its low propensity for inducing resistance. The data presented in this article help elucidate the mechanism by which cefditoren, an oral third-generation cephalosporin, binds to PBPs and provide theoretical support for the wider use of cefditoren as an antibiotic therapy.

Monitoring Over a Decade in the Serotype Prevalence of Streptococcus pneumoniae in Iran: A Systematic Review and Meta-analysis

BACKGROUND

There is no comprehensive information about the circulating serotypes of Streptococcus pneumoniae in Iran in recent years. This study aimed to summarize information about the changes over a decade in the serotype prevalence of S. pneumoniae in Iran.

METHODS

We performed a comprehensive search in PubMed/Medline, Web of Science, Science Direct, and the Iranian Database, such as Magiran and SID, from January 2011 to February 2023. The systematic process, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), was carried out by two researchers who were both independent and calibrated. Statistical analyses were carried out using Comprehensive Meta-Analysis software. Identifying and measuring heterogeneity were done using I2 and the chi-square test. Finally, Begg's rank correlation test was used in combination with a funnel plot to evaluate any possible publication bias.

RESULTS

The search returned 16 relevant results, with a total of 1575 isolates. Of those studies, eight studies reported the distribution of S. pneumoniae serotypes among patients, three studies among healthy individuals, and five studies among both groups. As the meta-analysis revealed, the most common serotypes were 23F (n = 299, 14.1% [95% CI: 9.7-19.9]; I2 = 84.3%; P<0.001 for heterogeneity), 19F (n = 221, 13.4% [95% CI: 9.9-17.9; I2 = 76.7%; P<0.001 for heterogeneity]), and 19A (n = 102, 8.7% [95% CI: 6.5-11.7; I2 = 54.3%; P<0.001 for heterogeneity]). Moreover, Begg's test (P = 0.160, 0.173, and 0.176 for 23F, 19F, and 19A, respectively) showed no evidence of publication bias.

CONCLUSION

Based on our pooled results, the majority of the serotypes of pneumococci in the Iranian population were 23F, 19F, and 19A, respectively, over the last decade. The findings can be valuable in selecting effective pneumococcal vaccine candidates and targeted antibiotics in Iranian patients.

Is Penicillin-Nonsusceptible Streptococcus pneumoniae a Significant Challenge to Healthcare System? A Systematic Review and Meta-Analysis

BACKGROUND

In recent years, antibiotic-resistant pathogens including penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) have posed serious threats against human health. The aim of this meta-analysis was to investigate the prevalence of Streptococcus pneumoniae drug resistance particularly the incidence of PNSP strains in Iran.

METHODS

A systematic search was done in national and international electronic databases using Persian and English keywords. Up until May 20, 2020, a total of 58 publications were detected as eligible articles based on the inclusion and exclusion criteria, and then the selected studies were enrolled for data extraction and meta-analysis according to the PRISMA guidelines.

RESULTS

A high rate of PNSP (46.9%) and multidrug-resistant (MDR) S. pneumoniae (45.3%) in our isolates were evident. Furthermore, total frequency resistance to other drugs in S. pneumoniae was as follows: erythromycin 41.1%, azithromycin 53.2%, tetracycline 39.9%, levofloxacin 1.7%, rifampin 1.2%, clindamycin 31.7%, vancomycin 1.7%, trimethoprim/sulfamethoxazole 63.9%, chloramphenicol 20%, ceftriaxone 10.9%, amoxicillin 30.5%, ciprofloxacin 8.3%, imipenem 6.1%, linezolid 0%, and cefotaxime 8.3%.

CONCLUSION

Although the overall prevalence of cephalosporin- and carbapenem-resistant Streptococcus pneumoniae was low, penicillin-resistant strains, especially PNSP, could become a significant challenge to the healthcare system in Iran. Hence, the prescription of penicillin as the first-choice antibiotic in the treatment of S. pneumoniae infections should be avoided.

Ruminal resistome of dairy cattle is individualized and the resistotypes are associated with milking traits

BACKGROUND

Antimicrobial resistance is one of the most urgent threat to global public health, as it can lead to high morbidity, mortality, and medical costs for humans and livestock animals. In ruminants, the rumen microbiome carries a large number of antimicrobial resistance genes (ARGs), which could disseminate to the environment through saliva, or through the flow of rumen microbial biomass to the hindgut and released through feces. The occurrence and distribution of ARGs in rumen microbes has been reported, revealing the effects of external stimuli (e.g., antimicrobial administrations and diet ingredients) on the antimicrobial resistance in the rumen. However, the host effect on the ruminal resistome and their interactions remain largely unknown. Here, we investigated the ruminal resistome and its relationship with host feed intake and milk protein yield using metagenomic sequencing.

RESULTS

The ruminal resistome conferred resistance to 26 classes of antimicrobials, with genes encoding resistance to tetracycline being the most predominant. The ARG-containing contigs were assigned to bacterial taxonomy, and the majority of highly abundant bacterial genera were resistant to at least one antimicrobial, while the abundances of ARG-containing bacterial genera showed distinct variations. Although the ruminal resistome is not co-varied with host feed intake, it could be potentially linked to milk protein yield in dairy cows. Results showed that host feed intake did not affect the alpha or beta diversity of the ruminal resistome or the abundances of ARGs, while the Shannon index (R² = 0.63, P < 0.01) and richness (R² = 0.67, P < 0.01) of the ruminal resistome were highly correlated with milk protein yield. A total of 128 significantly different ARGs (FDR < 0.05) were identified in the high- and low-milk protein yield dairy cows. We found four ruminal resistotypes that are driven by specific ARGs and associated with milk protein yield. Particularly, cows with low milk protein yield are classified into the same ruminal resistotype and featured by high-abundance ARGs, including mfd and sav1866.

CONCLUSIONS

The current study uncovered the prevalence of ARGs in the rumen of a cohort of lactating dairy cows. The ruminal resistome is not co-varied with host feed intake, while it could be potentially linked to milk protein yield in dairy cows. Our results provide fundamental knowledge on the prevalence, mechanisms and impact factors of antimicrobial resistance in dairy cattle and are important for both the dairy industry and other food animal antimicrobial resistance control strategies.

Proteomic and Metabolomic Analyses Provide Insights into the Mechanism on Arginine Metabolism Regulated by tRNA Modification Enzymes GidA and MnmE of Streptococcus suis

GidA and MnmE, two important tRNA modification enzymes, are contributed to the addition of the carboxymethylaminomethyl (cmnm) group onto wobble uridine of tRNA. GidA-MnmE modification pathway is evolutionarily conserved among Bacteria and Eukarya, which is crucial in efficient and accurate protein translation. However, its function remains poorly elucidated in zoonotic Streptococcus suis (SS). Here, a gidA and mnmE double knock-out (DKO) strain was constructed to systematically decode regulatory characteristics of GidA-MnmE pathway via proteomic. TMT labelled proteomics analysis identified that many proteins associated with cell divison and growth, fatty acid biosynthesis, virulence, especially arginine deiminase system (ADS) responsible for arginine metabolism were down-regulated in DKO mutant compared with the wild-type (WT) SC19. Accordingly, phenotypic experiments showed that the DKO strain displayed decreased in arginine consumption and ammonia production, deficient growth, and attenuated pathogenicity. Moreover, targeted metabolomic analysis identified that arginine was accumulated in DKO mutant as well. Therefore, these data provide molecular mechanisms for GidA-MnmE modification pathway in regulation of arginine metabolism, cell growth and pathogenicity of SS. Through proteomic and metabolomic analysis, we have identified arginine metabolism that is the links between a framework of protein level and the metabolic level of GidA-MnmE modification pathway perturbation.

A Single Amino Acid Replacement in Penicillin-Binding Protein 2X in Streptococcus pyogenes Significantly Increases Fitness on Subtherapeutic Benzylpenicillin Treatment in a Mouse Model of Necrotizing Myositis

Invasive strains of Streptococcus pyogenes with significantly reduced susceptibility to β-lactam antibiotics have been recently described. These reports have caused considerable concern in the international infectious disease, medical microbiology, and public health communities because S. pyogenes has remained universally susceptible to β-lactam antibiotics for 70 years. Virtually all analyzed strains had single amino acid replacements in penicillin-binding protein 2X (PBP2X), a major target of β-lactam antibiotics in pathogenic bacteria. We used isogenic strains to test the hypothesis that a single amino acid replacement in PBP2X conferred a fitness advantage in a mouse model of necrotizing myositis. We determined that when mice were administered intermittent subtherapeutic dosing of benzylpenicillin, the strain with a Pro601Leu amino acid replacement in PBP2X that confers reduced β-lactam susceptibility in vitro was more fit, as assessed by the magnitude of colony-forming units recovered from disease tissue. These data provide important pathogenesis information that bears on this emerging global infectious disease problem.

Serotype Distribution and Antibiotic Susceptibility of Streptococcus pneumoniae Isolates in Tehran, Iran: A Surveillance Study

Introduction

Encapsulated Streptococcus pneumoniae strains cause high morbidity and mortality, mainly in countries with no pneumococcal conjugate vaccines (PCVs) immunization program. This study investigated the epidemiological changes of S. pneumoniae isolates including serotype distribution and antimicrobial susceptibility in Tehran, Iran.

Methods

A total of 80 S. pneumoniae samples were collected from patients admitted to Shariati hospital over two periods. Half of the isolates were collected from February to September 2017 and the other half from July 2018 to March 2019. The antimicrobial susceptibility testing and PCV-13 serotype coverage of S. pneumoniae isolates were evaluated among patients with invasive and non-invasive infections.

Results

The most common serotypes were 23F (17.5%), 14 (16.3%), 3 (16.3%) 19F (12.5%), and 19A (12.5%) in the present study. The vaccine coverage rates of PCV-7, PCV-10 and PCV-13 were 52.6%, 52.6%, and 83.7%, respectively. S. pneumoniae isolates with the serotype of the PCV-13 showed an increasing trend during the study. Nearly half of the S. pneumoniae strains were MDR, while MDR serotype 19A increased (40%) during the study periods. A small minority of isolates (16%) belonged to non-vaccine serotypes, 65% of which were assigned to MDR. In general, the frequency of penicillin resistant and MDR strains were estimated about 27.5% and 51%, respectively. An increase was observed in resistance to erythromycin and co-trimoxazole.

Conclusion

The results showed that majority of the circulating serotypes in our study are related to PCV-13 serotypes. The use of conjugate vaccine in the immunization program and surveillance of antimicrobial resistance can be effective in reducing the pneumococcal clinical burden.