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. 2021 May 14;21(1):148.
doi: 10.1186/s12866-021-02217-y.

Effectiveness of antibacterial agents against cell-invading bacteria such as Streptococcus pyogenes and Haemophilus influenzae

Hiroyuki Iuchi  1 , Junichiro Ohori  2 , Satoshi Kiyama  2 , Naoko Imuta  3 , Junichiro Nishi  3 , Yuichi Kurono  2 , Masaru Yamashita  2
Affiliations

Effectiveness of antibacterial agents against cell-invading bacteria such as Streptococcus pyogenes and Haemophilus influenzae

Hiroyuki Iuchi et al. BMC Microbiol. .

Abstract

Background: Recurrent tonsillitis is one of the most common otolaryngological disorders caused by cell-invading bacteria, such as Streptococcus pyogenes (S. pyogenes) and Haemophilus influenzae. The aim of this study was to investigate the effect of antibacterial agents against cell-invading bacteria.

Methods: The intracellular invasion of Detroit 562 cells by five strains of nontypeable Haemophilus influenzae (NTHi) and four strains of S. pyogenes was investigated. The antibacterial agents used were garenoxacin (GRNX), clarithromycin (CAM), amoxicillin (AMPC), cefditoren pivoxil (CDTR-PI), and levofloxacin (LVFX).

Results: Both NTHi and S. pyogenes fully invaded Detroit 562 cells in 6 h and were less sensitive to CAM. GRNX, CAM, and LVFX were effective against bacteria invading the cells, but AMPC and CDTR-PI were not effective. GRNX was the most effective.

Conclusion: GRNX was the most effective agent against bacteria invading cells.

Keywords: Antibacterial agents; Garenoxacin; Haemophilus influenzae; Streptococcus pyogenes; Susceptibility; emm typing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1
Bacterial invasion time. Nontypeable Haemophilus influenzae (NTHi) entered the cells 2 h after adhering to the cells (a). The maximum invasion was at 6 h (a). There were no differences between the numbers of bacteria invading the cells after 6 h and 8 h (a). Similar results were also observed with Streptococcus pyogenes, which invaded the cells 2 h after cell adhesion (b). The maximum invasion was at 6 h (b). No differences were found between the numbers of cell-invading bacteria after 6 h and 8 h (b). *p < 0.05. N.S., not significant; CFU, colony-forming units
Fig. 2
Fig. 2
Effects of antibacterial agents on nontypeable Haemophilus influenzae. Cells invaded by bacteria and then treated with phosphate-buffered saline (PBS) served as the study control. A significant bactericidal effect on each NTHi strains was observed when 1 MIC of GRNX, CAM, or LVFX was used (a) (p < 0.05). However, no bactericidal effect was observed from treatment with AMPC or CDTR-PI (a). Similarly, treatment with 2 MIC of GRNX, CAM, or LVFX also had a significant bactericidal effect (p < 0.05), but when treated with AMPC or CDTR-PI, no bactericidal effect was observed (b). MIC, minimum inhibitory concentration; NTHi, nontypeable Haemophilus influenzae; GRNX, garenoxacin; LVFX, levofloxacin; CAM, clarithromycin; AMPC, amoxicillin; CDTR-PI, cefditoren pivoxil; CFU, colony-forming units. *p < 0.05
Fig. 3
Fig. 3
Effects of antibacterial agents on Streptococcus pyogenes. Cells invaded by bacteria and then treated with PBS served as the study control. When 1 MIC of GRNX, CAM, or LVFX was used, each S. pyogenes strain demonstrated a significant bactericidal effect (a) (p < 0.05). However, treatment with AMPC or CDTR-PI showed no bactericidal effect (a). Treatment with 2 MIC of GRNX, CAM, or LVFX also yielded a significant bactericidal effect (p < 0.05), but treatment with AMPC or CDTR-PI exhibited no bactericidal effect (b). MIC, minimum inhibitory concentration; S. pyogenes, Streptococcus pyogenes; GRNX, garenoxacin; LVFX, levofloxacin; CAM, clarithromycin; AMPC, amoxicillin; CDTR-PI, cefditoren pivoxil; CFU, colony-forming units. *p < 0.05
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