Antimicrobial and Anti-Biofilm Activity of Polymyxin E Alone and in Combination with Probiotic Strains of Bacillus subtilis KATMIRA1933 and Bacillus amyloliquefaciens B-1895 against Clinical Isolates of Selected Acinetobacter spp.: A Preliminary Study.

Munaf Al-Dulaimi,Alexey M Ermakov,Maria S Mazanko,Michael L Chikindas,Dmitry V Rudoy,Alyaa Abdelhameed,Ammar Algburi

doi:10.3390/pathogens10121574

Abstract

Acinetobacter spp., the nosocomial pathogen, forms strong biofilms and is resistant to numerous antibiotics, causing persistent infections. This study investigates the antibacterial and anti-biofilm activity of polymyxin E alone and in combination with the cell-free supernatants (CFS) of the tested probiotic bacilli, Bacillus subtilis KATMIRA1933 and Bacillus amyloliquefaciens B-1895 against the selected Acinetobacter spp. starins. Three isolates of Acinetobacter spp., designated as Acinetobacter spp. isolate 1; Acinetobacter spp. isolate 2, and Acinetobacter spp. isolate 3, were collected from patients with burns, wounds, and blood infections, respectively. Bacterial identification and antibiotic susceptibility testing were conducted using the VITEK2 system. Auto-aggregation and coaggregation of the tested bacilli strains with the selected Acinetobacter spp. isolates were evaluated. A disk diffusion assay was used to identify the microorganism’s susceptibility to the selected antibiotics, alone and in combination with the CFS of the bacilli. The MIC and MBIC (minimum inhibitory and minimum biofilm inhibitory concentrations) of polymyxin E combined with bacilli CFS were determined. Acinetobacter spp. isolates were (i) sensitive to polymyxin E, (ii) able to form a strong biofilm, and (iii) resistant to the tested antibiotics and the CFS of tested bacilli. Significant inhibition of biofilm formation was noticed when CFS of the tested bacilli were combined with polymyxin E. The bacilli CFS showed synergy with polymyxin E against planktonic cells and biofilms of the isolated pathogens.

Highlights

Acinetobacter spp. is a Gram-negative, obligate aerobe, cocco-bacilli, and one of the most prevalent causative agents of several hospital and community-acquired infections [1]
Our findings showed that bacilli strains were susceptible to the majority of the selected antibiotics (Table 2), while they were tolerant to polymyxin E
Our data showed a significant increase in the selected Acinetobacter spp. strains growth inhibition when the cell-free supernatants (CFS) of bacilli strains was combined with polymyxin E, compared to the use of the antibiotic alone (Figure 8)

Summary

Introduction

Acinetobacter spp. is a Gram-negative, obligate aerobe, cocco-bacilli, and one of the most prevalent causative agents of several hospital and community-acquired infections [1]. This bacterium is related to skin, soft tissue, and urinary tract infections, in addition to meningitis, bacteremia, and pneumonia [2]. Polymyxin E (or colistin) has recently been used as a “last line” therapeutic substance to control the growth of multidrug resistant Gram-negative bacteria [7]. Effective approaches using antimicrobial combinations are urgently required as alternative and safe strategies to combat bacterial resistance to antibiotics. One of the suggested methods is using probiotics and their metabolites as antimicrobial substances in combination with conventional antibiotics to increase the sensitivity of pathogenic strains [10]

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Conclusion