Relationship between Antibiotic Resistance, Biofilm Formation, and Biofilm-Specific Resistance in Acinetobacter baumannii

Abstract

In this study, we aimed to examine the relationships between antibiotic resistance, biofilm formation, and biofilm-specific resistance in clinical isolates of Acinetobacter baumannii. The tested 272 isolates were collected from several hospitals in China during 2010-2013. Biofilm-forming capacities were evaluated using the crystal violet staining method. Antibiotic resistance/susceptibility profiles to 21 antibiotics were assessed using VITEK 2 system, broth microdilution method or the Kirby-Bauer disc diffusion method. The minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) to cefotaxime, imipenem, and ciprofloxacin were evaluated using micro dilution assays. Genetic relatedness of the isolates was also analyzed by pulsedfield gel electrophoresis (PFGE) and plasmid profile. Among all the 272 isolates, 31 were multidrug-resistant (MDR), and 166 were extensively drug-resistant (XDR). PFGE typing revealed 167 pattern types and 103 clusters with a similarity of 80%. MDR and XDR isolates built up the main prevalent genotypes. Most of the non-MDR isolates were distributed in a scattered pattern. Additionally, 249 isolates exhibited biofilm formation, among which 63 were stronger biofilm formers than type strain ATCC19606. Population that exhibited more robust biofilm formation likely contained larger proportion of non-MDR isolates. Isolates with higher level of resistance tended to form weaker biofilms. The MBECs for cefotaxime, imipenem, and ciprofloxacin showed a positive correlation with corresponding MICs, while the enhancement in resistance occurred independent of the quantity of biofilm biomass produced. Results from this study imply that biofilm acts as a mechanism for bacteria to get a better survival, especially in isolates with resistance level not high enough. Moreover, even though biofilms formed by isolates with high level of resistance are always weak, they could still provide similar level of protection for the isolates. Further explorations genetically would improve our understanding of these processes and provide novel insights in the therapeutics and prevention against A. baumannii biofilm-related infections.

The Relationship Between Antibiotic Resistance Phenotypes and Biofilm Formation Capacity in Clinical Isolates of Acinetobacter baumannii

“…It seems that susceptible isolates have an inherent tendency to develop stronger biofilms. In agreement with our findings, two previous studies reported a negative relationship between biofilm formation ability and antimicrobial resistance phenotype in A. baumannii (5,6). Consistent with our findings, their results provided evidence that the ability to develop biofilm may be a crucial determinant in the survival of susceptible or non-MDR bacteria.…”

“…The biofilm-forming capacity was quantified using the crystal violet staining technique in triplicates and at three independent replicates, as previously defined (6). Briefly, after overnight culture of A. baumannii on nutrient agar, one colony was isolated and suspended in Luria Bertani (LB) broth (Himedia, India).…”

Virulence Factors of Acinetobacter baumannii Environmental Isolates and Their Inhibition by Natural Zeolite

“…Statistically stronger biofilm formation at solid-liquid and air-liquid interfaces was confirmed for antibiotics-sensitive isolates as compared to MDR isolates. This observation is in accordance with statements published for clinical isolates of A. baumannii that isolates sensitive to antibiotics form stronger biofilm (Kaliterna et al, 2015;Perez et al, 2015;Qi et al, 2016). Biofilm protects sensitive isolates from the harmful effect of antibiotics, while MDR isolates have already developed mechanisms to protect themselves from antibiotics and therefore do not tend to assemble cells in biofilm.…”

Temporal Expression of Genes in Biofilm-Forming Ocular Candida albicans Isolated From Patients With Keratitis and Orbital Cellulitis

“…Similar studies on Acinetobacter baumannii have also demonstrated that of 63 strong biofilm makers, 79.4% are non-multidrug-resistant strains. 44 C. albicans L-391/2015 was the best biofilm producer, and the thickness of the biofilm increased with time of incubation from 24 to 72 hours as judged both by SEM and CLSM. However, by 96 hours of growth, biofilm thickness was reduced and appeared to be less dense and more dispersed; in the confocal micrographs, the biofilm at 96 hours revealed single cells of C. albicans, implying the occurrence of biofilm dispersal cells.…”