The development of antibiotics ushered in a new era of medicine in which bacterial infections could be easily treated. However, the emergence of antibiotic-resistant bacteria has rendered these drugs ineffective. Almost 5 million deaths were associated with drug-resistant infections in 2019 [1]. Acinetobacter baumannii is a multidrug-resistant opportunistic pathogen that causes various infections with a mortality rate of up to 44% [2]. Due to limited treatment options and a high mortality rate, the World Health Organization designated A. baumannii as a critical priority for new antibiotic development [2]. Although this pathogen is clinically relevant there is a lack of understanding about its virulence [3]. It is known that polysaccharide capsule plays a role in A. baumannii’s ability to survive desiccation, evade the host immune system and resist antibiotics [4]. Therefore, it is important to evaluate the impact of capsular polysaccharides on A. baumannii resistance to antibiotics.
This study aimed to compare the resistance of A. baumannii wild-type isolate and its capsule-deficient mutant (∆galU) to different classes of antibiotics. This was achieved by assessing antibiotic minimal inhibitory concentrations in a liquid medium by microdilution. Bacteria were incubated for 24 hours at 37 °C with antibiotics and then the bacterial growth in different antibiotic concentrations was evaluated.
In this research, 13 antibiotics (tetracycline, colistin, gentamicin, ciprofloxacin, ampicillin, kanamycin, streptomycin, chloramphenicol, imipenem, meropenem, cefazolin and a mixture of sulfamethoxazole/trimethoprim) were used. It was found that wild-type strain and ∆galU mutant displayed different growth profiles when tetracycline, colistin and gentamicin were applied. Further research is required to investigate how the genes responsible for capsule production are regulated in response to these antibiotics.