Agarwal Gunjan, Kapil Arti, Kabra S K, Das Bimal K, Dwivedi S N
Department of Microbiology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India.
Natl Med J India. 2005 Jul-Aug;18(4):184-6.
Infection with Pseudomonas aeruginosa is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). With chronicity of infection, the organism acquires a mucoid phenotype and grows as microcolonies in a biofilm in the respiratory passages of the host. This acts as a protective niche and helps the organism to evade the host immune response. In the biofilm the organism has a high resistance to antibiotics, leading to problems in eradication, and poses a therapeutic challenge. We studied the antimicrobial susceptibility of P. aeruginosa ATCC 27853 in a biofilm and as free-living forms against ciprofloxacin and gentamicin, the commonly used antibiotics in patients with CF.
Biofilm formation of P. aeruginosa ATCC 27853 was characterized by in vitro biofilm formation assay. The biofilm was detected by light microscopy and quantitated by measuring the absorbance at 575 nm and by viable bacterial counts. After the maximal biofilm was established, the effect of various concentrations of ciprofloxacin (1, 2 and 4 microg/ml) and gentamicin (4, 8, 16, 32 and 64 microg/ml) was observed and the minimal biofilm eradication concentration (MBEC) determined. The minimal bactericidal concentration (MBC) of both the antibiotics was determined against the free-living forms of the organism. The MBEC of the two antibiotics was further compared with the MBC.
On microscopic examination, the maximal biofilm of P. aeruginosa was established on a coverslip at 12 hours, the maximum absorbance was at 575 nm and viable counts were observed at 12 hours, which corresponded to the maximal biofilm production. The organisms in the biofilm showed a 4-fold greater resistance against ciprofloxacin and gentamicin as compared to the free-living forms.
In biofilm, P. aeruginosa shows greater resistance against antibiotics. This renders these antibiotics ineffective, leading to chronic and persistent infections.
铜绿假单胞菌感染是囊性纤维化（CF）患者发病和死亡的主要原因。随着感染的慢性化，该菌获得黏液样表型，并以微菌落形式在宿主呼吸道的生物膜中生长。这形成了一个保护性生态位，有助于该菌逃避宿主免疫反应。在生物膜中，该菌对抗生素具有高度抗性，导致根除困难，构成了治疗挑战。我们研究了铜绿假单胞菌ATCC 27853在生物膜状态下以及游离状态下对环丙沙星和庆大霉素（CF患者常用的抗生素）的药敏情况。
通过体外生物膜形成试验对铜绿假单胞菌ATCC 27853的生物膜形成进行表征。通过光学显微镜检测生物膜，并通过测量575 nm处的吸光度和活菌计数进行定量。在形成最大生物膜后，观察不同浓度的环丙沙星（1、2和4 μg/ml）和庆大霉素（4、8、16、32和64 μg/ml）的作用，并确定最小生物膜根除浓度（MBEC）。测定这两种抗生素对该菌游离状态的最小杀菌浓度（MBC）。进一步比较这两种抗生素的MBEC和MBC。
显微镜检查显示，铜绿假单胞菌在盖玻片上12小时时形成最大生物膜，575 nm处吸光度最大，且在12小时时观察到活菌计数，这与最大生物膜产生相对应。与游离状态的菌相比，生物膜中的菌对环丙沙星和庆大霉素的抗性高4倍。
在生物膜中，铜绿假单胞菌对抗生素表现出更高的抗性。这使得这些抗生素无效，导致慢性和持续性感染。
