Role of Tween 80 and Triton X-100 in Diagnosis of Ascitic Fluid Infection

Abstract

Spontaneous bacterial peritonitis (SBP) is a frequent and severe complication of decompensated cirrhosis, polymorphonuclear (PMN) cell count in the ascitic fluid is essential for its diagnosis and management. Following the clinical diagnosis of SBP, ascitic fluid collection and blood cultures should be carried out before initiating antibiotic administration. Tween 80 and Triton X-100 are 100% pure, non-anionic surfactant agents. They are believed to yield a better growth of organisms as compared with direct plating methods. The aim of this work is to compare between the utility of conventional cultures, culture of ascitic fluid from blood culture bottles, culture of specimen on media supplemented with non- anionic surfactant agents such as Tween 80 and culture of specimen treated with Triton X-100 in diagnosis of ascitic fluid infection. This study was conducted on 140 samples of ascitic fluid collected from the Microbiology Laboratory of Ain Shams University Hospitals for routine culture and susceptibility testing. The collected samples were subjected to macroscopic and microscopic examination, conventional culture on blood agar and MacConkey agar, culture using Oxoid blood culture bottles, culture on blood agar supplemented with 2% Tween 80 and culture of treated specimens with Triton X-100 on blood agar and MacConkey agar incubated at 37°C for 48 hours. In our study, (27/140) (19.3%) samples were diagnosed as SBP or its variants. The most common variant was monomicrobial non- neutrocytic bacterascites (MNB) as it was detected in (21/27) (77.8%) of samples followed by culture negative neutrocytic ascites (CNNA) in 11.1% (3/27), full fledged (classical) SBP in 7.4% (2/27) and polymicrobial non-neurocytic bacterascites in 3.7% (1/27). Conventional culture showed positive results in 17/140 (12.1%), culture on blood culture bottles showed positive results in 29/140(20.7%) while blood agar supplemented with Tween 80 showed positive results in 13/140(9.3%) and samples treated with Triton X-100 showed positive results in 11/140 (7.9%). There was a highly significant difference between the positive results of conventional culture (12.1%) and culture on blood culture bottles (20.7%) (P<0.01). Also, there was a highly significant difference between culture on blood culture bottles (20.7%) and culture of samples treated with Triton X-100(7.9%)(P<0.01). While, there was no significant difference between the positive results of conventional culture (12.1%) and each of culture on blood agar supplemented with Tween 80 (9.3%) and samples treated with Triton X-100 (7.9%) (P>0.05). Conventional culture of samples was positive in 17/140 (12.1%), 9/17 (52.9%) of them were Gram positive bacteria and 5/17 (29.4%) were Gram-negative bacteria and there was mixed growth of three Gram-negative organisms in 1/17(5.9%) and mixed growth of both Gram-positive and Gram-negative bacteria in 2/17(11.8%). The most commonly isolated organisms were Staphylococcus coagulase negative in 8/11 samples (72.7%), Acinetobacter in 3 samples (30%) and E. coli in 3 samples (30%). Whereas Enterococci, Klebsiella and Citrobacter were the least common; each was isolated from only one sample (9.1%, 10%, 10% respectively).