ABSTRACT
This study was carried out to observe thermotolerance ability of Acanthamoeba spp. A total of 32 Acanthamoeba spp. isolates obtained from water taps, sinks, swimming pools and sea water were used. Trophozoites of Acanthamoeba spp. were inoculated onto non-nutrient agar (NNA) seeded with heat-killed Escherichia coli using aseptic technique and incubated for 14 days at 30°C to obtain the cyst. The cysts were subcultured onto new agar plates for thermotolerance test at 37°C and 42°C. The plates were observed until 96 hours after incubation for excystation of Acanthamoeba before being declared negative. Overall, 81.25% of samples were able to excyst at 37°C while 37.5% were able to excyst at 42°C. Thermotolerant Acanthamoeba is associated with high pathogenicity potential.
ABSTRACT
The aim of the present study was to evaluate the effect of storage conditions,pretreatment,temperature,time and excystation solutions on in vitro excystation of Cryptosporidium oocyst.Cryptosporidium andersoni oocyst was used as a model and the results showed that 0.5% sodium hypochlorite could enhance the excystation rates.But there was no significant difference compared with oocysts untreated by sodium hypochlorite(P＞0.05).0.75% synthetic sodium taurocholate and 1% bile solution could urge the excystation of oocysts,which were significantly different compared with the excystation rate of oocysts in 0.25% trypsin solution or in PBS(P<0.05).The excystation rates of oocysts in acidic water (pH =3) were similar with the rates in PBS (pH =7.2) but significantly different from the rates in alkaline water (pH =9) (P<0.01).Additionally,the excystation rate of oocysts in water of 24℃ was significantly lower than in water of 37℃(P<0.01),and the excystation rate of oocysts raised gradually at 37℃ with the passage of time.It's concluded that temperature,acidity and excystation solution were vital factors for the in vitro excystation of Cryptosporidium oocyst.A higher excystation rate could be observed when oocysts were pretreated with 0.5% sodium hypochlorite and treated with 0.75% synthetic sodium taurocholate at 37℃ for 3 hours.
ABSTRACT
Differentiation into dormant cysts and vegetative trophozoites is an inherent character intimately associated with the life cycle and infectivity of pathogenic amoebae. In the case of human intestinal amoebiasis encystation and excystation are of immediate relevance to the process of transmission of the disease from healthy carriers to susceptible individuals. Using a pathogenic free living amoeba Acanthamoeba culbertsoni as a model, considerable progress has been achieved in understanding the mechanism and control of the process of differentiation. The turnover of the regulatory molecule cyclic 3: ‘5’ adenosine monophosphate is responsible for triggering the process of encystation. Amoebae bind effector molecules such as biogenic amines to a membrane localized receptor which itself resembles the β- adrenergic receptor of mammalian organisms. The activation of adenylate cyclase or inhibition of cyclic AMP phosphodiesterase maintain the dynamic intracellular cyclic AMP. The cytosol fraction of amoebae has a cyclic AMP binding protein. During encystation, enzymes needed for synthesis of cellulose and glycoproteins are induced. Control is exercised at transcriptional level and the process is subject to catabolic repression. Excystation of mature amoebic cysts is mediated by glutamic acid and certain other amino acids by an as yet unelucidated mechanism. During excystation there is dormancy break, induction of deploymerizing enzymes viz. two proteases, a cellulase and a chitinase. The empty cysts or cyst walls are digested by these enzymes and their break down products are used for cellular growth. By invoking a flip-flop mechanism of repression and derepression some plausible explanation can be offered for the cascade of biochemical events that sets in when amoeba is ‘turned on’ to encystation or excystation.