Virion Conformational FormsandtheComplexInactivation Kinetics ofEchovirus byChlorine inWater

Aberrant inactivation kinetics wereobserved whenmonodispersed echovirus type1(Farouk) was inactivated withchlorine. Aninitial 1-to2-logl0-unit decrease intiter was followed bya lagperiod, during whichthetiter stayed thesame orincreased, andthis was followed byafinal decline intiter. First-order kinetics were obtained withpoliovirus type1underthesame conditions. Isoelectric focusing studies ofechovirus before chlorine treatment showedthatthevirus distributed intotwopH-dependent andinterconvertible isoelectric forms. After chlorine treatment allremaining virus infectivity was associated with a third pH-independent isoelectric form.Thecomplex inactivation kinetics appeared tobeduetoshifts between these conformational forms during inactivation incertain ionic environments. Undercertain conditions theconformational shifts resulted insubstantial resistance ofmonodispersed echovirus tochlorine. Inaprevious publication, wereported complex inactivation kinetics whenechovirus type1(Farouk) wasinactivated with20,uMHOClatpH6.0and20°C(17). Aninitial 1-to 2-log10-unit decrease intiter inthefirst second ofinactivation wasfollowed byalagperiod of15sbefore afinal decline intiter. We demonstrated thatthis unusual departure from first-order kinetics wasnotduetovirion aggregation, genetic heterogeneity ofthevirus suspension, ordepletion ofchlorine andsuggested that conformational changes inthevirion capsid mightbeinvolved. Atthetimetheseresults were observed, thehalogen inactivation experiments carried out inthis laboratory withreovirus andpoliovirus hadshown first-order kinetics oronlyslight departures fromfirst-order kinetics whenvirion aggregation waseliminated (2-4, 14-16). However, thereisnow evidence thatsuggests thatthe complex inactivation kinetics originally observed withechovirus aremorecommonthanwasfirst expected. Kenyonand Schaub (9)havereported complex inactivation kinetics with poliovirus type1(LSc), andexperiments inthis laboratory havedemonstrated complex kinetics forcoxsackieviruses B3andB5(8). Thesefindings suggest that (i) different enteric viruses maybeinactivated bydifferent mechanisms and(ii) somemaybecome, inthecourse ofinactivation, temporarily resistant totheeffects oftheinactivating agent. Theexperiments reported herewereperformed toexaminetheeffects ofpH,salt concentration, temperature, and chlorine concentration ontheunusual inactivation kinetics ofechovirus. Isoelectric focusing studies wereperformed to determine virion conformational formsduring disinfection. Evidence ispresented insupport ofthehypothesis that the complex inactivation kinetics ofechovirus arerelated to conformational changes incapsid structure. MATERIALSAND METHODS Viruspreparation andassay. Echovirus type1(Farouk) wasobtained fromMarkSobsey, School ofPublic Health, University ofNorthCarolina. Details ofitsproduction in