Providencia akalifaciens isamemberofthefamily Enterobacteriaceae. There arereports that P.akalfaciens cancause diarrhea, butthemechanism(s) bywhichitcauses diarrhea isnotknown. Westudied P.akalfaciens isolated fromachild andtwoadults withdiarrhea forenteropathogenicity.

intheSereny test. Twoisolates invaded cultured HEp-2cell monolayers, producing localized bacterial clusters andactin condensation. Thepattern ofactin condensation wasdifferent fromthatproduced byenteropathogenic Escherichia coli butsimilar tothatproduced byShigeUla jlexneri. Invasion andactin condensation werepoorforthethird isolate. Histology ofadult rabbit small intestinal loops inoculated withall three isolates revealed bacterial attachment to,penetration of,andmicroulcer formation on thesurface epithelium andhyperemia, edema, andpolymorphonuclear cell infiltration oflamina propria. All theisolates produced diarrhea inrabbits withremovable intestinal ties, andsomeofthese rabbits developed hindlimb paralysis. Intestinal histology oftherabbits withremovable intestinal ties whichdeveloped diarrhea showedchanges similar tothatinadult rabbits onwhichileal loopassays hadbeenperformed. Transmission electron microscopy ofintestinal tissues also confirmed tissue penetration bytheisolates. Nervetissue histology oftworabbits that developed hindlimb paralysis showedfocal mononuclear cell infiltration aroundperipheral nervesheaths. Itisconcluded thatsomestrains ofP.akahfaciens areenteropathogenic andthattheycause diarrhea byinvading theintestinal mucosal epithelium. However, therelevance tohumandisease ofthe hindlimb paralysis observed inthis animal modelisnotclear. Providencia alcalifaciens isamemberofthefamily Enterobacteriaceae andacomponent ofthenormal flora ofthe feces(7). Somestudies inthepasthaveimplicated the Providence groupoforganisms inthecausation ofdiarrhea (16, 18), andarecent study suggested that P.alcalifaciens cancausetraveler's diarrhea (10). However, themechanism bywhichP.alcalifaciens causes diarrhea isnotknown. Inourclinical laboratories, wehavesometimes isolated P. alcalifaciens either asthepredominant organism orasapure culture fromthediarrheal stools ofsomepatients inthe absence ofrecognized enteric pathogens. Thisprompted us tostudy theenteropathogenicity ofsomeP.alcalifaciens isolates.