SHIGELLA

1. SHIGELLA
Shigellaisagenusof Gram-negative,facultativeanaerobic,nonspore-forming,nonmotile,rod-shaped
bacteriacloselyrelatedtoSalmonella.
The genusis namedafterKiyoshi Shiga,whofirstdiscovereditin1897.
Theyare fermentative,facultative anaerobicnonspore forminggramnegative bacilli.nonmotile,
catalase positive (exceptShigelladysentriae type 1),oxidasenegative,donotproduce gas form
carbohydrateswithfewexceptions.
None formsacetylmethylcarbinol orfermentsadonitol,inositol orsalicin,lysine decarboxylase,liquifies
gelatin,deaminatesphenylalanine,utilisesmalonate orproduce H2S.Basedon DNA- DNA hybridisation
studies,thisgenusiscloselyrelatedtoEscherichia coli .G+C contentof DNA variesfrom48-53 mol%. –
Shigellaisacommon,highlycontagiousgermthatcausesdiarrhea.The usual symptomsassociatedwith
thisinfectionare diarrhea,cramping,abdominal pain,chills,headache andfever.The diarrheamay
containbloodandmucus.
Morphology of Shigella
Theyare short,gram negative rods,about2-4 µm in lengthx 0.6µm in breadth.Theyare nonspore
forming,noncapsulated,nonmotilebacilli.Type1fimbriaoccursonlyin Shigella flexnerri.
Cultural characteristics of Shigella
Theyare aerobesandfacultative anaerobewithagrowthtemperature rangingfrom10o
C – 45o
C
(optimal temperature being37o
C). S.sonneigrow well evenat10o
C and 45o
C.
Theygrow well onconventional ordinarymediabutnone growsona simple glucose ammoniumsalts
mediumunlesssupplementedwithnicotinicacidandfor some strainsothergrowth
On nutrientagarafterovernightincubation,coloniesare small often2-3mmin diameter, circular,
convex ,greyishor colorless,smoothand translucent. Coloniesof S.sonneiare slightlylargerand more
opaque thanotherShigella.
sonneihas twoantigenicforms:Form1is like the coloniesof otherShigella while form2arise by
irreversible variationfromform1and are seeninearlysubculturesfromprimaryisolates,are largerand
lessopaque and have irregular,mattsurface anda crenatededge.
On Monkeyagar, coloniesare pale andyellowishdue tothe absence of lactose fermentation.An
exceptionis S.sonnei, whichisalate lactose fermenterandcoloniesbecome pinkwhenincubationis
prolongedbeyond24hours.Deoxycholate citrate agarandXylose lysine deoxycholateagarisa useful
selectivemedium(Shigelladonothave blackcentresonthese mediumasSalmonella).Growthis
inhibitedonWilsonandBlair’sbismuthsulphitemedium.

2. Scientificname:Shigella
Higher classification:Enterobacteriaceae
Lower classifications:Shigellaboydii
Rank: Genus
Scientific Classification:
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Shigella
Castellani & Chalmers 1919
Species
S. boydii
S. dysenteriae
S. flexneri
S. sonnei

3. Classification:
Shigella speciesare classifiedbyfour serogroups:
 Serogroup A:S. dysenteriae(15 serotypes)
 Serogroup B: S.flexneri (six serotypes)
 SerogroupC:S. boydii(19 serotypes)
 Serogroup D: S.sonnei(one serotype)
GroupsA–C are physiologicallysimilar; S.sonnei(group D) can be differentiatedonthe basisof
biochemical metabolismassays. Three Shigella groupsare the majordisease-causingspecies:S.
flexneriis the most frequentlyisolatedspeciesworldwide,andaccountsfor60% of casesinthe
developingworld;
S. sonneicauses77% of cases inthe developedworld,comparedtoonly15% of casesinthe developing
world;and S. dysenteriaeisusuallythe cause of epidemicsof dysentery,particularlyinconfined
populationssuchasrefugee camps.
Each of the Shigella genomesincludesavirulenceplasmidthatencodesconservedprimaryvirulence
determinants.The Shigella chromosomes share mostof theirgeneswiththose of E.coli K12 strain
MG1655. PhylogeneticstudiesindicateShigella ismore appropriatelytreated
as subgenus of Escherichia,and that certainstrainsgenerallyconsidered E.coli – such as E.
coli O157:H7 – are betterplacedin Shigella
Resistance:
Shigellaspscanbe killedbyheatingat56o
C in one hourand by 1% phenol in30 minutes.Theycan
survive inice for1-6 months.Infaeces,theydie withinhoursdue totha acidityproducedbygrowthof
coliforms. S.sonneiisthe mostresistantspecies.
How is this germ spread?
It istransmitted primarilyfrompersontopersonthroughthe fecal-oral route.Anyone canbecome
infectedbytouchingsomethingcontaminatedbystool fromaninfectedperson.Thisincludessurfacesin
restrooms,othercommonsurfaces,toysandevenfoodpreparedbysomeone whoisinfected.This
germis easilyspreadinfamiliesandothersettingswhere large numbersof people gather.Infact,a
personwhohas hadthe germcan continue tospreadit for30 daysaftertheyare well if theyare not
treatedwiththe propermedication.
Why should I be concerned?
The Marion CountyHealthDepartmenthasseenasubstantial increaseinthe reportedcasesof Shigella.
Thisfact alongwiththe upcomingholidaybreakhaspromptedthe healthdepartmenttonotifythe
communityaboutthe recentincrease incases.

4. Is this a problem in schools?
The majorityof those becomingsickare in the preschool age group.However,recentlyalargerthan
anticipatednumberof casesinschool-agedchildrenhave beenreported.
What can be done?
Good hand-washingisessential topreventthe spreadof thisgerm.Anyone experiencingShigella-like
symptomsshouldexclude themselvesfromwork,school orothersettingswherelarge numbersof
people interact.Anyone whoissymptomaticshouldcontacttheirmedical providerforfurtherdirection.
Anyone withdiarrheashouldnotprepare foodforothers.Restrooms,toysandotherpotentially-
contaminatedsurfacesshouldbe frequentlycleanedanddisinfectedwithacommercially-prepared
disinfectantora1:100 bleachsolution(approximately1/4cup bleachpergallonof tap water).
What if my someone in my family has symptoms?
Contact hisor her medical providerfordirection.Certaintestingmustbe done toconfirma diagnosisof
Shigellaandcertainmedications mustbe prescribedfortreatment.Where canIgetmore information?
For more information,contactthe MarionCountyHealthDepartment’sCommunicable Disease program
at 221- 2117.
What Is Shigellosis?
Shigellosisisabacterial infectionthataffectsthe digestive system.Shigellosisiscausedbyagroup of
bacteriacalledShigella.The Shigellabacteriumisspreadthroughcontaminatedwaterorfoodor
throughcontact withcontaminatedfeces.The bacteriarelease toxinsthatirritate the intestines.The
primarysymptomof shigellosisisdiarrhea.
Accordingto the U.S. CentersforDisease Control andPrevention(CDC),about14,000 people inthe
UnitedStatesreporthavingshigellosiseveryyear(CDC).The symptomsvaryinintensity.Youmayhave a
mildshigellosisinfectionandnotevenrealize orreportit.
Toddlersandpreschoolersare more likelytogetshigellosisthanolderchildrenandadults.Thismaybe
because youngchildrenputtheirfingersintheirmouthsoftenandare more likelytoingestthe bacteria.
The large numberof diaperchangesinchildcare centerscanalsoincrease the concentrationof infection
inthisage group.
 Recognizing the Symptoms of Shigellosis:
Frequentboutsof waterydiarrheaare the mainsymptomof shigellosis.Abdominal cramping,nausea,
and vomitingmayalsooccur.Many people whohave shigellosisalsohave eitherbloodormucusintheir
stool,andtheymay run a fever.
Symptomsusuallybeginwithinthree daysof comingincontactwithShigella.Insome cases,however,
symptomsof infectionmayappearasmuch as a weekaftercontact.

5. Diarrheaand othersignsof shigellosisusuallylastbetweentwoandsevendays.Mildinfectionlastinga
couple of daysmay not require treatment.However,stayinghydratedinbetweenboutsof diarrheais
crucial.Call yourdoctor if you have diarrheaformore than three days.Thisisveryimportant,
particularlyif youcannotkeepdownfoodorwater.Dehydration isa real dangerassociatedwith
shigellosis.
 Treatment for Shigellosis:
Combatingdehydrationisthe maingoal of treatmentformost casesof shigellosis.Itisimportantto
drinkplentyof fluids,especiallyelectrolyte solutions,manyof whichare availableoverthe counter.Itis
usuallynotadvisable totake anytype of medicationtorelieveyourdiarrhea,asthiswill keepthe
bacteriainyour systemlongerandmaymake the infectionworse.
Moderate-to-severe infectionmayrequire medical treatment.Medical treatmentwill usuallyinclude
antibioticstoeliminate the bacteriafromyourdigestivetract.Your doctormay testyour stool to
confirmthat Shigella is the source of the infection.Confirmationof Shigella helpsyourdoctorchoose
the right medicationtofightshigellosis.Drugoptionsinclude powerfulantibioticmedications:
 azithromycin(Zithromax)
 ciprofloxacin(Cipro)
 co-trimoxazole(Bactrim)
Hospitalizationforshigellosisisrare inthe UnitedStates.However,in some severe situations,itis
required.Patientswhohave extreme nauseaandvomitingmayneedintravenousfluidsandmedication.
 Complications Associated With Shigellosis:
Most people have nolastingill effectsfromshigellosis.
The CDC reportsthat approximatelytwopercentof people infectedwith Shigella flexneri(one of several
typesof Shigella) developaconditioncalledpost-infectionarthritisafterhavingshigellosis(CDC).
Symptomsof post-infectionarthritisinclude jointpain,painful urination,andeye irritation.Post-
infectionarthritiscanbecome achronicconditionthatlastsseveral months,years,orthe restof your
life.Itiscausedby a reactionto theShigella infectionandhappensonlyinpeople whoare genetically
predisposedtoit.
 Can you Be Re-Infected by the Shigella Bacteria?
Shigella isa group of several differentbacteria.Once youhave beeninfectedwithone type of Shigella,
youare not likelytobe infectedbythe same bacteriaagain.However,youmaybecome infectedbya
differentbacteriumfromthe same family.

6.  Preventing Shigellosis
You can preventshigellosisbypracticinggoodpersonal hygiene.Washyourhandsbefore andafteryou
use the bathroomor change a diaper.Discarddirtydiapersina closedbagor trashcan to preventthe
spreadof the bacteria.Use soap andwarm watereverytime youwashyourhands.Wipe downchanging
tablesandkitchencounterswithantibacterialwipesbefore andafteruse.
Avoidclose personal contactwithsomeonewhoisinfectedwith Shigella until atleasttwodaysafter
the diarrheahas ended.
People whohave shigellosisshouldnotprepare foodforothersuntil theyfeelbetterandstophaving
diarrhea.Yourdoctor may testyour stool againafteryoursymptomsendto be sure Shigellaisnolonger
present.
REFERENCES:
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ciprofloxacin with standard 5-day therapy - a randomized, blinded trial. Ann Int
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Dis. 1986;154:817.[PubMed]
3. Davis H, Taylor JP, Perdue JN. et al. A shigellosis outbreak traced to commercially distributed shredded
lettuce.Am J Epidemiol. 1988;128:1312. [PubMed]
4. Fasano A, Noriega FR, Maneval DR, et al: Shigella enterotoxin 1: an enterotoxin of Shigella flexneri 2a
active in rabbit small intestine in vivo and in vitro. J Clin Invest 95:000, 1995. (in press)[PMC free article]
[PubMed]
5. Goldberg MB, Bârzu O, Parsot C. Unipolar localization and ATPase activity of IncA, a Shigella
flexneri protein involved in intracellular movement. J Bacteriol. 1993;175:2189. [PMC free article]
[PubMed]
AbasynUniversityPeshawar