YERSINIA AND PASTEURELLA

Eligius Lyamuya, MD, MMed, PhD

Department of Microbiology and Immunology, Muhimbili University of Health

and Allied Sciences

LEARNING OBJECTIVES• Know the general characteristics of Yersinia and

Pasteurella • Understand the growth characteristics, virulence

factors and pathogenesis of infection caused by Y. Pestis, Y enterocolitica, Y. pseudotuberculosis and P. multocida

• Know the various methods for laboratory diagnosis of infections due to Yersiniae

• Know the general principles of treatment, prevention and control of plague

• Know the general principles of treatment, prevention and control of other infections caused by Yersinia spp and Pasteurella spp

YERSINIA

Family: Enterobacteriaceae

Genus: Yersinia

Species of medical importance:• Yersinia pestis• Yersinia enterocolitica• Yersinia pseudotuberculosis

GENERAL CHARACTERISTICS

• Coccobacillary, ovoid or rod shaped, bipolar staining

• Gram negative

• Aerobic or facultatively anaerobic

• Grow on ordinary media

• Best growth temp. 25-30C• Oxidase -ve, Catalase +ve, Indole -ve, ONPG

+ve, Urease +ve except Y. pestis

Stained preparation showing Yersinia pestis

Yersinia pestis

CULTURAL CHARACTERISTICS

• Polymorphism in old cultures

• Capsulated forms in exudates from lesions

• In broth, stalactites (hanging growth) seen with oil overlay, granular deposits if no oil

• Colonies on MCA disappear after 2-3 days due to autolysis

Biotypes

Biotype Glycerol Nitrite

acidification reduction

Y. pestis var orientalis - +

Y. pestis var antiqua + +

Y. pestis var medievalis + -

ANTIGENIC STRUCTURE-1

• LPS

• Capsular (envelope) antigenic complexF1 antigenHeat labileDevelops at 37C

• Somatic antigenic complexV and W antigensHeat stableDevelops at 20C and 37C

ANTIGENIC STRUCTURE-2

• Other virulence factors:-

Low calcium response (lcr) geneYops (Yersinia outer proteins)

Coagulase produced at 28CPlasminogen activator

PATHOGENESIS

• Agent for plague• Transmission: Wild rodent epizootics

semidomestic rodents domestic rodents fleas man man transmission: fleas, Pulex irritans, airborne (pneumonic)

• Injection into man by fleas regional lymph nodes blood stream organs (spleen, liver, kidneys, others)

• Causes infarcts, necrosis and haemorrhage

CLINICAL TYPES

• Bubonic

• Septicaemic

• Pneumonic

• Others:Plague meningitisTonsillar or pharyngeal plaguePlague carbuncle

LABORATORY DIAGNOSIS

• SpecimensBubo aspirateSputumBloodOthers depending on clinical presentation

• TestsStaining (Wayson’s, methylene blue, Gram)CultureSerology

EPIDEMIOLOGY-1

• Disease of antiquity

• First documented epidemic ?1320 BC (Biblical evidence)

• Major pandemics:Justinian plague: -6th CBlack death: -14th COriental plague: -Late 19th C

EPIDEMIOLOGY-2

• Primarily a disease of rodents and their fleas• Case fatality if untreated: 50-75% for bubonic

plague; 100% for septicaemic plague• Incidence declining globally since early 20th C• Some countries (including Tanzania) continue to be

affected• Reservoirs: Rodents, Fleas (Xenopsilla spp)• Plague foci: World wide in countries lying between

50N and 35S; in Tanzania-central, northern and eastern parts

EPIDEMIOLOGY-3

• Epidemic types: Sylvatic (rural) plague, Domestic (urban) plague

• Risk factors:Occupation (hunters, farmers)Poor housingSleeping on the floorNot keeping catsSocio-cultural factors

CONTROL AND PREVENTION-1

• Control of epidemicsMitigate public hysteriaTreat casesClosely monitor contactsInvestigate all deathsKill fleas (insecticides)Kill rodents (rodenticides) when flea index <0.5

CONTROL AND PREVENTION-2

• Case recognition, medical intervention and field investigation Identify the most likely source of infection in the area Institute appropriate sanitation and control measures to

stop the exposure sourceEnsure dissemination of information concerning areas

with active plague transmission, the clinical features of plague and the case definition to health workers

Verify that patients have been placed on appropriate antibiotic treatment and that local supplies of antibiotics are adequate to handle further cases

Isolate pneumonic plague patients

CONTROL AND PREVENTION-3

• Vaccine not available for wide use• Continuous surveillance of rodent and human

plagueConduct investigation to identify animals and flea species

that are implicated in the plague enzootic cycle in the region and develop a programme on environmental management to limit its potential spread

Active long-term surveillance of zoonotic foci and rapid response to reduce exposure during epizootic outbreaks

Yersinia enterocolotica

CULTURAL CHARACTERISTICS

• Capsules in vivo, not in culture

• Multiplies at 4C• Slow growth on artificial media

• Selective/enrichment media needed for isolation from faecal specimens

ANTIGENIC STRUCTURE

• 6 biotypes• Several serotypes, 3, 8 and 9 responsible for most

human infections

• Enterotoxin produced at T <30C

PATHOGENESIS • Faeco-oral transmission• Causes gastroenteritis; sometimes septicaemia

and mesenteric lymphadenitis in the elderly

LAB. DIAGNOSIS• Specimens

Faeces, Blood

• TestsCulture: cold enrichment, subculture on selective

mediaSerology

Yersinia pseudotuberculosis

GENERAL FEATURES•Non capsulated•Grows poorly on MCA

ANTIGENIC STRUCTURE•Serotypes 1-6, type 1 most common•Six O groups (I-IV)

PATHOGENESIS •Zoonosis•Causes mesenteric adenitis in man

LAB. DIAGNOSISSpecimens•Mesenteric lymphnode biopsy, Blood

Tests•Culture: incubate at 37C for 18 hrs•Serology

PASTEURELLA

Genus: Pasteurella

Species of importance:

• P. multocida

• P. haemolytica

• P. pneumotropica

• P. ureae

P. multocida

• Gram negative coccobacilli, smaller than Yersiniae

• Non-motile, non-sporing

• Capsulated in culture

• Bipolar staining with methylene blue

• Aerobic, facultatively anaerobic

• Does not grow on MCA

• Oxidase positive

ANTIGENIC STRUCTURE•15 serotypes, 4 capsular Ags and 11 somatic Ags

PATHOGENESIS •Zoonosis, virulent to animals and birds•Rare human infections:

local abscessMeningitisRT infections

LAB. DIAGNOSISSpecimens•Depending on clinical presentationTests •Culture