Gram-Negative Rods Related to Animal Sources (Zoonotic Organisms) - Yersinia PDF

Gram-Negative Rods Related to Animal Sources (Zoonotic Organisms) Dr. Nada A. Abdelrahim 1 2 3 Yersinia Species 4  Yersinia spp. (Y. pestis, Y. enterocolitica & Y. pseudotuberculosis) are Gram- negative coccobacilli which show Bipolar Staining Are Catalas...

Gram-Negative Rods Related to Animal Sources (Zoonotic Organisms) Dr. Nada A. Abdelrahim 1 2 3 Yersinia Species 4  Yersinia spp. (Y. pestis, Y. enterocolitica & Y. pseudotuberculosis) are Gram- negative coccobacilli which show Bipolar Staining Are Catalase & Oxidase & Indole Positive Non – Lactose Fermenting, Aerobes & Facultative Anaerobes Capable of growth at wide temperatures ranging from 4°C to 43°C They exhibit unusual Bipolar staining (when smears are examined by Giemsa or Wayson stains) Based on composition of LPS in outer membrane, colonies may present with: o Rough Form lacking O-specific polysaccharide chain (Y. pestis), OR o Smooth Form containing lipid A-oligosaccharide core & the complete O- polysaccharide (Y. pseudotuberculosis & Y. enterocolitica) 5  Complex typing systems exist to differentiate various Yersinia spp., including: o Standard Biochemical Methods coupled with Biotyping (biochemical phenotypic methods) o Serotyping o Bacteriophage typing & o Antibiogram Analysis Epidemiologic studies include Pulsed-Field Gel Electrophoresis (PFGE) studies 6 Yersinia pestis 7 8 Historical Plague Doctors — Newcastle Castle 9  Pathogenicity Y. pestis causes Plague (Formerly: Black Death) Plague is a Zoonotic disease which is transmitted from Rats & other Rodents to Humans by infected fleas (main vectors: Xenopsylla cheopis & X. brasiliensis) Infection may occurs by: o Inhaling the organisms in Airborne Droplets o Or by Handling Infected Rodents or Domestic Animals (e.g. fleas infected cats, dogs) There are 3 Main Forms of the Disease → Xenopsylla 10 11 12 1) Bubonic Plague: Is the commonest form, is characterized by High Fever & Acute Lymphadenitis with painful Haemorrhagic Swellings called Buboes (usually in the groin area). Lymph nodes in the Neck or Armpits may be involved (depending on the site of flea bite). There is markedly Raised White Cell Count with Neutrophilia 2) Pneumonic Plague: Occurs following inhalation or its spread to the lungs via blood stream. Pulmonary infection causes Severe Bronchopneumonia with Haemorrhaging. It is rapidly fatal unless treated at an early stage. It is Highly infectious, Can spread quickly in conditions of poverty & overcrowding. Sputum contains large numbers of plague bacilli and is often blood stained 3) Septicaemic Plague: a Serious Haemorrhagic Condition ---- Large numbers of Y. pestis are present in blood (Yersiniae can often be seen in peripheral blood smears). Buboes are usually Absent. There is Haemorrhagic Rash. Septicaemic plague is Rapidly Fatal 13 Clockwise from top left: Yersinia pestis in blood; blackened tissue from acral necrosis, a symptom common in Bubonic Plague; swollen inguinal lymph nodes or buboes; pulmonary pathology caused by pneumonic plague 14 15  r t a nt o Imp ce N o t i ❖ Clinical Features of Bubonic & Pneumonic Plague may sometimes resemble the Suppurative Skin Nodule (at site of infection) & Necrotizing Pneumonitis associated with Melioidosis (caused by Burkholderia pseudomallei ) ❖ Melioidosis is found mainly in Southeast Asia ❖ Like Y. pestis, B. pseudomallei also shows Bipolar Staining ❖ Knowing the case history is most important in making an early presumptive diagnosis of plague when bipolar stained organisms are detected in bubo aspirates 16 Outbreaks of Plague: Areas of the world where wild rodent plague exists (e.g. parts of North & South America, Madagascar, Africa, India, central and Southeast Asia) are high risk areas for human plague In some parts of Africa, the incidence of plague is increasing Outbreaks occur when humans come into close contact with infected rodents & their fleas (e.g. following man-made or natural disasters, or when rodents infest poorly constructed homes and there are no flea or rodent control measures, or when deforestation or other situations force rodents closer to where people live) Humans are also at risk following rodent plague epidemics when the fleas leave dead rodents and infest humans 17 18  LABORATORY FEATURES Y. pestis is a Highly Infectious Pathogen (Hazard Risk Group 3) (specimens should be handle with care) When plague is suspected, the Central Public Health Laboratory should be notified (Isolation should be done in this laboratory) Specimens: Bubo Aspirates, Sputum & Blood for culture, and Blood for smear looking for bipolar stained organisms (when Septicaemic Plague is suspected) Specimens should be collected before antibiotic treatment is started 19  Morphology: Y. pestis is Small Gram Negative, Non-Motile Coccobacillus It is Capsulated In smears from specimens it shows Bipolar Staining (Safety Pin Appearance) when stained with Methylene Blue, Giemsa, or Wayson’s rapid stain When seen in blood smears, it is Extracellular Giemsa stained Blood Film Showuing Yersinia pestis 20 Dark stained bipolar ends of Yersinia pestis can clearly be seen in this Wright's stain of blood from a plague victim (1993) 21  Y. pestis is Aerobe & Facultative Anaerobe It grows over a wide temperature range (14 – 37 ºC) optimum of 27 ºC (cultures are incubated at room temperature) Blood agar: Y. pestis grows well on Blood agar (producing small shiny, non- haemolytic colonies after 24 – 48 h incubation at room temperature) MacConkey agar: Very small translucent pink colonies formed after 24 – 48 h incubation (it does not ferment lactose but appears ‘lactose-fermenting’ because it takes up the red dye of the indicator in the medium) Microscopical examination: They form Chains Yersinia Selective Medium & Congo Red Agar If colonies are to be tested for F1 (Fraction 1) capsular antigen, cultures require incubation at 37 ºC to produce the antigen 22  Y. pestis is Catalase +ve & Oxidase –ve (oxidase reaction differentiates Y. pestis from B. pseudomallei which is oxidase positive) ❖ A microbiology specialist laboratory is required to identify Y. pestis A rapid easy to perform Immunochromatographic Strip Test (Dipstick) is available to detect specific antigen to Y. pestis in Bubo Aspirates & Sputum in Bubonic & Pneumonic Plague (has 100% sensitivity & specificity) 23  Antimicrobials with activity against Y. pestis (early stages of infection) include: o Streptomycin o Tetracycline & o Chloramphenicol Some strains show resistance to Streptomycin & Tetracycline Resistance to other antimicrobials was also reported 24 Other Yersinia Species 25 Yersinia enterocolitica & Yersinia pseudotuberculosis Y. enterocolitica & Y. pseudotuberculosis are Gram-negative, Oval Rods that are Larger than Yersinia pestis Virulence factors produced by Y. pestis are not produced by these species Are transmitted to humans by contamination of food with the excreta of domestic animals (such as dogs, cats & cattle) Yersinia infections are relatively infrequent (in US, but number of documented cases increased during the past few years ---- as a result of improved laboratory diagnostics) 26  Y. enterocolitica causes Gastroenteritis (mainly in infants & young children) and occasionally Acute Mesenteric Lymphadenitis Enteric infection usually produces Watery Diarrhoea Some strains are invasive & toxigenic ---- producing inflammatory reaction with dysentery In adults: infection is usually accompanied by Lower Abdominal Pain, Fever, & Leucocytosis which may suggest Acute Appendicitis Y. enterocolitica is more commonly found in Temperate Climates But it has also been reported from South Africa, Zaire & Nigeria Y. enterocolitica can multiply in Food Refrigerated at 4 – 8 ºC When cultured at 22 ºC it is Motile & Nonmotile at 37 ºC Selective medium (such as MacConkey agar, CIN or SS) is required to isolate Y. enterocolitica from faecal specimens (after 24–48h incubation at 20–28 ºC (room temperature) Y. enterocolitica produces Small Non-Lactose Fermenting colonies 27  Y. enterocolitica causes Enterocolitis that is clinically indistinguishable from that caused by Salmonella or Shigella Both Y. enterocolitica & Y. pseudotuberculosis can cause Mesenteric Adenitis that clinically resembles acute appendicitis Mesenteric adenitis is the main finding in appendectomies in which a normal appendix is found Rarely, these organisms are involved in Bacteremia or Abscesses of the Liver or Spleen (mainly in persons with underlying disease) Yersinia infection is associated with 2 Autoimmune diseases: Reactive Arthritis & Reiter’s Syndrome Other enteric pathogens such as: Salmonella, Shigella & Campylobacter also trigger these diseases Reactive arthritis and Reiter’s syndrome 28  Y. enterocolitica is usually isolated from stool specimens ---- form lactose- negative colony on MacConkey’s agar It grows better at 25°C than at 37°C; most biochemical test results are positive at 25°C & negative at 37°C Incubation of stool sample at 4°C for 1 week (a technique called cold enrichment) increases the frequency of recovery of the organism Y. enterocolitica can be distinguished from Y. pseudotuberculosis by biochemical reactions Laboratory is usually not involved in the diagnosis of Y. pseudotuberculosis (cultures are rarely performed in cases of mesenteric adenitis, the organism is rarely recovered from stool specimens) Serologic tests are not available in most hospital clinical laboratories 29 Identification of a suspect Y. enterocolitica isolate An isolate can be identified Presumptively as Y. enterocolitica if it is: Motile at 20–28 ºC (But Non-Motile at 35–37 ºC) Urease Positive (usually after overnight incubation) Oxidase Negative In KIA: Red/Yellow with No Gas production or Blackening Most strains show Bipolar stained coccobacilli (when smear are examined by Giemsa or Wayson stains) 30  Enterocolitis & Mesenteric adenitis caused by the organisms do not require treatment For Bacteremia or Abscess: either Trimethoprim-Sulfamethoxazole or Ciprofloxacin is usually effective No preventive measures except to guard against contamination of food by excreta of domestic animals 31 32 33