Chapter XIII Miscellaneous pathogenic bacteria Learning objective At

Chapter XIII Miscellaneous pathogenic bacteria

Learning objective: At the end of this chapter the students will be able to: • List the medically-important species of Genus Listeria, Legionella, Erysipelothrix and Gardnerella • Describe general characteristics of Genus Listeria, Legionella, Erysipelothrix and Gardnerella • Recognize diseases caused by Genus Listeria, Legionella, Erysipelothrix and Gardnerella • Describe the virulent factor of pathogenic species of Genus Listeria, Legionella, Erysipelothrix and Gardnerella • Discuss pathogenicity, clinical manifestations, laboratory diagnosis, prevention & control of members of the Genus Listeria, Legionella, Erysipelothrix and Gardnerella

Genus Listeria General characteristics • An intracellular pathogen • Is a small pleomorphic, coccoid, Gram-positive bacilli • Six species of listeria are recognized – which are differentiated by a small number of biochemical tests – It includes L. monocytogenes, L. innocua, L. ivanovi, L. welshimeri, L. sceligeri, and L. grayi • Almost all human listeria infection are caused by L. monocytogenes

L. monocytogenes • is a Gram positive non-capsulate, small rod or coccobacillus • often stains unevenly and is easily decolorized. • When seen in groups it can resemble diphtheroids. Motility: • At 35– 37 ºC L. monocytogenes is nonmotile or weakly motile • at low temperature (18– 22 ºC), it is motile with a characteristic tumbling and rotating motility in broth cultures. • Is a natural pathogen of wide range of animals, birds, fish, tick and crustacea. The organism appear to be saprophytic in soil. • Common sources of infection are contaminated meats, chicken, soft cheeses and vegetables.

Virulence factor • Internalin (membrane protein) – Probably facilitate ingestion of the organism by machrophage, endothelial cells, etc. • Listeriolysin O (haemolytic protein) – Responsible for the disruption of the phagolysosome membrane – It is a major virulence factor • Phospholipases • Help cell to cell spread of the organism by dissolving cell membrane

Pathogenesis • Development of infection depends on host susceptibility, gastric acidity, inoculum size, and virulunce factors • L. monocytogenes causes meningitis and septicaemia mainly in neonates, pregnant women, the elderly and immunosuppressed persons. • Listeriosis in pregnancy may lead to abortion and stillbirth.

Clinical manifestation • Neonatal infection – Infection of foetus in early pregnancy results in a condition called granulomatous infantiseptica leading to abortion – Characterized bt the formation of dissiminated abscess and granulomas in multiple organ

Lab. Diagnosis • Specimens: – Mainly cerebrospinal fluid and blood for culture. • In rare positive smear preparation, extra-and interacellular gram positive bacilli are seen Culture • L. monocytogenes is an aerobe and facultative anaerobe. • It is unusual in that it is capable of growth at refrigeration temperatures. • The temperature range for growth is 3– 45 ºC with an optimum of 30 ºC.

Blood agar: • L. monocytogenes produces small, grey, translucent drop-like colonies surrounded by a small zone of indistinct beta-haemolysis • Incubation for up to 48 h may be required to produce visible growth. • Check the morphology of the colonies by examining a Gram smear. Clear tryptose agar (or Mueller Hinton agar): • Colonies appear pale blue-green when viewed from the side (45 ºC angle) with a beam of white light. • The bacteria act as a diffraction grating, reflecting back the blue part of the spectrum.

Biochemical test • Catalase and -methl-D-mannoside positive • Indole, oxidase, D-xylose and urease negative. • Ferments glucose and maltose with acid production. Note: The characteristic motility and cultural characteristics of L. monocytogenes are usually sufficient to identify it without the need to use many biochemical tests.

Treatment • Penicillin or Ampicillin, ether alone or with Gentamicin are the drugs of choice • Erythromycin is useful in patients allergic to penicillin Prevention and control • Prevention and control are difficult • Hygienic food habit is beneficial

Genus Legionella • • • Gram-negative bacilli Legionella species are widespread in the environment. Most legionellae produce gelatinase and β-lactamase Stains poorly or not at all by Gram stain or the usual histologic stains. can be demonstrated by certain silver impregnation methods (Dieterle stain) Polar, subpolar, and lateral flagella may be present. Most species of Legionella are motile. Produce catalase and Spores are not found. The species designation of the prime human pathogen, Legionella pneumophila, reflects its propensity to cause pneumonia.

Legionella pneumophila • A thin, pleomorphic, Gram-negative rod that may show elongated, filamentous forms. • Structurally, L. pneumophila has features similar to those of Gram-negative bacteria with a typical outer membrane, thin peptidoglycan layer, and cytoplasmic membrane. • Most strains are motile due to polar or sub-polar flagella • Legionella grow only on special medium in an atmosphere containing 5% CO 2. • Facultative intracellular pathogen multiplies in alveolar macrophages

• Most human infections are caused by L. pneumophila, which is subdivided into 12 serogroups. • Human infections are caused mainly by serogroup 1. Virulence Factor – Adhesion – Ability to survive intracellularly – Toxin production • Exotoxin: Haemolysin, cytotoxin • Endotoxin – Outer membrene proteins

Pathogenesis and clinical manifestation • These organisms are facultative intracellular bacteria that can survive in professional phagocytes and in alveolar macrophages. • They are capable of preventing the phagosome from fusing with lysosomes. • They also produce a toxin that blocks the oxidative burst • Two clinical forms of legionellosis have been described: – Legionnaire’s disease and Pontiac fever

Legionnaire’s disease: • It is a pneumonic illness typically begins with abrupt prodrome of malaise, headache, myalgia and weakness • Infection results from inhalation of droplets containing the pathogens. • The incubation period is two to 10 days. • The clinical picture is characterized by a multifocal, sometimes necrotizing pneumonia. • Occurrence is more likely in patients with cardiopulmonary primary diseases or other immunocompromising conditions.

Pontiac fever – Present as a flu-like syndrome without lung involvement – A self limiting disease and characterized by fever and chills, myalgia, malaise, and headache that develop over 6– 12 hours. – Dizziness, photophobia, neck stiffness, and confusion also occur. – Respiratory symptoms are much less prominent in Pontiac fever than in Legionnaire's disease and include mild cough and sore throat.

Lab diagnosis Specimens • bronchial washings, pleural fluid, lung biopsy specimens, or blood. • Isolation of legionella from sputum is more difficult because of the predominance of bacteria of the normal flora. • Legionella is rarely recovered from other anatomic sites. Smears – Legionellae are not demonstrable in Gram-stained smears of clinical specimens. – Direct fluorescent antibody tests of specimens can be diagnostic, but the test has low sensitivity compared with culture. – Silver stains are sometimes used on tissue specimens.

Culture • Specimens are cultured on Buffered Charcoal Yeast Extract agar (BCYE) supplemented by ferric salt plus Lcystine • Cultured organisms can be rapidly identified by immunofluorescence staining. Detection of Legionella antigen • A rapid diagnostic method is available to detect the antigen by ELISA • Can also be demonstrated in the patient's urine by immunologic methods (EIA).

Serological Tests – Antibodies can be assessed using the indirect immunofluorescence technique – Levels of antibodies to legionellae rise slowly during the illness. – have a sensitivity of 60– 80% and a specificity of 95– 99%. – are most useful in obtaining a retrospective diagnosis in outbreaks of legionella infections.

Biochemical reaction • catalase-positive. • oxidase-positive • hydrolyzes hippurate, starch and gelatine • Produce opacity around colonies on an egg yolk medium Treatment • Macrolide antibiotics (azithromycin, clarithromycin, erythromycin) are now the agent of choice • Doxycycline, rifampin and flouroquinolon are also effective

Prevention and control Hyperchlorination and superheating of water can help control the multiplication of legionellae in water and in air- conditioning systems

Genus Erysipelothrix • The genus has two species – E. rhusiopathiae – E. tonsillarum Erysipelothrix rhusiopathiae • Erysipelothrix rhusiopathiae (also called Erysipelothrix insidiosa) • gram-positive, non-motile bacillus that produces small, transparent glistening colonies.

Pathogenesis and clinical manifestation • It causes disease in domestic swine, turkeys, ducks, and sheep. • The most important impact is in swine, where it causes erysipelas. • The most common E rhusiopathiae infection in humans is called erysipeloid, a rare skin infection. • In humans, erysipelas is caused by group A beta-hemolytic streptococci and is much different from erysipelas of swine. • It usually occurs on the fingers by direct inoculation at the site of a cut or abrasion (and has been called "seal finger" and "whale finger"). After 2– 7 days' incubation, pain, which can be severe, and swelling occur. The lesion is raised, and violaceous in color.

• Additional clinical forms of infection (both rare) are a diffuse cutaneous form and bacteremia with endocarditis. Lab diagnosis • Specimen: wound secretion • On Gram stains it sometimes looks gram-negative because it decolorizes easily. • The bacteria may appear singly, in short chains, randomly, or in long non-branching filaments. • The colony morphology and Gram stain appearance vary depending upon the growth medium, incubation temperature, and p. H. • It may be alpha-hemolytic on blood agar. • Erysipelothrix is – Negative for catalase, oxidase, and indole – Produce hydrogen sulfide in TSI

Erysipelothrix rhusiopathiae…Cont’d Treatment • Erysipeloid can resolve after 3– 4 weeks, or more rapidly with antibiotic treatment • Erysipelothrix is highly susceptible to penicillin G, the drug of choice for severe infections. • The organism is intrinsically resistant to vancomycin.

Gardnerella vaginalis • G. vaginalis is a Gram-variable, non-motile, nonencapsulated rod bacterium. • It has been designated as Corynebacterium vaginalis and Haemophilus vaginalis. • Based on DNA hybridization, the pathogen is now classified with the regularly shaped, Gram-positive, nonsporing rod bacteria. • The natural habitat of this organism is the vagina of sexually mature women. • It can also cause vulvovaginitis (vaginosis). • There is offensive vaginal discharge with high p. H. • G. vaginalis is found in over 90% of women showing the symptoms of this infection, usually together with other bacteria

• The organism can be detected in vaginal discharge by means of microscopy and culturing. • Microscopic analysis, – clue cells (vaginal epithelia densely covered with Gram-labile rods) provide evidence of the role played by G. vaginalis. • This bacterium can be cultured on blood-enriched agar incubated in an atmosphere containing 5% CO 2. Treatment • The therapeutic agent of choice is metronidazole.