Corynebacterium, Listeria and Actinomyces MCQs

Pathogenesis of listeriosis: Intracellular survival : After entry into the intestinal epithelium, it survives inside the host cell, mainly due to lysis of phagosome by forming pores (mediated by listeriolysin O) Then it causes host cell actin polymerization , which helps the bacterium to reach near the cell membrane. Finally, it migrates to the adjacent epithelial cells/ macrophages by direct cell-to-cell spread, mediated by listeriopods . Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 698.

Dental caries and periodontal diseases: Mainly caused by naeslundii and A. odontolyticus. Oral-cervicofacial actinomycosis: This is the most common form, usually presented as a painless, slow growing, hard mass with cutaneous fistulas, a condition commonly known as lumpy jaw. Thoracic actinomycosis may present as cavitary lesions and pleural effusion. Abdominal form: It occurs due to spillage of intestinal flora secondary to bowel surgery or other conditions of bowel such as appendicitis. Pelvic form: It occurs following intrauterine contraceptive devices (IUCDs) insertion. Brain abscesses. Bone destruction and soft tissue infections. Disseminated form: It may occur due to hematogenous spread. Lungs and liver are the common sites; where multiple nodules are formed. Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 543.

Diphtheria is disease of childhood, it can be of various types. Faucial, cutaneous etc. Faucial is most common. In his patient has white to grey membrane on tonsil which bleeds on touch. Treatment of Diphtheria is diphtheria antitoxin is to be given. It is made up of antibodies used in the treatment of diphtheria. Dose is as below. Less than 48 hrs duration Pharyngeal/laryngeal - 20000 to 40000 units. Nasopharyngeal - 40000 to 60000 units More than 72 hrs duration 80000 to 120000 units. So all the options given are not true. Key Takeaways: Diphtheria Antitoxin (DAT) neutralizes circulating toxin Given along with antibiotics (penicillin/erythromycin) Dose depends on severity and duration of symptoms

C.Jeikeium: It is a lipophilic species, colonizing the skin of hospitalised patients. It can cause bacteremia, endocarditis and meningitis. especially in immunocompromised hosts. It is usually multidrug resistant, responsive to only vancomycin. U.urealyticum: It is skin commensal, rarely causes urinary tract infection (pyelonephritis) and alkaline encrusted cystitis (struvite stones in alkaline urine) in immunocompromised and renal transplant patients Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 605

Listeriosis is caused by \Listeria monocytogenes, which is a food-borne pathogen that can cause serious infections, particularly in neonates, pregnant women and elderly people. It is also a ubiquitous saprophyte and known to cause epizootic disease in birds and animals. Listeriosis is common among extremes of age (neonate and old age). Use of proton pump inhibitors increases the risk by reducing the gastric acid mediated killing of Listeria. Other risk factors: Pregnant women and immunocompromised individuals are at higher risk. Due to its ability to survive refrigeration (4°C), it is commonly found in stored foods especially aged soft cheeses, packaged meats, milk and cold salads. Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 698.

Pathogenesis of listeriosis: Intracellular survival: After entry into the intestinal epithelium, it survives inside the host cell, mainly due to lysis of phagosome by forming pores (mediated by listeriolysin O ) Then it causes host cell actin polymerization, which helps the bacterium to reach near the cell membrane. Finally, it migrates to the adjacent epithelial cells/ macrophages by direct cell-to-cell spread, mediated by listeriopods. Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 698.

Explanation: Sporothrix (Option B) Patients with sporotrichosis will usually present with a history of thorn prick followed by ulcers/pustules formation at the trauma site and lymphadenopathy. Histoplasma (Option C) is caused by bat or bird droppings and affects the reticuloendothelial system. Candida (Option D) on microscopy, candida will appear as both buds and pseudohyphae forms.

Erysipelothrix rhusiopathiae is a gram-positive bacillus that causes erysipeloid ; characterized by violaceous swelling with severe pain, but no pus; which differentiates it from staphylococcal and streptococcal erysipelas where pus is seen at the infection site. Most common site is fingers (called " seal finger" and "whale finger" ). Transmission: It usually infects animal handlers ( abattoir workers, butchers) and fishermen; transmitted by direct inoculation from animals or animal products. Treatment: Penicillin G is the drug of choice for severe infections. Reference : Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page no: 547.