Corynebacteria, Listeria, Brucella

• Corynebacterium spp. are Gram-positive bacilli arranged in V or L shapes, aerobic/facultative anaerobic, non-spore forming, and colonize the skin, upper respiratory tract, and genitourinary tract
• Important species of Corynebacterium include C. diphtheriae, C. jeikeium, C. ulcerans, and C. haemolyticum (now known as Arcanobacterium haemolyticum)
• Corynebacterium diphtheriae has a worldwide distribution, with humans being the only known reservoir, and spread occurs through droplets
• Diphtheria toxin, a virulence factor, is an exotoxin secreted by the bacteria causing the disease, with complications like myocarditis and neuritis
• Clinical features of diphtheria include an incubation period of 2-6 days, with classifications based on the site of infection such as anterior nasal, tonsillar and pharyngeal, laryngeal, and cutaneous
• Diphtheria diagnosis involves clinical history, examination, and nasal/throat/pharyngeal swab for NAAT and culture on selective media
• Diphtheria management includes treatment with diphtheria antitoxin, antibiotics like penicillin or erythromycin, support & monitoring, infection prevention and control with droplet precautions, and follow-up cultures to ensure eradication
• Listeria monocytogenes is a Gram-positive bacillus, non-spore forming, aerobe/facultative anaerobe, with characteristic tumbling motility at 25ºC, isolated from soil, water, vegetation, and can grow in refrigerated foods
• Listeria monocytogenes transmission can occur through animal contact, eating contaminated foods like milk, soft cheeses, pate, undercooked meat, unwashed vegetables, and vertical transmission from mother to fetus
• Listeria monocytogenes:

  • Clinical presentation: incubation period varies from 1-2 weeks up to 90 days
  • Most infections are asymptomatic or present as a mild influenza-like illness or diarrhea in healthy adults
  • Occupational exposure includes farmers, vets, and butchers
  • Pregnant women, neonates, and immunosuppressed individuals are at risk
• When suspecting a meningeal infection, the most important investigation to confirm the diagnosis is a lumbar puncture
• Opportunistic infection in Pregnancy:

  • Clinical presentation: perinatal listeriosis usually occurs in the 3rd trimester with symptoms like fever, myalgia, backache, headaches, and arthralgia
  • Perinatal infection may result in miscarriage, premature labor, and infected infants
• In a case of neonatal meningoencephalitis secondary to Listeria monocytogenes, treatment involves amoxicillin and an aminoglycoside as per neonatal dosing guidelines, with the aminoglycoside given for synergy
• Synergy in the context of antimicrobial therapy refers to the combined effect of two antibiotics being greater than the sum of their individual effects
• For a patient with night sweats, weight loss, and joint aches and pains, generalized lymphadenopathy, and a history of consuming unpasteurized milk and cheese, a concern would be brucellosis
• Brucellosis:

  • Clinical presentation: acute brucellosis has an incubation period of 2-4 weeks with symptoms like influenza-like illness, dry cough, arthralgia, myalgia, headache, weight loss, fever, lymphadenopathy, and hepatosplenomegaly
  • Chronic brucellosis can recur over months or years with symptoms like evening depression, distinctive sweating episodes, arthritis, and insomnia
• Brucella is an intracellular pathogen that can be transmitted through unpasteurized dairy or meat processing, with different species affecting various animals
• The virulence factor important for Brucella's virulence and clinical manifestation is its ability to be ingested by polymorphonuclear leukocytes and macrophages, multiply in regional lymph nodes, enter the bloodstream, spread to organs, and produce small granulomata in target sites
• Portals of entry for human brucellosis include ingestion, inhalation, and skin/mucous membrane contact
• Diagnosis of brucellosis involves clinical suspicion with geographical association, blood cultures, bone marrow aspirate, serology, and nucleic acid amplification tests
• Treatment of brucellosis typically involves doxycycline and rifampicin for 6 weeks, with alternatives for pregnant patients, children, or those intolerant to doxycycline
• Prevention of brucellosis includes culling infected livestock, immunizing healthy livestock, pasteurizing milk, avoiding unpasteurized goat or sheep soft cheese, and post-exposure prophylaxis in high-risk situations