Gram Positive Rods - Aerobic Flashcards
Examples of aerobic GPRs
- Corynebacterium spp
- Corynebacterium diphtheriae
- Corynebacterium ulcerans, jeikeium & minutissimum - Bacillus spp
- Bacillus anthracis
- Bacillus cereus - Listeria monocytogenes
- Nocardia asteroides
- Others (lactobacillus, arcanobacterium haemolyticum, rhodococcus equi, erysipelothrix rhusopathiae)
Transmission of C. diphtheriae
- Respiratory droplets
- Aided by asymptomatic carriers
- infects upp resp tract (throat, nasal mucosa, larynx, trachea), and skin (part of normal flora)
Clinical presentations of C. diphtheriae
Diphtheria
- Local effects
- pseudomembrane formation (dirty white, becomes darker with time)
- infected area becomes red & swollen, may result in airway obstruction & suffocation, or “bull neck” - swollen neck tissue
- sternocleidomastoid & collapsing ribcage - sign of intense effort to draw in air - Distant effects (toxin is absorbed)
- myocarditis (arrhythmias, heart damage)
- nerve damage (peripheral neuritis) resulting in muscle weakness incl resp muscles - Non toxigenic strains cause pharyngitis, skin abscesses, invasive infections
Diagnosis of C. diphtheriae (2)
- Clinical - need for early treatment
- Culture, throat swabs on selective medium (Tinsdale’s) which suppresses normal flora
- suspect colonies confirmed via sugar fermentation reactions
- Elek plate test to check for toxigenicity (toxin production, indicated by precipitin line)
Treatment of C. diphtheriae (3)
- IV antiserum - Abs neutralize toxin before it can bind to & neutralise cells
- Erythromycin
- Supportive/symptomatic treatment for other complications, heart & resp failure
Prevention of C. diphtheriae (2)
- Vaccine: diphtheria toxin chemically modified - toxoid
- immunization programmes effectively eliminate disease in the community
- secondary cases occur in older patients whose immunity has declined with time - Protect contacts: administer diphtheria toxoid & prophylactic antibiotic
- erythromycin clears throat colonisation in carriers
- isolate pt until they are non infectious + immunise them
Clinical presentations of corynebacterium ulcerans
- Throat lesions resembling diphtheria
2. Diphtheria-like systemic illness
Features of corynebacterium jeikeium
- often multiresistant, opportunistic, nosocomial infection
- can cause wound infections, infect implanted devices like replacement heart valves, IV lines
Clinical presentations of corynebacterium minutissimum
- Causes erythrasma - fluoresces coral pink using Wood’s lamp
- Sometimes invasive infections
Transmission of B. anthracis
- Zoonosis, spores can be carried with animal products like bone meal & hides
- infects animals
- spores often visible within bacterium, resistant & can survive long
Virulence factors of B. anthracis (3)
- Antiphagocytic capsule (protein, not saccharide)
- Toxins
- Soluble factors - Protective antigen, edema factor, lethal factor (lyses macrophages)
Clinical presentations of B. anthracis (4)
- Cutaneous anthrax
- spores introduced into the skin
- forms eschars (central dark area) surrounded by a ring of vesicles & an area of edema which may spread - Respiratory anthrax
- spores inhaled, causes severe infection with hemorrhage - Intestinal anthrax
- eating meat of an infected animal
- causes hemorrhagic diarrhea - Septicaemia & death
Diagnosis of B. anthracis
- Culture - blood, vesicle fluid, sputum
- grows well on blood agar aerobically
- pink stained capsule (McFadyean’s stain)
Treatment of B. anthracis (2)
- Penicillin
- Ciprofloxacin
- worry that a MDR strain may be used as biological warfare weapons (aerosol delivery is easy)
Transmission of B. cereus
Food poisoning - often from fried rice
- bacterial spores survive boiling
- contaminated cooked rice allowed to stand at room temp allows for spores to germinate & bacteria to grow & secrete toxin
- preformed toxin is heat stable
Clinical presentations of B. cereus (2)
- Food poisoning
- rapid onset - within 6h, due to pre-formed toxin, vomiting
- slower onset - 8-24h, by enterotoxins formed in intestine, diarrhea & abdominal pain - Wound & invasive infection eg post traumatic ophthalmitis
Diagnosis of B. cereus
Culture from food/stool - grows well on blood agar aerobically
Prevention of B. cereus
- Store cooked rice in refrigerator
2. Cook thoroughly
Transmission of listeria monocytogenes
- replicates in cold (even 4C)
- GIT flora of animals
- Food borne (chilled foods, meat contaminated at slaughter)
Clinical presentations of L. monocytogenes (3)
- Febrile gastroenteritis
- Infections in pregnancy & neonates
- mother is usually asymptomatic/has flu-like illness
- foetus may be aborted/induced premature labour/still birth/severely ill with multi system infection (granulomatosis infantisepticum) or go on to develop early onset neonatal listeriosis or late onset meningitis (acquired by cross infection in hospitals) - Infections in other patients (usually immunosuppressed)
- meningitis, febrile bacteremic sepsis, endocarditis
Diagnosis of L. monocytogenes (3)
- Pregnancy/neonatal infections: Culture (blood, high vaginal swab, amniotic fluid, baby skin swabs)
- Meningitis: Culture (CSF, blood), CSF (changes in white cell count & chemistry)
- Beta hemolytic colonies grow aerobically on blood agar
Treatment of L. monocytogenes
- Ampicillin +/- genatmicin
2. Resistant to all cephalosporins
Features of nocardia asteroides
- Branching beaded filaments
2. Found in soil & other environmental sources
Clinical presentations of nocardia asteroides (2)
- Nosocomial infections (developed countries)
- usually opportunistic, in immunosuppressed, AIDS
- lung infection followed by disseminated infection with abscesses in many organs including the brain + primary skin infections - Non-opportunistic infections (tropical countries)
- Madura foot: chronic destructive infection of bone & soft tissue following inoculation into the skin
Diagnosis of nocardia asteroides
- Culture
- sputum, pus - appears beaded as stain is not taken up so well
- blood - slow growth
Treatment of nocardia asteroides
Co-trimoxazole, long course of treatment
Features of lactobacillus
- Normal flora of mouth, gut, vagina (more at puberty, low pH, protects)
- Dental caries (but S. mutans more crucial)
- possibly probiotic, helps in prevention & treatment of GI infections
Clinical presentations of arcanobacterium haemolyticum
- Unusual cause of sore throat
2. May be accompanied by skin rash resembling scarlet fever
Features of rhodococcus equi
- Opportunistic lung infection - in immunocompromised
2. From animals
Features of erysipelothrix rhysopathiae
- Causes erysipeloid (a form of cellulitis with a blue-red discolouration of the skin)
- Typically in those who handle meat/fish
