anaerobic gram positive rods Flashcards
name the sporing anaerobic gram positive rods
clostridium spp.: c. perfringens, c. tetani, c. septicum, c. botulinum, c. difficile
clostridium perfringens: character
frequently present in human faeces, may colonise the skin particularly below the waist, often causes outbreaks in geriatric wards
clostridium pefringens: culture
nagler plate test for alpha toxin; breaks down lipids of egg yolk in agar to produce insoluble fat droplets which is seen as an area of opacity
clostridium pefringens: virulence
alpha toxin (lecithinase): destroys cell membranes
clostridium perfringens: clinical presentations
gas gangrene (clostridial myonecrosis) occurs after spores are introduced into area of tissue which is anaerobic, resulting in rapid spreading tissue damage; gas is produced in this process (detected by pressing and feeling a crepitus or by x-rays)
local signs include pain, discolouration, fluid filled blebs and thin smely discharge; systemic illness also occurs, leading to shock and septicaemia
food poisoning: spores survive cooking, depths of food, presents with abdominal cramps and diarrhoea 12-24 hours after consumption
pigbel: necrotising enteritis in new guinea after eating pork feasts
clostridium perfringens: diagnosis
histology, culture, (blood, discharge, tissue)
clostridium perfringens: treatment
gas gangrene: benzylpenicillin + clindamycin (targets infetions involving toxins), removal of dead tissue
for food poisoning: rehydration therapy, anitibiotics are not indicated
clostridium septicum: clinical presentations
gas gangrene
isolation from the blood is associated with leukemia and colon cancer
clostridium difficile: character
found in faeces of a minority of the population
clostridium difficile: virulence factors
exotoxin
clostridium difficile: clinical presentations
antibiotics-associated pseudomembrane colitis
pseudomembrane formed in colon, usually precipitated by the use of antibiotics that wipe out normal gut flora
not all infections result in pmc, some cause a mild diarrhoeal disease
cdad: c. difficile associated diarrhoea
clostridium difficile: diagnosis
colonoscopy, stool culture, toxin detection (either through cytotoxicity or immuno-assays), pcr, gde antigen detection
clostridium difficile: treatment
stop antibiotics if possible, oral metronidazole or oral vancomycin; isolate patient + be wary of relapse
clostridium botulinum: character
direct wound ingection, ingestion of preformed toxin in contaminated food especially honey
clostridium botulinum: virulence factors
botulinum toxin blocks acetylcholine release at the neuromuscular junction
clostridium botulinum: clinical presentations
botulism - flaccid paralysis
early signs: diplopia, ptosis, nausea, vomitting, usually no fever
severe conditions: paralysis of respiratory muscles
clostridium botulinum: diagnosis
culture (patient sample or food), test for toxin by inoculation of mouse
clostridium botulinum: treatment
antiserum to neutralise free toxin, mechanical ventilation
clostridium tetani: histology + character
drumstick appearance (long thin rod with a large terminal spore)
found in faeces of large farm animals, human gut; soil; spores are widespread in environment
clostridium tetani: virulence factors
tetanospasmin; a very potent neurotoxin which blocks inhibitory stimuli received by lower motor neurons
clostridium tetani: clinical presentations
tetanus - spastic paralysis
local signs: pain and stiffness at site of infection
mild symptoms: lockjaw (masseter affected early); risus sardonicus
serious symtoms: opisthotonus (all muscles of back contract, body assumes rigid posture determined by the stronger of each antagonistic set of muscles), autonomic disturbance and eventually cvs derangements
*infection itself does not produce immunity to the toxin and immunisation is required
clostridium tetani: treatment
human tetanus immunoglobulin (htig) to neutralise free toxin that is unbound to motor neurons
remove unhealthy tissue, prescribe antibiotics to kill remnant clostridia
paralysis and ventilation of patients with difficulty breathing due to spasms (wait until bound toxin is degraded); immunize after recovery since the infection is not immunogenicc
clostridium tetani: prevention
toxoid vaccine in the national childhood immunisation schedule (beware of neonatal tetanus; every child has a wound that is the umbilicus)
most non-sporing anaerobic gram positive and negative rods: antibiotics sensitivity
antibiotics sensitive:
metronidazole-sensitive
above umbilicus - penicillin sensitive, below unmbilicus: penicillin resistant (e.g. bacteroids fragilis that is part of the colonic flora produces beta lactamase)
most non-sporing anaerobic gram positive and negative rods: nature of infections
often mixed, involving the aerobic species as well
seldom spontaneous, often involves precipitating cause (surgery, gut perforation, diabetes, cancer)
usually endogenous in nature (own flora), except for animal bites
produces disgusting smells
most non-sporing anaerobic gram positive and negative rods: clinical presentations (head and neck)
vincent’s infection - acute necrotising ulcerative gingitvitis; painful ulcerations of the gums with bleeding, may spread to tonsils causing painful swallowing (vincent’s angina)
dental sepsis
abscess/cellulitis - submandibular infection leads to ludwig’s angina
chronic ent infection (sinusitis, otitis media, matoiditis)
brain abscess that involves streptococci too
treatment: metronidazole or penicillin (above umbilicus, hence susceptible)
most non-sporing anaerobic gram positive and negative rods: clinical presentations (pleuropulmonary)
follows aspiration of mouth flora
pneumonia, lung abscess, empyema
most non-sporing anaerobic gram positive and negative rods: clinical presentations (abdominal)
secondary to appendicitis, diverticulitis, abdominal surgery
peritonitis, abscess, wound infection, liver infection
- diverticulitis: inflamed pouches in the GIT
treatment: metronidazole or penicillin (above umbilicus, hence susceptible)
most non-sporing anaerobic gram positive and negative rods: clinical presentations (skin and soft tissue)
infections of diabetic foot ulvers, decubitus ulvers, sebaceous cysts, hydradenitis suppuravita (infected blocked aprcrine glands)
acne (propionibacterium spp.)
anaerobic cellulitis (spreading infection of subcutaneous tissues, often involves clostridium spp and aerobic bacteria too)
most non-sporing anaerobic gram positive and negative rods: clinical presentations (genital tracts)
male genital tract: scrotal and prostate infections
female genital tract:
bacterial baginosis
endometritis, tubo-ovarian sepsis, bartholin’s abscess, septic abortion, intrauterine devices associated infections, chronic pelvic inflammatory diseases
neonatal pneumonitis
treatment: metronidazole or clindamycin
most non-sporing anaerobic gram positive and negative rods: clinical presentations (others)
urinary tract - very rare, often involves fistula connecting to bowel due to tumour invasion; suspected with foul smelling urine but no aerobic culture
bone and joint - uncommon cause of chronic osteomyelitis and septic arthritis
bacteraemia: commonly bacteroides fragilis (which has beta lactamase)
synergistic infections between aerobic and anaerobic bacteria
necrotising fasciitis: s. pyogenes, anaerobes, clostridium spp., mrsa, vibrio vulnificus
meleney’s synergistic gangrene: spreading area of skin necrosis causing ulceration, usually starting at a post-operative abdominal wound site or colostomy; s. aureas + microaerophilic or anaerobic streptococci
fourneir’s gangrene: mixed infection of scrotum causing gangrene
name the exceptions to the generalisation of non-sporing anaerobic gram positive and negative rods
actinomyces israelii
fusobacterium necrophorum
actinomyces israelii: histology + character
gram positive branching filaments that are isolated from sulphur granules in pus
normal flora
actinomyces israelii: clinical presentations
invasive infections following disease or trauma at mucosal surgaces, spreads slowly across tissue planes and causes fibrosis - hard swelling forms and eventually pus drains from sinus tracks onto skin surface
common sits: cervicofacial (commonst, predisposed by dental extraction and caries), thoracic (lung infection eventually invading chest well), abdominal (originates from diseased appendix or colon), pelvic (associated with use or intrauterine devices)
actinomyces israelii: diagnosis
culture (slow-growing)
actinomyces israelii: treatment
penicillin/amoxicillin, intravenous benzylpenicillin for serious disease
**resistant to metronidazole
fusobacterium necrophorum: clinical presentation
gram negative
necrobacillosis - lemierre’s disease
severe sore throat, progressing to septicaemia which seeds bacteria to multiple organs, forms multiple abscesses
infection may locally invade the jugular vein and carotid artery
fusobacterium necrophorum: diagnosis
culture (blood, abscess fluid)
fusobacterium necrophorum: treatment
benzylpenicllin, drain abscesses
