anaerobic gram positive rods

Question 1

name the sporing anaerobic gram positive rods

Answer 1

clostridium spp.: c. perfringens, c. tetani, c. septicum, c. botulinum, c. difficile

Question 2

clostridium perfringens: character

Answer 2

frequently present in human faeces, may colonise the skin particularly below the waist, often causes outbreaks in geriatric wards

Question 3

clostridium pefringens: culture

Answer 3

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

Question 4

clostridium pefringens: virulence

Answer 4

alpha toxin (lecithinase): destroys cell membranes

Question 5

clostridium perfringens: clinical presentations

Answer 5

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

Question 6

clostridium perfringens: diagnosis

Answer 6

histology, culture, (blood, discharge, tissue)

Question 7

clostridium perfringens: treatment

Answer 7

gas gangrene: benzylpenicillin + clindamycin (targets infetions involving toxins), removal of dead tissue
for food poisoning: rehydration therapy, anitibiotics are not indicated

Question 8

clostridium septicum: clinical presentations

Answer 8

gas gangrene

isolation from the blood is associated with leukemia and colon cancer

Question 9

clostridium difficile: character

Answer 9

found in faeces of a minority of the population

Question 10

clostridium difficile: virulence factors

Answer 10

exotoxin

Question 11

clostridium difficile: clinical presentations

Answer 11

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

Question 12

clostridium difficile: diagnosis

Answer 12

colonoscopy, stool culture, toxin detection (either through cytotoxicity or immuno-assays), pcr, gde antigen detection

Question 13

clostridium difficile: treatment

Answer 13

stop antibiotics if possible, oral metronidazole or oral vancomycin; isolate patient + be wary of relapse

Question 14

clostridium botulinum: character

Answer 14

direct wound ingection, ingestion of preformed toxin in contaminated food especially honey

Question 15

clostridium botulinum: virulence factors

Answer 15

botulinum toxin blocks acetylcholine release at the neuromuscular junction

Question 16

clostridium botulinum: clinical presentations

Answer 16

botulism - flaccid paralysis
early signs: diplopia, ptosis, nausea, vomitting, usually no fever
severe conditions: paralysis of respiratory muscles

Question 17

clostridium botulinum: diagnosis

Answer 17

culture (patient sample or food), test for toxin by inoculation of mouse

Question 18

clostridium botulinum: treatment

Answer 18

antiserum to neutralise free toxin, mechanical ventilation

Question 19

clostridium tetani: histology + character

Answer 19

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

Question 20

clostridium tetani: virulence factors

Answer 20

tetanospasmin; a very potent neurotoxin which blocks inhibitory stimuli received by lower motor neurons

Question 21

clostridium tetani: clinical presentations

Answer 21

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

Question 22

clostridium tetani: treatment

Answer 22

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

Question 23

clostridium tetani: prevention

Answer 23

toxoid vaccine in the national childhood immunisation schedule (beware of neonatal tetanus; every child has a wound that is the umbilicus)

Question 24

most non-sporing anaerobic gram positive and negative rods: antibiotics sensitivity

Answer 24

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)

Question 25

most non-sporing anaerobic gram positive and negative rods: nature of infections

Answer 25

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

Question 26

most non-sporing anaerobic gram positive and negative rods: clinical presentations (head and neck)

Answer 26

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)

Question 27

most non-sporing anaerobic gram positive and negative rods: clinical presentations (pleuropulmonary)

Answer 27

follows aspiration of mouth flora

pneumonia, lung abscess, empyema

Question 28

most non-sporing anaerobic gram positive and negative rods: clinical presentations (abdominal)

Answer 28

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)

Question 29

most non-sporing anaerobic gram positive and negative rods: clinical presentations (skin and soft tissue)

Answer 29

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)

Question 30

most non-sporing anaerobic gram positive and negative rods: clinical presentations (genital tracts)

Answer 30

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

Question 31

most non-sporing anaerobic gram positive and negative rods: clinical presentations (others)

Answer 31

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)

Question 32

synergistic infections between aerobic and anaerobic bacteria

Answer 32

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

Question 33

name the exceptions to the generalisation of non-sporing anaerobic gram positive and negative rods

Answer 33

actinomyces israelii

fusobacterium necrophorum

Question 34

actinomyces israelii: histology + character

Answer 34

gram positive branching filaments that are isolated from sulphur granules in pus

normal flora

Question 35

actinomyces israelii: clinical presentations

Answer 35

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)

Question 36

actinomyces israelii: diagnosis

Answer 36

culture (slow-growing)

Question 37

actinomyces israelii: treatment

Answer 37

penicillin/amoxicillin, intravenous benzylpenicillin for serious disease

**resistant to metronidazole

Question 38

fusobacterium necrophorum: clinical presentation

Answer 38

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

Question 39

fusobacterium necrophorum: diagnosis

Answer 39

culture (blood, abscess fluid)

Question 40

fusobacterium necrophorum: treatment

Answer 40

benzylpenicllin, drain abscesses