Anaerobic bacteria Flashcards
Discuss the classification of bacteria in relation to aerotolerance
- obligated aerobes : Requires 15 -20% of O2 to grow
- Facultative anaerobes : Grows equally well in absence or presence of oxygen
- Microaerophila: Grow in decreased O2 and better when CO2 is increased
- Aerotolerant anaerobe : Able to grow 2-8% of O2
5.Obligated anaerobe : Will not grow in O2 concentration is more than 0.50%
Discuss the characteristics of anaerobes (6)
- Ubiquitous and commensals of skin ,pulmonary ,intestinal and urogental tract
- Surces of infecting microbe-mostly host’s endogenous flora
- Alterations of hosts tissue provide suitable niche for acquiring opportunistic infections
- Weak pathogens but involved in polymicrobial infections with aerobes
- Suppurative ,causing abscess formation and tissue necrosis and often gas formation
- Some produce most potent paralytic toxins
Discuss the epidemiology of anaerobic bacteria
- They are ubiquitous (widespread) -soil ,water , food and animals
- Prevalent in normal flora of the body
- Incidence of bacteremic episodes vary from 5-15%
- Commonest isolates
* bacteriodes(75%)
* Closridium (10-20%)
* peptostreptococcus and fusobacterium (10-15%)
* propionibacteriun acnes(2-5%)
5.Exogenous infections :spore-forming organisms in soil ,water ,sewage
- Endogenous infections :indigenous flora
* skin;propionbacterium
* Upper respiratory :Propionibacterium
* Mouth ;fusbacterium,actinomyces
* intestines: clostridium ,bacteriodes,fusbacterium
* Vagina ;lactobacillus
Discuss 3 differences between the endogenous infections and exogenous infections of the body
1.Frequency
Endo: most frequent cause of anaerobic infections
Exo: Uncommon
- Gain into the body
* Endo: Gains entry via trauma or disruption of the mucous membrane to allow entry of microorganism into normally sterile sites eg blood, brain and joints
*Exo: Gains access via contaminated food or water ,trauma or disruption of body surfaces
Endogenous occuring mircobes rae found in indigenous flora eg oral cavity ,pharynx ,GIT and genitourinary
Exo: Frequent Causes ; Gram pos spore forming bacilli- clostridium spp
Discuss the pathogenesis of anaerobic infections
- Attachment and adhesion : polysaccharide capsule and pilli
- Invasion : Alteration in host tissue (trauma ,surgery ,disease
- Establishment of infection
* polysaccharide capsule (Bacteroides)
* spore
* formation (clostridium ) - Tissue damage
* elaboration of toxins
* degrading enzymes
what are the clinical features suggesting anaerobic infections
FIB GAP H
- foul smelling discharge /odour
- infection assciated with malignancy
- blood containing exudates
- abscesses ,black necrotic tissue and gangrene
- gas in pus or infected tissue
- polymicrobial findings on gram stain or culture ,gram stain organisms seen but no growth on culture
- human bites
- previous antibiotic therapy
- sulphur granules
Factors predisposing to anaerobic infections
Environment with reduced redox potential :
- Crush injuries with interruption of blood supply
- tissue damage
- co-infection wih aerobic infection
- contamination of foreign body
- burns
- peripheral vascular insufficiency
general
- Diabetes
- corticosteroids
- hypogammaglobulinemia
- leukopenia
- immunosuppression
- cytotoxic drugs
- splenectomy
- collagen diseases
- Environmental exposure
* contaminated food
* contaminated wounds
* flora can be modified to favor anaerobes: antacids, bowel motility, and antibiotics
4.Specific clinical scenarios
*malignancy {tissue associated malignancy =colon,uterus,lng and leukemia
*GIT and female pelvic surgery
*GIT trauma,dental extraction
*human and anml bites
*aminoglycoside therapy
*
discuss the disease spectrum of anaerobic infections
clostridium tetani and clostridium perfringens
*They are gram pos spore forming bacilli
*
Causes tetanus
- types of infection;
- Wound, cephalic and neonatal
1. * AB exotoxins - tetanospasmin ( neurotoxins) - Targets presynaptic nerve terminal, blocks release of inhibitory neurotransmitters (GABA) into synapses
- Prolonged muscle spasms, rigidity, respiratory arrest, and death if toxins do is high
Gram pos spore forming bacilli-Clostridium perfringens
- Soft tissue infections (histotoxins)
* clostridial myonecrosis ( gas gangrene
* Suppurative myositis
* Crepitant cellulitis
* polymicrobial infections - Enteric infections
* food poisoning
* enteritis necroticans
* neutropic enterocolitis
Discuss disease spectrum of anaerobic infections
Clostridium botulium and clostridium difficile
- Clostridium botulium
* gram pos spore forming bacillli ,strictly anaerobic
* highly resistant spores ,released during vegetable growth ,found in feces ,soil, blood and food sources
-Food borne infection
Produces a potent neurotoxin in food and spores are resistant to activation. Does not need a live bacteria
-wound infection
-Neonatal infection
*ingestion of spores (honey) germinates resulting in toxins (A B C F)
*When ingested ,it gets into the blood and invade peripheral nerves (with hours or days ) and blocks the release of ACh ,resulting flaccid paralysis
{ ocular / respiratory muscles ultimately resulting in blurred vision ,and difficulty in swallowing
2.Clostridium difficile :
Gram pos spore forming bacilli
*Antibiotic association diarrhea ,causes nosocomial infection spreads by hands
*Antibiotic treatment causes suppression of normal GIT flora replaced by C.difficile which multiply and produces toxins ,enterotoxins
May give rise to Pseudomembranous colitis
Discuss the disease spectrum of anaerobic infections
Propionbacterium spp and Eubacterium spp peptosreptococcus spp
Gram pos non spore forming bacilli
- Propionibacterium
* Opportunistic infection (intravascular /prosthetic device (heart ,ventricle and CNS shunt) - Eubacterium spp
* Female IUCD infections
Gram pos cocci 1.Peptostreptococci spp *Found on normal flora of the body ,skin, oral cavity and genitourinary tract -intra-abdomianl infections Aspiration pneumonia
-
Discuss the disease spectrum of anaerobic diseases
- Gram neg bacilli
* Bacteriodes ,Prevotella ,Fusobacterium
Commonly foun inintra abdominal pyogenic infection and genital and respiratory infections
2.Gram negative cocci infection
veionella spp
found in oral flora and isolated from human bites
Principles of laboratory diagnosis of anaerobic infections
- Collect appropriate clinical specimen from site containing necrosis tissue
- Aspirated material or tissue are the preferred specimen specimen ,no swabs because by the time they arrive at the lab , the microbes will be dead
* specimen should be in a lab within 1-2 hours of collection
* Tissue should be sent in a container with normal saline
* Sample should be incubated for 48 hrs
Clinical specimens for diagnosis of anaerobic infections
- Appropriate specimen types
* Aspirated material from abscess
* Tissue obtained from a biopsy or autotopsy
* Sterile fluid eg blood /CSF
* GIT(bile ,peritoneal fluid
* GUT
Inappropriate specimen
- Swabs from any site when investigating anaerobic infection
- stool except for clostridium difficile
- nasopharyngeal and oropharyngeal
- lleostomy colostomy drainage
