9. Lab diagnosis of anaerobic infections

what are obligate anaerobes?

bacteria that can not survive in presence of high oxygen content

they lack certain enzymes that can detoxify the products that bacteria can produce from oxygen, and can not groww in healthy tissue due to its oxygen content

most common gram + pathogens of anaerobic infections?

clostridium

actinomyces

peptostreptococcus

most common gram - pathogens of anaerobic infections?

bacteroides

fusobacterium

prevotella

porphyromonas

endogenous infection characteristics?

most anaerobes in the normal flora are non-spore formers and anaerobic infection often occur from this source

exogenous infection characteristics?

contamination of wounds

common in the environment, like soil

where can we find anaerobes in normal flora?

predominant component of bacterial flora of normal human skin and mucous membrane

what are the most common anaerobes found in normal flora?

enterobacteriaceae and bacteroides fragilis

what are the risk factors of anaerob infections?

exposure to sterile body sites

poor blood supply or necrotic tissue

DM

splenectomy

immunosuppression

collagen vascular disease

what are the key points of good anaerobic diagnostics?

1. proper sample collection from the right site

2. storage

3. transportation

4. labratory tests

what are the clinical signs of anaerobic infection?

foul smelling discharge

proximity to mucosal surface

gas in tissue → in soft tissues, crepitation on palpation can be produced when gas is in an area it should not be

abscess formation

bite wounds

wounds contaminated with soil

general rules for sample collection?

sample from the right site

aseptic sample collection

avoid contamination with normal flora

avoid or minimalize exposure with O2

what are the appropriate specimens for anaerobic culture?

blood → special anaerobic bottle

CSF

deep wounds

aspirates from body fluids or wounds

urine collected by suprapubic bladder aspiration

abscess contents

transtracheal or lung aspirate

bronchoalveolar lavage

what are the methods of sample collection?

abscess contents → aspiration with syringe and needle, put into transport tube

perioral or gingival abscess → aspiration is best

collection with sterile blade or swabbing the involved areas of the skin

surgery → 5ul tissue sample into transport media, 1 ml into sterile container

how should the sample be stored and transported?

room temperature

not plastic or glass tube

specimen should be protected from O2 → anaerobic transporter

enrichment used in anaerobic culture?

Holman medium layered with vaseline

Thioglycolate broth

which media is used for anaerobic sample?

basic media: BA, CA, EMB

pre-reduced anaerobically sterilized culture media: egg-yolk agar and liquid enrichment media

anaerobic culturing?

5-7 days

anaerobic jar

anaerostat

anaerobic incubator

anaerobic jar?

chemical will absorb the O2 in the jar

anaerostat?

O2 jar is removed by a high vaccu pump, then jar is refilled with N2 or CO2 and sealed

API 20 A strip?

analytical profile index

biochemical identification

21 tests that are carried out quickly to check for anaerobes

20 microtubes containing dehydrated substrates

ATB ID 32A ?

automated computer-assisted system

standardized system for the identification of anaerobes in 4 hrs

uses 29 miniaturized enzymatic tests and a datapase

what is used for clostridioides difficile identification?

API

ATP ID32A

MALDI_TOF

what is used to antibiotic sensitivity testing?

disc dffusion method

sensitivity testing in liquid medium

agar dilution test

E-test

empiric antibiotic therapy for anaerobic infection?

metronidazole

anaerobic antibiotics → B-lactam, clindamycin, flurochiolones

why are aminoglycosides not a good choice for anaerobic infections?

they require oxygen for uptake, making them ineffective against anaerobic bacteria.

clostridium perfringens identification?

anaerobic BA: dull colonies with double hemolytic zone

positive Naglet test

reverse CAMP test

gas production