LAB - Gram Positive Bacilli & Candida Flashcards
majority of Corynebacterium species are found in normal flora here
skin and mucous membranes
Corynebacterium diphtheriae is the major human pathogen in the genus and causes these two disease forms:
respiratory & cutaneous diphtheria
3 biotypes of Corynebacterium diphtheriae
gravis
mitis
intermedius
T or F. C. diphtheriae is only found in humans
T
C. diptheriae infects the URT to cause diphtheria in which…
a pseudomembrane forms in the oropharynx and obstructs the airway
T or F. just bc C. diphtheriae is present, does not mean the patient has diphtheria
T! some strains do not produce the toxin
diagnosis depends in isolate producing DT (Elek test)
C. diphtheriae is isolated most commonly from the following swabs:
throat swabs (pharyngeal) also from skin lesions, nasal swabs, or ear swabs
T or F. C. diphtheriae can grow on BAP as a facultative organism
T! but better growth on:
Tellurite media (cystine tellurite, Hoyle’s or Tinsdale’s agar)
Loeffler’s Blood Seum (LBS)
Tellurite media
- potassium tellurite, a colorless salt = inhibits most normal flora bacteria from the respiratory tract
- also reduced by Corynebacterium to metallic tellurium which stains colonies brown-black
- some g+c may present with black colonies
- selective and differential by H2S production (from Na2S2O3 and L-cysteine) so presumptive C. diptheriae are seen by the brown-black halo
Loeffler’s Blood Serum
- enriched w serum and egg to enhance growth C. diphtheria
- formation of metachromatic granules
- used more frequently for secondary isolation of diphtheria from telluride media in order to obtain organisms in pure culture + to enhance granule morphology when stained w methylene blue
dips
- resemble C. diphtheriae morphologically but NO toxin
- no halo on Tinsdale
- normal human skin and mucous membrane flora and are invariably found in many specimens
- palisades
- facultative, small, dry wh colonies that are
- strongly cat pos
- can be opportunistic in compromised hosts
- exhibit resistance to antimicrobial agents
Bacillus
- aerobic, gram pos
- endospores
- spores do not stain on gram stain
- often a lab contaminant
- grows well on BAP; large colonies, raised, beta-hemolytic with frosted green-grayish glassy appearance
- majority of species are not pathogenic
primary pathogen of Bacillus
B. anthracis
- common disease of livestock worldwide
- most cases associated with imported animal hair or wool = skin necrotic lesions = BLACK ESCHAR
Bacillus cereus
food poisoning
- opportunistic
B. anthracis and B. cereus common characteristics
- catalse, lectithinase postiive
- oxidase negative
- produce acid from glucose
B. cereus vs. B. anthraci
- cereus = beta-hemolytic and motile; anthracis is NOT
- B. anthracis = large and filamentous colonies = medusa head
- B. anthracis is susceptible to penicillin disc test while other species are resistant
Listeria monocytogenes
- facilitate anaerobe with beta hemolysis
- catalase pos
- bile esculin, bile hydrolysis pos
- CAMP positive
- tumbling motility at 25 C but not at 37 C
- semi-solid motility media = umbrella-like growth
- neonatal sepsis/meningitis puerperal sepsis/ sepsis
- meningitis in immunocompromised patients and pregnant women
specimens for isolation of Listeria
- blood
- CSF
- amniotic fluid
Gardnerella vaaginalis
- cell wall = gram pos characteristics but stains gram variable to gram neg (bc of pleomorphic nature of CB)
- nonmotile, facultative bacteria that is present in vagina of up to 70% of women
- BV infections
- 5-10% CO2 for a minimum of 48 hours
- positive for Hippurate hydrolysis
what is bacterial vaginosis?
- vaginal inflammation
- vag discharge with a fishy odor, vag pH over 4.5
- smears w decreased lactobacillus
- “clue cells” = epithelial cells covered with gram variable bacilli
> normal = epi ells with many Lactobacilli
T or F. G. vaginalis is beta-hemolytic on sheep BAP
F! only shows hemolysiss on HUMAN BAP
T or F. Culturing is not necessary for G. vaginalis diagnosis
T
Lactobacillus
- normal vaginal flora
- g + b in chains
- nonhemolytic
- catalase negative
what is the “whiff” test
- used for presumptive diagnosis of BV
- 1 drop of 10% KOH
= fish-like odor?
Actinomycetes
- may be aerobic or anaerobic
- aerobic = soil and water; gram pos branching filaments that often fragment into gram variable cb
- slowly grow (4 weeks in CO2)
- Nocardia and Streptomyces (main pathogens)
> chronic tissue disease, systemic infections in immunocompromised patients
Candida albicans normal flora
- various body sites
- endogenous to alimentary or digestive tract + mucocutaneous areas of body
- most common cause of serious fungal disease or candidiasis
- most often opportunistic
this organism has characteristic sugar fermentation and assimilation
C. albicans
- assimilation = ability to grow in the presence of the specific carbohydrate; growth or turbidity is looked for in the presence of O2
BUT since any organism that can ferment a carb can also assimilate it, most labs use only assimilation tests
Candida is approximately equivalent in size to
RBCs
germ tube test
- 2 hrs incubation or else pseudohyphae will develop
- slide examination at 10X and 40X
- germ tube pos = bike seats; albicans
- germ tube neg = pseudohyphae (constriction); Candida sp.
a feathery filamentous fringe that may develop around Candida colonies as they age
feet
this can prevent germ tube formation
too heavy if an inoculum
these must always be set up when doing a germ tube test
positive and negarive controls
to make sure that there are no inhibitory factors present in the high protein media
