Gram negative bacteria Flashcards
Facultative anaerobe
Growth both aerobically and anaerobically
Capnophilic
CO2 required for growth
Microaerophilic
Grows in a low concentration of oxygen, but not in its absence or in ambient air
Enterobacteriaceae family characteristics
Large family of gram - rods All are facultative anaerobes All ferment glucose Oxidase negative (except Plesiomonas) Grow rapidly Many are motile All reduce nitrate to nitrite
MacConkey agar
Selective and differential
Selective because it has bile salts and crystal violets, so no growth of gram positives
Differential because it has lactose - only half enterobacteriaceae ferment lactose - pink = positive)
Can come without crystal violet too (none = enterococcus can grow)
Cytochrome oxidase
An enzyme involved in the reduction of oxygen at the end of the ETC
Oxidase positive if you have this
3 genera that are oxidase positive
Vibrio
Pseudomonas
Aeromonas
The nitrate test
Detects ability of bacteria to use nitrate as an electron acceptor (has nitrate reductase)
Innoculate broth, incubate, add reagent. If there is nitrite it will turn red. But if it doesn’t, that might mean it was reduced all the way to ammonia or N2. So have to add zinc dust, if that turns red it is a negative test (because nitrate is still in the tube). Unchanged means it was reduced all the way.
Triple sugar iron slants
1% glucose, 10% lactose, and 10% sucrose. Also sodium thiosulfate and FeSO4 for H2S detection. Phenol red indicator too.
Slant = aerobic reactions
Butt/deep = anaerobic reactions
Begins with glucose fermentation, acid produced = yellow. Then must either go to next sugar, or amino acids for C source. Sugars = slant stays yellow. Amino acids = aerobic process, so slant turns red. Black in between if H2S formed. Afermenter = whole thing is pink still
3 similarities and 1 difference between Vibrio/Aeromonas and Enterbacteriaceae
Sim: 1. Gram negative 2. Facultative anaerobes 3. Fermentative (glucose) Diff: 1. Oxidase pos (entero is neg)
3 key tests for Vibrio
Salt tolerance 6% NaCl
Oxidase
Susceptibility of O/129
O/129
Vibriostatic agent
Most Vibrio spp are susceptible
Most other bacteria are resistant
Thiosulfate citrate bile salts sucrose agar (TCBS Agar)
Highly selective for Vibrio spp Oxgall added to inhibit gram + organisms Able to detect H2S Sucrose CHO source Vibrio = yellow
Haemophilus influenzae
Gram negative bacilli Oxidase positive Facultative anaerobic (CO2 enhances growth) Fastidious Does NOT grow on MacConkey Requires heme and NAD Associated with resp tract infections
Porphyrin Test
Determines if the bacteria requires heme or not
Positive test means it does not require heme (haemophilus is negative)
Heavy suspension of organism in aminolevulinic acid, incubate, and then illuminate with UV light and look for red fluorescence (means it is creating porphyrins and does not need heme)
