Medically Relevant Bacteria - Gram Negative Cocci and Rods - SRS Flashcards
Gram negatives take up and but do not retain crystal violet stain when (decolorized with alcohol). Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane. The alcohol degrades the outer membrane making the cell wall more porous and incapable of retaining the crystal violet.
What is the counter stain used to identify gram negatives?
Safranin or fuchsin
What does the outer membrane of gram negatives contain that is unique to them?
Lipopolysaccharide (LPS) endotoxin
A 17 y/o male presents to your office with copous urethral exudate that contains the coffee bean shaped diplococci organisms shown in the attached picture. They are gram negative and grew under aerobic and and facultative anaerobic conditions. They tested positive for oxidase.
What is the organism?
How does it attach to host cells?
N. gonnorrhoeae
Fimbriae (pili) are very important for attachment
Opa proteins - facilitate adherence and invasion
N. gonorrhoeae only oxidizes glucose, and there are four types, based on the presence of fimbriae (T1,2,3,4). What are the virulence factors we need to know for this organism?
- Fimbriae
- Porin A or Porin B - proinvasive, antigenic
- Opa proteins
- Cytotoxic substances (LPS endotoxin)
- Extracellular proteases - cleaves a proline-threonine bond in IgA
What are the host animals for N. gonorrhoeae?
How does it affect women?
what other infections does it cause?
What might end up happening if a person with C5-9 deficiency were infected?
Humans
Infects the cervix, often asymptomatic
pharyngeal and anorectal infections
Can lead to sepsis
What happens to neonates infected with N. gonorrhoeaei during delivery?
What do 9-15% of women affected with this organism contract?
Conjunctivitis in neonates (opthalmia neonatorum)
Pelvic inflammatory disease (PID) - can lead to scarring and infertility
What media is used to culture N. gonorrhoeae?
How would you treat this infection?
What is it resistant to?
- Thayer-Martin VCN lysed RBC media
- ceftriaxone + azithromycin or doxycycline for gonorrhea
- Resistant to - penicillin and quinolones
An infectious outbreak occurres this summer at the Airforce basic training camp. S.D. Aaron Brooks is brought to the base clinic with petechial rash, headache and fever. An LP is performed and the organism shown in the attached image is cultured.
What is the organism?
Apart from a lasting detriment to his foosball abilities, what are we most concerned with in the progression of this organisms infection?
What are the mortality rates for this infection?
How do we treat him to stave this off?
- N. meningitidis
- Can lead to DIC and Watehouse-Friderichsen syndrome (adrenal hemorrhage)
- Untreated mortality rate is ~85%
- Treated, mortality rate drops to ~10%
- Treat with Third gen. cephalosporin
N. meningitidis oxidises glucose and maltose, and is serotyped by the antigenic character of its capsular polysaccharides. It commonly inhabits the human nasopharynx.
What are the virulence factors it posesses?
- •Virulence associated with antiphagocytic capsule (also used for antigenic grouping)
- •Pili allow attachment
- •Meningococcal endotoxin LPS is toxic (hemorrhage/petichiae and sepsis)
- •IgA1 protease found in pathogenic Neisseria can cleave IgA
What populations are at highest risk for N. meningitidis infection?
•Infants 6-24 months and young adults in dorms/barracks are at highest risk
What is the best option for dealing with N. meningitidis?
As always, prevention… via:
- meningococcal polysaccharide vaccine or meningococcal conjugate vaccine, variable recommendations and dosing schedules for different vaccines but usually 1-2 doses by college age
Moraxella catarrhalis Colonizes the upper respiratory tract in 28-100% of humans in the first year of life via direct contact with contaminated secretions by droplets. What three things does it cause commonly?
- Common cold
- Otitis media
- sinusitis
What is M. catarrhalis resistant to?
beta-lactams
What does M. lacunata cause?
Catarrhal conjunctivitis
E. coli are gram negative bacilli that ferment lactose. Some are motile, and possess what antigen?
H (flagellar) antigen
What is the capsular antigen of E. coli?
K antigen
Enterotoxigenic strains of E. coli may have colonization factor antigens (CFA/I, CFA/II). What do E. coli with the K1 antigen have a propensity for?
What does the K1 antigen do?
Propensity for producing neonatal meningitis
K1 antigen provides the organism with an increased resistance to phagocytosis and the action of complement.
What are the four types of diarrhea seen with E. coli?
- Enterotoxigenic
- Enteroinvasive
- Enteropathogenic
- Enterohemorrhagic
What type of diarrhea is this? What causes it? Where is the infection?
“fever, cramps, watery diarrhea, followed by scant, bloody stool”
Shigella-like diarrhea - enteroinvasive diarrhea
Caused by tissue invasion and shiga-like toxin destruction of cells
Large intestine
What type of diarrhea is this? What causes it? Where is the infection?
“Severe abdominal pain, watery diarrhea then grossly bloody stool”
Hemorrhagic colitis - Enterohemorrhagic
EHEC - O157:H7; SLT-I, SLT-II, shiga-like cytotoxins (verotoxins)
Large intestine
What type of diarrhea is this? What causes it? Where is the infection?
“Salmonella-like with fever, nausea, vomiting”
Infantile Diarrhea - Enteropathogenic
Adherence and destruction of epithelial cells (plasmid mediated)
Small intestine
During his fourth year audition rotation in the University hospital burn trauma unit, due to lack of sleep and stress, S.D. Michael Plump acquires a hemorrhagic pneumonia. After culturing the organism from his red currant jelly sputum the colony shown in the image is obtained.
What is this organism? What specific types is it likely to be?
What is the media we see it cultured on here?
Why the shiny appearance?
What would you give him to treat this infection?
Klebsiella pneumoniae
Capsular type 1 or 2, both are associated with bacterial pneumoniae
Cultured on McConkey’s agar
Shiny appearance d/t capsule
Give ceftriaxone!
A 24 year old male presents to your clinic complaining of the painless genital ulcers and swelling around his penis shown in the picture. Culture on McConkey’s agar yields the depicted colonies.
What is the organism?
What would you see if you took a smear and visualized it under the microscope?
What does this infection lead to?
- Klebsiella granulomatis
- Minute encapsulated coccobacillus, (Donovan bodies in macrophages in smears)
- Causes granuloma inguinale (donovanosis) with painless genital ulcers
- Can progress to scarring with lymphatic blockage (lymphedema of genitalia)
TQ alert on this one.
S.D. Luke Mosel suffers burns to >35% of his body while jumping over four burning couches in celebration of the latest(of many) Nebraska Huskers victory. While recouperating in the Linconl general hospital burn ward he notices the hospital staff isn’t diligent about washing up between patients. A couple of days later he develops vasculitis and skin lesions.
The staff cultures the organism present in his skin lesions and obtain the results depicted in the images.
- What is the nosocomial infection at work here?
- What are the skin lesions he has known as?
- What are the primary substances this organism produces that are causing damage to the surrounding tissues?
- Pseudomonas
- Skin lesions are called ecthyma gangrenosum
- Produces many exozymes including hemolysins, leukocidins and proteases, the ones we most need to know are:
- Exotoxin A is the most toxic and causes ADP-ribosylation of translation factor EF-2, leading to loss of host cell protein synthesis capability. (identical mechanism to diphtheria toxin)
- Exoenzyme S - another ADP-ribosyltransferase which transfers the ADP-ribose from NAD
Your hospital charges you with randomly sampling and growing isolates from hospital equipment. You obtain the attached culture from a patient’s indwelling catheter.
What is the organism?
Why does it appear red when grown on MacConkey’s agar?
Serratia marcescens
non-lactose fermenter, but red on MacConkey agar anyway due to the production of prodigiosin, a characteristic red pigment.
Your patient comes in complaining of lower left flank pain. Imaging shows a mass in the left kidney that is far too large for ultrasonic disruption. The kidney must be removed. After removal you open up the kidney, see attached picture.
What is this thing in the kidney called?
What infection do you think led to this, and how?
Staghorn Calculi (AKA Struvite stones)
Proteus mirabilis likely caused this, by formation of urease. This alkalinizes urine, (urea to ammonia) for a survivable environment. This leads to precipitation of organic and inorganic compounds forming struvite stone (magnesium ammonium phosphate)
RVU’s global track is working a syrian refugee camp when a large contingent of the camp contracts sudden onset of cramps and watery/bloody diarrhea with fever.
The fearless student doctors turn to their mobile culture kits and grow an isolate from a sample of the bloody diarrhea. An image of the organims in the culture is at right.
With additional testing the organism is found to be:
- gram negative rod
- non-lactose fermenter
- does not produce H2S
- Facultative anaerobe
- non-motile
What is the organism causing the outbreak?
What is the virulence factor that is characteristic of this organism and how does it work?
Shigella dysenteriae
Shiga toxin: The A subunit inhibits the 60S ribosome and protein synthesis
What is the treatment protocol for shigella infection?
- fluid with electrolytes as most infections are self limited, zinc can decrease diarrheal period
- Many antibiotics may be effective (but there is variable resistance worldwide) and there has been a recent outbreak of Shigella sonnei resistant to ciprofloxacin
How can we distinguish salmonella from shigella?
It produces H2S, culture it on X.L.D. Agar and it will show up black.
Your patient with cystic fibrosis is presenting with a pulmonary infection. After culturing the organism you find that it is…
- gram negative rod
- oxidase positive
- non-lactose fermenting
- motile
- aerobic
Microscopy of the isolate revealed the image attached.
What is the most likely organism?
Burkholderia cepacia
