Dr. Cluck Flashcards
What is an infection?
A microorganism that is able to replicate invades host tissue and causes an immune response (disease)
Example of an infection
A gram-negative bacteria in a septic environment of the body –> in the blood stream
What is a Contaminant?
On the outside
Organism as a normal part of the skin flora, isolated from the bloodstream
-but there could be some bacteria as Contaminants in the bloodstream
-Almost never requires treatment
What is a Colonization?
An organism that is endemic to a specific part of the body
-MRSA colonization after being in the hospital
-Usually doesn’t require treatment
What are Gram-resistant Organisms?
-They need special forms of staining or cant be stained (lack of cell wall)
Why do Gram-resistants need special staining or cant be stained?
-Mycobacteria and Nocardia have a wax-like outer layer -> cant take up the stain -> acid-fast
-Treponema requires fluorescent AB staining
-Intracellular pathogens - cant be stained
-Mycoplasma lacks cell wall - cant be stained
What is an atypical organism?
EXAM
-Gram-resistant
-Neither Gram-positive nor Gram-negative
-bacteria that do not get colored by gram-staining but rather remain colorless
What are the most common morphological forms of bacteria?
-Rod-shaped: E. coli
-Cocci in chains: Streptococcus spp.
-Grapelike cluster: Staphylococcus spp.
How are Cocci-shaped gram (+) bacteria specified?
with Catalase
Clusters: Staphylococcus spp.
w/o Catalase
Pairs/chains: Streptococcus spp.
How is Staphylococcus specified?
(+) Coagulase: S. aureus -> causes disease
(-) Coagulase: S. epidermidis, S. saprophyticus
How is Streptococcus specified?
-alpha hemolysis: partial, green
-beta hemolysis: complete, clear
-gamma hemolysis: no hemolysis
How are rods specified:
Aerobic and Anaerobic
Assays to identify Gram (+):
Gram staining (cluster VS strips)
Biochemical: Catalase, Coagulase
Lancefield antigens (carbohydrate side chain)
Hemolytic reaction on blood agar
Why should Staph aureus NEVER be considered Contaminant?
-most virulent gram-positive pathogen
-can cause multiple diseases: bacteremia, skin tissue infections, endocarditis, pneumonia, foodborne, toxic shock
Characteristics of Staph. aureus
-produces ß-lactamases
-Catalase and Coagulase positive (only coagulase pos. staph.)
-Methicilin-resistance through mecA gene (PBP2a protein)
Function of Catalase
Function of Coagulase
Catalase: reduces phagocytic killing
Coagulase: facilitates abscess formation
How does Penicillin work?
-It inhibits the Transpeptidase in the cell wall of bacteria
-mecA creates PBP2a -> the cell wall is able to continue its replication
What is the therapeutical approach to Staph aureus?
Vancomycin
If Severe -> IV therapy
If MSSA -> antistaphylococcal penicillin C D M N O (penicillinase-resistant penicillin) or 1st gen cephalosporin
PO: dicloxacillin, cephalexin (1st gen cephalosporin)
Why do penicillinase-resistant penicillins work against bacteria with ß-lactamase?
Because of the bulky sidechain (steric hindrance), bacterias ß-lactamase cant access the ß-lactam ring and hydrolyze it
Which antibiotic doesn’t work for MSSA?
Vancomycin ????
-studies show poor outcome
EXAM Question: Know which antibiotics are IV and which are PO
If severe -> IV: Nafcillin
Cephalexin (PO) would be the best choice
What are therapeutic options to treat MRSA?
If invasive (f.e. Pneumonia), not superficial -> Vancomycin
If superficial -> PO: doxycyclin, clindamycin, TMP-SMX
Alternatives: linezolid, daptomycin, tigecycline, ceftaroline
What is the difference between Staph aureus and epidermidis
Staph epidermidis is Coagulase negative
often considered contaminant, but still cause disease -> often on prosthetic devices (pacemakers) -> because they are sticky and build biofilms
How to treat Staph epidermidis?
If there is an infection Vancomycin is necessary
due to mecA and methicillin-resistance
How are staph. saprophyticus different from other spp?
-dont produce ß-lactamase -> can be treated with ß-lactams, TMP-SMX or fluoroquinolone
-mostly cause UTI in young sexually active females
What are Lancefield Antigens?
-antigenic differences in cell wall carbohydrates of Streptococcus spp.
-Gr. A, B, D
Possible Examq: Which Strep doesn’t have Lancefield Antigen -> Streptococcus pneumoniae?
Hemolytic reactions
Alpha: partial, green
Beta: complete, clear
Gamma: no hemolysis
What else makes Streptococcus spp. different from Staphylococcus?
-they DO NOT produce b-lactamase
-> Amoxicillin/Clavulanate (Augmentin) won’t work ???(adverse effect: diarrhea)
-> use Penicillin
How to treat Streptococcus pyogenes?
Penicillin; if PCN allergic -> Clindamycin or TMP-SMX
Streptococcus agalactiae - Group B strep
-often found with wound infections in diabetics, obese patients
-neonatal infection (meningitis) - colonizer of the vagina –> take Penicillin to decolonize
-normal inhabitant of the GI
What is the susceptibility of Group A and B strep to Penicillin?
100%
any ß-lactam can be used (one exception)
What is S. gallolyticus (bovis) known for?
-Group D Strep –> treat with Penicillin
-Normal inhabitant of the GI
-when found in the blood -> marker for colonic neoplasia
-can cause endocarditis
What does Streptococcus pneumoniae cause?
-Triad of endocarditis, meningitis, and pneumonia
-30% PCN resistance -> different ß-lactam or FQ (fluoroquinolone)
Viridans streptococci
+ Streptococcus anginosus
-part of the normal GI flora (including oral
cavity)
-endocarditis secondary to poor dentition or damaged heart valves
-Penicillin, resistance is rising
What is Enterococcus known for?
-normal bowel flora
-not very pathogenic (BYSTANDER analogy), unless it is found where it is not supposed to be (blood)
-very resistant
-can cause wound infections, endocarditis, UTI
Name two important Enterococci
-E. faecalis - responds better to drugs
-E. faecium is more drug resistant
How to treat Enterococcus?
-Use two drugs - the concept of drug SYNERGY (2 different MOAs)
-one ß-lactam is just bacteriostatic
-1st line for E. faecalis line is Amino penicillins plus an aminoglycoside
-for E. faecium (more resistant) -> Vancomycin
-Alternative: Linezolid, daptomycin
Diseases caused by Mycobacteria
-wide range of diseases - Tuberculosis, leprosy
Identification and treatment of Mycobacteria
-lipid-rich cell wall -> acid-fast
-differentiated by the rate of growth
tuberculosis requires 4 drug therapy (1 year or longer)
-Non-tuberculosis mycobacteria -> most are resistant: M. abscessus, M. fortuitum, M. marinum
Disease caused by Bacillus anthracis
Anthrax
-B. cereus in reheated rice
-antibiotics is not necessary
Listeria monocytogenes
-can cause meningitis, but often mild
-food-borne illness
-treat with ampicillin or TMP-SMX or Vancomycin
-Neprosporin wont work!
Diseases caused by Clostridium
-C. perfringens can cause food-borne illness as well as gas gangrene
-C. difficile is responsible for pseudomembranous colitis
-C. tetani and C. botulinum cause different types of paralysis
How to treat Clostridium
-Almost all Clostridia spp. are penicillin-susceptible
-C. difficile - oral Vancomycin; in severe case add IV metronidazole
What is the only organism that is treated with oral Vancomycin?
Clostridium difficile
Bacteria causing infection the upper respiratory tract
-Moraxella catarrhalis -> CA-pneumonia, otitis
media, and sinusitis
-Haemophilus influenzae (type B capsule) - vaccine available
Acinetobacter sbb.
-Very resistant pathogen (hospital outbreaks)
-VAP and wound infections
-sulbactam has microbiologic activity (ß-lactam inhibitor usually don’t have activity)
Neisseria
- N. meningitidis is responsible for meningitis
-> 3rd generation cephalosporin/Pen G - N. gonorrhoeae is responsible for gonorrhea, septic arthritis, and PID
-> cephalosporins
Alternative: FQ, macrolides
What are Enterics?
-Enterobacterales (big class)
-commonly seen in hospital-acquired syndromes and immunocompromised patients
-Salmonella and Shigella are NOT part of normal flora
What are the Resistance Patterns Associated with
Enterobacterales?
-E.coli and Klebsiella can produce extended spectrum β-lactamases (ESBLs)
AmpC-ß-lactamase hydrolyze many ß-lactams
-use carbapeneme to treat
Pseudomonas aeruginosa
-significant in hospital-acquired infections
-often multidrug-resistant
Characteristics of Anaerobes
-a harmless commensal relationship with the host
-Trauma and host factors can cause infection
-treat -> agents with activity against anaerobes (eg
metronidazole, clindamycin, carbapenems)
Use of carbapenems:
-against anaerobes
-Enterobacterels with resistance pattern -> E. coli and Klebsiella
Rocky Mountain Spotted Fever
Rickettsia rickettsii
-gram-negative intracellular coccobacillus
-transmission via arthropods (ticks)
-treat with Doxycycline 100 mg BID
in pregnancy chloramphenicol
Lyme Disease
-Borrelia burgdorferi (intracellular)
-Transmission also occurs via an arthropod vector – ticks
-Treatment is doxycycline or a β-lactam (usually ß-lactams don’t work for intracellular pathogens)
Chlamydophila vs.Chlamydia
-Chlamydophila pneumoniae: atypical pneumonia -> Community acquired -> Doxycyline
-Chlamydia trachomatis: STD -> Doxycycline
-need high intracellular concentrations such as macrolides or tetracyclines
