MLS 334 Exam 4

Antibiotics

are medications used to treat bacterial infections by inhibiting the growth or destroying bacteria. They are ineffective against viral infections.

Bacteriostatic

drugs that stop bacterial reproduction

(ex: erythromycin)

Bactericidal

drugs that kill bacteria

(ex: penicillin)

Antimicrobial Agent

a chemical compound that kills or inhibits the growth of microorganisms

(ex: antibiotic, antifungal, etc.)

Antibiotic

-class of drugs that target bacterial infections

-can be natural, semisynthetic, or synthetic molecules that can treat or prevent disease

Intrinisic Resistance

natural-occurring resistance to antibiotics - found in chromosomes of bacteria

(ex: biofilms)

Acquired Resistance

Acquired from exogenous DNA (plasmid or through conjugation)

(ex: mutation)

enzymatic inactivation (b-lactamases)

Broad Spectrum Antibiotic

antibiotic that targets multiple types of bacteria

(ex: penicillin)

Narrow Spectrum Antibiotic

antibiotic that targets only a few bacteria

(ex: vancomyocin)

decrease likelihood of organism acquiring resistance

Targets of Antibiotics

cell wall

metabolic functions (basic metabolic functions - protein synthesis, nucleic acid synthesis, metabolism)

Which antibiotics target the cell wall?

b-lactams

penicillin

cephalosporins

vancomycin

Which antibiotics target the cell membrane?

Polymyxins

Whch antibiotics interfere with DNA synthesis?

nalidixic acid

fluroquinolones

Which antibiotics target protein synthesis through RNA polymerase?

rifampin

aminoglcosides

macrolides

B-Lactam Antibiotic - Target

cell-wall

bind penicillin binding proteins and inhibit synthesis of peptidoglycan layer in bacterial cell wall

B-Lactam Antibiotic - Mechanism

bind penicillin binding proteins and inhibit synthesis of peptidoglycan layer in bacterial cell wall

B-Lactam Antibiotic - Species Targeted

aerobic and anaerobic gram positive and gram negative organisms (broad)

Examples of B-lactam Antibiotics

Examples: "PCCM" Narrow to broad spectrum

Penicillin = The "OG" > used for Strep pyogenes and Syphilis

Cephalosporins

Carbapenems = Broad champions but handle with care

Monobactams = One goal, gram negatives only

Glycopeptide Antibiotics - Target

cell-wall

bind to peptidoglycan precursor and inhibit peptidoglycan synthesis

Glycopeptide Antibiotics - Mechanism

bind to peptidoglycan precursor and inhibit peptidoglycan synthesis

Glycopeptide Antibiotics - Species Targeted

gram-positive organisms

Glycopeptide Antibiotics - Example

Vancomycin - Last line Drugs - Use Wisely

Polymyxin Antibiotics - Target

cell membrane

bind outer cell membrane and increase permeability = bacterial lysis (expand then explode)

Polymyxin Antibiotics - Mechanism

bind outer cell membrane and increase permeability = bacterial lysis (expand then explode)

Polymyxin Antibiotics - Species Targeted

gram-negative organisms

Polymyxin Antibiotics - Example

polymyxin B, polymyxin E

Aminoglycoside Antibiotics - Target

30S ribosomal subunit

inhibit intiation complex -> protein mistranslation = inhibiton of protein synthesis

Aminoglycoside Antiobiotics - Mechanism

inhibit intiation complex -> protein mistranslation = inhibiton of protein synthesis

Aminoglycoside Antiobiotics - Species Targeted

aerobic gram positive and negative organism AND M. tuberculosis

Aminoglycoside Antiobiotics - Example

G = Gentamicin- most common, effective against wide range of gram negatives

N = Neomycin- topically or orally for bowel prep and superficial skin infections

A = Amikacin- "armor plated" against resistance- resistant hospital pathogens

T = Tobramycin- Pseudomonas aeruginosa

S = Streptomycin- historical drug- used primarily for TB, plague and tularemia

Macrolide Antibiotics - Target

50S ribosomal subunit

Macrolide Antibiotics - Mechanism

Protein Synthesis Inhibitor - bind 23S rRNA and inhibit translocation and chain elongation = decreased protein synthesis

Macrolide Antibiotics -Species Targeted

aerobic and anaerobic gram negative and positive organisms

Macrolide Antibiotics - Example

Erythromycin

Azithromycin

Clarithromycin

Fluoroquinolone Antibiotics - Target

DNA gyrase

Inhibit DNA gyrase and topioisomerase IV = inhibition of DNA synthesis

Fluoroquinolone Antibiotics - Mechanism

inhibit DNA gyrase and topioisomerase IV = inhibition of DNA synthesis

Fluoroquinolone Antibiotics - Species Targeted

aerobic gram positve and negative organisms (some anaerobic gram negative)

Fluoroquinolone Antibiotics - Example

Examples: Ciprofloxacin (workhorse for gram negatives), Levofloxacin

F = Fluoroquinolone family-"all roads end with - floxacin"

L = Locks DNA gyrase > prevents unwinding of bacterial DNA

O = Only aerobes (primarily)

X = Crosses tissue walls > Achieves high levels in lungs, urine, bone and prostate

Sulfonamide Antiobiotics - Target

folic acid synthesis

Sulfonamide Antiobiotics - Mechanism

prevent bacterial THF (active form of folic acid) = decreased DNA methylation

Sulfonamide Antiobiotics - Species Targeted

aerobic gram positive and negative organisms

Sulfonamide Antiobiotics - Bacteriocidal or Bacteriostatic

both bactericidal AND bacteriostatic

Sulfonamide Antiobiotics - Example

Examples: Trimethoprim-sulfamethoxazole (Bactrim)

Sulfa starts it- Tri ends it

Used in uncomplicated UTI when local resistance is low (UTI-> Bactrim for 3)

The minimal inhibitory concentration (MIC) is the ______ antibiotic concentration needed to _____ the growth of an organism.

lowest; inhibit

When does antimicrobial suscpetibility testing need to be performed?

• Susceptibility Testing
  - culture results in isolation of bacteria that is involved in patient infection

-isolate is involved in pt infection and suscpetibility against particular antibiotics is unknown or uncertain

What agency is responsible for providing guidance for AST reporting?

Clinical and Laboratory Standards Insititute (CLSI)

Why should AST not be performed on organisms that are considered normal flora or considered contaminants?

does not provide useful information and may promote unnecessary antibiotic usage

Streptococcus pyogenes is universally susceptible to what antibiotic?

peniciliin

Dilution Susceptibility Testing

-Serially dilute the antibiotic in broth or agar, add a fixed inoculum of bacteria to each concentration

-Bacteria will grow in the tubes up to the drug concentration at which they are inhibited

-interpret as suscpetible, intermediate, or resistant

Dilution Susceptibility Testing - Priniciple

determine the lowest concentraion of antimicrobial required to inhibit growth of bacterial isolate (MIC value)

Antibacterial Resistance

Intrinsic resistance- innate characteristic of organism

Acquired resistance- changes in usual genetic makeup leading to altered cellular

physiology

Mechanisms of resistance

" Lack of affinity of the drug for bacterial target

. Prevent access of drug to relevant site of action

. Biofilms

. Efflux

· Enzymatic inactivation

. Example: B- laotamases

McFarland Standard

A standardized reference solution used to estimate the concentration of bacteria in a culture, allowing for consistent comparisons in antimicrobial susceptibility testing. It typically contains a specific concentration of suspended bacteria, equivalent to a certain optical density.

Disk Diffusion Testing

-disks impregnated with specific drugs are placed on agar plates inoculated with test microbe in 0.5 McFargland Standard

-drug diffuses from disk into agar, establishing concentration gradient

-observe clear zones (no growth = zone of inhibition) around disks and compare to standard table

-reported as susceptible, intermediate, or resistant

Kirby Bauer Principle

Priniciple of Disk Diffusion Testing

bacteria are placed on a MacFardland plate of solid growth medium and antibiotic disks are added to the plate.

allow the bacteria to grow overnight

areas of clear media surrounding the disks indicate that the antibiotic inhibits bacterial growth

Report result as Resistant (R), Intermediate (I) or Susceptible (S).

Broth-Microdilution Tests

.Good for an occasional antibiotic, not an entire panel

Good for fastidious organisms with high growth requirements

.Use less media and antibiotics

Breakpoint (cutoff)

. Point where effective tissue concentration can be achieved for bacterial inhibition

.Results based on two wells

What is a zone of inhibition?

the area around the antibiotic disk in which bacteria cannot grow (area of no growth)

E-test

-Uses strips instead of disks

-strips contain varying concentrations of antibiotic

-Intersection of elliptical zone of inhibition with strip indicates MIC

What is the purpose of infection prevention and control?

reduce dissemination (spread) of infections

Healthcare-associated infection (HAI)

an infection the patient acquires while recieving treatment for medical/surgical issues

>48 hrs after med tx

<30 days surgery

Examples of HAIs

-catheter associated urinary tract infection (CAUTI)

-central line associated bloodstream infection (CLABI)

-ventilator associated pneumonia (VAP)

-surgical site infection (SSI)

- clostridium difficle (C. diff) common in patients with multiple Abx

Surveillance

ongoing, systematic collection, analysis, interpretation and dissemination of data regarding a health-related event for use in public health action to reduce morbidity and mortality and to improve health (CDC)

Causes of HAIs

-instrumentation

-increased use of antimicrobial agents

-lack/failure of aspetic technique

-healthcare not just in hospitals (changing landscape)

Total Surveillance

All infections recorded, analyzed and assessed

Infection Rate

Analysis of the speed of spread or frequency of an infectious disease within a population

(can compare to other facilities)

Targeted Surveillance

focus on specific, high-risk, high-volume procedures

Baseline Data

Historical occurrence of infections over time

Outbreak

Upward trend of infections above baseline data

Index Case

first case in an outbreak

Incidence

# new HAIs during month / # patient days durng month

Prevalence

# of active HAIs / # of pts in hospital

Standardized Infection Ratio (SIR)

actual # infection / predicted # infections

Charecteristics of a Virus

Obligate intracellular parasites

microscopic "parasites" that lack the ability to live and reproduce outside a host

much smaller than bacteria

known for widespread diseases and outbreaks

Steps of an Outbreak Investigation

1. Verify the diagnosis and confirm the outbreak

(establish definition)

2. Confirm that an outbreak exists

(cases meet definiton)

3. Find additional cases

4. Charecterize cases

(collect demo info about cases)

5. Form a hypothesis

6. Test the hypothesis

(control groups and data collected)

7. Insititute control measures

8. Evaluate effectiveness of control measures

9. Communicate the findings

Viral Structure

-made of genetic material, a protein coat, and an envelope containing lipids

-capsid --> protein coat

-envelope (if present) surrounds capsid

Viral Genome

genetic material of a virus (double or single stranded DNA or RNA)

Viral Capsid

protein coat that surrounds the genetic material of the virus

Viral Nucleocapsid

genome + capsid

Virus Envelope

-surrounds the capsid of some viruses

-helps the virus to enter the cell

-makes it more susceptible to enviornmental changes (pH, temp, chemicals)

Virion

complete virus particle

Viral Classification

-Type of nucleic acid (DNA or RNA)

-Number of strands to the nucleic acid (Single stranded or double stranded)

-morphology

-Presence or absence of viral envelope

Viral Replication Steps

1. Absorption or Attachment

2. Penetration

3. Uncoating

4. Replication and Translation

5. Assembly or Maturation

6. Release or Egress

Nonenvoloped ssDNA Viruses

parvovirdiae

Nonenveloped dsDNA virues

adenovidiae

papillomaviridae

Enveloped dsDNA viruses

herpesviridae

hepadnaviridae

poxviridae

Nonenveloped ssRNA virus

picornaviridae

calcividae

hepeviridae

enveloped ssRNA viruses

Flaviviridae

Togaviridae

Retroviridae

Orthomyxoviridae

Paramyxoviridae

Rhabdoviridae

Coronaviridae

Arenaviridae

Bunyaviridae

Deltavirus

Filoviridae

and MANY MORE

nonenveloped dsDNA viruses

reoviridae

Viral Replication - Absorption

step 1

virus attaches to specific cell-receptors (glycoproteins) through adhesion molecules

Viral Replication - Penetration

step 2

naked virons = directly into cell membrane

enveloped virons = membrane fusion into cell

endocytosis = enter in cytoplasmic vacuole

Viral Replication - Uncoating

step 3

genome release from capsid

DNA -> nucleus

RNA -> cytoplasm

Viral Replication - Replication and Translation

step 4

viral genomes tells host to make more viral proteins and replicate viral genome

Viral Replication - Assembly or Maturation

step 5

building blocks:

capsid protein subunits -> capsomers -> combine form capsid -> capsid and genome form nucleocapsid -> form genomes

Viral Replication - Release or Egress

step 6

naked virus = lysis

enveloped = budding

What type of virus structure makes it more susceptible to environmental changes?

envelope

What type of specimens are preferred for viral specimen collection?

aspirated secretions

What type of swab may be used for viral specimen collection?

dacron or rayon

(NOT calcium alginate)

What is the preferred transport time for viral specimen collection?

immediatetly

<2 hours

within 4 days?

Advantages of Serological Assays

detect nonculturable viruses (hepatitis)

Help determine immune status (MMR, VZV, HAV, HBV)

Help monitor immunosuppressed or transplant patients

Good for epidemiology and prevalence

Disadvantages of Serological Assays

Not good for severe immunosuppression

Reactivating viruses always have antibodies

Infants with maternal antibodies

Rarely have paired sera samples

Cross-reactivity of viruses

What is the principle of serologic assays?

detect viral antibodies to measure host response using paired sera samples (2 sampels 7-10 days apart = acuate and convalescent stages)