Principles of Antimicrobial Therapy (God Help Our Soul)

Veterinarians must use ____ judiciously, not only to protect their patients but to protect local and global medical communities

antimicrobials

How do bacteria become superbugs?

Through mutation and selective pressure, which allow resistant bacteria to survive and multiply while susceptible ones die.

What role does antibiotic use play in resistance?

Inappropriate or repeated antibiotic use (wrong drug, dose, or duration) creates selective pressure, giving resistant bacteria a survival advantage

How can resistance spread between bacteria?

Via gene transfer (plasmids, transformation, or transduction), which allows resistance traits to spread quickly among different bacterial species.

Why is reducing the use of antimicrobials important for controlling resistance?

Because it reduces selection pressure, which means fewer opportunities for resistant bacteria to survive and multiply—helping to slow the spread of antimicrobial resistance

What is the step by step in how genetic mutations cause drugs resistance?

1.) non- resistant bacteria exist

2.) bacteria multiples hella (by the billions)- a few will mutate

3.) some mutations make the bacteria drugs resistant ( in the presence of drugs, only drug resistant bacteria survive)

4.) drug resistance bacteria multiply and thrive

What is the most obvious goal of antimicrobial therapy?

antimicrobial therapy is signs

What can occur if there is failure to kill the entire infecting inoculum?

post-treatment recurrence of infection with microbes now resistant to the drug

What is one major challenge of judicious antimicrobial therapy?

The goal is not just to relieve clinical signs, but to completely eliminate the infecting pathogen while avoiding harm to the host.

Why must all three components of the chemotherapeutic triangle be considered in antimicrobial therapy?

Because the host, microbe, and drug factors all interact to influence treatment success.

Pathogens have developed resistance mechanisms that help them survive antimicrobial effects, reducing the effectiveness of even our strongest (“big gun”) drugs over time.

What type of therapy is used without identifying the causative organisms and its susceptibility patterns. It is directed the most likely cause of infectious disease

Empiric antimicrobial therapy

What type of therapy is based on the laboratory evidence from culture and susceptibility test?

definitive therapy

Why might veterinarians use empirical therapy before culture and susceptibility results are available?

Because waiting for C&S results can be risky in serious or life-threatening infections like sepsis or bacterial pyelonephritis.

How do veterinarians choose an antimicrobial drug during empirical therapy?

They select it based on the most likely microorganisms that cause the infection in that specific host or body system.

What is produced by microorganism to harm other microorganisms

Antibiotic

What is any compound that suppresses microorganisms?

antimicrobial

What are the THREE sources of antimicrobials?

Natural (antibiotic)

Semi-synthetic

Synthetic

T/F An antibiotic is produced by one organism in order to harm another ("anti-life").

True

How does antibiotics relate to antimicrobials?

Many antimicrobials are antibiotics that suppress harmful microbes—for example, penicillins.

How do semisynthetic and synthetic antimicrobials differ?

Semisynthetic antimicrobials, like amoxicillin, are modified antibiotics with improved properties such as safety or spectrum, while synthetic antimicrobials, like fluoroquinolones, are completely man-made.

What types of organisms can antimicrobials target besides bacteria?

Antimicrobials can also target fungi (antifungals), protozoa, and rickettsia, though viruses are generally not considered microbes.

What type of bacteria is normal non harmful colonizing flora and is something that you should not treat?

Commensals

What type of bacteria possess virulence factors that cause disease and is what you should treat?

Pathogenic

What type of bacteria are normally harmless microbes that cause disease when the host's defenses are weakened or when they gain access to normally sterile areas.

Opportunistic

Why is determining whether an infection truly exists a challenge in judicious antimicrobial use?

Because finding a microbe at a potential infection site doesn't always mean there's an infection — many microbes are harmless commensals that are part of the normal microbiota and even help maintain health.

Where can you find information on which organisms are most often associated with disease in a patient?

You can use clinical history data and antibiograms, which summarize the most common pathogens and their antimicrobial susceptibility patterns in a given region or clinic.

What is an infecting inoculum?

An infecting inoculum is the population of microbes causing an infection.

Why is its size important in determining infection?

Its size (measured in CFU) helps determine whether true infection exists — a higher CFU count (around 10⁵ or more) indicates infection, while smaller numbers might reflect contamination or commensal presence.

Why do infection thresholds (CFU counts) differ between tissues like the urinary tract and the lung?

Because some tissues (like the urinary tract) are easily contaminated by commensals and require higher CFU counts (≥10⁵/mL) to confirm infection, while normally sterile tissues (like the lung) can be infected with fewer CFU.

What refers to a genus or species?

Organism

What is a genetic variant within a species?

Strain

What is a single CFU cultured from the infecting population — representing one member of that microbial "community."?

Isolate

T/F Most bacteria can live in a low oxygen tension environment and as such are referred to as facultative anaerobes.

True

How are organisms with minimal resistance characterized?

They have a low minimum inhibitory concentration (MIC) for lower-tier drugs, meaning they are easily killed or inhibited by weak antibiotics

What are examples of bacteria that are typically susceptible to lower-tier drugs? (2)

Pasteurella and Streptococcus species (they are often called “whimps” because they respond well to simple drugs like penicillin)

Which bacteria commonly show multidrug resistance and require higher-tier drugs?

Pseudomonas aeruginosa and Enterococcus faecium (they often resist many antibiotics and need stronger, higher-tier treatments)

Order the Gram NEGATIVE in order from lowest to highest "ease of kill"

•Pseudomonas

•Pasteurella sp.

•Klebsiella sp.

•Proteus sp.

•Enterobacter sp.*

•E. coli

•Pasteurella sp.

•Proteus sp.

•E. coli

•Klebsiella sp.

•Enterobacter sp.*

•Pseudomonas

Order the Gram POSITIVE in order from lowest to highest "ease of kill"

Streptococcus

Staphylococcus

Corynebacterium

Rhodococcus

Enterococcus

Streptococcus

Rhodococcus

Enterococcus

Staphylococcus

Corynebacterium

What are the FOUR obligate anaerobes?

Clostridium, Bacteroides, Fusobacterium, Peptostreptococcus

T/F Enterococcus faecium by nature is MDR and thus is more difficult than E. faecalis.

True

Should antimicrobial therapy be started just because a microbe is found?

No, treatment should not be based solely on finding a microbe.

What should be present before starting antimicrobial therapy?

There should be clinical signs of infection, such as fever, inflammation, or abnormal lab findings, indicating that the microbe is actually causing disease.

T/F Culture indicates bacteria as being present.

True

What factors increase the likelihood that a cultured organism is a true pathogen?

If the growth is pure (only one organism present) and vibrant or heavy, it’s more likely to be a true pathogen rather than contamination.

What might the presence of multiple organisms in a culture suggest?

It may indicate contamination with commensal or environmental microbes instead of a true infection.

How might molecular techniques improve infection diagnosis in the future?

They could become more specific and accurate, helping distinguish true infections from contamination or harmless microbes.

What type of bacteria is typically seen in the GI tract?

gram-neg aerobes

What type of bacteria is seen in the abdomen?

initially, gram-neg aerobes, followed by anerobes

What type of bacteria is seen in the skin?

Staphylococcus pseudointermedius

What type of bacteria is seen with Abscess?

anaerobes and Pasteurella sp

What type if bacteria is seen with UTI?

E coli

What is the TWO goals of judicious antimicrobial use?

•Therapeutic success

•Preventing the emergence of antimicrobial

resistant bacteria

How do we achieve this goal?

1.Decontaminate

2.De-escalate: infection VS inflammation

3.Design: dosing regimen

What is meant when we say to de-escalate antimicrobial use?

De-escalate antimicrobial use, but once you have made the commitment to using a drug, especially systemically, then decontaminate but most importantly accurately

What is meant when we say to design antimicrobial use?

Design the dosing regimen with the intended (but largely unachievable) goal of killing the entire infecting inoculum. .

T/F Among the ways to de-escalate antimicrobial use is to simply do systemic therapy if it is not indicated

False, you should NOT do systemic therapy

What are examples of infections that may be better managed without systemic antimicrobials? (sorry)

Feline abscesses from cat bites and equine strangles are examples that can often be treated more effectively with debridement and decontamination instead of systemic antibiotics

If systemic antimicrobial therapy is needed, what should be done first?

The infection site should be decontaminated, reducing the bacterial population as much as possible before starting systemic treatment.

T/F Fewer bugs = fewer drug (molecules) needed to inhibit or kill

true

What tier drug should you begin with?

lowest tier drug

T/F When choosing the lowest tier drug, one needs to have a pretty good idea of the bug causing infection and the drugs to which that bug is susceptible

True

Why are "at risk" patients more likely to experience antimicrobial failure?

Because patients already receiving antimicrobials or with weak immune systems can have microbes that develop resistance or fail to fight infections effectively, increasing the chance of treatment failure

Why is drug distribution to the infection site important in antimicrobial therapy?

The drug must reach the site of infection to be effective, poor penetration is a common but often overlooked cause of treatment failure

What factors may require higher doses or shorter dosing intervals?

Conditions like hard-to-reach tissues (sanctuaries), large bacterial loads (inoculum), or immunosuppression require stronger or more frequent dosing to ensure effective bacterial killing, because “dead bugs don’t mutate.”