Normal Flora and Antimicrobial Resistance Study Guide

Comprehensive vocabulary flashcards covering human normal flora by body site, the nature of pathogens, and the genetic and biochemical mechanisms of antimicrobial resistance.

Normal Human Flora

A population of microorganisms that are part of different body sites in a healthy person; also known as "normal human microbiota" or "microbial flora".

Microbiome

The specific genomes of the microorganisms that make up the normal flora.

Key Roles of Commensal Organisms

Essential functions including digestion, immune function, and providing protection against pathogens.

Normal Flora of the Skin

Includes Staphylococcus spp. (especially S. epidermidis), Streptococcus spp. (usually S. viridans), Diphtheroids (Corynebacterium spp.), Anaerobes (Propionibacterium spp.), and Fungi (Candida spp. in skin folds).

Normal Flora of the Nasopharynx

Includes Staphylococcus spp., Streptococcus spp., Haemophilus spp., and various anaerobes.

Normal Flora of the Mouth & Throat

Mainly Streptococcus viridans and Anaerobes such as Fusobacterium, Prevotella, and Peptostreptococcus.

Normal Flora of the Stomach

Consists of Candida spp. and Lactobacilli.

Normal Flora of the Colon

Similar microorganisms to the small intestine (Enterococcus spp., S. viridans, Enterobacteriaceae, Clostridium spp., Bacteroides spp., and Candida spp.), but over $90\%$ are anaerobes.

Normal Flora of the Vagina

Includes Lactobacillus spp., Candida spp., and Streptococcus spp. (including Streptococcus agalactiae/Group B Strep).

Sterile Sites

Body locations where flora is NOT present, including blood, internal organs, bone, and fluids such as CSF, pleural, peritoneal, pericardial, and synovial.

Endogenous Pathogens

Pathogens that originate from the host's own normal flora, usually causing infection when introduced into foreign locations or due to an imbalance like antibiotic use.

Exogenous Pathogens

Pathogens originating from external sources such as the environment, animals, or other people.

Antimicrobial Resistance

The ability of a microorganism (bacteria, viruses, fungi) to stop an antimicrobial from working against it, allowing infections to persist and spread.

The Critical Factor of Resistance

Antimicrobial use is identified as the most critical factor leading to increased resistance.

Superinfection

Persistent infections resulting from ineffective standard treatments that may eventually become untreatable "superbugs."

Collateral Damage

The disruption to the gut microbiome and other non-GI resident microbiota caused by the use of antimicrobials.

Intrinsic (Innate) Resistance

Resistance present from the beginning in all strains of a species, unrelated to antimicrobial exposure and transferred only vertically.

Acquired Resistance

Resistance that develops after drug exposure in only some strains of a species, related to antimicrobial use and capable of vertical or horizontal transfer.

Intrinsic Resistance Example (Deficient Uptake)

Vancomycin is too large to pass through the Gram-negative outer membrane.

Intrinsic Resistance Example (Lack of Target Site)

Amoxicillin cannot work on viruses like Influenza because they lack a bacterial cell wall.

Horizontal/Lateral Transfer

The mechanism by which resistance genes are transferred between different bacteria, rather than from parent to offspring.

Random Mutation

A genetic basis for resistance involving a change in the genes already present within the bacteria's own DNA.

Acquisition of New Genes

When bacteria obtain entirely new resistance genes from other bacteria, primarily via plasmids.

Plasmids

Mobile genetic elements that can contain multiple resistance genes at once and are transmitted between bacteria.

Enzyme Inactivation

A biochemical mechanism where bacteria produce an enzyme to degrade the drug, such as S. aureus producing penicillinase to break down penicillin.

Efflux Pumps

Specialized pumps developed by bacteria to actively transport the antibiotic out of the cell.

Target Site Modification

Alteration of a drug's specific target so the antimicrobial can no longer bind; for example, MRSA developing PBP2a so beta-lactams cannot inhibit it.

Porin Loss

A biochemical basis of resistance where a reduction in the number or function of porin channels prevents the drug from entering the bacterial cell.

Alternative Pathway

A mechanism where bacteria bypass a drug's effect by developing a different metabolic pathway to achieve the same result.