Which organism is the MOST common cause of surgical site infections?

Staphylococcus aureus. Staphylococcus aureus (including MRSA) is the single most common cause of surgical site infections (SSIs). It is a gram-positive bacterium found on the skin and in the nasal passages of approximately 30% of the population. This is why preoperative skin decolonization (mupirocin nasal ointment and CHG body wash) is recommended for high-risk patients.

Prophylactic antibiotics should be administered within what time frame before surgical incision?

Within 60 minutes. Prophylactic antibiotics should be administered within 60 minutes of the surgical incision to ensure adequate tissue levels at the time of incision. The exception is vancomycin and fluoroquinolones, which require 120 minutes due to longer infusion times. Giving antibiotics too early or too late reduces their effectiveness in preventing SSIs.

A patient with active pulmonary tuberculosis requires surgery. Which type of precautions should be used?

Airborne Precautions with N95 respirator. Pulmonary tuberculosis (TB) is transmitted via airborne particles (droplet nuclei < 5 microns) that can remain suspended in air for hours. Airborne Precautions require an N95 respirator (minimum), a negative-pressure isolation room, and restricted entry. Standard Precautions are always applied in addition.

Preoperative hair removal at the surgical site should be performed using:

Electric clippers. If hair must be removed from the surgical site, electric clippers should be used. Razors cause micro-cuts in the skin that become colonized with bacteria, significantly increasing the risk of SSI. Hair removal with clippers (ideally done in the OR or prep area just before surgery) does not cause skin damage.

Key Takeaways

Microorganisms include bacteria, viruses, fungi, and prions — each has different characteristics and treatment
Bacteria are classified as gram-positive (retain crystal violet stain) or gram-negative (retain safranin counterstain)
Staphylococcus aureus (including MRSA) is the most common cause of surgical site infections
Standard Precautions apply to ALL patients and involve hand hygiene, PPE, and safe handling of sharps and waste
Transmission-Based Precautions are added for known/suspected infections: Contact, Droplet, and Airborne
Airborne Precautions require an N95 respirator (TB, measles, varicella); Droplet Precautions require a surgical mask (flu, COVID)
The chain of infection has 6 links: infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host
Surgical site infection (SSI) prevention includes preoperative antibiotics within 60 minutes of incision, proper skin prep, normothermia, and glycemic control

Microbiology & Infection Control

Microbiology appears as 6 scored questions (4% of the exam), but infection control concepts permeate every domain. Understanding pathogens and prevention is essential.

Types of Microorganisms

Type	Characteristics	Examples	Treatment
Bacteria	Prokaryotic, single-celled; gram-positive or gram-negative	S. aureus, E. coli, Pseudomonas	Antibiotics
Viruses	Smallest; require host cell to replicate; not killed by antibiotics	HIV, Hepatitis B/C, COVID-19	Antivirals (limited); vaccines
Fungi	Eukaryotic; includes yeasts and molds	Candida, Aspergillus	Antifungals
Prions	Misfolded proteins; extremely resistant to sterilization	Creutzfeldt-Jakob Disease (CJD)	No treatment; special instrument handling
Protozoa	Single-celled eukaryotes	Plasmodium (malaria)	Antiparasitics

Gram Staining

Classification	Stain Result	Cell Wall	Examples
Gram-positive	Purple (retains crystal violet)	Thick peptidoglycan	Staphylococcus, Streptococcus, Clostridium
Gram-negative	Pink/red (retains safranin)	Thin peptidoglycan + outer membrane	E. coli, Pseudomonas, Klebsiella

Surgical Site Infection (SSI)

Most Common SSI Pathogens

Staphylococcus aureus (including MRSA) — most common overall
Coagulase-negative staphylococci (e.g., S. epidermidis) — common in implant infections
Enterococcus species
Escherichia coli — common in GI surgery
Pseudomonas aeruginosa — common in burn and wound infections

SSI Risk Factors

Patient factors: Diabetes, obesity, malnutrition, immunosuppression, smoking, advanced age
Surgical factors: Long operative time, contaminated wound class, poor sterile technique, hypothermia
Environmental factors: Poor air quality, high OR traffic, breaks in sterile technique

SSI Prevention Bundle (SCIP / CMS Measures)

Prophylactic antibiotics: Given within 60 minutes of incision (120 minutes for vancomycin/fluoroquinolones)
Appropriate skin prep: CHG-alcohol for most; povidone-iodine for contraindicated sites
Normothermia: Maintain core temperature ≥ 36°C (96.8°F)
Glycemic control: Keep blood glucose < 200 mg/dL
Hair removal: Use clippers (NOT razors) if hair removal is needed — shaving increases SSI risk
Supplemental oxygen: Maintain adequate tissue oxygenation

Chain of Infection

The six links that must ALL be present for infection to occur:

Infectious agent (the pathogen)
Reservoir (where the pathogen lives: humans, environment, equipment)
Portal of exit (how it leaves the reservoir: blood, respiratory droplets, wound drainage)
Mode of transmission (how it reaches a new host: direct contact, droplet, airborne, vehicle, vector)
Portal of entry (how it enters the new host: surgical wound, mucous membrane, respiratory tract)
Susceptible host (a person with inadequate defenses)

Breaking any link prevents infection.

Standard Precautions & Transmission-Based Precautions

Standard Precautions (Apply to ALL Patients)

Hand hygiene: Before/after patient contact, after removing gloves, after contact with body fluids
PPE: Gloves, gowns, masks, eye protection — based on anticipated exposure
Sharps safety: Puncture-resistant containers, neutral zone
Respiratory hygiene/cough etiquette: Cover coughs, offer masks
Safe injection practices: One needle, one syringe, one patient

Transmission-Based Precautions (Added to Standard)

Type	Pathogen Examples	Requirements
Contact	MRSA, VRE, C. difficile, scabies	Gown and gloves; dedicated equipment
Droplet	Influenza, COVID-19, pertussis, meningococcal	Surgical mask within 3-6 feet
Airborne	TB, measles, varicella (chickenpox)	N95 respirator; negative pressure room

CST Certified Surgical Technologist Exam

1Introduction: CST Exam Overview

2Chapter 1: Perioperative Care — Preoperative Preparation

3Chapter 2: Perioperative Care — Intraoperative Procedures

4Chapter 3: Postoperative Procedures & Ancillary Duties

5Chapter 4: Basic Science

6Chapter 5: Exam Strategy & Practice