“One also should consider obtaining wound cultures in patients who develop SSIs and who have been hospitalized or reside in long-term care facilities due to the increasing incidence of infection caused by multidrug-resistant organisms.”

Biliary tract: “Enteric gram-negative bacilli, enterococci, clostridia.”

• Clean, skin-dominant operations such as cardiac, orthopedic, breast, vascular, and many hernia procedures: S. aureus is a leading, often the most likely, isolate.
• Biliary, gastrointestinal, colorectal, and other hollow-viscus procedures: S. aureus is less predictive. For biliary tract operations, Schwartz lists expected pathogens as enteric gram-negative bacilli, enterococci, and clostridia. Thus, if the SSI follows a biliary procedure, a positive culture has a more mixed enteric/anaerobic microbiological expectation rather than an expectation of S. aureus.
• Hospitalized patients or long-term-care residents: resistant organisms become more likely, which is why Schwartz recommends considering wound cultures in those SSI settings.

• Biliary-source or organ-space infection: more often enteric Gram-negative bacilli, enterococci, and sometimes anaerobes.
• Superficial or deep incisional SSI: can be caused by skin flora, including S. aureus, even after biliary surgery.

Can a precise percentage be given?

• the exact operation, such as open cholecystectomy, bile-duct exploration, biliary reconstruction, or hepatectomy
• superficial versus deep versus organ-space SSI
• preoperative biliary obstruction, cholangitis, stents, or drains
• local hospital microbiology and prophylactic antibiotic practices
• whether cultures are high-quality deep tissue/pus specimens or superficial swabs
• prior antibiotics and length of hospitalization

Practical interpretation

• S. aureus is not a typical biliary organism. Enteric Gram-negative bacilli, enterococci, and anaerobes are more expected.
• Published data cited in a biliary S. aureus series report S. aureus in about 0.8% to 5.6% of bile cultures in cholecystectomy patients. This is a prevalence in bile cultures, not the percentage of postoperative SSIs caused by S. aureus.
• Biliary S. aureus is more plausible with biliary instrumentation or drainage/stents, malignancy, recent broad-spectrum antibiotics, or serious healthcare exposure. A study of S. aureus bacteremia found a biliary source in 42 of 1,818 cases, or 2%, with these risk factors prominent. Yang et al., 2020

1. No skin source, but biliary S. aureus present before surgery:
   Yes. The open procedure can expose the wound to infected bile and plausibly produce an S. aureus SSI.
2. No skin source and no S. aureus in bile/biliary tract:
   No direct biliary mechanism is apparent. The operation itself would not generate S. aureus. Another source must be considered, such as an unrecognized healthcare-associated exposure, contaminated device, hematogenous seeding from bacteremia, or specimen contamination.
3. Postoperative wound culture alone grows S. aureus:
   This does not establish that the organism came from bile. To attribute the SSI to a biliary source, the strongest evidence would be S. aureus recovered from an intraoperative bile culture or biliary drain culture and the wound culture, ideally with matching susceptibility patterns or strain typing.

Biliary spillage is usually associated with enteric Gram-negative organisms, enterococci, and anaerobes. However, if bile itself contains Staphylococcus aureus, spillage during an open biliary operation can plausibly inoculate the surgical wound and contribute to an S. aureus SSI. This is uncommon, not impossible.

What the textbooks support

Evidence that makes “cannot” incorrect

What can be said for an individual SSI

1. Skin/endogenous or exogenous wound contamination, which is often the more likely explanation.
2. Hematogenous seeding from S. aureus bacteremia.
3. A genuine biliary-source inoculation, if the bile also contained S. aureus.

• An intraoperative bile or drain culture that grows S. aureus
• A postoperative deep wound/pus culture that grows S. aureus
• Matching antimicrobial susceptibility profiles, preferably molecular strain typing if attribution is important
• Clinical timing and operative documentation consistent with bile spillage

“instrumentation in infected bile or urine”

“Aerobic Gram-negative bacilli are often responsible, but Staphylococcus aureus and fungi may be involved.”

• A peer-reviewed report/review states that S. aureus isolation accounts for approximately 0.8% to 5.6% of organisms cultured from cholecystectomy specimens. It also cites a review of 13 biliary-infection case series in which S. aureus represented 2% of 782 isolates. See the full report and review.
• A 2022 clinical series specifically identified 28 patients with bile cultures positive for S. aureus, demonstrating that it can be recovered from bile. Skorochod et al., 2022.
• A 2020 cohort found biliary-source S. aureus bacteremia in 42 of 1,818 S. aureus bacteremia cases, particularly in patients with pancreaticobiliary malignancy, biliary stents/drainage, or recent broad-spectrum antibiotics. Yang et al., 2020.

“Although enteric Gram-negative bacilli, enterococci, and anaerobes are the usual organisms in biliary infection, Staphylococcus aureus has been documented in bile cultures and is an uncommon biliary pathogen. Therefore, if S. aureus is present in bile, biliary spillage could plausibly contaminate an operative wound.”

• Escherichia coli and other enteric Gram-negative bacilli
• Klebsiella species
• Enterococcus species
• anaerobes, depending on the site and procedure

Staphylococcus aureus is among the most common causes of surgical site infection overall, particularly in clean incisional surgery; enteric Gram-negative organisms and enterococci predominate more often in gastrointestinal and biliary-source infections.

• Bailey & Love’s Short Practice of Surgery, 28th ed.
• Chapter 5: Surgical infection
• Section: Systemic infection
• Subsection: Bacteraemia
• The passage begins under the heading “Bacteraemia” and is followed by Summary box 5.10.

“Bacteraemia is unusual following superficial SSIs, which tend to drain through the wound, but common after deep space SSIs, such as following an intestinal anastomotic breakdown. It is usually transient and can follow procedures undertaken through infected tissues (particularly instrumentation in infected bile or urine). … Aerobic Gram-negative bacilli are often responsible, but Staphylococcus aureus and fungi may be involved.”

O’Connell PR, McCaskie AW, Sayers RD, eds. Bailey & Love’s Short Practice of Surgery. 28th ed. CRC Press; 2023. Chapter 5, “Surgical infection,” subsection “Bacteraemia.”