Indwelling device infections

Question 1

What is an implant?

Answer 1

• an object or material inserted or grafted into

the body for prosthetic, therapeutic, diagnostic, or experimental purposes.

Question 2

What is the concern with medical implants and bacteria?

Answer 2

• These provide non-shedding surfaces which can be readily colonised. Importantly, they may be contaminated with skin and other bacteria when implanted.
• They are also often essential to a patient’s recovery or survival

Question 3

How are biofilms involved in contaminating implants?

Answer 3

Organisms can leave the biofilm, enter bulk phase (urine, blood etc) and could potentially colonise on another surface, contaminating a different implant

Question 4

Why are biofilms recalcitrant (difficult to manage)?

Answer 4

• nutrients may not permeate as well
• Persister cells are a dormant form on microorganism which are difficult to kill with antimicrobials but often after treatment can potentially redivide and re-establish an infection

Question 5

What type of implant infections can you get?

Answer 5

Early Infections: Skin bacterial origin, during procedure

Late Infections: Bacteria can circulate in blood, and in rare cases seed implants. Also called “blood-borne” infections.

Question 6

What are the phases of periprosthetic infection?

Answer 6

Acute postoperative: within three months after the surgery.

Late chronic: delayed sepsis occurs 3 to 24 months after the surgery

Acute hematogenous: expressed at any time postoperatively, but it is necessary to demonstrate causal and chronological relations to running infection at any site in the host body

Question 7

What is the evidence that biofilms are significant in surgical site infections (SSIs)?

Answer 7

Therapeutic challenges of almost all device-related infections is itself compelling evidence

But, systematic research has confirmed this beyond doubt

Question 8

What are the problems with identifying biofilms?

Answer 8

Difficulty in isolating, by traditional culture methods,

Adherent bacteria in the biofilm

Systemic or local (cement) antibiotics

Mild ultrasonication of the prosthesis after removal (can help remove bacteria and make culture more likely), anaerobiosis, etc.

But, highly fastidious and non-cultivable, or viable but
non-cultivable could be present…

Question 9

What is the dempsey study?

Answer 9

Ten consecutive revisions were performed by two surgeons, which were all clinically and radiologically loose.

Five of the hip replacement revision surgeries were performed because of clinical infections and five because of aseptic loosening.

Preoperative and perioperative specimens were obtained from each patient and subjected to routine microbiological culture.

The prostheses removed from each patient were subjected to mild ultrasonication to dislodge adherent bacteria, followed by aerobic and anaerobic microbiological culture.

Bacterial DNA was extracted from each sonicate and the 16S rRNA gene was amplified with the universal primer pair 27f/1387r.

All 10 specimens were positive for the presence of bacteria by both culture and PCR.

Question 10

What are the principals of surgical therapy in the treatment of infections associated with surgical implants?

Answer 10

• cure of infection likely to require removal of implants infected by virulent organisms such as staph aureus and candida, but removal may not be required in the case of infection by less pathogenic coagulase negative staph
• regardless of the microbiologic cause of infection, remove the infected implant if the patient has not had a response to seemingly appropriate antibiotic therapy
• remove all components of an infected implant to prevent a recurrence of infection
• ensure the absence of clinical and, if necessary, microbiological evidence of infection before embarking on the second stage of surgical replacement

Question 11

What is the most abundant bacteria found on prosthetic hip joints?

Answer 11

Lysobacter gummosus was the most abundant (31.6%).

*Molecular detection of transcriptionally-active bacteria identified a total of 42 phylotypes

Question 12

How are joint infections managed initially?

Answer 12

Are all 3 of the criteria present?:

• duration of clinical manifestations of infection <10 days
• mechanically stable prosthesis
• infecting pathogen susceptible to oral antibiotics

*follow on treatment on flow chart

Question 13

If all 3 criteria is present, what is the next step in joint infection management?

Answer 13

• may attempt to salvage prosthesis:
• perform aggressive surgical debridement and provide a prolonged course of systemic (total duration 3-6 months) selected on the basis of the susceptibility profile (a quinolone plus rifampicin given IV for at least the first 2 weeks; other options include a beta lactam plus rifampicin and trimethoprim-sulfamethoxazole)
• if there is still recurrent staph infection or new infection then proceed to removal/replacement

Question 14

If all 3 criteria is NOT present, what is the next step in joint infection management?

Answer 14

• proceed with a replacement of the prothesis:
• stage 1: remove infected implant, insert antimicrobial-impregnated spacer, and administer systemic antibiotics for 6 weeks
• stage 2: implant a new joint prothesis if no clinical or microbiologic evidence of infection exists

Question 15

What is included in treatment?

Answer 15

One-stage direct exchange of infected hip arthroplasty (reimplantation) may be successful in almost 83 %

Delayed reimplantation the rate of success may reach 94 %.

Economic implications. Eg. in the United States, the
annual cost to treat 3,500 to 4,000 cases equaled 150 to
200 million USD.

Early recognition of infection and aggressive treatment by implant removal will reduce patient risk and health care expense”.

Question 16

How do you prevent or treat biofilms?

Answer 16

• When bacteria attaches to a surface it becomes immediately more difficult to treat when the biofilm matrix is formed
• Idea that you can treat before they are attached in planktonic form – prophylactic antibiotics may achieve this (before biofilm forms)
• Design of intelligent surfaces that are:
  i. difficult to colonise or
  ii. are antimicrobial

Question 17

What could be done to the implant to try to prevent biofilm formation?

Answer 17

• antimicrobial coated implants
• This strategy can delay colonization. Effectiveness depends on application
  i. e. occlusion with conditioning films over long-term applications etc.

Question 18

What are the advantages of antimicrobial coated implants (when they work)?

Answer 18

Preventing biofilm formation may help avoid the need for long-term, possibly ineffective systemic use of antibiotics

Prevention reduces risks of resistance generation in target bacteria, also in intestinal microbes

Obviates the need to remove the implant

Question 19

What is the Parsek–Singh criteria for recognising “biofilm infections” ?

Answer 19

Pathogenic bacteria are associated with a surface

Direct examination of infected tissue demonstrates aggregated cells in cell clusters encased in a matrix, which may be of bacterial and host origin.

Infection is confined to a particular site in the host.

Recalcitrance to antibiotic treatment despite demonstrated susceptibility of planktonic bacteria

Culture-negative result in spite of clinically documented high suspicion of infection (since localized bacteria in a biofilm may be missed in a conventional blood sample or aspirate).

Ineffective host clearance evidenced by the location of bacterial cell clusters (macrocolonies) in discrete areas in the host tissue associated with host inflammatory cells.