Osteomyelitis and Staphylococcus Aureus

 Thomas Antony 

Microbiology Grand Rounds Case Scenario VI

Case Scenario #VI Summary

Objective #1: What is the pathogenesis of this infection?

• Osteomyelitis occurs when:
• You experience trauma leading to bone damage
• Organism inoculation
• Presence of a foreign material
• Most commonly, in children, it arises as a consequence of a hematogenous spread of bacteria (ex. Staphylococcus Aureus)
• Begins in areas with high vascularity due to slower blood flow

Objective #2: What is Staphylococcus Aureus? How does it relate to the normal flora? What are the portals of entry?

• Staphylococcus aureus is :
• Gram positive cocci, catalase-positive, and coagulase-positive
• Facultative aerobe
• Is a potentially lethal opportunistic pathogen
• Enzymes (ex. Coagulase, lipase, staphylokinase, beta-lactamase)
• Toxins (ex. Cytolytic toxins, leukocidin, exotoxin, toxic shock syndrome toxins)
• Structural defences (ex. Protein A, slime layer).
• Normal Flora:
• Human commensal, asymptomatically colonizing about 30% of the human population
• Found in nasal passages, axillae, inguinal, perineal areas, skin (along with S. epidermidis)
• Those who are colonized have a higher risk for developing infections
• Portals of entry:
• Staphylococcal infections remain localized at the portal of entry by the normal host defenses
• Skin, mucous membranes, respiratory system, gastrointestinal system, genitourinary tract, conjunctiva of the eye, placenta, parenteral route

Objective #3: Is Owen at risk for this infection as well?

• S. aureus transmission is by:
• Direct contact with colonized individuals, contaminated objects and inhalation of infected droplets
• Children are more commonly affected than adults because:

• Prone to hematogenous osteomyelitis
• Improper handwashing/hygiene (too young)
• Rich vasculature
• Immune system not fully developed

Objective #4: What is osteomyelitis? How did this infection develop? Who is most at risk for this type of infection? Why?

• Osteomyelitis is inflammation of the bone
• Majorly caused by bacterial infection, tissue injury/trauma (Direct), bacteremia.
• Symptoms of pain, swelling and redness around the infected area, fever
• Hematogenous osteomyelitis, injury → Blood vessels → Bacteremia → Bones
• People who are most at risk are those with::

• Recent injuries, circulation disorders, impaired immune system, IV line or catheter, and the elderly

• Infants and young children are more susceptible because they are:

• Prone to hematogenous osteomyelitis
• Improper handwashing/hygiene
• Clumsy → Injury
• Rich vasculature
• Immune system not fully developed

Objective #5: What was the purpose of the prescribed orders? Why did the antibiotic therapy change?

• Start with empiric therapy because of broad spectrum and to control the spreading
• After confirming we use targeted therapy
• Ampicillin – Possible lactamase resistance
• Gentamicin – Not sufficient in killing intracellular bacteria

Objective #6: What is the rationale for IV therapy? What is the rationale for 6 weeks of therapy?

• Higher bioavailability through the IV route compared to the oral route as it goes directly into the blood stream; PICC lines generally have a 100% bioavailability.
• For osteomyelitis, bacteria might be thriving even with lessened symptoms. Patients should continue taking antibiotics until they have finished the 6 week course as it makes sure the bacteria is gone and the infection is dealt with.

Objective #7: What steps could be taken to reduce the risk of acquiring this type of infection?

• Avoiding infection
• Improving your health by:
• Stopping smoking, healthy diet, managing your weight, alcohol, an regular exercise

References

Bauman, R. W. (2014). Microbiology with diseases of the body systems. Toronto: Pearson Education, Inc.

Brown, A. F., Leech, J. M., Rogers, T. R. & McLoughlin, R. M. (2014). Staphylococcus aureus colonization: modulation of host immune response and impact on human vaccine design. Frontiers. doi: 10.3389/fimmu.2013.00507

Bush, L. M. & Schmidt, C. E. (n.d.). Staphylococcus aureus Infections (Staph Infections). Merck Manual. Retrieved from http://www.merckmanuals.com/en-ca/home/infections/bacterial-infections/staphylococcus-aureus-infections

Culver, K. (2017). Central Nervous System Infections. [Powerpoint Presentation].

Communications, R. (2013, January 30). Comparing Oral and Intravenous Antibiotics. Retrieved March 30, 2017, from http://blog.research.chop.edu/comparing-oral-and-intravenous-antibiotics/

Kanjilal, S. (2016). Staphylococcus aureus. DynaMed Plus. Retrieved from http://www.dynamed.com/topics/dmp~AN~T904266

Kiechl-Kohlendorfer, U. & Griesmaier, E. (n.d.). Neonatal Osteomyelitis. INTECH. doi: 10.5772/54320

Mohamed, W. (2014). Intracellular Proliferation of S. Aureus in Osteoblasts and Effects of  Gentamicin.European Cells and Materials,28, 258-268. doi:10.22203/eCM.v028a18

Nhs. (2014, October). Osteomyelitis – Prevention. Retrieved March 30, 2017, from http://www.nhs.uk/Conditions/Osteomyelitis/Pages/Prevention.aspx

Osteomyelitis Risk factors. (2015, September 25). Retrieved March 26, 2017, from  http://www.mayoclinic.org/diseases-conditions/osteomyelitis/basics/risk-factors/con-20025518

Osteomyelitis in Children. (2014, August 23). Retrieved March 27, 2017, from  http://www.chop.edu/conditions-diseases/osteomyelitis-children

Sopirala, M. M. (2015). Pathogenesis of osteomyelitis. UpToDate. Retrieved from https://www.uptodate.com/contents/pathogenesis-of-osteomyelitis#H18562386