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15 Cards in this Set
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Pseudomonas aeruginosa
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Gram negative rods in pairs and singles
Does Not ferment carbohydrates; Obligate anaerobe Blood Agar (BAP)- brown colonies, semi clearing MacConkey Agar- colorless colonies lactose-non fermenting Nutrient Agar- blue-green colonies Associated with long term catheterization |
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Hematogenous seeding in Children
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CA-Staphylococcus aureus, Strep. pneumoniae, Haemophilus influenzae type B
metaphysis In neonates the most common organisms are group B streptococci and E. coli. |
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Hematogenous Osteomyelitis of the Adult
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In adults hematogenous osteomyelitis most often affects the spine.
S. aureus and coagulase negative Staphylococci Elderly are also more prone to pelvic infections and theoretically, retrograde flow from pelvic tissues (urethra, prostate, bladder) to lumbar vertebrae can explain the spread of pelvic infections preferentially to lumbar vertebrae. less likely to have seeding in the long bones. |
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Contiguous-focus Osteomyelitis without Generalized Vascular Insufficiency
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S. aureus
can be poly microbial including gram-negative bacilli and anaerobic organisms caused by Surgical reduction, internal fixation of factures, prosthetic devices, soft tissue infections |
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Acute Ischaemic Neuropathic Osteomyelitis and/or Vascular Insufficiency
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Mostly polymicrobial including aerobic and anaerobic organisms: coagulase positive and negative Staphylococci, Streptococcus spp. Enterococcus spp, gram negative bacilli.
causes: Foot ulcer due to neuropathy, vascular insufficiency and hyperglycemia |
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Intravenous Drug Users and Osteomyelitis
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S. aureus, Pseudomonas, Candida, Eikenella corrodens. Also Mycobacterial osteomyelitis is more common in these patients.
Sternoclavicular, sternochondral joint, sacroiliac joint and symphysis pubis |
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Patients with Indwelling Catheters & Hemodialysis patients
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catheters: S. aureus, sacroiliac joint infections
hemodialysis: Vertebral osteomyelitis, S. aureus and S. epidermidis Oxacillin resistant S. aureus is common in this setting |
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Sickle cell Disease and Osteomyelitis
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Salmonella, S. aureus, other gram negatives
HLA class II DRB 15 is protective while HLA class II DQB1 03 is susceptible Patchy ischemic infarction in the bowel due to sickling, permitting transient mucosal barrier breakdown Long bone and septic arthritis |
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Salmonella
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Gram-negative facultative, rod-shaped, with peritrichous flagella.
Can be isolated on MacConkey agar Usually Non-lactose fermenters Acid and gas from glucose fermentation Produce H2S Usually cause two diseases: Salmonellosis; enteric fever (typhoid) |
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Mycobacterium tuberculosis’ in Spinal Osteomyelitis
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Acid Fast, rods , intracellular
Resistant to chemicals and drying due to thick cell wall with mycolic acids. Strictly aerobic and slow growing Vertebral osteomyelitis due to M. tuberculosis =Pott’s disease HIV patients, IV drug users and other immunocompromised patients are at risk of Mycobacterium infection |
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Review of Staphylococcus aureus
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Gram + cocci, non-motile
Catalase + Facultative anaerobe β-hemolytic Salt and Temp tolerant Golden pigmented colonies Anti-phagocytic polysaccharide capsule Coagulase producer Invasion: Hyaluronidase, Staphylokinase, Lipase, Dnase Adherence: The MSCRAMMS adhesion proteins are important to S. aureus adhesion to host intracellular matrix proteins including that of bone: Collagen binding protein – cna Fibronectin binding proteins – fnbA, fnbB, clf A, clfB Sialoglycoprotein adhesin Tissue destruction: Cytolytic toxins: α, β, δ, γ and the P-V leukocidin |
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Penicillin resistant S. aureus
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Penicillinase encoded by bla
Plasmid encoded and easily transferable Other B-lactams resistant to penicillinase where introduced cephalosporin, methicillin, nafcillin |
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MRSA: Methicillin Resistant S. aureus
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Defined as having oxacillin MIC of greater than 4μg/ml
All MRSAs have the mecA gene. mecA codes for a very low-affinity PBP2A The transpeptidases link the NAM-NAG chains together by way of a pentapeptides Diagnosis of MRSA: MIC testing, growth on Oxacillin agar, disk diffusion tests PCR analysis for mecA gene |
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VISA and VRSA: Vancomycin intermediate and resistant S. aureus
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Transposon TN1546 (vanA) is on a multi-resistance conjugative plasmid.
Van A gene products modify the Nam-peptide terminus from D-ala-D-ala to D-ala –D-lactate The modified precursors don’t bind vancomycin and therefore can be used for cell wall assembly. Alternative Treatment : Daptomycin |
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Acquiring Antibiotic Resistance
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Conjugation between E. faecalis and S. aureus followed by transposition into the S. aureus multiple drug resistance plasmid..
75% of Enterococcus faecalis isolates are vancomycin resistant (VRE) Transduction followed by transposition into the multi-drug R plasmid The TN1545 transposon is self-transferable. |