The patient was a 45-year-old male who was in his usual state of good health whe

Question

The patient was a 45-year-old male who was in his usual state of good health when he awoke at 3 a.m. with pain in the lateral aspect of his left calf. He looked at his calf and thought that the pain was due to an ingrown hair and went back to sleep. At 10 a.m., he expressed a small amount of pus from the ingrown hair. Over the next 8 hours, the patient developed an area of cellulitis on the lateral aspect of the calf of approximately 5 by 10 cm. At that time, a small amount of pus was again expressed from the area of the ingrown hair. The next morning, the area of cellulitis extended from just below the knee to just above the ankle. The patient visited his physician. His vital signs at that visit, includ- ing pulse, respirations, blood pressure, and temperature, were all within normal limits. Physical exam was significant for an area of cellulitis as described that was red and warm to the touch but with no area of obvious fluctuance. No lym phadenopathy was observed. The central area of the cellulitis, near the area that the patient described as where the ingrown hair had been, was punctured three times with a 20-gauge needle but no pus was drained. The patient was referred to the surgery service. The surgeons examined the patient and said they would follow him. The patient was given 2 g of ceftriaxone intramuscularly and begun 3 on oral cephalexin. The patient returned to the surgical clinic 48 hours later with an obvious area of fluctuance in the center of the area of cellulitis. Over the preceding 48 hours, the patient reported low-grade fevers. Approximately 1 ml of pus was aspirated and was sent for Gram stain and culture (Fig. 1 and 2). When pus was aspirated from the lesion, the surgeon decided to excise and drain the lesion (Fig. 3) 1. Based on Gram stain and culture, what is the o most likely causing this patient's infection? How do you think he became infected with this organism? Figure 1 Figure 2

Explanation / Answer

1. The most likely caustive agent of this condition is Staphylococcus. This is a gram positive strain ( as evident from the purple colored image of gram stain). The colonies on blood agar shows obvious pigmented colonies (S. aureus) and the white colonies of S. epidermdidis. The posible way of infection is by wounds and skin damage.
2. The Staph infections are often associated with the extoxin production by the pathogen. These will trigger cytokine release from certain T cells, causing serious systemic effects (eg, skin lesions, shock, organ failure, death). In order to reduce such toxin effects, the pus is drained from the wound.
3. Staph can cause various skin infections, Pneumonia, Endocarditis, Osteomylitis, Septic arthritis..etc.
4. The disc image shows the zone of clearance to different antibiotics. The larger the zone, the more susceptible the organism is to the antibiotic and smaller the zone, the more resistent it is. In the given image, the bacteria appears to be more resistent to penicillin and erythromycin. The penicillin acts on the bacterial cell wall and inhibits the cell division process.The erythromycin acts on the 23s ribsomal subunit and disrupts the translation process , thus inhibiting protein synthesis. The resistence to penicillin is most commonly found in these species. Hence the penicillin no longer is recommended as a drug in most of the cases.
5. This organism is completely resistent to both cell wall inhibitor penicillin and to protien synthesis inhibitor erythromycin. This combination effect makes this organism very dangerous. Most of the drugs in the market either act at cell wall or on ribosomes. Since this organism has resistence to both of them, very few drug options are left to treat the infection. The other antibiotic which target cell wall synthesis like oxacillin and vancomycin are also less effective compared to the clindomycin. The patient might get recurring infections from this pathogen as drugs which target cell wall and ribosomes would be less effective against it.
6. If the patient is having fever, low blood pressure and diarrhea , it is most likely the case of toxin shock syndrome. The bacteria produces lot of exotoxins TSS toxin-1. These toxins cause higher release of cytokins from T cells. This causes several systemic failures and over reactivity of the body. This results in profuse loss of fluid from the body which might result in shock and death. This can also cause multiple organ dynfunction.

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