Bacterial infection: illustrated

Presentations of infections including an infected sebaceous cyst, tonsillitis, a dental abscess, mycoplasma pneumonia and mastitis.

Sebaceous cyst
Sebaceous cyst

Infected sebaceous cyst

Sebaceous cysts are very commonly seen in general practice. As a rule, I leave them alone, having spent a lot of time trying to dissect out cysts in the past. They can become infected at any time, however, often discharging a cheesy-smelling purulent substance. Early in this process, they may respond to an oral antibiotic, but they often need incision and drainage once the infection is established.



A very common problem is the accurate diagnosis of sore throats. Differentiating between viral and bacterial streptococcal infections can be quite tricky. The decision to prescribe antibiotics is dependent on this. I sometimes do a throat swab to try to get a retrospective answer, but the decision is still a clinical one. This patient did have a group A streptococcus on his swab and responded to penicillin V.



This elderly man presented with a swollen, very painful right testicle. He was treated with antibiotics (ciprofloxacin) and his pain resolved. Unfortunately, the testicle did not reduce in size, and it became clear the swelling had been present for some time. He therefore underwent right orchidectomy in case of possible malignancy. In fact, the histology failed to show anything suspicious, just chronic inflammation.

Dental abscess

Dental abscess

I have often been frustrated by my inability to treat patients with dental problems attending the surgery, but GPs are not trained dentists and should not dabble. This elderly woman with dementia presented with a small but apparently non-painful swelling below the right side of her jaw. I was unsure of the diagnosis, so had to refer her. It was due to a dental abscess.

Mycoplasma pneumonia

Mycoplasma pneumonia

This 29-year-old woman had a cough for a couple of weeks. She was not particularly ill and was eventually treated with amoxicillin. This made no difference. She subsequently developed this rash, which was mildly uncomfortable, and became more unwell. She ended up in hospital, where a chest X-ray showed significant infection. Investigation revealed this was due to a mycoplasma infection.



This 84-year-old woman presented with acute painful inflammation in a localised area of her breast. She responded to IV antibiotics, but there remained a concern about a possible underlying malignancy. Following resolution, however, there was no sign of this and she had no further problems.

Foreign body

Foreign body

Gardening is a very popular pastime and can lead to a range of injuries. Foreign bodies are very common. This patient had noticed a splinter in the palm of his hand a few days earlier. It became increasingly painful and formed this small abscess, which eventually discharged the splinter along with a quantity of pus. The wound settled quickly after this.

Postoperative infection

Postoperative infection

This 75-year-old man had colon cancer and underwent bowel resection. Patients often worry about possible infection when wounds ooze a little. This situation was somewhat different, with significant purulent discharge from the distal end of the wound, as well as an open portion at the proximal end of the wound. There was no significant surrounding cellulitis in the tissues and although it looked infected, the wound was treated by the practice nurses and settled down without antibiotics.

  • Dr Phil Marazzi is a GP in Surrey, UK

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