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Pseudomonas

Anaerobes

Citrobacter

Bacteroides

Morganella morganii

Clostridium

Serratia

Peptostreptococcus

Acinetobacter

Peptococcus

Proteus

bacteria are isolated from a deep ulcer swab or curet-tings they should not, therefore, be regarded as automatically insignificant

• When a positive culture is found, it is then possible to focus antibiotic therapy according to sensitivities of the bacteria cultured (Table 5.2)

• However, at initial presentation we believe that it is important to prescribe a wide spectrum of antibiotics for three reasons:

(a) it is impossible to predict the number and type of organisms from the clinical presentation

(b) there is no way of predicting who will develop a rapidly ascending infection which becomes limb-threatening and even life-threatening

(c) diabetic patients are immunosuppressed. The neuropathy and ischaemia of the diabetic foot reduces the local resistance to invading bacteria. As Louis Pasteur said: 'The germ is nothing. It is the terrain in which it grows that is everything'.

Duration of antibiotic therapy will depend on the clinical progress of the foot and ulcer, tissues involved, severity of the initial infection and also on individual factors relating to the patient.

The route by which therapy is given will depend on the severity of the infection. Intravenous therapy is required for serious infections. Intestinal absorption is unreliable in these circumstances.

Staphylococcus aureus

This is the commonest pathogen in the diabetic foot. Flucloxacillin is the ideal treatment. Clindamycin can also be used but beware of antibiotic-induced colitis especially in the elderly and postoperative patients. Erythromycin may increase the risk of myositis from statin therapy. When taking erythromycin, patients should be advised to stop their statin therapy temporarily.

Rifampicin and fucidin are also good antistaphylococ-cal agents, but they should not be given alone as resistance will develop rapidly. They should each be accompanied by a further antistaphylococcal agent.

Methicillin-resistant Staphylococcus aureus (MRSA) MRSA can cause serious infections and in these circumstances give vancomycin 1 g IV bd, dosage to be adjusted according to serum levels, or teicoplanin 400 mg IV 12-hourly for three doses and then 400 mg daily. These antibiotics may need to be accompanied by either sodium fusidate 500 mg tds or rifampicin 300 mg tds orally (according to sensitivities).

If MRSA is isolated with moderate signs of infection, oral therapy can be given with two of the following: sodium fusidate 500 mg tds, rifampicin 300 mg tds, trimethoprim 200 mg bd or doxycycline 100 mg daily, according to sensitivities.

Streptococcus group B is the commonest and can cause severe infection although A, C, E, F and G can infect the foot.

The streptococci milleri group of organisms related to Streptococcus group F can cause abcesses in the foot.

Streptococci can be treated with amoxicillin. Clindamycin, rifampicin and erythromycin are also active against streptococci.

Enterococcus

Enterococcus faecalis is rarely pathogenic. It may be selected out by cephalosporin treatment. If it is causing definite infection then treat with amoxicillin. Enterococcus faecium may need vancomycin.

Anaerobes

These are commonly found in deep infections but anaerobes are also a feature of many chronic wounds even when they are superficial.

Metronidazole is the treatment of choice. Clindamycin and augmentin (amoxicillin/clavulanic acid) also have antianaerobic activity. Meropenem intravenously is also active against anaerobes.

Gram-negative organisms

Klebsiella, Escherichia coli, Proteus, Enterobacter, Citrobacter, Serratia, Pseudomonas and Acinetobacter and other Gram-negative bacteria can be definitely pathogenic in the diabetic foot especially when they are in a pure growth or as part of a polymicrobial deep infection.

Table 5.2 Antibiotics for treating the infected foot
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