Comparative post-antibiotic effect of five antibiotics against ten aerobic gram-positive cocci.

The post-antibiotic effect (PAE) is the persistent suppression of bacterial growth after a short antibiotic exposure. It is well documented with a variety of antibiotics and micro-organisms and may have important therapeutic implications. The authors have evaluated the PAE produced by teicoplanin, fucidin, gentamicin, rifampicin and ciprofloxacin against a total of ten Gram-positive organisms (S. aureus (2), MRSA (2), S. epidermis (2) S. haemolyticus (2) and E. faecalis (2)). All the organisms were clinical isolates with variable sensitivity patterns confirmed by disc and MIC testing. MICs were performed by the broth dilution method using a final inoculum of 10 x 5 cfu/ml. The PAE was estimated by adding 5 x MIC of each antibiotic to a log phase of growth of approximately 10 x 7 cfu/ml, and incubating at 37 degrees C for 1 h. Antibiotic was removed by 1000-fold dilution in nutrient broth, and total viable counts were carried out hourly by the Miles and Misra method for a further 9 h. All the antibiotics tested showed a PAE against the organisms tested, except for fucidin and ciprofloxacin against the enterococci. Overall, teicoplanin showed a maximum PAE of 5 h against MSRA and a minimum of 0.6 h against E. faecalis. Gentamicin, rifampicin and ciprofloxacin also showed a variable range. Fucidin showed the least PAE against the ten organisms, ranging from 0-1.3 h, except for S. epidermidis (FUC-R) which had a PAE of up to 4.5 h. The duration of PAE of each antibiotic/organism combination varied and was associated with the sensitivity pattern of the organism.(ABSTRACT TRUNCATED AT 250 WORDS)