Abstract
Patients who have received oral penicillin may carry in the oropharynx alpha hemolytic streptococci, of which varying proportions are resistant to one or more units of penicillin per milliliter. Since the use of oral penicillin is increasing and penicillin is the drug of choice for prevention of endocarditis before oral or pharyngeal trauma, semiquantitative methods have been used to document (1) the frequency of α-streptococci resistant to 1 or more units of penicillin per milliliter in patients receiving prophylactic penicillin orally and intramuscularly, (2) the frequency and rate with which significant numbers of α-streptococci appear after exposure to oral penicillin, (3) the proportion and degree of resistance of α-streptococci which emerge resistant, and (4) the rate at which the numbers of resistant organisms are reduced to a presumably insignificant level when penicillin is withdrawn. The results show that there is a statistically significant increase (P <.001) in the proportion of α-streptococci resistant to at least 1 U per milliliter of penicillin in the pharynx of patients receiving their prophylactic penicillin in oral form (75%) in comparison with those on intramuscular penicillin prophylaxis (15%). Similarly, 17 of 22 patients on oral penicillin therapy developed flora containing resistant streptococci. Six such patients carried α-streptococcal populations, 7 to 50% of which were resistant to 1 but not 5 U. Eleven carried streptococci, 1 to 100% of which were resistant to 5 or more units per milliliter. Of 12 patients followed closely, 8 developed resistant streptococci within the first week of therapy, one after 2 days. Resistant streptococci decreased rapidly when therapy was discontinued. Eleven of 12 patients showed less than 20% of their streptococcal population resistant to 1 unit at 15 days and less than 10% at 30 days. Low levels (< 10%) persisted in six patients followed for intervals longer than 30 days and up to 144 days.
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