The sensitivity of four groups of gonococcal strains to ampicillin (Am), penicillin (P), tetracycline (T), rifampicin (Ri), spectinomycin (Sp), sulphamethoxazole (Su), trimethoprim (Tr), and a combination of Su and Tr in the ratio 5:1 (Su/Tr 5:1) has been determined. The various groups of strains were isolated from male civilians (MC), female civilians (FC), and sailors (S) in Rotterdam (R) in 1972, and from FC in Amsterdam (A) in 1967. The S-R strains, which may be regarded as mainly imported, were compared with the MC-R and FC-R (which may be considered as mainly of Dutch origin). Also investigated was whether the incidence of relative resistance to the antibiotics investigated among Dutch strains has changed in the period from 1967 to 1972. For this purpose, the FC-A and FC-R strains were compared. The MC-R and FC-R strains were also compared with one another. Finally, Spearman's rank correlation coefficient r were calculated between the sensitivity distributions for each pair of antibiotics investigated, for all strains. The S-R strains were significantly less sensitive to Am, P, T, Ri, and Tr than the MC-R and FC-R strains. Comparison of the FC-A and FC-R strains revealed that the FC-R strains were significantly less sensitive only to Su/Tr 5:1. A possible explanation for this finding is given. With the exception of one FC-A strain, all gonococcal strains were sensitive to Sp. High values of r (larger than or equal to 0.50) were found between Am and P, Am and T, and P and T for all groups of strains. The values of r between any pair of the antibiotics Am, P, T, Ri, and Tr (with the exception of the pair Am-P) were always highest for the S-R strains. High values of r (larger than or equal to 0.50) were found between Su and Su/Tr 5:1 for all groups of strains. The FC-A strains, unlike the R strains, gave low values of r between Su and Tr and between Tr and Su/Tr 5:1. A possible explanation for this is given. Finally, a hypothesis is put forward to explain the fact that no significant changes were found in the sensitivity of Dutch gonococcal strains to Am, P, T, Ri, Sp, Su, and Tr in the period from 1967 to 1972, while the S strains (which may be regarded as imported) showed a significantly higher percentage of strains relatively resistant to Am, P, T, Ri, and Tr.
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