Growth inhibition by phenylalanine (0.25 mmol/L in defined agar media) was present in about 1% of over 1000 clinical isolates of Neisseria gonorrhoeae isolates tested. Turbidometry of several phenylalanine-sensitive isolates showed that their growth rates decreased in proportion to phenylalanine concentrations up to about 1 mmol/L. The growth rate was unaffected if 0.04 mmol/L tyrosine was also present. The phenylalanine analogue DL-3-fluorophenylalanine inhibited the growth of all 23 isolates further tested on agar. This inhibition was depressed by phenylalanine in all 17 phenylalanine-resistant isolates. Phenylalanine plus tyrosine were required to derepress the analogue inhibition in the other six phenylalanine-sensitive isolates. Phenylalanine-sensitive isolates may have a defect in aromatic amino acid synthesis, not involving auxotrophy, but manifested through regulation of the pathways. Phenylalanine effectively repressed tyrosine and phenylalanine synthesis. In 125 isolates including 85 beta-lactamase producers (PPNG) and 32 phenylalanine-sensitive isolates, phenylalanine inhibited 63.2% of 38 PPNG isolates carrying the 3.2 megadalton (Md) plasmid, but only one of 47 PPNG isolates carrying the 4.5 Md plasmid. PPNG isolates are most often of the proline, ornithine, or nonrequiring auxotypes. Phenylalanine sensitivity did not appear to be auxotype dependent.

The antibiotic susceptibility of 2609 Salmonella isolates, collected during the period 1975-1976, was tested and the relationships between antibiotic-resistance pattern, source of isolation, and serovar and phagovar were determined. Of 95 serovars examined, 40 were sensitive to all of the antibiotics tested. Salmonella typhimurium was the major contributor to multiple resistance from both human and non-human sources. Multiply resistant strains were not found from animal feed sources and, in addition, S. typhimurium, one of the most predominant serovars, was found in every source but animal feeds. 90% of phagovar 10 was sensitive to all antibiotics tested whereas over 80% of phagovars 3-aerogenic, 92, and 123 were multiply resistant.

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