456 Notes Eur. J: Clin. Microbiol. Infect. Dis. formula was responsible for these infections. The three patients came from different areas, and there had been no relationship between them previously. However, they had all been fed the same dry-milk formula. Our suspicions were con- firmed when the Microbiology Department of the Centre Nacional de Alimentaci6n (Dr. Blanco Vidal) isolated an identical strain from a batch of contaminated milk which the patients had been given. The identification of this lactose-positive strain was not difficult in blood and CSF cultures when initial cultures were made on blood agar and chocolate agar. However, identification from stool samples was more difficult because of the similarities with Escherichia coli and other lactose-fermenting members of the Enterobac- teriaceae on salmonella-shigella (SS) agar and MacConkey agar. Perhaps for this reason, stool cultures were negative in cases 1 and 2. In case 3 we were aware of the possibility of this strain, and we were able to isolate it. With this specimen we were able to see that if the SS agar plates were in- cubated for 48 h, hydrogen sulfide production was evident and the colour of the colonies changed from red to colourless with black in the centre. We believe that it is necessary to be aware of the possibility of lactose-positive Salmonella spp. in- fections. If false-negative results are to be avoided in stool cultures, revision of the tradi- tional methods used to isolate these particular strains from feces is necessary. References 1. Rubin RH, Weinstein L: Salmonellosis. Microbiologic, pathologic and clinical features. Stratton Intercontinental, New York, 1977, 2. Cherubin CE, Neu HC, Imperato PJ, Harvey RP, Bellen N: Septicemia with non-typhoid Salmonella. Medicine (Baltimore) 1974, 53: 365-376. 3. Jacobs JL, Gold JWM, Murray HW, Roberts RB, Arm. strong D: Salmonella infections in patients with the ac- quired immunodefictency syndrome. Annals of Internal Medicine 1985, 102: 186-188. 4. Dube S: Outbreak of food poisoning caused by lac- tose-fermenting Salmonellatuebingen. Journalof Clinical Microbiology 1983, 17: 698-699. 5. Kohbata S, Takahashi M, Yabuuchi E: Lactose-fer- menting, multiple drug-resistant Salmonellatyphistralns isolated from a patient with postoperativetyphoid fever. Journal of Clinical Microbiology 1983, 18: 920-925. 6. National Committee for Clinical Laboratory Standards: Performance standards for antimicrobial susceptibility testing. Fourth informational supplement. Document M100-$4. NCCLS, Villanova, PA, 1992. 7. Mishu B, Koehler J, Lee LA, Rodrigue D, Brenner FH, Blake P, Tauxe RV: Outbreaks of Salmonella enteritidis infections in the United States, 1985-1991. Journal of Infectious Diseases 1994, 169: 547-552. 8. Garcfa RodriguezJA, Garcfa SgmchezJE, Mufioz-Betlido JL, Garcia-Gamia MI: Salmonelosis focal en Espafia. Prasentaci6n de 14 cases y revisi6n de la literatura. Enfermedades Infecciosasy Microbiologia Clfnica 1990, 8:134-143. 9. Usera MA, EcheitaMA, Aladuefio A: Estudiode las cepas de Salmonella remitidas al Laboratorio de Referencia det Servicio de Bactedologfa del CNMVIS durante el afio 1992, Boletfn Epidemiol6gico y Micmbiol6gico del Ministerio de Sanidad y Consume 1993, 1: 145-153. 10. Ashdown LR, Ryan PJ: Invasive disease due to Sa/- monel/a virchow: a North Queensland problem. Medical Journal of Australia 1990, 153: 330-335. Multicenter Spanish Study of Ciprofloxacin Susceptibility in Gram-Negative Bacteria J.A. Garcfa-Rodriguez 1., M.J. Fresnadillo 1, M.I. Garc!a Garcfa 1, E. Garcfa-S~inchez 1, J.E. Garcla-Sanchez 1 , - I. Trujillano 1, and the Spanish Study Group on Quinolone Resistance 2 The susceptibility of 2,426 gram-negative bacteria obtained from 18 Spanish hospitals to ciprofloxacin was evaluated. Among different medical centers, susceptibility to ciprofloxacin ranged from 83 to 100 % for Enterobacteriaceae, from 35 to 100 % for Pseudomonas aeruginosa, from 0 to 100 % for Xanthomonas maltophilia, Acinetobacter spp. and other gram-negative non-fermenting bacilli, and from 33 to 100 % for Campylobacterspp. All clinical isolates of Haemophilus influenzae, Moraxella 1Departamento de Microbiologia y Parasitologfa, Hospital Universitario, Paseo de San Vicente 108, 37007 Salamanca, Spain. 2 Spanish Study Group on Quinolone Resistance: J.A. Gar- cfa-Rodrfguez, J.E. Garcia-S~inchez, E. Garcfa-S~fnchez, I. Trujillano, M.I. Garcfa Garcfa, M.J. Fresnadillo (Salamanca); E Baquero, J. Martfnez Beltr~in, E. Bouza, M. Rodrfguez, M. L6pez Brea, J.J. Picazo, F. Soriano (Madrid); E. Perea (Sevilla); M. de la Rosa, G. Pi6drola (Granada); F. Martfn Luengo (Murcia); J. Garcfa de Lomas, M. Gobernado (Valencia); R. Martin, G. Prats (Barcelona); R. G6mez Lus, M.L Aisa (Zaragoza); R. Cisterna (Vizcaya); C. Garcfa Riestra (Santiago de Com- postela).