Our objective was to determine whether strains of Pseudomonas aeruginosa can adapt to growth in increasing concentrations of the disinfectant benzalkonium chloride (BKC), and whether co-resistance to clinically relevant antimicrobial agents occurs. Attempts were made to determine what phenotypic alterations accompanied resistance and whether these explained the mechanism of resistance. Strains were serially passaged in increasing concentrations of BKC in static nutrient broth cultures. Serotyping and genotyping were used to determine purity of the cultures. Two strains were examined for cross-resistance to other disinfectants and antibiotics by broth dilution MIC determination. Alterations in outer membrane proteins and lipopolysaccharide (LPS) expressed were examined by SDS-PAGE. Cell surface hydrophobicity and charge, uptake of disinfectant and proportion of specific fatty acid content of outer and cytoplasmic membranes were determined. Two P. aeruginosa strains showed a stable increase in resistance to BKC. Co-resistance to other quaternary ammonium compounds was observed in both strains; chloramphenicol and polymyxin B resistance were observed in one and a reduction in resistance to tobramycin observed in the other. However, no increased resistance to other biocides (chlorhexidine, triclosan, thymol) or antibiotics (ceftazidime, imipenem, ciprofloxacin, tobramycin) was detected. Characteristics accompanying resistance included alterations in outer membrane proteins, uptake of BKC, cell surface charge and hydrophobicity, and fatty acid content of the cytoplasmic membrane, although no evidence was found for alterations in LPS. Each of the two strains had different alterations in phenotype, indicating that such adaptation is unique to each strain of P. aeruginosa and does not result from a single mechanism shared by the whole species.

We tested 53 clinical isolates of Branhamella catarrhalis recovered from patients with respiratory symptoms to determine the susceptibility of the isolates to 25 antimicrobial agents, including the newer I8-lactam antibiotics. Of the 53 strains, 46 (86.7%) were P-lactamase producers. All the strains were susceptible to the majority of the new penicillins and cephalosporins.-The combinations of amoxacillin-clavulanic acid and ticarcillin-clavulanic acid were also very active against the P-lactamase-prodiicing strains.Branhamella catarrhalis, formerly known as Neisseria catarrhalis, is generally considered a harmless oropharyngeal commensal bacterium. However, in the past few years it has been recognized as the etiologic agent of otitis media in children (9) and has been isolated in pure culture from patients with acute bronchitis and pneumonia (2,7,10,12,16,17), acute laryngitis (15), acute sinusitis (1), septicemia (3), meningitis (3, 13), and endocarditis (6, 14). P-Lactamase production by B. catarrhalis has occurred in 4 to 100% of isolates (5, 7-9, 16). Despite this fact, very little information is available on the susceptibility of B. catarrhalis to antimicrobial agents, especially the newer 1B-lactam antibiotics.We report here on the antimicrobial susceptibility and the incidence of 1-lactamase in 53 clinical isolates of B. catarrhalis from hospitalized patients with respiratory disease. Organisms. A total of 53 clinical isolates of B. catarrhalis were obtained from hospitalized patients with lower respiratory symptoms admitted to the Veterans Administration Medical Center, Johnson City, Tenn. The isolates were obtained from blood, transtracheal aspirates, and expectorated sputum from patients with pneumonia or acute exacerbation of chronic bronchitis. The clinical isolates were identified by conventional methods previously described (4): gram-negative diplococci, oxidase production, growth on 5% sheep blood agar incubated at 37°C under humidified 10% C02, lack of pigmentation, failure to produce acid from glucose, maltose, and sucrose, and reduction of nitrate to nitrite. P-Lactamase production. The production of ,B-lactamase was determined in each strain by the use of the chromogenic cephalosporin disk nitrocefin (Cefinase; BBL Microbiology Systems, Cockeysville, Md.).Antibiotics. Antibiotics were kindly provided by the manufacturers as reagent-grade powders and included penicillin