Resistance to antibiotics and biocides among non-fermenting Gram-negative bacteria

Objectives To investigate the antibiotic and biocide susceptibilities of cl inical isolates of rarely encountered Gram-negative, non-fermenting bacteri a. Methods Thirty Gram-negative non-fermenting bacterial strains were isolated from blood cultures of oncology patients. These were studied for their res istance to 11 antibiotics. Their susceptibilities to seven biocides used in hospitals were also examined. Results Isolates of Stenotrophomonas maltophilia and Ochrobactrum anthropi were generally resistant to at least five of the antibiotics, whereas isola tes of Comamonas acidivorans, Flavobacterium oryzihabitans, Aeromonas hydro phila, Sphingobacterium spiritivorum, Acinetobacter junii and Acinetobacter lwoffi were generally sensitive to at least nine of the antibiotics. Trova floxacin and trimethoprim-sulfamethoxazole were the most effective antibact erial agents tested, with 0% and 7%, respectively, of isolates being resist ant, whereas 63% of isolates were resistant to aztreonam. Some isolates, se nsitive to meropenem and/or ceftazidime in vitro, possessed very high MBC/M IC ratios for these beta -lactams. Two out of three biocides used in hospit al pharmacies showed lethal activity towards all strains tested when used a t less than one-third of their recommended in-use concentration. Proceine 4 0 failed to give a 5 log reduction in bacterial cell number for the isolate s tested when used at its 'in-use' concentration. A concentration of > 500 mg/L chlorhexidine was required to achieve a 5 log reduction for the same i solates. Conclusions We have examined the antibiotic susceptibilities of non-ferment ing Gram-negative bacterial strains isolated from immunocompromised patient s. Despite being sensitive to certain antibiotics in vitro, some isolates w ere still able to cause serious bacteremia. We have also reported for the f irst time the susceptibilities of non-fermenting Gram-negative bacteria to common biocides used in hospital infection control, and have shown that som e strains are able to persist at the 'in-use' concentration of particular b iocides. It is therefore important to study further this particular group o f organisms, and, in particular, to examine whether there exists a link bet ween resistance to antibiotics and resistance to biocides.