F. W. Goldstein

BACKGROUND: Bartonella (Rochalimaea) quintana is the agent of trench fever and is transmitted by the body louse. We searched for this organism in three alcoholic homeless men with endocarditis. METHODS: Blood samples were cultured on a human endothelial cell line and on blood agar. Bacteria were identified by sequencing the amplified 16S ribosomal RNA gene. The presence of bartonella in tissue was assessed by Gram's staining, immunostaining, and polymerase-chain-reaction amplification. Serologic studies for antibodies to bartonella species were performed by indirect immunofluorescence and Western immunoblotting. RESULTS: B. quintana was isolated from one patient in the blood-agar culture and from the other two patients in the endothelial-cell culture. The organism was also identified by both immunostaining and molecular techniques in the valvular vegetations from the three patients and in a cervical lymph node from one patient. The 16S ribosomal RNA gene sequences of the three isolates were almost identical to that of the prototype strain of B. quintana. High titers of antibodies to B. quintana were detected in all three patients, but so were cross-reacting antibodies to chlamydia species. In all three patients studies were repeatedly negative for antibodies to the human immunodeficiency virus. CONCLUSIONS: B. quintana is a cause of endocarditis in homeless patients and may be serologically misdiagnosed as a chlamydial infection.

The emergence of resistance to fluoroquinolones in virtually all species of bacteria was recognized soon after the introduction of these compounds for clinical use more than 10 years ago. Various resistance mechanisms, often interdependent, may explain different levels of resistance. Epidemiological factors, local antibiotic policies, patients' characteristics, origin of the strains, and geographic location are among the factors contributing to highly variable resistance rates. During the last several years, resistance to fluoroquinolones has remained very high among methicillin-resistant Staphylococcus aureus strains and in intensive care unit patients, and it has increased among nosocomial isolates of Klebsiella pneumoniae, Serratia marcescens, and Pseudomonas aeruginosa. More worrisome are recent reports of an overall increase in resistance to fluoroquinolones among bacteria responsible for community-acquired infections, such as Escherichia coli, Salmonella species, Campylobacter species and Neisseria gonorrhoeae.

We studied in vitro mutants of Klebsiella, Enterobacter, and Serratia cross-resistant to nalidixic acid, trimethoprim, and chloramphenicol that were similar to mutants found in vivo. The sole mechanism for this type of resistance appeared to be a reduction in permeability of the cell envelope. The mutants had significantly lower rates of uptake of glucose and chloramphenicol, but binding of chloramphenicol to ribosomes was normal. In addition, the amounts of dihydrofolate reductase were similar in both wild-type and cross-resistant mutants of Klebsiella. Examination of the bacterial outer membrane revealed that the amount of at least one major protein, with a molecular size of approximately 40 kilodaltons, was decreased in the mutants. Therefore the resistance seemed likely to be due to the reduction in quantity of these outer membrane proteins, possibly porins, in the mutant bacteria.

The antibacterial efficacy of the combination of amoxicillin and cefotaxime was assessed against 50 clinical strains of Enterococcus faecalis. For 48 of 50 strains, the MIC of amoxicillin that inhibited 50% of isolates tested decreased from 0.5 microgram/ml (range, 0.25 to 1 microgram/ml) to 0.06 microgram/ml (range, 0.01 to 0.25 microgram/ml) in the presence of only 4 micrograms of cefotaxime per ml. Alternatively, the MIC of cefotaxime that inhibited 50% of isolates tested decreased from 256 micrograms/ml (range, 8 to 512 micrograms/ml) to 1 micrograms/ml (range, 0.5 to 16 micrograms/ml) in the presence of only 0.06 microgram of amoxicillin per ml. For JH2-2, a reference strain of E. faecalis, the MICs of amoxicillin, cefotaxime, and amoxicillin in the presence of cefotaxime (4 micrograms/ml) were 0.5, 512, and 0.06 microgram/ml, respectively. By using a penicillin-binding protein (PBP) competition assay, it was shown that with cefotaxime, 50% saturation of PBPs 2 and 3 was obtained at very low concentrations (< 1 microgram/ml), while 50% saturation of PBPs 1, 4, and 5 was obtained with > or = 128 micrograms/ml. With amoxicillin, 50% saturation of PBPs 4 and 5 was obtained at 0.12 and 0.5 microgram/ml, respectively. Therefore, the partial saturation of PBPs 4 and 5 by amoxicillin combined with the total saturation of PBPs 2 and 3 by cefotaxime could be responsible for the observed synergy between these two compounds.