FINAL DIAGNOSIS: LACTOBACILLUS SEPSIS WITH PSOAS MUSCLE ABSCESSES AND OSTEOMYELITIS
The genus Lactobacillus consists of non-spore-forming, gram positive bacilli, and is defined in part by the metabolic product produced. Most of the species are homofermentative: they form lactic acid from glucose as their major fermentation product. When the metabolic products are analyzed with gas chromatography, a characteristic single peak representing lactic acid usually provides the defining feature of the genus lactobacillus. Lactobacilli, ubiquitous microorganisms, are widely distributed in nature and in humans. They can be found in the mouth, gastrointestinal tract, vagina and other sites as part of the indigenous flora, as commensals or as isolates of little significance. Although lactobacilli have rarely been associated with clinically significant infections, they are implicated as infrequent causes of serious infections in either immunocompromised hosts or in patients with severe underlying conditions. Antony et al reviewed the clinical and micrological findings of 55 cases of lactobacillus infection including 12 cases from their own institution(4). They confirmed that subacute bacterial endocarditis was the most commonly reported clinical infection. Other clinical presentations included postoperative fever, urosepsis, pneumonia, oral abscess, peritonitis. and abscesses of solid organs such as liver and spleen. Bacteremia with lactobacillus alone occurred in 62% of cases, and 22% of the patients had bacteremia with other organisms. Lactobacillus was isolated from other sites in 33% of cases. Intravenous catheter infections were not reported in these patients. Common underlying conditions were recent surgery (22%), organ transplantation (16%), cancer (12%), and diabetes mellitus (10%). Fever occurred in all patients and 15% of patients experienced a sepsis syndrome. The mortality rate was 14%, but only three deaths were attributed to lactobacillus sepsis alone. Treatment of infections caused by lactobacillus usually consisted of a combination of penicillin or other beta-lactamase agent and an aminoglycoside, especially when deep infection was suspected. For unknown reasons, lactobacillus consistently demonstrated vancomycin resistance, and is variably resistant to the cephalosporins and quinolones. Because of its unusual and variable antimicrobial susceptibility pattern, treatment of infections caused by lactobacillus should be guided by the results of susceptibility testing, and failure to do so may lead to inadequate treatment of these patients.
In this case, the patient suffered a previously unrecognized diabetes mellitus, which is one of the common predisposing conditions for developing lactobacillus infections. Although gas chromatography was not performed in this case, the lactobacillus genus was identified as the pathogen of this patient's psoas muscle abscesses on the basis of microscopic appearance, colony morphology, motility, catalase reaction and biochemical features. Antimicrobial susceptibility testing showed that the isolated lactobacillus was sensitive to penicillin, clindamycin and ciprofloxacin but resistant to vancomycin. The relationship of the patient's severe lactobacillus sepsis and progressive heart failure is not known at this point.
In summary, the incidence of infections caused by lactobacillus may be underreported in the literature because of the failure to recognize it as a pathogen, especially in patients with severe underlying diseases. The possibility of lactobacillus as a pathogen should be considered in patients with bacteremia caused by gram-positive rods by whose conditions respond poorly to vancomycin therapy. Finally, the treatment of infections caused lactobacillus should be guided by antimicrobial susceptibility tests.
Contributed by Jianzhou Wang, MD, PhD, Wen-Wei Chung, MD, PhD, Shaila Fernandes, MD and William A Pasculle, ScD