an 81-year - old diabetic male came to our hospital to seek medical attention for 2 weeks of productive cough , fever and chills , and a 10 kg weight loss .
physical examination revealed a fatigued - looking man with mild respiratory distress . except for bilateral crackles in both lungs , more on the right side ; the remainder of the physical examination was unremarkable , including the oral cavity .
complete blood count revealed mild anemia , however , the patient did not have leukopenia / neutropenia .
a chest x - ray showed a right lung infiltrate ; thus , community - acquired pneumonia ( cap ) was suspected and the patient was admitted for treatment of cap .
the patient was started on intravenous gatifloxacin 400 mg daily . however , the patient 's symptoms continued to deteriorate while on gatifloxacin .
a chest computed tomography ( ct ) done on hospital day 3 , showed a right upper lobe cavitary lesion ( figure 1 ) . because of the cavitary lesion , pulmonary diseases more complicated than cap ( such as lung cancer or vasculitis involving the lung ) were suspected .
the patient underwent a bronchoscopy on hospital day 4 , which was reported as unremarkable .
the bronchial washing cytology examination did not reveal malignant cells , but it showed scattered elongated bacilli ( figure 2 ) . within 24 hours
the bronchial washing culture grew the same gram - negative bacillus , methicillin - sensitive staphylococcus aureus , viridans streptococcus and group b streptococcus .
the gram - negative bacillus was eventually identified as ls at the north dakota state laboratory ( figure 3 ) .
blood cultures were drawn - once before starting antibiotics and three more times during treatment ; however , none of these cultures grew organisms . because of the clinical unresponsiveness to gatifloxacin , on hospital day 6 ,
the antibiotic was changed to intravenous vancomycin 1.5 g daily and piperacillin - tazobactam ( pip - tazo ) 3.375 g every 8 hours . 

figure 1computed tomography - scan of the chest shows a cavitary lesion in the right upper lobe . 
 
computed tomography - scan of the chest shows a cavitary lesion in the right upper lobe . 

magnification 400. 
  papanicolaou stain of the bronchial washing reveals the elongated bacilli ( arrow ) .
the pneumonia was suspected to be caused by one of the above gram positive cocci and the ls was considered an oral contaminant ; therefore , after a 9-day course of vancomycin and pip - tazo , vancomycin was continued but pip - tazo was discontinued on hospital day 15 . on hospital day 19 , after reconsidering ls a remotely possible pathogen of the pneumonia , we added oral amoxicillin 500 mg / clavulanate 125 mg every 8 hours to the vancomycin regimen . while on vancomycin and amoxicillin - clavulanate , the patient began to have spiked fever , rigors and increased dyspnea . on hospital day 23 , a chest radiograph indicated worsening of the pneumonia .
pip - tazo was continued for 4 weeks , followed by 2 weeks of intravenous aqueous penicillin g 2 million units every 8 hours .
the patient continued to do well and has had no recurrence of pneumonia to date .
ls is an anaerobic gram - negative bacillus that resides in the oral cavity and usually does not cause disease .
bacteremia , endocarditis , and hepatic abscess caused by leptotrichia buccalis have been reported in patients with neutropenia , hematologic malignancies and in bone marrow transplant recipients .
mucosal disruptions such as oral mucositis , esophageal ulcers , or diverticulitis are possible risk factors for infected patients . by gram stain alone , ls can be confused with other oral commensals , such as the elongated gram negative fusobacteria sp , capnocytophaga sp or even with the gram positive lactobacillus sp as ls can sometimes be gram - variable .
the ls in this case report was identified by gram stain and phenotypic analysis , but not by gene sequencing because the north dakota state laboratory was not equipped to perform the test .
one case is cavitary pneumonia with bacteremia caused by l. buccalis in an immunocompromised host .
the other case is a severe pneumonia caused by ls in an apparently immunocompetent male patient .
our patient has type 2 diabetes mellitus , but he is not immunocompromised from other underlying diseases or from immunosuppressive agents ; therefore , i believe this is the first case report of cavitary pneumonia caused by ls in an immunocompetent patient .
although the patient had good dental hygiene without dental caries , gingivitis , or oral mucosa lesions ; the oral cavity could still be the portal of entry in this patient 's pneumonia .
pneumonia caused by ls could be underreported because ls is usually considered a normal oral flora and is difficult to identify .
therefore ; if ls grows from bronchoalveolar lavage or lung tissue , a clinician should consider it one of the etiologic agents causing pneumonia .
due to the rarity of human infection caused by ls , the duration of treatment for pneumonia caused by this bacterium is not clear . in our case , because the pneumonia recurred after we administered pip - tazo for only 9 days , we aggressively gave the patient 4 weeks of piptazo followed by 2 weeks of intravenous aqueous penicillin g. although there are no clinical and laboratory standards institute ( clsi ) breakpoints for ls , penicillins are considered the drugs of choice .
thus , the patient continued to be clinically stable while on either pip - tazo or penicillin g. we postulate that the pneumonia recurred while on amoxicillin - clavulanate was likely due to the oral agent at a subtherapeutic level in the lung tissue .
therefore , we do not advocate treating pneumonia caused by ls with an oral -lactam antibiotic .
 leptotrichia species ( ls ) is an anaerobic gram negative bacillus in the bacteroidaceae family and part of the normal human oral flora . 
 it is rarely pathogenic , but occasionally causes diseases in immunocompromised hosts . 
 i am reporting a case of cavitary pneumonia caused by ls in an immunocompetent host . 