a 70-year - old man complained of a calloused right hemiscrotum for three weeks and pain for 24 h. in the previous year , the patient had tongue cancer that required surgical removal .
examination of the patient s social history revealed that he had retired 10 years previously and had since lived with his wife .
a detailed medical history revealed that he did not have an apparent dietary or travel history that indicated exposure to l monocytogenes .
however , the patient did report that he consumed sashimi ( raw fish ) daily .
the patient presented with a blood pressure of 123/77 mmhg , a heart rate of 81 beats / min , a temperature of 36.4c , and a conscious and alert state . on examination , erythema and blackish discolouration of the skin around the right buttock toward the back of the scrotum with a foul odour
he immediately underwent surgical debridement of the necrotic tissue , suprapubic cystostomy and resection of an incidentally identified rectal tumour ( figure 1 ) .
blood cultures were performed , and intravenous antimicrobial treatment was administered empirically using meropenem ( 1 g every 12 h ) , clindamycin ( 600 mg every 8 h ) and vancomycin ( 15 mg / kg of body weight every 12 h ) .
gram stain of necrotic tissue specimens obtained during surgery demonstrated dominance of gram - positive rods , and the blood culture and the necrotic tissue specimens yielded l monocytogenes .
species identification of l monocytogenes was performed using the microscan walkaway 96si pc3.1j panel ( siemens healthcare diagnostics , usa ) .
the serotype of the isolate was assessed using commercial listeria antisera ( denka seiken , japan ) according to the manufacturer s instructions and was determined to be 4b .
the treatment was subsequently switched to ampicillin / sulbactam at a dose of 3 g intravenously every 4 h. the antimicrobial treatment regimen was continued for a period of 21 days .
in addition , the rectal tumour was identified as an adenocarcinoma , and the patient consequently underwent stoma and abdominoperineal resection along with d2 lymph node dissection .
the incidence of l monocytogenes infection is much lower in japan than in western europe and north america .
a questionnaire - based nationwide surveillance of hospitals in japan estimated the incidence of l monocytogenes infection to be 0.65 cases per 1,000,000 individuals ( 1 ) .
however , the incidence was 2.9 cases per 1,000,000 individuals in the united states ( 2 ) , and 6.3 cases per 1,000,000 individuals in 2006 in europe ( 3 ) .
it is speculated that l monocytogenes is primarily transmitted vertically or feco - orally through the consumption of contaminated foods including processed meats , unpasteurized milk and soft cheeses .
however , the patient in the current case lacked a diet or travel history indicative of l monocytogenes exposure .
furthermore , older age and immunosuppression due to an associated rectal adenocarcinoma were considered to be possible risk factors .
there are no published reports of l monocytogenes causing necrotizing skin and soft tissue infection . in our case ,
fournier s gangrene was possibly caused by undiagnosed rectal adenocarcinoma and l monocytogenes invasion from the tumour , similar to a previously reported case ( 4 ) .
further investigation of colorectal lesions as a portal for entry of l monocytogenes is , therefore , warranted .
individuals of japanese descent often consume a unique diet comprising large quantities of raw ready - to - eat ( rrte ) seafood , including sashimi and sushi .
examination of rrte seafood in japan revealed that raw minced tuna , which is a common appetizer in japan , and fish roe products are frequently contaminated with l monocytogenes ( 5.7% to 12.1% of the time ) ( 5 ) .
the rrte seafood has been reported to be relatively safe from contamination as long as it is consumed immediately after purchase .
however , bacterial cell number will rapidly increase , especially when rrte seafood is not properly maintained under refrigeration ( 5 ) .
in japan , elderly individuals generally do not eat large quantities of food and the japanese culture is careful not to let food waste ( a practice referred to as 
mottainai ) . therefore , elderly individuals living alone or with their partner will often store foods in a refrigerator for extended periods of time and eat them slowly . furthermore
, frequent opening and closing of the refrigerator door may increase the temperature inside the refrigerator above the recommended temperature for extended periods of time .
therefore , it is quite conceivable that consumption of rrte seafood , such as sashimi , may result in ingestion of l monocytogenes , resulting in infection .
the united states food and drug administration has established preventive regulatory guidelines for raw seafood , such as rte foods , that can support l monocytogenes growth ( 6 ) , and these guidelines have been effective in reducing the incidence of l monocytogenes infection ( 7 ) .
however , in japan , regulation of foods linked with l monocytogenes infection is limited to dairy products and rte meat products .
it should also be noted that there are no official statistics regarding the prevalence of l monocytogenes infection from rrte seafood in japan owing to the lack of a mandatory reporting system .
therefore , we propose that such a system be established for the control of l monocytogenes infection in japan . in the present case ,
the l monocytogenes isolate was determined to be of serotype 4b , which is the most frequently occurring form , accounting for 64% of cases in the united kingdom ( 8) and 59.9% of cases in japan ( 9 ) .
interestingly , the 4b serotype is not the leading serotype isolated from samples in western countries .
in addition , serotype 4b has been found to account for only 10.2% of reported cases associated with commercial foods in japan . in a 2002 review ,
kathariou ( 10 ) suggested that such a discrepancy between food incidence and prevalence of illness may exist because serotype 4b is more virulent to humans than any of the other known serotypes .
the strain isolated from blood culture was susceptible to penicillin g ( minimum inhibitory concentration [ mic ] 0.25 mg / ml using e - test [ biomrieux , france ] ) and ampicillin ( mic 0.25 mg / ml ) according to the breakpoints of clinical laboratory standards institute m45-a2 .
l monocytogenes isolated from humans has been rarely reported to be resistant to penicillins ( 11 ) .
however , most ( 92% ) l monocytogenes isolated from dairy farms is resistant to ampicillin ( mic 2 mg / ml ) ( 12 ) .
furthermore , statistical analysis showed an increase in mics for aminopenicillins in l monocytogenes isolated from humans , which was not associated with clinical failure ( 11 ) .
this could be explained by increased use of beta - lactams in human and animals , particularly in recent years .
this indicates that continuous surveillance of the susceptibility of l monocytogenes to antibiotics may be useful . to our knowledge , this is the first report of fournier s gangrene caused by l monocytogenes infection .
old age and immunodeficiency due to undiagnosed rectal adenocarcinoma may have supported the direct invasion of l monocytogenes from the rectal adenocarcinoma , thereby causing infection .
the consumption of rrte seafood should be considered to be a possible risk factor associated with l monocytogenes infection . moreover
, the findings suggest that l monocytogenes should be considered to be a possible pathogen when patients with known risk factors for listeriosis present with skin and soft tissue infection .
 fournier s gangrene is a necrotizing infection of the scrotal region , and is typically caused by exterobacteriaceae and anaerobic bacteria . 
 this report describes a case involving a 70-year - old man of japanese descent who developed fournier s gangrene that was found to be caused by listeria monocytogenes . 
 the patient s unique risk factors are discussed . 
CASE PRESENTATION
DISCUSSION