INTRODUCTION

Pasteurella multocida are small gram-negative coccobacillary bacteria present in nasopharyngeal and gastrointestinal flora of many animals1. Infection in humans is commonly acquired through zoonotic contact following animal bite or scratch. Skin and soft tissue infection is the most common clinical manifestation1. Tenosynovitis is the most frequent local complication of Pasteurella soft tissue infection2. Pasteurella multocidais a non-fastidious microorganism. The role of Pasteurella multocida in zoonotic infection through cat bite has further been emphasized in the presentation.

CASE REPORT

A 55-year-old Malay lady with background medical illness of type ll diabetes mellitus and hypertension was admitted to the Orthopaedic Ward of the National University of Malaysia Medical Centre with history of cat bite on her right forearm. The incidence happened four days prior to admission when her cat suddenly bite and scratched her right forearm on the extensor surface. Initially, there was just redness over the area but later progressed to localized swelling and increased in pain intensity. She also noticed pus was coming out from the wound. For the past four days occasionally she experienced fever. Apart from that, there was no other relevant complaint.

Her blood pressure was 137/77 mmHg with pulse rate of 90 beats per minute. She was febrile with body temperature 39˚C. Examination of the right forearm showed presence of multiple scratch marks on the extensor surface. There was an area of induration and erythematous. Purulent discharge was noted draining out from the wound. The wound did not extend to the elbow joint. The peripheral circulation was good.

The baseline laboratory investigations noted the presence of leukocytosis (11 x 109/L) predominantly neutrophils. The C-reactive protein was raised (17.29 mg/dL). Her diabetic was poorly controlled with random blood sugar of 15.8 mmol/L and Hba1c of 13.5%. X-ray of the right forearm showed no evidence of osteomyelitis changes and no gas shadow.

She was treated as case of right forearm abscess secondary to domestic cat bite. Intravenous amoxicillin-clavulanic acid 1.2 grams 8-hourly was started empirically. Prompt incision and drainage of the abscess with wound debridement was done under emergency operation. Pus and tissue samples were sent for microbiological culture.

Intravenous amoxicillin-clavulanic acid was continued post operatively at the similar dose. The pus and tissue cultures grew Pasteurellamultocida, which were susceptible to amoxicillin-clavulanic acid and ciprofloxacin. The antibiotic was continued intravenously for 10 days. She was discharged well with oral amoxicillin-clavulanic acid for one week. Upon discharged both white cell count and C-reactive protein were normalized. Repeated tissue and pus cultures were no growth.

DISCUSSION

Pasteurellamultocida is an inhabitant of  oropharyngeal and gastrointestinal tracts of the cats and many other animals1. Human infection is usually zoonotic in nature and in most case occur after animal bite2,4,5. In our case cat bite was the mode of transmission of the infection. Other modes of transmission have been reported which include animal licking on the open wound and inhalation of animal aerosols6. Surprisingly there is also report on vertical transmission occurred in human7.

Clinical manifestation depends on mode of transmission. In animal biting the cat  is found to be the most common mode of acquisition, thus skin and soft tissue infection becomes the most common infection in humans. In most of the cases, the infection appears as non-purulent cellulitis, lymphangitis or both8. This is followed by purulent wound with or without abscess formation8. Our case the patient presented with purulent type of infection with abscess formation. Cellulitis occurs hours to few days at the bite site2. However, in another study, respiratory tract infections were found to be the most common clinical presentation of Pasteurellamultocida infection followed by skin and soft tissue infections9. 

Human infections following cat bites are frequently polymicrobial particularly if it is associated with abscess formation8. In abscesses, mixed aerobic and anaerobic infections are common. This did not occur in our case as we managed to isolate only Pasteurellamultocida in the pus and tissue specimens from our patient. Our anaerobic culture showed no anaerobic bacteria isolated. Pasteurellamultocidais a non-fastidious organism and it is not difficult to isolate them in clinical specimens. They grow well on blood agar but do not grow on Mac Conkey agar. They are non-motile and cytochrome oxidase positive. API 20NE commercial kit was shown and proved to be the best identification kit to identify these bacteria. API 20NE performed better than API20E for this purpose3. Here we used API20NE to help us identify the isolate as Pasteurella  multocida.

Molecular technique such as polymerase chain reaction (PCR) can be used to further differentiate between Pasteurellamultocida   subspecies. Pasteurellamultocidasubsp.septicaand Pasteurellamultocidasubsp.multocidaare among the most common subspecies isolated in human infection. These two subspecies have been proven to be associated with specific clinical manifestations. For instance, the Pasteurellamultocidasubsp. septicais associated with more skin and soft tissue infections rather than respiratory tract infections1. In our opinion, in our case the identification until to the subspecies level is not important because the management of the patient will not be changed by this factor. The molecular technique such as PCR is most likely to be helpful if further research is needed in this area to sub identify these bacteria.

Good initial therapy results in better prognosis. Early surgical intervention (if required) and appropriate antimicrobial therapy are crucial10. In our case, the wound exploration and debridement were carried out promptly after admission. The use of amoxicillin-clavulanic acid as empirical therapy is a good choice for the treatment of animal bites because it encompasses broad coverage of microorganisms including aerobic and anaerobic bacteria10. In our case amoxicillin-clavulanic acid was continued as definitive antimicrobial treatment as the Pasteurellamultocidais susceptible to amoxicillin-clavulanic acid.

Zoonotic infection by Pasteurella multocida through cat bites has been confirmed further in our hospital. The patient was treated by a combination of surgical intervention and appropriate antimicrobial therapy. She responded to the treatment and was discharged well. The public should be made aware of the danger of animal bites particularly those at risk of getting infection. Pasteurella multocida should be considered as one of the causative organism in patient presenting with clinical infection due to cat bite. Antibiotics that have both aerobic and anaerobic coverage should be used as an empirical antibiotic in clinical infection due to animal bites.