Microbiology Case Study: A 57 Year Old Man with an Infected Drain Site

Clinical History

The patient is a 57 year old male with a history of traumatic brain injury in 2005 resulting in quadriplegia and subsequent neurogenic bladder with chronic spasms. In 2016 the patient underwent cystoprostatectomy, proctectomy, and ureteroenteric anastomosis to colon. The post-operative period was complicated by the formation of a presacral abscess consisting of MSSA and E. coli. Drain placement failed to resolve the abscess and drain studies showed the formation of a fistula to the patient’s rectal stump. The subsequent 3-year period consisted of repeat drain placements and laparotomy to drain and wash out multiple small collections of fluid seen on imaging. Bacterial cultures during this interval grew mixed gram positive and gram negative enteric bacteria, treated primarily with ertapenem. In January of 2020, the patient underwent exploratory laparotomy with debridement and drainage of pelvic abscess. Tissue cultures from the procedure grew MRSA and vancomycin was prescribed for treatment. Vancomycin was switched to daptomycin for more favorable dosing and ertapenem was added to his treatment plan. Four weeks after his operation, the patient reported pain at his drain site and the fluid in his Jackson-Pratt (JP) drain had turned green. Fluid from the JP drain was submitted for microbiological work-up.

Laboratory Findings

Gram stain of the fluid from the JP drain showed neutrophils, many gram negative bacilli, and beaded gram-positive bacilli. Modified Kinyuon testing was positive for acid-fast bacilli (AFB) and cultures were ordered for mycobacteria as well as Nocardia. The gram negative bacilli was isolated and identified as Pseudomonas aeruginosa by MALDI-ToF. The beaded gram-positive bacilli were isolated on CNA agar and identified by MALDI as Mycobacterium chelonae. Concordant morphology was observed on mycobacterial culture. Nocardia culture was overgrown by P. aeruginosa.

Image 1. Gram stain of specimen taken from the patient’s JP drain.
Image 2. CNA agar plate growing gram positive bacilli.
Image 3. 7H11 plate growing acid fast bacilli.

Discussion

Rapidly growing mycobacteria (RGM) include the three most common clinically relevant species: Mycobacterium abscessus, Mycobacterium fortuitum, and Mycobacterium chelonae.

The RGM are environmental organisms found worldwide that usually grow in subculture within one week (eg, rapidly, as compared with other mycobacteria). M. abscessus is the most commonly encountered species of this group isolated from clinical respiratory specimens, M. fortuitum is the most common from non-respiratory specimens, and M. chelonae primarily impacts immunosuppressed patients and may also cause surgical wound infections.

Postoperative infections with RGM have occurred following various procedures including cosmetic surgery procedures, augmentation mammoplasty, laser in situ keratomileusis (LASIK), and heart surgery.1-8 Infection is characterized by multiple recurrent abscesses around the surgical wound.

Diagnosis for non-pulmonary disease is made by culture of the specific pathogen from drainage material or biopsy of the affected site. The isolation of organisms from sterile, closed sites, such as bone marrow or blood or from a skin biopsy (in the setting of multiple lesions), is diagnostic of the disease. Once an isolate has been identified as a nontuberculous mycobacteria (NTM), the species should be identified. However, identification of RGM in most laboratories is either incomplete or imprecise. M. abscessus isolates are frequently identified simply as “M. chelonae/abscessus complex,” or if they are specifically identified as “M. abscessus,” they are not accurately sub-speciated.

Susceptibility testing should be performed against a number of antibacterial agents, however, there is no established minimum inhibitory concentration (MIC) cutoff for susceptibility or resistance. M. chelonae is typically treated with Macrolide antibiotics, particularly azithromycin and clarithromycin. M. fortuitumM. abscessus, and M. chelonae are resistant to the antituberculosis agents rifampinethambutol, and isoniazid, so susceptibility testing of RGM should not be performed with these.

The clinicians in our case suspected that the M. chelonae culture from the patient’s JP drain was most likely a contaminant as the same organism was never isolated from previous tissue or fluid cultures. He was continued on daptomycin, ertapenem, and ciprofloxacin was added to cover P. aeruginosa. The patient responded well with resolution of his localized symptoms at the site of the JP drain. Unfortunately, he continues to suffer from multiple, recurring presacral abscesses.

References

  1. Rimmer J, Hamilton S, Gault D. Recurrent mycobacterial breast abscesses complicating reconstruction. Br J Plast Surg 2004; 57:676.
  2. John T, Velotta E. Nontuberculous (atypical) mycobacterial keratitis after LASIK: current status and clinical implications. Cornea 2005; 24:245.
  3. Freitas D, Alvarenga L, Sampaio J, et al. An outbreak of Mycobacterium chelonae infection after LASIK. Ophthalmology 2003; 110:276.
  4. Sampaio JL, Junior DN, de Freitas D, et al. An outbreak of keratitis caused by Mycobacterium immunogenum. J Clin Microbiol 2006; 44:3201.
  5. Edens C, Liebich L, Halpin AL, et al. Mycobacterium chelonae Eye Infections Associated with Humidifier Use in an Outpatient LASIK Clinic–Ohio, 2015. MMWR Morb Mortal Wkly Rep 2015; 64:1177.
  6. Toy BR, Frank PJ. Outbreak of Mycobacterium abscessus infection after soft tissue augmentation. Dermatol Surg 2003; 29:971.
  7. Centers for Disease Control and Prevention (CDC). Mycobacterium chelonae infections associated with face lifts–New Jersey, 2002-2003. MMWR Morb Mortal Wkly Rep 2004; 53:192.
  8. Wallace RJ Jr, Brown BA, Onyi GO. Skin, soft tissue, and bone infections due to Mycobacterium chelonae chelonae: importance of prior corticosteroid therapy, frequency of disseminated infections, and resistance to oral antimicrobials other than clarithromycin. J Infect Dis 1992; 166:405.
  9. Wallace RJ Jr, Brown BA, Onyi GO. Susceptibilities of Mycobacterium fortuitum biovar. fortuitum and the two subgroups of Mycobacterium chelonae to imipenem, cefmetazole, cefoxitin, and amoxicillin-clavulanic acid. Antimicrob Agents Chemother 1991; 35:773.

-Will Humphery, MD is a 1st year anatomic and clinical pathology resident at the University of Vermont Medical Center.

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

Microbiology Case Study: 41 Year Old Male with Complaints of Abdominal Pain for One Month

Case History

A 41 year old African male presented to the ED with complaints of abdominal pain, weight loss, and decreased appetite over one month. He immigrated from Zimbabwe 10 years prior, and most recently visited 4 months ago. His past medical history is non-contributory. He was found to have microcytic anemia (Hgb 9.3 g/dL, MCV 77.0 fL), pneumonia, and focal small bowel dilation with thickening and inflammatory changes on abdominal CT.

Endoscopy revealed a large, villous, infiltrative mass in the third portion of the duodenum. On histologic examination of the duodenum biopsy, viable Schistosoma eggs were seen within the vessels in the lamina propria and associated with adenocarcinoma (Images 1 and 2). Schistosoma mansoni eggs were identified on stool ova and parasite exam (Image 3), and serology was positive for Schistosoma IgG antibody.

Image 1. 10x objective magnification of a hematoxylin and eosin stained histology slide of the duodenal biopsy with associated adenocarcinoma and multiple eggs can be visualized.
Image 2. 40x objective magnification of a hematoxylin and eosin stained slide from the duodenal biopsy of a man from Africa who presents with abdominal pain who is found to have a mass on endoscopy. Seen is a viable egg with intact miracidium and no evidence of calcification.
Image 3. 100x oil immersion objective magnification of an iodine prep from a concentrated formalin-fixed stool specimen demonstrating a Schistosoma mansoni egg with its characteristic large lateral spine.

Discussion

Although this is not a common infection to encounter in the US, prevalence in endemic areas ranges from 30-100%. Infection occurs through contact with water contaminated with human feces; common circumstances are irrigation ditches as well as bathing and washing water.1

Schistosomiasis may be an indolent infection in many immunocompetent hosts. Chronic infection requires a shift from inflammatory TH1 response to a modulatory TH2 response.2 There is also evidence that Schistosoma infection may downregulate the immune response by inducing M2 differentiation of macrophages.3 These anti-inflammatory macrophages have been associated with a microenvironment favorable to malignancy. It has also been shown that S. mansoni is a risk factor for hepatocellular carcinoma (HCC) and colonic adenocarcinoma, possibly by altering p53 activation, initiation of chronic granulomatous response that blocks venules, increasing cell turnover, and promotion of ROS and RNOS production.4 Anti-idiotype antibodies produced in chronic infection may also down-regulate both specific and non-specific immune responses.5

This case is an unusual presentation in the US in that viable ova are typically not seen, and S. mansoni is more likely to involve the distal colon and liver rather than the small bowel. There is a known association between S. mansoni infection and HCC, and there are sporadic reports of association with tumors of the prostate, ovary, uterus, and cervix.5,6 To our knowledge however, there are no other reported cases of duodenal adenocarcinoma with concurrent schistosomiasis.

References

  1. Chai J and Jung B. Epidemiology of Trematode Infections: An Update. 2019. Adv Exp Med Biol. 1154:359-409.
  2. Barsoum RS, et al. Human Schistosomiasis: Clinical Perspective: Review. 2013. Journal of Advanced Research. 4:433-44.
  3. Hussaarts L, et al. Chronic helminth infection and helminth-derived antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice. 2015. FASEB J. 29(7):3027-39.
  4. El-Tonsy MM, et al. Schistosoma mansoni infection: Is it a risk factor for development of hepatocellular carcinoma? 2013. Acta Trop. 128(3):542-7.
  5. Palumbo E. Association Between Schistosomiasis and Cancer. 2007. Infectious Diseases in Clinical Practice. 15(3):145-8.
  6. Peterson MR and Weidner N. Gastrointestinal neoplasia associated with bowel parasitosis: real or imaginary? 2011. J Trop Med. 2011:234254.

-Daniel Welder, MD is a second year Clinical Pathology resident at UT Southwestern Medical Center in Dallas, Texas. He has interests in Hematopathology, Transfusion Medicine and dabbles in Microbiology.

-Dominick Cavuoti, DO is a Professor at UT Southwestern in the Department of Pathology. He is multifaceted and splits his time as the Medical Director of the Parkland Hospital Clinical Microbiology Laboratory and Parkland Cytology attending among other administrative and educational activities.

-Clare McCormick-Baw, MD, PhD is an Assistant Professor of Clinical Microbiology at UT Southwestern in Dallas, Texas. She has a passion for teaching about laboratory medicine in general and the best uses of the microbiology lab in particular.

An Asymptomatic 52 Year Old Female with a Surprise Finding on Colonoscopy

Case Presentation

A 52-year-old female with no significant past medical history is seen for a routine annual examination and is scheduled for a colonoscopy due to her age being over 50 years. The colonoscopy was performed and an isolated single worm was found within the cecum (Images 1-2). The worm was removed with cold forceps and subsequently placed in paraffin and sectioned (Images 3-5).

Image 1. The worm is depicted within the cecum attached to the mucosal wall by its anterior end.
Image 2. The worm is captured using cold forceps.
Image 3. Hematoxylin and eosin stained section of the worm.
Image 4. Higher power magnification, showing eggs with distinctive characteristic bilateral polar plugs and barrel shape.
Image 5. Higher power magnification, showing eggs with distinctive characteristic bilateral polar plugs and barrel shape.

Discussion

The worm was identified as Trichuris trichiura. The common name for this organism is the whipworm. It belongs to the Nematode classification of parasites, which are commonly referred to as roundworms. Adults measure up to 5 cm in length and have a tapered or whip-like anterior end. The eggs measure 50 x 25 µm, and have brownish thick shells on stool smear. The eggs also have a barrel shape and distinctive protruding polar plugs at each end. These morphologic characteristics of the egg are diagnostic of Trichuris trichiura. The lack of a tissue migration phase and a relative lack of symptoms characterize whipworm infection, with only those with a heavy parasite burden becoming symptomatic. If these symptoms do arise, they are usually mild, ranging from loose stools with minimal blood loss and nocturnal stools, to iron deficiency anemia and vitamin deficiency. As parasite burden increases, however, symptoms can progress to dysentery, colitis, or rectal prolapse. Prolapse is more frequent in the Pediatric population, but has been described in adults as well.

Trichuris trichiura has one of the simplest of the Nematode life cycles. Eggs are unintentionally ingested, hatching in the small intestine by way of exploitation of signaling molecules from the intestinal microbiome. The larvae then burrow through the villi and continue maturing in the wall of the small intestine. They then return to the intestinal lumen, migrating to the cecum and subsequently into the large intestine, where they finish the process of maturation. Finally, the worm uses its anterior end to anchor into the bowel mucosa, where it feeds on tissue secretions and uses its posterior end for reproduction and laying eggs. Female worms can live from 1-5 years and can lay up to 20,000 eggs per day.

Whipworm infection is principally a problem in tropical Asia and, to a lesser degree, in Africa and South America. Children are most commonly infected, and can experience failure to thrive as well as cognitive and developmental defects. Transmission is by the fecal-oral route, explaining the large incidence of infection in children from developing countries, as they are far more likely to be in physical contact with soil and environmental contaminants, with subsequent placement of their fingers in their mouths. The fecal-oral route can also be facilitated by improper washing and cooking of fruits and vegetables, as well as overall poor hygiene, no matter what the geographical location. In the United States, whipworm infection is exceedingly rare. When it does happen, it is most commonly seen in the rural Southeast. Although it is rare, the incidence of infection is reported to be as high as 2.2 million individuals within the United States, with 1-2 billion cases worldwide.

Studies often reveal eosinophilia in nematode infections from ongoing tissue invasion. However, the lack of a tissue migration phase in Trichuris life cycles makes this a rare laboratory finding. Other studies such as anemia can give an indication to the presence of the worm. Characteristic egg morphology on stool smear remains the cheapest and easiest way to diagnose infection, but polymerase chain reaction using new sequencing techniques are now available in some laboratories to detect the presence of Trichuris with great sensitivity and specificity. The parasite burden can be quantified per gram of stool by the Kato-Katz technique. This procedure filters stool through mesh, with the filtered sample being placed within a template on a glass slide. The template is then removed and the remaining fecal material is removed with a piece of cellophane soaked in glycerol, leaving only eggs on the slide.

Discovery of T. trichiura in our patient was an unexpected finding, as our patient had no symptoms.  Asymptomatic detection of T. trichiura has been described in the past, so this finding is not unique. The medication of choice is mebendazole, showing a cure rate of 40-75%. The drug works well by inhibiting glucose uptake from the gastrointestinal tract of the helminth. However, this drug is very expensive, and as a result is difficult to obtain. The patient is currently receiving an alternative drug called albendazole as outpatient therapy and will be switched to mebendazole as soon as resources become available should the need remain. The patient is following up with her primary care physician and is expected to make a full recovery.

References

  1. Donkor, Kwame; Lundberg, Scott;
    https://emedicine.medscape.com/article/788570-overview. Trichuris trichiura (Whipworm) Infection (Trichuriasis).
  2. Sunkara T, Sharma SR, Ofosu A. Trichuris trichiura-An Unwelcome Surprise during Colonoscopy. Am J Trop Med Hyg. 2018 Sep;99(3):555-556. doi: 10.4269/ajtmh.18-0209. PubMed PMID: 30187847; PubMed Central PMCID: PMC6169157.

-Cory Gray, MD is a second year resident in anatomic and clinical pathology at the University of Chicago (NorthShore). His interests include hematopathology and molecular and genetic pathology, as well as medical microbiology.

-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois. Follow Dr. McElvania on twitter @E-McElvania. 

Microbiology Case Study: A 52 Year Old with a Liver Abscess

Clinical history

A 52 year old patient with a history of recent travel to India presented to interventional radiology from an outside hospital for aspiration of a liver abscess, and was subsequently returned to the outside hospital. The patient had spent 2 months in India before returning to the US, and about 1 month later developed right upper quadrant pain. Abdominal CT showed 2 cystic masses measuring 2-4cm. Aspiration of the cysts yielded 0.5mL of bloody fluid, which was sent for bacterial culture and smear. Infectious disease prescribed antimicrobial treatment consisted of ceftriaxone and metronidazole, followed by paromomycin and levofloxacin.

Laboratory findings

A gram smear of the patient’s liver mass aspirate showed few neutrophils and no bacteria. Culture of the aspirate showed no growth at 5 days. Multiple sets of blood cultures collected at the outside hospital all showed no growth at 5 days.

Image 1. Entamoeba coli trophozoite seen in the patient’s stool ova and parasite exam, demonstrating an eccentric karyosome and coarse, irregular peripheral chromatin.

A single ova and parasite exam of the patient’s stool was sent and showed few Entamoeba coli trophozoites. A sample of the patient’s blood was sent to the Mayo reference lab for serum Entamoeba histolytica antibody testing, which came back positive. Stool was sent for Entamoeba histolytica antigen testing which was negative.

Discussion

Entamoeba coli is a non-pathogenic protozoan that can exist as a commensal organism in the human gastrointestinal tract. This organism has not been established to have any disease causing effect per se, but its presence may indicate exposure to water sources that could contain parasitic organisms. (3)

Entamoeba histolytica, by contrast, is a parasitic protozoal pathogen. Most infections are asymptomatic, but they can manifest as amebic dysentery or extraintestinal disease. The most common extraintestinal manifestation is amebic liver abscesses.1

Intestinal amebiasis occurs via ingestion of amebic cysts, typically through contaminated food or water, but also through other forms of fecal-oral contact. Infections are seen most commonly in areas with poor sanitation, but can be found in developed countries in patients who have migrated from or traveled to endemic areas.2

Once the amebic cysts pass into the small intestine, they form trophozoites, which are able to penetrate the mucous barrier of the gut and destroy intestinal epithelial cells. This leads to blood and mucus in the stool. (2) Once the amebae penetrate the gut wall, they are able to reach the blood and ascend through the portal system to the liver and form amebic liver abscesses.3

Clinical presentation of these abscesses typically includes right upper quadrant pain and fever in a patient with a history of travel to an endemic area. Serologic testing is used for confirmation if clinical presentation and imaging are suggestive, but this cannot distinguish between current infection and prior exposure, and up to 35 percent of uninfected inhabitants of endemic areas show positive serology.3 Stool microscopy may be the initial, and indeed only test available in some areas, but cannot differentiate E. histolytica from non-pathogenic E. dispar and E. moshkovskii strains.2

Image 2. E. histolytica trophozoite with ingested red blood cell, visible as a dark inclusion, as well as demonstrating a central karysome and fine, uniformly distributed chromatin. (CDC: https://www.cdc.gov/dpdx/amebiasis/index.html) Erythrophagocytosis is suggestive of E. histolytica.

Empiric treatment in the setting of consistent epidemiology, clinical picture, and radiology consists of metronidazole or tinidazole for tissue clearance followed by paromomycin, diiodohydroxyquin, or diloxanide furoate for intraluminal clearance.

Infectious diseases was taking care of this patient and decided her clinical syndrome is probably extraintestinal Entamoeba histolytica amoebiasis based on the results of the CT findings and the antibody in the right clinical setting.  Although her stool ova and parasite only showed Entamoeba coli, she clearly has been exposed to contaminated food or water.  In addition, the Entamoeba histolytica stool antigen was negative, but this can be an insensitive test.

References

  1. Leder, Karin, and Peter F. Weller. “Extraintestinal Entamoeba histolytica amebiasis.” UpToDate, Wolters Kluwer, 27 Jan. 2020, http://www.uptodate.com/contents/extraintestinal-entamoeba-histolytica-amebiasis?search=entamoeba%20histolyticatreatment&topicRef=5727&source=see_link. Accessed 4 Feb. 2020.  
  2. Leder, Karin, and Peter F. Weller. “Intestinal Entamoeba histolytica amebiasis.” UpToDate, Wolters Kluwer, 27 Jan. 2020, http://www.uptodate.com/contents/intestinal-entamoeba-histolytica-amebiasis?search=entamoeba%20histolyticatreatment&source=search_result&selectedTitle=1~46&usage_type=default&display_rank. Accessed 4 Feb. 2020.
  3. Weller, Peter F. “Nonpathogenic enteric protozoa.” UpToDate, Wolters Kluwer, 25 July 2019, http://www.uptodate.com/contents/nonpathogenic-enteric-protozoa?search=entamoeba%20coli%20treatment&source=search_result&selectedTitle=1~6&usage_type=default&display_rank=1. Accessed 4 Feb. 2020.

-Tom Koster, DO is a 1st year Anatomic and Clinical Pathology Resident at the University of Vermont Medical Center.

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

Microbiology Case Study: A Teenager with an Infected Wound

Case History

A male teenager presented to the emergency department following a 4 wheeler accident. He sustained extensive trauma to his right lower leg with a large, dirty laceration and grossly exposed muscle. His pulses were intact and motor & sensory nerve function were preserved. The wound was irrigated at the bedside and the patient was admitted with a plastic surgery consult for wound coverage. Cefepime was empirically started. After 10 days in the hospital and multiple surgeries to care for the wound, the patient developed a fever and increased pain, erythema, and swelling at surrounding the wound. The trauma service ordered blood and wound cultures.

Laboratory Identification

Image 1. The wound culture grew lavender-green colonies on blood agar (48 hours of incubation in CO2).
Image 2. Clear, lactose-negative colonies on MacConkey agar (48 hours of incubation in CO2).
Image 3. Gram stain from the blood agar plate showed gram negative rods (100x, oil immersion).

The oxidase reaction was negative. MALDI-TOF mass spectrometry identified the isolate as Stenotrophomonas maltophilia from the wound culture. Blood cultures were negative.

Discussion

Stenotrophomonas maltophilia is a common non-fermenting gram negative rod that is ubiquitous in moist environments but is not commonly a member of human flora. S. maltophilia can readily be isolated from hospital surfaces and those with traumatic injuries, prolonged hospitalizations, on mechanical ventilation, and with in-dwelling devices are more susceptible to nosocomial infections by this organism. Those who are immunocompromised or have cystic fibrosis are also at an increased risk.  

In the laboratory, S. maltophilia is characterized as an aerobic, Gram-negative rod that grows as lavender-green colonies on blood agar (Image 1) and has an ammonia-like odor. This organism is catalase and oxidase negative and DNase positive. S. maltophilia is motile and is able to utilize glucose and maltose by oxidative fermentation. Current automated identification systems and MALDI-TOF mass spectrometry are able to accurately identify S. maltophilia.  

S. maltophilia is intrinsically resistant to many broad-spectrum antibiotics, including carbapenems and aminoglycosides. Beta-lactam resistance is due to two beta-lactamases and renders beta-lactam inhibitors ineffective. Trimethoprim-sulfamethoxazole (TMP-SMX) is the antibiotic of choice to treat S. maltophilia infections; however, resistance can develop. In the case TMP-SMX resistance, ceftazidime, minocycline, ticarcillin-clavulanate, ciprofloxacin, and levofloxacin can be tested. 

In the case of our patient, susceptibility testing was performed on the Vitek2 instrument and the isolate was susceptible to TMP-SMX. He was switched to TMP-SMX and underwent additional surgical procedures to wash out the infected area.

-Karla Perrizo, MD, is a Clinical Pathology resident at the University of Mississippi Medical Center.

-Lisa Stempak, MD is the System Director of Clinical Pathology at University Hospitals Cleveland Medical Center in Cleveland, Ohio. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. Her interests include infectious disease histology, process and quality improvement, and resident education.

Microbiology Case Study: A 60 Year Old with Non-Healing Wound

Clinical history

A 60 year old patient with a past medical history of type II diabetes mellitus, right Charcot foot, and cirrhosis presented to the emergency department with altered mental status and several days of subjective fevers, as well as a 2 month history of right lateral malleolar non-healing ulcer which had subacutely increased in size and volume of drainage.

The patient’s spouse reported the wound had been showing purulent discharge for 3 weeks. Nine days before presentation, the patient had seen a foot and ankle specialist for evaluation of his Charcot foot and the ulcer. Radiographs were taken at this time, but no treatment was initiated. Worsening of the wound was associated with an episode of long travel, after which the patient reported being able to see bone.

Infectious disease noted that the patient had a pet corgi.

On exam, the patient was febrile with dry mucous membranes and oriented only to person. MRI showed evidence of possible osteomyelitis. The patient subsequently underwent a right below the knee amputation.

Laboratory findings

Gram smear of a sample taken from the patient’s ankle wound in the emergency department showed many neutrophils, moderate gram positive cocci and moderate gram negative bacilli, with intraleukocytic organisms seen. Growth was observed on blood and chocolate agar plates, but there was no growth on the MacConkey plate. The organisms were identified as few Pasteurella multocida, few vancomycin resistant Enterococcus faecalis, and few usual skin flora.

Image 1. Gram stain of the sample taken from the patient’s ankle wound.

Blood cultures drawn in the emergency department were positive at 10 hours in both bottles, and again on planting showed growth on blood and chocolate agar, but no growth on MacConkey. The organism was identified as P. multocida, consistent with that which grew from the ankle wound culture.

The patient underwent a right below the knee amputation, and anaerobic cultures taken from the right foot again grew P. multocida.

Discussion

Pasteurella multocida is a nonmotile gram negative bacillus which is part of the normal oropharyngeal flora in domestic dogs and cats. It is a facultative anaerobe, positive for oxidase, catalase, and indole. It grows on chocolate and blood agar, forming small, gray, non-hemolytic colonies. It does not typically grow on MacConkey agar.

P. multocida is classically associated with a zoonotic soft tissue infection in humans who suffer bite wounds from a pet, as well as licking of any broken skin by a pet. These infections have a characteristic rapid onset and intense inflammatory response, and can progress to necrotizing fasciitis. Cases of Pasteurella osteomyelitis can be associated with significant wound infections. Conditions such as diabetes, liver dysfunction, and organ transplantation can predispose patients to Pasteurella bacteremia.

Pasteurella spp. are susceptible to beta-lactam antibiotics in most cases, and since Pasteurella wound infections are usually polymicrobial, recommended treatment is broad-spectrum such as amoxicillin-clavulanate. In isolated Pasteurella infections, first line treatment is penicillin, although there are some that favor testing isolates from sterile sites for the presence of beta-lactamase production, and treating those infections with ampicillin-sulbactam, pipercillin-tazobactam, or ceftriaxone. (Weber)

References

  1. Weber, David J., and Sheldon L. Kaplan. “Pasteurella infections.” UpToDate, Wolters Kluwer, 15 June 2018, http://www.uptodate.com/contents/pasteurella-infections?search=pasteurella%20treatment&source=search_result&selectedTitle=1~25&usage_type=default&display_rank=1#H14. Accessed 4 Feb. 2020.

-Tom Koster, DO is a 1st year Anatomic and Clinical Pathology Resident at the University of Vermont Medical Center.

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

Microbiology Case study: A 42 Year Old Male with Bacteremia

Case History

A 42 year old male with past medical history of diabetes mellitus and essential hypertension presented to the emergency department with high fever and chills which developed two days prior. His examination revealed a painful ulcer on the planter aspect of his right toe with surrounding erythema. According to patient, the exact duration of the ulcer is unclear as it was on planter aspect of his foot and he does not inspect his feet regularly. However, the ulcer grew in size and symptoms over the past week. He denies any cough, diarrhea or abdominal pain. He is on oral anti-diabetics with well-controlled blood sugar. Complete blood count revealed leukocytosis. Blood was collected and sent to microbiology laboratory for gram stain and culture.

Laboratory identification

Cultures signaled positive after 32 hours of incubation and gram negative rods were identified on Gram stain (Image 1). The organism grew after 24 hours of incubation on 5% sheep blood, chocolate, and MacConkey agars (Images 2 & 3). MALDI-TOF mass spectrometry identified the isolate as Salmonella spp. The isolate was sent to the public health department for additional testing by molecular typing where it was identified as Salmonella enterica subsp. enterica serovar Brandenburg (Salmonella Brandenburg). Later, MRI revealed osteomyelitis of right third toe which was considered as the likely source of patient’s bacteremia.

Image 1. Gram stain of positive blood culture broth showing gram negative rods
Image 2. Non-lactose fermenting colonies growing on MacConkey agar
Image 3. Colonies producing hydrogen sulfide making them appear black on Hektoen enteric agar

Discussion

Salmonella is a genus of the family Enterobacteriaceae in the order Enterobacterales. They are non-spore forming gram negative facultative anaerobes. Salmonella spp. are lactose non-fermenters and usually produce H2S on triple sugar iron and Hektoen enteric agar.

The genus has only two species: Salmonella enterica, divided into 6 subspecies and containing over 2500 serovars, and Salmonella bongori. Subspecies and serotype determination is necessary for epidemiological investigations. Serotyping is used to classify Salmonella based on bacterial surface antigens; the thermostable polysaccharide cell wall or somatic (“O”) antigens and the thermo-labile flagella proteins or “H” antigens. It is also possible to identify Salmonella serotypes on the basis of phage typing, plasmid profiling, ribotyping and pulsed field gel electrophoresis (PFGE) of DNA fragments generated from restriction enzyme digestion.

Salmonella are zoonotic bacteria that can cause abortion, metritis, and systemic illness in ewes and does. Natural reservoirs of Salmonella are domestic and wild animals, including poultry, swine, cattle, birds, dogs, rodents, tortoises, turtles and cats. Humans also serve as a natural host. The most common source of transmission of Salmonella is the consumption of contaminated poultry and meat products. Person-to-person, fecal–oral transmission does occur and has been a problem in health care facilities traced to inadequate hand washing.

Salmonella brandenburg ranked 16th among the serovars responsible for human infections. It causes acute diarrhea and severe illness in a variety of animals and was first isolated in New Zealand in 1986. Since 1996 Salmonella Brandenburg has been associated with an emerging epidemic of abortions and deaths in sheep in the southern regions of the South Island. Subsequently, the same strain was reported to cause disease in horses, goats, deer, pigs and humans. The disease is known to have high morbidity and mortality within a flock or herd, rapid local spread and an occupational, health and safety risk to farm workers and their families.

There are three clinically distinguishable forms of salmonellosis in humans. These include gastroenteritis, enteric fever and septicemia. Established Salmonella bacteremia requires aggressive antimicrobial treatment with ciprofloxacin, ceftriaxone, or less frequently trimethoprim-sulfamethoxazole. A careful search for focal metastatic disease should be undertaken, especially when relapse follows cessation of treatment. Surgical drainage of metastatic abscesses may be required, with surgical intervention. Resistance to any of the drugs used to treat invasive infection may occur, so treatment should be supported by susceptibility testing.

In the case of our patient, he was treated with ceftriaxone and underwent toe amputation. The patient had an uncomplicated hospital course and made a complete recovery.

References[EMT1] 

  1. Alvseike O., Skjerve E. (2000). Probability of detection of Salmonella using different analytical procedures, with emphasis on subspecies diarizonae serovar 61:k:1,5,(7) [S. IIIb 61:k:1,5,(7)]. International Journal of Food Microbiology, 58, 49-58.
  2. Clark G, Swanney S, Nicol C, and and Fenwick S. Salmonella Brandenburg – the 1999 Season. Proceedings of the Sheep and Beef Cattle Society of the New Zealand Veterinary Association, 151-156, 2000
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  4. Baumler A.J., Tsolis R.M., Heffron F. (2000). Virulence Mechanisms of Salmonella and their Genetic Basis. In “Salmonella in Domestic Animals” (Ed. C. Wray and A. Wray). CAB International 2000, pp. 57-72

-Ansa Mehreen, MD. 1st year AP/CP resident at University of Chicago hospital program based at Evanston Hospital. Her academic interests include gastrointestinal pathology.

-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois. Follow Dr. McElvania on twitter @E-McElvania.