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Vibrio vulnificus: an unusual mode of acquisition and novel use of rapid susceptibility testing
  1. D G Partridge,
  2. R Townsend,
  3. S Larkin,
  4. H K Parsons
  1. Department of Microbiology, Sheffield Teaching Hospitals NHS Trust, Northern General Hospital, Sheffield, UK
  1. David G Partridge, Department of Microbiology, Sheffield Teaching Hospitals NHS Trust, Northern General Hospital, Herries Road, Sheffield S5 7AU, UK; david.partridge{at}sth.nhs.uk

Abstract

Infection with Vibrio vulnificus is uncommon in Europe but is associated with necrotising wound infections and life-threatening septicaemia. This case is one of infection most likely to have been acquired from a thermal pool in Turkey without preceding exposure to seawater or shellfish. The report also describes how early management was optimised using gradient diffusion antibiotic strips to provide rapid susceptibility data.

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CASE REPORT

In September 2007, a 66-year-old man presented with a 1 day history of fever and rigors in association with a painful, swollen and erythematous left leg. The erythema surrounded a puncture wound, thought to have been caused by an insect bite sustained 1 week earlier in the Mediterranean resort of Marmaris, Turkey. The presumed bite occurred while the patient was asleep in his hotel bedroom and, despite being rather large, it was otherwise unremarkable until the presenting symptoms developed. The patient returned to the UK 4 days prior to his presentation and had no history of chronic liver disease, diabetes or immunosuppression.

Despite intravenous flucloxacillin 2 g and benzylpenicillin 1.2 g four times daily, necrotic bullae rapidly appeared and the patient became increasingly septic requiring admission to the intensive care unit and inotropic support. The spectrum of antimicrobial therapy was broadened, changing to a combination of piperacillin–tazobactam 4.5 g three times daily and clindamycin 600 mg four times daily, and, with a suspicion of necrotising fasciitis, the patient proceeded to urgent debridement of the left leg.

Gram-negative bacilli grew in both bottles of blood cultures taken at admission after 4 h incubation, with similar organisms found on Gram stain of operative samples. As part of an ongoing evaluation, rapid sensitivity testing of the blood culture isolate was performed using Etests (AB Biodisk, Solna, Sweden) directly applied to a chromogenic Mueller–Hinton agar (Reactivos para Diagnostica, Barcelona, Spain) inoculated with seven drops from the positive aerobic bottle and incubated in 5% CO2 at 37°C. Etest strips testing susceptibility to cefoxitin, ceftazidime, cefotaxime, piperacillin–tazobactam, meropenem and vancomycin were used. Minimum inhibitory concentrations (MICs) were initially interpreted at 4 h and ellipses of inhibition at this point indicated a cefoxitin MIC of 12 mg/l, implying resistance. MICs to the other four agents active against Gram-negative organisms lay well within the susceptible range. Growth at 20 h is shown in fig 1. The isolated cefoxitin resistance suggested the possibility of an inducible AmpC-type β-lactamase and supported a change in therapy from piperacillin–tazobactam 4.5 g three times daily to meropenem 1 g three times daily.

Figure 1

Direct Etest of contents of positive aerobic blood culture bottle after 18 h incubation on chromogenic Mueller–Hinton agar. Minimum inhibitory concentrations were interpretable at 4 h, though growth would have been insufficient to photograph. Etest strips used clockwise from top were: vancomycin, cefoxitin, cefotaxime, ceftazidime, piperacillin–tazobactam and meropenem.

The 4 h sensitivities predicted by the Etest method were confirmed by standard breakpoint methods at 24 h, with resistance to cefotetan 4 μg/ml and aztreonam 1 μg/ml but in vitro sensitivity to cefotaxime 1 μg/ml, ceftazidime 2 μg/ml and meropenem 4 μg/ml. At this stage, the organism was also growing on standard media, producing creamy-grey colonies on blood agar; these colonies were oxidase, indole and orthonitrophenyl-d-galactopyranoside positive. The severity of the illness in combination with colonial morphology and biochemical profile suggested the possibility of Vibrio vulnificus infection, which was subsequently confirmed by API 20E (BioMérieux, Marcy l’Etoile, France) and the Division of Enteric Pathogens, Health Protection Agency, Colindale, London, UK.

Following identification of the organism, further enquiry focused upon route of acquisition. The patient had no exposure to seawater during the trip and ate fried white fish and chips once at the beginning of his holiday, but had consumed no shellfish and handled no raw fish at any stage. Interestingly, on the day following the presumed bite, the gentleman visited a thermal area at Dalyan and bathed in the volcanic mud.

Despite appropriate antibiotic cover and early surgical debridement, the patient remained septic and examination of the leg on the second hospital day revealed further necrosis requiring above knee amputation. Meropenem 1 g three times daily was continued for a further 4 days, at which stage it was replaced by oral doxycycline 100 mg twice daily (to which the isolate was also susceptible), completing a 14 day course. The patient was discharged home 3 weeks later and remains well.

DISCUSSION

V vulnificus is a well recognised but uncommon cause of gastroenteritis, septicaemia, wound infection and necrotising fasciitis. The organism grows optimally in warm water of moderate salinity and is readily isolated from temperate coastal waters or from the shellfish that inhabit the waters. Human infection usually occurs following ingestion of raw shellfish or through skin wounds exposed to contaminated seawater. Individuals with haemochromatosis or other liver diseases, diabetes mellitus, chronic renal failure or depressed immunity are at particular risk, though a large proportion of those with wound infections have no identified co-morbidity.1 Warm water temperatures and the popularity of raw seafood result in incidence being greatest in East Asia, but V vulnificus is also the leading cause of seafood-related deaths in the USA, and infections with the organism have been reported in South America, Australasia and European countries including Germany, Denmark and Sweden.1 There have been relatively few reports of infections acquired in Mediterranean areas despite the warm water temperatures, and it may be that this is related to the high salinity of seawater in the region.2 A few cases have been reported in Spain,2 and the organism can be isolated from mussels harvested off the coast of France3 and Italy.4 It is possible that the incidence of infection with Vvulnificus in Europe will increase due to the effects of global climate change,5 a suggestion supported by outbreaks associated with previous warm summers.6

The patient described is unusual in having neither eaten nor handled uncooked seafood and reporting no exposure to seawater. The most likely route of acquisition is contamination of his wound by bacteria residing in the volcanic spring. A previous case of V Vulnificus wound infection following exposure to brackish water and seawater in Dalyan has been reported7 but specific mention of volcanic pools was not made. In 2001, however, two patients were infected with V vulnificus after recreational exposure to a thermal pool in Puna, Hawaii.8

Early and appropriate antibiotic and surgical therapy are essential in the management of infection caused by V vulnificus.9 In this case, the rapid sensitivities provided by performing Etests on a plate inoculated directly from the positive blood culture bottle supported a broadening in the spectrum of antimicrobial therapy. Use of Etests for rapid testing in this manner is possible because of the rapidity with which the antibiotic gradient is adsorbed onto the agar and the relative inoculum independence of the method.10 With the development of increasing resistance in Gram-negative organisms, the desirability of such rapid susceptibility data is only likely to increase. Selection of an appropriate antibiotic with a low MIC is particularly important in severe wound infections due to V vulnificus as there is typically impaired tissue perfusion and a consequent reduction in local concentrations of antimicrobials. Although a survey of 210 environmental isolates of V vulnificus in Korea found over 30% to be cefoxitin resistant,11 studies of 151 isolates from raw oysters in the USA and over 40 clinical isolates from Taiwan demonstrated almost universal susceptibility to ampicillin, third-generation cephalosporins, aminoglycosides, tetracyclines and quinolones.12 13 The origin and mechanism of resistance to cefoxitin and cefotetan in our isolate has not been defined but previous studies have demonstrated that plasmid carriage is relatively uncommon in V vulnificus6 and bears little relationship to antibiotic susceptibility patterns. A recent review of 1210 non-foodborne Vibrio infections in the USA, in which Vvulnificus was the most frequently isolated species, suggested that tetracyclines, third-generation cephalosporins or quinolones represented most appropriate initial therapy and that administration of these agents within 24 h of admission was associated with a trend towards reduced mortality.9

Take-home messages

  • Vibrio vulnificus should be considered early as a cause of wound infection in those with a history of shellfish or seawater exposure.

  • The organism may be more common in European waters than previously thought.

  • Infection may result from exposure to volcanic thermal pools and those at particular risk of disease (immunocompromise, liver disease) should be advised not to bathe in these pools.

  • Rapid susceptibility testing of blood culture isolates permits early optimisation of antimicrobial therapy.

Despite its unusual features, this case demonstrates the importance of obtaining a full exposure history in guiding the management of skin and soft tissue infections. Although Vvulnificus wound infections usually present within 48 h, this case demonstrates the importance of its consideration in cases of soft tissue infection in all returning travellers who have a history of exposure to seawater or shellfish, and incubation periods of up to 12 days have been reported.1

With further evidence of a possible association between infection with the organism and exposure to volcanic pools, recommendations suggesting that individuals with liver disease, iron storage disorders, immunocompromise or broken skin avoid these environments may be appropriate.

REFERENCES

Footnotes

  • Funding: The Media and Etest gradient diffusion strips were provided by Inverness Medical UK as part of an ongoing evaluation but the company had no role in the decision to publish this case or in the writing of the manuscript.

  • Competing interests: Dr Robert Townsend has received an honorarium for providing a lecture on behalf of AB Biodisk.

  • Patient consent: Obtained.