bs_bs_banner

Environmental Microbiology (2014) 16(5), 1222–1224

doi:10.1111/1462-2920.12384

Correspondence Colonization of Cimex lectularius with Methicillin-resistant Staphylococcus aureus

Alexis M. Barbarin,1* Baofeng Hu,2 Irving Nachamkin3 and Michael Z. Levy1** Departments of 1Biostatistics & Epidemiology and 3 Pathology and Laboratory Medicine and 2 Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA. Summary A recent paper published by Lowe and Romney in Emerging Infectious Diseases titled, Bed bugs as Vectors for Drug-Resistant Bacteria has sparked a renewed interest in bed bug vector potential. We followed a pyrethroid resistant strain of the human bed bug (Cimex lectularius, L.) fed either human blood or human blood with added methicillin resistant Staphylococcus aureus (MRSA) for 9 days post-feeding. Results indicated that while the bed bug midgut is a hospitable environment for MRSA, the bacteria does not survive longer than 9 days within the midgut. Additionally, MRSA is not amplified within the midgut of the bug as the infection was cleared within 9 days. Due to the weekly feeding behaviours of bed bugs, these results suggest that bed bug transmission of MRSA is highly unlikely.

Cimex lectularius, the common bed bug, has made a global resurgence over the past two decades. After being nearly eradicated in the 1950s due to the widespread use of carbamates, organophosphates and dichlorodiphenyltrichloroethane (DDT), regulatory restrictions on these insecticides have spurred the concurrent return of these pests in Australia, Europe and the Americas since the late 1990s (Davies et al., 2012). As bed bug infestations continue to rise worldwide, so does fear that they may carry pathogens. To date, no report has demonReceived 4 October, 2013; accepted 31 December, 2013. For correspondence. *E-mail [email protected]; Tel. (+919) 515 1820; Fax (+919) 515 7746. **E-mail [email protected]; Tel. (+215) 746 8131; Fax (+215) 573 6262.

© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd

strated conclusively that they are in fact an infectious disease vector. Prior to the mid-1990s, MRSA infections were confined to health-care facilities, hospitals and their patients. Since then, the number of Methicillin-resistant Staphylococcus aureus (MRSA) infections in populations with no exposure to health-care systems has risen exponentially (David and Daum, 2010). This increase has been closely linked to the recognition of new MRSA strains, often termed community-associated MRSA (CA-MRSA) strain (David and Daum, 2010). A recent report published in Emerging Infectious Diseases suggests bed bugs could be vectors of MRSA (Lowe and Romney, 2011). The report could not discern whether the bed bugs were harbouring the bacteria internally, or simply carrying it on their cuticle. We therefore performed an experiment to determine whether bed bugs are able to harbour MRSA in their midgut, and if so, for how long. The study Bed bugs used in this study were derived from the ECL-05 ‘field’ colony collected from six commercial properties located in Florida, Minnesota, New Jersey and Wisconsin in 2005 (Olson et al., 2009). Adult bed bugs of both sexes were randomly selected from the main colony and placed into control or treatment groups (n = 40). Both groups were starved for ∼14 days prior to experimentation. The control group was fed 18 ml whole human blood mixed (obtained from Division of Transfusion Medicine at our institution) with 180 μl saline solution using an artificial feeder (Montes et al., 2002). The treatment group was fed 18 ml whole human blood containing 180 μl saline solution containing a 106 CFU ml−1 concentration of Methicillin-resistant S. aureus (ATCC 43300). Both groups were allowed to feed for 12 h to ensure adequate access to blood. Five bed bugs of each treatment were dissected at day one, three, five, seven and nine post blood feeding. Gut contents were directly plated onto CHROMAgar MRSA (Becton Dickinson, Sparks, Maryland, USA) plates. Sample inoculated plates were then incubated at 37°C for 48 h. Following incubation, colony growth was scored using the semi-quantitative +1 to +4

Colonization of C. lectularius with MRSA

Fig. 1. A. Daily distribution of MRSA recovered from bed bugs following day zero feeding. Colony growth was scored using the semi-quantitative +1 to +4 scoring method, indicating the quadrant of colony growth.

scoring method; +1 corresponded to limited bacterial growth restricted to the first quadrant and 4+ corresponded to heavier growth over the majority of the plate, extending into the fourth quadrant. The remaining blood in the artificial feeders was plated onto CHROMAgar MRSA plates as a control for potential contamination of materials. The experiment was replicated three times. Methicillin-resistant Staphylococcus aureus was recovered from bed bugs in all trials, though the duration of bacterial recovery varied from 1 to 7 days following feeding (Fig. 1A). The quantity of organisms generally declined over time, suggesting that the bacteria was not replicating significantly within the insect. We fit the trend in our data using a Poisson regression, along with 95% confidence intervals, which also revealed a significant decrease in bacteremia levels in our successive measures (Fig. 1B).

1223

pierces the abdominal wall of the female to inseminate directly into her body cavity, despite the presence of a functional female genital tract (Siva-Jothy, 2006). The female paragenital tract is abundant with hemocytes (Usinger, 1966), which serve as a major component in the removal of microbes. It is possible that hemocytes are also playing a role in the removal of MRSA and other microbes, further hindering the vector potential of bed bugs. Our study had a number of limitations. Bacteremia levels in the bed bug were not individually quantified. We used only a semi-quantitative measure of bacterial abundance, and the variation inherent in the processing of the insects and plating of the bacteria likely contributed to the high variation between our replicate experiments. Additionally, the presence of MRSA in the treatment group was not determined on a daily basis. Daily monitoring of MRSA presence in the bed bug midgut would provide a more precise estimate of when MRSA is evacuated from the bed bug. Examination of faecal material may help to illustrate MRSA survival following ingestion and digestion by bed bugs. We did swab the bed bug rearing jars for the presence of MRSA on the jar surface; none was ever recovered. The first step to demonstrating the casual relationship between any vector and disease is establishing vector competence. Laboratory experiments must demonstrate the vector’s ability to acquire a pathogen from another animal or infected blood, to maintain or amplify the pathogen and then to transmit it to another animal (Klempner et al., 2007). While we did illustrate that bed bugs can acquire MRSA from infected blood, results suggest that bed bugs do not amplify MRSA within the midgut. Our findings suggest that bed bugs are unlikely to be important in the active transmission of MRSA.

Conclusions Our findings suggest that the midgut of bed bugs is a hospitable environment for MRSA. However, the survival time of the bacteria in bed bugs is relatively short, and less than survival times reported on a variety of fomites (Huang et al., 2006; Desai et al., 2009). Bed bug feeding cycles average every 7 days in laboratory populations (Usinger, 1966; Siva-Jothy, 2006) and weekly in naturally infested rat cages (Mellanby, 1939). Our results indicate that, according to the natural feeding pattern of bed bugs, any MRSA acquired via feeding on infected blood would most likely be evacuated prior to the next feeding. Additionally, immunological responses to microbes in bed bugs are not uncommon. Bed bugs mate via traumatic insemination, in which the males’ intromittent organ

Fig. 1. B. Poisson regression and 95% confidence intervals (indicated by dashed lines) of daily distribution of MRSA recovered from bed bugs following day zero feeding.

© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology, 16, 1222–1224

1224 A. M. Barbarin, B. Hu, I. Nachamkin and M. Z. Levy Acknowledgements Funding for this study was provided by a grant from the University Research Foundation of the University of Pennsylvania.

References David, M.Z., and Daum, R.S. (2010) Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic. Clin Microbiol Rev 23: 616–687. Davies, T.G., Field, E.L.M., and Williamson, M.S. (2012) The re-emergence of the bed bug as a nuisance pest: implications of resistance to the pyrethroid insecticides. Med Vet Entomol 26: 241–254. Desai, R., Pannaraj, P.S., Agopian, J., Sugar, C.A., and Liu, G.Y. (2009) Survival and transmission of community associated methicillin-resistant Staphylococcus aureus from fomites. Am J Infect Control 39: 219–225. Huang, R., Mehta, S., Weed, D., and Price, C.S. (2006) Methicillin-resistant Staphylococcus aureus survival on hospital fomites. Infect Control Hosp Epidemiol 27: 1267– 1269.

Klempner, M.S., Unnasch, T.R., and Hu, L.T. (2007) Taking a bite out of vector-transmitted infectious diseases. NEJM 356: 2567–2569. Lowe, C.F., and Romney, M.G. (2011) Bedbugs as vectors for drug-resistant bacteria. Emerg Infect Dis 17: 1132– 1134. Mellanby, K. (1939) The physiology and activity of the bedbug (Cimex lectularius L.) in a natural infestation. Parasitology 31: 200–211. Montes, C., Cuadrillero, C., and Vilella, D. (2002) Maintenance of a laboratory colony of Cimex lectularius (Hemiptera: Cimicidae) using an artificial feeding technique. J Med Entomol 39: 675–679. Olson, J.F., Moon, R.D., and Kells, S.A. (2009) Off-host aggregation behavior and sensory basis of arrestment by Cimex lectularius (Heteroptera: Cimicidae). J Insect Physiol 55: 580–587. Siva-Jothy, M.T. (2006) Trauma, disease and collateral damage: conflict in cimicids. Philos Trans R Soc Lond B 361: 269–275. Usinger, R. (1966) Monograph of Cimicidae (Hemiptera, Heteroptera). College Park, MD, USA: Entomological Society of America. 585 pp.

© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd, Environmental Microbiology, 16, 1222–1224

Colonization of Cimex lectularius with methicillin-resistant Staphylococcus aureus.

A recent paper published by Lowe and Romney in Emerging Infectious Diseases titled, Bed bugs as Vectors for Drug-Resistant Bacteria has sparked a rene...
158KB Sizes 1 Downloads 3 Views