Letter to the Editor

Unusual Cytopathic Effect in Tissue C u l t u r e

To the Editors: We recently observed an unusual

pattern of cytopathic effect (CPE) in a rabbit kidney (RK) cell culture inocu- lated with a genital specimen. RK and human diploid fibroblast (MAC-5) cell cultures are used in our laboratory to isolate herpes simplex virus (HSVL One particular RK cell culture, which had been inoculated with a vaginal specimen, developed suspicious cel- lular alterations that initially might have been confused with HSV-induced CPE. The cell monolayer showed clumping and rounding, an appearance indicative of HSV infection. An alter- native cause of the CPE (as opposed to HSV-induced) was suspected, how- ever, when the virologist noted a number of actively motile cells. The presence of Trichomonas vaginalis was confirmed by observing typical mo- tility and morphology of the flagellates in a wet-mount preparation as well as by darkfield examination.

Growth and induction of cytolytic changes in cell culture by T. vaghlalis were demonstrated 40 years ago (2). In vitro studies with RK epithelial cells have shown that T. vaghzalis in- fection proceeds in three stages: I) The flagellates rosette and swarm to yield aggregates of up to 200 cells. 2)

A firm and stationary attachment to the host-cell monolayer follows. Mo- tility of the flagellates is restricted to internal movement. 3) Visible cell in- jury occurs subsequently, as the para- sites cause lesions in the monolayer by cytolysis. Pathogenicity appears to de- pend on close contact between the par- asite and its host epithelial cell (1).

The in vitro studies of the action of T. vaginalis on RK epithelial cells pro- vide important information for virolo- gists. Rosetting, adherence, and le- sion formation on RK cells by T. va- ginalis can be confused with viral- induced CPE. The development of a large clump of rounded cells, which results from trichomonads rosetting and adhering, may resemble CPE caused by HSV. Additionally, the de- velopment of lesions in the RK mono- layer by T. vaghtalis' cytolytic activity can mimic the initial stages of HSV- induced CPE. A particularly con- fusing occurrence is the swelling of host cells in the initial stages of cyto- lysis as the trichomonads cause in- creased cell membrane permeability (1). The swollen cells may be easily confused with HSV-induced giant cells.

Differentiation between cytopathic effect and the presence of tricho- monads can be achieved by closer ob- servation of rounded cells in the main- tenance media. Motility is a hallmark

of the parasites, but during interme- diate phases of parasitism, the or- ganism may lack active progressive motion. To facilitate the observation of questionable cells, a wet-mount preparation or darkfield examination may be performed.

Because coinfection with herpes simplex virus and T. vaginalis occurs in some patients (2, 3), in cases where a dual infection is suspected or the in- oculated carrier medium is turbid, specimens may be filtered prior to cell culture inoculation.

References 1. Heath, J. P. 1980. Behavior and

pathogenicity of Trichomonas vaginalis in epithelial cell cultures: a study by light and scanning electron micros- copy. Br. J. Vener. Dis. 57:106-117.

2. Hogue, N. J. 1943. The effect of Tri- chomonas vaginalis on tissue culture cells. Am. J. Hyg. 37:142-152.

3. Spence, N. R. et al. 1980. The clin- ical and laboratory diagnosis of Tri- chomonas vaghzalis infection. Sex. Transm. Dis. 7:168-171.

Susan Rogers, M.T. (ASCP) Microbiology Division St. Francis Hospital and Medical Center Hartford, Connecticut 06105

Dale W. Vance, Jr., Ph.D. Bureau of Disease Control and Laboratory Services Michigan Department of Public Health Houghton, Michigan 44931

Workshops and Meetings

Eastern Pennsylvania Branch of the American Society for Microbiology: "Community and Hospital Acquired Respiratory Infections". Thomas Jefferson University, Philadel- phia, Pennsylvania. February 2, 1985. Contact: Dr. Irving Nachamkin, De- partment of Pathology and Laboratory of Medicine, 3400 Spruce Street/Gl,

University of Pennsylvania, Philadel- phia, Pennsylvania 19104 or 215-662- 6651.

Annual Meeting of the Northeast As- sociation for Clinical Microbiology and Infectious Disease. Radisson Femcroft Hotel, Danvers, Massachusetts.

May 15, 16, and 17, 1985. Contact: Mary Keville, Microbiology Laboratory, University of Massachu- setts Medical Center, 55 Lake Avenue North, Worcester, Massachusetts 06105.

Clinical Microbiology Newsletter 7:1, 1985 © 1985 Elsevier Science Publishing Co., Inc. 0196-4390,'85:50.00 + 02.20

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