Non-O1/non-O139 Vibrio cholerae carrying multiple virulence factors and V. cholerae O1 in the Chesapeake Bay, Maryland

Abstract

Non-O1/non-O139 Vibrio cholerae inhabits estuarine and coastal waters globally, but its clinical significance has not been sufficiently investigated, despite the fact that it has been associated with septicemia and gastroenteritis. The emergence of virulent non-O1/non-O139 V. cholerae is consistent with the recognition of new pathogenic variants worldwide. Oyster, sediment, and water samples were collected during a vibrio surveillance program carried out from 2009 to 2012 in the Chesapeake Bay, Maryland. V. cholerae O1 was detected by a direct fluorescent-antibody (DFA) assay but was not successfully cultured, whereas 395 isolates of non-O1/non-O139 V. cholerae were confirmed by multiplex PCR and serology. Only a few of the non-O1/non-O139 V. cholerae isolates were resistant to ampicillin and/or penicillin. Most of the isolates were sensitive to all antibiotics tested, and 77 to 90% carried the El Tor variant hemolysin gene hlyAET, the actin cross-linking repeats in toxin gene rtxA, the hemagglutinin protease gene hap, and the type 6 secretion system. About 19 to 21% of the isolates carried the neuraminidase-encoding gene nanH and/or the heat-stable toxin (NAG-ST), and only 5% contained a type 3 secretion system. None of the non-O1/non-O139 V. cholerae isolates contained Vibrio pathogenicity island-associated genes. However, ctxA, ace, or zot was present in nine isolates. Fifty-five different genotypes showed up to 12 virulence factors, independent of the source of isolation, and represent the first report of both antibiotic susceptibility and virulence associated with non-O1/non-O139 V. cholerae from the Chesapeake Bay. Since these results confirm the presence of potentially pathogenic non-O1/non-O139 V. cholerae, monitoring for total V. cholerae, regardless of serotype, should be done within the context of public health.

FIG 1

Isolation of V. cholerae by enrichment over the course of the 43-month study in the Chester River (top) and Tangier Sound (bottom). Shown are water temperatures in degrees Celsius (right y axis) and V. cholerae detection (left y axis) in sediment (S), oysters (O), the plankton fraction (P), water (W), and plankton-free water (PFW).

FIG 2

Percentages of antibiotic-resistant environmental non-O1/non-O139V. cholerae isolates. R, resistant; I, intermediate; S, sensitive; AM, ampicillin; CIP, ciprofloxacin; C, chloramphenicol; E, erythromycin; K, kanamycin; NA, nalidixic acid; P, penicillin; SPT, spectinomycin; S, streptomycin; SXT, sulfamethoxazole-trimethoprim; T, tetracycline.