Bacterial cultures and chemical analyses were performed from cloacal and oral swabs taken from 43 American crocodiles Crocodylus acutus and 28 Morelet's crocodiles C. moreletii captured in Quintana Roo State, Mexico. We recovered 47 bacterial species (28 genera and 14 families) from all samples with 51.1% of these belonging to the family Enterobacteriaceae. Fourteen species (29.8%) were detected in both crocodile species and 18 (38.3%) and 15 (31.9%) species were only detected in American and Morelet's crocodiles, respectively. We recovered 35 bacterial species from all oral samples, of which 9 (25.8%) were detected in both crocodile species. From all cloacal samples, we recovered 21 bacterial species, of which 8 (38.1%) were detected in both crocodile species. The most commonly isolated bacteria in cloacal samples were Aeromonas hydrophila and Escherichia coli, whereas in oral samples the most common bacteria were A. hydrophila and Arcanobacterium pyogenes. The bacteria isolated represent a potential threat to crocodile health during conditions of stress and a threat to human health through crocodile bites, crocodile meat consumption or carrying out activities in crocodile habitat. We especially warn about the presence of Salmonella arizonae and S. typhi, which cause enteritis and septicemia in crocodiles and salmonellosis and typhoid fever in humans. The risk of bacterial contamination from crocodiles to humans could increase in the future because of the accelerated destruction of crocodile habitat, which could lead to an augmentation of human−crocodile interactions. Information on bacterial diversity reported here could help in the choice of antibacterial products in case of infections that are of crocodile origin.KEY WORDS: Bacterial flora · Crocodylus acutus · Crocodylus moreletii · Salmonella · Cozumel · Río Hondo · Banco Chinchorro · Mexico Resale or republication not permitted without written consent of the publisherDis Aquat Org 98: [27][28][29][30][31][32][33][34][35][36][37][38][39] 2012 Besides the physical damage, survivors of attacks from crocodilians can develop wound infections caused by bacteria or fungi (Flandry et al. 1989, Caldicott et al. 2005, Wamisho et al. 2009, Langley 2010. Several studies display the existence of many bacteria and fungi in the oral cavity of wild and captive crocodilians (Doering et al. 1971, Gorden et al. 1979, Flandry et al. 1989, Matushima & Ramos 1995, Anderson 1999, Cupul-Magaña et al. 2005, Silva et al. 2009). While several antibiotics provide protection from wound infections, in some cases patients can die from sepsis (Vanwersch 1998, Caldicott et al. 2005. Crocodilians show great resistance and healing capacity to injuries and illness, but several studies report diseases or symptoms in crocodilians related to bacterial infections, which can even lead to the death of individuals (Shotts et al. 1972, Novak & Seigel 1986, Hernández-Hurtado & Cupul-Magaña 1996, Mehrotra et al. 2000, Huchzermeyer 2003, Bishop et al. 2007, Garcia et al. 2008.The Quintan...