Marathon Veterinary Hospital, Medicine, Surgery and Wildlife, Marathon, FL, USA
It has been well established that the majority of bacterial pathogens affecting reptile patients are of the gram-negative type. However, proper isolation of the pathogens and evaluation of the resulting laboratory data can often times be somewhat confusing. The practice of treating all gram-negative isolates is no longer acceptable as it is now realized that many reptiles harbor gram negatives as part of their normal flora, and are either commensals or opportunists.
The decision to treat or not to treat depends on many factors. The source of the isolate, the type of animal patient, its physical or clinical condition, the pharmaceuticals available, owner compliance, experience of the clinician, and of course, the isolate itself.
Proper sample collection for bacterial culture and sensitivity data is a critical step in initiating appropriate clinical care. It is often the practice to collect bacterial culture samples, and then while waiting for the results, start the patient on an empirically selected antibiotic. This practice is wise as it gives the clinician a head start in treatment while waiting for results. Improperly collected samples will offer little information towards tailoring antibiotic therapy.
An old, but still performed practice, is to collect a combo culture from the oral cavity and cloaca in a sick animal as a screening tool. While this may be easy, it does not always give very specific information regarding bacterial pathogens. The oral cavity contains a garbage can of bacteria from the environment. Although the actual pathogen might be included in the culture sample, it is often dwarfed by a myriad of other microorganisms. A similar problem is encountered when randomly culturing the cloacal region.
Site-specific bacterial sampling is preferable to random sampling. Snakes presenting with infectious stomatitis, or mouth rot, will benefit from appropriate antimicrobial therapy based on proper bacterial isolation. However, as mentioned, a sample collected by swabbing a culturette over the affected gingiva will usually yield a mixed-bag of oral cavity and environmental flora. Some sort of gram-negative isolate is almost always found, but its significance is nebulous at best.
A better technique would be to prep the area with alcohol, make a small stab incision through the infected area with #11 scalpel blade, and then using a micro-culturette swab, sample the affected tissue from within the incision. An isolate here will have far greater clinical significance.
Cloacal cultures can be used in patients with diarrhea or other gastrointestinal disturbances. Proper diagnostics and rule-outs should be executed prior to the testing. Fecals for ova and parasites, including protozoal pathogens, is a must. Interpretation of the culture results can be confusing since many different bacterial are normally present. However, certain isolates should be cause for immediate concern. These will be discussed later in the manuscript.
Patients displaying respiratory signs should be cultured. Again, random culturing of the saliva or tracheal exudate within the mouth will be non-diagnostic. If time and cost restraints are imposed, a preferable sampling site would be high within the choanal slit. Since, anatomically, this is the area where the glottis opens, you are more likely to identify a real pathogen. An even better technique would be to perform a tracheal wash. An appropriately sized sterile, red-rubber catheter is inserted transglottally and directed into the lung region. Sterile saline (approximately one percent of the animal›s body weight) is infused through the catheter. The patient is then gently invert ed, rolled side to side, or in some way rocked to allow mixing and washing of the saline within the lung. After this, as much fluid as possible is withdrawn. It is not uncommon to only get back a small portion of the infused saline. Do not let this alarm you. Any remaining fluid will be readily absorbed through the lungs.
Occasionally, in cases of severe pneumonia, quantities greater than the amount infused will be retrieved. The fluid collected can now be used for both cytology and bacterial culture and sensitivity testing.
Open abscesses should be debrided and the cultures taken from deep within the lesion. Closed abscesses can be sampled by aspirating material using sterile techniques. Cystic and vesicular fluid can cultured in a similar fashion.
Cultures can be taken from body fluids such as blood and urine using standard techniques. Properly collected samples, either via cystocentesis or direct venipuncture, yield invaluable diagnostic information.
A study on the bacterial flora of infirmed reptiles revealed that approximately 50% of all bacterial cultures contained anaerobic bacteria. This could account for laboratory reports of “NO GROWTH”, even when you know that you collected an adequate sample.
A second reason for a lack of bacterial growth on sampling results from an excessive collection of sample material, thus overgrowing the transport medium prior to getting plated at the diagnostic laboratory. Technical difficulties, such as prolonged storage, overheating of the sample, and inappropriate or out-dated culture media are just a few reasons for sampling failure.
Fungal infections, such as CANV, can be diagnosed by several methods. Skin scrapings, skin biopsies and skin cultures are possible.
As mentioned, the gram-negative bacteria are most frequently implicated as pathogens. Deciding which bacteria to treat can often be confusing. Arbitrarily starting a patient on antibiotics just because gram negatives are present is not appropriate. A review of the most common bacteria will help the clinician decide which isolates require treatment.
Salmonella/Arizona - Most of the Salmonella spp., and Salmonella arizona group (fomerly Arizona arizonae), are considered pathogenic. Many reptiles harbor these organisms as part of their normal flora, and interpreting their presence can often be difficult. This group has public health significance because of their zoonotic potential.
Pseudomonas spp. - Pseudomonas spp., such as P. aeruginosa, are commonly found as part of the normal flora in the oral cavity and intestinal tracts of reptiles. As such, it is often considered an opportunistic pathogen. In cases of poor husbandry, such as sub-optimal environmental temperatures and malnutrition, can predispose to pseudomonas infections. Pseudomonas has been isolated from cases of ulcerative stomatitis, pneumonia, cutaneous lesions and septicemias. Pseudomonas cultured in light numbers from the oral cavity or gastrointestinal tract in healthy patients probably need not be treated.
Aeromonas spp. - Aeromonas has been associated with pneumonias, oral cavity and cutaneous lesions, and septicemias. The snake mite, Ophionyssus natricis, has been implicated as a common vector of this bacteria. Aeromonas isolated from healthy animals in light growth may be part of the normal flora. However, where there is significant growth, or in patients with questionable clinical health, treatment should be considered.
Serratia spp. - Is part of the normal flora of the oral cavity in reptiles. It is commonly isolated from cutaneous lesions, and appears to be introduced from traumatic sources, such as bite wounds. Cutaneous infections with Serratia typically cause caseated abscesses which require surgical curretage for appropriate treatment.
Mycobacteria spp. - Mycobacteria are common environmental bacteria. Of significance to reptile patients are M. marinum, M. chelonia and M. thamnopheos. Although commonly isolated from cutaneous lesions. Mycobacteria can also cause systemic illness with nonspecific signs such as anorexia, lethargy and wasting. Acid fast organisms are readily identified with either skin scrapings or biopsies. There are no reported successful treatments. This disease may also have some zoonotic potential.
Providencia spp. - Commonly isolated from the oral cavity of healthy snakes. This is believed to be an opportunistic pathogen. Treatment should be considered in view of the clinical status of the patient.
Klebsiella spp. - K. pneumonia is commonly associated with pneumonia and hypopyon. These organisms are considered normal flora by some authors. When isolated from clinically ill reptiles the organism should be treated.
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