Opportunistic Bacteria From Sinks and Antibiotic Resistance

Sobh, Caroleen, Farrah Isso, Andrew Namou, Miranda Marion, and James Graves

Assessment of the potential health risk of bacteria from sinks was performed. Bacteria in samples from swabs were inoculated onto MacConkey agar and separated by the streak plate method. After incubation at 37oC, plates demonstrated colony counts that ranged from 15 to several hundred per plate. Gram stains of cultures purified by serial streak plates showed gram-negative bacilli. Isolates were initially examined by standard biochemical tests (glucose, lactose, sucrose, citrate and urea). Selected strains were further characterized by the Biolog automated redox-based system which assays the ability of a microorganism to oxidize an array of 95 carbon sources in a 96-well microplate. Test results indicated that lactose-nonfermenting and lactose-fermenting bacteria resembled Pseudomonas and klebsiella respectively. No Escherichia coli was found. Isolates were screened by the antibiotic disc procedure against carbenicillin, chloramphenicol, kanamycin and tetracycline. Resistance was found to exist to each of the antibiotics. Some bacteria were multiply antibiotic resistant (MAR). The minimum inhibitory concentration (MIC) of tetracycline for one MAR strain of Pseudomonas was 2.5 mcg/ml at 24 hours of incubation but increased to 20 mcg/ml after 48 hours. None of the isolates were sensitive to a genetically engineered bacterial virus (λNK1098) when tested by the cross-streak method. Opportunistic bacteria that carry antibiotic resistance appear common in sinks. Sinks should be regularly scrubbed and disinfected to decrease the likelihood of infection.