Purpose: This study compared biofilm formation by seven serogroups of Escherichia coli (i.e., O157, O26, O45, O103, O111, O121, O145) and two or three phenotypes of Salmonella Newport and S. Typhimurium (i.e., susceptible, multidrug-resistant [MDR], and/or multidrug-resistant with acquired ampC gene [MDR-AmpC]). In addition, their reduction by water, quaternary ammonium compound-based (QAC), and acid-based (AB) sanitizers were investigated.
Methods: Seven strain mixtures of the above pathogen groups were separately spot-inoculated onto stainless steel coupon surfaces for a target level of 2 log CFU/cm2. Coupons were stored statically, partially submerged in 10% (w/v) non-sterilized meat homogenate at 4, 15, and 25°C. Microbial counts on days 0, 1, 4, and 7 and survivors after exposure (submersion in 30 ml for 1 min) to water, QAC and AB of one-week mature biofilms were enumerated.
Results: At 4°C, pathogen counts on inoculation day ranged from 1.6 ± 0.4 to 2.4 ± 0.6 log CFU/cm2 and changed to 1.2 ± 0.8 to 1.9 ± 0.8 log CFU/cm2 on day 7 with no appreciable difference among the pathogen groups. Biofilm formation at higher temperatures was more enhanced. E. coli O157:H7, as an example, increased (P < 0.05) from 1.4 ± 0.6 and 2.0 ± 0.3 log CFU/cm2 on day 0 to 4.8 ± 0.6 and 6.5 ± 0.2 log CFU/cm2 on day 7 at 15 and 25°C, respectively. As compared to 4°C, after sanitation, more survivors were observed for 15 and 25°C treatments with no appreciable differences among the seven pathogen groups. MDR-AmpC S. Newport, as an example, were reduced to <1.6 ± 1.3 and 1.9 ± 0.9 log CFU/cm2 after exposure to QAC and AB at 15°C, while at 25°C were reduced to 5.5 ± 0.5 and 6.0 ± 0.4 log CFU/cm2, respectively.
Significance: Overall, patterns of growth and susceptibility to QAC and AB sanitizers were similar among the seven tested pathogens, with enhanced biofilm formation capability and higher numbers of survivors at higher temperatures.