Study of some risk factors for fungal contamination of dental unit waterlines in Alexandria, Egypt.

INTRODUCTION: Monitoring the microbial quality of water in dental unit waterlines is an important part of infection control measures carried out in dental clinics. Fungal contamination of such waterlines has not been extensively studied, compared with bacterial contamination. This study aimed at assessing the magnitude and risk factors for fungal contamination of dental unit waterlines. METHODOLOGY: This cross-sectional study included 82 dental units, randomly collected from 3 private clinics and 8 governmental hospitals in Alexandria, Egypt. A total of 204 water samples from dental unit waterlines output were membrane-filtered and cultured for fungal enumeration and species identification. The biofilm forming-ability was assessed for the most prevalent fungal species. The acceptability of samples was determined according to the Swedish drinking water guidelines. RESULTS: The acceptability of samples was 89.7%. The most common mould was Aspergillus flavus, while Candida spp. was the most common yeast (10 isolates), with unusual predominance of Candida dubliniensis (9 isolates). All isolates of Aspergillus flavus and Candida dubliniensis were biofilm-formers. The risk factors for fungal contamination of dental unit waterlines included: dental specialty (p = 0.042), time of sample collection (p < 0.001), older age of dental unit (p < 0.001) and use of 5-15% of sodium hypochlorite. CONCLUSIONS: The presence of biofilm-forming fungi in dental unit waterlines is a potential hazard, even when samples have acceptable levels of fungal counts. Risk factors for contamination are numerous and should be addressed.

The Dynamic Transition of Persistence toward the Viable but Nonculturable State during Stationary Phase Is Driven by Protein Aggregation.

Decades of research into bacterial persistence has been unable to fully characterize this antibiotic-tolerant phenotype, thereby hampering the development of therapies effective against chronic infections. Although some active persister mechanisms have been identified, the prevailing view is that cells become persistent because they enter a dormant state. We therefore characterized starvation-induced dormancy in Escherichia coli. Our findings indicate that dormancy develops gradually; persistence strongly increases during stationary phase and decreases again as persisters enter the viable but nonculturable (VBNC) state. Importantly, we show that dormancy development is tightly associated with progressive protein aggregation, which occurs concomitantly with ATP depletion during starvation. Persisters contain protein aggregates in an early developmental stage, while VBNC cells carry more mature aggregates. Finally, we show that at least one persister protein, ObgE, works by triggering aggregation, even at endogenous levels, and thereby changing the dynamics of persistence and dormancy development. These findings provide evidence for a genetically controlled, gradual development of persisters and VBNC cells through protein aggregation. IMPORTANCE While persistence and the viable but nonculturable (VBNC) state are currently investigated in isolation, our results strongly indicate that these phenotypes represent different stages of the same dormancy program and that they should therefore be studied within the same conceptual framework. Moreover, we show here for the first time that the dynamics of protein aggregation perfectly match the onset and further development of bacterial dormancy and that different dormant phenotypes are linked to different stages of protein aggregation. Our results thereby strongly hint at a causal relationship between both. Because many conditions known to trigger persistence are also known to influence aggregation, it is tempting to speculate that a variety of different persister pathways converge at the level of protein aggregation. If so, aggregation could emerge as a general principle that underlies the development of persistence which could be exploited for the design of antipersister therapies.

The bacterial community of the lone star tick (Amblyomma americanum).

BACKGROUND: The lone star tick (Amblyomma americanum), an important vector of a wide range of human and animal pathogens, is very common throughout the East and Midwest of the USA. Ticks are known to carry non-pathogenic bacteria that may play a role in their vector competence for pathogens. Several previous studies using the high throughput sequencing (HTS) technologies reported the commensal bacteria in a tick midgut as abundant and diverse. In contrast, in our preliminary survey of the field collected adult lone star ticks, we found the number of culturable/viable bacteria very low. METHODS: We aimed to analyze the bacterial community of A. americanum by a parallel culture-dependent and a culture-independent approach applied to individual ticks. RESULTS: We analyzed 94 adult females collected in eastern Kansas and found that 60.8% of ticks had no culturable bacteria and the remaining ticks carried only 67.7 ± 42.8 colony-forming units (CFUs)/tick representing 26 genera. HTS of the 16S rRNA gene resulted in a total of 32 operational taxonomic units (OTUs) with the dominant endosymbiotic genera Coxiella and Rickettsia (> 95%). Remaining OTUs with very low abundance were typical soil bacterial taxa indicating their environmental origin. CONCLUSIONS: No correlation was found between the CFU abundance and the relative abundance from the culture-independent approach. This suggests that many culturable taxa detected by HTS but not by culture-dependent method were not viable or were not in their culturable state. Overall, our HTS results show that the midgut bacterial community of A. americanum is very poor without a core microbiome and the majority of bacteria are endosymbiotic.

Efficient microbial colony growth dynamics quantification with ColTapp, an automated image analysis application.

Populations of genetically identical bacteria are phenotypically heterogeneous, giving rise to population functionalities that would not be possible in homogeneous populations. For instance, a proportion of non-dividing bacteria could persist through antibiotic challenges and secure population survival. This heterogeneity can be studied in complex environmental or clinical samples by spreading the bacteria on agar plates and monitoring time to growth resumption in order to infer their metabolic state distribution. We present ColTapp, the Colony Time-lapse application for bacterial colony growth quantification. Its intuitive graphical user interface allows users to analyze time-lapse images of agar plates to monitor size, color and morphology of colonies. Additionally, images at isolated timepoints can be used to estimate lag time. Using ColTapp, we analyze a dataset of Staphylococcus aureus time-lapse images including populations with heterogeneous lag time. Colonies on dense plates reach saturation early, leading to overestimation of lag time from isolated images. We show that this bias can be corrected by taking into account the area available to each colony on the plate. We envision that in clinical settings, improved analysis of colony growth dynamics may help treatment decisions oriented towards personalized antibiotic therapies.

Direct interaction network inference for compositional data via codaloss.

16S rRNA gene sequencing and whole microbiome sequencing make it possible and stable to quantitatively analyze the composition of microbial communities and the relationship among microbial communities, microbes, and hosts. One essential step in the analysis of microbiome compositional data is inferring the direct interaction network among microbial species, bringing to light the potential underlying mechanism that regulates interaction in their communities. However, standard statistical analysis may obtain spurious results due to compositional nature of microbiome data; therefore, network recovery of microbial communities remains challenging. Here, we propose a novel loss function called codaloss for direct microbes interaction network estimation under the sparsity assumptions. We develop an alternating direction optimization algorithm to obtain sparse solution of codaloss as estimator. Compared to other state-of-the-art methods, our model makes less assumptions about the microbial networks. The simulation and real microbiome data results show that our method outperforms other methods in network inference. An implementation of codaloss is available from https://github.com/xuebaliang/Codaloss.

Association of Staphylococcus aureus Colonization and Pneumonia in the Intensive Care Unit.

Importance: Carriage of Staphylococcus aureus is associated with S aureus infection. However, associations between S aureus carriage and the development of S aureus intensive care unit (ICU) pneumonia (SAIP) have not been quantified accurately, and interpretation of available data is hampered because of variations in definitions. Objective: To quantify associations of patient-related and contextual factors, including S aureus colonization status, with the occurrence of SAIP. Design, Setting, and Participants: This cohort study was conducted in ICUs of 30 hospitals in 11 European countries, geographically spread across 4 regions. Among patients with an anticipated length of stay 48 hours or longer who were undergoing mechanical ventilation at ICU admission, S aureus colonization was ascertained in the nose and lower respiratory tract. From this group, S aureus-colonized and noncolonized patients were enrolled into the study cohort in a 1:1 ratio. Data analysis was performed from May to November 2019. Main Outcomes and Measures: SAIP was defined as any pneumonia during the ICU stay developing 48 hours or more after ICU admission with S aureus isolated from lower respiratory tract specimens or blood samples. The incidence of SAIP was derived in the study cohort and estimated on the weighted incidence calculation for the originating overarching population, while taking competing events into account. Weighted risk factor analysis was performed using Cox multivariable regression. Results: The study cohort consisted of 1933 patients (mean [SD] age, 62.0 [16.0] years); 1252 patients (64.8%) were men, and 950 patients (49.1%) were S aureus carriers at ICU admission. In all, 304 patients (15.7%) developed ICU-acquired pneumonia, of whom 131 patients (6.8%) had SAIP. Weighted SAIP incidences were 11.7 events per 1000 patient-days in the ICU for S aureus-colonized patients and 2.9 events per 1000 patient-days in the ICU for noncolonized patients (overall incidence, 4.9 events per 1000 patient-days in the ICU). The only factor independently associated with SAIP was S aureus colonization status at ICU admission (cause-specific hazard ratio, 3.6; 95% CI, 2.2-6.0; P < .001). There were marked regional differences in SAIP incidence and cause-specific hazard ratios for colonization status. Conclusions and Relevance: SAIP incidence was 4.9 events per 1000 ICU patient-days for patients undergoing mechanical ventilation at ICU admission (or shortly thereafter). The daily risk of SAIP was 3.6 times higher in patients colonized with S aureus at ICU admission compared with noncolonized patients.

Impacts of Habitual Diets Intake on Gut Microbial Counts in Healthy Japanese Adults.

Although diet is an important factor influencing gut microbiota, there are very few studies regarding that relationship in Japanese people. Here, we analyzed the relationship between habitual dietary intake surveyed by food frequency questionnaire and the quantitative features of gut bacteria by quantitative PCR and next generation sequencer in 354 healthy Japanese adults. The α-diversity of gut microbiota was positively correlated with the intake of mushrooms and beans and negatively correlated with the intake of grains. The ß-diversity was significantly associated with the intake of fruits, mushrooms, seaweeds, seafoods, and alcoholic beverages. Multiple linear regression analysis of the relationship between food groups associated with the diversity of gut microbiota and the number of gut bacteria at the genus level found 24 significant associations, including a positive association between alcoholic beverages and the number of Fusobacterium. These results support that habitual dietary intake influenced the diversity of gut microbiota and was strongly associated with the number of specific gut bacteria. These results will help us to understand the complex relationship between habitual diet and gut microbiota of the Japanese.

Commercial bacterial and fungal broad-range PCR (Micro-Dx™) used on culture-negative specimens from normally sterile sites: diagnostic value and implications for antimicrobial treatment.

The aim of this study was to evaluate the clinical value of partial 16S/18S rRNA gene sequencing with the commercial kit Micro-Dx™ used with the SelectNA™plus instrument on culture-negative samples. A retrospective study of microbiological and clinical data from a 2.5-year period was performed. Assessment of the clinical relevance of the 16S/18S rRNA gene sequencing results was based on evaluation of the results in the clinical context and changes in antimicrobial therapy. Included were 529 samples from 223 patients, representing 251 episodes. In 191 samples (36.1%), bacterial/fungal DNA was detected. Positive results were judged clinically relevant in 79 (31.5%) episodes. Antimicrobial treatment was adjusted according to the 16S/18S rRNA gene sequence analysis result in 42 (16.7%) episodes. The results from 16S/18S rRNA gene sequence analysis were highly clinically relevant. These findings support the use of this analysis in a routine setting.

Risk factors and outcomes of culture-proven acute Coccidioides spp. infection in San Diego, California, United States.

BACKGROUND: Coccidioides spp. are dimorphic fungi endemic to parts of the United States, Mexico, Central and South America. Infection can cause a range of disease from self-limited acute pneumonia to severe disseminated disease. METHODS: We performed a retrospective chart review of medical records of cases of culture-proven acute coccidioidomycosis at the University of California San Diego between 1 April 2015 and 31 December 2019 and described the demographics, risk factors and outcomes of these cases. RESULTS: Over the study period, fifteen evaluable cases of culture-proven acute coccidioidomycosis were identified. Of these, 87% (13/15) had traditional risk factors for coccidioidomycosis infection while two lacked known risk factors, including one patient with cirrhosis and one with chronic hepatitis C infection. Seven of fifteen (47%) had primary coccidioidomycosis of the lungs without dissemination and 7/15 (47%) disseminated disease. Of those with disseminated disease, 6/7 (86%) had either high-risk ethnicity or blood type as their only risk factor. At 90 days, 11/15 (73%) were alive, 3/15 (20%) deceased and 1/15 (7%) lost to follow-up. Of those not alive at 90 days, 1/3 (33%) had disseminated disease and 2/3 (67%) primary coccidioidomycosis, both on immunosuppressive therapy. DISCUSSION: Coccidioides spp. infection occurs in a variety of hosts with varying underlying risk factors, with the majority in our cohort overall and 86% with disseminated disease lacking traditional risk factors for invasive fungal infection other than ethnicity and/or blood phenotype. Clinicians should be aware of these non-traditional risk factors in patients with coccidioidomycosis infection.

Characterization of Escherichia coli possessing the locus of heat resistance isolated from human cases of acute gastroenteritis.

The purpose of this study was to identify Escherichia coli isolates obtained from patients experiencing acute gastroenteritis that possess the locus of heat resistance (LHR) and characterize their heat resistance upon exposure to temperatures of 60 °C and 71 °C. From a collection of 613 clinical E. coli strains, 3 heat resistant E. coli isolates were identified. Two of the 3 isolates were stx1 positive; no isolates possessed stx2 as determined by qPCR. D60-values of heat resistant isolates all exceeded 10.20 min with one isolate's D60-values ranging from 20.46 to 72.47 min. The presence of 4% additional NaCl significantly increased D60-values of 2 clinical isolates. Cell reductions of heat resistant isolates in ground beef patties grilled to 60 °C and 71 °C remained above 2.8 and 4.9 log CFU/mL, respectively, compared to reductions of 6.1 log CFU/mL and greater in heat sensitive E. coli. Constitutive expression of novel Clp protease ClpK, encoded on open reading frame 3 of the LHR, was identified in all heat resistant isolates by SDS-PAGE and peptide mass fingerprinting. This data is the first to report heat resistant E. coli possessing the LHR involved in clinical infection, highlighting the potential threat of heat resistant enteric pathogens on food safety.

Zinc-Impregnated Mesh for Abdominal Wall Repair Reduces Infection in a Rat Model of Peritonitis.

BACKGROUND: The objective of this study was to assess whether a zinc-impregnated polypropylene mesh (ZnMesh) has better antibacterial properties in a contaminated environment compared with a regular polypropylene mesh. MATERIALS AND METHODS: Thirty-eight Wistar Han rats underwent cecal ligation and puncture to induce peritonitis 24 h before implantation of an intraperitoneal ZnMesh or a regular polypropylene mesh. Primary outcome was the number of colony forming units (CFU) per sample (mesh and abdominal wall). Secondary outcomes were macroscopic (incorporation of mesh, abscesses, and adhesions on mesh surface) and histological (inflammatory cell reaction, mesh-specific parameters, and collagen deposition) parameters. All outcomes were evaluated after 30 and 90 d. RESULTS: After 30 d, no significant difference in CFU per sample was present between the ZnMesh and control groups. After 90 d, a lower number of CFU per sample was present in the ZnMesh group compared with the control group (trypticase soy agar with 5% sheep blood: 0 log10 CFU/sample IQR: 0-1.40 versus 1.58 log10 CFU/sample IQR: 0-4.30, P = 0.012; MacConkey: 0 log10 CFU/sample IQR: 0-2.65 versus 1.18 log10 CFU/sample IQR: 0-4.04, P = 0.438). After 90 d, the percentage of adhesions on mesh surface was significantly higher in the ZnMesh group (95% IQR: 60%-100% versus 50% IQR: 23%-75%, P = 0.029). No differences were seen in other macroscopic outcomes or histology. CONCLUSIONS: A significantly lower number of CFU per sample was found in the ZnMesh group after 90 d. After 30 d, no statistically significant differences in CFU per sample were seen. This result suggests that the ZnMesh group has better antibacterial properties in a contaminated environment. However, this is at the cost of a significantly higher percentage of adhesions.

Evaluation of ATP bioluminescence for monitoring surface hygiene in a hospital pharmacy cleanroom.

The usefulness of the ATP bioluminescence method for monitoring surface hygiene was evaluated in a hospital pharmacy cleanroom. The sensitivity of the method was found to be appropriate for assessing the efficiency of cleaning and disinfection. ATP bioluminescence was superior to the traditional microbiological culture-based method for detecting unclean surfaces (p < .05).

Seasonal changes in indoor airborne fungal concentration in a hematology ward.

Invasive fungal disease (IFD) is an important infectious complication of hematological disorders, especially in hematopoietic stem cell transplantation recipients. Evidences suggest seasonal and/or geographical variations in the airborne fungal counts and a relationship between those counts and the incidence of IFD. We evaluated the concentrations of indoor airborne fungi quantitated over the course of one year in a hematology ward in Japan. In January, April, July, and October, fixed volumes of air samples were obtained by an air sampler in a hematology ward not equipped with a high-efficiency particulate air filter and incubated in fugal cultures. Samples were also obtained from a protective environment in the same ward and were evaluated. The number of fungal colonies per 50 L of sampled air was highest in October (median 2.25 (range, 0.2-7.0)), which was significantly higher than those in the other three months (0.1 (range, 0-1.0) in January; 0 (0-0) in April; 0.55 (0-2.5) in July; P < 0.01)). Commonly identified pathogens included Penicillium and Cladosrporium species, but Aspergillus species was detected only in July and October samples. These results suggest a seasonal variation in indoor airborne fungal concentrations in Japan, which could affect the epidemiology of IFD.

Sensitivity of differential time to positivity compared to pour plates for diagnosing catheter-related blood stream infection: An evaluation in patients with chronic intestinal failure.

BACKGROUND & AIMS: A retrospective evaluation was undertaken in intestinal failure (IF) patients with long term CVCs to evaluate differential time to positivity (DTP) against paired quantitative blood cultures (PP) for the diagnosis of CRBSI. METHODS: A list of patients with a diagnosis of CRBSI was obtained from the intestinal failure unit database for a five year period, 2013 to 2017. Microbiology records were reviewed to obtain further information about blood culture and pour plate examinations. Organisms and times of collection, loading and positivity were recorded. Patients with a contemporaneous set of central and peripheral PP and blood cultures were included in an analysis of the sensitivity of DTP compared to PP. RESULTS: There were 61 (45.5%) episodes in 56 patients where complete sets of central and peripheral blood cultures and PP were received. All 61 episodes had positive central blood cultures, 59 (96.7%) had positive central line PP and 17 (27.9%) had positive peripheral PP. Using PP as the gold standard, DTP sensitivity was 96.0% for 50 episodes where PP were consistent with CRBSI. Sensitivity increased to 100% for 17 episodes where there were no delays in either collection or loading of blood cultures. CONCLUSIONS: This is the first evaluation to support the use of DTP as a sensitive test in diagnosing CRBSI in patients with IF and provides confidence to IF centers where pour plate cultures are not available.

Microbial study of household hygiene conditions and associated Listeria monocytogenes infection risks for Peruvian women.

OBJECTIVES: To develop an exposure and risk assessment model to estimate listeriosis infection risks for Peruvian women. METHODS: A simulation model was developed utilising Listeria monocytogenes concentrations on kitchen and latrine surfaces in Peruvian homes, hand trace data from Peruvian women and behavioural data from literature. Scenarios involving varying proportions of uncontaminated, or 'clean', surfaces and non-porous surfaces were simulated. Infection risks were estimated for 4, 6 and 8 h of behaviours and interactions with surfaces. RESULTS: Although infection risks were estimated across scenarios for various time points (e.g. 4, 6, 8 h), overall mean estimated infection risks for all scenarios were ≥ 0.31. Infection risks increased as the proportions of clean surfaces decreased. Hand-to-general surface contacts accounted for the most cumulative change in L. monocytogenes concentration on hands. CONCLUSIONS: In addition to gaining insights on how human behaviours affect exposure and infection risk, this model addressed uncertainties regarding the influence of household surface contamination levels. Understanding the influence of surface contamination in preventing pathogen transmission in households could help to develop intervention strategies to reduce L. monocytogenes infection and associated health risks.

OBJECTIFS: Développer un modèle d'exposition et d'évaluation des risques pour estimer les risques d'infection par la listériose chez les femmes péruviennes. MÉTHODES: Un modèle de simulation a été développé en utilisant des concentrations de Listeria monocytogenes sur la surface des cuisines et des latrines dans des foyers péruviens, des données de traces de mains de femmes péruviennes et des données comportementales de la littérature. Des scénarios impliquant différentes proportions de surfaces non contaminées ou «propres¼ et de surfaces non poreuses ont été simulés. Les risques d'infection ont été estimés pour 4, 6 et 8 heures de comportements et d'interactions avec les surfaces. RÉSULTATS: Bien que les risques d'infection aient été estimés pour tous les scénarios à différents moments (par ex. à 4, 6 ou 8 heures), les risques d'infection globaux moyens estimés pour tous les scénarios étaient ≥ 0,31. Les risques d'infection augmentaient à mesure que les proportions de surfaces propres diminuaient. Les contacts entre la main et les surfaces générales contribuent pour le plus de changement cumulatif de la concentration de L. monocytogenes sur les mains. CONCLUSIONS: En plus de comprendre comment les comportements humains affectent l'exposition et le risque d'infection, ce modèle a traité des incertitudes quant à l'influence des niveaux de contamination des surfaces ménagers. Comprendre l'influence de la contamination de surface dans la prévention de la transmission d'agents pathogènes dans les ménages pourrait aider à développer des stratégies d'intervention pour réduire l'infection à L. monocytogenes et les risques associés pour la santé.

Are bacterial culture quantifications reliable? Comparative performance of the WASP automated inoculation instrument in the era of ISO 15189 accreditation.

PURPOSE: Isolating colonies and obtaining accurate colony counts from bacterial cultures are critical steps for the optimal management of infected patients. The uncertainties in the colony count results from the bacterial cultures were evaluated by verifying the performance of the WASP inoculation system according to the International Organization for Standardization (ISO) 15189 standard. METHODOLOGY: We first (i) evaluated the cross-contamination and precision of the WASP instrument (Copan Diagnostics, Italy) and (ii) established enumeration reading grids for urine, swab, bronchopulmonary specimens (BPSs) and catheter tip cultures. Subsequently, 72 clinical samples were tested to compare the results of the WASP, PREVI Isola (bioMérieux, France) and manual inoculation methods. RESULTS: The WASP method did not show cross-contamination. The coefficient of variation for the colony counts in the repeatability experiment was evaluated for 10 µl and 30 µl loop protocols and determined to be 29 and 14 %, respectively. The agreement between the automated and manual methods and between the automated methods for the colony counts was high (94.4 and 100 %, respectively). The WASP method yielded better isolation quality compared to the manual method (P=0.020) and to the PREVI Isola only when polymicrobial specimens were considered (P=0.014). For quantification evaluation, the measurement uncertainty was evaluated to 1.8×103 c.f.u. ml-1 for a suspension of Escherichia coli at 104 c.f.u. ml-1. CONCLUSION: We report the verification of the performance of the WASP instrument and describe a rapid procedure for achieving semi-quantitative cultures from BPSs and catheter tips. Quantitative interpretation of the bacterial cultures should be performed with caution.

Perception and Practice of HIV/AIDS Counseling and Testing Among Secondary School Adolescents in Ogun Waterside Local Government Area, Ogun State, Southwest Nigeria.

A large proportion of Nigerian adolescents are sexually active and the country has one of the highest HIV prevalence among youths globally. This study was done to assess the perception and practice of HIV/AIDS counseling and testing (HCT) among secondary school adolescents in a rural community in Southwest Nigeria. A cross-sectional descriptive study was carried out using multistage sampling method. The results showed that despite high level of HCT awareness, majority of the adolescents (62.9%) had negative attitude toward it. The practice of HCT was poor among majority of the respondents as less than 15% of the adolescents had ever done HCT. This study recommends that adolescents should be better informed on the locations of the health centers within the community and services rendered by them. Peer education on HCT should also be intensified in schools to promote positive healthy sexual lifestyles among adolescents.

Robust fit of Bayesian mixed effects regression models with application to colony forming unit count in tuberculosis research.

Early bactericidal activity of tuberculosis drugs is conventionally assessed using statistical regression modeling of colony forming unit (CFU) counts over time. Typically, most CFU counts deviate little from the regression curve, but gross outliers due to erroneous sputum sampling are occasionally present and can markedly influence estimates of the rate of change in CFU count, which is the parameter of interest. A recently introduced Bayesian nonlinear mixed effects regression model was adapted to offer a robust approach that accommodates both outliers and potential skewness in the data. At its most general, the proposed regression model fits the skew Student t distribution to residuals and random coefficients. Deviance information criterion statistics and compound Laplace-Metropolis marginal likelihoods were used to discriminate between alternative Bayesian nonlinear mixed effects regression models. We present a relatively easy method to calculate the marginal likelihoods required to determine compound Laplace-Metropolis marginal likelihoods, by adapting methods available in currently available statistical software. The robust methodology proposed in this paper was applied to data from 6 clinical trials. The results provide strong evidence that the distribution of CFU count is often heavy tailed and negatively skewed (suggesting the presence of outliers). Therefore, we recommend that robust regression models, such as those proposed here, should be fitted to CFU count.